Predicting favorable and unfavorable consequences of perceptual learning: worsening and the peak shift.

Discrimination learning can cause improved and worsened ability to perceive differences. This subsequently affects how stimuli are associated with meanings and behaviors. Here, human listeners were trained with frequency-modulated (FM) tonal sweeps (500-1000 Hz) in a paradigm where one FM rate (8.29 octaves per second) required a 'Target' response, while a rate either slower (5.76 octaves per second) or faster (11.94 octaves per second) required a 'Non-Target' response. Training led to a shift in 'Target' responding along the FM rate dimension away from the 'Target' in a direction opposite the trained 'Non-Target'. This peak shift was paralleled by an asymmetry in acuity along the FM rate dimension in an untrained ABX task (a.k.a. match-to-sample). Performance improved relative to pre-training on trials where the 'Target' was contrasted with stimuli nearer the trained 'Non-Target'. Performance worsened on trials containing stimuli displaced along the FM dimension further from the trained 'Non-Target'. A connectionist model of perceptual learning containing non-associative representational modification and associative-based task-specific reweighting was able to simulate behavior. Simulations generated novel testable predictions regarding peak shift and worsening as a result of discrimination learning. Data have theoretical and practical consequences for predicting trends in the generalization of learned behaviors and modifiable perceptual acuities.