Collinear integration affects visual search at V1

Abstract

Perceptual grouping plays an indispensable role in figure-ground segregation and attention distribution. For example, a column pops out if it contains element bars orthogonal to uniformly oriented element bars. Jingling and Tseng (2013) have reported that contextual grouping in a column matters to visual search behavior: When a column is grouped into a collinear (snakelike) structure, a target positioned on it became harder to detect than on other noncollinear (ladderlike) columns. How and where perceptual grouping interferes with selective attention is still largely unknown. This article contributes to this little-studied area by asking whether collinear contour integration interacts with visual search before or after binocular fusion. We first identified that the previously mentioned search impairment occurs with a distractor of five or nine elements but not one element in a 9 × 9 search display. To pinpoint the site of this effect, we presented the search display with a short collinear bar (one element) to one eye and the extending collinear bars to the other eye, such that when properly fused, the combined binocular collinear length (nine elements) exceeded the critical length. No collinear search impairment was observed, implying that collinear information before binocular fusion shaped participants' search behavior, although contour extension from the other eye after binocular fusion enhanced the effect of collinearity on attention. Our results suggest that attention interacts with perceptual grouping as early as V1.

Invisible collinear structures impair search

“…In this experiment, we replicated the previous finding that search impairment was observable only with a collinear distractor equal to, or longer than, 5 elements (Chow et al, 2013) with the gradual appearance of search display.…”

“…Collinearity as illustrated in our collinear search impairment and other studies using collinear facilitation helps address the awareness question as (1) collinear information is reported to be consistent with the dynamics of long-range horizontal interactions within primary visual cortex (V1) (Cass & Alais, 2006), and (2) collinear search impairment operates at a monocular level (Chow et al, 2013) which is again a property of V1. In Chow et al (2013), different parts of the collinear distractor were presented to different eyes through a mirror stereoscope. It was found that search impairment was determined by the monocular distractor length -search impairment was not significant if the monocular distractor was too short, even when the binocular fused length was longer than the critical length.…”

“…Previous reports found that the length of a collinear distractor is critical to search impairment: the search performance for overlapping targets was significantly compromised only when the distractor is longer than 9 elements in a 21 Â 27 display or 5 elements in a 9 Â 9 display (Chow, Jingling, & Tseng, 2013). To establish the size effect baseline to be compared with subsequent experiments, the search display contained a collinear distractor of length 3, 5, or 9 element bars ( Fig.…”

Collinear masking effect in visual search is independent of perceptual salience

“…Not all salient items inform visual searching. Our previous studies revealed a complex interaction between salience and perceptual grouping by demonstrating that some types of salient structures hinder search (Chiu & Jingling, 2014Chow, Jingling, & Tseng, 2013Jingling, Tan, & Tseng, 2013;Jingling, Tseng, & Zhaoping, 2013;Tseng & Jingling, 2015). In these earlier studies, the search display was filled by horizontal bars, except for one salient and collinearly grouped column (Fig.…”

“…We recruited 20 participants, and this number was estimated from our previous studies that showed that about 10 to 15 participants were enough to obtain statistical power for our interest (Chiu & Jingling, 2014Chow et al, 2013;Jingling, Tan, & Tseng, 2013;Tseng & Jingling, 2015;Jingling, Tseng, & Zhaoping, 2013). All the participants had normal or corrected-to-normal vision according to self-reports.…”