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1. chinaXiv:201605.01805 [pdf]

Attention-Dependent Early Cortical Suppression Contributes to Crowding

Chen, Juan; He, Yingchen; Zhu, Ziyun; Peng, Yujia; Zhang, Xilin; Fang, Fang; Chen, Juan; He, Yingchen; Zhu, Ziyun; Peng, Yujia; Zhang, Xilin; Fang, Fang; Fang, Fang; Fang, Fang; Zhou, Tiangang
Subjects: Biology >> Biophysics >> Neurosciences

Crowding, the identification difficulty for a target in the presence of nearby flankers, is ubiquitous in spatial vision and is considered a bottleneck of object recognition and visual awareness. Despite its significance, the neural mechanisms of crowding are still unclear. Here, we performed event-related potential and fMRI experiments to measure the cortical interaction between the target and flankers in human subjects. We found that the magnitude of the crowding effect was closely associated with an early suppressive cortical interaction. The cortical suppression was reflected in the earliest event-related potential component (C1), which originated in V1, and in the BOLD signal in V1, but not other higher cortical areas. Intriguingly, spatial attention played a critical role in the manifestation of the suppression. These findings provide direct and converging evidence that attention-dependent V1 suppression contributes to crowding at a very early stage of visual processing.

submitted time 2016-05-18 Hits3454Downloads1881 Comment 0

2. chinaXiv:201605.01530 [pdf]

Topology-defined units in numerosity perception

He, Lixia; Zhou, Ke; Zhou, Tiangang; He, Sheng; Chen, Lin
Subjects: Biology >> Biophysics

What is a number? The number sense hypothesis suggests that numerosity is "a primary visual property" like color, contrast, or orientation. However, exactly what attribute of a stimulus is the primary visual property and determines numbers in the number sense? To verify the invariant nature of numerosity perception, we manipulated the numbers of items connected/enclosed in arbitrary and irregular forms while controlling for low-level features (e.g., orientation, color, and size). Subjects performed discrimination, estimation, and equality judgment tasks in a wide range of presentation durations and across small and large numbers. Results consistently show that connecting/enclosing items led to robust numerosity underestimation, with the extent of underestimation increasing monotonically with the number of connected/enclosed items. In contrast, grouping based on color similarity had no effect on numerosity judgment. We propose that numbers or the primitive units counted in numerosity perception are influenced by topological invariants, such as connectivity and the inside/outside relationship. Beyond the behavioral measures, neural tuning curves to numerosity in the intraparietal sulcus were obtained using functional MRI adaptation, and the tuning curves showed that numbers represented in the intraparietal sulcus were strongly influenced by topology.

submitted time 2016-05-12 Hits1586Downloads991 Comment 0

3. chinaXiv:201605.01366 [pdf]

Sharpened cortical tuning and enhanced cortico-cortical communication contribute to the long-term neural mechanisms of visual motion perceptual learning

Chen, Nihong; Li, Sheng; Fang, Fang; Chen, Nihong; Li, Sheng; Fang, Fang; Chen, Nihong; Li, Sheng; Fang, Fang; Chen, Nihong; Fang, Fang; Bi, Taiyong; Bi, Taiyong; Zhou, Tiangang; Liu, Zili
Subjects: Biology >> Biophysics >> Neurosciences

Much has been debated about whether the neural plasticity mediating perceptual learning takes place at the sensory or decision-making stage in the brain. To investigate this, we trained human subjects in a visual motion direction discrimination task. Behavioral performance and BOLD signals were measured before, immediately after, and two weeks after training. Parallel to subjects' long-lasting behavioral improvement, the neural selectivity in V3A and the effective connectivity from V3A to IPS (intraparietal sulcus, a motion decisionmaking area) exhibited a persistent increase for the trained direction. Moreover, the improvement was well explained by a linear combination of the selectivity and connectivity increases. These findings suggest that the long-term neural mechanisms of motion perceptual learning are implemented by sharpening cortical tuning to trained stimuli at the sensory processing stage, as well as by optimizing the connections between sensory and decision-making areas in the brain. (C) 2015 Elsevier Inc. All rights reserved.

submitted time 2016-05-12 Hits2907Downloads1442 Comment 0

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