Activation of Visual Cortices by Constrasts of Various Visual Attributes: A fMRI Study

Lee, Kyoung-Min; Kim, Soo Kyoung

Ann Clin Neurophysiol > 2001 ;3(1) > Article

Ann Clin Neurophysiol. 2001; 3(1): 99-110.

Kyoung-Min Lee, and Soo Kyoung Kim

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

Visual Segmentation is an important function of our visual system as it eventually enables us to form correct representation of the outer world objects or events. We used fMRI in search for cortical activity related to the perception of visual scene segmented by contrast of three visual cues in human beings. The stimuli used were three kinds of flickering random dot checkerboard: defined by 1)texture orientation contrast 2)color contrast 3)motion direction contrast. Using these stimuli, 9 healthy subjects were functionally scanned with 1.5T MR machine while they fixated their eyes and passively viewed the stimuli presented. In experiment 1, these three conditions sequentially appeared from a flickering random dot field, while in experiment2 they appeared from a dark screen with fixation point in the center. Even though all three checkerboard conditions were the same in both experiments, the overall activation patterns were quite different. The extrastriate areas, especially V4, and Parietal lobe were activated cue-invariantly in the first experiment, while only V1 was activated cue-invariantly in the second experiment. To investigate the effect of the flickering random dot field, experiment3 was carried out with 4 of the ex-subjects and it showed activation of V1 and deactivation of extrastriate area including MT area for the flickering random dot field perception. As flickering effect might have removed the V1 activation in experiment1 while comparing checkerboard conditions with flickering random dot field condition, it can explain the absence of V1 activation in experiment1, still it cannot explain the absence of V4 activation or Parietal lobe activation in experiment2. As V1 has been localized for boundary perception and V4 for shape perception and parietal lobe for binding different visual attributes, activation of these areas can be interpreted as such. However, the differences in the results of experiment1 and experiment2 suggest that differences of the start line in perceptual flow can activate visual cortices differentially.

Key words: Visual segmentation, Visual cortex, fMRI, Checkerboard