Modulation of Neural Stereoscopic Processing in Primate Area V1 by the Viewing Distance

Abstract

Accurate binocular depth perception requires information about both stereopsis (relative depth) and distance (absolute depth). It is unclear how these two types of information are integrated in the visual system. In alert, behaving monkeys the responsiveness of a large majority of neurons in the primary visual cortex (area V1) was modulated by the viewing distance. This phenomenon affected particularly disparity-related activity and background activity and was not dependent on the pattern of retinal stimulation. Therefore, extraretinal factors, probably related to ocular vergence or accommodation, or both, can affect processing early in the visual pathway. Such modulations could be useful for (i) judging true distance and (ii) scaling retinal disparity to give information about three-dimensional shape.

Spatiotopic Adaptation in Visual Areas

“…We found evidence for a transfer of spatiotopic information between visual areas as indicated by both our behavioral and functional data. First, at the behavioral level, and in agreement with our previous report (Zimmermann et al, 2013), adaptation aftereffects were observed after a saccade was executed. Second, fMRI adaptation was shifted from one to the opposite hemisphere consistent with a transsaccadic information transfer of adapter activity (Duhamel et al, 1992).…”

“…This finding implies that neural adaption generated in the left hemisphere was interhemispherically transferred and became effective in the right hemisphere. This shift of neural adaption activity might result from an active process, which accounts for the behavioral spatiotopic aftereffects observed in this and previous studies (Melcher, 2005;Turi and Burr, 2012;Zimmermann et al, 2013). Although our adapter and our probe stimuli activated expectedly ventral areas, our retinotopic mapping analysis revealed that the shift of adapter activity occurred in dorsal visual area V3 and in higher areas visual, including V4 and VO.…”

“…In Experiments 1 and 2, we investigated spatiotopic adaptation with the standard procedure used in most behavioral setups (Melcher, 2005;Turi and Burr, 2012;Zimmermann et al, 2013). We found a broad cluster of activation in occipital cortex.…”

“…Several hypotheses have been advanced to explain how visual space is stabilized across eye movements: Objects may generally be coded in real-world coordinates, thereby rendering visual space invariant to displacements of the eye. Electrophysiological studies, however, failed to identify explicit spatiotopic maps of external space (Wurtz et al, 2008). Functional imaging studies in humans reported mixed evidence for spatiotopic processing.…”

“…A saccade between the presentation of the adapter and a probe stimulus allows dissociating retinal and external space coordinates: Following the saccade, the probe stimulus can either be shown at the spatiotopic position, which matches the adapter location on the screen; or at the retinotopic position, which matches the adapter location on the retina. Measurable adaptation effects are expected at both the retinotopic and the spatiotopic positions (Melcher, 2005;Zimmermann et al, 2013).…”