Sound-induced flash illusion is modulated by the depth of auditory stimuli: Evidence from younger and older adults

Sound-induced flash illusion (SiFI) refers to an auditory dominance effect in which observers misperceive the number of visual flashes due to the simultaneous presentation of a different number of auditory beeps. Although the SiFI remains robust despite many factors, little is known about how the dominance of audition over vision changes as a function of spatial location in 3D space and how this corresponds with aging. In the present study, we recruited younger (18-26 years old) and older adults (60-76 years old) and presented visual stimuli in near space and auditory stimuli in far space (Vnear_Afar) or visual stimuli in far space and auditory stimuli in near space (Vfar_Anear), with the aim of exploring the effect of aging on spatial dominance in SiFI. The results showed that both participant groups exhibited a SiFI auditory dominance effect; however, older adults were more susceptible to illusions than younger adults. More importantly, for younger adults, when auditory stimuli were presented in far space, the accuracy and d' indicated that SiFI was significantly enhanced in the fission illusion, and the reaction time (RT) results showed that RT became longer in the fusion illusion. However, for older adults, the SiFI was not affected by the spatial location. Therefore, the present results reveal for the first time that the SiFI effect is modulated by the depth of auditory stimuli. Moreover, older adults were not susceptible to the depth dimension, thus showing age-related sensory decline and specifically showing a decreased ability to localize visual and auditory stimuli.