More than meets the eye: neural correlates of consciousness in the sound-induced flash illusion

The visual awareness negativity (VAN) is a brain signal thought to reflect conscious perception. This event-related potential study tested whether the VAN appears during visual illusions, where people report seeing something that is not physically present. Using the sound-induced flash illusion—a single flash accompanied by two beeps often creates the illusion of a second flash—the researchers compared brain responses from 47 participants on trials where the illusion was perceived versus not perceived. An enhanced negativity over posterior electrodes between 250 and 300 milliseconds appeared during illusory trials. Lower pre-stimulus alpha power also accompanied illusion trials, consistent with prior work linking alpha brain waves to perceptual variability. These results suggest the VAN reflects conscious perception even for illusory experiences, supporting its role as a neural correlate of consciousness.

Study at a glance

Abstract

Abstract The visual awareness negativity (VAN) has been identified as a potential neuronal correlate of consciousness (NCC). The VAN is typically found when comparing experimental trials in which a stimulus was perceived with trials in which the same stimulus was not perceived. However, if the VAN represents a reliable NCC, it should also be observed under conditions in which participants report conscious perception despite the absence of a corresponding visual stimulus, i.e., a visual illusion. Our event-related potential (ERP) study ( N = 47) aimed to investigate this question by using a suited stimulation design, the sound-induced flash illusion (SIFI), for which a visual stimulus is presented once together with two short beeps, leading - on about half the trials - to the illusory perception of a second flash, with graded levels of reported awareness of these trials. When comparing illusory with non-illusory trials, we found an enhanced negativity over posterior electrodes between 250 and 300 ms. Frequency analyses additionally revealed lower pre-stimulus alpha power in illusion trials, aligning with prior work linking alpha dynamics to perceptual variability. Our findings suggest that even illusory perceptions enhance negative potentials over posterior regions during the VAN interval, supporting the interpretation of the VAN as a NCC.