Selective manipulation of target identification demands in visual search: the role of stimulus contrast in CDA activations

• Published in: Journal of vision (Charlottesville, Va.) Vol. 13; no. 3; p. 23
• Main Authors: Töllner, Thomas, Conci, Markus, Rusch, Tessa, Müller, Hermann J
• Format: Journal Article
• Language: English
• Published: United States 02-08-2013
• Subjects: Adult; Attention - physiology; Contrast Sensitivity - physiology; Female; Form Perception - physiology; Humans; Male; Memory, Short-Term - physiology; Orientation; Photic Stimulation; Reaction Time - physiology; Young Adult; recurrent processing; electroencephalography; attention; stimulus contrast
• ISSN: 1534-7362; 1534-7362
• DOI: 10.1167/13.3.23

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.