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Leslie A Notman, Paul T Sowden; Learned categorical perception is spatial frequency specific: an effect of categorisation on early visual processing. Journal of Vision 2003;3(9):257. doi: 10.1167/3.9.257.
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© ARVO (1962-2015); The Authors (2016-present)
The term Categorical Perception (CP) is used to describe an observers' superior ability to distinguish between members of different categories compared to equally different members of the same category. However, although CP can be acquired as a result of learning (Goldstone, 1994, JEP, 123, 178–200) the mechanisms involved remain unknown and there is little evidence that it is indeed a perceptual phenomenon. Using a transfer of learning paradigm, we explore whether a perceptual learning (PL) process localised to early visual processing can explain certain CP effects. Last year (Notman & Sowden, 2002, J. Vis., 7, 65a) we reported that acquired CP for orientation defined categories could be partially specific to spatial frequency (SF). In this study, we examine this in more detail.
On day 1, we used a same different judgement task to measure sensitivity to orientation differences between briefly presented pairs of Gabor patches. They varied in orientation from 10 deg to 80 deg (in 10 deg steps) and were presented in the periphery at each of two SFs (0.86 & 6.9 cpd). Spatial phase was randomly varied for each stimulus. Next observers were trained to categorise stimuli into one of two categories that were defined by dividing the orientation continuum in half. During training, stimuli were presented at just one of the SFs. Categorisation training was then repeated on day 2. Finally on day 3 observers' orientation discrimination was re-measured for stimuli presented at both SFs.
We found that observers' orientation discrimination between stimuli that cross the category boundary was significantly improved following training. This is consistent with a learned CP effect for orientation categories. Furthermore, the learned CP effect was specific to the trained SF. Our findings are consistent with the possibility that a perceptual learning process operating on early SF tuned stages of visual analysis results in the observed CP effects.
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