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Attentional and Oculomotor Components of Multiple Location Inhibition of Return Holec, Victoria 2010

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       Atentional and Oculomotor Components of Multiple Location Inhibition of Return    Victoria Holec Honours Student   Submited in partial fulfilment of the requirements for the Bachelor of Arts (Honours) Psychology degree  in  The Irving K. Barber School of Arts and Sciences                         The University of British Columbia Okanagan April 2010     2 Abstract People engage in visual search during everyday tasks such as looking for a friend in a crowd.  Inhibition of return (IOR) facilitates visual search by inhibiting atention from returning to previously inspected locations.  IOR is believed to be mediated both by atention and eye movements (i.e., oculomotor).  The aim of the present research was to determine whether oculomotor IOR is operating when multiple locations are searched.  In this study, participants were instructed to keep their eyes at central fixation to measure atentional IOR or move their eyes to peripheral locations to measure oculomotor IOR.  Results suggest a trend for oculomotor IOR to develop more slowly than atentional IOR, with no diferences in magnitude betwen the two forms of IOR.     3 Table of Contents 1. Introduction 5 i. Studying Atentional Orienting 6 ii. Importance of Inhibition of Return (IOR) in Visual Search 8 iii. Atentional IOR 11 iv. Oculomotor IOR 13 v. Towards a Combined View of Atentional and Oculomotor Contributions 15 vi. Research Question 17 2. Method 19 3. Results 21 4. Discussion 24 5. Conclusions and Future Directions 27 6. References 28             4 List of Figures Figure 1: Sequence of events in a trial 20 Figure 2: Mean correct RT as a function of target location and order of orienting 23 Figure 3: Mean IOR efects as a function of target location and type of orienting 24   5 Introduction When we try to find our car in the parking lot, our  misplaced keys on a counter, a friend in the crowd, or the latest version of our thesis on a cluttered desktop, we are engaging in visual search.  There is litle wonder that visual search is considered an esential task because we engage in it multiple times a day.  Atentional proceses including orienting to and detecting environmental signals and events are necesary in almost al everyday tasks such as crossing the street, driving a car, as wel as in social interactions such as talking to a friend..  These atentional proceses have also been found to facilitate visual search, thereby increasing the eficiency of our searches (Eriksen & Hoffman, 1973; Posner, 1980; Posner, Snyder, & Davidson, 1980).  Specificaly, when atention is alocated to a stimulus in the environment, response time (RT) for orienting to and detecting that stimulus is generaly faster and visual search becomes more eficient. In this way, atention alows us to operate eficiently in our complex environment. Importantly, atention can be alocated to a stimulus in diferent ways.  First, atention can be deployed either overtly or covertly.  Overt atentional orienting is acomplished by physicaly orienting the receptors to a stimulus via eye, head, or body movements.  It is at play when we move our head, and hence our eyes and atention, in search of our car in the parking lot.  In contrast, covert atentional orienting is acomplished without physicaly orienting the receptors to the stimulus.  It is at play when a flash of lightening captures our atention "out of the corner of the eye" while driving, as we keep our eyes focused on the road ahead.   Second, atention can be deployed either endogenously or exogenously.  Endogenous atentional orienting is under the control of the observer and involves voluntarily directing atention to a particular stimulus.  It is at play overtly when we look both ways before crossing   6 the street to prevent a potential disaster.  It is at play covertly when we keep our eyes focused straight ahead on the basketbal court but monitor the position and movement of other players "out of the corner of the eye".  Exogenous atentional orienting is not under the control of the observer and involves the involuntary capture of atention by salient features of an object or an abrupt onset in the peripheral visual field.  It is at play overtly when our atention is involuntarily captured by a fast-approaching car in the periphery as we cross the street and we then align our eyes and atention with the car to determine its position and speed.  It is at play covertly when our atention is involuntarily captured as we notice a parent waving to us as we proced down the aisle at convocation, while keeping our eyes fixed straight ahead at the stage. Studying Attentional Orienting Atentional orienting is typicaly studied in a laboratory seting using either an endogenous or exogenous atentional orienting paradigm (Posner, 1980).  In both versions, a central fixation stimulus is flanked by two boxes.  In the endogenous version, as observers keep their eyes focused on the fixation stimulus, a second stimulus (i.e., the cue), such as an arrow that points to the left or right box replaces the fixation stimulus, and following a delay, a target (e.g., an asterisk) appears in one of the two boxes.  This cue is predictive of target location as it directs the observer’s atention to the likely location of the upcoming target – approximately 80% of the time it wil occur at the pointed at (i.e., the cued) location and approximately 20% of the time it wil occur at the other (i.e., the uncued) location.  Overt atention is engaged if the experimental procedure requires an eye movement to be executed to the predicted location and then back to the central stimulus prior to target onset.  However, covert atention is engaged if the experimental procedure requires that eyes remain at the central stimulus for the duration of the trial.  Regardles of whether endogenous atention is deployed overtly or covertly to one of the   7 two peripheral locations, RT for subsequent target detection is faster at the cued than the uncued location – the facilitation efect.  In the exogenous version of the atentional orienting paradigm (Posner, Rafal, & Cohen, 1982), again, a central fixation stimulus is flanked by two boxes.  But here, as participants keep their eyes focused on the central fixation stimulus, an abrupt onset in the periphery (i.e., the cue), such as the brief brightening of one of the boxes, occurs and following a brief delay, a target appears.  Although the cue draws the observer’s atention to the location of the cue, it does not predict the likely location of the target – as it wil occur equaly often at the cued and the uncued location.  Overt exogenous atention is engaged if an eye movement is executed to the brightened box and then returned to central fixation.  Covert exogenous atention is engaged if the eyes remain at central fixation throughout the trial.  Again, regardles of whether endogenous atention is deployed overtly or covertly, a facilitation efect is observed with RT for subsequent target detection at the cued location (Posner, 1980). Criticaly, although this facilitation efect is long-lasting with the endogenous deployment of atention, it is relatively short-lived with the exogenous deployment of atention – only occuring at short cue-target intervals (i.e., les than 100 ms).  However, at long cue-target intervals (i.e., exceding 300 ms), RT for subsequent target detection is slower at the cued location than at the uncued location (Posner & Cohen, 1984).  This slowing in RT at the cued location was hypothesized to result from atention being inhibited from returning to the previously atended location, and was later termed inhibition of return (IOR; Posner, Rafal, Choate, & Vaughan, 1985). As with the facilitation efect, IOR occurs with the exogenous deployment of atention when observers orient to the cue either overtly or covertly, but it only occurs with the endogenous deployment of atention when observers orient overtly to the cue   8 (Posner & Cohen, 1984; Maylor, 1985).  Specificaly, when using a predictive endogenous central cue to orient atention, IOR wil occur if an eye movement is made to the cued location and returned to central fixation, but not if the eyes remain at fixation. IOR and Its Importance in Visual Search Early on, IOR was hypothesized to facilitate visual search by inhibiting atention from returning to previously inspected locations (Klein, 1988; Posner & Cohen, 1984).  Klein (1988) found that IOR was generated as a result of atention being alocated to distractor locations when searching for a target in conjunction search.  And importantly, it was not found not in feature search, where atention was not alocated to distractor locations.  Further evidence that IOR helps in everyday search comes from findings that IOR: can occur in discrimination tasks (Prat & Abrams, 1995; Prat, Kingstone, & Khoe, 1997) as wel as simple detection tasks; is coded in environmental rather than retinotopic coordinates (Maylor & Hockey, 1985; Posner & Cohen, 1984); and occurs for both static and moving objects (Tipper, Driver, & Weaver, 1991). These findings demonstrate that IOR occurs in a variety of setings (se Klein, 2000; and Lupiáñez, Klein, & Bartolomeo, 2006 for reviews), supporting the hypothesis that IOR is important for eficient visual search.  However, if IOR is useful in visual search, one would expect to find it at more than one location in a search, as was demonstrated in Klein’s (1988) study following conjunction search.  Yet, initialy there was substantial debate regarding the number of locations that could be concurrently inhibited by IOR.  For instance, when Prat and Abrams (1995) cued two locations in succesion, IOR was observed only at the most recently cued location.  Tipper, Weaver, and Watson (1996) re-examined this isue by cueing three of the four locations in succesion and found IOR at al three cued locations, with the largest IOR effect observed at the most recently   9 cued location.  In a follow-up study, Abrams and Prat (1996) cued three of six locations in succesion and failed to replicate Tipper et al.'s (1996) finding of multiple location IOR.  Importantly, in Abrams and Prat’s (1996) study, the cued locations were non-adjacent, and therefore the authors suggested that multiple location IOR only occurs when the cued locations can be spatialy grouped. And finaly, Danziger, Kingstone, and Snyder (1998) suggested that paradigms using a fixed number of cues and re-cueing the central fixation stimulus prior to target onset might alow observers to predict when the target would occur and that the temporal predictability of target onset might be a critical factor in whether multiple-location IOR is obtained.  To test this hypothesis, they designed a five-location paradigm where either zero, one, two, or three peripheral cues could occur before target onset, thereby reducing temporal predictivenes of target onset.  And indeed, IOR was found at al three cued locations, with the largest IOR efect at the most recently cued location as previously established by Tipper et al. (1996).  Building on Danziger et al.'s (1998) findings, Snyder and Kingstone (2000) determined that IOR can be observed at five locations concurrently.  Again, their data supported previous findings that IOR has the greatest magnitude at the most recently cued location and smaler magnitudes at less recently cued locations (se also Snyder & Kingstone, 2001, 2007). Having established that multiple locations can be concurrently inhibited, much of the recent research has focused on multiple locations IOR and its utility in visual search. For instance, using "Where's Waldo?" scenes in a search task, Klein and MacInnes (1999) were the first to demonstrate that IOR operates as a foraging factor in an ecologicaly valid orienting paradigm.  Eye movements were tracked as observers searched for Waldo.  After several eye movements were made, a target probe to which the observer made an eye movement was   10 presented at previously inspected or uninspected locations.  Slower eye movements were made to probes presented at previously inspected locations, which indicated the presence of IOR.  More recently, Thomas et al. (2006) used a 3-D virtual foraging task to mimic visual search employed by real life search tasks.  In this simulation, leaves on a tree served as the stimuli that participants could flip up to se if a piece of fruit was underneath by pointing a virtual wand at a leaf.  If the fruit was not found after a specified number of atempts, one of the leaves flickered (i.e., the probe) and participants were required to detect this event with a key pres. The probe could be at one of the previously inspected leaves/locations or one of the uninspected leaves/locations.  And indeed, IOR was observed at two of the previously inspected locations concurrently in this ecologicaly valid virtual foraging task, providing evidence that IOR can serve as a foraging factor as proposed by Klein & MacInnes (1999).   Further research conducted by Snyder and Kingstone (2007) investigated the role of atention on the magnitude of IOR in visual search using a combined visual search and multiple-location IOR paradigm.  Here, four cues preceded onset of an eight-item visual search display that contained one of two target leters.  In the feature search display, the seven distractor leters were identical, whereas in the conjunction search display, the seven distractor leters were al unique.  And while they found multiple-location IOR for both feature and conjunction search, IOR was greater and more robust in conjunction than in feature search, corresponding to the higher atentional demands of conjunction search.  And most recently, a study by Dodd, Van der Stigchel, and Hollingworth (2009) confirmed that IOR is specific to visual search and does not extrapolate to general visual (i.e., non-search) behaviour.  Specificaly, the authors found that participants exhibited IOR when they were required to search for a target item in a display (i.e.,   11 in a visual search task), but not for tasks requiring pleasantnes ratings, subsequent memory recal, or simply free viewing of a scene. Attentional IOR Early on, there were two opposing explanations regarding how IOR was generated.  Initialy, it was proposed that IOR was an atentional efect (Posner & Cohen, 1984).  Shortly thereafter, this proposal was countered by the suggestion that IOR was an oculomotor efect (Rafal, Calabresi, Brennan, & Sciolto, 1989).  The evidence supporting an atentional component of IOR wil be examined first followed by evidence supporting an oculomotor component of IOR. When it was discovered, the inhibitory efect at long cue-target intervals (i.e., IOR) was described as a function of atention that was similar to the previously described facilitation efect observed at short cue-target intervals.  Specificaly, IOR was postulated to occur as a result of covert atentional orienting (Posner et al., 1985) – when atention is reflexively captured by a peripheral cue and subsequently disengaged, atention is then inhibited from returning to the previously atended location (Posner & Cohen, 1984).  Importantly, although atention has been linked to eye movements, both the facilitatory and inhibitory effects can occur when the eyes remain fixated at centre, in the absence of eye movements (Posner, 1980). Klein (1988) was the first to demonstrate that IOR is an atentional efect by having observers perform two visual search tasks where they searched for a target amongst distractor items.  In a conjunction search task, two features define the target (e.g., shape and colour) and atention must be systematicaly alocated to items in the display to for succesful target detection.  In a feature search task, a single feature defines the target (e.g., shape) and atention is not required for succesful target detection as the target "pops out."  On half of the trials, after observers completed the search task, a probe dot requiring detection was presented in a location   12 previously occupied by a distractor.  Klein posited that IOR would be found following conjunction search as the result of atention being alocated to distractor locations, but not following feature search where atention was not alocated to distractor locations.  And that is exactly what he found, concluding that IOR facilitates complex search (se also Müller & von Mühlenen, 2000; Takeda & Yagi, 2000).   Direct evidence for the atentional component of IOR comes from a study by Reuter-Lorenz, Jha, and Rosenquist (1996).  In a series of experiments, manipulation of factors known to influence atentional proceses were applied to IOR paradigm to establish the underlying mechanisms and atentional contribution to IOR.  These factors included target modality (i.e., visual and auditory) and target intensity (i.e., dim and bright).  Importantly, the factor of response modality (i.e., manual and oculomotor), should not afect IOR as it is a motor, rather than an atentional, factor.  The previous findings from the atention studies held true for IOR.  That is, the magnitude of the IOR efect did not difer for manual and oculomotor responses but it was greater for visual than auditory targets and it was greater for dim than bright targets. Because IOR was afected by the same factors and in the same way that atentional proceses were afected, Reuter-Lorenz et al. concluded that IOR is primarily an atentional efect. And finaly, indirect evidence for an atentional acount of IOR was demonstrated by Lupiáñez, Milán, Tornay, Madrid, and Tudela (1997).  They examined acuracy and RT in a target detection task and in a target discrimination task.  As expected, IOR was found consistently in both detection and discrimination tasks.  Additionaly, IOR was found in measures of response acuracy with greater acuracy at cued than uncued locations.  Atention is known to afect acuracy rates in exactly that manner.  Thus, the authors argued that if IOR was   13 not an atentional efect, acuracy would not have been affected, but because it was, IOR must have an atentional component. Taken together, these findings demonstrate the existence of a strong atentional basis of exogenously-produced IOR.  It follows that both facilitation and inhibition can be described as functions of covert atentional orienting as put forward by Posner and Cohen (1984).   Oculomotor IOR In an early review of the cognitive inhibition of atention, Klein and Taylor (1994) questioned the view that IOR was primarily an atentional efect.  An important piece of evidence for this chalenge came from a study by Posner et al. (1985) that failed to find IOR in patients with lesions of the superior colliculus (SC), a midbrain oculomotor structure responsible for the generation of reflexive eye movements.  Further evidence came from Rafal et al.'s (1989) investigation of IOR where: (1) the eyes remained at fixation throughout the trial; (2) eye movements were executed to a peripheral cue and back to centre; and (3) eye movements were prepared to the cued location but not executed.  When exogenous cues (i.e., abrupt onsets in the periphery) were used, IOR was found with both overt and covert atentional orienting, but when endogenous cues (i.e., directional arrows at fixation) were used, IOR was found with overt but not covert atentional orienting.  This finding held true even when an eye movement was prepared but not executed.  The authors concluded that the activation of the oculomotor system is not only necesary, but it is sufficient to generate IOR.  Once generated by the oculomotor system, IOR may then operate by biasing covert atentional orienting away from the inspected location.  They concluded that in endogenous versions of the paradigms covert atentional orienting does not activate the oculomotor system, and thus IOR cannot be found.   14 However, a recent study by Chica, Klein, Rafal, and Hopfinger (2009) failed to replicate Rafal et al.'s (1989) finding that eye movement preparation is necesary and sufficient to generate IOR.  In this modification of Rafal et al.'s (1989) earlier experiment, participants had to make an eye movement to the "prepared" location, even when the target did not appear at that location.  Failure to replicate Rafal et al.'s (1989) findings suggested that endogenous sacade preparation is not sufficient for the generation of oculomotor IOR, and supported Klein and Taylor's (1994) proposal that diferent mechanisms underlie diferent manifestations of IOR.  Specificaly, Chica et al. (2009) suggest that the mechanisms difer for atentional and oculomotor IOR. More direct evidence for oculomotor IOR comes from a study of a patient who had suffered a hemorrhagic lesion to the right SC leaving the left SC intact, which alowed for a comparison of IOR generated by the right and left SC, respectively (Sapir, Soroker, Berger, & Henik, 1999).  Using a modified version of the atentional orienting paradigm, stimuli were presented monocularly to the patient to measure IOR in the temporal and nasal visual hemifields of each eye, separately.  In this patient, the damaged right SC received projections from the temporal hemifield of the left eye and the nasal hemifield of the right eye, whereas the intact left SC received projections from the temporal hemifield of the right eye and nasal hemifield of the left eye.  The authors predicted that IOR would not be generated by the damaged right SC to stimuli presented to the temporal hemifield of the left eye and nasal hemifield of the right eye, but that it would be generated in a typical fashion by the intact left SC to stimuli presented to the temporal hemifield of the right eye and nasal hemifield of the left eye.  Indeed, this is what they found, supporting the involvement of the SC in the generation of IOR and confirming an oculomotor component of IOR.    15 Towards a Combined View of Attentional and Oculomotor Contributions While early research suggested that IOR was either an atentional efect (e.g., Posner & Cohen, 1984; Reuter-Lorenz et al., 1996), or an oculomotor efect (e.g., Klein & Taylor, 1994; Rafal et al., 1989), recent research converges on the joint contributions of atentional and oculomotor components to IOR (e.g., Hunt & Kingstone, 2003; Chica, Taylor, Lupiáñez, & Klein, 2010; Klein & Taylor, 1994).  Specificaly, it is now proposed that diferent mechanisms may underlie diferent manifestations of IOR. When examining the atentional component of IOR and its relation to eye movements, Abrams and Dobkin (1994) demonstrated that atentional IOR but not oculomotor IOR moves with the atended-to object.  This finding suggests that atention precedes eye movements in IOR, and has since been replicated (Abrams & Prat, 2000; Hoffman & Subramaniam, 1995).  More recently, Hunt and Kingstone (2003) advocated the view that diferent response modalities (i.e., manual and oculomotor) generate diferent forms of IOR, rather than being merely an atentional efect as Reuter-Lorenz et al. (1996) posited. Hunt and Kingstone (2003) suggested that manual responses, which engage covert atentional orienting because eyes remain at central fixation, should produce atentional IOR.  On the other hand, oculomotor responses, which engage overt atentional orienting because an eye movement to the target is executed, should produce oculomotor IOR.  This hypothesis was supported by the succesful replication of Reuter-Lorenz et al.'s (1996) finding that target intensity interacted with IOR only with manual but not oculomotor responses.  In addition, in an atempt to replicate Abrams and Dobkin's (1994) finding that the fixation offset efect (FOE), which is an efect related to the SC, Hunt and Kingstone (2003) found that the FOE interacts with oculomotor but not manual responses.  Thus, these authors succesfully demonstrated a double disociation betwen the atentional and   16 oculomotor components of IOR.  That is, while oculomotor efects interacted with oculomotor IOR, atentional efects interacted with atentional IOR, but not vice versa.  This disociation of IOR acording to response modality suggests that atentional and oculomotor IOR occur under diferent circumstances and reconciles the two explanations of IOR. Moreover, when Briand, Larrison, and Sereno (2000) examined the time course of manual and oculomotor responses, they found greater facilitation for manual responses than for oculomotor responses.  That is, facilitation efects lasted longer for manual responses, whereas IOR was generated faster for oculomotor responses.  Further, the authors found an overlap in the time course of IOR generation where manual responses were facilitated, while oculomotor responses were inhibited.  This finding strongly suggests that IOR has both an atentional and an oculomotor component and that they can operate somewhat independently. And lastly, Chica et al. (2010) investigated the atentional and oculomotor components of IOR in a spatial detection task and in a non-spatial discrimination task.  Specificaly, they compared detection and discrimination tasks in which eye movements were either required – to assess oculomotor IOR – or prevented – to ases atentional IOR.  Robust IOR was found in the spatial detection tasks regardles of whether or not the eyes moved.  Robust IOR was also found in the non-spatial discrimination task when the eyes did not move.  However, when the eyes moved, although IOR appeared to be evident in RT (i.e., slower RT at cued than uncued locations), a facilitation efect was observed in acuracy (i.e., greater acuracy for cued than uncued locations) which revealed that a shift in criterion, rather than IOR, was underlying the effect.  Indeed, when this speed-acuracy trade-off was controlled for, oculomotor IOR was absent in the discrimination task.  Importantly, when oculomotor IOR was generated, there was no deficit in atentional IOR, supporting the view of independent contributions of the atentional   17 and oculomotor components to IOR.  Preventing eye movements generated atentional, but not oculomotor IOR, while requiring eye movements generated oculomotor, but not atentional IOR.  Therefore, the authors suggest that either oculomotor or atentional IOR is at play depending on the activation or inhibition of the oculomotor system.   Research Question While atentional and oculomotor components of IOR have been examined in studies employing the typical atentional orienting paradigm with two locations, only the atentional component of IOR has been established and confirmed in multiple location IOR paradigms (Danziger et al., 1998; Snyder & Kingstone, 2000, 2001). The goal of this experiment was to establish whether there is also an oculomotor component to IOR when multiple locations are cued in succesion. And if there is an oculomotor component, whether it co-occurs at al cued locations, or only at the most recently cued location.  It may be the case that oculomotor IOR only occurs at the most recently cued location, because the SC, which is responsible for the control of reflexive eye movements is believed to be capable of coding for a single eye movement (Posner et al., 1985; Rafal et al., 1989).  These questions wil be investigated using a six-location paradigm where three succesive exogenous cues are followed by a central re-fixation event prior to target onset.  First, atentional IOR wil be measured via covert orienting to the cues (i.e., participants wil keep their eyes at a central fixation stimulus).  Second, oculomotor IOR wil be measured via overt orienting to the cues (i.e., participants wil make an eye movement to each cued location).  Oculomotor IOR wil be determined by subtracting the atentional IOR generated via covert orienting from the oculomotor and atentional IOR generated via overt orienting.  Participants' eyes wil be monitored to ensure that eyes remain at fixation – covert orienting, and that eyes moved to each of the cued locations – overt orienting.    18 Finaly, given that eye movements have never been monitored in a multiple location paradigm, it may be the case that previous asesments of atentional multiple location IOR may have been inflated IOR effects as a result of inadvertent eye movements.  Thus, eye movement monitoring wil alow for such an asesment. Finding oculomotor IOR for multiple locations would contribute to the evidence aserting the importance and utility of IOR in visual search.  When we search our environment, not only atention, but also eye movements are deployed.  If there is an oculomotor component to IOR, the question remains whether oculomotor and atentional components are additive, because both atentional and oculomotor IOR are at play during overt atentional orienting (Hoffman & Subramaniam, 1995), or whether atentional and oculomotor components are mutualy exclusive, depending on the activation or inhibition of the oculomotor system (Chica et al., 2010).   Firstly, given that overt orienting to an exogenous cue would produce an additive efect of the atentional and oculomotor components, a greater IOR efect should be found for overt than for covert atentional orienting.  Specificaly, if there is an oculomotor component to multiple location IOR, and if it is evident at al cued locations, the IOR efect would be expected to be greater for overt orienting than for covert orienting for al cued locations.  If the oculomotor component is only evident at the most recently cued location, as suggested by the limited capacity of the SC, the IOR efect would be expected to be greater for overt orienting than for covert orienting only at the most recently cued location, but equal for al other cued locations at which only atentional IOR is generated.   Secondly, if the atentional and oculomotor components are mutualy exclusive, IOR efects of a similar size should be found for overt orienting and covert orienting.  If oculomotor IOR is evident at al cued locations, IOR efects for overt orienting and covert orienting should   19 be equal across al cued locations.  Again, if oculomotor IOR is evident at the most recently cued location only, the IOR efect for overt orienting would be smaler than for covert orienting at the most recently cued location, and equal across al other cued locations.  However, given that atention precedes eye movements (Hoffman & Subramaniam, 1995), a delay in the generation of oculomotor IOR should be found.  That is, oculomotor IOR should be smaler than atentional IOR at the most recently cued location, and comparable in size to the previous cued location of the atentional IOR efect. Method Participants.  Forty-one experimentaly naïve undergraduate university students (30 female, 11 male; mean age 19 years, SD = 1.83) participated for course credit.  Al participants had normal or corrected-to-normal vision. Aparatus and stimuli.  The stimulus display was presented on a 43 cm computer screen.  On a black background, six rectangular, grey figure eights measuring .5° × 1° of visual angle (va) were arranged in an imaginary circle (8.5° va radius) around a central figure eight.  Cueing was achieved by superimposing a white figure eight over the grey figure eight, which created a brightening efect.  The target stimulus was a white square (.3° va × .3° va).  A video camera was afixed to the top or bottom of the computer screen to ensure participants' compliance regarding eye position. Procedure.  Participants were seated at a distance of 57 cm in front of a computer screen.  At the start of a trial, participants were instructed to fixate the central figure eight.  A 100 ms warning tone indicated the start of a trial.  At 1000 after the onset of the tone, three diferent peripheral figure eights and then the central figure eight were brightened in succesion. Following the final central cue, a target appeared in any of the six peripheral figure eights until a   20 response was executed via a key pres or for 1000 ms, whichever came first.  On catch trials, where there was no target, the trial timed out after 1000 ms.  All cue durations were 500 ms and all stimulus onset asynchronies (SOAs) betwen succesive cues and the final central cue and the target were 1250 ms (se Figure 1).   Figure 1.  Sequence of events on a trial. In this example, the target apears at the first location that was cued. See text for timing details.  In the overt orienting trials, participants were instructed to move their eyes to each peripheral cue as quickly as possible and keep their eyes there until the next cue appeared.  When the next cue occurred, they were to move their eyes to that cue and so on until finaly returning their eyes to the central figure eight.  In the covert orienting trials, they were instructed to keep their eyes fixated on the central figure eight throughout each trial.  For both orienting   21 instructions, participants were informed that the peripheral cues were not predictive of target location.  Finaly, they were instructed to pres the space bar on the keyboard in front of them as quickly and as acurately as possible upon target detection.  A brief error tone, distinct from the warning tone, sounded when an error occurred. Al participants received both overt and covert orienting instructions in separate blocks of trials. Design.  Both types of orienting (i.e., overt and covert) were completed during the same one-hour sesion and were counterbalanced across participants.  For each type of orienting, participants received 15 practice trials followed by five blocks of 35 trials, resulting in a total of 175 trials.  In each block, there were 25 trials in which the target occurred at each of the 1st, 2nd, and 3rd cued locations, 75 trials in which the target occurred randomly at one of the uncued locations, and 25 catch trials in which the target was absent.  Cue locations were randomly selected with the caveat that each location could only be cued once on the same trial.  The inter-trial interval was 1000 ms.  Participants were instructed to take a break betwen blocks of trials as desired. Results Of the 41 participants in this study, eight were tested without video monitoring.  Data from three participants were excluded due to a response acuracy of les than 90%.  Overal acuracy was 96.1%.  Errors were false alarms (responding before target appearance; 2.5%), mises (failure to respond to the target; 1.6%), or anticipatory responses (responding within 150 ms of target appearance; < 1%).  Before proceding with the analyses, it is crucial to clarify the terminology used for describing target location.  If the target appeared at the most recently cued location, it was a cued 1-back trial, because it occurred at the location that was one cue back from target onset.  If the   22 target appeared at the second cued location, it was a cued 2-back trial, because it occurred two cues back from target onset.  If the target appeared at the first cued location, it was a cued 3-back trial, because it occurred three cues back from target onset.  Finaly, if the target appeared at one of the locations that had not been cued, it was an uncued trial. RT data.  A mixed analysis of variance (ANOVA) was conducted on mean correct RT with video monitoring (present, absent), order (overt first-covert second, covert first-overt second) as betwen-subjects factors, and target location (cued 1-back, cued 2-back, cued 3-back, uncued) and orienting (overt, covert) as the within-subjects factors to determine whether there were any RT diferences as a function of video monitoring.  The analysis revealed no statisticaly significant main efect or interactions involving video monitoring (all Fs < 3.73, al ps > .06).  Therefore, this factor was collapsed across and a second mixed ANOVA was conducted on mean correct RT to determine whether the order in which the overt and covert orienting instructions was administered matered.   Although there was no statisticaly significant main efect of order on RT, all of the interactions involving order were statisticaly significant: order × orienting, order × target location, and order × orienting × target location (all Fs > 2.73, al ps < .05).  The interactions revealed that the RT data across target location varied as a function of order as ilustrated in Figure 21.  Specificaly, when overt orienting was administered first, the RT patern was atypical, with no statisticaly significant diferences in RT at any of the target locations and hence, no IOR.  When covert orienting was administered first, RTs followed a more typical patern with reliable IOR found at the cued 1- and 2-back locations but not found at the cued 3-back location.                                                   1 These findings are consistent with participants' unsolicited reports that moving from the overt orienting trials to the covert orienting trials was dificult. They are further suported by an analysis of the accuracy data that revealed that participants who completed overt orienting first responded significantly more acurately on overt than the covert trials, t(94) = 2.5, p < .05.  In contrast, participants who completed covert orienting first responded equivalently on overt than the covert trials, t(94) = -1.98, p > .05.   23 Because of these order efects, it was necesary to conduct a mixed ANOVA with orienting as a betwen-subjects factor and target location as a within-subjects factor.  Thus, only the data collected with the first set of orienting instructions was analyzed.  Results showed a statisticaly significant main efect of target location, F(3, 108) = 8.41, p < .001, with planned contrasts revealing IOR at the cued 1- and 2-back locations (all Fs > 16 2 decimal places needed, all ps < .001) but not at the cued 3-back location, F(1, 108) = 2.61, p > .1.  Figure 2. Mean correct RT as a function of target location and order of orienting.  IOR data.  A second mixed ANOVA on IOR efects (e.g., cued 1-back – uncued) with orienting as betwen-subjects factor and target location as within-subjects factor also revealed a statisticaly significant main efect of target location, F(2, 72) = 3.95, p < .05. Planned contrasts revealed no statisticaly significant diferences in IOR betwen the cued 1- and 2-back locations, F(1, 72) = .04, p = .9.  However, IOR was statisticaly significantly greater for the cued 1- and 2-back locations than for the cued 3-back location, F(1, 72) = 7.87, p < .01.  Neither the main efect of orienting nor the target location × orienting interaction were statisticaly significant (all 400 410 420 430 440 450 460 470 480 490 500 overt 1st covert 1st RT (ms) Order of Orienting cued 1-back cued 2-back  cued 3-back uncued   24 Fs < 2, al ps > .2) indicating that IOR did not vary as a function of orienting.  A visual inspection of the data hints at the possibility of an alternative story (see Figure 3).     Figure 3. Mean IOR efects as a function of target location and type of orienting.   Acuracy data.  A mixed design ANOVA was conducted on the acuracy data with orienting (overt, covert) as a betwen-subjects factor and trial type (cued 1-, 2-, 3-back, uncued, catch) as factors. This analysis revealed no statisticaly significant main efects or interactions (al Fs < 1.2, al ps > .33).  Discusion The purpose of this experiment was to determine whether there is an atentional and an oculomotor component to IOR when multiple locations are cued in succesion, and if so, whether IOR co-occurs at al cued locations or only at the most recently cued location and whether the atentional and oculomotor components are additive or mutualy exclusive.  Although IOR did not statisticaly difer across orienting instructions, the conclusion that oculomotor IOR does not 0 5 10 15 20 25 30 35 overt covert IOR Effect (ms) Orienting cued 1-back cued 2-back cued 3-back   25 exist in a multiple location paradigm cannot be drawn for several reasons.  First, although there were no statistically significant diferences in IOR across orienting, visual inspection of the data in Figure 3 is suggestive that IOR efects arising from overt and covert orienting may in fact be diferent and that perhaps with more statistical power, these diferences would emerge.  Specificaly, with overt orienting, the IOR efects follow an atypical patern of results with the greatest magnitude of IOR found at the cued 2-back rather than at the cued 1-back location with the smalest efect at the more typical cued 3-back location.  This finding suggests that IOR may take longer to develop when eye movements must be executed to the cue.  Indeed, under covert orienting, atention may leave the cued location faster, while under overt orienting, the eyes and presumably atention remain at the cued location until the next cue occurs – more than a full second later.  Therefore, rather than being greater than atentional IOR, oculomotor IOR may merely develop more slowly.   This finding is in line with the proposition that atentional and oculomotor IOR are mutualy exclusive, rather than additive. In agreement with Chica et al.'s (2010) finding, it appears that oculomotor IOR did not impair atentional IOR.  The data revealed that oculomotor IOR at the cued 2-back location was greater than atentional IOR at that same location when directly comparing the two.  However, if there is simply a lag in the development of oculomotor IOR, the cued 2-back location for oculomotor IOR should be comparable to the cued 1-back location for atentional IOR.  Indeed, this sems to be the case (M = 24 ms for cued 2-back oculomotor vs. 25 ms for cued 1-back atentional).  Further, if oculomotor IOR develops more slowly, it may be the case that it is stil building at the cued 2-back location, and the mean may approach the mean for cued 1-back atentional IOR even more closely.  As previous research has demonstrated, atention precedes eye movements (Abrams & Dobkin, 1994; Hoffman &   26 Subramaniam, 1995), and atentional IOR precedes oculomotor IOR (Rafal et al., 1994).  Additionaly, for covert orienting, despite following a typical patern, the IOR efect at the cued 3-back location was almost eliminated. Second, there was a trend for greater IOR efects for overt orienting, suggesting that oculomotor IOR occurs when the multiple location IOR paradigm is used and that the atentional and oculomotor components may be additive.  Third, a major limitation to this experiment was that eye position was only monitored via video cameras and eye position could not be observed in real-time.  That is, there was no way of ensuring that participants followed the orienting instructions either overtly – moving to and staying at the cued location until the next cue appeared – or covertly – fixating centre throughout the trial.  This uncertainty with respect to eye position does not alow for a definite conclusion with respect to oculomotor IOR. Surprisingly, the data revealed an atypical patern of atentional IOR.  Although previous research has repeatedly shown that IOR robustly occurs at up to five locations in an exogenous atentional orienting paradigm (Snyder & Kingstone, 2000; 2001), this was not the case in the present study, as IOR was not observed at the cued 3-back location when eyes remained at fixation.  However, it may be the case that SOAs were simply too long for IOR to stil be present at the cued 3-back location.  With 1250 ms SOAs, the cued 3-back location occurred 5000 ms before target onset – wel beyond the tested limits of multiple location IOR using a short cue duration.  Thus, this time period may simply be too long to maintain IOR. Moreover, again, it is possible that participants did not follow orienting instructions, and did not keep their eyes at fixation, or perhaps they did and atentional IOR does not co-occur for more than two locations – only further research wil tel.    27 Conclusion and Future Directions  Overal, a trend towards a statisticaly significant diference betwen oculomotor and atentional IOR emerged in this experiment.  In particular, this trend manifested as a delayed development of oculomotor IOR as compared to atentional IOR.  Modifications to the experimental design are necesary in order to confirm this trend.  Specificaly, this design revealed two major limitations that suggest a basis for modification.  First, and most importantly, to make valid conclusions about the oculomotor component of IOR, there is a need to replicate this experiment using an eye tracker to ensure that orienting instructions are followed.  Second, it sems advisable to implement the experiment as a betwen-subjects rather than a repeated measures design to eliminate order efects.     28 References Abrams, R. A., & Dobkin, R. S. (1994). Inhibition of return: Efects of atentional cuing on eye movement latencies.  Journal of Experimental Psychology: Human Perception and Performance, 20(3), 467-477. doi: 10.1037/0096-1523.20.3.467 Abrams, R. A., & Prat, J. (1996). Spatialy difuse inhibition afects multiple locations: A reply to Tipper, Weaver, and Watson (1996). Journal of Experimental Psychology: Human Perception and Performance, 22(5), 1294-1298. doi: 10.1037/0096-1523.22.5.1294 Abrams, R. A., & Prat, J. (2000). Oculocentric coding of inhibited eye movements to recently atended locations. Journal of Experimental Psychology: Human Perception and Performance, 26(2), 776-788. doi: 10.1037//0096-1523.26.2.776 Briand, K. A., Larrison, A. L., & Sereno, A. B. (2000). Inhibition of return in manual and sacadic response systems. Perception & Psychophysics, 62(8), 1512-1524. Retrieved from http:/app.psychonomic-journals.org/ Chica, A. B., Klein, R. M., Rafal, R. D., & Hopfinger, J. B. (2009). Endogenous sacade preparation does not produce inhibition of return: Failure to replicate Rafal, Calabresi, Brennan, & Sciolto (1989). Manuscript submited for publication. Chica, A. B., Taylor, T. L., Lupiáñez, J., & Klein, R. M. (2010). Two mechanisms underlying inhibition of return. Experimental Brain Research, 201, 25-35. doi: 100.1007/s00221-009-2004-1 Danziger, S., Kingstone, A., & Snyder, J. J. (1998). Inhibition of return to succesively stimulated locations in a sequential visual search paradigm. Journal of Experimental Psychology: Human Perception and Performance, 24(5), 1467-1475. doi: 10.1037/0096-1523.24.5.1467   29 Dodd, M. D., Van der Stigchel, S., & Hollingworth, A. (2009). Novelty is not always the best policy. Psychological Science, 20(3), 333-339. doi: 10.1111/j.1467-9280.2009.02294.x Eriksen, C. W., & Hoffman, J. E. (1973). The extent of procesing of noise elements during selective encoding from visual displays. Perception & Psychophysics, 14(1), 155-160. Retrieved from http:/app.psychonomic-journals.org/ Hoffman, J. E., & Subramaniam, B. (1995). The role of visual atention in sacadic eye movements. Perception & Psychophysics, 57(6), 787-795. Retrieved from http:/app.psychonomic-journals.org/ Hunt, A. R., & Kingstone, A. (2003). Inhibition of return: Disociating atentional and oculomotor components. Journal of Experimental Psychology: Human Perception and Performance, 29(5), 1068-1074. doi: 10.1037/0096-1523.29.5.1068 Kingstone, A., & Prat, J. (1999). Inhibition of return is composed of atentional and oculomotor proceses. Perception & Psychophysics, 61(6), 1046-1054. Retrieved from http:/app.psychonomic-journals.org/ Klein, R. M. (1988). Inhibitory tagging system facilitates visual search. Nature, 334(4), 430-431. doi: 10.1038/334430a0 Klein, R. M. (2000). Inhibition of return. Trends in cognitive Sciences, 4(4), 138-147. doi: 10.1016/S1364-6613(00)01452-2 Klein, R. M., & MacInnes, W. J. (1999). Inhibition of return is a foraging facilitator in visual search. Psychological Science, 10(4), 346-352. doi: 10.1111/1467-9280.00166 Klein, R. M., & Taylor, T. L. (1994). Categories of cognitive inhibition with reference to atention. In D. Dagenbach & T. H. Carr (Eds.), Inhibitory proceses in attention, memory, and language (pp. 113-150). San Diego, CA: Academic Pres.   30 Lupiáñez, J., Milán, E. G., Tornay, F. J., Madrid, E., & Tudela, P. (1997). Does IOR ocur in discrimination tasks? Yes, it does, but later. 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