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Kyeong-Jin Tark, Sunyoung Park, Insub Kim, Won Mok Shim; Neural representations of ensemble coding for visual features in the early visual and fronto-parietal cortex. Journal of Vision 2017;17(10):173. doi: 10.1167/17.10.173.
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The human brain is endowed with the ability to summarize the properties of similar objects to efficiently represent a complex visual environment. Although previous behavioral studies demonstrated that we can extract the mean orientation, size and speed from sets of items (Ariely, 2001; Chong & Treisman, 2003; Dakin & Watt, 1997; Watamaniuk & Duchon, 1992), the underlying neural mechanism remains poorly understood. Here, we investigated the neural substrates of visual statistical summary representation. More specifically, using fMRI and encoding methods we examined 1) whether the mean orientation is represented in population-level orientation tuning responses in early visual areas as well as high-level fronto-parietal regions and 2) whether this tuning profile is modulated by the variance of orientation in sets of items. In the experiment, 30 small Gabor patches varying in orientation briefly appeared at random locations within a hypothetical circle and subjects were instructed to estimate their mean orientation and indicate it by a button press. Our behavioral data showed that the averaging performance was impaired as the orientation of Gabor patches became heterogeneous. We also found robust activation in parietal and dorsolateral prefrontal cortices while subjects performed the averaging task. Next, we estimated the tuning responses of the mean orientation in parietal and dorsolateral frontal cortices as well as early retinotopic visual areas. The results showed that the population-level orientation tuning functions peak at the mean orientation of sets of Gabor patches, and the tuning strength was attenuated as the variance in orientation increased, which reflects the decrease in behavioral performance. Our results suggest that early visual cortex and frontoparietal regions may serve to process ensemble coding, whereby summary statistics of visual stimuli are extracted.
Meeting abstract presented at VSS 2017
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