| Wei, M., DeAngelis, G., Angelaki, D. Do visual cues contribute to the neural estimate of viewing distance used by the oculomotor system ? The Journal of Neuroscience 2003 (23)23:8340-8350 [pdf] |
| Perceived shape and depth judgments that require knowledge of viewing distance are strongly influenced by both vergence angle and the pattern of vertical disparities across large visual fields. On the basis of this established contribution of visual cues to the neural estimate of viewing distance,wehypothesized that the oculomotor system would alsomakeuse of high-level visual cues to distance. To address this hypothesis, we investigated how compensatory eye movements during whole-body translation scale with viewing distance. Monkeys viewed large-field (85 68°) random-dot stereograms that were rear projected onto a fixed screen and simulated either a textured wall or pyramid at different viewing distances. In these stereograms, we independently manipulated vergence angle, horizontal and vertical disparity gradients, relative horizontal disparities, and textural cues to viewing distance. For comparison, random-dot patterns were also projected onto a moveable screen placed at different physical distances from the animal. Several cycles of left right sinusoidal motion of the monkey at 5Hz were interleaved with several cycles of motion in darkness, and the relationship between eye movement responses and viewing distance was quantified. As expected from previous work, the amplitude of compensatory eye movements depended strongly on vergence angle. Although visual cues to distance had a statistically significant effect on eye movements, these effects were 20-fold weaker than the effect of vergence angle.Weconclude that sensory and motor systems do not share a common neural estimate of viewing distance and that the oculomotor system relies far less on visual cues than the perceptual system. |
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| Srinivasan, R., Russell, D.P., Edelman, G.M., Tononi, G. Increased Synchronization of Neuromagnetic Responses during Conscious Perception The Journal of Neuroscience 1999 (19)13:5435-5448 [html] |
| In binocular rivalry, the observer views two incongruent images, one through each eye, but is conscious of only one image at a time. The image that is perceptually dominant alternates every few seconds. We used this phenomenon to investigate neural correlates of conscious perception. We presented a red vertical grating to one eye and a blue horizontal grating to the other eye, with each grating continuously flickering at a distinct frequency (the frequency tag for that stimulus). Steady-state magnetic fields were recorded with a 148 sensor whole-head magnetometer while the subjects reported which grating was perceived. The power of the steady-state magnetic field at the frequency associated with a grating typically increased at multiple sensors when the grating was perceived. Changes in power related to perceptual dominance, presumably reflecting local neural synchronization, reached statistical significance at several sensors, including some positioned over occipital, temporal, and frontal cortices. To identify changes in synchronization between distinct brain areas that were related to perceptual dominance, we analyzed coherence between pairs of widely separated sensors. The results showed that when the stimulus was perceived there was a marked increase in both interhemispheric and intrahemispheric coherence at the stimulus frequency. This study demonstrates a direct correlation between the conscious perception of a visual stimulus and the synchronous activity of large populations of neocortical neurons as reflected by stimulus-evoked steady-state neuromagnetic fields. |
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