Crowding is the deleterious effect of nearby objects on object recognition in the peripheral (Pelli, 2008). In three visual search experiments the contribution of visual crowding to reaction time performance in an efficient search task was evaluated by varying the factors known to affect the strength of crowding: spacing between objects and similarity. Traditionally, pop-out search is believed to isolate the first stage of visual processing and has been characterized as producing shallow search slopes (<10 ms/item), which are independent of set size. Recent results from our lab suggest discrimination pop-out search has a logarithmic relationship between reaction time and set size, which is modulated by the lure-target similarity (Buetti et al., in press). These results have been interpreted as resulting from the first stage of visual processing that is exhaustive, unlimited-in-capacity and resolution limited. Items sufficiently dissimilar to the target are rejected by stage-one processing, and items sufficiently similar to the target are inspected with focused attention. Here we ask if the limitation in resolution in stage-one processing is a result of crowding and evaluate the contribution of crowding to our previous logarithmic search slope findings. In three experiments reaction time performance was compared on two possible display types which differed in the spatial arrangements. The results from three experiments converge on the same pattern of results: reaction times increased logarithmically with set size and were modulated by lure-target similarity for both display types.
efficient search, visual search, crowding
University of Illinois - Urbana-Champaign
Networked Digital Library of Theses and Dissertations
University of Illinois at Urbana-Champaign