title: Selective manipulation of target identification demands in visual search: the role of stimulus contrast in CDA activations.
abstract: In classic visual pop-out search, response times are slowed remarkably when participants are required to precisely identify (e.g., vertical vs. horizontal orientation) as compared to simply localize (e.g., left vs. right position) a feature singleton target. This cost associated with stimulus identification has been recently proposed (Töllner, Rangelov, & Müller, 2012) to derive from the engagement of postselective recurrent processes that via feedback connections extract the information required for motor-response selection. Here, we examined whether the contralateral delay activity (CDA), an asymmetric neural marker generally assumed to reflect active maintenance of stimulus information in visual short-term memory (vSTM), may further index the degree of postselective processing requirements in visual search. Employing a compound-search task, we selectively manipulated the ease/difficulty of identifying the response-critical target orientation attribute (horizontal vs. vertical)--irrespective of the target-defining color feature (red vs. green)--by introducing different levels of stimulus-background contrast. As expected, we found a monotonic reaction time increase to be associated with gradually increasing CDA magnitudes as the stimulus contrast decreased. Thus, our findings provide direct evidence that CDA activations provide a useful tool to estimate the amount of postselective recurrent processing recruited to extract detailed object information from vSTM.
authors.affiliation: Department of Experimental Psychology, Ludwig-Maximilians-University, Munich, Germany. ttoellner@gmail.com
authors.forename: Thomas
authors.initials: T
authors.lastname: Töllner
authors.forename: Markus
authors.initials: M
authors.lastname: Conci
authors.forename: Tessa
authors.initials: T
authors.lastname: Rusch
authors.forename: Hermann J
authors.initials: HJ
authors.lastname: Müller
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology; D009949:Orientation; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology; D055815:Young Adult
keywords: attention; electroencephalography; recurrent processing; stimulus contrast