Abstract: PURPOSE: Both adaptation and perceptual learning can change how we perceive the visual environment, reflecting the plasticity of the visual system. Our previous work has attempted to investigate the interaction between the two processes and found that contrast adaptation effect attenuated after multiple days of training (Dong, Gao, Lv, & Bao, 2016), which is speculated to be result from habituation to the adapters or to the process of adaptation. To test these two hypotheses, we used the SSVEP method to investigate how the neural responses to the adapting gratings change after repeated contrast adaptation.
METHODS: 10 subjects were trained with top-up contrast adaptation for 6 days. A spatial 2AFC method was used to track the threshold elevation aftere?ect (TEAE) of each session. The TEAE and SSVEP signals of the trained adapter and an untrained control adapter were measured before and after training.
RESULTS: The repeated measurements ANOVA on TEAE showed a significant interaction between Session (pre-training vs post-training) and Condition (trained vs control). Repeated adaptation produced progressively decreased TEAE in the trained condition but not in the control condition. The SSVEP amplitudes of the adapters were not different between pre- and post-test in both conditions. While a three-way ANOVA revealed a significant main effect of the adaptation timecourse (the first minute vs last minute), the SSVEP amplitude within each session became smaller over time.
CONCLUSIONS: Contrast adaptation effect attenuated over training. This phenomenon may relate to the change of adaptation process after training rather than the habituation to the adapter.

Key words: perceptual learning, contrast adaptation, SSVEP, habituation