Biology subjects

Spivak, O.

Publications and source records attributed to Spivak, O..

3 recordsLinked to original sources

bioRxiv2022

The scotopic band: primate detailed scotopic vision and perceptual uncertainty

Primates perceive detailed images in photopic (daylight) vision via a preferred-processing, high-acuity pathway, made up of a small photopic center (the fovea), and dedicated eye movements, whose function is to shift images of target objects to the fovea and keep them while foveal cones sense the image. Thus, the preferred processing pathway processes images serially, not in parallel. No such pathway is known for scotopic (night-light) vision or mesopic (twilight) vision - though details are informative in dim light, even vital; it remains unclear whether and how scotopic vision of details is accomplished. Here we show that primates do have a scotopic preferred-processing pathway. It consists of a scotopic center, located on a scotopic band, and eye movements that shift target images not to the fovea but directly to the scotopic center. In contrast to the stationary fovea, the scotopic center can relocate over the scotopic band. The scotopic center relocates to match changing visual conditions and contextual needs. Ambient light intensity is mapped monotonically onto the scotopic band, with mesopic vision at one end. The dimmer the light is, the more dorsal the scotopic center relocates on the scotopic band. Importantly, the scotopic center relocates (or set) not only in passive response to ambient light but also actively, driven by internal factors. In near-threshold conditions the scotopic center relocates to a more dorsal band location than in salient conditions. That the same relocation of the scotopic center can be instigated both by dimming the ambient light and by reducing the detectability of targets indicates that, at the core, the longitudinal axis of the scotopic band encodes the level of perceptual uncertainty.

neuroscience↗

bioRxiv2019

Individual variation of the dark-background-contingent upshift of gaze: effect of past habituation

We studied the shift of gaze direction induced by dark background in monkeys. Faced with large inter-individual variability, we asked how common the upshift is, and how the upshift size is distributed. Furthermore, we sought to reckon processes influencing the variability. Approaching these questions necessitates a large sample. Here we report data from 10 rhesus monkeys recorded in Tubingen, together with reported data from 4 cynomolgus monkeys studied in Rehovot. In all 14 monkeys, dark background induced upshift - but no systematic horizontal shift. The upshift might be thought of as a simple sensorimotor response; nevertheless, surprisingly, the monkeys previous experience appeared to have a decisive role in influencing the upshifts size. All the monkeys were previously trained in tasks that involved vision and eye movements; by their previous training, the monkeys were naturally divided into two groups. Monkeys of the first, bright-habituated group, previously trained in photopic, bright ambient-light conditions; monkeys of the second, dark-habituated group previously trained mostly with isolated dots of light appearing in dim ambient lighting or in full darkness. The dark-habituated monkeys had a larger upshift than the bright-habituated: the groups were separated by a border-value such that 6/7 of the dark-habituated monkeys had upshift larger than the border, and 5/7 of the bright-habituated monkeys had upshift smaller than the border. Thus, the size of the dark-background-induced upshift largely reflects the extent to which a monkey is habituated to work in the dark. Though the upshift is reflex-like sensorimotor behavior, its amplitude largely reflects cumulative experience.

neuroscience↗

bioRxiv2018

Monkeys use the rod-dense retinal region rather than the fovea to visually fixate small targets in scotopic vision

Monkeys appear to visually fixate targets in scotopic conditions. The function fixations fulfill in photopic vision, keeping the targets image on the fovea, is nullified in scotopic vision, because the fovea, with its cones, is desensitized in dim light. Here we followed the hypothesis that a previously described retinal region, the locus of maximal rod density, functionally replaces the fovea; we found that with dark background, most of the fixations direct the fovea above the target, so that the targets image appears to fall on the line connecting the fovea with the locus of maximal rod density. There is considerable trial-by-trial variation in the fixation positions along this line. On the whole, the closer the visual conditions are to full scotopic, the higher is this gaze upshift, indicating the closer does the target fall to the locus of maximal rod density. Mesopic background induces low mean upshift. Full (45-min) dark adaptation was essential to achieving high upshift values. There is no analogous photopic effect - 45-min bright adaptation did not shift the locus of photopic fixation.

neuroscience↗