fMRI reveals that non-local processing in ventral retinotopic cortex underlies perceptual grouping by temporal synchrony.

Full Abstract

When spatially separated objects appear and disappear in a synchronous manner, they perceptually group into a single global object that itself appears and disappears. We employed functional magnetic resonance imaging (fMRI) to identify brain regions involved in this type of perceptual grouping. Subjects viewed four chromatically-defined disks (one per visual quadrant) that flashed on and off. We contrasted %BOLD signal changes between blocks of synchronously flashing disks (Grouping) with blocks of asynchronously flashing disks (no-Grouping).

RESULTS:
A region of interest analysis revealed %BOLD signal change in the Grouping condition was significantly greater than in the no-Grouping condition within retinotopic areas V2, V3, and V4v. Within a single quadrant of the visual field, the spatio-temporal information present in the image was identical across the two stimulus conditions. As such, the two conditions could not be distinguished from each other on the basis of the rate or pattern of flashing within a single visual quadrant. The observed results must therefore arise through nonlocal interactions between or within these retinotopic areas, or arise from outside these retinotopic areas. Furthermore, when V2 and V3 were split into ventral and dorsal sub-ROIs, ventral retinotopic areas V2v and V3v preferentially differentiated between the two conditions whereas the corresponding dorsal areas V2d and V3d did not. In contrast, within hMT+, %BOLD signal was significantly greater in the no-Grouping condition.

CONCLUSION:
Nonlocal processing within, between, or to ventral retinotopic cortex at least as early as V2v, and including V3v, and V4v, underlies perceptual grouping via temporal synchrony.Copyright 2007 Wiley-Liss, Inc.

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Author information

Author/s: Caplovitz, Gideon P (GP); Barroso, Diego J (DJ); Hsieh, Po-Jang (PJ); Tse, Peter U (PU);

Affiliation: Department of Psychological and Brain Sciences, Moore Hall, Dartmouth College, Hanover, New Hampshire 03755, USA. gideon.p.caplovitz@dartmouth.edu

Grants: F31 EY016386 (Agency:United States NEI) ; R03 MH0609660-01 (Agency:United States NIMH)

Journal and publication information

Publication Type: Journal Article; Research Support, N.I.H., Extramural; Research Support, U.S. Gov't, Non-P.H.S.

Journal: Human brain mapping (Hum Brain Mapp), published in United States. (Language: eng)

Reference: 2008-Jun; vol 29 (issue 6) : pp 651-61

Dates: Created 2008/05/19; Completed 2008/08/21;

PMID: 17598165, status: MEDLINE (last retrieval date: 11/6/2008)

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Brain Mapping
Fixation, Ocular - physiology
Form Perception - physiology
Humans
Linear Models
Magnetic Resonance Imaging

Models, Neurological
Photic Stimulation
Reaction Time - physiology
Time Perception - physiology
Visual Cortex - physiology
Visual Fields - physiology

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