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Burying as a defensive response in rats Treit, Dallas R. 1978

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BURYING AS A DEFENSIVE RESPONSE IN RATS by DALLAS R. TREIT B.A., U n i v e r s i t y o f B r i t i s h Columbia, 1975  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS  in  THE FACULTY OF GRADUATE STUDIES (Department o f Psychology]  We accept t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d  THE UNIVERSITY OF BRITISH COLUMBIA October, 1978  0  D a l l a s R. T r e i t , 1978  In  presenting  an  advanced  the  Library  I  further  for  degree shall  agree  scholarly  by  his  of  this  wr i t t e n  thesis  in  at  University  the  make that  thesis  purposes  for  partial  freely  permission may It  for  gain  of of  British  "7  /  of  of  Columbia,  British  Columbia  for  extensive by  the  is understood  p e rm i s s i o n .  University  fulfilment  available  be g r a n t e d  financial  2075 Wesbrook Place Vancouver, Canada V6T 1W5  Date  it  representatives.  Department The  this  shall  Head  be  requirements  reference copying  that  not  the  of  agree  and  of my  I  this  or  allowed  without  that  study. thesis  Department  copying  for  or  publication my  ABSTRACT In t y p i c a l  l a b o r a t o r y s e t t i n g s , the d e f e n s i v e r e a c t i o n s o f animals  appear t o be l i m i t e d t o f r e e z i n g , f l e e i n g , and a t t a c k i n g .  However, i n  the p r e s e n t i n v e s t i g a t i o n s , r a t s . t e s t e d i n the presence o f movable terial  ma->  i n c o r p o r a t e d i t i n t o a s t r i k i n g and a d a p t i v e b e h a v i o u r a l sequence.  Rats shocked once through a s t a t i o n a r y prod b u r i e d t h i s shock ^ s o u r c e , even when the shocks-test i n t e r v a l was  20 days.  This burying behaviour  o c c u r r e d a t a v a r i e t y o f shock i n t e n s i t i e s and seemed t o be c o n t r o l l e d sp c i f i c a l l y by the r e l a t i o n between the shock and the p r o d ; r a t s  shocked  through a g r i d d i d not bury the p r o d , and r a t s shocked by one o f two i d e n t i c a l prods b u r i e d o n l y the shock-prod.  Both the p o s i t i o n and b r i g h t  ness o f the p r o d seemed t o c o n t r o l the b u r y i n g b e h a v i o u r . t h e s e cues was  When e i t h e r o f  changed p r i o r t o the t e s t , b u r y i n g b e h a v i o u r was  disrup-  t e d compared t o c o n t r o l c o n d i t i o n s i n which t h e s e cues were u n a l t e r e d . Although b u r y i n g was shock, i t was  a d i r e c t e d and c o n s i s t e n t response o f r a t s t o p r o d  not a s i m p l e , r e f l e x i v e b e h a v i o u r ; r a t s c o u l d adapt  their  b u r y i n g b e h a v i o u r t o changes i n both the k i n d and d i s p o s i t i o n o f b u r y i n g materials.  Thus, the u s u a l assumption t h a t the r a t ' s d e f e n s i v e reper^-  t o i r e i s l i m i t e d t o a few s i m p l e b e h a v i o u r s appears t o have been  shaped  by the c o n s t r a i n t s o f s t a n d a r d t e s t i n g environments r a t h e r than by the a c t u a l p r o p e n s i t i e s o f the r a t .  These r e s u l t s were d i s c u s s e d i n terms  o f t h e i r i m p l i c a t i o n s f o r a " b i o l o g i c a l " approach t o a v e r s i v e  learning.  iii TABLE OF CONTENTS Page ABSTRACT  i i  TABLE OF CONTENTS  .  LIST OF FIGURES  iii . .  ACKNOWLEDGEMENTS  =. .  INTRODUCTION  ............  Response problem , nie^respoifse f r o D i e m  ......  SSDRS;h^o*t'h"es!i?'s2sis  ,.,  r  D e f e n s i v e Behaviours o f the r a t F r e e z i n g and f l e e i n g  v vi' 1 „ 2 6  .... ............  8 8  Fighting  11  Thigmotaxis  12  R a t i o n a l e and purpose  13  Rationale  ,'. ,  Purpose  . ,. ,  GENERAL METHODS  15 ,.  Subjects '  13  .,  17 17  Apparatus  17  Procedures  17  Habituation  17  Shock a d m i n i s t r a t i o n s Behavioural  observation  Statistical  analysis  Experiment  § quantification  Experiment  18  ,.  18 19  1  20  Method Results  ,.  20 and d i s c u s s i o n 2.  .,  20 24  Method  24  Results, and d i s c u s s i o n  24  Table o f Contents (cont'd)  iv Page  Experiment 3  .  24  Method Results  2  and d i s c u s s i o n  •  Experiment 4  *>  2  :  Method Results  and "discussion  29  and d i s c u s s i o n  ......  30  ...........  33  Experiment 6  33  :  Method  34: and d i s c u s s i o n  ,,  34  Experiment 7  39  Method Results  39 and d i s c u s s i o n  40  Experiment '8  43  Method Results  ,, ,, . and d i s c u s s i o n  '  Experiment 9  .  45  5,2 and d i s c u s s i o n  53  GENERAL DISCUSSION 1.  44  52  Method Results  ^  26  Method  Results  2  26  Experiment. 5 '  Results  5  55  B u r y i n g as a defense response i n the  rat  55  I I , ' B u r y i n g b e h a v i o u r and a b i o l o g i c a l approach t o a v e r s i v e  learning  59"  iJefDefensdv.e.hbeKaviiour  60  PriRr.i'nG.ip,le,s~ c5#fd'efen'sdv.eatear,n;ing  61  REFERENCES  71  V  LIST OF FIGURES Page Figure  1.  F i g u r e 2.  F i g u r e 3.  F i g u r e 4.  F i g u r e 5.  F i g u r e 6.  F i g u r e 7.  Mean d u r a t i o n o f b u r y i n g (Panel A) and the mean o f the r a t i o between t h e h e i g h t o f the h i g h e s t p i l e and i t s d i s t a n c e from t h e p r o d p o s i t i o n (Panel B) a t each o f t h e s h o c k - t e s t i n t e r v a l s f o r s u b j e c t s i n Experiment 1  21  Mean d u r a t i o n o f b u r y i n g and the mean h e i g h t o f bedding m a t e r i a l a t the p r o d a t each o f the f i v e shock i n t e n s i t i e s f o r s u b j e c t s i n E x p e r i ment .4.  27  D u r a t i o n o f b u r y i n g (Panel A) d i r e c t e d a t t h e shock prod and c o n t r o l p r o d and the f i n a l h e i g h t o f the bedding m a t e r i a l a t t h e shock p r o d and c o n t r o l p r o d (Panel B) f o r each o f ' the s u b j e c t s i n Experiment 5. Mean d u r a t i o n o f b u r y i n g (Panel A) and the mean h e i g h t o f bedding m a t e r i a l a t the p r o d (Panel B) f o r each o f the f o u r cue combinations i n Experiment 6.  ..31  36  Mean d u r a t i o n o f b u r y i n g d i r e c t e d a t t h e shock p r o d and c o n t r o l p r o d and t h e mean h e i g h t o f b e d d i n g m a t e r i a l a t each prod f o r s u b j e c t s i n Experiment 7  ...41  Mean d u r a t i o n o f b u r y i n g t h e shock and c o n t r o l prod with d i f f e r e n t materials f o r subjects i n Experiment 8  46  Mean h e i g h t o f b u r y i n g m a t e r i a l s a t . t h e shock and c o n t r o l prods f o r s u b j e c t s i n Experiment 8.  • ' 49  ACKNOWLEDGEMENTS  The author wishes to express h i s gratitude to John Pinel for the guidance and support which he provided throughout a l l phases o f t h i s research.  For t h e i r helpful comments and sug<-  gestions for- the'•• improvement of the manuscript special thanks f  are extended to Don'Wilkie and Jim Johnson,  1 INTRODUCTION  I t has been argued t h a t i n o r d e r t o understand  animal  avoidance  l e a r n i n g , the s u b j e c t ' s i n n a t e , defense r e a c t i o n s must be known 1970). 1973;  T h i s v i e w p o i n t has s t e a d i l y gained c r e d i b i l i t y  Mackintosh,  1974;  Wong, 1976;  H i n e l i n e , 1977;  (e.g.,  l a b o r a t o r y animals has escaped  serious attention.  Fantino,  Schwartz,  the t a s k o f documenting the n a t u r a l d e f e n s i v e b e h a v i o u r s One  (Bolles,  1978), w h i l e  o f common  reason the study  o f d e f e n s i v e responses has not p r o g r e s s e d a t a r a t e commensurate w i t h its  t h e o r e t i c a l importance  i s the assumption  t h a t l a b o r a t o r y animals  as the r a t are capable o f o n l y a few simple responses 'threats'  (e.g., B o l l e s , 1975).  to  such  environmental  However, s t u d i e s t h a t have shaped  this  view o f the r a t ' s n a t u r a l d e f e n s i v e c a p a c i t i e s have been conducted i n l a b o r a t o r y s e t t i n g s t h a t s e v e r e l y l i m i t the s u b j e c t ' s b e h a v i o u r . p r e s e n t s t u d i e s p r o v i d e evidence t h a t apparent defensive a b i l i t y ?  cal  l i m i t a t i o n s i n the r a t ' s  are as much a f u n c t i o n o f the a r b i t r a r y  s e t t i n g s i n which - i t has  0  The  experimental  been t e s t e d as they are a p r o d u c t o f b i o l o g i -  constraints. It i s well established  animal's b e h a v i o u r s and the problem  t h a t o n l y a few o f an  can r e a d i l y s e r v e as avoidance  responses.  These d a t a  they pose f o r g e n e r a l t h e o r i e s o f b e h a v i o u r are b r i e f l y  summarized i n the f i r s t tion, Bolles'  (e.g., Meyer, 1960)  section of this  (1970) approach  Introduction.  t o t h i s problem  In the second  i s presented.  sec-  His view i s .  t h a t animals respond i n n a t e l y to dangerous events by f i g h t i n g ,  fleeing,  o r f r e e z i n g , and t h a t i t i s o n l y these  can  be r e a d i l y l e a r n e d i n an avoidance ance o f B o l l e s ' assumption  defense reactIons that  ta,sk,  However, i n s p i t e o f the  import-  t h a t f i g h t i n g , f l e e i n g , and f r e e z i n g are the  o n l y defense r e a c t i o n s a v a i l a b l e t o e x p e r i m e n t a l animals  (Bolles,  1975),  2 he p r o v i d e s no e m p i r i c a l s u p p o r t  for t h i s view.  Data s u p p o r t i n g  this  assumption are r e v i e w e d i n the t h i r d s e c t i o n o f the I n t r o d u c t i o n . the f i n a l  s e c t i o n , t h i s evidence i s e v a l u a t e d ,  purpose o f the p r e s e n t i n v e s t i g a t i o n s are  and the r a t i o n a l e  In and  presented,  Response p r o b l e m The purpose o f much o f t h e p s y c h o l o g i c a l r e s e a r c h w i t h animals c o n ducted i n t h i s c e n t u r y has been t o uncover the p r i n c i p l e s the e f f e c t s  o f e x p e r i e n c e on f u t u r e b e h a v i o u r ,  'behaviour' usually refers  In e x p e r i m e n t a l  t o a s i m p l e , q u a n t i f i e d response  t i o n o r b a r - p r e s s i n g ; whereas,  'experience'  responses.  settings,  such as  saliva-  t o an  arrange-  t y p i c a l l y refers  ment o f e n v i r o n m e n t a l events o r s t i m u l i t h a t a l t e r s future  thatunderly  the l i k e l i h o o d o f  S t i m u l i t h a t i n c r e a s e the p r o b a b i l i t y o f responses  t h a t t h e y precede are f r e q u e n t l y c a l l e d c o n d i t i o n e d s t i m u l i ,  and s t i m u l i  t h a t i n c r e a s e the p r o b a b i l i t y o f responses t h a t t h e y f o l l o w are c a l l e d reinforcers.  Out o f t h e s e two b a s i c ' arrangements o f responses arid s t i ^ -  m u l i have emerged t h e fundamental p r i n c i p l e s o f c l a s s i c a l and i n s t r u m e n t a l conditioning, respectively.  I t has o f t e n been assumed  (e.g.,  Teitelbaum,  1966) t h a t t h e s e p r i n c i p l e s a p p l y u n i f o r m l y t o any s p e c i e s and t o any combination o f s t i m u l u s , response, 1972).  and r e i n f o r c e r  (c.f,,  Shettleworth,  T h i s assumption has been c a l l e d ' ' e q u i v a l e n c e o f a s s o c i a b i l i t y "  ( S e l i g m a n , 1 9 7 0 ) , and i t s v a l i d i t y has.become t h e c e n t r e o f r e c e n t There are many e x p e r i m e n t a l f i n d i n g s t h a t are c o n s i s t e n t w i t h notion of "equivalence o f a s s o c i a b i l i t y " . demonstrated  debate, the  F o r example, P a v l o v (1927)  t h a t dogs c o u l d be t r a i n e d t o s a l i v a t e i n r e s p o n s e t o a wide  v a r i e t y o f s t i m u l i i f t h e s e ' ' c o n d i t i o n e d ' s t i m u l i had been f o l l o w e d b y  3 food p l a c e d i n the d o g ' s mouth.  Similarly,  S k i n n e r (1956) showed t h a t  v a r i o u s " s c h e d u l e s o f r e i n f o r c e m e n t " r e s u l t e d i n comparable c u r v e s i n a number o f d i f f e r e n t  performance  species,  However, t h e r e i s a l s o e v i d e n c e t h a t seems to c o n t r a d i c t the t i o n of equivalence.  Iri p a r t i c u l a r , t h e r e are many s t u d i e s  assump-  of  avoidance l e a r n i n g t h a t i n d i c a t e t h a t t h e p r i n c i p l e s t h a t govern behavi o u r do n o t a p p l y u n i f o r m l y , t o a l l r e s p o n s e s ; o f a chamber t o a v o i d shock i n one t r i a l  (Maatch, 1959), o r l e a r n t o run  down a n . a l l e y to a v o i d shock i n f i v e t r i a l s hundreds  o f t r i a l s t o l e a r n a levers-press  D'Amato, $ K e l l e r ,  Rats may l e a r n t o l e a p out  ( T h e i o s , 1 9 6 3 ) , but  avoidance t a s k  take  (Biederman,  1964), i f t h e y l e a r n i t at a l l (D'Amato § S c h i f f ,  S i m i l a r l y , p i g e o n s can l e a r n t o ' a v o i d shock by s h u t t l i n g t o the s i d e o f a box ( M a c p h a i l , 1968) but have g r e a t d i f f i c u l t y  1964).  'safe'  a v o i d i n g shock  by p e c k i n g a key ( H i n e l i n e § R a c h l i n , 1969; S c h w a r t z , 1 9 7 3 ) ,  It  appears  t h a t o r d e r l y r e l a t i o n s h i p s between s h o c k , s t i m u l u s , and response may be found i r i some s i t u a t i o n s b u t n o t i n o t h e r s  (cf., Bolles,  1971),  Although these i n c o n s i s t e n c i e s i n the r a t e s o f avoidance l e a r n i n g suggest t h a t the p r i n c i p l e s o f b e h a v i o u r change are not g e n e r a l , the response ant,  one chooses t o c o n d i t i o n w i t h shock may be p a r t i c u l a r l y importr-  alternative  interpretations  Berger § B r u s h , 1975), different  and t h a t  o f the d a t a have been o f f e r e d  (e.g.,  F o r example, the b a r - p r e s s a v o i d a n c e t a s k  is  from o t h e r avoidance task,s i n a number o f ways, any o f w h i c h  c o u l d account f o r d i f f e r e n c e s  i n the r a t e s o f avoidance a c q u i s i t i o n .  Data t h a t i m p l i c a t e t h e s e s i t u a t i o n a l v a r i a b l e s have come from s t u d i e s p r i m a r i l y designed to f a c i l i t a t e barrpress  performance  a c q u i s i t i o n o f b a r - p r e s s a v o i d a n c e has been a c c e l e r a t e d  i r i the r a t , by:  The  4 1) r e d u c i n g shock i n t e n s i t y  ( B o l l e s ^ Warren,  1965 j D'Amato  § F a z z a r o , 1966) 2) a d m i n i s t e r i n g b r i e f , i n t e r m i t t e n t shocks i n s t e a d o f cont i n u o u s shock  (Brush, 1964; D'Amato, K e l l e r , § D i C a r a ,  1964; H u r w i t z , 1964;  Berger S Brush, 1975).  3) a d m i n i s t e r i n g n o n c o n t i n g e n t shocks  ( D e l p r a t o § Holmes,  1977). 4) i n t e n s i f y i n g the s i g n a l  (CS) f o r shock  ( F a n t i n o , Sharp,  $ C o l e , 1966) . 5) l e n g t h e n i n g the i n t e r v a l between shock ( B o l l e s , Warren  £ O s t r o v , 1966;  (US) and i t s s i g n a l  Berger § Brush, 1975).  6) i n c r e a s i n g the d i s t a n c e between the CS and the manipulandum  (Biederman, D'Amato, § K e l l e r ,  1964).  7) i m m o b i l i z i n g the manipulandum d u r i n g and s h o r t l y shock  (Forgione,  1970),  8) i n t r o d u c i n g the manipulandum at t r i a l it  after  onset and  retracting  a f t e r a response ( H u l l , Myer, § Smith, 1975).  9) s h a p i n g b a r - p r e s s responses (Feldman P Bremmer, T  Keehn § Webster,  1963;  1968).  10) p r i o r a p p e t i t i v e c o n d i t i o n i n g  ( G i a l i a n § Schmaltz, 1973).  11) h a n d l i n g animals between t r i a l s  (Wahlsten, C o l e , Sharp,  £ F a n t i n o , 1968) . IZ)  r e d u c i n g the i n t e r t r i a l i n t e r v a l  (Pearl f F i t z g e r a l d , T  1966) .  13) r e d u c i n g the s i z e o f the chamber so i t i s j j . u s t ^ l a r g e : enough to .  accommodate the s u b j e c t  (Cahoon § Crosty , 1969; . A z r i n , 1  Hopwood f, P o w e l l , 1-967).  14) - p r o v i d i n g , e i t h e r exposure^or-access"-to • a ' s a f e ' ment  (Mast erson, 1970;  Crawford  Masters on,  compart-  1978) ,  5 15)  i n t e r r u p t i n g the t r a i n i n g schedule McDonough,  It  to  Jackson, §  1974),  i s c l e a r from t h e s e d a t a t h a t a number o f e n v i r o n m e n t a l  can a f f e c t b a r p r e s s avoidance performance; the  (Manning,  variables  however, the q u e s t i o n i s whether  improvement a t t r i b u t e d to these v a r i a b l e s  i s o f a magnitude  account f o r the o v e r a l l v a r i a n c e i n avoidance, l e a r n i n g .  sufficient  In. t h i s  con-  t e x t the most important c o n c l u s i o n t h a t can be drawn from t h e s e d a t a i s t h a t no e n v i r o n m e n t a l variables-ha's been found that makes . b a r - p r e s s i n g t o a v o i d shock ning  as easy f o r a r a t to l e a r n , a s jumping  ( T h e i o s , 1963),  avoidance took about  Evennihatheemost  trials  1959)  or run-  s u c c e s s f u l studies- o f b a r - p r e s s  ( e . g . , H u l l , Myer, $ Smith, 1975; 200  (Maatch,  D e l p r a t o $ Holmes, .. 1977), i t  b e f o r e the major p o r t i o n o f s u b j e c t s a v o i d e d  shock  1 consistently. l i e r studies  Although such r e s u l t s r e p r e s e n t an.improvement o v e r e a r (e.g., D'Amato f S c h i f f , T  1964),  they cannot  v a s t d i f f e r e n c e s i n the r a t e s at which d i f f e r e n t  account  f o r the  avoidance responses  are  learned. By f a r the most p o w e r f u l evidence a g a i n s t the " e q u i v a l e n c e o f associability"  assumption  Garcia § Koelling  was  (1966),  p r o v i d e d by a s t u d y o f a v e r s i v e c o n d i t i o n i n g by These r e s e a r c h e r s found t h a t r a t s  associated  a n o v e l t a s t i n g s o l u t i o n w i t h s i c k n e s s , even a f t e r a l o n g d e l a y between the  cue and the consequence;  s i o n " i f the consequence was  but t h e y d i d not develop t h i s shock,  " t a s t e aver-  O n l y i f the s o l u t i o n was  "bright  and  n o i s y " would r a t s a v o i d i t i f i t had been f o l l o w e d by shock. ' These r e sults  c l e a r l y showed t h a t . e a c h cue and each consequence c o u l d be  quite  e1f f e•c t i v e , but o n l y i n" c e r t a i n n o n - a r b i t r a r y c o m b i n a t i o n s . Because r a t s "Stable'" performance has .been r e p o r t e d i n fewer. t r i a l s (Berger § Brush, 1975). but "average avoidance" w a s i 1 , o n l y 60%. I t s h o u l d a l s o , b e noted t h a t , '&rc&bits •' -0s-£ *.ofinance nas. bscn ii-eiW-ueq .->xi cewav ;tirj a? * ,^6*1,.^ d i s c r e t e t r i a l - p r o c e d u r e s ' c o m m o n l y u s e d - i n " t r a i n i n g avoidance responses such as r u n n i n g o r jumping are d i f f i c u l t t o compare t o ' f r e e o p e r a n t ' p r o c e d u r e s t h a t are used i n t r a i n i n g barr.press avoidance;  6 seemed to a s s o c i a t e o n l y c e r t a i n arrangements  o f cue and consequence  these  f i n d i n g s were c l e a r l y i n c o n s i s t e n t w i t h the e q u i v a l e n c e 'of a s s o c i a b i l i t y !  2  assumption. T r a d i t i o n a l approaches  t o the s t u d y o f b e h a v i o u r have not been a b l e  to p r e d i c t o r e x p l a i n these l a r g e d i f f e r e n c e s i n the,-ease'of a v e r s i v e learning.  However, •Bo:Mre'sl)(li9^^^  problem t h a t was of  the organism.  the  a s o l u t i o n to t h i s  based on a g e n e r a l c o n s i d e r a t i o n o f the s u r v i v a l  requirements  I t i s B o l l e s ' h y p o t h e s i s t h a t s e r v e d as the focus f o r  present investigations. i'"  SSDR H y p o t h e s i s  1  B o l l e s argued t h a t the s u r v i v a l requirements o f an animal i n i t s n a t u r a l environment  demanded a d e f e n s i v e mechanism o t h e r than  l e a r n i n g as i t i s s t u d i e d i n p s y c h o l o g y experiments,  In the  avoidance laboratory,  a v i s u a l o r a u d i t o r y cue i s o f t e n used t o s i g n a l the onset o f the a v e r s i v e s t i m u l u s , but in, the w i l d an a t t a c k .  f  predators- do not o f t e n s i g n a l t h e i r p r e y ' b e f o r e  Furthermore, the r e s e a r c h e r may  avoidance performance  wait many t r i a l s  before stable  o c c u r s ; whereas, a p r e d a t o r i n the w i l d does- not  a l l o w p r e y enough " t r i a l s "  f o r " l e a r n i n g " to occur.  situations preclude this kind of t r i a l  S i n c e most n a t u r a l  and e r r o r l e a r n i n g , s u r v i v a l must  i n s t e a d depend upon a d e f e n s i v e mechanism w i t h which the animal i s a l r e a d y equipped, an i n n a t e s e t o f d e f e n s i v e responses t h a t o c c u r i n the p r e s e n c e of  any new  o r sudden s t i m u l u s ,  s p e c i f i c ' defense r e a c t i o n s  B o l l e s c a l l e d these responses  'species-  (SSDRs) and assumed t h a t t h e y took one  of  o n l y t h r e e forms: f l e e i n g , f r e e z i n g , o r f i g h t i n g , B o l l e s u t i l i z e d the n o t i o n o f SSDRs t o e x p l a i n l a b o r a t o r y avoidance l e a r n i n g i n t h e f o l l o w i n g way, _ _^  The n o r m a l l y v a r i e d b e h a v i o u r a l r e p e r t o i r e  R e c e n t l y , however, Krane and Wagner (1975), were a b l e t o demonstrate a v e r s i o n l e a r n i n g when the  'consequence'  was  delayed"shock.  taste  7  of the domesticated laboratory animal is"suddenly r e s t r i c t e d when an aversive stimulus i s presented.  Now the animal, l i k e i t s counterpart i n the,  wild, emit§.;0nly^innate defensiye^resggns  :„  o  freezes, f l e e s , or f i g h t s .  Thus, aversive laboratory s t i m u l i act i n a  manner s i m i l a r to any sudden or novel stimulus i n the animal's natural environment. These defense responses emitted during shock, bearge' the c r i t i c a l  sub-  strate upon .which l a t e r performance i n an avoidance s i t u a t i o n depends.' I f the response required i n the s i t u a t i o n happens to coincide with one of the  animals' SSDRs (e.g., f l e e i n g ) , then t r a i n i n g can proceed smoothly.  If, on the other hand, the required response i s not part of the animal's innate defensive repertoire, (e.g., barrpre.ssing) performance wis-uncertain and sometimes i t 'does noter..progress beyond the base-line l e v e l . Thus according to Bolles, anpundersitaridingaofitheovariabi'Iitybihit)' «.' t  avoidance learning involves an appreciation of the organism's SSDRs and an assessment of the comparability of these responses with the required avoidance response, In Bolles' view-, an avoidance response i s acquired rapidly i f i t i s an SSDR, not because i t i£ strengthened (reinforced) by .events that are. contingent on t h i s response (e.g., the avoidance of shock), but because competing SSDRs are suppressed (punished) by the aversive stimulus- For example, when the avoidance response i s running down a straight  alley,,,  other SSDRs which compete with f l e e i n g are quickly.suppressed because they are  paired with shock more often than is- f l e e i n g ,  Thus, the c r i t i c a l eonr-  tingency f o r the rapid emergence o f an SSDR i s punishment ( c f , , Dinsmoor, 1954), Bolles did agree that reinforcement could "strengthen ' certain avoid1  v anee responses- (Bolles,. 197Qj p, 42); however, he emphasized  that  8  c o n t i n g e n c i e s t h a t are e f f e c t i v e o n l y a f t e r Herrnstein § Hineline,  thousands o f shocks  (e.g.,  1966) cannot p o s s i b l y account f o r b e h a v i o u r changes  t h a t t a k e p l a c e i n the l a b o r a t o r y a ^ t e r / a - ^ how  animals l e a r n t o s u r v i v e i n . n a t u r e  ( B o l l e s , 1970).  T h i s .emphasis on  the e t h o l o g i c a l significance o f a v o i d a n c e b e h a v i o u r s is- p r o b a b l y the most unique and c o m p e l l i n g aspect o f the SSDR, h y p o t h e s i s .  I t s apparent  strength  l i e s i n i t s a b i l i t y t o p r e d i c t l a b o r a t o r y avoidance b e h a v i o u r from a knowledge o f the o r g a n i s m ' s ide£en.sd!veebehavibu3??vi6ur. sis,  L i k e any o t h e r h y p o t h e -  however, i t s u l t i m a t e v a l u e depends on e m p i r i c a l t e s t s o f i t s  validity.  The p i v o t a l c o n s t r u c t i n B o l l e s ' ' h y p o t h e s i s , i s the n o t i o n o f an i n 1  nate defensive r e p e r t o i r e ; yet B o l l e s p a i d l i t t l e systematic a t t e n t i o n the d e f e n s i v e r e p e r t o i r e i t s e l f , except t o s p e c i f y t h a t i t i s l i m i t e d freezing,  fleeing,  and f i g h t i n g ,  to to  What e v i d e n c e , o t h e r t h a n the f a c t t h a t .  a p a r t i c u l a r avoidance response i s l e a r n e d r a p i d l y , demonstrates  that a  3  behaviour i s . i n fact a n ' i n n a t e " defensive reaction? w i t h t h i s problem i n a footnote,  B o l l e s . (1972)  The d e f e n s i v e r e p e r t o i r e o f the  dealt subject  can be determined by a s s e s s i n g i t s . r e a c t i o n to s h o c k , and, " . . . a n y o n e who does t h i s w i t h a r a t w i l l s e e . t h a t i t e i t h e r runs away, f r e e z e s , aggressive,,"  ( B o l l e s , 1972, p , 129)',  A l t h o u g h B o l l e s d i d not conduct  the s t u d y t h a t h he p r e s c r i b e d , t h e r e i s now a growing body o f t h a t , f o r the most p a r t ,  o r becomes  confirms h i s views,  literature  These d a t a w i l l now be r e r  viewed, D e f e n s i v e behaviours- o f the r a t 1  1  ' ' F r e e z i n g artd f l e e i n g , v  B l an chard and B l a n c h a r d (1969a;  1970a,b)  found t h a t the predominant d e f e n s i v e r e a c t i o n s o f r a t s exposed t o v  as,sb ci\at ed. w i t h \ s h o e h were f r e e z i n g and f l e e i n g , s  3  s  ~~~' '  r r  r  stimuli  The r a p i d i t y w i t h which  •' ' .  I t i s a l s o n o t e w o r t h y t h a t B o l l e s n e g l e c t e d t o d e f i n e the t e r m , " i n n a t e defense r e a c t i o n " . F o r the purposes o f t h e p r e s e n t i n v e s t i g a t i o n , a '.defense r e a c t i o n ' i s v i e w e d as an a d a p t i v e response to a v e r s i v e s t i m u l a t i o n . N o t h i n g i s assumed about t h e "innate" status, either than the suggestion (see  9 t h e s e responses developed suggested t h a t t h e y were s p e c i e s - s p e c i f i c defense  reactions  (cf,,  'unlearned',  i„e.,  B l a n c h a r d § B l a n c h a r d , 1971}.  S i m i l a r l y , b o t h o f t h e s e r e s p o n s e s were found t o be prominent o f the r a t ' s r e a c t i o n to a c a t  components  ( B l a n c h a r d § B l a n c h a r d , 1971; 1 9 7 6 ) .  responses o c c u r r e d i n the absence o f p r i o r e x p e r i e n c e . w i t h c a t s , the absence o f a g o n i s t i c c o n t a c t s between the r a t and t h e c a t 1935).  These  and i n '  (cf,,  Curti,.  B l a n c h a r d , K e l l e y and B l a n c h a r d (1974) p r o v i d e d e v i d e n c e t h a t ,  novelty i t s e l f can produce defensive reactions ;  (cf.,  B o l l e s , 1970).  found t h a t p r e e x p o s u r e to a n o v e l s i t u a t i o n reduced r a t s ' enter i t .  latencies  They to  C o n v e r s e l y , r a t s f l e d from a n o v e l t o a l e s s ' n o v e l s i t u a t i o n ,  even when r e q u i r e d t o c r o s s an e l e c t r i f i e d g r i d .  These r e s u l t s  suggested  t h a t the h y p e r a c t i v i t y observed i n r a t s t h a t are p l a c e d i n n o v e l  situations  may r e f l e c t a b o r t i v e d e f e n s i v e r e a c t i o n s . s u c h as f l i g h t . ( c f . W a l k e r , 1 9 5 9 ) . Many o f the B i a n c h a r d s ' f i n d i n g s have been c o n f i r m e d and extended i n a recent  s t u d y o f the ontogeny o f d e f e n s i v e r e a c t i o n s  i n the r a t ,  Bronstein  and H i r s c h (1976) found t h a t i m m o b i l i t y i n response t o a f o o t s h o c k , caged c a t ,  a  o r a s u d d e n l y moving o b j e c t tended to i n c r e a s e as a f u n c t i o n  o f the age o f the r a t . the p r e d a t o r  The s i m i l a r i t y o f the ontogeny o f r e a c t i v i t y t o  and t o the f o o t s h o c k was i n t e r p r e t e d  as s u p p o r t  for  (1970} 1972) c o n t e n t i o n t h a t responses* t o s t i m u l i a s s o c i a t e d w i t h represent innate defensive reactions  (cf.,  o f the r a t s ' n a t u r a l d e f e n s i v e  can be d i s c o v e r e d b y e x p o s i n g the r a t t o  footshock  B l a n c h a r d P, B l a n c h a r d , 1971),  T h i s o b s e r v a t i o n a l s o appears t o add some s u b s t a n c e t o B o l l e s ' a s s e r t i o n t h a t the a t t r i b u t e s  Bolles'  'unnatural'  (1972) repertoire-  a v e r s i v e s t i m u l i such  as s h o c k , B l a n c h a r d , M a s t , and B l a n c h a r d (1975) d e s i g n e d an experiment  to.  1  i d e n t i f y the p a r t i c u l a r f e a t u r e s o f c a t s t h a t e l i c i t e d f r e e z i n g i r i r a t s , g e n e r a l d i s c u s s i o n ) t h a t t h e r e m a y ' b e . a s t r o n g g e n e t i c component i t s -expression.  to  10 They found t h a t the sound and s m e l l o f a c a t were r e l a t i v e l y i n e f f e c t i v e c u e s ; whereas, v i s u a l cues a s s o c i a t e d w i t h movement o f t h e c a t , i t was a l i v e o r dead, were p o t e n t ' r e l e a s e r s ' ' o f f r e e z i n g . the movement o f a c a t ,  Furthermore,  a dog, o r an i n a n i m a t e c a r d produced f r e e z i n g , a l -  though the d u r a t i o n o f the e f f e c t w a s . l e s s f o r the l a t t e r f o r the o t h e r two.  whether  s t i m u l u s than  These experiments suggested t h a t movement i t s e l f  an i m p o r t a n t " r e l e a s e r " o f  f r e e z i n g i n the r a t ,  f r e e z i n g may depend on a d d i t i o n a l f a c t o r s  is  w h i l e the maintenance o f  such as t h e p h y l o g e n e t i c  vance » o f : tK^^^  'rele-  c o n t r o l : the  size,ispeed',-' and shape o f the r e l e a s i n g s t i m u l u s may c l a r i f y t h i s  issue.  B l a n c h a r d , Fukunaza, and B l a n c h a r d (1976) extended t h i s l i n e o f rers e a r c h b y examining o t h e r e n v i r o n m e n t a l f a c t o r s r e s p o n d i n g i n the r a t .  that control  defensive  They h y p o t h e s i z e d t h a t the type o f d e f e n s i v e be^  h a v i o u r e l i c i t e d i n _ a. r.at:_by. a.;cat ( i , e , , f r e e z i n g o r f l e e i n g ) might depend on the p o t e n t i a l f o r escape fromthe t e s t environment,  and n o t  s a r i l y on the d i f f e r e n t i a l punishment o f d e f e n s i v e r e a c t i o n s (1970) had suggested  (but see B o l l e s , 1975a, 1976).  as  neces-  Bolles  In o r d e r t o t e s t  this  " e l i c i t a t i o n " h y p o t h e s i s , t h e y employed t h e i r p r e v i o u s methodology ( B l a n c h a r d § B l a n c h a r d , 1971) i n w h i c h no d e f e n s i v e responses were by punishment  followed  ( i . e . , no r a t - c a t c o n t a c t ) , w i t h the a d d i t i o n a l p r o v i s i o n  t h a t some r a t s were g i v e n a b r i e f exposure t o the i n e s c a p a b l e t e s t p r i o r t o the i n t r o d u c t i o n o f the t e s t s t i m u l u s .  Rats t h a t had been  chamber "famil-  i a r i z e d ' ' w i t h the i n e s c a p a b l e chamber were f a r l e s s a c t i v e when exposed t o a c a t than a s i m i l a r l y t r e a t e d group t h a t had not been  familiarized.  However, the a c t i v i t y s c o r e s o f t h e more a c t i v e group g r a d u a l l y d e c l i n e d o v e r the 5-min t e s t p e r i o d u n t i l b o t h e x p e r i m e n t a l groups f r o z e e q u a l l y o f t e n but r e l i a b l y more t h a n a n o - c a t c o n t r o l group,  Thus, f r e e z i n g ,  11 r a t h e r than f l i g h t ,  appears t o o c c u r when animals are  w i t h a s i t u a t i o n i n w h i c h escape i s i m p o s s i b l e .  "familiarized"  The B l a n c h a r d s a l s o  argued t h a t t h i s f a c t o r seemed t o account f o r the g r a d u a l a c t i v i t y r e d u c t i o n o f the " n o n - f a m i l i a r i z e d " r a t s ; t h e i r i n i t i a l  a c t i v i t y may have  s e r v e d t o " f a m i l i a r i z e " them w i t h the i n e s c a p a b l e environment and thus f r e e z i n g g r a d u a l l y became t h e i r dominant d e f e n s i v e Fighting.  F i g h t i n g i s another b e h a v i o u r o f r a t s t h a t has been viewed  as a d e f e n s i v e r e a c t i o n  (cf.,  Bolles,  1970; 1975; B l a n c h a r d § B l a n c h a r d ,  1977).  When a r a t  object,  and shock i s a d m i n i s t e r e d , the r a t w i l l  i s p l a c e d i n a chamber w i t h another r a t ,  u p r i g h t p o s t u r e and a t t a c k i t and A z r i n  response.  o r an i n a n i m a t e  face the s t i m u l u s i n an  ( f o r a r e v i e w , see U l r i c h ,  1967),  Ulrich  (1962) showed t h a t t h i s s h o c k r - e l i c i t e d f i g h t i n g can v a r y as a  f u n c t i o n o f the d u r a t i o n , i n t e n s i t y , and frequency o f s h o c k ; the s i z e o f the t e s t chamberj  and the i n i t i a l  The age o f the r a t s  o r i e n t a t i o n o f t h e r a t s t o each  (Hutchinson, U l r i c h § A z r i n ,  1965) and the  other.  duration  o f the shock test i n t e r v a l ( A z r i n , H u t c h i n s o n , § S a l l e r y , 1964) can a l s o affect  shock-elicited fighting,  snakes,  I t has been demonstrated  r a c c o o n s , opossums, monkeys, and c a t s  1964; U l r i c h , . W o l f f ,  § Azrin,  1964).  hamsters,  ( U l r i c h et a l , , 1962; A z r i n , .  Even b l i n d e d r a t s can show s h o c k -  e l i c i t e d f i g h t i n g (Elory, U l r i c h , § Wolff, i n the same manner by extreme h e a t  in rats,  (Ulrich,  1965).  F i g h t i n g can be e l i c i t e d  1967), subcutaneous  electrode  shock ( U l r i c h et a l . , 1962), o r p h y s i c a l cbMws'i.ng ( A z r i n , Hake, § H u t c h i n son,  1964), B l a n c h a r d and h i s a s s o c i a t e s  ( B l a n c h a r d , B l a n c h a r d , $ T a k a h a s h i , 1977;  B l a n c h a r d , T a k a h a s h i , £ K e l l e y , 1977; B l a n c h a r d § B l a n c h a r d , 1977). have r e c e n t l y r e f i n e d the a n a l y s i s o f d e f e n s i v e f i g h t i n g . i c i n t e r a c t i o n s which occurfedwwhentrats  They s t u d i e d  from o u t s i d e an  agonist-  established  12 l a b o r a t o r y c o l o n y were i n t r o d u c e d t o dominant male r a t s w i t h i n the c o l o n y . B e h a v i o u r s t y p i c a l o f the dominant males were p i l o e r e c t i o n , l a t e r a l d i s p l a y , and b i t i n g ; whereas, the i n t r u d e r s b o x e d , f r o z e , and l a y on t h e i r b a c k s , b e h a v i o u r s which appeared t o i n h i b i t a g g r e s s i o n ( B l a n c h a r d , Blanchard, Takahashi, § Kelley,  1977).  . From t h e s e f i n d i n g s , the B l a n e h a r d ' s argued t h a t t h e a g o n i s t i c behavi o u r s o f c o l o n y r a t s and i n t r u d e r r a t s appeared t o f a l l of attack  and d e f e n c e , r e s p e c t i v e l y .  i n t o the  A s i m i l a r e x a m i n a t i o n o f the  i c behaviours o f p a i r s o f r a t s i n a r e f l e x i v e f i g h t i n g task § Azrin,  1962) r e v e a l e d t h a t the  'defensive  ' pattern  (see  agonist-  Ulrich  ( e . g . , b o x i n g ) was'  f a r more c h a r a c t e r i s t i c o f t h e i r b e h a v i o u r t h a n was the (e.g., biting).  categories  'attack'  pattern  These o b s e r v a t i o n s suggested t h a t t h e b e h a v i o u r s t r a d i -  t i o n a l l y measured i n the r e f l e x i v e f i g h t i n g t a s k do not s i m p l y r e f l e c t " s h o c k - e l i c i t e d aggression" ( c f , , U l r i c h § A z r i n , p r e s e n c e o f a c o n s p e c i f i c may i n s t e a d e l i c i t  1962),  Shock i n the  a g o n i s t i c defense  responses.  P e a r , Moody, and P e r s i n g e r (1972) conducted a s t u d y o f s h o c k r e l i c i t e d f i g h t i n g that w a s ' p a r t i c u l a r l y r e l e v a n t to B o l l e s ' researchers  found t h a t many l e v e r - p r e s s e s  as i n s t a n c e s o f ' o p e r a n t ' at the l e v e r .  SSDR h y p o t h e s i s .  t h a t o r d i n a r i l y would be counted  avoidance were a c t u a l l y s h o c k - e l i c i t e d a t t a c k s  Thus, a l t h o u g h B o l l e s '  (1970) has s u g g e s t e d t h a t r a t s  t h i s t a s k by b e i n g r e i n f o r c e d f o r i n a d v e r t e n t l y f r e e z i n g on t h e t h e r e are o t h e r  These  'learn'  lever,  ' s p e c i e s - t y p i c a l ' accounts o f l e v e r ^ p r e s s a v o i d a n c e t h a t  are j u s t as p l a u s i b l e . Thigmotaxis,  Grossen and K e l l e y (1972) s t u d i e d an i n t e r e s t i n g  response t h a t d i d n o t o b v i o u s l y f a l l o f defensive behaviour, i.e.,  i n t o one o f B o l l e s ' t h r e e  defensive  categories  They found t h a t f o o t s h o c k i n c r e a s e d t h l g m o t a x i s ,  the amount o f t i m e t h a t r a t s spent i n c o n t a c t w i t h the w a l l s o f the  apparatus.  In a second e x p e r i m e n t , r a t s l e a r n e d t o . ' j u m p :  from a g r i d to a  13 safe platform more r e a d i l y when i f was'adjacent to the walls ofthe apparatus. of  These data supported Bolles ,(1970) argument that the-acquisition an avoidance response i s enhanced i f i t i s related to the organism's  defensive repertoire.  Although the evidence suggests that thigmotaxis  should be added to the l i s t of the rat's defensive behaviours, i t i s not clear that Grossen and Kelley's description of thigmotaxis represents anything more than a refined measure of freezing behaviour, ( i . e . , freezing close to w a l l s ) .  In any case, these data cshouldial'ert'susotohthe.ipds'sibility  that knowledge of the rat's defensive capacities may be  incomplete.  Rationale -and ^Purpose Rationale,  The aforementioned  studies of defensive behaviour.-, con-  firm Bolles' view that freezing, f l e e i n g , and f i g h t i n g are defensive behav-. iours,  However, since there does not appear to have been any concerted  e f f o r t to i d e n t i f y defensive responses other.than freezing, f l e e i n g , and f i g h t i n g , Bolles' assumption (Bolles, 1975)  that a l l defensive behaviours ,  f a l l into one of these three categories remains untested, argues that avoidance  Because Bolles  learning involves, the elimination by punishment of  a l l defensive responses i n an animal's repertoire u n t i l only the most eff e c t i v e oife^remainsaccurate predictions about avoidance  learning must be  based on a knowledge of an animal's complete defensive repertoire. It i s apparent  from the l i t e r a t u r e on defensive reactions (e.g.,  U l r i c h § Azrin, 1962;  Blanchard § Blanchard, 1976)  that a p a r t i c u l a r defen-  sive behaviour may depend upon certain environmental f u l l expression.  'supports* f o r i t s  For example, an avenue of escape may  support f l e e i n g be-,  haviour: the absence of support f o r f l e e i n g and f i g h t i n g may ing.  lead to freez-  To some researchers (e.g., Bolles, 1972), these observations simply  14 suggested t h a t a p a r t i c u l a r t e s t fensive reactions,  s i t u a t i o n may.favor one  However, taken one  step f u r t h e r , these observations  suggest that the p r o b a b i l i t y o f d i s c o v e r i n g the f u l l d e f e n s i v e r e p e r t o i r e may  o f the t h r e e de-  e x t e n t o f the r a t ' s  v a r y as a f u n c t i o n o f the v a r i e t y o f s i t u a t i o n s  i n which d e f e n s i v e b e h a v i o u r s have been s t u d i e d .  Appropriate  environmental  c o n d i t i o n s may,be n e c e s s a r y f o r c e r t a i n d e f e n s i v e b e h a v i o u r s to, occur.': Simply s h o c k i n g a r a t on a g r i d f l o o r i s , t h e r e f o r e , an i n s u f f i c i e n t  test  o f : t h e p r o p o s i t i o n t h a t the " f r i g h t e n e d " r a t can o n l y f r e e z e , f l e e , o r ( c f . , B o l l e s , 1972;  fight  1975).  T r a d i t i o n a l l y , b e h a v i o u r a l s c i e n t i s t s have r e s t r i c t e d the- b e h a v i o u r o f t h e i r s u b j e c t s to one o r two  a l t e r n a t i v e s i n o r d e r t o study the p r o c e s -  ses t h a t presumably u n d e r l i e a l l b e h a v i o u r s this and  e x p e r i m e n t a l t a c t i c may  (e.g., P a v l o v , 1927).  Although  have r e v e a l e d some p r i n c i p l e s o f c l a s s i c a l  i n s t r u m e n t a l l e a r n i n g , i t s a p p l i c a t i o n seems i n a p p r o p r i a t e when the  o b j e c t o f study I s the d i s c o v e r y o f b e h a v i o u r s .  In o r d e r t o d i s c o v e r be-  h a v i o u r , the makeup o f the e x p e r i m e n t a l s e t t i n g should be t a i l o r e d t h e r e s t r i c t i o n o f b e h a v i o u r s than f o r t h e i r p r o l i f e r a t i o n , s e a r c h on d e f e n s i v e b e h a v i o u r s has been r e s t r i c t i v e , ' The  less for  Most o f the r e -  r e s e a r c h has  been i n a p p r o p r i a t e l y c o n t r o l l e d i n the sense t h a t i t has been c o n f i n e d mostly to s i t u a t i o n s s i m i l a r t o those i n which avoidance phenomena have been t r a d i t i o n a l l y s t u d i e d (e.g., B l a n c h a r d et a l , , 1969,  1970).  i s not s u r p r i s i n g , t h e r e f o r e , t h a t the d e f e n s i v e b e h a v i o u r s observed i n 4  t h e s e s i t u a t i o n s s h o u l d be q u i t e c o n s i s t e n t w i t h what "anyone"  4  Bolles  (1972, p,  129)  can  see  It  i n s t a n d a r d avoidance apparatuses, and not at v a r i a n c e w i t h what are assumed by p s y c h o l o g i s t s t o ,be the r a t ' s c h a r a c t e r i s t i c modes o f d e f e n s e . In  s h o r t , I,am  s u g g e s t i n g t h a t the e x p r e s s i o n o f the r a t s ' d e f e n s i v e c a ^  p a c i t i e s has been shaped more by the c o n s t r a i n t s o f t y p i c a l t e s t enviornments Purpose. ted  than by the r a t i t s e l f ,  The study o f the r a t s ' d e f e n s i v e r e p e r t o i r e may  by a l t e r i n g the s t a n d a r d l a b o r a t o r y s e t t i n g so t h a t  s t r a i n t s on the r a t ' s b e h a v i o u r are reduced. environments  laboratory  be  facilitar  a r b i t r a r y con^  Although a v a r i e t y o f t e s t  have been w i d e l y used t o i n v e s t i g a t e the responses o f l a b o r a -  t o r y animals to a v e r s i v e s t i m u l a t i o n , -m^t^hi-yerjLonifo f^fei^e-'^.'-^pnimon':..'  #hea"zfil.0®a^oifi.^hji^fpayiitiH^sisp^ss&gsd  -met^livgi-i^  .;-r.j_  f e c e s and u r i n e can drop and shock can be a d m i n i s t e r e d , c o n s t r a i n d e f e n s i v e b e h a v i o u r i n two ways,  T h i s > f e a t u r e may  5  F i r s t , u n l i k e more n a t u r a l  s e t t i n g s , t h e r e i s l i t t l e i f a n y t h i n g on the f l o o r o f the apparatus t h a t the rat jCould move o r manipulate f o r i t s own ;  defense,  s t i m u l u s i n t h i s s e t t i n g i s r e l a t i v e l y d i f f u s e and may  Second,  the a v e r s i v e  not support a d e f e n  r  s i v e b e h a v i o u r t h a t i s n o r m a l l y d i r e c t e d at l o c a l i z e d sources o f a v e r s i v e stimulation. P r e l i m i n a r y work i n t h i s l a b o r a t o r y has supported t h i s h y p o t h e s i s . We found t h a t a r a t housed o f t e n pushed shock s o u r c e .  i n a chamber w i t h bedding m a t e r i a l  t h i s m a t e r i a l toward  (Sanri-cel)  and over ( i . e . , b u r i e d ) a w e l l - d e f i n e d  Blhi.s:sbui^ingbbeh^  . ;  ,p.aft^d.f.'.:-t?hej ..  r-at lis cdcfensrvesfep'erfcoiree andethusTn,mdre:nsystematiAi study', o f this-.,.response Was.warranted. Thesgenerafeepurp.^ bute t o the development 'of a v i a b l e  • ..... ' b i o l o g i c a l ' approach t o avoidance  l e a r n i n g by s t u d y i n g the b u r y i n g response,  The purpose o f each s t u d y was  16  t o p r o v i d e two k i n d s o f evidence t o support t h e v i e w t h a t b u r y i n g behavi o u r i s a prominent  d e f e n s i v e response o f r a t s .  Each experiment was de-  s i g n e d t o show t h a t b u r y i n g i s a r e l i a b l e response t o l o c a l i z e d  aversive  s t i m u l a t i o n , and/or t o show t h a t t h e b u r y i n g response i s a d a p t i v e ; t h a t is., t h a t i t a f f o r d s t h e animal some p r o t e c t i o n from the. noxious  agent.  17  GENERAL METHODS This section contains a description o f the methodological features common to each of the nine experiments i n this thesis..  In each experi-  ment, the effect of forepaw shock on the amount and duration o f burying behaviour i n rats was assessed. Subjects,  The subjects i n each of the experiments were 250- to 550 g.  male, hooded rats purchased from Canadian Breeding Farm and Laboratories, La P r a i r i e , Quebec.  Each rat was i n d i v i d u a l l y housed i n a 24 x 18 x 18 cm,  wire-mesh cage under controlled illumination (12-hr light/dark cycle) with continuous access to Purina laboratory chow and water, Apparatus.  Animals were tested i n a small, closed room, adjacent to  the behavioural recording apparatus,  Behaviours were viewed v i a closed  c i r c u i t t e l e v i s i o n and recordedoon video tape. Inside the t e s t i n g room, a t e l e v i s i o n camera was mounted 50 cm d i r e c t l y above the 44 x 30 x 44 cm transparent Plexiglas test chamber.  The chamber  f l o o r was covered evenly ;#riith r.egulary gr.ade'^  Sf ground'corn  cob ,.$Pa^6nhBrd.o.e'S9in;g..G6', ?aRaxt-on?.rtMn-);/In the center of each of the r  four walls of the chamber,2 cm above the l e v e l o f the bedding material, was a hole, 1.2 cm i n diameter through which a wooden prod ; 4 § , ' 5 xeOtS.x 0.5 cm). ^^i^x^S,£ §f$i§dsin) ,.• \ i n some experiments, two prods were inserted through n  the holes at opposite ends o f the chamber.  Shocks were delivered through .  the two uninsulated wires wrapped around the stationary prods. Procedures Habituation:  P r i o r to each experiment, a l l animals were handled  and placed i n the Plexiglas test chamber i n groups of f i v e or s i x f o r  18 30-min p e r i o d s on each o f 4 c o n s e c u t i v e d a y s , Shock a d m i n l s t r a t i o n .  On the 5 t h d a y , t h e shock p r o d was i n t r o d u c e d  i n t o the e x p e r i m e n t a l chamber through t h e h o l e i n an end w a l l ; t h e n ,  each  e x p e r i m e n t a l animal was p l a c e d i n d i v i d u a l l y i n the c e n t r e o f the  chamber  f a c i n g away from the p r o d .  touched  When each e x p e r i m e n t a l s u b j e c t  first  t h e p r o d w i t h a foewpaw, a ' b r i e f s h o c k , i n i t i a t e d by the e x p e r i m e n t e r and t e r m i n a t e d by the w i t h d r a w a l o f t h e s u b j e c t , power s o u r c e .  was d e l i v e r e d from an 800 V AC  The s i n g l e shock e l i c i t e d a sudden w i t h d r a w a l toward the  back o f the chamber.that  i n most cases was accompanied by v o c a l i z a t i o n .  In some experiments the r a t s were removed from the chamber i m m e d i a t e l y after  shock and r e t u r n e d  l a t e r f o r t e s t i n g ; however, i n most c a s e s ,  shock s i g n a l l e d the b e g i n n i n g o f the t e s t  session.  C u r r e n t from t h e 800 V power source was a t t e n u a t e d w i t h dropping r e s i s t o r .  the  a.series  In a l l but one e x p e r i m e n t , the v a l u e o f the d r o p p i n g  r e s i s t o r was 80,000 ohms.  The c u r r e n t  f l o w i n t h i s shock c i r c u i t was,  m o n i t o r e d by a s t o r a g e o s c i l l o s c o p e t o determine the a c t u a l i n t e n s i t y and d u r a t i o n o f shocks r e c e i v e d b y r a t s under the c o n d i t i o n s i n which t h e y would be t e s t e d .  The 10 n a i v e , a d u l t , hooded r a t s s e l e c t e d f o r t h i s  pose r e c e i v e d shocks t h a t averaged 7,9 mA i n i n t e n s i t y (SD = 1 , 4 7 ) , msec.  (SD = 9 . 8 )  pur42.9  i n duration,  B e h a v i o u r a l o b s e r v a t i o n and q u a n t i f i c a t i o n .  The b e h a v i o u r o f each  s u b j e c t was viewed f o r the 15 min t e s t p e r i o d , and the i n c i d e n c e and d u r a t i o n o f b u r y i n g sequences were r e c o r d e d on an event  recorder.  The b u r y i n g b e h a v i o u r o f r a t s i n t h i s s i t u a t i o n c o n s i s t e d o f a of stereotyped  sequences t h a t began w i t h the r a t  d i s t a n t p a r t o f the a p p a r a t u s ,  series  f a c i n g the p r o d from a  T h e . r a t t h e n moved d i r e c t l y toward t h e  p r o d , p u s h i n g and s p r a y i n g a p i l e o f b e d d i n g m a t e r i a l o v e r the p r o d w i t h  1 9 its  snout  and r a p i d movements o f i t s forepaws,  punctuated  1  Often, t h i s behaviour  by p e r i o d s when t h e r a t s t r e t c h e d forward,  was  i t s vibrissae  n e a r l y t o u c h i n g the p r o d b e f o r e withdrawing a b r u p t l y t o t h e r e a r o f the chamber from where i t began another•sequence o f p u s h i n g  and s p r a y i n g .  The  i n v a r i a n t component o f t h i s , b e h a v i o u r a l p a t t e r n was the r a p i d , a l t e r n a t i n g , forward-motion o f t h e f o r e l i m b s by which the r a t d i s p l a c e d m a t e r i a l toward the prod.  Tt was the d u r a t i o n s o f these d i r e c t e d b u r s t s o f f o r e l i m b  s p r a y i n g t h a t were monitored by t h e experimenter, behaviour  i n the present  t h e s i s . ' Routine  always c o r r o b o r a t e d the o r i g i n a l  and t h a t d e f i n e d b u r y i n g  checks o f v i d e o t a p e d  test  sessions  measures,  A f t e r each t e s t , t h e h e i g h t o f t h e bedding m a t e r i a l from t h e f l o o r o f the P l e x i g l a s chamber was measured a t t h e j u n c t i o n between t h e p r o d and the w a l l .  T h i s measure, and t h e r a t i o formed b y t h e h e i g h t o f the h i g h e s t  mound o v e r i t s d i s t a n c e from t h e prod, burying  s e r v e d as a d d i t i o n a l i n d i c e s o f  behaviour!  Statistical presented  analysis,  In most'cases, t h e designs  i n this thesis j u s t i f i e d  a priori  p r i o r i comparison o f c e n t r a l i n t e r e s t  statistical  o f the experiments analyses;  An a  i n t h e e a r l y experiments was between  the mean s c o r e s o f shocked and unshocked r a t s ; i n subsequent experiments the comparison was.between the mean s c o r e s a s s o c i a t e d w i t h prods]  In g e n e r a l , t h e o v e r a l l  'shock' and ' c o n t r o l '  e f f e c t o f t h e shock was so c l e a r t h a t  c a s u a l i n s p e c t i o n o f i n d i v i d u a l s c o r e s was as c o n v i n c i n g as t h e r e s u l t s o f statistical  analyses.  A n a l y s i s o f v a r i a n c e was o c c a s i o n a l l y used t o e v a l u -  ate e f f e c t s t h a t c o u l d n o t be assessed by i n d i v i d u a l  comparisons.  1  .20 Experiment 1  The purpose of Experiment 1 was to demonstrate that when adequate materials are available burying i s both a prominent and enduring response of rats to aversive stimulation. Method After.4 days of habituation, the 120 rats were randomly assigned to one of three basic conditions on Day 5,  The'ratseinsohe  condition  (shock subjects, n = 60) were shocked (8 mA) from a single prod i n . •• #.h.<?n«»aniiefcP:tevaouslyhde-sg^ibed...^e€l<^llp.win.gt-Jhg«'sh,©gk;>yeach -;v sn. •' of these subjects was removed from the chamber.  Rats i n the second condir-  t i o n (prod controls, n = 30) were not shocked but otherwise were treated i n the same manner.  Subjects i n the t h i r d condition (no^prod controls,  n = 30) were placed i n d i v i d u a l l y i n the test chamber f o r a few seconds but were exposed to neither the shock nor the prod. The rats i n each o f the three conditions were returned to the chamber for a 15-min shock-free test with the prod 10 sec, 5 min, 5 hr, 3 days., or 20 days "later.  Thus, 12-shock *ajs$c6 pr©d^  .......  s  prod control ^-ratscts • were tested at each o f the five i n t e r v a l s .  The behave  iour o f each ariaimalt was viewed and recorded by closed c i r c u i t t e l e v i s i o n as described i n the General Methods section.  Results and Discussion Figure 1 shows, that burying was a prominent part o f the behavioural repertoire of the shocked subjects,  Two-way analysis o f variance of the  "duration" data (Figure 1, Panel A) r e s t r i c t e d to the two control conditions revealed no s i g n i f i c a n t effects (p>,05).  However, planned  orthogonal  21  F i g u r e 1.  Mean d u r a t i o n o f b u r y i n g  (Panel A) and the mean o f  the r a t i o between t h e h e i g h t o f the h i g h e s t p i l e and i t s d i s t a n c e from the p r o d p o s i t i o n vals  (Panel B) a t each o f t h e s h o c k - t e s t  f o r s u b j e c t s i n t h e shock ( c i r c l e s ) , prod  and no-prod c o n t r o l  (squares)  groups.  control  inter-  (diamonds),  10sec  5min  Shock—test  5 h r 3day  20day  i n t e r v a l (log scale)  comparisons between the duration of burying i n the shocked and the control subjects combined at each of the f i v e shock-test intervals indicated that shock subjects spent s i g n i f i c a n t l y more time burying at each i n t e r v a l CIO sec, t_(22> = 4.01, p_<,0005;'5 min; t(22) = 5,93, p_<,0001 j 5 hr, t(22) = 2.48, p_<,05; 3 days, t(22) = 2.19, p_<,05; 20 days, t_(22) = 2.61, p_<.02). The present data c l e a r l y demonstrate that i n the presence of adequate materials burying i s a prevalent response of rats to aversive stimulation. At the two shortest shock-test i n t e r v a l s , rats engaged i n burying f o r about 25% of the entire test period, and the duration of burying at i n t e r vals as long as 20 days was s t i l l well above control l e v e l s .  At no time  were rats observed to push or spray material i n any d i r e c t i o n other than toward the prod, The height of the highest p i l e accumulated by each rat divided by the distance of the peak of that p i l e from the usual prod p o s i t i o n formed a r a t i o which served as the basis f o r objectively assessing the r e l a t i v e effectiveness of each rats' burying behaviour.  Rats with large height/  distance-from-prod ratios were those that accumulated the highest p i l e s closest to the prod p o s i t i o n .  It i s clear from Figure 1 (Panel B) that  these ratios provided an independent and objective confirmation of the behavioural data.  Although there were no s i g n i f i c a n t differences between  the two control conditions (p_s>.05), planned orthogonal comparisons between the shock and combined control means at each of the shock-test intervals revealed s i g n i f i c a n t differences (10 sec, t_(22) = 3.42, p_<.005; 5 min, t(22) = 3.23, p_<.005; 5 hr, •t_(22) = 2.32, p_<.05; 3 days, t(22) = 2.09, p_<,05; 20 days, t_(22) = 2.89, P_<.01).  24  Experiment 2 The purpose of Experiment 2 was to determine whether rats shocked i n one environment would bury the source of an aversive stimulation when confronted with i t i n another. Method The 20 naive s.^atgjg, handled and exposed to the test chamber on the f i r s t 4 days, were randomly assigned to shock (n = 10) or control (n = 10) conditions on Day 5.  Each experimental rat was shocked when i t  contacted a prod inserted through the wire mesh of i t s home cage.  Then  the prod was.removed and mounted on the wall of the test chamber,  The  controls received the same treatment but were not shocked.  A l l subjects  were tested i n the chamber 1 min following prod contact. Results § Discussion When rats were confronted i n the test chamber with a prod through which they had been shocked i n t h e i r home cages, they buried i t .  The  shocked ^anjipals (M_.= 108 sec) spent s i g n i f i c a n t l y (t(l8) = 3.16, p_<,005) more time burying the prod than did the control (M = 5 sec) rats,  Fm>  thermore the height/distancer-from-prod ratios were f a r greater (t (18) =• 4.29, p_<.0005) f o r the p i l e s of bedding material accumulated by the shocked animals (M = 6.2) than f o r those accumulated by control (M = 0,7) subjects.  Experiment 3 In Experiments 1 and 2, rats buried the prod through which they had been shocked.  Would the rats have buried this test object i f they had  received shock from a d i f f e r e n t source?  In other words, i s shock per se  ,.25: a sufficient  c o n d i t i o n f o r b u r y i n g , o r must the shock be a d m i n i s t e r e d  through the t e s t o b j e c t ?  Method The methods were t h e same as- those ofExperiment Day 5 the shock  animals  (n = 15) were shocked  2 except t h a t on  (1 s e c , 2.5 m A ) t h r o u g h  the f l o o r o f a 43 x 21 x 29 cm g r i d box 1 min b e f o r e b e i n g exposed t o the p r o d on the w a l l o f the t e s t chamber.  The c o n t r o l animals  (n = 10)  were n o t shocked b u t were otherwise t r e a t e d i n the same way. R e s u l t s and D i s c u s s i o n The r e s u l t s o f Experiment sufficient animals  3 i n d i c a t e d t h a t shock p e r se i s not a  c o n d i t i o n f o r the b u r y i n g response,  N e i t h e r the g r i d r s h o c k e d  (M = 6 s e c ) nor t h e i r unshocked c o n t r o l s (M = 2 see) spent V  sub-  s t a n t i a l p e r i o d s o f time b u r y i n g the p r o d , ' T h i s o b s e r v a t i o n was c o n f i r m e d by an examination o f the h e i g h t / d i s t a n c e f r o m r p r o d r a t i o s f o r the h i g h e s t r  p i l e s 'of bedding m a t e r i a l accumulated (X = 0.3) s u b j e c t s .  by the shock  Thus, the two groups  (X =C!,8) and c o n t r o l  d i d not d i f f e r s i g n i f i c a n t l y i n  terms o f e i t h e r measure ( d u r a t i o n o f b u r y i n g : t_(23) = .61, p_>.50; h e i g h t / d i s t a n c e - f r o m - p r o d r a t i o : 1^(23) = ,55, p_>.50). The b e h a v i o u r o f the g r i d - s h o c k e d animals i n Experiment in  s t r i k i n g c o n t r a s t t o the performance  ment 2.  o f the prod-shocked  3 was, t h u s , rats i n Experi-  The l a t t e r s u b j e c t s spent an average o f 108 s e c accumulating  p i l e s o f bedding m a t e r i a l w i t h h e i g h t / d i s t a n c e - f r o m - p r o d r a t i o s  averaging  6.2. >ci"caouglx th-. - c o ' i i t i ^ o u i n g r e s u l t s o f pxperiment 5-  —  2 and  .  •  r—  "Although t h e r e i s no obvious way.to equate the i n t e n s i t y - o f shock t h a t r a t s r e c e i v e through a g r i d f l o o r w i t h t h e i n t e n s i t y t h e y r e c e i v e through the p r o d , the i n i t i a l b e h a v i o u r a l r e a c t i o n s o f r a t s t o g r i d - s h o c k a t these parameters seemed t o be comparable t o t h e i r i n i t i a l r e a c t i o n t o prod-shock at the parameters used i n p r e v i o u s experiments.  26  Experiment 4  The purpose o f Experiment 4 was t o show t h a t r a t s b u r y s o u r c e s o f shock d e s p i t e s u b s t a n t i a l v a r i a t i o n s i n shock  intensity.  Method  On Day 5, t h e 60 n a i v e r a t s were randomly a s s i g n e d t o one o f f i v e conditions  (n = 12).  E v e r y animal was t r e a t e d i n the same manner throughout  the experiment, except t h a t t h e i n t e n s i t y o f the shock was v a r i e d f o r subj e c t s i n each c o n d i t i o n .  Upon f i r s t  c o n t a c t i n g the p r o d , the e x p e r i m e n t a l  r a t s were shocked a t ,5, 5,0, 10,0, o r 15,0 mA, were not shocked.  whereas the c o n t r o l  rats  Shock i n t e n s i t i e s were manipulated by a d d i n g t h e appro-  p r i a t e r e s i s t o r i n s e r i e s w i t h the 800-V shock g e n e r a t o r , r e n t flow was o s c i l l o s c o p i c a l l y r e c o r d e d i n each case,  The a c t u a l c u r ^  F o l l o w i n g p r o d con-  t a c t , each s u b j e c t was removed from the t e s t chamber f o r 1 min b e f o r e b e i n g r e t u r n e d t o the. chamber f o r the 15-min o b s e r v a t i o n p e r i o d .  R e s u l t s and D i s c u s s i o n F i g u r e 2 shows t h a t r a t s b u r i e d the l o c a l i z e d s o u r c e o f shock a t a v a r i e t y o f shock i n t e n s i t i e s , tal  A p r i o r i comparisons between each experimen-  group mean and the c o n t r o l group mean confirmed t h a t shock . s u b j e c t s  spent s i g n i f i c a n t l y more time b u r y i n g the p r o d at each shock i n t e n s i t y ex-, cept  .5 mA  (duration o f burying,  = 3,91, p_<„0007; 10 mA,  .5 mA, .t_(22) = 1,36, p_<, 10; 5 mA,  t ( 2 2 ) = 4.23, p_<,0003;  t_(22)  15 mA, .tf22) = 5.29, p_<,00002).  A s i m i l a r a n a l y s i s o f the " h e i g h t " d a t a c o r r o b o r a t e d t h e b e h a v i o u r a l  results  27  F i g u r e 2.  Mean d u r a t i o n o f b u r y i n g  m a t e r i a l a t the prod  and the mean h e i g h t  f o r each o f f i v e shock  intensities.  o f bedding  SHOCK  INTENSITY  [mA]  29  (Height at prod, ,5 mA, £(22) = 1,18, p_>.10; 5 mA, t_(22) = 2.96, 10 mA,  t_C22) = 3,14, p_<,004.5 15 mA,  p_<.6l;  t(22) = 3,50, p_<.002) .  6  Evidence of a p o s i t i v e relationship between shock i n t e n s i t y and the amount of burying was provided by a product moment correlation c o e f f i c i e n t computed between each experimental animal's oscilloscopically-determined shock i n t e n s i t y and i t s duration of burying score.  The r e s u l t i n g c o e f f i -  cient of ,285, although i t did not account f o r a large part of the v a r i ance, was s i g n i f i c a n t at p_<,05. Taken together, these results confirm that burying occurs r e l i a b l y at a variety of shock l e v e l s , and thus i t i s d i f f i c u l t to attribute the extreme differences i n the results ofExperiment 2 and Experiment 3 to divergent shock parameters.  Although burying seems to be f a c i l i t a t e d as shock  i n t e n s i t y i s increased (cf,, U l r i c h § Azrin, 1962), vigorous burying behaviour occurred at a l l shock intensities,.  ThuSi  variations i n shock  parameters may not have as great an effect on burying behaviour as v a r i a tions i n the relationship between the shock and the test object; rats shocked through the test object buried i t (Experiment 1 and 2), whereas rats shocked from a d i f f e r e n t source did not bury the test object  (Experi-  ment 3) .  Experiment 5 To argue convincingly that a p a r t i c u l a r behaviour i s a defensive response, two basic conditions must be met.  F i r s t , the behaviour must be  shown to occur i n response to aversive stimulation. Tfr  In this regard, bury-  .  ** Because the a p r i o r i comparisons i n this study were nonorthogonal (Winer, 1962), a per-comparison alpha levelaof ,0125 was u t i l i z e d , making the overall experiment-wise alpha ,05,  30  i n g was  found i n Experiments  1, 2,and 4 t o be a common response o f l a -  b o r a t o r y r a t s to p r o d shock when the a p p r o p r i a t e m a t e r i a l s were a v a i l a b l e . Second, the response must be a d a p t i v e ; t h a t i s , i t p . o t e n t i a l l y must a f f o r d the animal some p r o t e c t i o n from the noxious agent.  In o r d e r f o r  b u r y i n g to, be a d a p t i v e i t must.be d i r e c t e d , but more i m p o r t a n t l y , i t must be d i r e c t e d a t the source o f a v e r s i v e s t i m u l a t i o n . how  Tt i s d i f f i c u l t  to see  b u r y i n g d i r e c t e d at n e u t r a l o b j e c t s f o l l o w i n g a v e r s i v e s t i m u l a t i o n  could be.adaptive. Experiment  While the b u r y i n g b e h a v i o u r o f the shocked  1, 2, and 4 el.earlyawas, d i r e c t e d at the p r o d , i t was  whether the b u r y i n g b e h a v i o u r was  d i r e c t e d at the prod because  v i o u s a s s o c i a t i o n w i t h shock; b u r y i n g may because  i t was  i t s p r e v i o u s rpafecingioji'' w i t h shock, 1, 2 and 4) b u r i e d i t ;  vant t o t h i s  of i t s pre-  3) d i d n o t .  o f Experiment  four  experiments  b u r i e d because  The r a t s shocked by the p r o d  whereas, those t h a t r e c e i v e d g r i d  of  (Ex- . shock  However, l i k e the r e s u l t s o f a l l " n e g a t i v e " ex-  p e r i m e n t s , the r e s u l t s o f Experiment The purpose  clear  the o n l y nobjiect-bincthentest chamberOTiber,  do p r o v i d e some support f o r the view t h a t the p r o d was  (Experiment  not  have been d i r e c t e d at the p r o d  When c o n s i d e r e d t o g e t h e r , the r e s u l t s o f the f i r s t  periments  rats i n  5 was  3 must be i n t e r p r e t e d w i t h c a u t i o n .  t o p r o v i d e more c o n c l u s i v e evidence  rele-  issue,.  Method On Day  5, two  i d e n t i c a l prods were mounted on the w a l l s o f the  chamber, one at each end. was  The b e h a v i o u r o#*each o f the 10 n a i v e s u b j e c t s  r e c o r d e d f o r 15 min a f t e r i t had been shocked  predetermined)  test  o f the two p r o d s , . Before shock,  to c o n t a c t each p r o d at l e a s t once without b e i n g  (8 mA)  by one  each animal shocked.  (randomly  was.allowed,  31  F i g u r e 3. prod  and  Duration of burying c o n t r o l prod  at the shock p r o d  and  j e c t s i n Experiment 5.  (Panel A) d i r e c t e d at the shock  and the f i n a l h e i g h t o f the bedding m a t e r i a l c o n t r o l prod  (At the b e g i n n i n g  h e i g h t o f the b e d d i n g m a t e r i a l was chamber).  (Panel B) f o r each o f the subo f each s e s s i o n the  5 cm i n a l l p a r t s o f the  test  3a. - Oo  250  • shock I control  C/5  200  prod prod  150 100 o  ~  1  50  CO  • s h o c k prod I • control  1  2  3  4  5  6  Subjects  7  8  prod  9  10  33  R e s u l t s and D i s c u s s i o n The r e s u l t s o f Experiment  5 were so c l e a r t h a t i n s p e c t i o n o f i n d i v i -  d u a l s c o r e s ( F i g u r e 3) rendered s t a t i s t i c a l fluous.  a n a l y s i s o f group.scores super-  A l l 10 s u b j e c t s spent time b u r y i n g t h e p r o d through which  had been shocked  (M_ = 125 s e c ) ; whereas, o n l y one s u b j e c t b r i e f l y  to bury the c o n t r o l p r o d , b u t not u n t i l covered.  attempted  the shock p r o d had been c o m p l e t e l y  S i m i l a r l y , a l l 10 s u b j e c t s accumulated h i g h e r p i l e s o f bedding  m a t e r i a l a t the shock p r o d than a t the c o n t r o l p r o d , ject  they  One s u b j e c t  (Sub-  2, F i g u r e 3) a c t u a l l y removed m a t e r i a l from under t h e c o n t r o l p r o d t o  b u r y t h e shock p r o d ,  Experiment 6 The r e s u l t s o f Experiment  5 p r o v i d e d f u r t h e r evidence t h a t t h e b u r y -  i n g b e h a v i o u r was b e i n g eontr6ia;edc-spfeci'fi;ea^JIythy thearei'ataoiiwbe.tween the prod and the shock: r a t s s e l e c t i v e l y b u r i e d the prod t h a t w a s . a p a d r e d - w i t h shock.  Thus, b u r y i n g appears t o be a p o t e n t i a l l y a d a p t i v e response  o f r a t s t o - s p e c i f i c environmental  'threats'.  However, a l t h o u g h i t i s c l e a r  t h a t b u r y i n g w a s . d i r e c t e d toward t h e a v e r s i v e s t i m u l u s , the r e s u l t s o f p r e v i o u s experiments mental  d i d n o t i n d i c a t e which o f the many cues i n the e x p e r i -  s e t t i n g a c t u a l l y c o n t r o l l e d the response,  T r a d i t i o n a l methods o f  s t u d y i n g the s t i m u l u s c o n t r o l o f b e h a v i o u r ( S k i n n e r , 1938; T i n b e r g e n , 1951) were employed t o approach t h i s i s s u e i n t h e next two experiments. s p e c i f i c purpose o f b o t h Experiments  6 and 7 was t o determine whether  b u r y i n g b e h a v i o u r changes s y s t e m a t i c a l l y when the p o s i t i o n and/or ness o f the p r o d a r e changed a f t e r  The  prod-shock,  bright-  34  Method On tKe f i f t h day.each t o one o f f i v e groups  o f t h e 50 n a i v e  o f 10 s u b j e c t s C '6 r  u:r  ^'rat s. was * -randomly/.as s i gned _ e x p e r i m e n t a l groups  and one  c o n t r o l group), b e f o r e b e i n g p l a c e d i n d i v i d u a l l y i n the c e n t r e o f the chamber f a c i n g away from t h e p r o d , p r o d had been f i x e d  The end o f the chamber t o which t h e  ( f r o n t o r back) and t h e b r i g h t n e s s o f the prod ( b l a c k  o r white), were randomly pre-determined  f o r each r a t b e f o r e the t e s t began.  As each e x p e r i m e n t a l animal touched t h e p r o d , the 8 mA shock was administ e r e d i n , t h e u s u a l way; immediately f o l l o w i n g shock the s u b j e c t was removed. C o n t r o l s u b j e c t s (n = ,10) were t r e a t e d i n e x a c t l y the same manner-except t h a t shock was not a d m i n i s t e r e d . Each r a t i n the f o u r • e x p e r i m e n t a l groups  (n = 10) was i n d i v i d u a l l y  p l a c e d i n the chamber 1 min l a t e r w i t h e i t h e r , 1) the-same p r o d  (black or  white) on the same w a l l , 2) t h e same p r o d on t h e o p p o s i t e w a l l , 3) the d i f f e r e n t prod on t h e same w a l l , o r 4) t h e d i f f e r e n t p r o d on the o p p o s i t e wall.  E i t h e r two o r t h r e e c o n t r o l r a t s were t e s t e d w i t h each o f . t h e s e f o u r  stimulus  combinations.  R e s u l t s and D i s c u s s i o n Almost  a l l o f the r a t s i n t h e f o u r shock  toward t h e p r o d .  groups moved some m a t e r i a l  A l l 10 animals t e s t e d w i t h prod b r i g h t n e s s and p o s i t i o n  unchanged engaged i n some b u r y i n g , w h i l e b u r y i n g b e h a v i o u r was observed in  10n, e i g h t , and e• ,8ht o f the s u b j e c t s i n t h e "same p r o d - d i f f e r e n t p l a c e , "  " d i f f e r e n t prod-same p l a c e , " and " d i f f e r e n t p r o d - d i f f e r e n t p l a c e " groups, respectively.  On t h e o t h e r hand, b u r y i n g b e h a v i o u r was almost n o n e x i s t e n t  i n unshocked, c o n t r o l s u b j e c t s . ' O n l y frSi'ee o f the 10 c o n t r o l r a t s bedding m a t e r i a l a t the p r o d , and  none o f  directed  these d i d so f o r more than 5 s e c ,  35  Thus, the mean d u r a t i o n o f b u r y i n g b e h a v i o u r  was l e s s than  a s e c f o r con-  t r o l s u b j e c t s , and the mean h e i g h t o f b e d d i n g m a t e r i a l accumulated a t the p r o d was l e s s than .</} 1 cm g r e a t e r than the i n i t i a l priori  comparison between the combined experimental  c o n t r o l mean confirmed  l e v e l o f 5 cm.  An a .  group means and t h e  t h a t the d u r a t i o n o f b u r y i n g b y shocked r a t s was  s i g n i f i c a n t l y g r e a t e r than t h a t o f c o n t r o l r a t s ±F(1,45) '= 11,34, p_<,002 , S i m i l a r l y , the h e i g h t o f m a t e r i a l accumulated a t t h e p r o d by shocked r a t s was s i g n i f i c a n t l y g r e a t e r than t h a t accumulated by c o n t r o l r a t s 9.18,  p_ <.004 . Control o f the burying behaviour  o f the experimental  b r i g h t n e s s and p o s i t i o n cues i s i l l u s t r a t e d the b r i g h t n e s s o f t h e prod of burying  s u b j e c t s by  i n F i g u r e 4.  and/or i t s p o s i t i o n decreased  Changing e i t h e r both  the d u r a t i o n  (Panel A) and the h e i g h t o f m a t e r i a l accumulated at t h e p r o d  (Panel B) r e l a t i v e t o t h e performance o f experimental prod  F(l,45) =  and p o s i t i o n cues u n a l t e r e d ,  subjects t e s t e d with  The d a t a were s u b j e c t e d t o a two-way  a n a l y s i s o f v a r i a n c e , the two f a c t o r s b e i n g b r i g h t n e s s and p o s i t i o n , w i t h two l e v e l s  (same o r d i f f e r e n t ) .  each  The a n a l y s i s o f t h e " d u r a t i o n " d a t a  r e v e a l e d a s i g n i f i c a n t i n t e r a c t i o n between b r i g h t n e s s and p o s i t i o n  F(l,36)  = 7.11, p_£.01  differ-  t  M u l t i p l e comparison t e s t s , (Dunn's T e s t , . c r i t i c a l  ence = 46.89, p_£-,05) i n d i c a t e d t h a t changing e i t h e r , b r i g h t n e s s o r p l a c e cues l e d t o a s i g n i f i c a n t r e d u c t i o n i n the d u r a t i o n o f b u r y i n g b u t t h a t :  changing both tion,  cues t o g e t h e r d i d n o t produce a s i g n i f i c a n t l y g r e a t e r  A comparable s e t o f a n a l y s e s  behavioural r e s u l t s .  o f t h e " h e i g h t " d a t a confirmed  The i n t e r a c t i o n e f f e c t was again s i g n i f i c a n t  reducthese F(l,36)  = 5.53, p '^,02 ; the s u b j e c t s t e s t e d w i t h n e i t h e r b r i g h t n e s s n o r p o s i t i o n cues changed accumulated s i g n i f i c a n t l y h i g h e r - p i l e s a t t h e p r o d than d i d the r a t s i n the o t h e r t h r e e experimental  groups, and these  latter-three  36  F i g u r e 4.  Mean d u r a t i o n o f b u r y i n g  o f b e d d i n g m a t e r i a l a t the t e s t p r o d f o u r cue  combinations.  (Panel A) and the mean h e i g h t (Panel B) f o r each o f the  37  ;38  groups d i d not d i f f e r s i g n i f i c a n t l y from each o t h e r (Dunn's T e s t , c r i t i cal  d i f f e r e n c e = 2,17, p=0.05), Although i n t h e f i r s t  f i v e experiments,  r a t s had never been observed  to push bedding m a t e r i a l i n any d i r e c t i o n o t h e r than at the shock s o u r c e , 8 o f the 40 shocked animals i n the p r e s e n t experiment " d i r e c t e d bedding m a t e r i a l a t the h o l e i n the w a l l o f t h e apparatus d i r e c t l y o p p o s i t e t h e prod p o s i t i o n . the  However, such responses were r e s t r i c t e d t o s u b j e c t s i n  two c o n d i t i o n s i n which t h e p o s i t i o n o f t h e prod had been  Cx Cl) 2  =  10J p_<.005).  changed  A f t e r b u r y i n g t h e p r o d i n i t s new p o s i t i o n , these  s u b j e c t s sprayed bedding m a t e r i a l a t the h o l e through which t h e prod had been i n s e r t e d d u r i n g shock a d m i n i s t r a t i o n .  No animal e v e r d i r e c t e d bedding  m a t e r i a l a t t h e h o l e s i n the c e n t r e o f t h e two s i d e w a l l s . The r e s u l t s o f Experiment  6 demonstratedtfchat both t h e b r i g h t n e s s and  p o s i t i o n o f t h e prod e x e r t e d some c o n t r o l o v e r . t h e b u r y i n g response o n l y a s i n g l e prod-shock p a i r i n g .  after  When the p o s i t i o n o f t h e p r o d was un-  changed, changing t h e b r i g h t n e s s o f t h e p r o d  (from b l a c k t o white o r from  white t o b l a c k ) s i g n i f i c a n t l y reduced t h e amount o f b u r y i n g .  Similarly,  i f the b r i g h t n e s s o f t h e prod was h e l d c o n s t a n t , moving i t t o the o p p o s i t e w a l l d u r i n g the t e s t , jsubsttantiiabl^-rediiGed  pWd'bury4n-g.,piTI^ebyr  identity o f t h e cues t h a t d e f i n e d the. l o c a t i o n o f the p r o d was not r e a d i l y apparent s i n c e e x t e r n a l room cues were v i s i b l e through t h e P l e x i g l a s w a l l s of  the t e s t chamber i n a d d i t i o n t o t a c t u a l , o l f a c t o r y , arid v i s u a l  p r o v i d e d by the chamber  cues  itself.  C o n t r o l o f the b u r y i n g b e h a v i o u r by b r i g h t n e s s and p o s i t i o n cues.was not  additive  (Weiss, 1972); changing both cues d i d not s i g n i f i c a n t l y r e -  duce the l e v e l o f b u r y i n g below t h a t observed i n t h e two c o n d i t i o n s i n which o n l y one o f the cues had been changed,  39 ' The f a c t t h a t some o f the r a t s i n the two groups i n which the  posi-  t i o n o f the p r o d was changed b u r i e d t h e h o l e on the o t h e r end o f the chamber - t h r o u g h which the p r o d had been i n s e r t e d d u r i n g shock a d m i n i s t r a t i o n suggests t h a t ' p o s i t i o n cues were i m p o r t a n t i n more than one  sense.  Not o n l y d i d p o s i t i o n cues e x e r t c o n t r o l o v e r b u r y i n g by- t h e i r r o l e i n d e f i n i n g p r o d p o s i t i o n but l o c a t i o n cues t h a t were a s s o c i a t e d w i t h  the  shock were themselves c a p a b l e o f i n d u c i n g the b u r y i n g response i n some' subjects.  Experiment 7 In Experiment 7, s t i m u l u s c o n t r o l o f b u r y i n g was i n v e s t i g a t e d u s i n g a simultaneous d i s c r i m i n a t i o n procedure  (Experiment- 5 ) ; each s u b j e c t was  shocked and t e s t e d i n the p r e s e n c e o f two p r o d s ,  Method The- 24 n a i v e hooded r a t s were randomly a s s i g n e d t o S w i t c h (n = 12) , o r Same (n = .12) c o n d i t i o n s ,  On Day 5 , a l l s u b j e c t s were shocked,once  when . t h e y , c o n t a c t e d e i t h e r the b l a c k p r o d o r the w h i t e p r o d which had been mounted t h r o u g h the h o l e s at o p p o s i t e ends o f the t e s t chamber.  I t was,  randomly p r e d e t e r m i n e d w h i c h s u b j e c t s would be shocked b y which p r o d , w i t h the p r o v i s o t h a t h a l f the s u b j e c t s i n each o f the two groups were shocked by each p r o d . at l e a s t once,  Before s h o c k , each s u b j e c t w a s . a l l o w e d t o ' c o n t a c t each p r o d Immediately a f t e r s h o c k , each s u b j e c t was removed from t h e  t e s t apparatus f o r 1 m i n .  Each s u b j e c t i n the Same C o n d i t i o n was t h e n , r e -  t u r n e d t o the chamber w i t h t h e prods i n t h e i r o r i g i n a l p o s i t i o n s ^ ' whereas, s u b j e c t s i n the S w i t c h C o n d i t i o n were r e t u r n e d to the chamber w i t h p o s i t i o n s o f the p r o d s r e v e r s e d ,  the  40  Results- and D i s c u s s i o n Although the i n c i d e n c e o f b u r y i n g was tions  (10 o f the 12 s u b j e c t s i n each c o n d i t i o n d i s p l a y e d some b u r y i n g ) ,  t h e r e was of  comparable i n the two c o n d i -  a s t r i k i n g d i f f e r e n c e between the two  the b u r y i n g .  I t i s apparent  c o n d i t i o n s i n the  direction  from F i g u r e 5 t h a t those r a t s t e s t e d w i t h  the prods i n t h e i r o r i g i n a l p o s i t i o n s d i r e c t e d almost a l l o f t h e i r b u r y i n g a c t i v i t y at the prod through which they had been shocked5 whereas, when the p o s i t i o n s o f the prods were r e v e r s e d p r i o r t o the t e s t , the b u r y i n g b e h a v i o u r was The  d i s t r i b u t e d almost e q u a l l y between both prods,.•  s i g n i f i c a n c e o f the d i f f e r e n c e s r e p r e s e n t e d i n F i g u r e 5 were  e v a l u a t e d w i t h a s e r i e s o f t_-tests f o r dependent measures.  In the Same  C o n d i t i o n , s u b j e c t s spent s i g n i f i cantly more time b u r y i n g the shock than they d i d b u r y i n g the c o n t r o l p r o d [ t _ ( l l ) = 4.60, h e i g h t o f the bedding m a t e r i a l accumulated prod was  p_<i.0005] .  those o b t a i n e d i n Experiment In  p_ .0008 ] and the  by these animals, at the  s i g n i f i c a n t l y g r e a t e r than the h e i g h t accumulated  p r o d [ t f l l ) = 4.81,  prod  at the  shock control  These r e s u l t s are e s s e n t i a l l y the same as  5, wfren'e b a s i c a l l y the same p r o c e d u r e was  used.  c o n t r a s t , i n the Switch C o n d i t i o n an a n a l y s i s o f b o t h the height."[ t _ ( l l )  = 1.27,  p_ )> . I>]  and d u r a t i o n [ t _ ( l l ) = 1.38,  p^.ll  measures i n d i c a t e d  that  the r a t s d i d not bury e i t h e r prod s i g n i f i c a n t l y more than the o t h e r . should be emphasized the two  that this  It  l a c k o f d i f f e r e n c e i n mean b u r y i n g between  s i t e s when the prods were switched r e f l e c t e d the f a c t t h a t  indivi-  dual s u b j e c t s were d i s t r i b u t i n g t h e i r b u r y i n g at both s i t e s , not t h a t the s u b j e c t s were b u r y i n g one prod and the r e m a i n i n g h a l f t h e o t h e r , 10 o f the Switch s u b j e c t s t h a t d i s p l a y e d b u r y i n g b e h a v i o u r d i r e c t e d m a t e r i a l at b o t h p r o d s .  half All  bedding  In c o n t r a s t , o n l y 3 s u b j e c t s i n the Same C o n d i t i o n  41  F i g u r e 5.  Mean d u r a t i o n o f b u r y i n g d i r e c t e d at the shock p r o d  and c o n t r o l p r o d and the mean h e i g h t o f bedding m a t e r i a l a t each p r o d i n c o n d i t i o n s where the p r o d p o s i t i o n s were s w i t c h e d o r l e f t the same a f t e r  shock.  4*  100  • •  75  -  9  -  8  duration height  -  > X  W t—i o  50  -  -  7  a  H o  25  jnl shock control prod prod  shock prod  S A M E  SWITCH  control prod  -  6  i  5  43 d i r e c t e d m a t e r i a l at both prods [ x ( l ) = 10.76, p_< .005 ]. 2  As w e l l as d i s p l a y i n g the s t e r e o t y p e d b u r y i n g p a t t e r n d e s c r i b e d i n p r e v i o u s experiments, r a t s t h a t had been t e s t e d w i t h t h e p o s i t i o n o f t h e prods r e v e r s e d d i s p l a y e d an i n t e r e s t i n g b e h a v i o u r not seen i n t h e o t h e r rats.  P r i o r t o b u r y i n g the p r o d s ; e i g h t o f the Switch r a t s s c u r r i e d back  and f o r t h between t h e two p r o d s ,  Moreover, t h i s v a s c i l l a t i n g  behaviour  o f t e n p e r s e v e r a t e d i n t o the b u r y i n g sequence i t s e l f , w i t h animals b e d d i n g m a t e r i a l toward one o f the p r o d s , then q u i c k l y r e v e r s i n g d i r e c t i o n and s p r a y i n g toward  the opposite prod,  directing their  This i s i n contrast to  the b e h a v i o u r o f t h e t h r e e r a t s i n t h e Same C o n d i t i o n t h a t d i r e c t e d terial  ma-  a t b o t h t h e shock p r o d and t h e c o n t r o l p r o d ; the l a t t e r animals d i d  not s p r a y m a t e r i a l at the c o n t r o l p r o d u n t i l shock p r o d .  they had f i n i s h e d b u r y i n g t h e  S i m i l a r l y , the r a t s i n Experiment  6 that b u r i e d both the prod  and the h o l e on t h e o p p o s i t e w a l l d i d n o t s p r a y m a t e r i a l a t t h e h o l e u n t i l they had b u r i e d the prod, Evidence t h a t p o s i t i o n was an important c o n t r o l l i n g f a c t o r was demons t r a t e d by the consequences the performance  o f changing t h e p o s i t i o n o f the p r o d s .  Unlike  o f t h e s u b j e c t s i n t h e Same C o n d i t i o n , s u b j e c t s i n t h e  Switch C o n d i t i o n d i s t r i b u t e d t h e i r b u r y i n g between the two p r o d s .  This r e -  s u l t a l s o p r o v i d e s evidence t h a t b r i g h t n e s s too was e x e r t i n g c o n t r o l the b u r y i n g .  over  I f b r i g h t n e s s had n o t been a c o n t r o l l i n g f a c t o r , s w i t c h i n g  the p o s i t i o n s o f t h e two p r o d s , which d i f f e r e d o n l y i n b r i g h t n e s s , would have been without e f f e c t . , The r e s u l t s o f Experiment of  Experiment  7 thus c o n f i r m those  6.  Experiment  8  Each o f the p r e v i o u s seven experiments p r o v i d e d some evidence t h a t b u r y i n g can be an a d a p t i v e response o f r a t s t o s p e c i f i c  environmental  44  threats.  Although t h e r e can be l i t t l e q u e s t i o n t h a t the response  i n the presence o f a v e r s i v e s t i m u l i and i s d i r e c t e d by s p e c i f i c  occurs  shock-  a s s o c i a t e d cues , t h e r e are o t h e r grounds f o r q u e s t i o n i n g i t s a d a p t i v e v a l u e and c o n s e q u e n t l y i t s s t a t u s as a v i a b l e d e f e n s i v e response, example, the s t e r e o t y p e d n a t u r e o f the response, its initial  :  although  facilitating  i n v e s t i g a t i o n , a l s o r a i s e d some q u e s t i o n s c o n c e r n i n g i t s  adaptiveness i n the r a t ' s n a t u r a l h a b i t a t , p a t t e r n would be o f m a r g i n a l u t i l i t y  Such a s t e r e o t y p i c a l  response  i n h a b i t a t s where a v a i l a b l e b u r y i n g  m a t e r i a l s r e q u i r e more v a r i e d responses- f o r t h e i r d i s p o s i t i o n , the s t e r e o t y p i c a l n a t u r e o f the b u r y i n g response t i o n s may  For  However,  i n previous investigar  s i m p l y have r e f l e c t e d the homogeneity o f the commercial  bedding  which s e r v e d as the o n l y a v a i l a b l e b u r y i n g m a t e r i a l , A c c o r d i n g l y , the purpose s t r a t e that r a t s kind  o f the next two  experiments- was  t o demon-  x an ^change t h e i r b u r y i n g -responses- w i t K h f e s p e G t J t b  the  (<Experi!mentes8) i o n d i s p o s i t i o n ^Experimeritu9Xeofuayai:labile'burying In Experiment  three materials.  8, each s u b j e c t was One  t e s t e d i n the p r e s e n c e o f one  o f t h e m a t e r i a l s (wooden b l o c k s ) was  i t would be extremely d i f f i c u l t  chosen  mat  of  because  f o r a r a t t o p i l e t h i s m a t e r i a l over the  p r o d u s i n g the snout and forepaw p u s h i n g motions c h a r a c t e r i s t i c o f b u r y i n g i n previous  experiments.  Method Each o f the 30 n a i v e r a t s was.randomly a s s i g n e d to one o f t h r e e ditions  (n = 10),  the experiment,  Every s u b j e c t was  t r e a t e d i n the same manner.throughout  except t h a t the type o f m a t e r i a l a v a i l a b l e . i n the  chamber d i f f e r e d f o r the s u b j e c t s i n each c o n d i t i o n . the experiment  the chamber f l o o r was  con-  1  test  D u r i n g a l l phases o f  covered w i t h e i t h e r  (1) 5 cm o f Sanr-i  45  eel,  (2) 5 cm o f sand, o r (3) 100 24 x 1,6 x 1,0 cm wooden b l o c k s  so t h a t t h e h e i g h t o f each w a s l cm. ;  placed  On Day 5, f o l l o w i n g the u s u a l  days o f h a b i t u a t i o n i n the p r e s e n c e o f t h e d e s i g n a t e d  four  burying material,  the s u b j e c t s were p l a c e d i n d i v i d u a l l y i n t h e c e n t r e o f t h e t e s t  chamber  between t h e two i d e n t i c a l prods which had been mounted i n t h e middle o f the two end w a l l s , 2 cm above t h e l e v e l o f the sand o r . b e d d i n g and 6 cm above t h e b l o c k s . and t o c o n t a c t each prod  material  Each animal was.allowed t o ' e x p l o r e the chamber  at l e a s t once without  consequence,  When the r a t  next touched one (randomly predetermined) o f the-two p r o d s , the 8 mA shock was  administered.  F o l l o w i n g t h e shock, the b e h a v i o u r o f each s u b j e c t was  viewed f o r 15 min and then t h e h e i g h t s o f t h e m a t e r i a l s accumulated at the shock and c o n t r o l prods were  Results  recorded.  and D i s c u s s i o n  F i g u r e 6 shows t h a t the s u b j e c t s spent  a substantial portion of their  time b u r y i n g r e g a r d l e s s o f which m a t e r i a l was a v a i l a b l e . 30 s u b j e c t s , an animal i n t h e Blocks some b u r y i n g . was  Only one o f t h e  C o n d i t i o n , d i d not engage i n at l e a s t  I t i s a l s o apparent i n F i g u r e 6 t h a t t h e b u r y i n g  well-directed.  A l l 29 o f the s u b j e c t s t h a t engaged i n b u r y i n g  some time b u r y i n g the prod which f o r them had been t h e source whereas, o n l y 3 r a t s , a l l i n t h e Bedding C o n d i t i o n , spent the c o n t r o l prod.  behaviour  Even i n these  spent  o f t h e shock;  any time b u r y i n g  t h r e e c a s e s , the s u b j e c t s spent  most o f  t h e i r time b u r y i n g t h e shock p r o d ; t h e y . d i d n o t move m a t e r i a l toward t h e c o n t r o l prod u n t i l t h e shock prod had been completely comparisons  covered.  (t_ t e s t s f o r dependent measures) between t h e t o t a l  A priori burying  times accumulated by each s u b j e c t at t h e r e s p e c t i v e prods confirmed- t h a t the s u b j e c t s i n a l l t h r e e c o n d i t i o n s spent  s i g n i f i c a n t l y more time b u r y i n g  the p r o d t h a t had been a s s o c i a t e d w i t h shock  (Bedding C o n d i t i o n , t ( 9 ) = 7.83,  46  F i g u r e 6. prod with  Mean d u r a t i o n o f b u r y i n g the shock and c o n t r o l different burying material.  4? 150  Shock Prod  u LU  Control Prod  CD  100  50  LU  Bedding  Sand  BURYING  Blocks  MATERIAL  48  p_<. 0002; Same C o n d i t i o n t(9) 2.75,  = 6.19,  p_<.0001; Blocks C o n d i t i o n , t ( 9 ) =  p_<.02) . A n a l y s e s o f the m a t e r i a l s accumulated  (Figure 7) p r o v i d e d an independent  a t each o f the two  prods  c o n f i r m a t i o n o f the b e h a v i o u r a l r e s u l t s .  In each o f the t h r e e experimental c o n d i t i o n s , t h e average h e i g h t o f the b u r y i n g m a t e r i a l at the shock prod was the c o n t r o l prod t i o n , ;t(9) = 6.16,  s i g n i f i c a n t l y g r e a t e r than t h a t at  (Bedding, C o n d i t i o n , t ( 9 ) = 7,15,  p_<,00005; Sand Condi-  p_<.0001; Blocks C o n d i t i o n , t_(9) = 2.68,  p_<,02) .  The p a t t e r n o f b u r y i n g b e h a v i o u r d i s p l a y e d by the animals i n the Bedding C o n d i t i o n was the Sand C o n d i t i o n . sponse was  i n d i s t i n g u i s h a b l e from t h a t d i s p l a y e d by those i n In both c o n d i t i o n s the topography  the same as t h a t observed i n p r e v i o u s experiments  General Methods).  (see the  The r a t s began each b u r y i n g episode f a c i n g the  p r o d from a d i s t a n t p a r t o f the chamber,  Then t h e y moved d i r e c t l y  the p r o d , p u s h i n g and s p r a y i n g the m a t e r i a l toward forepaws.  o f the b u r y i n g r e -  toward  the p r o d w i t h snout  As i n p r e v i o u s experiments, these b u r y i n g sequences  q u e n t l y i n t e r r u p t e d by i n t e r v a l s o f approach-avoidance the r a t would s t r e t c h forward u n t i l  shock  and  were f r e -  b e h a v i o u r i n which  f u l l y extended with i t s nose n e a r l y  t o u c h i n g the p r o d and then a b r u p t l y withdraw t o the r e a r o f the chamber. S i m i l a r b e h a v i o u r s were a l s o observed i n those animals b u r y i n g w i t h blocks.-  They would move toward  them w i t h snout and forepaws.  the shock prod p u s h i n g b l o c k s ahead o f Although t h i s b e h a v i o u r was  a c c u m u l a t i n g b l o c k s near the p r o d ,  i t was  the b l o c k s up i n o r d e r t o form a p i l e . spent some time moving b l o c k s toward  e f f e c t i v e iri  n e c e s s a r y f o r s u b j e c t s to p i c k  Seven o f the 10 r  r a t s c t h a t . ..  the shock p r o d p i c k e d b l o c k s up i n  t h e i r t e e t h and p l a c e d tham i n a p i l e w i t h t e e t h and forepaws,  None o f  these,seven managed t o completely cover the prod,.6 cm above the o r i g i n a l  49  F i g u r e 7.  Mean h e i g h t o f b u r y i n g m a t e r i a l s at the shock and  control prods. the b e g i n n i n g  Arrows i n d i c a t e the h e i g h t o f the m a t e r i a l at o f the t e s t .  s<=>  •  Bedding  Sand  BURYING  Shock Prod  Blocks  MATERIAL  i-51  l e v e l o f t h e b l o c k s , b e f o r e the end o f the t e s t p e r i o d ; whereas, i n t h e ,  level-of  o t h e r two c o n d i t i o n s , in"which•the 'prod was c l o s e r to the i n i t i a l the b u r y i n g m a t e r i a l , most o f the s u b j e c t s the p r o d .  The r a t s ' b e h a v i o u r  (18 out o f 20) a c t u a l l y  covered  i n d i c a t e d that the c o n s t r u c t i o n o f the  p i l e s o f b l o c k s was n o t haphazard; on s e v e r a l o c c a s i o n s a b l o c k  just  p l a c e d on top o f a p i l e t o p p l e d t o the bottom from where i t was q u i c k l y r e t r i e v e d and r e t u r n e d t o i t s o r i g i n a l p o s i t i o n atop the p i l e . The  r e s u l t s o f Experiment 8 c o n f i r m p r e v i o u s demonstrations  ments 5 and 7) o f d i s c r i m i n a t e d b u r y i n g b e h a v i o u r  i n rats.  (Experi-  Every r a t  shocked b y one o f two prods mounted on o p p o s i t e w a l l s o f t h e chamber l i n e d w i t h commercial bedding buried i t ,  m a t e r i a l r e t u r n e d t o the shock prod and  and t h e few t h a t pushed bedding  d i d n o t do so u n t i l  m a t e r i a l at t h e c o n t r o l  t h e shock p r o d had been completely  covered.  prod  Of g r e a t e r  i n t e r e s t h e r e , however, i s t h e f i n d i n g t h a t d e f e n s i v e b u r y i n g i s n o t limited to  s i t u a t i o n s i n which t h e r e i s a supply o f commercial  bedding  m a t e r i a l ; a l l o f the r a t s i n t h e Sand C o n d i t i o n attempted t o bury t h e shock prod,  as d i d a l l b u t one o f t h e s u b j e c t s i n the Blocks C o n d i t i o n .  This  f i n d i n g i s c o n s i s t e n t w i t h s e v e r a l i n c i d e n t a l o b s e r v a t i o n s t h a t have been made i n our l a b o r a t o r y .  In one case, a r a t shocked i n i t s home cage d i s -  mantled i t s n e s t o f shredded paper and used i t as b u r y i n g m a t e r i a l , and i n another  case s e v e r a l r a t s shocked by a p r o d on the P l e x i g l a s f l o o r o f  a b a r r e n t e s t chamber p l a c e d t h e i r own f e c e s on t o p o f i t , The  r e s u l t s o f Experiment 8 a l s o show t h a t b u r y i n g b e h a v i o u r  a ^gjfS^-x^ef?^  i s not 1  r a t h e r i t i s a complex b e h a v i o u r a l sequence which v a r i e s as a f u n c t i o n o f the a v a i l a b l e b u r y i n g m a t e r i a l .  In t h e Blocks C o n d i t i o n , the p u s h i n g and  .52  f o r e l l m b s p r a y i n g movements t h a t r a p i d l y produced l a r g e p i l e s shock prod  i n the Bedding and Sand C o n d i t i o n s were not s u f f i c i e n t t o  g a i n the same blocks  at the  end.  Such movements were sometimes used.to  i n t h e v i c i n i t y o f the p r o d , but t o construct' p i l e s  accumulate at'the  prod  p o s i t i o n , the r a t s p i c k e d t h e b l o c k s up i n t h e i r t e e t h and d e p o s i t e d them around the p r o d . These r e s u l t s c o n s i d e r e d  together  strengthen  b e h a v i o u r c o u l d be o f c o n s i d e r a b l e a d a p t i v e •Rats a r e capable with  value  t h e view t h a t  burying  iri n a t u r a l settings.'  o f u s i n g a v a r i e t y o f m a t e r i a l t o bury o b j e c t s a s s o c i a t e d  a v e r s i v e s t i m u l i even.when t h e use o f these m a t e r i a l s n e c e s s i t a t e s  changes i n t h e topography o f the b u r y i n g  sequence.  Experiment 9 The  purpose o f Experiment 9 was t o demonstrate t h a t r a t s w i l l  t o b u r y a source  attempt  o f a v e r s i v e s t i m u l a t i o n even when a l l o f t h e b u r y i n g  m a t e r i a l has t o be t r a n s p o r t e d by t h e r a t t o the s i t e ,  Method The  s u b j e c t s were 20 n a i v e hooded r a t s , h a b i t u a t e d  t o the P l e x i g l a s  Chamber i n t h e u s u a l manner, except t h a t t h e chamber f l o o r was covered  with  100, 2.4 x 1,6 x 1.0 cm wooden b l o c k s ,  evenly  Each b l o c k was p o s i -  t i o n e d d u r i n g a l l phases o f the experiment so t h a t i t s h e i g h t was,1  cm,  On day 5, the s u b j e c t s were randomly d i v i d e d i n t o two groups o f 10, and shocked by one (randomly predetermined) o f the two i d e n t i c a l p r o d s , . F o r the s u b j e c t s i n one o f the groups, the 100 b l o c k s were d i s t r i b u t e d on t h e h a l f o f the chamber c o n t a i n i n g t h e shock prod; whereas, f o r s u b j e c t s i n the o t h e r group, t h e b l o c k s were i n i t i a l l y o f t h e box.  r e s t r i c t e d t o the d i s t a l h a l f  The b e h a v i o u r o f each s u b j e c t and t h e r e s u l t i n g  redistribution  53  o f b l o c k s was.measured  as i n p r e v i o u s  experiments.  R e s u l t s and D i s c u s s i o n B u r y i n g b e h a v i o u r was a g a i n a r e l i a b l e consequence prod-shock.  With the e x c e p t i o n o f t w o ^ s u b j e c t s  i n the  o f the  single  condition'where  the b l o c k s were a d j a c e n t t o t h e shock p r o d , a l l of the s u b j e c t s i n at l e a s t  some b u r y i n g .  engaged  M o r e o v e r , a l l "18 o f the s u b j e c t s w h i c h d i s -  p l a y e d the b u r y i n g b e h a v i o u r d i r e c t e d i t p r i m a r i l y at the shock p r o d ; o n l y two o f ' t h e s e 18 moved any b l o c k s ^towafdtt-hexcontsol^p.rod;.  --  Thus> the s u b j e c t s spent s i g n i f i c a n t l y more t i m e b u r y i n g the shock p r o d t h a n they d i d the c o n t r o l p r o d i n b o t h c o n d i t i o n s , when thebb l o c k s ..were a d j a c e n t t o the shock p r o d (M = 36 and 0 s e c , r e s p e c t i v e l y ; t ( 9 )  = 2.35,  p_<. 04) and when the b l o c k s were r e s t r i c t e d t o the f a r end o f the  chamber  (M = 108 and .7 s e c , r e s p e c t i v e l y ; 1^(9) = 2 . 4 5 / j K . 0 4 ) , These b e h a v i o u r a l d i f f e r e n c e s were c o n f i r m e d by s t a t i s t i c a l  analysis  o f the h e i g h t o f the p i l e s accumulated a t each o f the two p r o d s :  Because  f o r each s u b j e c t  the i n i t i a l h e i g h t o f the b l o c k s at the two prods was not ,  e q u a l at the s t a r t o f t h e t e s t , the i n c r e a s e  i n the h e i g h t o f the b l o c k s  at each p r o d r a t h e r than t h e a b s o l u t e h e i g h t was used as t h e i n d e x o f b u r y ing.  In b o t h c o n d i t i o n s , the average i n c r e a s e  i n t h e h e i g h t o f the b l o c k s  was 3.7 cm, but i n n e i t h e r c o n d i t i o n was t h e r e a s i n g l e i n s t a n c e the h e i g h t o f the p i l e at the c o n t r o l p r o d was i n c r e a s e d jacent  i n which  ( w i t h b l o c k s ad-.  t o the shock p r o d , t_(9) = 3 . 3 6 , p_<,008; w i t h b l o c k s , r e s t r i c t e d  the f a r end o f the chamber, t_(9) = 2 . 9 3 , p_<,02), ment 8, t h r e e s u b j e c t s ,  In c o n t r a s t  to  to  Experi-  one i n the " d i s t a l " c o n d i t i o n and two i n the  " a d j a c e n t " c o n d i t i o n , were a b l e t o c o m p l e t e l y c o v e r the p r o d w i t h b l o c k s i n the 15-min t e s t p e r i o d .  54 •I.:' '  Between group'analyses  d i d not r e v e a l any s i g n i f i c a n t d i f f e r e n c e s be-  tween t h e two groups on e i t h e r dependent measure ( d u r a t i o n o f  burying  shock p r o d , t_(18) = 1.54, p_>.10; h e i g h t a t shock p r o d , t_(18) = .024, p_>.10; d u r a t i o n o f b u r y i n g c o n t r o l prod, £(18) = 1,48, p_>. 10; h e i g h t at c o n t r o l p r o d , t_(18) = 0, p_>.10). In a l l p r e v i o u s s t u d i e s o f b u r y i n g , b u r y i n g m a t e r i a l was.always a v a i l a b l e i n t h e area immediately  a d j a c e n t to. the source o f t h e shock.  In  Experiment 9 r a t s attempted t o b u r y the shock p r o d even when t h e b u r y i n g m a t e r i a l w a s ' i n i t i a l l y r e s t r i c t e d t o t h e o t h e r end o f t h e chamber.  After  b e i n g shocked, the r a t s c a r r i e d o r pushed t h e b l o c k s toward t h e shock-prod f o r use i n i t s subsequent b u r i a l .  T h i s o b s e r v a t i o n supports  b u r y i n g can f u n c t i o n as an e f f e c t i v e d e f e n s i v e response  t h e view t h a t  i n the r a t ' s  a l environment, an environment where b u r y i n g m a t e r i a l s a r e n o t always readily  available,  natur-  55  GENERAL DISCUSSION The G e n e r a l D i s c u s s i o n i s o r g a n i z e d around d i s c u s s e d under s e p a r a t e headings.  The  first  two  issues, that  s e c t i o n marshals  t h a t suggests t h a t b u r y i n g i s a d e f e n s i v e response  of rats,  are  evidence  In t h i s r e r  gard, both the p r e s e n t e x p e r i m e n t a l d a t a and r e l e v a n t e t h o l o g i c a l v a t i o n s are reviewed. " b i o l o g i c a l " approach  The  obser-  c o n t r i b u t i o n o f the p r e s e n t s t u d i e s t o the  t o avoidance  l e a r n i n g i s d i s c u s s e d i n the  second  s e c t i o n o f the General D i s c u s s i o n and the r e l a t i o n s h i p o f the b u r y i n g phenomenon t o P a v l o v i a n c o n d i t i o n i n g i s examined i n t h i s  I.  B u r y i n g as a d e f e n s i v e response In the- r a t  In each o f the n i n e experiments was  presented i n t h i s t h e s i s ,  evidence  p r o v i d e d to support the argument t h a t b u r y i n g b e h a v i o u r i s a  d e f e n s i v e response o f r a t s . fundamental  These data can be o r g a n i z e d around  animal'  prominent the  '2^)ei.tn^ust p o t e n f l a l l y ' a f f o r d  'protee-ti'ojiffxom. .tketfsburciatiof  Experiment  'the aversive  stimulation.  1 p r o v i d e d ample evidence t h a t b u r y i n g i s a p r e v a l e n t r e -  sponse o f r a t s t o a v e r s i v e shock. a f t e r a s i n g l e shock attempted  Almost  a l l o f the r a t s t e s t e d  shortly  t o bury the shock s o u r c e , and even 20 days  l a t e r the time spent b u r y i n g w a s . s t i l l s i g n i f i c a n t l y above c o n t r o l Furthermore, quent was  two  c r i t e r i a : pres'bntedhiHitheoIntro'duclioh'?! l^s^h^sbehavi'our^must  ©e:cu*ltrii*espeiise2^ the  context.  b u r y i n g was  experiments.  a reliable  levels.  consequence o f p r o d shock i n a l l subse-  Perhaps the most c o n v i n c i n g demonstration  p r o v i d e d by the r e s u l t s o f Experiment  of this  effect  4 i n which i n c r e a s e s i n the i n -  t e n s i t y o f - t h e a v e r s i v e s t i m u l u s l e d t o . i n c r e a s e s i n the amount o f b u r y i n g . T h i s r e l a t i o n s h i p i s c o n s i s t e n t w i t h what i s known about between shock i n t e n s i t y and o t h e r d e f e n s i v e b e h a v i o u r s  the r e l a t i o n s h i p  (e.g., U l r i c h  § Azrin,  56 1962),  Even i n c a s e s where t h e t y p e  (Experiment  8) and d i s p o s i t i o n  9) o f b u r y i n g m a t e r i a l s made t h e response more d i f f i c u l t t o  execute, t h e b u r y i n g b e h a v i o u r s t i l l animals.  (Experiment  o c c u r r e d i n over 80% o f shocked  The r o b u s t n a t u r e o f t h e r e l a t i o n s h i p between a v e r s i v e s t i m u l a -  t i o n and b u r y i n g b e h a v i o u r i n t h e p r e s e n t e x p e r i m e n t a l s i t u a t i o n s  appeared  t o s u p p l a n t o t h e r common d e f e n s i v e b e h a v i o u r s ; p e r i o d s o f i m m o b i l i t y l a s t i n g more than a few seconds,  attempts t o escape fromthe  apparatus, and  a g g r e s s i v e b e h a v i o u r d i r e c t e d at t h e prod were r a r e l y observed i n t h e p r e sent s t u d i e s .  Evidence o f t h e p o t e n t i a l a d a p t i v e n e s s o f t h e response was  p r o v i d e d by t h r e e d i f f e r e n t o b s e r v a t i o n s ,  F i r s t , t h e immediate consequence  o f t h e b e h a v i o u r on t h e s u r r o u n d i n g environment  i n most cases was a "bar-  r i e r " between t h e r a t and t h e source o f a v e r s i v e s t i m u l a t i o n . was  This b a r r i e r  e f f e c t i v e i n t h e l a b o r a t o r y i n k e e p i n g t h e r a t s from making  further  c o n t a c t s w i t h a p o t e n t i a l l y harmful o b j e c t , and t h e r e i s no obvious to b e l i e v e that t h e consequences  o f t h i s b e h a v i o u r i n more n a t u r a l  s i v e s e t t i n g s would n o t be s i m i l a r  ( c f ,<, Calhoun,  Second, t h e b e h a v i o u r was,well  directed.  reason aver-  1962),  I f b u r y i n g was randomly  d i r e c t e d a f t e r a v e r s i v e s t i m u l a t i o n , i t s a d a p t i v e v a l u e would be q u e s t i o n able.  However, except i n t h o s e cases where t h e cues a s s o c i a t e d w i t h  had been r e a r r a n g e d between shock  and t e s t i n g  shock  (Experiments 6 § 7 ) , few r a t s  were ever observed t o push bedding m a t e r i a l i n a n y - d i r e c t i o n o t h e r than toward t h e shock s o u r c e ; the b u r y i n g seemed t o be c o n t r o l l e d s p e c i f i c a l l y by the r e l a t i o n between t h e prod and t h e shock. floor  (Experiment  Rats shocked through a g r i d  3) d i d n o t bury t h e p r o d , arid r a t s shocked by one p r o d  d i d n o t bury an i d e n t i c a l p r o d mounted on t h e o p p o s i t e w a l l o f the t e s t chambers  (Experiment  5).  T h i s l a t t e r f i n d i n g was s u b s e q u e n t l y r e p l i c a t e d  i n every study i n which the two prod p r o c e d u r e was employed 7, 8, and 9 ) ,  (Experiments  However, s y s t e m a t i c d e c r e a s e s i n t h e amount o f b u r y i n g were  57 observed  when the b r i g h t n e s s o r p o s i t i o n o f the prod was,changed i n the  i n t e r v a l , between the shock and c o m p e l l i n g evidence  the t e s t .  These d a t a s e r v e d as even more  t h a t the r a t s ' b u r y i n g behaviour  l a t i o n between shock and  i s guided by the r e -  the cues which o c c a s i o n shock,  Thus, t h i s behav-  i o u r c o u l d have an a d a p t i v e v a l u e i n n a t u r a l s e t t i n g s ; whereas i f b u r y i n g was  randomly d i r e c t e d with r e s p e c t to a v e r s i v e cues,  to imagine how  i t c o u l d be  That b u r y i n g c o u l d be  i t would be  difficult  adaptive. a d a p t i v e i n a n a t u r a l s e t t i n g i s i m p l i e d by  t h i r d o b s e r v a t i o n , the o b s e r v a t i o n t h a t r a t s were capable  a  of using a varie-  t y o f m a t e r i a l s t o bury the shock prod., even when the use. o f these  materials  n e c e s s i t a t e d changes i n the topography o f . t h e b u r y i n g sequence o r when t e r i a l s had  t o be  first  t r a n s p o r t e d to the p r o d ,  This observation  ma-  supports  the view t h a t b u r y i n g c o u l d be an e f f e c t i v e d e f e n s i v e response i n the r a t ' s n a t u r a l environment,  an environment where b u r y i n g m a t e r i a l s are not  r e a d i l y a v a i l a b l e and where a v a i l a b l e m a t e r i a l s may topography f o r t h e i r d i s p o s i t i o n .  require a varied  always response'  Furthermore, t h i s o b s e r v a t i o n shows t h a t  b u r y i n g i s not a.-i.r^,'fd.ex¥ve'iiPesp©ns'-e--t'Onobjec'tS'bpaif,edpw.ith-.dpainful s t i m u l i , r a t h e r , i t i s a complex b e h a v i o u r a l to accommodate d i f f e r e n t r e s o u r c e s  sequence t h a t can be  o f the environment.  Thus, t h r e e o b s e r v a t i o n s - - t h e p h y s i c a l consequence o f the the d i r e c t e d n e s s o f the response, gest t h a t b u r y i n g behaviour However, t h i s evidence i s adaptive.  modified  and  the f l e x i b i l i t y o f the  response,  response--sug-  c o u l d have a d a p t i v e v a l u e i n a n a t u r a l s e t t i n g .  o n l y lends p l a u s i b i l i t y to the argument t h a t b u r y i n g  More d i r e c t evidence  must come from n a t u r a l i s t i c  observations  i n which a p o s i t i v e r e l a t i o n s h i p i s demonstrated between i n s t a n c e s o f the behaviour  and the . a b i l i t y o f the animal  i o u r occurs  to survive.  i n a n a t u r a l environment, although  of adaptiveness,  i s therefore a necessary  Showing t h a t the behav-  i t i s not  sufficient  step toward d i r e c t  evidence  confirmation  58  of  a d a p t i v e v a l u e , • Tn t h i s r e g a r d , t h e r e a r e . a number o f more n a t u r a l i s t i c  observations that  extend  F i r s t , Calhoun  the p r e s e n t  observations.  (1962) r e p o r t e d t h a t "lower s t a t u s rats." exposed t o  " t e r r i t o r i a l t h r e a t " would p l u g the entrance h o l e s to t h e i r underground nests.  The n o t i o n t h a t "lower  s t a t u s " rodents may  ' b a r r i c a d e ' themselves  away from more dominant members o f the s p e c i e s i s g i v e n f u r t h e r credance by the o b s e r v a t i o n o f Johnston semi-natural shavings difficult at bay. far  A male golden hamster housed under  c o n d i t i o n s b l o c k e d the entrance h o l e o f i t s chamber w i t h wood  a f t e r i t had been " d e f e a t e d " by a " h i g h e r r a n k i n g " male. to b e l i e v e t h a t these However, the  more important  Blanchard  ' b a r r i e r s " c o u l d keepbburrpW4digging  than t h e i r e f f e c t inhibit  f Blanchard, T  rodents be  as p h y s i c a l b a r r i e r s ; s p e c i f i c  'dis-  f u r t h e r a g g r e s s i o n from c o n s p e c i f i c s  1977).  Second, Hudson (1950) obs-erved what he c a l l e d i n g s " i n r a t s i n a p a s s i v e avoidance, s i t u a t i o n . and  It i s  ' s i g n a l i n g f u n c t i o n ' o f these o b s t r u c t i o n s may  p l a y s ' o f d e f e a t e d rodents (cf.,  (1975)-,  '-'pushing o f wood' s-havr-  Although  this  behaviour-  i t s r e l a t i o n s h i p to a d e f e n s i v e r e p e r t o i r e were not the focus o f  ex-  p e r i m e n t a l s c r u t i n y i n Hudson's study, Hudson went on to s p e c u l a t e about its  a d a p t i v e f u n c t i o n i n the willd.  was  u n c l e a r , he a s s e r t e d t h a t thisbbehaM'Ourvwasaaceommonrresponse.Of-gophers  to  Although  the b a s i s f o r h i s s p e c u l a t i o n s  t r a p s s e t i n t h e i r burrows,and;.a g e n e r a l response  (Hudson, 1950,  p.  o f rodents  the o b s e r v a t i o n s o f Owings and Coss  behaviour  reptiles  127),  Hudson's s p e c u l a t i o n s have gained some c r e d i b i l i t y  (1977).  to  These r e s e a r c h e r s found toward snakes was  i n the l i g h t  (1977) and Owings, B o r c h e r t , and  of Virginia  t h a t a major p a r t o f the ground s q u i r r e l s  " s a n d - k i c k i n g " , and the a u t h o r s ' v e r b a l and  p i c t o r i a l d e s c r i p t i o n s o f the b e h a v i o u r  are n e a r l y i d e n t i c a l to the p r e s e n t  .59.  d e s c r i p t i o n o f the responses o f the r a t s i n the p r e s e n t shock.  That " s a n d - k i c k i n g " was  s t u d i e s to p r o d -  an e f f e c t i v e a n t i - p r e d a t o r b e h a v i o u r  i n d i c a t e d by the subsequent r e t r e a t o f the snakes In a more s y s t e m a t i c  l a b o r a t o r y study,  between s a n d - k i c k i n g  and  a variety of  was  (Owings e t a l . , 1977),  aisitgnifi&ari^ ' d e f e n s i v e ' behaviours  o f the  snakes.  (Owings S Coss, 1977). Thus, t h e r e i s some evidence  that  n a t u r a l s i t u a t i o n s ' a n d t h a t i t may  'burying b e h a v i o u r '  have two  b a s i c adaptive  a defense a g a i n s t both c o n s p e c i f i c s and p r e d a t o r s , a l i s t i c s t u d i e s o f rodent b e h a v i o u r populations  f u n c t i o n s ; as  S i n c e most major  (e.g., Calhoun, 1962)  natur-'  have i n v o l v e d  not been f r e q u e n t l y r e p o r t e d to be  a p a r t o f the w i l d  defensive r e p e r t o i r e ,  II,  The  in  p r o t e c t e d from t r a p p i n g and p r e d a t i o n , i t i s not s u r p r i s i n g  t h a t b u r y i n g has rodent's  occurs  Burying b e h a v i o u r and a b i o l o g i c a l approach to a v e r s i v e l e a r n i n g  g e n e r a l purpose o f the p r e s e n t  i n v e s t i g a t i o n s was  to c o n t r i b u t e ,  to the development o f a ' b i o l o g i c a l ' approach to a v e r s i v e l e a r n i n g by ing  the b u r y i n g response.  Any  approach t o a v e r s i v e l e a r n i n g t h a t i s based  on a knowledge o f the animal's n a t u r a l d e f e n s i v e b e h a v i o u r s  w i l l be  f o r the purposes o f t h i s d i s c u s s i o n , as a " b i o l o g i c a l approach". B o l l e s ' hypothesis learning.  study-  i s a s p e c i a l case o f a b i o l o g i c a l  two,  i s s u e s : 1) what the organism's i n n a t e defense r e a c t i o n s a r e , and p r o b a b i l i t i e s o f these r e a c t i o n s are changed as a r e s u l t o f  sues i s examined i n the l i g h t o f the p r e s e n t  Thus,  approach to a v e r s i v e  In g e n e r a l , a b i o l o g i c a l approach must d e a l w i t h  A c c o r d i n g l y , i n the f i n a l p a r t o f the p r e s e n t  viewed,  fundamental 2) how  the  experience.  d i s c u s s i o n , each o f these i s data.  60  Befensive Behaviour Bolles  (1970) has argued c o n v i n c i n g l y t h a t knowledge o f an a n i m a l ' s  s p e c i e s - t y p i c a l defense r e a c t i o n s i s e s s e n t i a l f o r u n d e r s t a n d i n g i t s c i t y t o . l e a r n avoidance r e s p o n s e s . e m p i r i c a l study of,these  B o l l e s , however, d i d n o t advocate  defensive behaviours,  Instead,  the  on the b a s i s o f  l i m i t e d o b s e r v a t i o n , he assumed t h a t r a t s . c o u l d respond t o n o v e l o r ous s t i m u l i i n o n l y a l i m i t e d number o f ways, i . e . , by f r e e z i n g , or f i g h t i n g .  capa-  danger-  fleeing,  The p r e s e n t d a t a i n d i c a t e t h a t t h i s assumption i s  inadequate  and t h a t the e m p i r i c a l s t u d y o f d e f e n s i v e b e a h v i o u r s i s e s s e n t i a l t o any b i o l o g i c a l account o f a v e r s i v e l e a r n i n g , A l t h o u g h i t seems obvious t h a t . t h e n a t u r e o f the d e f e n s i v e  reactions  o f organisms s h o u l d be viewed as an e m p i r i c a l q u e s t i o n , t h i s v i e w p o i n t r a i s e s s e v e r a l problems f o r a b i o l o g i c a l approach t o a v e r s i v e l e a r n i n g . F o r example, B o l l e s '  (1970) h y p o t h e s i s becomes d i f f i c u l t  t o a p p l y when i t  can no l o n g e r be assumed t h a t animals d i s p l a y o n l y t h r e e d e f e n s i v e behaviours.  As the number o f p o t e n t i a l d e f e n s i v e b e h a v i o u r s i n c r e a s e s ,  outcomes o f s t u d i e s o f a v e r s i v e l e a r n i n g become more d i f f i c u l t  the  to p r e d i c t .  In a d d i t i o n , many f i e l d and l a b o r a t o r y s t u d i e s would be r e q u i r e d to e s t i mate the d e f e n s i v e c a p a c i t i e s o f e v e n . a few, common o r g a n i s m s , and i t i s u n l i k e l y t h a t t h i s b e h a v i o u r a l c a t a l o g u e would be easy to assemble. such a c a t a l o g u e a l r e a d y e x i s t e d , i t may sometimes be d i f f i c u l t the d e f e n s i v e b e h a v i o u r s t h a t animals d i s p l a y under n a t u r a l  Even i f  t o compare  conditions  w i t h the b e h a v i o u r r e q u i r e d o f them i n an e x p e r i m e n t a l s e t t i n g .  F o r example,  ' r u n n i n g away' i n a n a t u r a l s i t u a t i o n i s not c l e a r l y comparable to i n a r u n n i n g w h e e l , so  t h a t i t might be d i f f i c u l t  'running'  to make a c c u r a t e p r e d i c -  t i o n s about l a b o r a t o r y performance t h a t are based s o l e l y on a knowledge o f  n a t u r a l d e f e n s i v e b e h a v i o u r s ( c f . , Schwartz,  1978).  In view o f these problems, B o l l e s ' s i m p l i f y i n g assumption about the d e f e n s i v e c a p a c i t i e s o f a n i m a l s , even i f i t does not a p p l y i n some s i t u a t i o n s , may  appear more a t t r a c t i v e than the'eempifiGal^st.udy^of ^defensive'' be-  haviours .  The major drawback o f B o l l e s ' approach i s t h a t i t i n c o r p o r a t e s  an assumption t h a t the p r e s e n t d a t a have shown t o be unfounded, more, the p r e s e n t d a t a i n d i c a t e t h a t the e m p i r i c a l  Further-  study o f d e f e n s i v e  c'ahtibeefraii-tffi b e h a v i o u r are r e l a x e d ,  reactions  on the animal * Thus, the e m p i r i c a l approach can a t l e a s t  l y l e a d t o a general b i o l o g i c a l  potential-  t h e o r y o f a v e r s i v e l e a r n i n g ; whereas,  an  h y p o t h e s i s t h a t i n c o r p o r a t e s u n t e s t e d assumptions o r assumptions based on l i m i t e d o b s e r v a t i o n s i s l i k e l y t o be s u c c e s s f u l o n l y w i t h i n h i g h l y  restricted  settings. Perhaps a more fundamental assumption on:v^hi'Ghtt:obb.aseaa*iibi0logical' approach t o a v e r s i v e l e a r n i n g i s t h a t the d e f e n s i v e b e h a v i o u r s o f a l l a n i mal s p e c i e s have been the p r o d u c t o f i n t e n s e but d i v e r s e s e l e c t i o n p r e s s u r e s . Indeed, the f a c t s o f animal defense appear t o be as numerous and d i v e r s e as animal s p e c i e s themselves  (Maier § M a i e r , 1970).  A f i r s t p r i o r i t y of a  b i o l o g i c a l approach t h e r e f o r e might be to o r d e r what i s a l r e a d y known about animal defense i n t o a coherent base f o r broad p r e d i c t i o n s about animal behaviour.  I t i s d i v e r s i t y o f t h i s magnitude, not s i m p l y the d i v e r s i t y  seen  i n l a b o r a t o r y r a t s exposed t o programmed e l e c t r i c shock, t h a t s h o u l d be the foundation o r . " f i r s t p r i n c i p l e "  ( B o l l e s , 1970, p. 34) o f a b i o l o g i c a l  count o f the d i v e r s e phenomena o f a v e r s i v e  ac-  learning.  The p r i n c i p l e s o f D e f e n s i v e L e a r n i n g The major i s s u e t h a t must be d e a l t w i t h i n any b i o l o g i c a l approach t o a v e r s i v e l e a r n i n g i s how  the p r o b a b i l i t y o f a d e f e n s i v e response  changes  . as  a r e s u l t of experience, . Bolles  (1970) p r o v i d e s two  account f o r changes i n response p r o b a b i l i t y .  o f b e h a v i o u r are emphasized.  For f a s t  sequence i s p u n i s h i n g shock, and  mechanisms to  These mechanisms  depending on whether l e a r n i n g i s slow or f a s t , but  62  differ  i n both the  consequences  (SSDR) l e a r n i n g t h e - i m p o r t a n t  con-  f o r slow (non-SSDR) l e a r n i n g i t i s  the  production of a r e i n f o r c i n g "safety-signal". Both o f these mechanisms o f d e f e n s i v e l e a r n i n g and  (i.e.,  punishment) have u s u a l l y been assumed to apply to any  chosen.response C e I n t r o d u c t i o n ) ,  Bolles  s e  that  reinforcement arbitrarily  (1970), however, has  argued  t h e r e are b i o l o g i c a l l i m i t a t i o n s ontthekki«ndsoofxresponses~(th^at a n i -  mais can  learn i n 'aversive'  situations.  l e a r n i n g such as r e i n f o r c e m e n t may 1972); 1975a).  not  Thus,  'general'  mechanisms o f  apply to a l l responses  (Bolles,  N e v e r t h e l e s s , B o l l e s must assume t h a t these mechanisms have  some g e n e r a l i t y a c r o s s responses; o t h e r w i s e , he would have no b a s i s p e c t , f o r example, t h a t the would be tic  e f f e c t s of  comparable t o i t s e f f e c t s on  to argue on the  dangerous events mechanisms t h a t  one  'punishment' on fleeing.  exr  f r e e z i n g behaviour  Thus, i t may  be  problema-  hand t h a t animals have e v o l v e d s p e c i a l responses to  (SSDRs), while, ont'the o t h e r hand envoking are  to  assumed t o operate i n the  learning  absence o f these " b i o l o g i c a l  constraints". Although i t may be  explained  t u r n out  t h a t the  facts of aversive  learning  cannot  without envoking a number,of d i f f e r e n t l e a r n i n g mechanisms,  each h a v i n g a l i m i t e d range o f a p p l i c a b i l i t y ,  a more parsimonious  alterna-  t i v e i s a s i n g l e t h e o r e t i c a l framework i n which s p e c i a l , n o n a r b i t r a r y t i o n s h i p s between c e r t a i n c l a s s e s principle".  o f s t i m u l i and  responses i s a  I propose t h a t such an a l t e r n a t i v e can be  vived Pavlovian  framework, and  "first  found w i t h i n  t h a t a b i o l o g i c a l approach to  rela-  a re-  aversive  63  l e a r n i n g might be more r e a d i l y subsumed.by a " c l a s s i c a l " P a v l o v i a n l e a r n i n g framework than by the " i n s t r u m e n t a l " framework envoked by  Bolles.  In g e n e r a l , - t h e r e ' c a r e : t w o - c r i t e r i a that-define': P a v l o v i a n ' c o n d i t i o n i n g . Thenfirst a  c r i t e r i o n invol'Vesnan- e x p e ^  'conditioned' stimulus  (CS).to an  'unconditioned'  second c r i t e r i o n i s a change i n b e h a v i o u r (Rescorla, The  stimulus  that r e s u l t s  (UCS),  from t h i s  operation  1969).  P a v l o v i a n c o n d i t i o n i n g o f a d e f e n s i v e response i s i l l u s t r a t e d i n  the f o l l o w i n g example.  The p r e s e n t a t i o n o f a s t i m u l u s t h a t r e l i a b l y  duces a v a r i e t y o f d e f e n s i v e responses occurrence  (the UCS)  of a stimulus that i s 'neutral' i n t h i s regard  to o c c u r i n the p r e s e n c e o f the CS,  pro-  i s made c o n t i n g e n t on (the CS).  some number o f these c o n t i n g e n t CS-UCS p r e s e n t a t i o n s , a d e f e n s i v e begins  The  After  response  I f i t can be shown t h a t  the  change i n the p r o b a b i l i t y o f the d e f e n s i v e response i s a r e s u l t o f the UCS  contingency, One  then i t i s a ' c o n d i t i o n e d ' response  advantage o f t h i s  with a b i o l o g i c a l  conceptual  the  CS-  (CR).  framework i s t h a t i t i s c o n s i s t e n t  approach to a v e r s i v e l e a r n i n g ,  In P a v l o v i a n c o n d i t i o n i n g ,  u n l i k e i n s t r u m e n t a l c o n d i t i o n i n g , i t i s acknowledged t h a t the c h o i c e o f  the  response • t o ^ b b . e c e o i i d i t i ' o n e d i i s s s e r i o u s i y r r e s t r l c t e d b b y t l t h e t t y p e o 6 f v s t i m u l u s used as the UCS. UCS  ( i . e . , o n l y i f i t belongs t o the c l a s s o f responses n o r m a l l y  by the UCS) on  Only i f t h i s response i s ' n o n a r b i t r a r i l y ' r e l a t e d to  will  c o n d i t i o n i n g occur.  This kind of b i o l o g i c a l  (CR)  produced  'constraint'  l e a r n i n g can be viewed as a more g e n e r a l argument f o r . B o l l e s '  i . e . , that a response  the  position;  can be r e a d i l y l e a r n e d i n an a v e r s i v e s i t u a t i o n  o n l y i f i t i s an SSDR (a response produced by the a v e r s i v e UCS).  Bolles,  64  however, looks p a s t the SSDR t o i t s consequences f o r an e x p l a n a t i o n o f behaviour  change; whereas, a P a v l o v i a n account c o n s i d e r s o n l y the s t i m u l i  c o n t i n g e n t l y r e l a t e d t o the UCS» A major o b s t a c l e t o a P a v l o v i a n account o f a v e r s i v e c o n d i t i o n i n g i s r e p r e s e n t e d by a t r a d i t i o n a l d i s t i n c t i o n  (e.g., Skinner,  instrumentaland  The i d e a i s  classical  conditioning.  1938) between  that  instrumental  c o n d i t i o n i n g c o n t r o l s a l l s k e l e t a l , o r v o l u n t a r y responses; classical  c o n d i t i o n i n g c o n t r o l s autonomic,  t h i s were t r u e , then  i t would be d i f f i c u l t  s i v e response such as running  whereas,  ' i n v o l u n t a r y ' responses.  If  t o argue t h a t a s k e l e t a l  defen-  c o u l d be c l a s s i c a l l y c o n d i t i o n e d ,  The f a c t  i s , however, t h a t autonomic responses s u c h ^ " s l i h e a r t i r £ t e c a p p S r e n t i y " c a n ' . ' h e Kie.CgT?^ DijGarae$,1^  :strum^  responses such as key pecks can be c l a s s i c a l l y c o n d i t i o n e d § Jenkins,  in-  1968).  The l a t t e r e f f e c t has been c a l l e d  (e.g., Brown  "autoshaping" or  " s i g n t r a c k i n g " and i t s r e l a t i o n s h i p t o the r e s u l t s o f t h e p r e s e n t  studies  w i l l now be d i s c u s s e d . Until of  1968, the pigeon's key peck was,considered t h e prime example  'voluntary' behaviour  § Jenkins view  c o n t r o l l e d by i t s consequences.  However, Brown  (1968) began an a r e a o f r e s e a r c h t h a t has l e d t o . t h e  current  ( e . g . , Schwartz 6 Gamzu, 1977) t h a t the key peck may be i n l a r g e measure a T  _br,esj>.d t-.d_tgra>irt iw.ith.ya; lift rkey;? in" spirt e;to£ntfce catisienceeof i a « i ^ n f o r m a * « e o n t i n g e f l c y bjej^tejeri sth-etf^geofr s^Kehaiviiour Tahd cac-cess':ttib' foo%v §ftier 1  eSi-iU^Supair.^  :  r  sa if ewhtr-iais' " o f t h e s e  tTwo5<k-i'nds i © f  eyj>_  65  dence suggested  that this  conditioning. contingency  First,  "autoshaping"  as i n a l l i n s t a n c e s o f P a v l o v i a n c o n d i t i o n i n g , the  between the CS and  the'behaviour  phenomenon was,due t o P a v l o v i a n  the UCS  was  c r i t i c a l f o r the emergence o f  (e.g., Brown P J e n k i n s , 1968; T  Gamzu § W i l l i a m s ,  1971).  Second, and perhaps most i m p o r t a n t l y , autoshaped key pecks p e r s i s t e d even when t h e r e was access  a negative  instrumental  to g r a i n (Williams § W i l l i a m s , 1969).  p l a i n i n instrumentaltt-erms  The  I t i s very d i f f i c u l t to  the o n l y response t h a t was  and ex-  followed  P a v l o v i a n c o n d i t i o n i n g o f d i r e c t e d s k e l e t a l responses  (Hearst,  by  gain i n strength.  has been p a r t o f what B o l l e s (1975a) has  behaviour  called a "revolution" in  t h e o r y ; the s t r a i g h t f o r w a r d i d e a t h a t  analyzed mainly lenge  why  between key p e c k i n g  not  food should  1975)  contingency  'operant  i n t t e r m s o f i t s consequences has  from the autoshaping  data  ( f o r reviews,  (Schwartz § Gamzu, 1977).  see Hearst  can  be  received a serious chal- .  s p i t e o f the i n t e n s i v e study t h a t t h i s phenomenon has p a s t ten y e a r s  behaviour'  However, i n  r e c e i v e d over  P J e n k i n s , 1974; T  Hearst,  the  1975;  Schwartz § Gamzu, 1977), i t s g e n e r a l i t y has been l i m i t e d by the f a c t t h a t 7 t h e r e are no c l e a r i n s t a n c e s o f autoshaping  w i t h an a v e r s i v e r e i n f o r c e r . '  The purpose o f the f i n a l p a r t o f t h i s d i s c u s s i o n i s t o b r i e f l y marshal evidence  t h a t suggests  t h e s i s may reaction  t h a t much o f the b e h a v i o u r  d e s c r i b e d i n the  r e p r e s e n t the P a v l o v i a n c o n d i t i o n i n g o f a d i r e c t e d d e f e n s i v e ( i . e . , a type o f a u t o s h a p i n g ) .  The  v a l i d i t y o f t h i s argument  i m p l i c a t i o n s f o r both the g e n e r a l i t y o f the autoshaping feasibility  phenomenon and  has the  o f a Pavlovian i n t e r p r e t a t i o n of defensive l e a r n i n g .  7w 'Ues.t^aable. example was p.rovided. by Racfc f 11^9"),. -.'... The c o n d i t i o n i n g o f a g g r e s s i v e - r e s p o n s e s an B e t t a splendens may r e p r e s e n t an e x c e p t i o n to t h i s g e n e r a l i z a t i o n , a  present  ,,. (Murray,  1973)  66  Tn the f o l l o w i n g t a b l e , s e v e r a l f e a t u r e s o f autoshaping s i v e b u r y i n g are d i r e c t l y  and defen-  compared.  Autoshaping  Defensive  Burying  1.  a h i g h 'percentagecof'subjects exposed to a contingency between a key CCS) and food access (UCS) l e a r n t o approach t h e cue. and 'peck' i t (CR)  a h i g h p e r c e n t a g e o f s u b j e c t s ex posedctotangontingency;between a p r o d (CS) and shock (UCS). l e a r n t o i approachtthe.shock source and bury i t (CR)  2.  Autoshaped b e h a v i o u r i s n o t a simple ' r e f l e x ' e l i c i t e d by cues a s s o c i a t e d w i t h food; i t is a directed, skeletal response,  B u r y i n g b e h a v i o u r i s not a, simple ' r e f l e x ' e l i c i t e d by cues a s s o c i a t e d w i t h shock; i t i s a directed, skeletal response.'  3. ' Autoshaping occurs i n t h e absence o f art i n s t r u m e n t a l cont i n g e n c y between food and pecki n g ; furthermore, t h e f i r s t i n ^ stance o f a b e h a v i o u r Ce.g,, key-peck) cannot be e x p l a i n e d by i t s consequences.  Burying b e h a v i o u r o c c u r s ' i n the absence o f an i n s t r u m e n t a l c o n t i n g e n c y between i t s e l f and shock; f u r t h e r m o r e , the f i r s t i n s t a n c e o f a b e h a v i o u r cannot be e x p l a i n e d by i t s consequence,  4.  A p o s i t i v e c o r r e l a t i o n between the o c c u r r e n c e o f t h e CS and theUCS i s m a i n l y r e s p o n s i b l e f o r the f i r s t approach and peck a t the CS, Common c o n t r o l s f o r Pav-. l o v i a n c o n d i t i o n i n g ( i . e . , CS a l o n e , UCS a l o n e , d i s c r i m i n a t i v e c o n d i t i o n i n g ) y i e l d e d r e s u l t s expected f o r a Pavlovian learning process,* Animals d i r e c t e d t h e i r b e h a v i o u r toward cues p o s i t i v e l y c o r r e l a t e d w i t h t h e UCS.  A p o s i t i v e c o r r e l a t i o n between the prod (CS) and t h e shock (UCS) appears t o be r e s p o n s i b l e f o r approach t o and b u r y i n g o f the CS. (Exps. 1-9). Common controls f o r Pavlovian.condition i n g ( i . e . , CS alone (Exps. 1,4, 6 ) , UCS a l o n e , (Exp. 3 ) , d i s c r i m i n a t i v e c o n d i t i o n i n g (Exps.,5, 7, 8, 9) g e n e r a l l y y i e l d e d r e s u i t s expected f o r a P a v l o v i a n learning process. Rats d i r e c t e d t h e i r b e h a v i o u r toward cues p o s i t i v e l y c o r r e l a t e d with t h e UCS.  5,  Approach t o and c o n t a c t w i t h t h e CS w i l l p e r s i s t even when t h e r e i s a ' n e g a t i v e ' i n s t r u m e n t a l cont i n g e n c y between pecks and food delivery.  Approach t o and b u r y i n g o f t h e CS occurs d e s p i t e a p r i o r , i m p l i c i t punishment contingency between approach and shock.  6.  Exposure t o the CS-UCS c o n t i n g e n c y i t s e l f i s s u f f i c i e n t f o r the l a t e r appearance o f the CR. Key-pecking does n o t have t o o c c u r d u r i n g t h e CS-UCS p a i r i n g . '  Exposure t o t h e CS-UCS c o n t i n gency i t s e l f i s s u f f i c i e n t f o r the l a t e r appearance o f t h e CR. B u r y i n g does n o t have t o o c c u r d u r i n g t h e CS-UCS p a i r i n g .  :  67  Although these s i m i l a r i t i e s between autoshaping and provocative, tical  burying  are  the d i f f e r e n c e s between these phenomena are o f equal  importance,  about 50 t r i a l s  One  d i f f e r e n c e i s t h a t the  to e s t a b l i s h (Hearst,  occurs a f t e r o n l y one  'trial'.  ences comprehensible.  The  Two  first  theore-  aut'oshaped response  1975), whereas the b u r y i n g  considerations  may  takes response  make these  consideration i s survival,  differ-  Animals i n  t h e i r n a t u r a l environment do not have much time to l e a r n about dangerous things. trial  The  last t r i a l  of aversive  l e a r n i n g f o r the p r e y i s the  o f . a p p e t i t i v e l e a r n i n g f o r the p r e d a t o r .  s u r v i v a l , the d e f e n s i v e ( B o l l e s , 1970).  On  the o t h e r hand, the  be  transmitted  a p p e t i t i v e l e a r n i n g o f an  l o n g e r time course without i l l e f f e c t . r a p i d a p p e t i t i v e l e a r n i n g i n the  rapid defensive  l e a r n i n g i n the. r a t .  such as these are d i f f i c u l t ing  p i g e o n may  be  t h a t i s more a c c e s s i b l e t o e x p e r i m e n t a l t e s t but  the UCS.  the  generally follow a  l e s s than t h a t  pressure for  considerations l e a d to i n t e r e s t -  account f o r the d i f f e r e n c e between  one  and  genera-  ( c f ; , B o l l e s , 1975a).  a c q u i s i t i o n rates of Pavlovian  CS  capacity  animal l i k e  d i r e c t l y , they may  the  t h a t may  to l a t e r  Although e v o l u t i o n a r y  to evaluate  A second c o n s i d e r a t i o n t h a t may  1927)  and,effective  In o t h e r words, s e l e c t i o n  p r e d i c t i o n s about comparative animal l e a r n i n g  much a t t e n t i o n :  facilitate  An organism equipped w i t h t h i s k i n d o f d e f e n s i v e  p i g e o n , a l t h o u g h j u s t as e s s e n t i a l f o r s u r v i v a l , can  for  to  l e a r n i n g o f the p r e y must be q u i c k  would have a s e l e c t i v e advantage t h a t may tions.  In o r d e r  first  key pecks and  conditioned  burying not  received  I t i s a n a t u r a l complement o f temporal c o n t i g u i t y  (Pavlov,  t u r n out The  to be  which has  is  j u s t as important: s p a t i a l  contiguity of  the  b u r y i n g paradigm i s • .unusualLnihnthat "the-UCS' (shock)  i s d e l i v e r e d through a w e l l - d e f i n e d ,  l o c a l i z e d CS  (prod), • Because n o x i o u s '  68  s t i m u l i i n the animal's n a t u r a l ous  w i t h the cues t h a t  assume  that  laboratory  environment are u s u a l l y s p a t i a l l y  contigu-  s i g n a l t h e i r o c c u r r e n c e , i t i s not unreasonable t o animals may be able t o l e a r n about s p a t i a l l y  conti-  guous events more e a s i l y than those t h a t are n o t . The h y p o t h e s i s i s c e r t a i n l y worth t e s t i n g , both i n the ease o f t h e pigeon's autoshaped key peck and  i n the case o f t h e r a t ' s c o n d i t i o n e d  burying  response.  A second apparent d i f f e r e n c e between autoshaping and the b u r y i n g  pheno-  menon concerns the n a t u r e o f the r e l a t i o n s h i p between t h e CR and the 'uncond i t i o n e d ' response  (UCR) t o t h e UCS,  The pigeon's c o n d i t i o n e d  though n o t t h e same as i t s u n c o n d i t i o n e d (Jenkins  § Moore, 1973),  Likewise,  response t o food,  several other  instances  key peck, al-r  i s very  similarj  o f Pavlovian  c o n d i t i o n i n g a r e c o n s i s t e n t w i t h the n o t i o n o f s t i m u l u s - s u b s t i t u t i o n : i . e . , the  subject  a c t s i n the same way toward t h e C S . a s i t  C l e a r l y , burying shock  (e.g.,  i s a d i f f e r e n t response from those i n i t i a l l y e l i c i t e d b y  withdrawal).  I t i s important t o remember t h a t s t i m u l u s the mechanism o f P a v l o v i a n on P a y l o v i a n  conditioning.  s u b s t i t u t i o n i s a theory  There i s n o t h i n g  about  i n the d a t a  c o n d i t i o n i n g t h a t suggests t h a t a l l CRs a r e t h e same as the  UCRs e l i c i t e d by t h e UCS, CRs  does toward t h e UCS.  In f a c t , t h e r e are many.examples o f P a v l o v i a n (  t h a t a r e n o t the same as t h e UCR,  showed t h a t an u n c o n d i t i o n e d  O b r i s t , S u t t e r e r , and Howard  (1972)  response t o e l e c t r i c shock was i n v a r i a b l y  c a r d i a c a c c e l e r a t i o n . ; however, when shock was p a i r e d w i t h a CS i n t h e u s u a l Pavlovian  manner, t h e CS l a t e r e l i c i t e d c a r d i a c d e c e l e r a t i o n . '  T h i s CR was  ;  69  adaptive  i n the sense that i t may  c a r d i o v a s c u l a r s t r a i n , but sponse t o  shock.  schedule,  The  i t was  have prepared the o p p o s i t e  unconditioned  ' c o n d i t i o n e d ' response was  i t was  Again,  e f f e c t o f i n s u l i n was  c l e a r l y adaptive,  not  an i n c r e a s e i n b l o o d  UCS  i s morphine, the CR  between CRs  alone  refixed  to lower b l o o d  sugar.  (saline injection),  their  an i n c r e a s e r a t h e r than a d e c r e a s e i n b l o o d  the CR d i d not  pain s e n s i t i v i t y  o f the u n c o n d i t i o n e d  S i e g e l (1972) i n j e c t e d i n s u l i n i n t o . r a t s on a  When' r a t s were l a t e r t e s t e d w i t h the CS  sugar,  the animal f o r impending  f i t the t h e o r y o f s t i m u l u s  A l t e r n a t i v e l y , i f the UCS sugar but  a decrease  i s g l u c o s e , the CR i s  (Deutsch,  i s not reduced p a i n s e n s i t i v i t y ;  ( S i e g e l , 1975,  and UCRs can be  1977),  s u b s t i t u t i o n but  1974),  When the  i t is.increased  Other i n s t a n c e s o f . d i s c o n t i n u i t i e s  found i n the autoshaping  literature.  For  ex-  ample, Wasserman (1973) found t h a t baby c h i c k s pecked at a key p r e d i c t i n g f o u r seconds o f h e a t , but they d i d not peck d u r i n g h e a t .  Grant  (1974)  showed t h a t responses toward a c o n s p e c i f i c CS were d i s s i m i l a r to those c i t e d by the  food UCS,  In t h i s i n s t a n c e ,  'social  grooming' was  eli-  the dominant  CR. Thus, i t may  be premature t o r e j e c t the n o t i o n o f a P a v l o v i a n  t i o n e d b u r y i n g response on the  grounds t h a t i t i s d i s s i m i l a r to the uncon-  d i t i o n e d response t o shock, or. because the a c q u i s i t i o n o f t h i s takes p l a c e i n one  ' t r i a l ' w h i l e the  a c o n d i t i o n e d b u r y i n g response gains  On the o t h e r hand, the i d e a o f  some c r e d i b i l i t y because o f s e v e r a l ,  s t r i k i n g s i m i l a r i t i e s between b u r y i n g b e h a v i o u r and  tioning.  The  response  a c q u i s i t i o n of other conditioned r e -  sponses u s u a l l y r e q u i r e s many more t r i a l s .  menon t h a t has  condi-  autoshaping,  a,pheno-  commonly been i n t e r p r e t e d as an i n s t a n c e o f P a v l o v i a n most important  s k e l e t a l responses,  similarities  condi-  are 1) t h a t both are d i r e c t e d ,  2) t h a t n e i t h e r phenomenon can be r e a d i l y e x p l a i n e d  by  70  instrumental  c o n t i n g e n c i e s , and  gency between a CS and the behaviour,  a UCS  Although  3) t h a t i n both  cases  seems to be c r i t i c a l  the p r e s e n t  a Pavlovian contin-  f o r t h e emergence o f  s t u d i e s o f d e f e n s i v e b u r y i n g were not  designed w i t h t h i s comparison i n mind, they do p r o v i d e some d a t a t h a t c o n s i s t e n t w i t h the argument t h a t b u r y i n g b e h a v i o u r Pavlovian conditioning of a d i r e c t e d s k e l e t a l The  vprdo'fty o f t h i s  also represent  the  response.  argument would extend  shaping phenomenon, and p r o v i d e substance  may  are  the g e n e r a l i t y o f the  auto-,  t o the " a l t e r n a t i v e " b i o l o g i c a l  approach to a v e r s i v e l e a r n i n g b e i n g p r e s e n t e d . h e r e .  A c c o r d i n g t o t h i s view,  s p e c i e s - t y p i c a l defense r e a c t i o n s such as r u n n i n g o r f r e e z i n g are d i r e c t e d by P a v l o v i a n r a t h e r than i n s t r u m e n t a l c o n t i n g e n c i e s i n the organism's vironment.  en-  Thus, the s u c c e s s f u l p r e d i c t i o n o f d e f e n s i v e l e a r n i n g must be  based on a thorough knowledge o f the organism's  'unconditioned'  defensive  r e p e r t o i r e , and on a f c a r e f u l a n a l y s i s o f the P a v l o v i a n c o n t i n g e n c i e s t h a t a c t on t h i s r e p e r t o i r e .  Study o f the b u r y i n g phenomenon may-serve as a  n a t u r a l s t a r t i n g p o i n t f o r the development o f such a . b i o l o g i c a l approach t o . aversive learning.  71 REFERENCES. Anger, D.  The r©le o f temporal d i s c r i m i n a t i o n s i n the r e i n f o r c e m e n t o f  Sidman avoidance b e h a v i o r .  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