The effect of crowding on orientation-selective adaptation in human early visual cortex

Abstract

Crowding is the identification difficulty for a target in the presence of nearby flankers. Based on psychophysical findings, many theories have been proposed to explain crowding at multiple levels. However, little is known about its neural mechanism. In this study, we combined psychophysical and fMRI adaptation techniques to search for the cortical locus of crowding. In the psychophysical experiment, when subjects' attention was controlled, we found that the threshold elevation aftereffect (TEAE) was not affected by crowding, regardless of the contrast level of adapting stimulus. In the fMRI experiment, the orientation-selective fMRI adaptation in V1 was not affected by crowding either. However, downstream from V1, we found that crowding weakened the adaptation effect in V2 and V3. Our results demonstrate that crowding occurs beyond V1 and provide one of the first pieces of direct evidence supporting the two-stage model of crowding (D. M. Levi, 2008).

Developmental changes during childhood in single-letter acuity and its crowding by surrounding contours

“…Recent evidence indicates that the locus of crowding occurs downstream beyond V1. For example, crowding modulates the functional magnetic resonance imaging (fMRI) BOLD signal in V2/V3 but not in V1 (Arman, Chung, & Tjan, 2006;Bi, Cai, Zhou, & Fang, 2009). Psychophysical evidence points to the involvement of area V4 (reviewed in Levi, 2008).…”

Perceptual Learning in Children With Infantile Nystagmus: Effects on Reading Performance

“…35 A probable candidate for the improvements of reading acuity and critical print size is better letter recognition due to enhanced sensory and/or attentional processing. Crowding is associated with enlarged responses in cortical areas V2 to V4, 36,37 and perceptual learning can reduce the size of visual receptive fields. 38 Our results support the hypothesis that enhanced sensory processing and attention are responsible for improved reading and vision in IN, because improvements in acuity and reductions in crowding were predictive of improvements in reading performance.…”

Contextual effects in human visual cortex depend on surface structure

“…The target location was always marked during both the adaptation and task periods to remove effects of location uncertainty on the detection task (Petrov et al 2006). To equate the attentional state across conditions, observers performed a contrast decrement task on the fixation mark during adaptation periods (Bi et al 2009). The contrast decrement (10%) was displayed for 150 ms, and the onset of the contrast decrement was selected randomly from a uniform distribution between 1 and 1.5 s. To quantify the amount of adaptation, we defined the threshold ratio between detection threshold before and after adaptation.…”