Long-range dichoptic interactions in the human visual cortex in the region corresponding to the blind spot

Abstract

Tbe region of tbe visual field of one eye tbat corresponds to tbe blind spot of the coutraIatera1 eye is beiieved to be monocular. We measured dicboptic coatour interaction in this region of tbe visual field in bumans by having observers report tbe orientation of a test letter "T" presenH to tbis region, in the presence of thud&g T's presented around tbe blind spot of the fellow eye. A large drop in performance was seen because of tbe Bauks, showing clearly tbe existence of dicboptic contour interaction in this 'cmonocular" region of tbe visual field. Tbis suggests that the cortical representatioa of the region of tbe visual field tbat corresponds to the -t&ate& eye's blind spot is sot strictly monocular. Tbe absence of direct retinal aiferents from oue eye to tbis region of cortex swggests tbe involvement of horizontal cortical connectious in tbe contour interaction phenomenon. Our estimates of the extent of contour interaction in mm of striate cortex are comparable to the reported lengths of the long-range horizontal connections in tbe striate cortex of monkeys. Our results are consistent with the proposition that long-range horizontal conuections of the striate cortex may mediate the eontour interaction p~~rnenon.

Action-Video-Game Experience Alters the Spatial Resolution of Vision

“…Some researchers have suggested important roles for interactions between the facilitatory and inhibitory regions within neuronal receptive fields in early visual areas or interactions between neurons via long-range horizontal connections (Flom, Heath, & Takahashi, 1963;Polat & Sagi, 1994;Tripathy & Levi, 1994). Others have suggested that crowding, particularly foveal crowding, is a form of spatial-frequency masking or contrast masking (Chung, Levi, & Legge, 2001; or is related to the physical properties of the stimulus (Hess, Dakin, & Kapoor, 2000).…”

Neural Responses in the Retinotopic Representation of the Blind Spot in the Macaque V1 to Stimuli for Perceptual Filling-In

“…Another view argues that surface-specific neuronal activity in the visual system occurs at a relatively early stage of visual processing and that the activity is topographically correlated with the perceptual consequence of filling-in. Although some psychophysical studies support the former idea (Cumming and Friend, 1980), other studies support the latter (Tripathy and Levi, 1994;Murakami, 1995).…”

Radial-tangential anisotropy of crowding in the early visual areas

“…Most importantly, they found that the targetflanker distance required for this crowding follows the cortical magnification of the striate cortex, and thus spans a constant distance in V1 regardless of eccentricity. These estimations by Levi and colleagues, along with a study using dichoptic interaction in the blind spot by Tripathy and Levi (1994) and the more recent calculation by Pelli (2008) based on letter crowding put the cortical distance of crowding somewhere between 3 and 8 mm in V1. This is broadly consistent with the estimated extent of horizontal connections in the striate cortex (ϳ6 -8 mm; Gilbert 1992;Stettler et al 2002).…”

“…Primary visual cortex (V1) has been implicated in some of the earliest behavioral studies on crowding Tripathy and Levi 1994), a view that was reiterated in some of the recent theories (Nandy and Tjan 2012; Pelli 2008). Specifically, Levi and colleagues found that vernier threshold was elevated by flankers placed far from the vernier target.…”

“…A robust hallmark of crowding is its anisotropy between the radial and tangential directions, i.e., the spatial extent of crowding is elongated along the radial axis connecting the target with the fovea (Chambers and Wolford 1983;Chung 2013;Petrov and Meleshkevich 2011;Toet and Levi 1992;van den Berg et al 2010). To look for the neural correlates of crowding, we sought to detect this radial-tangential anisotropy physiologically in the visual cortex.…”