As mentioned in the Section 1, there might be light-induced changes in neural excitability involved in the early perceptual analysis of visual properties (i.e., sensory gain control), because we observed that an early ERP such buy GSK269962 as N1 (an electrophysiological correlate of early attentional processing) as well as delayed reaction times were significantly modulated by the level of background illuminance. This explanation is based on our observation that the level of background illuminance significantly affected the early N1 ERP (an electrophysiological correlate of
an early attentional processing) and the delayed reaction times. The illuminance-induced changes in reaction time may be attributed to the physiological and dynamic aspects of the visual pathway to the motor cortex, which plays a major role in determining reaction times (Robinson, 1966). Such a bright see more light presumably generates an abnormal time delay from the retina to the motor cortex during button pressing since the photoreceptors in the retina behave in a light-dependent delayed manner (Pepperberg et al., 1992). Taken together, it seems that the background light might serve as a salient bottom–up or physically-driven feature, which might competitively interact with prestimulus
top-down states. Some of the previous studies examining luminance and EEG activity focus on the CYTH4 luminance of the stimulus, rather than the luminance of the background light (Johannes et al., 1995, Kobrick and Cahoon, 1968, Osaka and Yamamoto, 1978 and Yoto et al., 2007). Therefore, it is difficult to compare the results of those studies with our results in the present study. For instance, Johannes et al. (1995) observed that P1 and N1 amplitudes were increased when the stimulus luminance increased; whereas we observed N1 amplitude decreased when background light luminance increased.
Despite this difference, EEG activity was modulated by the luminance of both the stimulus and the background. Yoto et al. (2007) found significant modulation of EEG alpha power when participants viewed A2-sized colored paper; whereas we observed color changes in the background light modulated EEG alpha power. However, they observed this effect over the fronto-central region, whereas we observed this effect over the parietal region. Such a discrepancy might be because they manipulated stimulus-color and we manipulated background-color. Therefore, a direct relationship between EEG alpha and luminance cannot be confirmed on the basis of these few studies; further studies are needed to confirm such a relationship. Similar to our experiment, Maher et al. (2001) modulated background illumination while recording EEG activity in human subjects.