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Abstract:
The processing of motion in the primate brain is distributed across multiple regions of the cerebral cortex. The two well-studied visual areas MT and MST have been linked to conscious perception and decision-making related to simple flow stimuli as well as to integration of component plaid motion into a coherently moving pattern. However, it is unclear whether processing and perception of other types of global motion, which require large-scale integration of the local signals, is related to activity of the same areas.
In the current study we used fMRI to investigate neural responses to a bi-stable visual motion stimulus. The stimulus consisted of four pairs of dots, each pair coherently moving on a circular path. Perception alternated spontaneously between two states: local dot motion in each of the four quadrants of the visual field or global planar motion of two illusory squares spanning all four visual quadrants [1]. Importantly, these alternations were purely perceptual and involved no stimulus manipulation. We localized visual areas that are known to respond to visual movement (V3a, V6, V7, MT, MST, IPS1-4, and the recently described cingulate sulcus visual area (CSv) [2,3]) individually in each subject. We then investigated responses of these areas to global and local perceptual states of our subjects, while they viewed the bistable stimulus and reported their perception.
We found that activity of two of the areas, CSv and IPS4, specifically correlated with global, but not the local perceptual states, while V6 showed a trend in the opposite direction. Interestingly, neither V5/MT, nor MST, nor any other motion-responsive region differentiated between global and local perceptual states.
Our results suggest that CSv and IPS4 may be involved in the computation of global motion by large-scale integration of similar motion directions, or by spatial binding between distant loci in the visual field, respectively. Importantly, these results imply a certain 'blindness' of V5/MT and of MST to vivid changes in the conscious perception of large-scale motion stimuli. The perception of global, large-scale motion may therefore be mediated by higher-level motion-processing regions with larger receptive fields, such as by areas CSv and IPS4.
