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Leslie A. Notman, Paul T. Sowden; Does categorical perception result from perceptual learning?. Journal of Vision 2002;2(7):65. doi: 10.1167/2.7.65.
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© ARVO (1962-2015); The Authors (2016-present)
Categorical perception (CP) is apparent when equally different stimuli appear unequally different as a function of their category membership. Typically cross-category discrimination is better than within category discrimination of stimuli that are equally different on some physical metric. Although evidence suggests that CP effects can be acquired as a result of learning (Goldstone, 1994, JEP, 123, 178–200), the mechanism of this learning remains unknown. In fact, there has been little evidence that it is indeed a perceptual phenomenon. In contrast to explanations that CP results from linguistic labelling strategies (cf. Roberson & Davidoff, 2000, Memory & Cognition, 28, 977–986), we explored whether CP effects result from a perceptual learning (PL) process.
Specifically, we measured whether a CP effect, acquired as a result of training, was specific to stimulus spatial frequency and retinal location.
First, using a same-different judgement task we measured sensitivity to orientation differences between Gabor patches that varied in orientation from 0 deg to 3.5 deg. In separate experiments discrimination was measured for Gabors at each of two spatial frequencies (1 & 8 cpd) and at each of two retinal locations. Next observers were trained to categorise singly presented stimuli into one of two categories. These were defined by dividing the orientation continuum in half. During categorisation training stimuli were always presented with just one of the two possible spatial frequencies (exp. 1) or at one of the two possible retinal locations (exp. 2). Following category learning, observers' orientation discrimination was re-measured.
Specificity of acquired CP effects to stimulus parameters such as spatial frequency and retinal location suggests that CP results from perceptual learning in early visual processing mechanisms rather than central cognitive processing and argues for an influence of cognition on perception.
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