Perceptual learning modulates sensory evoked response during vowel segregation.

With practice, people become better at discriminating two similar stimuli, such as two sounds. The neural mechanisms that underlie this type of learning have been of interest to researchers investigating neural plasticity associated with learning and recovery of function following stroke. We utilized event related potentials (ERP) to study the neural substrates underlying auditory discrimination learning. Stimuli were five steady-state American English vowels. On each trial, participants were presented with a pair of vowels created by summing together the digital waveforms of two different vowels. Listeners were instructed to identify both vowels in the pair. ERPs were recorded during two sessions separated by 1 week. Half of the participants practised the discrimination task during the intervening week while the other half served as controls and did not receive any training. Trained listeners showed greater improvement in accuracy than untrained participants. In both groups, vowels generated N1 and P2 waves at the fronto-central and temporal scalp regions. The behavioral effects of training were paralleled by decreased N1 and P2 latencies as well as enhanced P2 amplitude in the trained compared with untrained listeners. The effects of training on sensory evoked responses are consistent with the proposal that perceptual learning is associated with changes in sensory cortices.