Learning of interpolation in 2 and 3 dimensions

Perceptual learning of Gabor orientation identification in visual periphery: complete inter-ocular transfer of learning mechanisms

We combined the external noise paradigm, the Perceptual Template Model approach, and transfer tests to investigate the mechanisms and eye-specificity of perceptual learning of Gabor orientation in visual periphery. Coupled with a fixation task, discriminating a 5 from an S in a rapid small character string at fixation, contrast thresholds were estimated for each of eight external noise levels at two performance criteria using 3/1 and 2/1 staircases. Perceptual learning in one eye was measured over 10 practice sessions, followed by five sessions of practice in the new eye to assess transfer. We found that monocular learning improved performance (reduced contrast thresholds) with virtually equal magnitude across a wide range of external noise levels with no significant change in central task performance. Based on measurements of learning effects at two performance criterion levels, we identified a mixture of stimulus enhancement and external noise exclusion as the mechanism of perceptual learning underlying the observed improvements. Perceptual learning in the trained eye generalized completely to the untrained eye. We related the transfer patterns to known physiology and psychophysics on orientation direction coding.

Spatiotemporal interpolation and quality of apparent motion

We investigate the conditions under which stimuli in apparent (sampled) motion are indistinguishable from those in smooth motion and compare this discrimination with the precision achieved by the visual system in interpolating apparent motion. In an initial experiment, observers were required to discriminate smooth from apparent motion, at variable step sizes, contrasts, velocities, and stimulus types (broadband line or bar stimuli and grating patches of different spatial frequency). Thresholds for discriminating smooth from sampled motion were approximately 40 arc min under optimal conditions, corresponding to the diameter of foveal photoreceptors. The tolerated step size between stations increased with velocity, more so for low- than for high-spatial-frequency stimuli. Tolerated step size decreased with presentation duration and with stimulus contrast. A separate experiment examined precision of interpolation. Vernier offsets were produced through temporal delays along the trajectory of an apparent motion, and thresholds for the discrimination of direction of offset were measured as a function of speed of motion and of distance between stations of apparent motion. Perfect interpolation was achieved for distances between stations of approximately 2 arc min. A model based on spatiotemporal filtering at an early stage of processing accounts well for the results of both types of experiments.

The effect of orientation learning on contrast sensitivity

Regan and Beverley [Regan, D., & Beverley, K. I. (1985). Postadaptation orientation discrimination. Journal of the Optical Society of America A, 2(2), 147-155] previously demonstrated that adapting to an oriented visual stimulus improves sensitivity to subtle orientation differences while impairing contrast sensitivity. Here, we investigated whether practice-based improvements in orientation sensitivity would, like adaptation, impair contrast sensitivity. To the contrary, we found that contrast sensitivity actually improved significantly after observers demonstrated practice-based increases in orientation sensitivity. Therefore, while orientation sensitivity can be enhanced either by orientation-discrimination training or by adapting to visual stimuli, these two procedures have opposite effects on contrast sensitivity. This difference suggests that adaptation and perceptual learning on orientation discrimination cannot be explained sufficiently by a shared underlying cause, such as a reduction in neural activity.