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Sonia Poltoratski, Alexander Maier, Allen Newton, Frank Tong; Cortical feedback mediates figure-ground modulation in the human lateral geniculate nucleus. Journal of Vision 2018;18(10):25. doi: 10.1167/18.10.25.
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The lateral geniculate nucleus (LGN) is the earliest site of the visual hierarchy that receives top-down feedback, yet the functional role of this feedback is poorly understood. However, growing research suggests that the human LGN is involved in more sophisticated visual and cognitive processes, showing modulation by covert attention (O'Connor et al., 2002) and evidence of orientation-selective processing (Ling et al. 2015). Here, we show that perceptual figures elicit an automatic form of feedback modulation that propagates from the binocular visual cortex to the LGN. This stimulus-driven feedback leads to the enhancement of figures in the LGN even in the absence of directed attention. Using high-resolution fMRI at 7 Tesla to record human brain activity, we first measured fMRI responses to orientation-defined figures presented to the left and right of fixation, cuing participants to spatially attend to one figure while ignoring the other. Spatial attention led to enhanced responses in the LGN, consistent with prior work, but more importantly, orientation-defined figures produced elevated responses even when the figure was unattended. In a second experiment, we manipulated whether the figure and the surround stimuli were presented to the same eye or to different eyes. This design leverages the binocular organization of the early visual system: V1 is considered the first stage along the visual hierarchy in which signals from the two eyes are strongly integrated. Nevertheless, we found that the LGN was reliably modulated when figure and ground were presented to different eyes, implicating a mechanism top-down feedback from binocular cortical neurons for figure-ground modulation in the LGN.
Meeting abstract presented at VSS 2018
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