Adaptation effects on cortical activities for AM flickering lights
Yosuke Okamoto, Seiji Nakagawa
For a sinusoidal flickering light amplitude modulated (AM) sinusoidally, flicker at a frequency corresponding to a periodicity of a temporal envelope of flickering light is detected although there is no frequency component at the flicker frequency. However, the mechanisms underlying the perception of the envelope are still unclear. Then, to consider where the processing of envelope extraction is carried out in the visual system, we investigated the effects of adaptation to temporal frequencies on the visual sensitivity and cortical activities for the envelope. It is known that there are two temporal channels with a lower and a higher peak frequency, respectively. Therefore, in this study, sinusoidal flickering lights with a low (2 Hz) and a high (16 Hz) temporal frequency were used as adapting stimuli. Following adaptation, the sinusoidal flickering lights of 2 and 16 Hz and an AM flickering light with a modulation frequency of 2 Hz and a carrier frequency of 16 Hz were presented as test stimuli. The results showed that the sensitivity and magnetoencephalographic (MEG) responses to the sinusoidal flicker were reduced more when the adapting and test stimuli had same frequency components than different ones. On the other hand, although the AM flickering light had a frequency component at the carrier frequency but not at the modulation frequency (envelope periodicity), the sensitivity and MEG responses to the envelope periodicity of AM flickering light were reduced more after adapting to the modulation frequency rather than the carrier frequency. Based on the present results, we discussed where the envelope component arises in the visual system.
Key words: Vision, Temporal processing, Flicker, AM, Adaptation