Vision Research 44 2004 1193 1207 www elsevier com locate visres The footprints of visual attention during search with 100 valid and 100 invalid cues Miguel P Eckstein Binh T Pham Steven S Shimozaki Vision and Image Understanding Laboratory Department of Psychology University of California Santa Barbara CA 93106 USA Received 26 August 2003 received in revised form 9 October 2003 Abstract Human performance during visual search typically improves when spatial cues indicate the possible target locations In many instances the performance improvement is quantitatively predicted by a Bayesian or quasi Bayesian observer in which visual attention simply selects the information at the cued locations without changing the quality of processing or sensitivity and ignores the information at the uncued locations Aside from the general good agreement between the effect of the cue on model and human performance there has been little independent confirmation that humans are effectively selecting the relevant information In this study we used the classification image technique to assess the effectiveness of spatial cues in the attentional selection of relevant locations and suppression of irrelevant locations indicated by spatial cues Observers searched for a bright target among dimmer distractors that might appear with 50 probability in one of eight locations in visual white noise The possible target location was indicated using a 100 valid box cue or seven 100 invalid box cues in which the only potential target locations was uncued For both conditions we found statistically significant perceptual templates shaped as differences of Gaussians at the relevant locations with no perceptual templates at the irrelevant locations We did not find statistical significant differences between the shapes of the inferred perceptual templates for the 100 valid and 100 invalid cues conditions The results confirm the idea that during search visual attention allows the observer to effectively select relevant information and ignore irrelevant information The results for the 100 invalid cues condition suggests that the selection process is not drawn automatically to the cue but can be under the observers voluntary control 2004 Elsevier Ltd All rights reserved 1 Introduction A common finding in visual search is that human performance measured either with response times or accuracy improves when a spatial cue indicates the probable location of the target Baldassi Verghese 2002 Eckstein 1998 Eckstein Thomas Palmer Shimozaki 2000 Foley Schwarz 1998 Palmer 1994 Palmer Ames Lindsey 1993 Posner 1980 Solomon Lavie Morgan 1997 Verghese 2001 Verghese Stone 1995 This result has been interpreted by some as suggesting that the cue allows the observer to allocate attentional resources to a single location rather than distribute them across many locations and therefore enhances processing at that cued attended location e g Bashinski Bacharach 1980 Downing 1988 Corresponding author E mail address eckstein psych ucsb edu M P Eckstein URL http www psych ucsb edu eckstein lab vp html 0042 6989 see front matter 2004 Elsevier Ltd All rights reserved doi 10 1016 j visres 2003 10 026 Hawkins et al 1990 Luck Hillyard Mouloua Hawkins 1996 However another hypothesis is that when the target is presented among visually similar distractors the presence of a 100 valid cue can benefit performance by allowing the observer to ignore potentially confusable distractors This benefit due to selection is expected even without considering limited attentional resources This concept has been formalized by the theory of signal detection Green Swets 1966 In this theory each element target and distractors elicits an internal response within the observer that is subject to noise A distractor might be confused for the target because it occasionally elicits a stronger response than the target In this context attention improves performance by allowing the observer to select responses from the relevant cued location and to ignore noisy responses arising from irrelevant noise locations that would otherwise bring additional unnecessary variability into the decision But how much improvement is expected in human performance based on these principles One sensible 1194 M P Eckstein et al Vision Research 44 2004 1193 1207 starting point is to compare humans to an observer that optimally uses the cue to perform the task the Ideal Bayesian observer The optimal observer uses all prior information about the data including that provided by the cue to calculate the posterior probability of the various hypotheses considered e g signal present vs signal absent for a yes no task interval location 1 vs interval location 2 for a 2 interval alternative forced choice and chooses the hypothesis with the highest posterior probability The posterior probability is calculated as the product of the likelihood of the data given the hypothesis and the prior probability In some cases e g yes no task in one of M locations the Bayesian observer decision rules are non linear cannot be calculated using closed form expressions and require Monte Carlo computer simulations Because running these simulations used to be time consuming given the available computer power historically investigators have used other models that can be computed from closed form expressions and are approximations to the optimal observer One commonly used model bases its decision on the maximum response among the considered responses max model In many instances the ideal Bayesian observer results in performance improvements of similar magnitude to the max model Many studies have used the set size effects predicted by the maximum model to compare to human performance In many situations the set size effects in human observers are comparable to that expected from this attentional selection model Baldassi Verghese 2002 Eckstein 1998 Palmer et al 1993 Solomon et al 1997 Verghese 2001 In other instances where the tasks involve more complex judgments Poder 1999 memory or a rapid temporal sequence of two possibly conflicting cues Dosher Lu 2000a Lu Dosher 2000 the set size effects present in humans were larger than predicted by these models Carrasco Williams Yeshurun 2002 Dosher Lu 2000b Poder 1999 A fundamental assumption of both the optimal Bayesian observer and maximum response observer is that for 100 valid cues humans can perfectly select the information at the relevant cued location and ignore the information at the
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