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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., Univ e r s i t y of 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 i n THE FACULTY OF GRADUATE STUDIES (Department of Psychology] We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1978 0 Dallas R. T r e i t , 1978 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l m a k e i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may b e g r a n t e d b y t h e H e a d o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t b e a l l o w e d w i t h o u t my w r i t t e n p e rm i s s i o n . D e p a r t m e n t o f T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook Place Vancouver, Canada V6T 1W5 D a t e "7 / ABSTRACT In t y p i c a l laboratory s e t t i n g s , the defensive reactions of animals appear to 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 attacking. However, i n the present 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 ma-> t e r i a l incorporated i t into a s t r i k i n g and adaptive behavioural sequence. Rats shocked once through a stationary prod buried t h i s shock ^source, even when the shocks-test i n t e r v a l was 20 days. This burying behaviour occurred at a v a r i e t y of shock i n t e n s i t i e s and seemed to 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 prod; rats shocked through a g r i d did not bury the prod, and rats shocked by one of two i d e n t i c a l prods buried only the shock-prod. Both the p o s i t i o n and bright ness of the prod seemed to control the burying behaviour. When eit h e r of these cues was changed p r i o r to the t e s t , burying behaviour was disrup-ted compared to control conditions i n which these cues were unaltered. Although burying was a dir e c t e d and consistent response of rats to prod shock, i t was not a simple, r e f l e x i v e behaviour; rats could adapt t h e i r burying behaviour to changes i n both the kind and d i s p o s i t i o n of burying materials. Thus, the usual assumption that the rat's defensive reper^-t o i r e i s l i m i t e d to a few simple behaviours appears to have been shaped by the constraints of standard t e s t i n g environments rather than by the actual propensities of the r a t . These r e s u l t s were discussed i n terms of t h e i r implications f o r a " b i o l o g i c a l " approach to aversive learning. i i i TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS . i i i . LIST OF FIGURES . v ACKNOWLEDGEMENTS =. . v i ' INTRODUCTION ............ 1 Response problem , „ nie^respoifse f r o D i e m ...... 2 rSSDRS;h^o*t'h"es!i?'s2sis , . , 6 Defensive Behaviours of the rat .... 8 Freezing and f l e e i n g ............ 8 Fighting 11 Thigmotaxis 12 Rationale and purpose 13 Rationale ,'. , 13 Purpose . ,. , 15 GENERAL METHODS ,. 17 Subjects ' . , 17 Apparatus 17 Procedures 17 Habituation 17 Shock administrations ,. 18 Behavioural observation § q u a n t i f i c a t i o n ,. 18 S t a t i s t i c a l analysis 19 Experiment 1 20 Method 20 Results and discu s s i o n ., 20 Experiment 2. 24 Method 24 Results, and discussion 24 Table of Contents (cont'd) i v Page Experiment 3 . 24 Method 2 5 Results and discussion • 2*> Experiment 4 : 2 ^ Method 26 Results and "discussion 26 Experiment. 5 ' 29 Method ...... 30 Results and discussion ........... 33 Experiment 6 33: Method 34: Results and discussion , , 34 Experiment 7 39 Method 39 Results and discussion 40 Experiment '8 43 Method ,, ,, . 44 Results and discussion ' . 45 Experiment 9 52 Method 5,2 Results and discu s s i o n 53 GENERAL DISCUSSION 55 1. Burying as a defense response i n the rat 55 II, ' Burying behaviour and a b i o l o g i c a l approach to aversive 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. Mean duration of burying (Panel A) and the mean of the r a t i o between the height of the highest p i l e and i t s distance from the prod p o s i t i o n (Panel B) at each of the shock-test i n t e r v a l s f o r subjects i n Experiment 1 21 Figure 2. Mean duration of burying and the mean height of bedding material at the prod at each of the f i v e shock i n t e n s i t i e s f o r subjects i n Experi-ment .4. 27 Figure 3. Duration of burying (Panel A) directed at the shock prod and control prod and the f i n a l height of the bedding material at the shock prod and control prod (Panel B) f o r each of' the subjects i n Experiment 5. . . 3 1 Figure 4. Mean duration of burying (Panel A) and the mean height of bedding material at the prod (Panel B) f o r each of the four cue combinations i n Experiment 6. 36 Figure 5. Mean duration of burying di r e c t e d at the shock prod and control prod and the mean height of bedding material at each prod f o r subjects i n Experiment 7 . . . 4 1 Figure 6. Mean duration of burying the shock and control prod with d i f f e r e n t materials f o r subjects i n Experiment 8 46 Figure 7. Mean height of burying materials at.the shock and control prods f o r subjects i n Experiment 8. • ' 49 ACKNOWLEDGEMENTS The author wishes to express his gratitude to John Pinel for the guidance and support which he provided throughout a l l phases of this research. For their helpful comments and sug<-gestions for- the'•• improvement of the manuscript f special thanks are extended to Don'Wilkie and Jim Johnson, 1 INTRODUCTION It has been argued that i n order to understand animal avoidance learning, the subject's innate, defense reactions must be known (Bolles, 1970). This viewpoint has s t e a d i l y gained c r e d i b i l i t y (e.g., Fantino, 1973; Mackintosh, 1974; Wong, 1976; Hineline, 1977; Schwartz, 1978), while the task of documenting the natural defensive behaviours of common laboratory animals has escaped serious attention. One reason the study of defensive responses has not progressed at a rate commensurate with i t s t h e o r e t i c a l importance i s the assumption that laboratory animals such as the rat are capable of only a few simple responses to environmental 'threats' (e.g., Bo l l e s , 1975). However, studies that have shaped t h i s view of the rat's natural defensive capacities have been conducted i n laboratory settings that severely l i m i t the subject's behaviour. The present studies provide evidence that apparent l i m i t a t i o n s i n the rat's defensive a b i l i t y ? are as much a function of the a r b i t r a r y experimental settings i n which - i t has 0 been tested as they are a product of b i o l o g i -c a l constraints. It i s well established (e.g., Meyer, 1960) that only a few of an animal's behaviours can r e a d i l y serve as avoidance responses. These data and the problem they pose f o r general theories of behaviour are b r i e f l y summarized i n the f i r s t section of this Introduction. In the second sec-t i o n , B o l l e s ' (1970) approach to t h i s problem i s presented. His view i s . that animals respond innately to dangerous events by f i g h t i n g , f l e e i n g , or freezing, and that i t i s only these defense reactIons that can be r e a d i l y learned i n an avoidance ta,sk, However, i n s p i t e of the import-ance of Bolles' assumption that f i g h t i n g , f l e e i n g , and fre e z i n g are the only defense reactions a v a i l a b l e to experimental animals (Bolles, 1975), 2 he p rov ides no e m p i r i c a l support f o r t h i s v i ew . Data suppo r t i ng t h i s assumption are reviewed 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 . In the f i n a l s e c t i o n , t h i s evidence i s eva lua t ed , and the r a t i o n a l e and purpose o f the present i n v e s t i g a t i o n s are p resen ted , Response problem The purpose o f much o f the p s y c h o l o g i c a l r e sea rch w i t h animals con-ducted i n t h i s century has been to uncover the p r i n c i p l e s t h a t u n d e r l y the e f f e c t s o f exper ience on fu ture behav iour , In exper imenta l s e t t i n g s , ' b e h a v i o u r ' u s u a l l y r e f e r s to a s i m p l e , q u a n t i f i e d response such as s a l i v a -t i o n o r b a r - p r e s s i n g ; whereas, ' e x p e r i e n c e ' t y p i c a l l y r e f e r s to an ar range-ment o f environmental events or s t i m u l i tha t a l t e r s the l i k e l i h o o d o f fu ture responses . S t i m u l i tha t i nc rease the p r o b a b i l i t y o f responses tha t they precede are f r e q u e n t l y c a l l e d cond i t i oned s t i m u l i , and s t i m u l i tha t i nc rease the p r o b a b i l i t y o f responses tha t they f o l l o w are c a l l e d r e i n f o r c e r s . Out o f these two b a s i c ' arrangements o f responses arid s t i^ -m u l i have emerged the 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 c o n d i t i o n i n g , r e s p e c t i v e l y . I t has o f ten been assumed ( e . g . , Te i t e lbaum, 1966) tha t these p r i n c i p l e s apply u n i f o r m l y to any spec ies and to any combinat ion o f s t i m u l u s , response , and r e i n f o r c e r ( c . f , , S h e t t l e w o r t h , 1972). This assumption has been c a l l e d ' ' equivalence o f a s s o c i a b i l i t y " (Sel igman, 1970), and i t s v a l i d i t y has.become the cen t re o f recent debate, There are many exper imenta l f i n d i n g s tha t are c o n s i s t e n t w i t h the n o t i o n o f "equiva lence o f a s s o c i a b i l i t y " . For example, Pav lov (1927) demonstrated tha t dogs c o u l d be t r a i n e d to s a l i v a t e i n response t o a wide v a r i e t y o f s t i m u l i i f these ' ' cond i t i oned ' s t i m u l i had been fo l l owed by 3 food p l a c e d i n the dog 's mouth. S i m i l a r l y , Sk inner (1956) showed tha t va r i ous "schedules o f re in forcement" r e s u l t e d i n comparable performance curves i n a number o f d i f f e r e n t s p e c i e s , However, there i s a l so evidence tha t seems to c o n t r a d i c t the assump-t i o n o f equ iva l ence . Iri p a r t i c u l a r , there are many s t u d i e s o f avoidance l e a r n i n g tha t i n d i c a t e tha t the p r i n c i p l e s tha t govern behav-i o u r do not app ly u n i f o r m l y , t o a l l responses; Rats may l e a r n to leap out o f a chamber to 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 avo id shock i n f i v e t r i a l s (Theios , 1963), but take hundreds o f t r i a l s to l e a r n a levers-press avoidance task (Biederman, D'Amato, $ K e l l e r , 1964), i f they l e a r n i t at a l l (D'Amato § S c h i f f , 1964). S i m i l a r l y , p igeons can l e a r n to ' avo id shock by s h u t t l i n g to the ' s a f e ' s i d e o f a box ( M a c p h a i l , 1968) but have great d i f f i c u l t y a v o i d i n g shock by peck ing a key ( H i n e l i n e § R a c h l i n , 1969; Schwartz , 1973), I t appears that o r d e r l y r e l a t i o n s h i p s between shock, 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 but not i n o thers ( c f . , B o l l e s , 1971), Al though 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 tha t the p r i n c i p l e s o f behaviour change are not g e n e r a l , and that the response one chooses to 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-an t , a l t e r n a t i v e i n t e r p r e t a t i o n s o f the data have been o f f e r e d ( e . g . , Berger § Brush , 1975), For example, the ba r -p ress avoidance task i s d i f f e r e n t from o ther avoidance task,s i n a number o f ways, any o f which c o u l d account f o r d i f f e r e n c e s i n the ra tes o f avoidance a c q u i s i t i o n . Data that i m p l i c a t e these 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 ba r rp ress performance i r i the r a t , The a c q u i s i t i o n o f ba r -p ress avoidance has been a c c e l e r a t e d by : 4 1) reducing shock i n t e n s i t y (Bolles ^ Warren, 1965 j D'Amato § Fazzaro, 1966) 2) administering b r i e f , intermittent shocks instead of con-tinuous shock (Brush, 1964; D'Amato, K e l l e r , § DiCara, 1964; Hurwitz, 1964; Berger S Brush, 1975). 3) administering noncontingent shocks (Delprato § Holmes, 1977). 4) i n t e n s i f y i n g the signal (CS) f o r shock (Fantino, Sharp, $ Cole, 1966) . 5) lengthening the i n t e r v a l between shock (US) and i t s signal (Bolles, Warren £ Ostrov, 1966; Berger § Brush, 1975). 6) increasing the distance between the CS and the manipulan-dum (Biederman, D'Amato, § K e l l e r , 1964). 7) immobilizing the manipulandum during and s h o r t l y a f t e r shock (Forgione, 1970), 8) introducing the manipulandum at t r i a l onset and r e t r a c t i n g i t a f t e r a response (Hull, Myer, § Smith, 1975). 9) shaping bar-press responses (Feldman PT Bremmer, 1963; Keehn § Webster, 1968). 10) p r i o r appetitive conditioning ( G i a l i a n § Schmaltz, 1973). 11) handling animals between t r i a l s (Wahlsten, Cole, Sharp, £ Fantino, 1968) . IZ) reducing the i n t e r t r i a l i n t e r v a l (Pearl fT F i t z g e r a l d , 1966) . 13) reducing the s i z e of the chamber so i t i s j j . u s t ^ l a r g e : enough to accommodate the subject (Cahoon § Crosty 1, 1969; .Azrin, . Hopwood f, Powell, 1-967). 14) - providing, e i t h e r exposure^or-access"-to • a 'safe' compart-ment (Mast erson, 1970; Crawford Masters on, 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 (Manning, Jackson, § McDonough, 1974), It i s c l e a r from these data that a number of environmental variables can a f f e c t bar press avoidance performance; however, the question i s whether the improvement att r i b u t e d to these variables i s of a magnitude s u f f i c i e n t to account for the o v e r a l l variance i n avoidance, learning. In. t h i s con-text the most important conclusion that can be drawn from these data i s that no environmental variables-ha's been found that makes .bar-pressing to avoid shock as easy f o r a rat to learn,as jumping (Maatch, 1959) or run-ning (Theios, 1963), Evennihatheemost successful studies- of bar-press avoidance (e.g., H u l l , Myer, $ Smith, 1975; Delprato $ Holmes, . 1977), i t took about 200 t r i a l s before the major po r t i o n of subjects avoided shock 1 con s i s t e n t l y . Although such r e s u l t s represent an.improvement over ear-l i e r studies (e.g., D'Amato fT S c h i f f , 1964), they cannot account f o r the vast differences i n the rates at which d i f f e r e n t avoidance responses are learned. By f a r the most powerful evidence against the "equivalence of asso-c i a b i l i t y " assumption was provided by a study of aversive conditioning by Garcia § K o e l l i n g (1966), These researchers found that rats associated a novel t a s t i n g s o l u t i o n with sickness, even a f t e r a long delay between the cue and the consequence; but they d i d not develop t h i s "taste aver-s i o n " i f the consequence was shock, Only i f the s o l u t i o n was "bright and noisy" would rats avoid i t i f i t had been followed by shock. ' These re-su l t s c l e a r l y showed that.each cue and each consequence could be quite e f f e c t i v e , but only i n c e r t a i n non-arbitrary combinations. Because rats 1 • " "Stable'" performance has .been reported i n fewer. t r i a l s (Berger § Brush, 1975). but "average avoidance" was i 1 ,only 60%. It should also,be noted that , '&rc&bits •' -0s-£ *.ofinance nas. bscn ii-eiW-ueq .->xi cewav ;tirj a? * ,^6*1,.^ d i s c r e t e trial-procedures'commonly used-in"training avoidance responses such as running or jumping are d i f f i c u l t to compare to 'free operant' procedures that are used i n t r a i n i n g barr.press avoidance; 6 seemed to associate only c e r t a i n arrangements of cue and consequence these findings were c l e a r l y inconsistent with the equivalence !'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 to the study of behaviour have not been able to p r e d i c t or explain these large differences i n the,-ease'of aversive learning. However, •Bo:Mre'sl)(li9^^^ a s o l u t i o n to t h i s problem that was based on a general consideration of the s u r v i v a l requirements of the organism. It i s B o l l e s ' hypothesis that served as the focus f o r the present i n v e s t i g a t i o n s . i'" SSDR Hypothesis 1 Bolles argued that the s u r v i v a l requirements of an animal i n its-natural environment demanded a defensive mechanism other than avoidance learning as i t i s studied i n psychology experiments, In the laboratory, a v i s u a l or auditory cue i s often used to signal the onset of the aversive stimulus, but in, the w i l d f predators- do not often signa l t h e i r prey'before an attack. Furthermore, the researcher may wait many t r i a l s before stable avoidance performance occurs; whereas, a predator i n the wild does- not allow prey enough " t r i a l s " f o r "learning" to occur. Since most natural s i t u a t i o n s preclude t h i s kind of t r i a l and er r o r learning, s u r v i v a l must instead depend upon a defensive mechanism with which the animal i s already equipped, an innate set of defensive responses that occur i n the presence of any new or sudden stimulus, Bolles c a l l e d these responses 'species-s p e c i f i c ' defense reactions (SSDRs) and assumed that they took one of only three forms: f l e e i n g , f r e e z i n g , or f i g h t i n g , Bolles u t i l i z e d the notion of SSDRs to explain laboratory avoidance learning i n the following way, The normally varied behavioural r e p e r t o i r e _ _^  Recently, however, Krane and Wagner (1975), were able to demonstrate taste aversion learning when the 'consequence' was delayed"shock. 7 of the domesticated laboratory animal is"suddenly restricted when an aversive stimulus is presented. Now the animal, like i t s counterpart in the, wild, emit§.;0nly^innateodefensiye^resggns :„ freezes, flees, or fights. Thus, aversive laboratory stimuli act in a manner similar to any sudden or novel stimulus in 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 later performance in an avoidance situation depends.' If the response required in the situation happens to coincide with one of the animals' SSDRs (e.g., fleeing), then training can proceed smoothly. If, on the other hand, the required response is not part of the animal's innate defensive repertoire, (e.g., barrpre.ssing) performance wis-un-certain and sometimes i t 'does noter..progress beyond the base-line level. Thus taccording to Bolles, anpundersitaridingaofitheovariabi'Iitybihit)' «.' 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 is acquired rapidly i f i t is an SSDR, not because i t i£ strengthened (reinforced) by .events that are. contingent on this 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 a l l e y , , , other SSDRs which compete with fleeing are quickly.suppressed because they are paired with shock more often than is- fleeing, Thus, the c r i t i c a l eonr-tingency for the rapid emergence of an SSDR i s punishment (cf,, Dinsmoor, 1954), Bolles did agree that reinforcement could "strengthen1' certain avoid-v anee responses- (Bolles,. 197Qj p, 42); however, he emphasized that 8 con t ingenc ies tha t are e f f e c t i v e o n l y a f t e r thousands o f shocks ( e . g . , H e r r n s t e i n § H i n e l i n e , 1966) cannot p o s s i b l y account f o r behaviour changes tha t take 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). Th i s .emphasis on the e t h o l o g i c a l significance o f avoidance behaviours 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 s t r eng th l i e s i n i t s a b i l i t y to p r e d i c t l a b o r a t o r y avoidance behaviour from a know-ledge o f the organism's ide£en.sd!veebehavibu3??vi6ur. L i k e any o ther hypothe-s i s , however, i t s u l t i m a t e va lue depends on e m p i r i c a l t e s t s o f i t s v a l i d i t y . The p i v o t a l cons t ruc t i n Bo l l e s ' 1 ' hypothesis , i s the n o t i o n o f an i n -nate defens ive r e p e r t o i r e ; ye t B o l l e s p a i d l i t t l e sys temat ic a t t e n t i o n to the defens ive r e p e r t o i r e i t s e l f , except to s p e c i f y tha t i t i s l i m i t e d to f r e e z i n g , f l e e i n g , and f i g h t i n g , What ev idence , o ther than the f a c t tha t . a p a r t i c u l a r avoidance response i s learned r a p i d l y , demonstrates tha t a 3 behaviour i s . i n f a c t a n ' i n n a t e " defens ive r e a c t i o n ? B o l l e s . (1972) d e a l t w i t h t h i s problem i n a foo tno te , The defens ive r e p e r t o i r e o f the sub jec t can be determined by a s se s s ing i t s . r e a c t i o n to shock, and, " . . . anyone who does t h i s w i t h a r a t w i l l s ee . t ha t i t e i t h e r runs away, f r e e z e s , o r becomes a g g r e s s i v e , , " ( B o l l e s , 1972, p , 129)', Al though B o l l e s d i d not conduct the s tudy thath he p r e s c r i b e d , there i s now a growing body o f l i t e r a t u r e t h a t , f o r the most p a r t , confirms h i s v i ews , These da ta w i l l now be r e r v iewed, Defensive behaviours- o f the 1 r a t  1 ' 'Freezing vartd f l e e i n g , B l an chard and Blanchard (1969a; 1970a,b) found tha t the predominant defens ive r e a c t i o n s o f r a t s exposed to s t i m u l i vas,sbsci\atsed. w i th \ shoeh were f r e e z i n g and f l e e i n g , The r a p i d i t y w i t h which 3 r~r~~' ' r •' ' . I t i s a l so noteworthy tha t B o l l e s neg lec ted to de f ine the te rm, " inna te de-fense r e a c t i o n " . For the purposes o f the present 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 viewed as an adapt ive response to ave r s ive s t i m u l a t i o n . Noth ing i s assumed about the "innate" status, either than the suggestion (see 9 these responses developed suggested tha t they were ' u n l e a r n e d ' , i „ e . , s p e c i e s - s p e c i f i c defense r eac t i ons ( c f , , Blanchard § B lancha rd , 1971}. S i m i l a r l y , bo th o f these responses were found to be prominent components o f the r a t ' s r e a c t i o n to a ca t (Blanchard § B lancha rd , 1971; 1976). These responses occur red 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 , and i n ' the absence o f a g o n i s t i c contac ts between the r a t and the cat ( c f , , C u r t i , . 1935). B lancha rd , K e l l e y and Blanchard (1974) p rov ided evidence tha t , n o v e l t y i t s e l f can ; produce defens ive r e a c t i o n s ( c f . , B o l l e s , 1970). They found tha t preexposure to a nove l s i t u a t i o n reduced r a t s ' l a t e n c i e s to en ter i t . Conve r se ly , r a t s f l e d from a nove l t o a less ' nove l s i t u a t i o n , even when r e q u i r e d to c ross 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 tha t the h y p e r a c t i v i t y observed i n r a t s tha t are p l a c e d i n nove l s i t u a t i o n s may r e f l e c t a b o r t i v e defens ive r e a c t i o n s . s u c h as f l i g h t . ( c f . Walker , 1959). Many o f the B iancha rds ' f i n d i n g s have been confirmed and extended i n a recent s tudy o f the ontogeny o f defens ive r e a c t i o n s i n the r a t , B r o n s t e i n and H i r s c h (1976) found tha t i m m o b i l i t y i n response t o a foo t shock , a caged c a t , o r a suddenly moving objec 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 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 to the p reda to r and to the footshock was i n t e r p r e t e d as support f o r B o l l e s ' (1970} 1972) con ten t ion tha 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 footshock represent inna te defens ive r e a c t i o n s ( c f . , Blanchard P, B l a n c h a r d , 1971), This obse rva t i on a l s o appears to add some substance to B o l l e s ' (1972) a s s e r t i o n tha t the a t t r i b u t e s o f the r a t s ' n a t u r a l de fens ive r e p e r t o i r e -can be d i s cove red by exposing the r a t to ' u n n a t u r a l ' a v e r s i v e s t i m u l i such as shock, B lancha rd , Mast , and Blanchard (1975) designed an experiment to. 1 i d e n t i fy the p a r t i c u l a r f e a t u r e s o f ca ts that e l i c i t e d f r e e z i n g i r i r a t s , general d i s c u s s i o n ) tha t there may 'be .a s t rong gene t i c component to i t s - express ion . 10 They found tha t the sound and smel l o f a ca t were r e l a t i v e l y i n e f f e c t i v e cues; whereas, v i s u a l cues a s soc i a t ed w i t h movement o f the c a t , whether i t was a l i v e or dead, were potent ' re leasers ' ' o f f r e e z i n g . Furthermore, the movement o f a c a t , a dog, o r an inanimate card 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 s t imu lus than f o r the o the r two. These experiments suggested tha t movement i t s e l f i s 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 , w h i l e the maintenance o f f r e e z i n g may depend on a d d i t i o n a l f a c to r s such as the p h y l o g e n e t i c ' r e l e -vance » o f : tK^^^ 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 imulus may c l a r i f y t h i s i s s u e . B lancha rd , Fukunaza, and Blanchard (1976) extended t h i s l i n e o f rer-search by examining o ther environmental f ac to r s tha t c o n t r o l defens ive responding i n the r a t . They hypothes ized tha t the type o f defens ive be^ h a v i o u r e l i c i t e d in_ a. r.at:_by. a.;cat ( i , e , , f r e e z i n g or f l e e i n g ) might de-pend on the p o t e n t i a l f o r escape fromthe t e s t environment, and not neces-s a r i l y on the d i f f e r e n t i a l punishment o f defens ive r e a c t i o n s as B o l l e s (1970) had suggested (but see B o l l e s , 1975a, 1976). In o rder to t e s t t h i s " e l i c i t a t i o n " h y p o t h e s i s , they employed t h e i r p rev ious methodology (Blanchard § B lancha rd , 1971) i n which no defens ive responses were fo l l owed by punishment ( 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 tha t some r a t s were g iven a b r i e f exposure to the inescapab le t e s t chamber p r i o r to 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 ha t had been " f a m i l -i a r i z e d ' ' w i t h the inescapable chamber were f a r l e s s a c t i v e when exposed to a ca t than a s i m i l a r l y t r e a t e d group tha t had not been f a m i l i a r i z e d . However, the a c t i v i t y scores o f the 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 over the 5-min t e s t p e r i o d u n t i l bo th exper imental groups f roze e q u a l l y o f ten but r e l i a b l y more than a no-ca 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 to occur when animals are " f a m i l i a r i z e d " w i t h a s i t u a t i o n i n which escape i s i m p o s s i b l e . The Blanchards a l so argued tha t t h i s f a c t o r seemed to account f o r the gradual a c t i v i t y reduc-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 served to " f a m i l i a r i z e " them w i t h the inescapab le 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 defens ive response . F i g h t i n g . F i g h t i n g i s another behaviour o f r a t s t ha t has been viewed as a defens ive r e a c t i o n ( c f . , B o l l e s , 1970; 1975; Blanchard § B lancha rd , 1977). When a r a t i s p l a c e d i n a chamber w i t h another r a t , or an inanimate o b j e c t , and shock i s admin i s t e r ed , the r a t w i l l face the s t imu lus i n an u p r i g h t pos ture and a t t ack i t ( fo r a r e v i e w , see U l r i c h , 1967), U l r i c h and A z r i n (1962) showed tha 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 va ry 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 shock; the s i z e o f the t e s t chamberj and the i n i t i a l o r i e n t a t i o n o f t h e r a t s to each o t h e r . The age o f the r a t s (Hutchinson, U l r i c h § A z r i n , 1965) and the d u r a t i o n o f the shock test i n t e r v a l ( A z r i n , Hu tch inson , § S a l l e r y , 1964) can a l so a f f e c t s h o c k - e l i c i t e d f i g h t i n g , I t has been demonstrated i n r a t s , hamsters , snakes, raccoons , opossums, monkeys, and ca t s ( U l r i c h et a l , , 1962; A z r i n , . 1964; U l r i c h , . W o l f f , § A z r i n , 1964). Even b l i n d e d r a t s can show shock-e l i c i t e d f i g h t i n g ( E l o r y , U l r i c h , § W o l f f , 1965). F i g h t i n g can be e l i c i t e d i n the same manner by extreme heat ( U l r i c h , 1967), subcutaneous e l ec t rode 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), Blanchard and h i s a s soc i a t e s (Blanchard , B lancha rd , $ Takahash i , 1977; B lancha rd , Takahash i , £ K e l l e y , 1977; Blanchard § B lancha rd , 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 defens ive f i g h t i n g . They s t u d i e d a g o n i s t -i c i n t e r a c t i o n s which occurfedwwhentrats from ou t s ide an e s t a b l i s h e d 12 l a b o r a t o r y co lony were i n t roduced to dominant male r a t s w i t h i n the c o l o n y . Behaviours 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 boxed, f r o z e , and l a y on t h e i r backs , behaviours which appeared to i n h i b i t aggress ion (B lancha rd , B lancha rd , Takahash i , § K e l l e y , 1977). . From these f i n d i n g s , the B laneha rd ' s argued tha t the a g o n i s t i c behav-i o u r s o f co lony r a t s and i n t r u d e r r a t s appeared to f a l l i n t o the ca t egor i e s o f a t tack and defence, r e s p e c t i v e l y . A s i m i l a r examinat ion o f the a g o n i s t -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 (see U l r i c h § A z r i n , 1962) r evea l ed tha t the ' de fens ive ' p a t t e r n ( e . g . , boxing) 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 behaviour than was the ' a t t a c k ' p a t t e r n ( e . g . , b i t i n g ) . These obse rva t ions suggested tha t the behaviours 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 task 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 aggres s ion" ( c f , , U l r i c h § A z r i n , 1962), Shock i n the presence 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 a g o n i s t i c defense responses . Pear , Moody, and P e r s i n g e r (1972) conducted a s tudy o f s h o c k r e l i c i t e d f i g h t i n g tha t 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 ' SSDR h y p o t h e s i s . These researchers found tha t many l e v e r - p r e s s e s tha t o r d i n a r i l y would be counted as ins t ances o f ' ope ran t ' 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 acks at the l e v e r . Thus, a l though B o l l e s ' (1970) has suggested tha t r a t s ' l e a r n ' t h i s task 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 the l e v e r , there are o ther ' s p e c i e s - t y p i c a l ' accounts o f l eve r^p res s avoidance tha t are j u s t as p l a u s i b l e . Th igmotax i s , Grossen and K e l l e y (1972) s tud i ed an i n t e r e s t i n g defens ive response tha t d i d not o b v i o u s l y f a l l i n t o one o f B o l l e s ' th ree c a t e g o r i e s o f defens ive behav iour , They found tha t footshock inc reased t h l g m o t a x i s , i . e . , the amount o f t ime tha t r a t s spent i n contac t w i t h the w a l l s o f the apparatus . In a second experiment , r a t s learned : to . ' jump from a g r i d to a 13 safe platform more readily when i f was'adjacent to the walls ofthe appara-tus. These data supported Bolles ,(1970) argument that the-acquisition of an avoidance response is enhanced i f i t is 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 is not clear that Grossen and Kelley's description of thigmotaxis represents any-thing more than a refined measure of freezing behaviour, (i.e., freezing close to walls). 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, fleeing, and fighting are defensive behav-. iours, However, since there does not appear to have been any concerted effort to identify defensive responses other.than freezing, fleeing, and fighting, Bolles' assumption (Bolles, 1975) that a l l defensive behaviours , f a l l into one of these three categories remains untested, Because Bolles argues that avoidance learning involves, the elimination by punishment of a l l defensive responses in an animal's repertoire until only the most ef-fective oife^remainsaccurate predictions about avoidance learning must be based on a knowledge of an animal's complete defensive repertoire. It is apparent from the literature on defensive reactions (e.g., Ulrich § Azrin, 1962; Blanchard § Blanchard, 1976) that a particular defen-sive behaviour may depend upon certain environmental 'supports* for i t s f u l l expression. For example, an avenue of escape may support fleeing be-, haviour: the absence of support for fleeing and fighting may lead to freez-ing. To some researchers (e.g., Bolles, 1972), these observations simply 14 suggested that a p a r t i c u l a r t e s t s i t u a t i o n may.favor one of the three de-fensive reactions, However, taken one step further, these observations suggest that the p r o b a b i l i t y of discovering the f u l l extent of the r a t ' s defensive r e p e r t o i r e may vary as a function of the v a r i e t y o f s i t u a t i o n s i n which defensive behaviours have been studied. Appropriate environmental conditions may,be necessary f o r c e r t a i n defensive behaviours to, occur.': Simply shocking a rat on a g r i d f l o o r i s , therefore, an i n s u f f i c i e n t t e s t of:the prop o s i t i o n that the "frightened" rat can only freeze, f l e e , or f i g h t (cf., B o l l e s , 1972; 1975). T r a d i t i o n a l l y , behavioural s c i e n t i s t s have r e s t r i c t e d the- behaviour o f t h e i r subjects to one or two a l t e r n a t i v e s i n order to study the proces-ses that presumably underlie a l l behaviours (e.g., Pavlov, 1927). Although t h i s experimental t a c t i c may have revealed some p r i n c i p l e s of c l a s s i c a l and instrumentallearning, i t s ap p l i c a t i o n seems inappropriate when the object of study Is the discovery of behaviours. In order to discover be-haviour, the makeup of the experimental s e t t i n g should be t a i l o r e d l e s s f o r the r e s t r i c t i o n of behaviours than for t h e i r p r o l i f e r a t i o n , Most of the re-search on defensive behaviours has been r e s t r i c t i v e , ' The research has been inappropriately c o n t r o l l e d i n the sense that i t has been confined mostly to s i t u a t i o n s s i m i l a r to those i n which avoidance phenomena have been t r a d i t i o n a l l y studied (e.g., Blanchard et a l , , 1969, 1970). It i s not s u r p r i s i n g , therefore, that the defensive behaviours observed i n 4 these s i t u a t i o n s should be quite consistent with what "anyone" can see 4 B o l l e s (1972, p, 129) i n standard avoidance apparatuses, and not at variance with what are as-sumed by psychologists to ,be the rat's c h a r a c t e r i s t i c modes of defense. In short, I,am suggesting that the expression of the r a t s ' defensive ca^ p a c i t i e s has been shaped more by the constraints of t y p i c a l laboratory t e s t enviornments than by the rat i t s e l f , Purpose. The study of the r a t s ' defensive r e p e r t o i r e may be f a c i l i t a r ted by a l t e r i n g the standard laboratory s e t t i n g so that a r b i t r a r y con^ s t r a i n t s on the rat's behaviour are reduced. Although a v a r i e t y of t e s t environments have been widely used to investigate the responses of labora-tory animals to aversive stimulation, -m^t^hi-yerjLonifo f^fei^e-'^.'-^pnimon':..' #hea"zfil.0®a^oifi.^hji^fpayiitiH^sisp^ss&gsd -met^livgi-i^ . ; - r . j _ feces and urine can drop and shock can be administered, This>feature may5 constrain defensive behaviour i n two ways, F i r s t , unlike more natural s e t t i n g s , there i s l i t t l e i f anything on the f l o o r of the apparatus that the rat ;jCould move or manipulate f o r i t s own defense, Second, the aversive stimulus 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 not support a defen r sive behaviour that i s normally directed at l o c a l i z e d sources of aversive stimulation. Preliminary work i n t h i s laboratory has supported t h i s hypothesis . We found that a r a t housed i n a chamber with bedding material (Sanri-cel) often pushed t h i s material toward and over ( i . e . , buried) a well-defined . ; shock source. Blhi.s:sbui^ingbbeh^ ,p.aft^ d.f.'.:-t?hej .. r-at lis cdcfensrvesfep'erfcoiree andethusTn,mdre:nsystematiAi study', of this-.,.-response Was.warranted. Thesgenerafeepurp.^ • ..... bute to the development 'of a v i a b l e ' b i o l o g i c a l ' approach to avoidance learning by studying the burying response, The purpose of each study was 16 to provide two kinds of evidence to support t h e v i e w that burying behav-iou r i s a prominent defensive response of r a t s . Each experiment was de-signed to show that burying i s a r e l i a b l e response to l o c a l i z e d aversive stimulation, and/or to show that the burying response i s adaptive; that is., that i t affords the animal some pro t e c t i o n from the. noxious agent. 17 GENERAL METHODS This section contains a description of the methodological features common to each of the nine experiments in this thesis.. In each experi-ment, the effect of forepaw shock on the amount and duration of burying behaviour in rats was assessed. Subjects, The subjects in each of the experiments were 250- to 550 g. male, hooded rats purchased from Canadian Breeding Farm and Laboratories, La Prairie, Quebec. Each rat was individually housed in 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 in a small, closed room, adjacent to the behavioural recording apparatus, Behaviours were viewed via closed circuit television and recordedoon video tape. Inside the testing room, a television camera was mounted 50 cm directly above the 44 x 30 x 44 cm transparent Plexiglas test chamber. The chamber floor was covered evenly ;#riith r.egulary gr.ade'^ Sf ground'corn cob ,.$Pa^ 6nhBrd.o.e'S9in;g..G6r', ?aRaxt-on?.rtMn-);/In the center of each of the four walls of the chamber,2 cm above the level of the bedding material, was a hole, 1.2 cm in diameter through which a wooden prod ; 4 § , ' 5 xeOtS.x 0.5 cm). ^^i^x^S,£n§f$i§dsin) ,.• \ in some experiments, two prods were inserted through the holes at opposite ends of the chamber. Shocks were delivered through . the two uninsulated wires wrapped around the stationary prods. Procedures Habituation: Prior to each experiment, a l l animals were handled and placed i n the Plexiglas test chamber in groups of five or six for 18 30-min p e r i o d s on each o f 4 consecu t ive days, Shock a d m i n l s t r a t i o n . On the 5th day , the shock p rod was i n t roduced i n t o the exper imenta l chamber through the ho le i n an end w a l l ; t hen , each exper imenta l animal was p l aced i n d i v i d u a l l y i n the cen t re o f the chamber f a c i n g away from the p rod . When each exper imental sub jec t f i r s t touched the p rod w i t h a foewpaw, a ' b r i e f shock, i n i t i a t e d by the experimenter and te rmina ted by the wi thdrawal o f the s u b j e c t , was d e l i v e r e d from an 800 V AC power source . The s i n g l e shock e l i c i t e d a sudden wi thdrawal 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 immediate ly a f t e r shock and re turned l a t e r f o r t e s t i n g ; however, i n most cases , the shock s i g n a l l e d the beg inn ing o f the t e s t s e s s i o n . Current from the 800 V power source was a t tenuated w i t h a . s e r i e s dropping r e s i s t o r . In a l l but one experiment , the va lue o f the dropping r e s i s t o r was 80,000 ohms. The cur ren t f low i n t h i s shock c i r c u i t was, monitored by a s torage o s c i l l o s c o p e to 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 by r a t s under the c o n d i t i o n s i n which they 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 p u r -pose r e c e i v e d shocks tha t averaged 7,9 mA i n i n t e n s i t y (SD = 1,47) , 42.9 msec. (SD = 9.8) i n d u r a t i o n , Behav ioura 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 behaviour o f each subjec t was viewed for 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 dur -a t i o n o f b u r y i n g sequences were recorded on an event r e c o r d e r . The b u r y i n g behaviour 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 s e r i e s o f s t e reo typed sequences tha t began w i t h the r a t f a c i n g the prod from a d i s t a n t pa r t o f the apparatus , The . r a t then moved d i r e c t l y toward the p r o d , push ing and s p r a y i n g a p i l e o f bedding m a t e r i a l over the prod w i t h 1 9 i t s snout and rapid movements o f i t s forepaws, 1 Often, t h i s behaviour was punctuated by periods when the rat stretched forward, i t s v i b r i s s a e nearly touching the prod before withdrawing abruptly to the rear of the chamber from where i t began another•sequence o f pushing and spraying. The invari a n t component of this, behavioural pattern was the rapid, a l t e r n a t i n g , forward-motion of the forelimbs by which the rat displaced material toward the prod. Tt was the durations of these directed bursts of forelimb spraying that were monitored by the experimenter, and that defined burying behaviour i n the present t h e s i s . ' Routine checks of videotaped t e s t sessions always corroborated the o r i g i n a l measures, Afte r each t e s t , the height of the bedding material from the f l o o r of the P l e x i g l a s chamber was measured at the junction between the prod and the w a l l . This measure, and the r a t i o formed by the height of the highest mound over i t s distance from the prod, served as a d d i t i o n a l i n d i c e s of burying behaviour! S t a t i s t i c a l analysis, In most'cases, the designs of the experiments presented i n t h i s thesis j u s t i f i e d a p r i o r i s t a t i s t i c a l analyses; An a p r i o r i comparison of central i n t e r e s t i n the early experiments was between the mean scores of shocked and unshocked r a t s ; i n subsequent experiments the comparison was.between the mean scores associated with 'shock' and 'control' prods] In general, the o v e r a l l e f f e c t of the shock was so c l e a r that casual inspection of i n d i v i d u a l scores was as convincing as the r e s u l t s of s t a t i s t i c a l analyses. Analysis of variance was occa s i o n a l l y used to evalu-ate e f f e c t s that could not 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 is 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 in . •• #.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 in the second condir-tion (prod controls, n = 30) were not shocked but otherwise were treated in the same manner. Subjects in the third condition (no^prod controls, n = 30) were placed individually in the test chamber for a few seconds but were exposed to neither the shock nor the prod. The rats in each of 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$c6spr©d^ ....... prod control ^-ratscts • were tested at each of the five intervals. The behave iour of each ariaimalt was viewed and recorded by closed circuit television as described in the General Methods section. Results and Discussion Figure 1 shows, that burying was a prominent part of the behavioural repertoire of the shocked subjects, Two-way analysis of variance of the "duration" data (Figure 1, Panel A) restricted to the two control conditions revealed no significant effects (p>,05). However, planned orthogonal 21 Figure 1. Mean duration of burying (Panel A) and the mean o f the r a t i o between the height of the highest p i l e and i t s distance from the prod p o s i t i o n (Panel B) at each of the shock-test i n t e r -vals f o r subjects i n the shock ( c i r c l e s ) , prod control (diamonds), and no-prod control (squares) groups. 1 0 s e c 5 m i n 5 h r 3day 2 0 d a y S h o c k — t e s t i n t e r v a l ( l o g s c a l e ) comparisons between the duration of burying in the shocked and the control subjects combined at each of the five shock-test intervals indicated that shock subjects spent significantly more time burying at each interval 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 clearly demonstrate that in the presence of adequate materials burying is a prevalent response of rats to aversive stimulation. At the two shortest shock-test intervals, rats engaged in burying for about 25% of the entire test period, and the duration of burying at inter-vals as long as 20 days was s t i l l well above control levels. At no time were rats observed to push or spray material in any direction 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 pile from the usual prod position formed a ratio which served as the basis for objectively assessing the relative effectiveness of each rats' burying behaviour. Rats with large height/ distance-from-prod ratios were those that accumulated the highest piles closest to the prod position. It is clear from Figure 1 (Panel B) that these ratios provided an independent and objective confirmation of the be-havioural data. Although there were no significant 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 significant 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 in one environment would bury the source of an aversive stimulation when confronted with i t in 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 in the chamber 1 min following prod contact. Results § Discussion When rats were confronted in the test chamber with a prod through which they had been shocked in their home cages, they buried i t . The shocked ^anjipals (M_.= 108 sec) spent significantly (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 far greater (t (18) =• 4.29, p_<.0005) for the piles of bedding material accumulated by the shocked animals (M = 6.2) than for 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 different source? In other words, i s shock per se ,.25: a s u f f i c i e n t condition for burying, or must the shock be administered through the test object? Method The methods were the same as- those ofExperiment 2 except that on Day 5 the shock animals (n = 15) were shocked (1 sec, 2.5 mA)through the f l o o r of a 43 x 21 x 29 cm g r i d box 1 min before being exposed to the prod on the wall of the tes t chamber. The control animals (n = 10) were not shocked but were otherwise treated i n the same way. Results and Discussion The r e s u l t s of Experiment 3 indicated that shock per se i s not a s u f f i c i e n t condition f o r the burying response, Neither the gridrshocked animals (M = 6 sec) nor t h e i r unshocked controls V(M = 2 see) spent sub-s t a n t i a l periods of time burying the prod, ' This observation was confirmed by an examination of the height/distance rfromrprod r a t i o s f o r the highest p i l e s 'of bedding material accumulated by the shock (X =C!,8) and control (X = 0.3) subjects. Thus, the two groups did not d i f f e r s i g n i f i c a n t l y i n terms of e i t h e r measure (duration of burying: t_(23) = .61, p_>.50; height/ distance-from-prod r a t i o : 1^(23) = ,55, p_>.50). The behaviour of the grid-shocked animals i n Experiment 3 was, thus, i n s t r i k i n g contrast to the performance of the prod-shocked rats i n Experi-ment 2. The l a t t e r subjects spent an average of 108 sec accumulating p i l e s of bedding material with height/distance-from-prod 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 of pxperiment 2 and . • 5- — r — "Although there i s no obvious way.to equate the intensity- of shock that rats receive through a g r i d f l o o r with the i n t e n s i t y they receive through the prod, the i n i t i a l behavioural reactions o f rats to grid-shock at these parameters seemed to be comparable to t h e i r i n i t i a l reaction to prod-shock at the parameters used i n previous experiments. 26 Experiment 4 The purpose o f Experiment 4 was to show that rats bury sources o f shock despite substantial v a r i a t i o n s i n shock i n t e n s i t y . Method On Day 5, the 60 naive r a t s were randomly assigned to one of f i v e conditions (n = 12). Every animal was treated i n the same manner throughout the experiment, except that t h e i n t e n s i t y of the shock was varied for sub-je c t s i n each condition. Upon f i r s t contacting the prod, the experimental rats were shocked at ,5, 5,0, 10,0, or 15,0 mA, whereas the control r a t s were not shocked. Shock i n t e n s i t i e s were manipulated by adding the appro-p r i a t e r e s i s t o r i n series with the 800-V shock generator, The actual cur^ rent flow was o s c i l l o s c o p i c a l l y recorded i n each case, Following prod con-t a c t , each subject was removed from the te s t chamber for 1 min before being returned to the. chamber for the 15-min observation period. Results and Discussion Figure 2 shows that rats buried the l o c a l i z e d source of shock at a v a r i e t y of shock i n t e n s i t i e s , A p r i o r i comparisons between each experimen-t a l group mean and the control group mean confirmed that shock .subjects spent s i g n i f i c a n t l y more time burying the prod at each shock i n t e n s i t y ex-, cept .5 mA (duration of burying, .5 mA, .t_(22) = 1,36, p_<, 10; 5 mA, t_(22) = 3,91, p_<„0007; 10 mA, t(22) = 4.23, p_<,0003; 15 mA, .tf22) = 5.29, p_<,00002). A s i m i l a r analysis of the "height" data corroborated the behavioural r e s u l t s 27 Figure 2. Mean duration of burying and the mean height of bedding material at the prod f o r each of f i v e shock i n t e n s i t i e s . S H O C K I N T E N S I T Y [ m A ] 29 (Height at prod, ,5 mA, £(22) = 1,18, p_>.10; 5 mA, t_(22) = 2.96, p_<.6l; 10 mA, t_C22) = 3,14, p_<,004.5 15 mA, t(22) = 3,50, p_<.002) .6 Evidence of a positive relationship between shock intensity and the amount of burying was provided by a product moment correlation coefficient computed between each experimental animal's oscilloscopically-determined shock intensity and i t s duration of burying score. The resulting coeffi-cient of ,285, although i t did not account for a large part of the vari-ance, was significant at p_<,05. Taken together, these results confirm that burying occurs r e l i a b l y at a variety of shock levels, and thus i t is d i f f i c u l t to attribute the extreme differences in the results ofExperiment 2 and Experiment 3 to diver-gent shock parameters. Although burying seems to be facil i t a t e d as shock intensity is increased (cf,, Ulrich § Azrin, 1962), vigorous burying be-haviour occurred at a l l shock intensities,. ThuSi variations in shock parameters may not have as great an effect on burying behaviour as varia-tions in 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 different source did not bury the test object (Experi-ment 3) . Experiment 5 To argue convincingly that a particular behaviour is a defensive re-sponse, two basic conditions must be met. Fi r s t , the behaviour must be shown to occur in response to aversive stimulation. In this regard, bury-Tfr . ** Because the a p r i o r i comparisons in 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 ing was found i n Experiments 1, 2,and 4 to be a common response of l a -boratory rats to prod shock when the appropriate materials were a v a i l a b l e . Second, the response must be adaptive; that i s , i t p.otentially must aff o r d the animal some protection from the noxious agent. In order f o r burying to, be adaptive i t must.be directed, but more importantly, i t must be directed at the source of aversive stimulation. Tt i s d i f f i c u l t to see how burying directed at neutral objects following aversive stimulation could be.adaptive. While the burying behaviour of the shocked rats i n Experiment 1, 2, and 4 el.earlyawas, dir e c t e d at the prod, i t was not c l e a r whether the burying behaviour was directed at the prod because of i t s pre-vious association with shock; burying may have been d i r e c t e d at the prod because i t was the only nobjiect-bincthentest chamberOTiber, When considered together, the r e s u l t s of the f i r s t four experiments do provide some support for the view that the prod was buried because of i t s previous rpafecingioji'' with shock, The rats shocked by the prod (Ex- . periments 1, 2 and 4) buried i t ; whereas, those that received g r i d shock (Experiment 3) did not. However, l i k e the r e s u l t s of a l l "negative" ex-periments, the r e s u l t s of Experiment 3 must be interpreted with caution. The purpose of Experiment 5 was to provide more conclusive evidence r e l e -vant to t h i s issue,. M e t h o d On Day 5, two i d e n t i c a l prods were mounted on the walls of the t e s t chamber, one at each end. The behaviour o#*each of the 10 naive subjects was recorded for 15 min a f t e r i t had been shocked (8 mA) by one (randomly predetermined) of the two prods,. Before shock, each animal was.allowed, to contact each prod at least once without being shocked. 31 Figure 3. Duration of burying (Panel A) directed at the shock prod and control prod and the f i n a l height of the bedding material at the shock prod and control prod (Panel B) f o r each of the sub-jects i n Experiment 5. (At the beginning of each session the height of the bedding material was 5 cm i n a l l parts o f the t e s t chamber). 3 a . - o 2 5 0 OC/5 2 0 0 1 5 0 1 0 0 o ~ 5 0 CO 1 • s h o c k p r o d I c o n t r o l p r o d • s h o c k p r o d I • c o n t r o l p r o d 1 2 3 4 5 6 7 S u b j e c t s 8 9 1 0 33 Results and Discussion The r e s u l t s of Experiment 5 were so cl e a r that inspection of i n d i v i -dual scores (Figure 3) rendered s t a t i s t i c a l analysis of group.scores super-fluous. A l l 10 subjects spent time burying the prod through which they had been shocked (M_ = 125 sec); whereas, only one subject b r i e f l y attempted to bury the control prod, but not u n t i l the shock prod had been completely covered. S i m i l a r l y , a l l 10 subjects accumulated higher p i l e s of bedding material at the shock prod than at the control prod, One subject (Sub-j e c t 2, Figure 3) a c t u a l l y removed material from under the control prod to bury the shock prod, Experiment 6 The r e s u l t s of Experiment 5 provided further evidence that the bury-ing behaviour was being eontr6ia;edc-spfeci'fi;ea^JIythy thearei'ataoiiwbe.tween the prod and the shock: rats s e l e c t i v e l y buried the prod that was.apadred--with shock. Thus, burying appears to be a p o t e n t i a l l y adaptive response of rats to -s p e c i f i c environmental 'threats'. However, although i t i s c l e a r that burying was.directed toward the aversive stimulus, the r e s u l t s of previous experiments did not indic a t e which of the many cues i n the experi-mental 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 of studying the stimulus control of behaviour (Skinner, 1938; Tinbergen, 1951) were employed to approach t h i s issue i n the next two experiments. The s p e c i f i c purpose of both Experiments 6 and 7 was to determine whether burying behaviour changes systematically when the p o s i t i o n and/or b r i g h t -ness of the prod are changed a f t e r prod-shock, 34 Method On tKe f i f t h day.each of the 50 naive ^'rat s. was * -randomly/.as s i gned _ to one of f i v e groups of 10 subjects Cr'6u:r experimental groups and one control group), before being placed i n d i v i d u a l l y i n the centre of the chamber facing away from the prod, The end of the chamber to which the prod had been f i x e d (front or back) and the brightness o f the prod (black or white), were randomly pre-determined f o r each rat before the tes t began. As each experimental animal touched the prod, the 8 mA shock was adminis-tered in,the usual way; immediately following shock the subject was removed. Control subjects (n = ,10) were treated i n exactly the same manner-except that shock was not administered. Each rat i n the four•experimental groups (n = 10) was i n d i v i d u a l l y placed i n the chamber 1 min l a t e r with e i t h e r , 1) the-same prod (black or white) on the same wal l , 2) the same prod on the opposite w a l l , 3) the d i f f e r e n t prod on the same w a l l , or 4) the d i f f e r e n t prod on the opposite w a l l . E i t h e r two or three control rats were tested with each of.these four stimulus combinations. Results and Discussion Almost a l l of the rats i n the four shock groups moved some material toward the prod. A l l 10 animals tested with prod brightness and p o s i t i o n unchanged engaged i n some burying, while burying behaviour was observed i n 10n, eight, and e• ,8ht of the subjects i n the "same prod-different p l ace," " d i f f e r e n t prod-same place," and " d i f f e r e n t prod-different p l a c e " groups, re s p e c t i v e l y . On the other hand, burying behaviour was almost nonexistent i n unshocked, control subjects. ' Only frSi'ee of the 10 control rats directed bedding material at the prod, and none of these did so f o r more than 5 sec, 35 Thus, the mean duration of burying behaviour was less than a sec f o r con-t r o l subjects, and the mean height of bedding material accumulated at the prod was less than .</} 1 cm greater than the i n i t i a l l e v e l of 5 cm. An a . p r i o r i comparison between the combined experimental group means and the control mean confirmed that the duration of burying by shocked rats was s i g n i f i c a n t l y greater than that of control rats ±F(1,45) '= 11,34, p_<,002 , S i m i l a r l y , the height of material accumulated at the prod by shocked rats was s i g n i f i c a n t l y greater than that accumulated by control rats F(l,45) = 9.18, p_ <.004 . Control of the burying behaviour o f the experimental subjects by brightness and p o s i t i o n cues i s i l l u s t r a t e d i n Figure 4. Changing either-the brightness of the prod and/or i t s p o s i t i o n decreased both the duration of burying (Panel A) and the height of material accumulated at the prod (Panel B) r e l a t i v e to the performance of experimental subjects tested with prod and p o s i t i o n cues unaltered, The data were subjected to a two-way analysis of variance, the two factors being brightness and p o s i t i o n , each with two lev e l s (same or d i f f e r e n t ) . The analysis of the "duration" data revealed a s i g n i f i c a n t i n t e r a c t i o n between brightness and p o s i t i o n F(l,36) = 7.11, p_£.01 t M u l t i p l e comparison te s t s , (Dunn's T e s t , . c r i t i c a l d i f f e r -ence = 46.89, p_£-,05) indicated that changing either,brightness or place cues led to a s i g n i f i c a n t reduction i n the :duration of burying but that changing both cues together d i d not produce a s i g n i f i c a n t l y greater reduc-t i o n , A comparable set of analyses of the "height" data confirmed these behavioural r e s u l t s . 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 F(l,36) = 5.53, p '^,02 ; the subjects tested with neither brightness nor 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 igher-piles at the prod than d i d the rats i n the other three experimental groups, and these l a t t e r - t h r e e 36 Figure 4. Mean duration of burying (Panel A) and the mean height of bedding material at the tes t prod (Panel B) f o r each of the four cue combinations. 37 ;38 groups did not d i f f e r s i g n i f i c a n t l y from each other (Dunn's Test, c r i t i -cal d ifference = 2,17, p=0.05), Although i n the f i r s t f i v e experiments, rats had never been observed to push bedding material i n any d i r e c t i o n other than at the shock source, 8 of the 40 shocked animals i n the present experiment "directed bedding material at the hole i n the wall of the apparatus d i r e c t l y opposite the prod p o s i t i o n . However, such responses were r e s t r i c t e d to subjects i n the two conditions i n which the p o s i t i o n of the prod had been changed Cx2Cl) = 10J p_<.005). A f t e r burying the prod i n i t s new p o s i t i o n , these subjects sprayed bedding material at the hole through which the prod had been inserted during shock administration. No animal ever d i r e c t e d bedding material at the holes i n the centre of the two side walls. The r e s u l t s of Experiment 6 demonstratedtfchat both the brightness and p o s i t i o n of the prod exerted some control over.the burying response a f t e r only a s i n g l e prod-shock p a i r i n g . When the p o s i t i o n of the prod was un-changed, changing the brightness of the prod (from black to white or from white to black) s i g n i f i c a n t l y reduced the amount of burying. S i m i l a r l y , i f the brightness of the prod was held constant, moving i t to the opposite wall during the test, jsubsttantiiabl^-rediiGed pWd'rbury4n-g.,piTI^ eby-identity of the cues that defined the. l o c a t i o n o f the prod was not r e a d i l y apparent since external room cues were v i s i b l e through the Plexiglas walls of the test chamber i n addition to t a c t u a l , o l f a c t o r y , arid v i s u a l cues provided by the chamber i t s e l f . Control of the burying behaviour by brightness and p o s i t i o n cues.was not additive (Weiss, 1972); changing both cues did not s i g n i f i c a n t l y re-duce the l e v e l of burying below that observed i n the two conditions i n which only one of the cues had been changed, 39 ' The f ac t that some o f the r a t s i n the two groups i n which the p o s i -t i o n o f the prod was changed b u r i e d the h o l e on the o ther end o f the chamber - through which the p rod 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 important i n more than one sense. Not o n l y d i d p o s i t i o n cues exer t c o n t r o l over 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 prod p o s i t i o n but l o c a t i o n cues tha t were a s s o c i a t e d w i t h the shock were themselves capable o f i n d u c i n g the b u r y i n g response i n some' s u b j e c t s . Experiment 7 In Experiment 7, s t imulus 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 s imultaneous d i s c r i m i n a t i o n procedure (Experiment- 5 ) ; each subjec t was shocked and t e s t ed i n the presence o f two p rods , Method The- 24 na ive hooded r a t s were randomly ass igned to Swi tch (n = 12) , o r Same (n = .12) c o n d i t i o n s , On Day 5, a l l sub jec ts were shocked,once when . they,contacted e i t h e r the b l a c k prod or the whi te p rod which had been mounted through the ho les at oppos i te ends o f the t e s t chamber. I t was, randomly predetermined which subjec ts would be shocked by which p r o d , w i t h the p r o v i s o tha t h a l f the sub j ec t s i n each o f the two groups were shocked by each p r o d . Before shock, each subjec t was .a l lowed t o ' c o n t a c t each prod at l e a s t once, Immediately a f t e r shock, each subject was removed from the t e s t apparatus f o r 1 min . Each subjec t i n the Same C o n d i t i o n was t h e n , r e -tu rned to the chamber 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 ^ ' whereas, sub jec t s i n the Swi tch C o n d i t i o n were re turned to the chamber w i t h the p o s i t i o n s o f the prods r eve r sed , 40 Results- and Discussion Although the incidence of burying was comparable i n the two condi-tions (10 of the 12 subjects i n each condition displayed some burying), there was a s t r i k i n g d i f f e r e n c e between the two conditions i n the d i r e c t i o n of the burying. It i s apparent from Figure 5 that those rats tested with 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 directed almost a l l of t h e i r burying 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 of the prods were reversed p r i o r to the t e s t , the burying behaviour was d i s t r i b u t e d almost equally between both prods,.• The s i g n i f i c a n c e of the differences represented i n Figure 5 were evaluated with a series of t_-tests f o r dependent measures. In the Same Condition, subjects spent s i g n i f i cantly more time burying the shock prod than they d i d burying the control prod [ t _ ( l l ) = 4.60, p_ .0008 ] and the height of the bedding material accumulated by these animals, at the shock prod was s i g n i f i c a n t l y greater than the height accumulated at the control prod [ t f l l ) = 4.81, p_<i.0005] . These r e s u l t s are e s s e n t i a l l y the same as those obtained i n Experiment 5, wfren'e b a s i c a l l y the same procedure was used. In contrast, i n the Switch Condition an analysis of both the height."[ t_(ll) = 1.27, p_ )> . I>] and duration [ t _ ( l l ) = 1.38, p ^ . l l measures indicated that the rats 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 other. It should be emphasized that t h i s lack of diffe r e n c e i n mean burying between the two s i t e s when the prods were switched r e f l e c t e d the fa c t that i n d i v i -dual subjects were d i s t r i b u t i n g t h e i r burying at both s i t e s , not that h a l f the subjects were burying one prod and the remaining h a l f the other, A l l 10 of the Switch subjects that displayed burying behaviour directed bedding material at both prods. In contrast, only 3 subjects i n the Same Condition 4 1 Figure 5. Mean duration of burying directed at the shock prod and control prod and the mean height of bedding material at each prod i n conditions where the prod p o s i t i o n s were switched or l e f t the same a f t e r shock. 4* 1 0 0 -7 5 -5 0 -2 5 - 9 • duration • height jnl - 8 - 7 - 6 i 5 shock control prod prod shock control prod prod > X W t—i o a H o S A M E S W I T C H 43 dire c t e d material at both prods [ x 2 ( l ) = 10.76, p_< .005 ]. As well as di s p l a y i n g the stereotyped burying pattern described i n previous experiments, rats that had been tested with the p o s i t i o n of the prods reversed displayed an i n t e r e s t i n g behaviour not seen i n the other r a t s . P r i o r to burying the prods; eight of the Switch r a t s scurried back and f o r t h between the two prods, Moreover, t h i s v a s c i l l a t i n g behaviour often perseverated into the burying sequence i t s e l f , with animals d i r e c t i n g bedding material toward one of the prods, then qu i c k l y reversing t h e i r d i r e c t i o n and spraying toward the opposite prod, This i s i n contrast to the behaviour of the three rats i n the Same Condition that d i r e c t e d ma-t e r i a l at both the shock prod and the control prod; the l a t t e r animals did not spray material at the control prod u n t i l they had f i n i s h e d burying the shock prod. S i m i l a r l y , the rats i n Experiment 6 that buried both the prod and the hole on the opposite wall d i d not spray material at the hole u n t i l they had buried the prod, Evidence that 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 demon-stra t e d by the consequences of changing the p o s i t i o n of the prods. Unlike the performance of the subjects i n the Same Condition, subjects i n the Switch Condition d i s t r i b u t e d t h e i r burying between the two prods. This re-s u l t also provides evidence that brightness too was exerting control over the burying. I f brightness had not been a c o n t r o l l i n g f a c t o r , switching the positions o f the two prods, which d i f f e r e d only i n brightness, would have been without e f f e c t . , The r e s u l t s of Experiment 7 thus confirm those of Experiment 6. Experiment 8 Each of the previous seven experiments provided some evidence that burying can be an adaptive response o f rats to s p e c i f i c environmental 44 threats. Although there can be l i t t l e question that the response occurs i n the presence of aversive s t i m u l i and i s dir e c t e d by s p e c i f i c shock-associated cues , there are other grounds for questioning i t s adaptive value and consequently i t s status as a viable defensive response, For example, the stereotyped nature of the response, : although f a c i l i t a t i n g i t s i n i t i a l i n v e s t i g a t i o n , also raised some questions concerning i t s adaptiveness i n the rat's natural habitat, Such a s t e r e o t y p i c a l response pattern would be of marginal u t i l i t y i n habitats where av a i l a b l e burying materials require more varied responses- f o r t h e i r d i s p o s i t i o n , However, the s t e r e o t y p i c a l nature of the burying response i n previous investigar tions may simply have r e f l e c t e d the homogeneity of the commercial bedding which served as the only a v a i l a b l e burying material, Accordingly, the purpose of the next two experiments- was to demon-stra t e that r a t s x an ^ change t h e i r burying -responses- witKhfespeGtJtb the kind (<Experi!mentes8) ion d i s p o s i t i o n ^Experimeritu9Xeofuayai:labile'burying mat In Experiment 8, each subject was tested i n the presence of one of three materials. One of the materials (wooden blocks) was chosen because i t would be extremely d i f f i c u l t f o r a rat to p i l e t h i s material over the prod using the snout and forepaw pushing motions c h a r a c t e r i s t i c of burying i n previous experiments. Method Each of the 30 naive rats was.randomly assigned to one of three con-d i t i o n s (n = 10), Every subject was treated i n the same manner.throughout the experiment, except that the type of material a v a i l a b l e . i n the t e s t chamber d i f f e r e d f o r the subjects i n each condition. During a l l phases of the experiment the chamber f l o o r was1 covered with e i t h e r (1) 5 cm of Sanr-i 45 e e l , (2) 5 cm of sand, or (3) 100 24 x 1,6 x 1,0 cm wooden blocks placed so that the height of each was ;l cm. On Day 5, following the usual four days of habituation i n the presence of the designated burying material, the subjects were placed i n d i v i d u a l l y i n the centre of the t e s t chamber between the two i d e n t i c a l prods which had been mounted i n the middle of the two end walls, 2 cm above the l e v e l o f the sand or.bedding material and 6 cm above the blocks. Each animal was.allowed to'explore the chamber and to contact each prod at least once without consequence, When the rat next touched one (randomly predetermined) of the-two prods, the 8 mA shock was administered. Following the shock, the behaviour of each subject was viewed f o r 15 min and then the heights of the materials accumulated at the shock and control prods were recorded. Results and Discussion Figure 6 shows that the subjects spent a substantial p o r t i o n of t h e i r time burying regardless of which material was av a i l a b l e . Only one of the 30 subjects, an animal i n the Blocks Condition, did not engage i n at least some burying. It i s also apparent i n Figure 6 that the burying behaviour was w e l l - d i r e c t e d . A l l 29 of the subjects that engaged i n burying spent some time burying the prod which f o r them had been the source of the shock; whereas, only 3 r a t s , a l l i n the Bedding Condition, spent any time burying the control prod. Even i n these three cases, the subjects spent most of t h e i r time burying the shock prod; they.did not move material toward the control prod u n t i l the shock prod had been completely covered. A p r i o r i comparisons (t_ tests f o r dependent measures) between the t o t a l burying times accumulated by each subject at the respective prods confirmed- that the subjects i n a l l three conditions spent s i g n i f i c a n t l y more time burying the prod that had been associated with shock (Bedding Condition, t(9) = 7.83, 46 Figure 6. Mean duration of burying the shock and control prod with d i f f e r e n t burying material. 4? 1 5 0 u LU CD 1 0 0 5 0 LU Shock Prod Control Prod B e d d i n g S a n d B l o c k s BURYING M A T E R I A L 48 p_<. 0002; Same Condition t(9) = 6.19, p_<.0001; Blocks Condition, t(9) = 2.75, p_<.02) . Analyses of the materials accumulated at each of the two prods (Figure 7) provided an independent confirmation of the behavioural r e s u l t s . In each of the three experimental conditions, the average height of the burying material at the shock prod was s i g n i f i c a n t l y greater than that at the control prod (Bedding, Condition, t(9) = 7,15, p_<,00005; Sand Condi-t i o n , ;t(9) = 6.16, p_<.0001; Blocks Condition, t_(9) = 2.68, p_<,02) . The pattern of burying behaviour displayed by the animals i n the Bedding Condition was ind i s t i n g u i s h a b l e from that displayed by those i n the Sand Condition. In both conditions the topography of the burying re-sponse was the same as that observed i n previous experiments (see the General Methods). The rats began each burying episode f a c i n g the shock prod from a distant part of the chamber, Then they moved d i r e c t l y toward the prod, pushing and spraying the material toward the prod with snout and forepaws. As i n previous experiments, these burying sequences were f r e -quently interrupted by i n t e r v a l s of approach-avoidance behaviour i n which the rat would s t r e t c h forward u n t i l f u l l y extended with i t s nose nearly touching the prod and then abruptly withdraw to the rear of the chamber. Similar behaviours were also observed i n those animals burying with blocks.- They would move toward the shock prod pushing blocks ahead of them with snout and forepaws. Although t h i s behaviour was e f f e c t i v e iri accumulating blocks near the prod, i t was necessary f o r subjects to pick the blocks up i n order to form a p i l e . Seven of the r10 rats cthat . .. spent some time moving blocks toward the shock prod picked blocks up i n t h e i r teeth and placed tham i n a p i l e with teeth and forepaws, None of these,seven managed to completely cover the prod,.6 cm above the o r i g i n a l 49 Figure 7. Mean height of burying materials at the shock and control prods. Arrows indi c a t e the height of the material at the beginning of the t e s t . s<=> • Shock Prod Bedding Sand Blocks B U R Y I N G M A T E R I A L i-51 l e v e l of the blocks, before the end of the tes t period; whereas, i n the, other two conditions, in"which•the 'prod was closer to the i n i t i a l level-of the burying material, most of the subjects (18 out of 20) a c t u a l l y covered the prod. The r a t s ' behaviour indicated that the construction of the p i l e s of blocks was not haphazard; on several occasions a block j u s t placed on top of a p i l e toppled to the bottom from where i t was qu i c k l y r e t r i e v e d and returned to 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 of Experiment 8 confirm previous demonstrations (Experi-ments 5 and 7) of discriminated burying behaviour i n r a t s . Every rat shocked by one of two prods mounted on opposite walls of the chamber li n e d with commercial bedding material returned to the shock prod and buried i t , and the few that pushed bedding material at the control prod did not do so u n t i l the shock prod had been completely covered. Of greater i n t e r e s t here, however, i s the f i n d i n g that defensive burying i s not li m i t e d to situa t i o n s i n which there i s a supply of commercial bedding material; a l l of the rats i n the Sand Condition attempted to bury the shock prod, as d i d a l l but one of the subjects i n the Blocks Condition. This f i n d i n g i s consistent with several i n c i d e n t a l observations that have been made i n our laboratory. In one case, a rat shocked i n i t s home cage d i s -mantled i t s nest o f shredded paper and used i t as burying material, and i n another case several rats shocked by a prod on the Pl e x i g l a s f l o o r of a barren t e s t chamber placed t h e i r own feces on top of i t , The r e s u l t s of Experiment 8 also show that burying behaviour i s not a ^ g j f S ^ - x ^ e f ? ^ 1 rather i t i s a complex behavioural sequence which varies as a function of the a v a i l a b l e burying material. In the Blocks Condition, the pushing and .52 forellmb spraying movements that r a p i d l y produced large p i l e s at the shock prod i n the Bedding and Sand Conditions were not s u f f i c i e n t to gain the same end. Such movements were sometimes used.to accumulate blocks i n the v i c i n i t y of the prod, but to construct' p i l e s at'the prod p o s i t i o n , the rats picked the blocks up i n t h e i r teeth and deposited them around the prod. These r e s u l t s considered together strengthen the view that burying behaviour could be of considerable adaptive value iri natural settings.' •Rats are capable of using a v a r i e t y of material to bury objects associated with aversive s t i m u l i even.when the use of these materials necessitates changes i n the topography of the burying sequence. Experiment 9 The purpose of Experiment 9 was to demonstrate that r a t s w i l l attempt to bury a source of aversive stimulation even when a l l of the burying material has to be transported by the rat to the s i t e , Method The subjects were 20 naive hooded r a t s , habituated to the Plexiglas Chamber i n the usual manner, except that the chamber f l o o r was evenly covered with 100, 2.4 x 1,6 x 1.0 cm wooden blocks, Each block was p o s i -tioned during a l l phases of the experiment so that i t s height was,1 cm, On day 5, the subjects were randomly divided into two groups of 10, and shocked by one (randomly predetermined) of the two i d e n t i c a l prods, . For the subjects i n one of the groups, the 100 blocks were d i s t r i b u t e d on the h a l f of the chamber containing the shock prod; whereas, for subjects i n the other group, the blocks were i n i t i a l l y r e s t r i c t e d to the d i s t a l h a l f of the box. The behaviour of each subject and the r e s u l t i n g r e d i s t r i b u t i o n 53 o f b l o c k s was.measured as i n p r ev ious exper iments . R e s u l t s and D i s c u s s i o n Bury ing behaviour was again a r e l i a b l e consequence o f the s i n g l e p rod-shock . With the excep t ion o f two^subjects i n the c o n d i t i o n ' w h e r e the b l o c k s were adjacent to the shock p r o d , a l l of the sub jec t s engaged i n at l e a s t some b u r y i n g . Moreover , a l l "18 o f the sub jec t s which d i s -p l ayed the b u r y i n g behaviour 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 sub jec t s spent s i g n i f i c a n t l y more t ime b u r y i n g the shock prod than they d i d the c o n t r o l prod i n bo th c o n d i t i o n s , when thebb l o c k s ..were adjacent to the shock prod (M = 36 and 0 sec , 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 sec , r e s p e c t i v e l y ; 1^(9) = 2 . 4 5 / j K . 0 4 ) , These behav iou ra l d i f f e r e n c e s were confirmed by s t a t i s t i c a l a n a l y s i s o f the he igh t o f the p i l e s accumulated at each o f the two p rods : Because f o r each subjec t the i n i t i a l he igh t o f the b l o c k s at the two prods was not , equal at the s t a r t o f the t e s t , the i nc rease i n the he igh t o f the b l o c k s at each p r od r a t h e r than the absolu te he igh t was used as the index o f bu ry -i n g . In both c o n d i t i o n s , the average inc rease i n the 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 there a s i n g l e i n s t ance i n which the he igh t o f the p i l e at the c o n t r o l prod was inc reased (wi th b l o c k s ad-. j a c e n t to the shock p r o d , t_(9) = 3 .36, p_<,008; w i t h b locks , r e s t r i c t e d to the f a r end o f the chamber, t_(9) = 2 . 9 3 , p_<,02), In con t r a s t to E x p e r i -ment 8, three s u b j e c t s , one i n the " d i s t a l " c o n d i t i o n and two i n the "adjacent" c o n d i t i o n , were able to comple te ly cover the prod 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 did not reveal any s i g n i f i c a n t differences be-tween the two groups on eit h e r dependent measure (duration of burying shock prod, t_(18) = 1.54, p_>.10; height at shock prod, t_(18) = .024, p_>.10; duration of burying control prod, £(18) = 1,48, p_>. 10; height at control prod, t_(18) = 0, p_>.10). In a l l previous studies o f burying, burying material was.always a v a i l a b l e i n the area immediately adjacent to. the source of the shock. In Experiment 9 rats attempted to bury the shock prod even when the burying material w a s ' i n i t i a l l y r e s t r i c t e d to the other end of the chamber. A f t e r being shocked, the rats c a r r i e d or pushed the blocks toward the shock-prod for use i n i t s subsequent b u r i a l . This observation supports the view that burying can function as an e f f e c t i v e defensive response i n the rat's natur-a l environment, an environment where burying materials are not always r e a d i l y a v a i l a b l e , 55 GENERAL DISCUSSION The General Discussion i s organized around two issues, that are discussed under separate headings. The f i r s t section marshals evidence that suggests that burying i s a defensive response of r a t s , In t h i s rer gard, both the present experimental data and relevant e t h o l o g i c a l obser-vations are reviewed. The contribution of the present studies to the " b i o l o g i c a l " approach to avoidance learning i s discussed i n the second section of the General Discussion and the r e l a t i o n s h i p of the burying phenomenon to Pavlovian conditioning i s examined i n t h i s context. I. Burying as a defensive response  In the- rat In each of the nine experiments presented i n t h i s t h e s i s , evidence was provided to support the argument that burying behaviour i s a prominent defensive response of r a t s . These data can be organized around the two fundamental c r i t e r i a : pres'bntedhiHitheoIntro'duclioh'?! l^s^h^sbehavi'our^must ©e:cu*ltrii*espeiise2^ '2^)ei.tn^ust p o t e n f l a l l y ' a f f o r d the animal' 'protee-ti'ojiffxom. .tketfsburciatiof 'the aversive stimulation. Experiment 1 provided ample evidence that burying i s a prevalent re-sponse of rats to aversive shock. Almost a l l of the rats tested s h o r t l y a f t e r a si n g l e shock attempted to bury the shock source, and even 20 days l a t e r the time spent burying w a s . s t i l l s i g n i f i c a n t l y above control l e v e l s . Furthermore, burying was a r e l i a b l e consequence of prod shock i n a l l subse-quent experiments. Perhaps the most convincing demonstration of t h i s e f f e c t was provided by the r e s u l t s of Experiment 4 i n which increases i n the i n -t e n s i t y of-the aversive stimulus led to.increases i n the amount of burying. This r e l a t i o n s h i p i s consistent with what i s known about the r e l a t i o n s h i p between shock i n t e n s i t y and other defensive behaviours (e.g., U l r i c h § A z r i n , 56 1962), Even i n c a s e s where the type (Experiment 8) and d i s p o s i t i o n (Experiment 9) of burying materials made the response more d i f f i c u l t to execute, the burying behaviour s t i l l occurred i n over 80% of shocked animals. The robust nature of the r e l a t i o n s h i p between aversive stimula-t i o n and burying behaviour i n the present experimental s i t u a t i o n s appeared to supplant other common defensive behaviours; periods of immobility l a s t -ing more than a few seconds, attempts to escape fromthe apparatus, and aggressive behaviour directed at the prod were r a r e l y observed i n the pre-sent studies. Evidence of the p o t e n t i a l adaptiveness of the response was provided by three d i f f e r e n t observations, F i r s t , the immediate consequence of the behaviour on the surrounding environment i n most cases was a "bar-r i e r " between the rat and the source of aversive stimulation. This b a r r i e r was e f f e c t i v e i n the laboratory i n keeping the rat s from making further contacts with a p o t e n t i a l l y harmful object, and there i s no obvious reason to believe that the consequences o f t h i s behaviour i n more natural aver-sive settings would not be s i m i l a r (cf ,<, Calhoun, 1962), Second, the behaviour was,well d i r e c t e d . I f burying was randomly direc t e d a f t e r aversive stimulation, i t s adaptive value would be question-able. However, except i n those cases where the cues associated with shock had been rearranged between shock and t e s t i n g (Experiments 6 § 7), few rats were ever observed to push bedding material i n any-direction other than toward the shock source; the burying seemed to 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 the prod and the shock. Rats shocked through a g r i d f l o o r (Experiment 3) di d not bury the prod, arid rats shocked by one prod did not bury an i d e n t i c a l prod mounted on the opposite wall of the t e s t chambers (Experiment 5). This l a t t e r f i n d i n g was subsequently r e p l i c a t e d i n every study i n which the two prod procedure was employed (Experiments 7, 8, and 9), However, systematic decreases i n the amount of burying were 57 observed when the brightness or p o s i t i o n of the prod was,changed i n the interval, between the shock and the t e s t . These data served as even more compelling evidence that the r a t s ' burying behaviour i s guided by the re-l a t i o n between shock and the cues which occasion shock, Thus, t h i s behav-iour could have an adaptive value i n natural s e t t i n g s ; whereas i f burying was randomly directed with respect to aversive cues, i t would be d i f f i c u l t to imagine how i t could be adaptive. That burying could be adaptive i n a natural s e t t i n g i s implied by a t h i r d observation, the observation that rats were capable of using a v a r i e -ty of materials to bury the shock prod., even when the use. of these materials necessitated changes i n the topography of.the burying sequence or when ma-t e r i a l s had to be f i r s t transported to the prod, This observation supports the view that burying could be an e f f e c t i v e defensive response i n the r a t ' s natural environment, an environment where burying materials are not always r e a d i l y a v ailable and where available materials may require a varied response' topography f o r t h e i r d i s p o s i t i o n . Furthermore, t h i s observation shows that burying 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 , rather, i t i s a complex behavioural sequence that can be modified to accommodate d i f f e r e n t resources of the environment. Thus, three observations--the p h y s i c a l consequence of the response, the directedness of the response, and the f l e x i b i l i t y of the response--sug-gest that burying behaviour could have adaptive value i n a natural s e t t i n g . However, th i s evidence only lends p l a u s i b i l i t y to the argument that burying i s adaptive. 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 instances of the behaviour and the . a b i l i t y of the animal to survive. Showing that the behav-iour occurs i n a natural environment, although i t i s not s u f f i c i e n t evidence of adaptiveness, i s therefore a necessary step toward d i r e c t confirmation 58 of adaptive value, • Tn this regard, there are.a number of more n a t u r a l i s t i c observations that extend the present observations. F i r s t , Calhoun (1962) reported that "lower status rats." exposed to " t e r r i t o r i a l t h r e a t " would plug the entrance holes to t h e i r underground nests. The notion that "lower status" rodents may 'barricade' themselves away from more dominant members of the species i s given further credance by the observation of Johnston (1975)-, A male golden hamster housed under semi-natural conditions blocked the entrance hole of i t s chamber with wood shavings a f t e r i t had been "defeated" by a "higher ranking" male. It i s d i f f i c u l t to believe that these ' b a r r i e r s " could keepbburrpW4digging rodents at bay. However, the 'signaling function' of these obstructions may be fa r more important than t h e i r e f f e c t 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-p lays' of defeated rodents i n h i b i t further aggression from conspecifics (cf., Blanchard fT Blanchard, 1977). Second, Hudson (1950) obs-erved what he c a l l e d '-'pushing of wood' s-havr-ings" i n rats i n a passive avoidance, s i t u a t i o n . Although t h i s behaviour-and i t s r e l a t i o n s h i p to a defensive repertoire were not the focus of ex-perimental scrutiny i n Hudson's study, Hudson went on to speculate about i t s adaptive function i n the willd. Although the basis f o r h i s speculations was unclear, he asserted that thisbbehaM'Ourvwasaaceommonrresponse.Of-gophers to traps set i n t h e i r burrows,and;.a general response of rodents to r e p t i l e s (Hudson, 1950, p. 127), Hudson's speculations have gained some c r e d i b i l i t y i n the l i g h t of the observations o f Owings and Coss (1977) and Owings, Borchert, and V i r g i n i a (1977). These researchers found that a major part of the ground s q u i r r e l s behaviour toward snakes was "sand-kicking", and the authors' verbal and p i c t o r i a l descriptions of the behaviour are nearly i d e n t i c a l to the present .59. d e s c r i p t i o n of the responses of the rats i n the present studies to prod-shock. That "sand-kicking" was an e f f e c t i v e anti-predator behaviour was ind i c a t e d by the subsequent r e t r e a t of the snakes (Owings et a l . , 1977), In a more systematic laboratory study, aisitgnifi&ari^ between sand-kicking and a v a r i e t y of 'defensive' behaviours of the snakes. (Owings S Coss, 1977). Thus, there i s some evidence that 'burying behaviour' occurs i n natural situations'and that i t may have two basic adaptive functions; as a defense against both conspecifics and predators, Since most major natur-' a l i s t i c studies of rodent behaviour (e.g., Calhoun, 1962) have involved populations protected from trapping and predation, i t i s not s u r p r i s i n g that burying has not been frequently reported to be a part of the wild rodent's defensive r e p e r t o i r e , I I , Burying behaviour and a b i o l o g i c a l  approach to aversive learning The general purpose of the present investigations was to contribute, to the development of a ' b i o l o g i c a l ' approach to aversive learning by study-ing the burying response. Any approach to aversive learning that i s based on a knowledge of the animal's natural defensive behaviours w i l l be viewed, for the purposes of t h i s discussion, as a " b i o l o g i c a l approach". Thus, Bo l l e s ' hypothesis i s a s p e c i a l case of a b i o l o g i c a l approach to aversive learning. In general, a b i o l o g i c a l approach must deal with two, fundamental issues: 1) what the organism's innate defense reactions are, and 2) how the p r o b a b i l i t i e s of these reactions are changed as a r e s u l t of experience. Accordingly, i n the f i n a l part of the present discussion, each of these i s -sues i s examined i n the l i g h t of the present data. 60 Befens ive Behaviour B o l l e s (1970) has argued c o n v i n c i n g l y tha 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 unders tanding i t s capa-c i t y t o . l e a r n avoidance responses . B o l l e s , however, d i d not advocate the e m p i r i c a l s tudy o f , t h e s e defens ive behav iour s , In s t ead , 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 tha t r a t s . c o u l d respond to nove l o r danger-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 , f l e e i n g , or f i g h t i n g . The present data i n d i c a t e tha t t h i s assumption i s inadequate and tha t the e m p i r i c a l s tudy o f defens ive beahviours i s e s s e n t i a l to 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 , Al though i t seems obvious t h a t . t h e nature o f the defens ive r e a c t i o n s o f organisms shou ld 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 iewpoin 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 to a v e r s i v e l e a r n i n g . For example, B o l l e s ' (1970) hypothes i s becomes d i f f i c u l t to apply when i t can no longer be assumed tha t animals d i s p l a y o n l y three defens ive behav-i o u r s . As the number o f p o t e n t i a l defens ive behaviours i n c r e a s e s , the outcomes o f s t u d i e s o f ave r s ive l e a r n i n g become more d i f f i c u l t 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 tud i e s would be r e q u i r e d to e s t i -mate the defens ive c a p a c i t i e s o f even.a few, common organisms, and i t i s un-l i k e l y tha t t h i s behav iou ra l catalogue would be easy to assemble. Even i f such a cata logue a l r eady e x i s t e d , i t may sometimes be d i f f i c u l t to compare the defens ive behaviours that animals d i s p l a y under n a t u r a l c o n d i t i o n s w i t h the behaviour r e q u i r e d o f them i n an exper imenta l s e t t i n g . For 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 ' r u n n i n g ' i n a running wheel , so tha t i t might be d i f f i c u l t to make accura te p r e d i c -t i o n s about l a b o r a t o r y performance tha t are based s o l e l y on a knowledge o f natural defensive behaviours ( c f . , Schwartz, 1978). In view of these problems, Bo l l e s ' s i m p l i f y i n g assumption about the defensive capacities of animals, even i f i t does not apply 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 of Bo l l e s ' approach i s that i t incorporates an assumption that the present data have shown to be unfounded, Further-more, the present data indi c a t e that the empirical study of defensive reactions c'ahtibeefraii-tffi on the animal * behaviour are relaxed, Thus, the empirical approach can at least p o t e n t i a l -l y lead to a general b i o l o g i c a l theory of aversive learning; whereas, an hypothesis that incorporates untested assumptions or assumptions based on li m i t e d observations i s l i k e l y to be successful only within h i g h l y r e s t r i c t e d s e t t i n g s . Perhaps a more fundamental assumption on:v^hi'Ghtt:obb.aseaa*iibi0logical' approach to aversive learning i s that the defensive behaviours of a l l ani-mal species have been the product of intense but diverse s e l e c t i o n pressures. Indeed, the facts of animal defense appear to be as numerous and diverse as animal species themselves (Maier § Maier, 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 therefore might be to order what i s already known about animal defense into a coherent base for broad predictions about animal be-haviour. It i s d i v e r s i t y of t h i s magnitude, not simply the d i v e r s i t y seen i n laboratory rats exposed to programmed e l e c t r i c shock, that should be the foundation o r . " f i r s t p r i n c i p l e " (Bolles, 1970, p. 34) of a b i o l o g i c a l ac-count of the diverse phenomena of aversive learning. The p r i n c i p l e s of Defensive Learning The major issue that must be dealt with i n any b i o l o g i c a l approach to aversive learning i s how the p r o b a b i l i t y of a defensive response changes . 62 as a r e s u l t of experience, . Bolles (1970) provides two mechanisms to account for changes i n response p r o b a b i l i t y . These mechanisms d i f f e r depending on whether learning i s slow or f a s t , but i n both the consequences of behaviour are emphasized. For f a s t (SSDR) learning the-important con-sequence i s punishing shock, and f o r slow (non-SSDR) learning i t i s the production of a r e i n f o r c i n g " s a f e t y - s i g n a l " . Both of these mechanisms of defensive l e a r n i n g ( i . e . , reinforcement and punishment) have us u a l l y been assumed to apply to any a r b i t r a r i l y chosen.response C s ee Introduction), B o l l e s (1970), however, has argued that there 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' s i t u a t i o n s . Thus, 'general' mechanisms of learning such as reinforcement may not apply to a l l responses (Bolles, 1972); 1975a). Nevertheless, Bolles must assume that these mechanisms have some generality across responses; otherwise, he would have no basis to exr pect, for example, that the e f f e c t s of 'punishment' on f r e e z i n g behaviour would be comparable to i t s e f f e c t s on f l e e i n g . Thus, i t may be problema-t i c to argue on the one hand that animals have evolved s p e c i a l responses to dangerous events (SSDRs), while, ont'the other hand envoking learning mechanisms that are assumed to operate i n the absence of these " b i o l o g i c a l constraints". Although i t may turn out that the facts of aversive learning cannot be explained without envoking a number,of d i f f e r e n t learning mechanisms, each having a l i m i t e d range of a p p l i c a b i l i t y , a more parsimonious al t e r n a -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 , nonarbitrary r e l a -tionships between c e r t a i n classes of s t i m u l i and responses i s a " f i r s t p r i n c i p l e " . I propose that such an a l t e r n a t i v e can be found within a re-vived Pavlovian framework, and that a b i o l o g i c a l approach to aversive 63 learning might be more r e a d i l y subsumed.by a " c l a s s i c a l " Pavlovian learn-ing framework than by the "instrumental" framework envoked by Bolles. In general, - t h e r e ' c a r e : t w o - c r i t e r i a that-define': Pavlovian'conditioning. T h e n f i r s t c r i t e r i o n invol'Vesnan- e x p e ^ a 'conditioned' stimulus (CS).to an 'unconditioned' stimulus (UCS), The second c r i t e r i o n i s a change i n behaviour that r e s u l t s from t h i s operation (Rescorla, 1969). The Pavlovian conditioning of a defensive response i s i l l u s t r a t e d i n the following example. The presentation of a stimulus that r e l i a b l y pro-duces a v a r i e t y of defensive responses (the UCS) i s made contingent on the occurrence of a stimulus that i s 'neutral' i n t h i s regard (the CS). A f t e r some number of these contingent CS-UCS presentations, a defensive response begins to occur i n the presence of the CS, I f i t can be shown that the change i n the p r o b a b i l i t y of the defensive response i s a r e s u l t of the CS-UCS contingency, then i t i s a 'conditioned' response (CR). One advantage of t h i s conceptual framework i s that i t i s consistent with a b i o l o g i c a l approach to aversive learning, In Pavlovian conditioning, unlike instrumental conditioning, i t i s acknowledged that the choice of the response • t o^bb.eceoiiditi'onediis s seriousiyrrestrlctedbby t l t he ttypeo6fvstimulus used as the UCS. 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 the UCS ( i . e . , only i f i t belongs to the class of responses normally produced by the UCS) w i l l conditioning occur. This kind of b i o l o g i c a l 'constraint' on learning can be viewed as a more general argument f o r . B o l l e s ' p o s i t i o n ; i . e . , that a response (CR) can be r e a d i l y learned i n an aversive s i t u a t i o n only i f i t i s an SSDR (a response produced by the aversive UCS). Bolles, 64 however, looks past the SSDR to i t s consequences f o r an explanation of behaviour change; whereas, a Pavlovian account considers only the s t i m u l i contingently r e l a t e d to the UCS» A major obstacle to a Pavlovian account of aversive conditioning i s represented 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, 1938) between instrumentaland c l a s s i c a l conditioning. The idea i s that instrumental conditioning controls a l l s k e l e t a l , or voluntary responses; whereas, c l a s s i c a l conditioning controls autonomic, 'involuntary' responses. I f th i s were true, then i t would be d i f f i c u l t to argue that a s k e l e t a l defen-sive response such as running could be c l a s s i c a l l y conditioned, The fact i s , however, that 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"can'.'h e i n -:strum^ Kie.CgT?^ DijGarae$,1^ responses such as key pecks can be c l a s s i c a l l y conditioned (e.g., Brown § Jenkins, 1968). The l a t t e r e f f e c t has been c a l l e d "autoshaping" or "sign t r a c k i n g " and i t s r e l a t i o n s h i p to the res u l t s of the present studies w i l l now be discussed. U n t i l 1968, the pigeon's key peck was,considered the prime example of 'voluntary' behaviour c o n t r o l l e d by i t s consequences. However, Brown § Jenkins (1968) began an area of research that has led to.the current view ( e.g., Schwartz 6T Gamzu, 1977) that the key peck may be i n large measure a _br,esj>.d t-.d_tgra>irt iw.ith.ya; lift rkey;? in" spirt e;to£ntfce catisienceeof i a « i ^ n forma*«eont i n g e f l c y b j e j ^ t e j e r i sth - e t f^geofr 1 s^Kehaiviiour Tahd:cac-cess':ttib'rfoo%v §ftier sa if ewhtr-iais' "of these eSi-iU^Supair.^ tTwo5<k-i'nds i © f eyj>_ 65 dence suggested that t h i s "autoshaping" phenomenon was,due to Pavlovian conditioning. F i r s t , as i n a l l instances of Pavlovian conditioning, the contingency between the CS and the UCS was c r i t i c a l for the emergence of the'behaviour (e.g., Brown PT Jenkins, 1968; Gamzu § Williams, 1971). Second, and perhaps most importantly, autoshaped key pecks p e r s i s t e d even when there was a negative instrumental contingency between key pecking and access to grain (Williams § Williams, 1969). It i s very d i f f i c u l t to ex-p l a i n i n instrumentaltt-erms why the only response that was not followed by food should gain i n strength. The Pavlovian conditioning of d i r e c t e d s k e l e t a l responses (Hearst, 1975) has been part of what Bolles (1975a) has c a l l e d a " r e v o l u t i o n " i n behaviour theory; the straightforward idea that 'operant behaviour' can be analyzed mainly intterms of i t s consequences has received a serious chal- . lenge from the autoshaping data (Schwartz § Gamzu, 1977). However, i n s p i t e of the intensive study that t h i s phenomenon has received over the past ten years (for reviews, see Hearst PT Jenkins, 1974; Hearst, 1975; Schwartz § Gamzu, 1977), i t s generality has been l i m i t e d by the fact that 7 there are no c l e a r instances of autoshaping with an aversive r e i n f o r c e r . ' The purpose of the f i n a l part of t h i s discussion i s to b r i e f l y marshal evidence that suggests that much of the behaviour described i n the present thesis may represent the Pavlovian conditioning of a directed defensive reaction ( i . e . , a type of autoshaping). The v a l i d i t y of t h i s argument has implications for both the generality of the autoshaping phenomenon and the f e a s i b i l i t y of a Pavlovian i n t e r p r e t a t i o n of defensive learning. 7wa'Ues.t^aable. example was p.rovided. by Racfc f 11^ 9"),. -.'... ,,. The conditioning of aggressive-responses an Betta splendens (Murray, 1973) may represent an exception to t h i s generalization, 66 Tn the following table, several features of autoshaping and defen-sive burying are d i r e c t l y compared. Autoshaping 1. a high 'percentagecof'subjects exposed to a contingency between a key CCS) and food access (UCS) learn to approach the cue. and 'peck' i t (CR) 2. Autoshaped behaviour i s not a simple ' r e f l e x ' e l i c i t e d by cues associated with food; i t i s a dire c t e d , s k e l e t a l re-sponse, 3. ' Autoshaping occurs i n the ab-sence of art instrumental con-tingency between food and peck-ing; furthermore, the f i r s t i n ^ stance of a behaviour Ce.g,, key-peck) cannot be explained by i t s consequences. 4. A p o s i t i v e c o r r e l a t i o n between the occurrence of the CS and the-UCS i s mainly responsible f o r the f i r s t approach and peck at the CS, Common controls f o r Pav-. lovian conditioning ( i . e . , CS alone, UCS alone, d i s c r i m i n a t i v e : conditioning) y i e l d e d r e s u l t s ex-pected f o r a Pavlovian learning process,* Animals dir e c t e d t h e i r behaviour toward cues p o s i t i v e l y c orrelated with the UCS. 5, Approach to and contact with the CS w i l l p e r s i s t even when there i s a 'negative' instrumental con-tingency between pecks and food d e l i v e r y . 6. Exposure to the CS-UCS contingency 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 of the CR. Key-pecking does not have to occur during the CS-UCS p a i r i n g . ' Defensive Burying a high percentage of subjects ex posedctotangontingency;between a prod (CS) and shock (UCS). learn toi approachtthe.shock source and bury i t (CR) Burying behaviour i s not a, simple ' r e f l e x ' e l i c i t e d by cues associated with shock; i t i s a di r e c t e d , s k e l e t a l response.' Burying behaviour occurs'in the absence of an instrumental contingency between i t s e l f and shock; furthermore, the f i r s t instance of a behaviour cannot be explained by i t s consequence, 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 the shock (UCS) appears to be responsible fo r approach to and burying of the CS. (Exps. 1-9). Common controls f o r Pavlovian.condition ing ( i . e . , CS alone (Exps. 1,4, 6), UCS alone, (Exp. 3), d i s c r i -minative conditioning (Exps.,5, 7, 8, 9) generally y i e l d e d re-sui t s expected f o r a Pavlovian learning process. Rats dir e c t e d t h e i r behaviour toward cues posi t i v e l y c o r r e l a t e d with the UCS. Approach to and burying of the CS occurs despite a p r i o r , impli c i t punishment contingency be-tween approach and shock. Exposure to the CS-UCS contin-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 of the CR. Burying does not have to occur during the 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 burying are provocative, the differences between these phenomena are of equal theore-t i c a l importance, One d i f f e r e n c e i s that the aut'oshaped response takes about 50 t r i a l s to e s t a b l i s h (Hearst, 1975), whereas the burying response occurs a f t e r only one ' t r i a l ' . Two considerations may make these d i f f e r -ences comprehensible. The f i r s t consideration i s s u r v i v a l , Animals i n t h e i r natural environment do not have much time to learn about dangerous things. The l a s t t r i a l of aversive learning f o r the prey i s the f i r s t t r i a l of .appetitive learning f o r the predator. In order to f a c i l i t a t e s u r v i v a l , the defensive learning of the prey must be quick and,effective (Bolles, 1970). An organism equipped with t h i s kind of defensive capacity would have a s e l e c t i v e advantage that may be transmitted to l a t e r genera-ti o n s . On the other hand, the appetitive learning of an animal l i k e the pigeon, although just as e s s e n t i a l for s u r v i v a l , can generally follow a longer time course without i l l e f f e c t . In other words, s e l e c t i o n pressure fo r rapid appetitive learning i n the pigeon may be less than that f o r rapid defensive learning i n the. r a t . Although evolutionary considerations such as these are d i f f i c u l t to evaluate d i r e c t l y , they may lead to i n t e r e s t -ing p r e d ictions about comparative animal learning (cf;, B o l l e s , 1975a). A second consideration that may account for the d i f f e r e n c e between the a c q u i s i t i o n rates of Pavlovian key pecks and conditioned burying i s one that i s more accessible to experimental t e s t but which has not received much at t e n t i o n : It i s a natural complement o f temporal c o n t i g u i t y (Pavlov, 1927) that may turn out to be j u s t as important: s p a t i a l c o n t i g u i t y of the CS and the UCS. The burying paradigm i s • .unusualLnihnthat "the-UCS' (shock) i s d e l i v e r e d through a well-defined, l o c a l i z e d CS (prod), • Because noxious' 6 8 s t i m u l i i n the animal's natural environment are usually s p a t i a l l y contigu-ous with the cues that s i g n a l t h e i r occurrence, i t i s not unreasonable to assume that laboratory animals may be able to learn about s p a t i a l l y c o n t i -guous events more e a s i l y than those that are not. The hypothesis i s cer-t a i n l y worth t e s t i n g , both i n the ease of the pigeon's autoshaped key peck and i n the case of the rat's conditioned burying response. A second apparent difference between autoshaping and the burying pheno-menon concerns the nature of the r e l a t i o n s h i p between the CR and the 'uncon-ditioned' response (UCR) to the UCS, The pigeon's conditioned key peck, al-r though not the same as i t s unconditioned response to food, i s very s i m i l a r j (Jenkins § Moore, 1973), Likewise, several other instances of Pavlovian conditioning are consistent with the notion of stimulus-substitution: i . e . , the subject acts i n the same way toward the C S . a s i t does toward the UCS. Cl e a r l y , burying 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 by shock (e.g., withdrawal). It i s important to remember that stimulus s u b s t i t u t i o n i s a theory about the mechanism of Pavlovian conditioning. There i s nothing i n the data on Paylovian conditioning that suggests that a l l CRs are the same as the UCRs e l i c i t e d by the UCS, In f a c t , ( t h e r e are many.examples of Pavlovian CRs that are not the same as the UCR, Obrist, Sutterer, and Howard (1972) showed that an unconditioned response to e l e c t r i c shock was i n v a r i a b l y cardiac acceleration.; however, when shock was paired with a CS i n the usual Pavlovian manner, the CS l a t e r e l i c i t e d cardiac deceleration.' This CR was ; 69 adaptive i n the sense that i t may have prepared the animal for impending cardiovascular s t r a i n , but i t was the opposite of the unconditioned re-sponse to shock. Siegel (1972) inje c t e d i n s u l i n i n t o . r a t s on a f i x e d schedule, The unconditioned e f f e c t of i n s u l i n was to lower blood sugar. When' rats were l a t e r tested with the CS alone (saline i n j e c t i o n ) , t h e i r 'conditioned' response was an increase rather than a decrease i n blood sugar, Again, the CR did not f i t the theory of stimulus s u b s t i t u t i o n but i t was c l e a r l y adaptive, A l t e r n a t i v e l y , i f the UCS i s glucose, the CR i s not an increase i n blood sugar but a decrease (Deutsch, 1974), When the UCS i s morphine, the CR i s not reduced pain s e n s i t i v i t y ; i t i s . i n c r e a s e d pain s e n s i t i v i t y (Siegel, 1975, 1977), Other instances of .discontinuities between CRs and UCRs can be found i n the autoshaping l i t e r a t u r e . For ex-ample, Wasserman (1973) found that baby chicks pecked at a key p r e d i c t i n g four seconds of heat, but they did not peck during heat. Grant (1974) showed that responses toward a conspecific CS were d i s s i m i l a r to those e l i -c i t e d by the food UCS, In t h i s instance, 'socia l grooming' was the dominant CR. Thus, i t may be premature to r e j e c t the notion of a Pavlovian condi-tioned burying response on the grounds that i t i s d i s s i m i l a r to the uncon-ditioned response to shock, or. because the a c q u i s i t i o n of t h i s response takes place i n one ' t r i a l ' while the a c q u i s i t i o n of other conditioned re-sponses usually requires many more t r i a l s . On the other hand, the idea of a conditioned burying response gains some c r e d i b i l i t y because of 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 burying behaviour and autoshaping, a,pheno-menon that has commonly been interpreted as an instance of Pavlovian condi-t i o n i n g . The most important s i m i l a r i t i e s are 1) that both are d i r e c t e d , s k e l e t a l responses, 2) that neither phenomenon can be r e a d i l y explained by 7 0 instrumental contingencies, and 3) that i n both cases a Pavlovian contin-gency between a CS and a UCS seems to be c r i t i c a l for the emergence of the behaviour, Although the present studies of defensive burying were not designed with this comparison i n mind, they do provide some data that are consistent with the argument that burying behaviour may also represent the Pavlovian conditioning of a d i r e c t e d s k e l e t a l response. The vprdo'fty of t h i s argument would extend the generality of the auto-, shaping phenomenon, and provide substance to the " a l t e r n a t i v e " b i o l o g i c a l approach to aversive learning being presented.here. According to t h i s view, sp e c i e s - t y p i c a l defense reactions such as running or f r e e z i n g are directed by Pavlovian rather than instrumental contingencies i n the organism's en-vironment. Thus, the successful p r e d i c t i o n of defensive learning must be based on a thorough knowledge of the organism's 'unconditioned' defensive r e p e r t o i r e , and on afcareful analysis of the Pavlovian contingencies that act on t h i s r e p e r t o i r e . Study of the burying phenomenon may-serve as a natural s t a r t i n g point f o r the development of such a . b i o l o g i c a l approach to. aversive learning. 71 REFERENCES. Anger, D. The r©le of temporal discriminations i n the reinforcement of Sidman avoidance behavior. Journal of the Experimental Analysis of Behavior, 1963, 6, 477-506. A z r i n , N.H, Aggression, Paper read at American Psychological Association Meeting, Los Angeles, 1964, " • • . . . . . . A z r i n , N,H,, Hake, D,F,, § Hutchison, R,R, E l l c x t a t i o n of aggression by a physical blow, Journal of the Experimental Analysis of Behavior, 1965, 8_, 55-57. Az r i n , H.N,, Hopwood, J , , § Powell, J , A rat chamber and electrode proce-dure f o r avoidance conditioning, Journal of the Experimental Analysis  of Behavior, 1967,10, 291-298, Az r i n , N.H,, Hutchison, R.R. , § S a l l e r y , R.D. Pain-raggression toward i n -animate objects. Journal of the Experimental Analysis of Behavior, 1964, 7, 9-11. Berger, D.F., § Brush, R.F. Rapid a c q u i s i t i o n o f ; d i s c r e t e - t r i a l lever-press avoidance: E f f e c t s of signal-shock i n t e r v a l , Journal of the  Experimental Analysis of Behavior, 1975, 2£, 227-239. Biederman, G.B., D'Amatoi,'. M.R. , § K e l l e r , D.M. F a c i l i t a t i o n of discrimina-ted avoidance learning by d i s s o c i a t i o n of CS arid mariipulandum, Psychonomic Science, 1964, 1_, 229-230. -Blanchard, R.J., § Blanchard, D.C. Crouching as an index of fear, Journal  o f Comparative arid P h y s i o l o g i c a l Psychology, 1969, 67_, 370-375(a). Blanchard, R.J., § Blanchard, D.C, Passive andactive reactions to fear e l i c i t i n g s t i m u l i . Journal of Comparative and Phy s i o l o g i c a l Psy-chology, 1969, 68_, 129-135, (b) Blanchard, R.J., § Blanchard, D.C, Dual mechanisms i n passive avoidance: ' I. Psychonomic Science, 1970, 19,- 1-2, (a), 72 B l a n c h a r d , R . J . , § B lancha rd , D . C . Dual mechanisms i n p a s s i v e a v o i d -ance: I I . Psychonomic S c i e n c e , 1970, 19_, 3-4. (b) B lancha rd , R . J . , § B lancha rd , D . C . Defensive r e a c t i o n s i n the a l b i n o r a t . Learn ing and M o t i v a t i o n , 1971, 2, 351-362. B lancha rd , R . J . , § B lancha rd , D . C . Aggress ive behav ior i n the r a t . Behav io ra l B i o l o g y , 1977, 21 , 197-224. B lancha rd , R . J . , B lancha rd , D . C , § Takahash i , L . K . R e f l e x i v e f i g h t i n g i n the a l b i n o r a t : Aggress ive o r defens ive b e h a v i o r ? . / Aggress ive Behavior , 1977,. 3_, 145-155. B l a n c h a r d , R . J . , B lancha rd , D . C , Takahash i , T. , $ K e l l e y , M . J . A t t ack and defens ive b e h a v i ' . ; : i n the a l b i n o r a t . Artimal Behavior I-. 1977, 25, 622-634. B lancha rd , R . J . , Fukunaga, K . K . , § B lancha rd , D . C . Environmenta l c o n t r o l o f defens ive r e a c t i o n s to a c a t . B u l l e t i n o f the Psychonomic So-c i e t y , 1976, 8_, 179-181. B lancha rd , R . J . , K e l l e y , M . J . , § B lancha rd , D . C . Defensive r e a c t i o n s and e x p l o r a t o r y b e h a v i o r , i n r a t s . J o u r n a l o f Comparative and P h y s i o l o -g i c a l Psycho logy , 1974, 87, 1129-1133. . B lancha rd , R . J . , Mas t , M . , § B lancha rd , D . C St imulus c o n t r o l o f defens ive r e a c t i o n s i n the a l b i n o r a t . J o u r n a l o f Comparative and P h y s i o l o g i - c a l Psycho logy , 1975, 8_8, 81-88. B o l l e s , R . C S p e c i e s - s p e c i f i c defense r e a c t i o n s and avoidance l e a r n i n g . P s y c h o l o g i c a l Review, 1970, 77, 32-48. B o l l e s , R . C . S p e c i e s - s p e c i f i c defense r e a c t i o n s . In F . R . Brush ( E d s . ) , A v e r s i v e c o n d i t i o n i n g and l e a r n i n g , New Y o r k : Academic P r e s s , 1971. 73 B o l l e s , R.C. The avoidance learning problem. In G.H. Bower (Ed.), The psychology of learning and motivation, Vol. 6: New York: Academic Press, 1972. Bol l e s , R.C. Learning, motivation and cognition. In W.K. Estes (Ed.), Handbook of learning and cognitive processes (Vol. 1). H i l l s d a l e , N.J.: Erlbaum, 1975.(a) Bo l l e s , R.C. Learning theory. New York: Holt, Rinehart § Winston, 1975. (b) B o l l e s , R.C, § C o l l i e r , A.C, The e f f e c t of p r e d i c t i v e cues on fre e z i n g i n r a t s . Animal Learning artd Behavior , 1976, 4_, 6-8. B o l l e s , R.C, § Warren, J.A.Jr., The a c q u i s i t i o n of bar press avoidance as a function of shock i n t e n s i t y . Psychonomic Science, 1965, 3_, 297-298. Bo l l e s , R.C,, Warren, J.A., J r . , § Ostrov, N, The r o l e of the CS-US i n -t e r v a l i n bar press avoidance learning. Psychonomic Science, 1966, 6, 113-114. Brogden, W.J.,.Lipman, E.A., § C u l l e r , E. The role of incentive i n condi-t i o n i n g and e x t i n c t i o n . American Journal of Psychology, 1938, 51, 109-117. Bronstein, P.M., § Hirsch,. S.M, Ontogeny of defensive reactions i n Norway ra t s . Journal of Comparative and P h y s i o l o g i c a l Psychology, 1976, 90y 620-629. Brown, P.L., § Jenkins, H.M. Autoshaping of the pigeon's key-peck. Journal of the Experimental Analysis of Behaviour, 1968, 11_, 1-8. 74 Brush,.F.R. Discrimination avoidance t r a i n i n g of r a t s . Science, 1964, 146, 1599-1600. Cahoon, D.D., § Crosby,R.M. A technique f or the automatic shaping of escape and avoidance behavio r\ i n the operant conditioning chamber. Psychological Record, 1969, 19_, 431-432. Calhoun, J.B. The ecology and sociology of the Norway r a t . Bethesda, Md.: U.S. Department of Health, Education, and Welfare, 1962. Crawford, M., § Masterson, F. Components o f the f l i g h t response can r e i n -force bar-press avoidance learning. Jourrtal of Experimental Psy-chology: Animal Behavior .'.'Processes, 1978, £,144-151. C u r t i , M.W; Native fear responses of white rats i n the presence of cats; Psychological Monographs, 1935, 46, 78-98. D'Amato, M,R., § Fazzaro, J . Discriminated lever-press avoidance learning as a function of'type and i n t e n s i t y of shock. Journal of Comparative  and Ph y s i o l o g i c a l Psychology, 1966, 61, .313-315. D'Amato, M.R., K e l l e r , D., § DiCara, L. F a c i l i t a t i o n of discriminated avoidance learning by discontinuous shock. , Journal of Comparative  and Ph y s i o l o g i c a l Psychology, 1964, 58, 344-349. D'Amato, M.R., § S c h i f f , D. Long-term discriminated avoidance performance i n the r a t . Jourrtal of Comparative and Phy s i o l o g i c a l Psychology, 1964, 57_, 123-126. Delprato, D.J., § Holmes, P.A. F a c i l i t a t i o n of discriminated lever-press avoidance by noncontingent shocks. Learning § Motivation, 1977, 8_, 232-246. Deutsch, R. Conditioned hypoglycemia: A mechanism f o r saccharin-induced s e n s i t i v i t y to i n s u l i n i n the r a t . Journal of Comparative and Physio- l o g i c a l Psychology, 1974, 86,- 350-358. 75 DiCara, L.V. , § M i l l e r , N.E. Changes i n heart-rate instrumentally learned by curarized rats as avoidance responses. Journal of  Comparative and Physiological Psychology, 1968, 65_, 8-12. Dinsmoor, J.A. Punishment: I. The avoidance hypothesis. Psychological  Review, 1954, 6J_, 34-4'6. Dinsmoor, J.A. Escape, avoidance, punishment: Where do we stand? Journal of the Experimental Analysis of Behavior , 1977, 28, 83-95. Fantino, E. Aversive c o n t r o l . In J.A. Nevin § G.S. Reynolds (Eds.), The Study of Behavior :', Glenview,.Ill.: Scott, Foresman, § Co., 1973. Fantino, E., Sharp, D., § Cole, M, Factors f a c i l i t a t i n g lever-press avoidance. Journal of Comparative and Physiological Psychology, 1966, 62,- 214-217. Feldman, R.S., § Bremmer, F,J. A method f o r rapid conditioning of stable avoidance bar pressing behavior. . Journal of the Experimental Analy- s i s of Behavior,. , 1963, 6_, 393-394. *~ Flo r y , R.K., U l r i c h , R.E., § Wolff, D.C. E f f e c t s of v i s u a l deprivation on f i g h t i n g behavio The Psychological Record, 1965, 15^ , 185-190. Forgione, A.G. The elimination of i n t e r f e r i n g response patterns i n lever-press avoidance. Journal of the Experimental Analysis of Behavior , 1970, 13, 51-56. Gamzu, E.R., § Williams, D.R. C l a s s i c a l conditioning of a complex s k e l e t a l act. Science, 1971, 171, 923-925. Garcia, J . , Clarke, J.C., § Hankins, W-G. Natural responses to scheduled rewards. In P.P.G. Bateson § P.H. Klopfer (Eds.), Perspectives i n Ethology, New York: Plenum Press, 1973. 76 Garcia, J . , § K o e l l i n g , R. Relation of cue to consequence i n avoidance learning. Psychonomic Science, 1966, 4_, 123-124. G i u l i a n , D., § Schmaltz, L.W. Enhanced discriminated barpress avoidance i n the rat through appetitive preconditioning. Journal of Compara- t i v e and Ph y s i o l o g i c a l Psychology, 1973, 83_, 106-112. Grant, D.L. An t i c i p a t o r y behaviour (autoshaping) i n rats to the presenta-t i o n of another rat p r e d i c t i n g food. Unpublished B.A. honours t h e s i s , Indiana U n i v e r s i t y , 1974. (In Hearst, 1975). Grosseri, N.E., § Kelley, M.J. S p e c i e s - s p e c i f i c behavior and a c q u i s i t i o n of avoidance behaviour i n r a t s . Journal of Comparative and Physio- l o g i c a l Psychology, 1972, 81_, 307-310. Hearst, E. Pavlovian conditioning and dir e c t e d movements. In G.H. Bower (Ed.), The Psychology of Learning § Motivation, V o l . 9. New York: Academic Press, 1975. Hearst, E., § Jenkins, H.M. Sign-tracking: The stimulus-reinforcer r e l a t i o n  and dir e c t e d action. Austin, Texas: Psychonomic Society, 1974. Herrnstein, R.J. Method and theory i n the study o f avoidance. Psychological  Review, 1969, 76_, 49-69. • Hin e l i n e , P.N. Negative reinforcement and avoidance. In W.K. Honig § J.E.R. Staddon (Eds.), Handbook of operant behavior'- , Englewood C l i f f s , N.J.: P r e n t i c e - H a l l , 1977. Hin e l i n e , P.N., § Rachlin, H. Escape and avoidance of shock by pigeons pecking a key. Journal of the Experimental Analysis o f Behavior..;, 1969, 12_, 533-538. Hudson, B.B. One-trial learning i n the domestic r a t . Genetic Psychology  Monographs, 1950, 41_, 99-145. 77 H u l l , J,H,, Myer, J,S (, § Smith, G,J, Consistent leverpress avoidance responding by r a t s . B u l l e t i n of the Psychonomic Society, 1975, 6_, 297-299. Hurwltz, H.M.B, Method f o r d i s c r i m i n a t i v e avoidance t r a i n i n g . Science, 1964; 145, 1070, Hutchinson, R,R,, U l r i c h , R.E,, § A z r i n , N.H, E f f e c t s of age and r e l a t e d factors on the pain-aggression reaction, Journal of Comparative and Physiological Psychology, 1965, 59, 365-369, Jenkins, H.M., § Moore, B.R. The form of the autoshaped response with food or water r e i n f o r c e r s . Journal, of the Experimental Analysis of Behavior, 1973, 20, 163-181, Johnston, R.E. Scent marking by male golden hamsters (Mesocricetus aura-tus) I I I . Behavior i n a seminatural environment. Z e i t s c h r i f t f u r Tierpsychologie, 1975, 37_, 213-221. Keehn, J.D., § Webster, C,D. Rapid discriminated bar-press avoidance through avoidance shaping. Psychonomic Science, 1968, 10, 21-22. Krane, R.V., § Wagner, A.R. Taste-aversion learning with a delayed shock vs, implications f or the "generality of the laws of learning". Journal of Comparative and P h y s i o l o g i c a l Psychology, 1975, 88, 882-889. 78 Maatsch, J,L, Learning and f i x a t i o n a f t e r a si n g l e shock t r i a l . Journal of Comparative and Ph y s i o l o g i c a l Psychology, 1959, 52, 408-415. Mackintosh, N.J. The psychology o f animal learning. New York: Academic Press, 1974. Macphail, E.M. Avoidance responding i n pigeons. Journal of the Experi-mental Analysis of Behavior, 1968, 1_1_, 625-632. Maier, R.A., § Maier, B.M. Comparative animal behavior. Belmont, C a l i -f o r n i a : Wadsworth Publishing Co., 1970. Manning, F.J., Jackson, M.C., § MeDonough, J,H, A simple method of im-proving leverpress "avoidance by r a t s , B u l l e t i n of the Psychonomic  Society, 1974, 4_, 5-8, Masterson, F.A. Is termination o f a warning signal an e f f e c t i v e reward f o r the r a t ? ' Journal of Comparative and Physiological Psychology, 1970, 72, 471-475, Meyer, D.R., Cho, C , § Wesemarin, A.F, On problems of conditioning d i s -criminated leverrpress avoidance responses, Psychological Review, 1960, 67_, 224-228. Mowrer, 0,H. On the dual nature of learning->-A r e - i n t e r p r e t a t i o n of "conditioning" and "problemrsolving". Harvard Educational^Review, 1947, -17_,. 102-148. Murray, C,S. Conditioning Betta splendens, Unpublished doctoral d i s s e r t t a t i o n . U n i v e r s i t y of Pennsylvania, 1973, Obrist, P.A., Sutterer, J,R., § Howard, J.L. Preparatory cardiac changes: A psychobiological approach. In A,H, Black § W.F. Prokasy (Eds,), C l a s s i c a l conditioning. I I , New York: Appleton-Century-Crofts, 1972, 79 Owings, D.H., Borchert, M. , § V i r g i n i a , R. The behaviour of C a l i f o r n i a ground s q u i r r e l s . Animal Behavior , 1977, 25, 221-270. Owings, D.H., £ Coss, R.G. Snake mobbing by C a l i f o r n i a ground s q u i r r e l s : Adaptive v a r i a t i o n and ontogeny. Behavior.:-, 1978, 62_, 50-69. Pavlov, I. Conditioned r e f l e x e s . Oxford: Oxford U n i v e r s i t y Press, 1927. Pear, J . J . , Moody, J.E., § Persinger, M.A. Lever attacking by rats during free-operant avoidance. Journal of the Experimental Analysis of Behaviour, 1972, 1_8, 517-523. Pe a r l , J . , § F i t z g e r a l d , J . J . Better discriminated bar-press avoidance at short i n t e r t r i a l i n t e r v a l s . Psychonomic Science, 1966, 4_, 41-42. R i c c i o , D.C, Rohrbaugh, M. , S Hodges, L.A. Developmental aspects of pas-sive and active avoidance learning i n r a t s . Developmental Psycho-biology, 1968, 1_, 108-111. Schoenfeld, W.N. An experimental approach to anxiety, escape and avoidance behaviour. 1 In P.H. Hoch § J . Zubin (Eds.), Anxiety. New York: Grune § Stratton, 1950. Schwartz, B. Maintenance of keypecking i n pigeons by a food avoidance but not a shock avoidance contingency. Animal Learning and Behavio r , 1973, 1_, 164-166. Schwartz, B. Psychology of learning and behaviorx. New York: W.W. Norton, 1978. Schwartz, B., § Gamzu, E. Pavlovian control of operant behaviour. In W.K. Honig § J.E.R. Staddon (Eds.), Handbook of operant behavior:. Englewood C l i f f s , N.J.: P r e n t i c e - H a l l , 1977. Seligman, M.E.P. On the generality of laws o f learning. Psychological Review, 1970, 77, 406-418. 80 Shettleworth, S. Constraints on learning. In D.S. Lehrman, R.A. Hinde, § E. Shaw (Eds.), Advances i n the, study of behavior : V ol. 4, New York: Academic Press, 1972. Sidmart, M. Two temporal parameters of the maintenance of avoidance be-havior;, by the white r a t . Journal of Comparative and Physiological Psychology, 1953, 46_, 253-261. S i e g e l , S. Conditioning of insulin-induced glycemia. Journal of Compara-t i v e and Physiological Psychology, 1972, 78, 233-241. Si e g e l , S. Evidence from rats that morphine tolerance i s a learned re-sponse. Jpjirnal_of_Com^ 1975, 89, 498-506. S i e g e l , S. Morphine tolerance a c q u i s i t i o n as an associative process. Journal of Experimental Psychology: Animal Behavior. - Processes, 1977, 3_, 1-13. Skinner, B.F. Behaviour of organisms. New York: Appleton-Century-Crofts, 1938. Skinner, B.F. A case h i s t o r y o f s c i e n t i f i c method. American Psychologist, 1956, 11_, 221-233. Solomon, R.L., § Wynne, L.C. Traumatic avoidance learning: The p r i n c i p l e s of anxiety conservation and p a r t i a l i r r e v e r s i b i l i t y . Psychological  Review, 1954, 61_, 353-385. Teitelbaum, P. The use of operant methods i n the assessment and control of motivational states. In W.K. Honig (Ed.), Operant behaviour: Areas of research and a p p l i c a t i o n . New York: Appleton-Century-Crofts, 1966, . 81 Theios, J . Simple conditioning as two-stage all-or-none learning. Psychological Review, 1963, 70,'403-417. U l r i c h , R.E. Pain-induced aggression. In G.A. Kimble (Ed.), Foundations o f conditioning and learning. New York: Appleton-Century-Crofts, 1967. U l r i c h , R.E., § A z r i n , N.H. Reflexive f i g h t i n g i n response to aversive stimulation. Journal of the Experimental Analysis of Behavior ", 1962, 5_, 511-520. U l r i c h , R.E., Wolff, P.C, § A z r i n , N.H. Shock as an e l i c i t o r of i n t r a -and inter-species f i g h t i n g behavior,;. Animal Behavior ., 1964, 12, 14-15. Wahlsten, D., Cole, M., Sharp, D., § Fantino, E.J. F a c i l i t a t i o n of bar-press avoidance by handling during the i n t e r t r i a l i n t e r v a l . Journal of Comparative and Phy s i o l o g i c a l Psychology, 1968, 65, 170-175. Wasserman, E.A. Pavlovian conditioning with heat reinforcement produces stimulus-directed pecking i n chicks. Science, 1973, 181, 875-877. Welker, W.I. Escape, exploratory, and food-seeking responses of rats i n a novel s i t u a t i o n . Journal of Comparative and Ph y s i o l o g i c a l Psy- chology, 1959, 52_, 106-111. Williams, D.R., § Williams, H. Automaintenance i n the pigeon: Sustained pecking despite contingent non-reinforcement. Journal of the Ex-perimental Analysis of Behavior-, 1969, 1_2, 511-520. Winer, B.J. S t a t i s t i c a l p r i n c i p l e s i n experimental design. New York: McGraw-Hill, 1962. Wong, R. Motivation: A bidbehavioral,, analysis of consummatory a c t i v i t i e s . New York: Macmillan, 1976. 

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