The roles of cortical image separation and size in active visual search performance

Abstract

Our previous research examined the effects of target eccentricity and global stimulus density on target detection during active visual search in monkey. Here, eye movement data collected from three human subjects on a standard single-color Ts and Ls task with varying set sizes were used to analyze the probability of target detection as a function of local stimulus density. Search performance was found to exhibit a systematic dependence on local stimulus density around the target and as a function of target eccentricity when density is calculated with respect to cortical space, in accordance with a model of the retinocortical geometrical transformation of image data onto the surface of V1. Density as measured by nearest neighbor separation and target image size as calculated from target eccentricity were found to contribute independently to search performance when measured with respect to cortical space but not with standard visual space. Density relationships to performance did not differ when target and nearest neighbor were on opposite sides of the vertical meridian, underscoring the hypothesis that such interactions were occurring within higher visual areas. The cortical separation of items appears to be the major determinant of array set size effects in active visual search.

The Effect of Aging and Attention on Visual Crowding and Surround Suppression of Perceived Contrast Threshold

“…An outer flanker would be closer to the target in cortical space than the inner flanker influencing target identification, although these distances in visual space are identical. 30 Petrov and Meleshkevich 21 identified the flanker asymmetry property as a characteristic that can be used to assist in disentangling the neural mechanism of crowding. They showed that the asymmetrical flanker effect can be eliminated by manipulating spatial attentional demands and interpreted this observation as evidence for an attentional mechanism contributing to the asymmetry effect.…”

“…Previous visual search experiments have used a range of stimulus types: for example, rectangular shapes, 32,33 circles and squares, 25 and letters T and L. 30 We used Gabor stimuli in our experiment to maintain similar low-level image content between all our tasks. Similar to previous literature, 25 we found a trend for the older group to require longer search times with increase in set size than the younger group (P ¼ 0.053).…”

Eye movement trajectories in active visual search: Contributions of attention, memory, and scene boundaries to pattern formation

“…During the last decade, definitive studies of the AC (or FVF) and its role in guiding eye movements and fixations have been conducted by Motter and his collaborators (Motter & Belky, 1998a, 1998bMotter & Holsapple, 2000, 2001Motter & Simoni, 2007, 2008. For a conclusive review, we can do no better than to refer to the study of Motter and Simoni (2008) in particular.…”

Saccade Target Selection in the Superior Colliculus: A Signal Detection Theory Approach

“…Because it is known that increasing the distance between targets and distractors can influence performance (Meinecke, 1989;Wolfe and O'Neill, 1998;Motter and Simoni, 2007), we reasoned that the variability in the monkeys' selection accuracy may result from differences in the location of the target relative to the fovea and relative to the other distractors. Because our stimulus configurations were constrained by the sites of electrode penetrations, we considered this possibility.…”