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Neuroscience Brown Bag

Thursday, October 25, 2018,

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  • Location: Wilson Hall • 111 21St Ave S • Nashville, TN 37240
  • Room: 316

Frank Tong, PhD

Department of Psychology

Vanderbilt University

"Characterizing the perceptual and attentional functions of the early visual system"

Much has been learned about the role of human V1 in perception and higher cognitive functions, whereas the functional role of the lateral geniculate nucleus (LGN) has been largely overlooked. The LGN is classically portrayed as a relay station that simply serves to transfer information from retina to cortex, but such an account fails to explain why the LGN receives far more afferents from the visual cortex than from the retina. In this talk, I will describe our recent and ongoing fMRI work at characterizing the visual and attentional functions of the LGN, and how its response to perceptual figures may reflect a form predictive coding. According to predictive coding theories, the top-down predictions of higher visual areas could conceivably propagate to the lowest possible site of the visual hierarchy, modulating the response of the LGN to figural regions that differ in appearance from the adjacent background. We find novel evidence of orientation processing in the human LGN; moreover, attentional feedback can modify the strength of these orientation-selective responses (Ling, Pratte & Tong, Nat Neurosci, 2015). Although the LGN does not appear to be sensitive to long-range interactions between orientation stimuli, which can give rise to visual salience (Poltoratski et al., 2017), our ongoing work suggests that both the LGN and V1 are sensitive to orientation-defined figures. These studies demonstrate that figure-ground processing involves distinct mechanisms of boundary enhancement and figure enhancement, and that both mechanisms operate in an automatic manner without requiring focal attention. Further experiments suggest that the sensitivity of the LGN to perceptual figures depends on automatic top-down feedback from the binocular visual cortex. Our research suggests that the LGN has an integral role in more complex visual processes, and that top-down feedback from the visual cortex serves to modulate visual responses in the LGN in a manner that appears consistent with predictive coding.