PubMed · 14873837
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M P SMITH. 1951. The stimulus trace gradient in visual discrimination learning.. https://doi.org/10.1037/h0053669
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We investigated the mechanisms that allow, via perceptual learning, selective modulation of a visual line-texture figure saliency in accordance with task relevance. Learning-dependent saliency increase was inferred by increased accuracy in orientation discrimination with task repetition. As a result of learning, accuracy increase was more pronounced when local and global orientation of the texture figure conflicted, and reached ceiling in both conflict and conflict-free conditions. This psychophysical effect was associated with a decrease in amplitude of negative VEP components in the configurations where global and local orientation conflicted, and to a weak increase of VEP's earliest negative component in the conflict-free condition. The VEP result is a direct demonstration that learning, in addition to increasing response of relevant channels, also reduces the weight of channels whose receptive field size and orientation tuning conflict with the task.
The two-point discrimination (2PD) test is the most frequently used test for the assessment of the sensory outcome after nerve repair. Here we focus on factors which explain the enormous and implausible variability in reported 2PD levels after nerve repair. We conclude that the 2PD testing technique is not at all standardized and that its use as the sole test for tactile gnosis recovery should be seriously questioned. Reports of 2PD results should always be accompanied by a detailed description of how the test was performed, especially with reference to the pressure applied and the testing protocol.
We studied perceptual learning in motion discrimination when the brain's middle temporal area (MT/V5) was functionally suppressed. This was achieved by using the "paired-dots" motion stimulus where the two dots in a pair always move in counter-phase over a short distance [J. Neurosci. 14 (1994) 7357]. The motion directional signal of the stimulus is therefore always 0 on average. As a result, this stimulus activates MT in Rhesus monkeys no more than flicker noise does [J. Neurosci. 14 (1994) 7367]. We added a new manipulation to eliminate the Glass pattern in the original stimulus that would have otherwise provided a static orientation cue. Two such new motion stimuli were presented sequentially, in a 2AFC task. Subjects decided if the global motion-axis of the stimuli changed clockwise or counter-clockwise. When the task difficulty was set at 60% correct, none of the subjects could learn with feedback, even though their performance was well above chance. However, when the task difficulty was set instead at 70% correct, a new group of subjects was able to learn. Hence, learning motion discrimination was possible when MT was presumably eliminated.