Effects of Categorization Training on Auditory Perception and Cortical Representations

Our ability to discriminate sounds is not uniform throughout acoustic space. One example of auditory space warping, the perceptual magnet effect, appears to arise from exposure to the phonemes of an infant’s native language. We have developed a neural model that accounts for the magnet effect in terms of neural map dynamics in auditory cortex. This model predicts that it should be possible to induce a magnet effect for nonspeech stimuli. This prediction was verified by a psychophysical experiment in which subjects underwent categorization training involving non-speech auditory stimuli that were not “categorical” prior to training. The model further predicts that the magnet effect arises because prototypical vowels have a smaller cortical representation than non-prototypical vowels. This prediction was supported by an fMRI experiment involving prototypical and non-prototypical examples of the vowel /i/. Finally, the model predicts that categorization training with non-speech stimuli should lead to a decreased cortical representation for stimuli near the center of the training category. This prediction was supported by an fMRI experiment involving categorization training with non-speech auditory stimuli.