| Practicing a new perceptual skill typically leads to the largest improvements in performance early in the course of training. Although these early, rapid improvements are commonly thought to stem from learning of general, conceptual aspects of the new skill, most perceptual studies instead provide evidence that they arise from learning associated with the specific stimulus used during training. Here we evaluated the contributions of both conceptual and stimulus learning to improvements on an auditory perceptual skill, interaural-time-difference (ITD) discrimination, over the first 24 hours after training. In the first experiment, we examined whether different sub-components of conceptual learning--- procedure and task learning--- as well as stimulus learning contribute to improvements observed on ITD discrimination 24 hours after training. In the second experiment, we investigated whether conceptual and stimulus learning on ITD discrimination emerge along different time courses within the first 24 hours by varying training amount, and the amount of time between training and testing.;The results indicated that (1) training amount influenced ITD discrimination performance immediately, but not 10 or more hours, after training, (2) 10 hours after training, improvements could be attributed to conceptual learning, and (3) 24 hours after training, both conceptual and stimulus learning contributed to overall improvements, but the improvements associated with conceptual learning reflected procedure and not task learning. Further, the patterns of improvement through which the emergence of conceptual and stimulus learning were observed differed between the two learning types. Thus, both conceptual and stimulus learning contributed to early rapid improvements on ITD discrimination, with conceptual learning emerging earlier, and with different behavioral consequences, than stimulus learning. The delayed emergence of both conceptual and stimulus learning may reflect processes of consolidation, in which case, differences in the rates and manifestations of these two learning types reveal two possible sub-stages of consolidation. Taken together, the current data support the ideas that perceptual training engages and modifies multiple processes, and that modifications to these processes occur along different time courses. |
