Abstract
Exposure to blue light not only contributes to vision, but also facilitates cognitive functions such as alertness, vigilance, and working memory. However, most studies examined the blue light effect only on the central visual field. The blue light facilitation effect may be due to vigilance increment or focused attention improvement. The vigilance increment view predicts that there is a general facilitation on both central and peripheral visual processing; however, the focused attention improvement view predicts that blue light is detrimental to peripheral visual processing. To test these hypotheses, we adopted the clock paradigm (Carlson, Hogendoorn, and Verstraten, 2006) to estimate the speed of exogenous and endogenous attention shift. Participants fixated at the center with 10 running clocks in the periphery positioned in an imaginary circle. Three conditions were manipulated: the peripheral-cue condition, where the target clock flashed as an exogenous cue; the central-cue condition, where a cuing line was presented at the fixation point as an endogenous cue; and the baseline condition as the control, where the cuing line was presented as a probe to exclude the time cost of attention shift, followed by the flash of the target clock. Participants reported the time of the target clock when either the peripheral or the central cue was presented. The speed of attention shift was estimated by the time latency between true and reported cue-onset time. We conducted experiments with blue and green background lights in Experiment 1, and with high and low S-cone stimulated background lights in Experiment 2. Results showed that exposure to blue light slowed down the speed of exogenous attention shift and these results were not due to the sluggish property of S-cone processing. This study supports the focused attention improvement view and shows a new blue light “impairment” different from previous studies.