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No Distributional Learning in Adults from Attended Listening to Non-Speech

Distributional learning is a perceptual process hypothesized to underlie the phenomena of phonetic recalibration and selective adaptation, as well as infant speech sound category learning. However, in order to be conclusively tied to the earliest stages of speech sound category development, that is, the formation of novel perceptual categories, distributional learning must be shown to operate on stimuli for which there are no pre-existing categories. We investigated this in a previous study, finding no evidence of distributional learning in adults from unattended listening to non-speech. Since attention to stimuli impacts distributional learning, the present study focused on distributional learning from attended listening to non-speech. The same paradigm was used as in the previous study, except that participants’ attention was directed towards stimuli by means of a cover task. Non-speech stimuli were spectrally rotated vowels and the mismatch negativity was used to measure perceptual categorization. No distributional learning was found, that is, no effect of attention on distributional learning was demonstrated. This could mean that the distributional learning process does not operate on stimuli where perceptual categories do not already exist, or that the mismatch negativity measure does not capture the earliest stages of perceptual category development.