hMT+ activity predicts the effect of spatial attention on surround suppression.

Surround suppression refers to the decrease in behavioral sensitivity and neural response to a central stimulus due to the presence of surrounding stimuli. Several aspects of surround suppression in human motion perception have been studied in detail, including its atypicality in some clinical populations. However, how the extent of spatial attention affects the strength of surround suppression has not been systematically studied before. To address this question, we presented human participants with "center" and "surround" drifting gratings and sought to find whether attending only to the center ("narrow attention") versus both to the center and surround ("wide attention") modulates the suppression strength in motion processing. Using psychophysics and functional magnetic resonance imaging (fMRI), we measured motion direction discrimination thresholds and cortical activity in the primary visual cortex (V1) and middle temporal complex (hMT+). We found increased perceptual thresholds and, thus, stronger surround suppression under the wide-attention condition. We also found that the pattern of hMT+ activity was consistent with the behavioral results. Furthermore, a mathematical model that combines spatial attention and divisive normalization was able to explain the pattern in the behavioral and fMRI results. These findings provide a deeper understanding of how attention affects center-surround interactions and suggest possible neural mechanisms with relevance to both basic and clinical vision science.