Temporal characteristics of global form perception in translational and circular Glass patterns

Hierarchical models of visual processing assume that global pattern recognition is contingent on the progressive integration of local elements across larger spatial regions, operating from early through intermediate to higher-level cortical regions. Here, we present results from neuropsychological fMRI that refute such models. We report two patients, one with lesions to intermediate ventral regions and the other with damage around the intraparietal sulcus (IPS). The patient with ventral damage showed normal behavioral and BOLD responses to global Glass patterns. The patient with IPS damage was impaired in discriminating global patterns and showed a lack of significant responses to these patterns in intermediate visual regions spared by the lesion. However, this patient did show BOLD activity to translational patterns, where local element relations are important. These results suggest that activation of intermediate ventral regions is not necessary to code global patterns; instead global patterns are coded in a heterarchical fashion. High-level regions of dorsal cortex are necessary to generate global pattern coding in intermediate ventral regions; in contrast, local integration processes are not sufficient.

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Global visual processing in macaques studied using Kanizsa illusory shapes

Visual Neuroscience ◽

10.1017/s0952523810000088 ◽

2010 ◽

Vol 27 (3-4) ◽

pp. 131-138 ◽

Cited By ~ 4

Author(s):

KIMBERLY A. FELTNER ◽

LYNNE KIORPES

Keyword(s):

Visual Processing ◽

Macaca Nemestrina ◽

Form Perception ◽

Performance Limits ◽

Form Discrimination ◽

Macaque Monkeys ◽

Match To Sample ◽

Form Processing ◽

Global Form ◽

Support Ratio

AbstractThe ability to extract form information from a visual scene, for object recognition or figure–ground segregation, is a fundamental visual system function. Many studies of nonhuman primates have addressed the neural mechanisms involved in global form processing, but few have sought to demonstrate this ability behaviorally. In this study, we probed global visual processing in macaque monkeys (Macaca nemestrina) using classical Kanizsa illusory shapes as an assay of global form perception. We trained three monkeys on a “similarity match-to-sample” form discrimination task, first with complete forms embedded in fields of noncontour-inducing “pacman” elements. We then tested them with classic Kanizsa illusory shapes embedded in fields of randomly oriented elements. Two of the three subjects reached our criterion performance level of 80% correct or better on four of five illusory test conditions, demonstrating clear evidence of Kanizsa illusory form perception; the third subject mastered three of five conditions. Performance limits for illusory form discrimination were obtained by manipulating support ratio and by measuring threshold for discriminating “fat” and “thin” illusory squares. Our results indicate that macaque monkeys are capable of global form processing similarly to humans and that the perceptual mechanisms for “filling-in” contour gaps exist in macaques as they do in humans.

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