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Tiffany N Saffell, Nestor Matthews; Perceptual learning reveals separate neural events for speed and direction. Journal of Vision 2003;3(9):260. doi: 10.1167/3.9.260.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: In principle, our ability to see subtle speed differences could be mediated by neural events that are the same as, or different from, the neural events mediating our ability to see subtle direction differences. Here, we sought to distinguish psychophysically between these possibilities by using a perceptual learning paradigm.
Method: Twenty-two Denison University undergraduates participated in the study. For each participant, we measured speed-discrimination thresholds and direction-discrimination thresholds before, during, and after extensive training. Half of the participants trained extensively on speed discrimination, while the other half trained extensively on direction discrimination. The speed judgments and direction judgments, for each participant, were made under identical stimulus conditions. The stimuli on each trial were two random-dot cinematograms (RDCs) that always differed from each other in speed and direction of motion. To ensure a fair comparison in learning rates, the initial levels of discriminability (d′=0.52) were equated across participants and tasks.
Results: The results indicated that the learning curves for direction discrimination were significantly steeper than those for speed discrimination (F(1,20) = 9.581, p=0.006). Additionally, the significant practice-based improvements on each motion task did not transfer to the other motion task.
Conclusions: The task-specific learning rates and the lack of transfer suggest that the neural events mediating speed discrimination are at least partially independent from those mediating direction discrimination, and vice versa, even under identical stimulus conditions.
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