Cortical Correlates of Motion Surround Suppression in Area MT H B Turkozer1, Z Pamir2, H Boyaci3 |
|---|
1Department of Psychiatry, Marmara University School of Medicine, Turkey |
| As the size of a high contrast moving pattern increases, it becomes harder to perceive its direction of motion (Tadin et al. 2003). This counter-intuitive effect, termed as “spatial suppression” was suggested to be a consequence of the center-surround antagonism in the cortical area MT. Here, using fMRI, we study the behavioral and neural processes underlying this mechanism, and investigate the role of attention. Five participants participated in the study. In the behavioral experiments, duration thresholds were assessed for detecting the direction of drifting Gabor patches in different sizes, contrasts and frequencies. Duration thresholds increased significantly as the size of the stimulus increased for high contrast (65%) but not for low contrast (2%) patches. In the fMRI experiments BOLD signals were recorded while observers viewed drifting Gabor patches in different contrasts and sizes. When observers performed a demanding fixation task, cortical activity in MT increased with increasing size for low contrast patches, and decreased for high contrast patches. When observers did not perform the attention task BOLD signal did not vary with size for high contrast patches, but increased for low contrast patches. These results are in line with the proposed role of MT in spatial suppression. |
| Up Home |
|---|