PubMed · 4767607
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I Pollack. 1973. Depth of visual information processing.. https://doi.org/10.1016/0001-6918(73)90004-8
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It is generally believed that the perception of moving targets is mediated by the magnocellular (M) pathway in primate vision, but evidence is emerging that the parvocellular (P) pathway may also play a role in motion perception. Human peripheral vision is susceptible to anomalous motion perception because of spatial aliasing, and in this study we used this fact to determine if the P pathway can mediate information about low- and high-velocity stimuli. Psychometric functions relating visual performance to stimulus spatial frequency were measured for the directional discrimination of drifting sinusoidal gratings presented at 40 degrees eccentricity. Applying the sampling theorem to our results, we estimated that the Nyquist frequency of the limiting sampling array for directional discrimination is 1.7 cycles per degree. This result was compared with the Nyquist limit and spatial filtering properties of M and P ganglion cells in the human peripheral retina, calculated from histological data on their density and dendritic field size. Our results provide evidence to suggest that the reversed motion illusion in human peripheral vision is due to spatial aliasing by the P ganglion cell mosaic. We conclude that the sampling density of P ganglion cells limits veridical motion acuity in human peripheral vision, even for high-velocity targets. This provides further evidence that the P pathway is involved in processing information about motion.
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1. Human perceptual learning in discrimination of the oblique orientation was studied using psychophysical methods. Subjects were trained daily to improve their ability to identify the orientation of a circular 2.5 deg diameter unidimensional noise field. Dramatic improvements in sensitivity to contour orientation occurred over a period of 15-20 days. The improved performance persisted for several months. Improvement was more evident between daily sessions than within sessions. This was partly due to fatigue interfering with the learning effect. Moreover, a consolidation period seemed to be required. 2. Improvement was restricted to the position of the stimulus being trained. This position dependency of the learning effect proved very precise. After training at a specific stimulus position, merely displacing the stimulus to an adjacent position caused a marked increase in thresholds. 3. No transfer of the training effect was observed between orientations. Following a shift of 90 deg away from the trained orientation, performance fell, even below the initial level. 4. We observed complete to almost complete transfer between the two eyes. 5. Our results suggest plastic changes at a level of the visual processing stream where input from both eyes has come together, but where generalization for spatial localization and orientation has not yet occurred.