Inhibition of return modulates the flash-lag effect

Transient events are known to draw exogenous attention, and visual processing at the attended location is transiently facilitated, but after several hundred milliseconds, attentional processing at the cued location becomes poorer than processing elsewhere, resulting in a slower reaction to a target stimulus that subsequently appears at the cued location. Despite a number of previous studies on this effect, termed inhibition of return (IOR), it is still unclear whether a perceptual process related to the subjective onset time of the target stimulus is disrupted when IOR occurs. In the present study, we used a distinct visual phenomenon termed the flash-lag effect (FLE) as a tool to quantify IOR. The FLE is an illusion in which a flashed stimulus appears to lag behind a moving stimulus, despite being physically aligned. We used an identical stimulus configuration and asked observers to conduct two independent tasks in separate sessions. The first was a simple reaction task to measure the onset reaction time (RT) to an abruptly appearing target. The second was an orientation judgment task to measure the degree of the FLE. Both the RT and the FLE were found to be altered in accordance with IOR, and a significant correlation was demonstrated between the changes in the RT and those in the FLE. These results demonstrate that the perceptual process related to the stimulus onset can be compromised by IOR.