Abstract: PURPOSE: Both external (e.g., auditory cues) and internal feedback (e.g., introduction of easy task) had been demonstrated to effectively enhance perceptual learning. However, whether there is difference between the effects of these two types of feedback are still awaiting exploration.
METHODS: Six groups of participants were trained to learn a 4-Alternative forced-choice (4-AFC) grating orientation discrimination task that differed in types of external feedback (no, simple, and complete) and presence of internal feedback (without internal feedback, i.e. both staircases converge to 35%; with internal feedback, i.e. one staircase converges to 35% and the other 70%). Simple feedback, using an auditory cue, provided the correctness of the response; complete feedback included an auditory cue indicating correctness as well as repetition of the displayed grating. High-accuracy task (i.e. 70%) in the mixed staircases provided internal feedback to low-accuracy task (35%).
RESULTS: Training decreased orientation discrimination thresholds for all groups. In the low-accuracy training condition (35%35%), subjects in the simple external feedback group demonstrated a faster learning rate, while subjects in the complete external feedback group exhibited both a faster learning rate and a lower initial threshold, as opposed to subjects in the no feedback group. Introducing internal feedback (i.e. high accuracy) lowered the initial threshold but left the learning rate unchanged. These observations cannot be explained by increased or decreased occurrences of grating presentation in the external and internal feedback conditions.
CONCLUSIONS: We found that external feedback can speed perceptual learning (simple feedback) and improve initial performance (e.g. with complete feedback), while internal feedback can only facilitate initial performance, indicating potential differences in the regulatory mechanism(s) of internal and external feedbacks on perceptual learning.

Key words: Visual perceptual learning, Feedback, Plasticity