Search time critically depends on irrelevant subset size in visual search

• Published in: Vision research (Oxford) Vol. 49; no. 3; pp. 398 - 406
• Main Authors: Benjamins, Jeroen S., Hooge, Ignace T.C., van Elst, Jacco C., Wertheim, Alexander H., Verstraten, Frans A.J.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.02.2009; Elsevier
• Subjects: Attention; Attention - physiology; Biological and medical sciences; Eye and associated structures. Visual pathways and centers. Vision; Eye movements; Field Dependence-Independence; Fixation, Ocular - physiology; Fundamental and applied biological sciences. Psychology; Humans; Pattern Recognition, Visual - physiology; Photic Stimulation - methods; Psychophysics; Reaction Time; Saccades - physiology; Vertebrates: nervous system and sense organs; Visual search; Visual search; Attention; Eye movements; Eye movement; Vision
• ISSN: 0042-6989; 1878-5646
• DOI: 10.1016/j.visres.2008.11.007

In order for our visual system to deal with the massive amount of sensory input, some of this input is discarded, while other parts are processed [Wolfe, J. M. (1994). Guided search 2.0: a revised model of visual search. Psychonomic Bulletin and Review, 1, 202–238]. From the visual search literature it is unclear how well one set of items can be selected that differs in only one feature from target (a 1 F set), while another set of items can be ignored that differs in two features from target (a 2 F set). We systematically varied the percentage of 2 F non-targets to determine the contribution of these non-targets to search behaviour. Increasing the percentage 2 F non-targets, that have to be ignored, was expected to result in increasingly faster search, since it decreases the size of 1 F set that has to be searched. Observers searched large displays for a target in the 1 F set with a variable percentage of 2 F non-targets. Interestingly, when the search displays contained 5% 2 F non-targets, the search time was longer compared to the search time in other conditions. This effect of 2 F non-targets on performance was independent of set size. An inspection of the saccades revealed that saccade target selection did not contribute to the longer search times in displays with 5% 2 F non-targets. Occurrence of longer search times in displays containing 5% 2 F non-targets might be attributed to covert processes related to visual analysis of the fixated part of the display. Apparently, visual search performance critically depends on the percentage of irrelevant 2 F non-targets.