Performing a task jointly enhances the sound-induced flash illusion

Abstract

Our senses are stimulated continuously. Through multisensory integration, different sensory inputs may or may not be combined into a unitary percept. Simultaneous with this stimulation, people are frequently engaged in social interactions, but how multisensory integration and social processing interact is largely unknown. The present study investigated if, and how, the multisensory sound-induced flash illusion is affected by a social manipulation. In the sound-induced flash illusion, a participant typically receives one visual flash and two auditory beeps and she or he is required to indicate the number of flashes that were perceived. Often, the auditory beeps alter the perception of the flashes such that a participant tends to perceive two flashes instead of one flash. We tested whether performing a flash counting task with a partner (confederate), who was required to indicate the number of presented beeps, would modulate this illusion. We found that the sound-induced flash illusion was perceived significantly more often when the flash counting task was performed with the confederate compared with performing it alone. Yet, we no longer find this effect if visual access between the two individuals is prevented. These findings, combined with previous results, suggest that performing a multisensory task jointly—in this case an audiovisual task—lowers the extent to which an individual attends to visual information, which in turn affects the multisensory integration process.

The impact of joint attention on the sound-induced flash illusions

“…While the present study investigated the impact of joint attention on the sound-induced flash illusion, an earlier study found that a division of labour manipulation, where the participant reported on the number of flashes while a confederate simultaneously reported on the number of beeps, induced a stronger fission illusion compared with performing the task alone (Wahn et al, 2020). The authors suggest that in their social manipulation, the participant's visual attention was divided between the visual flash-counting task and attending to the co-actor, which in turn increased the influence of the auditory stimuli and thus the number of perceived fission illusions.…”

“…The authors suggest that in their social manipulation, the participant's visual attention was divided between the visual flash-counting task and attending to the co-actor, which in turn increased the influence of the auditory stimuli and thus the number of perceived fission illusions. Since participants in a pair performed different tasks, participants likely showed a tendency to co-represent the other's task and monitor the other's performance (Wahn et al, 2020).…”

“…Given current literature on possible social effects on the sound-induced flash illusion, our estimate of a Cohen's d effect size is 0.41 (Wahn et al, 2020). We used the software G*Power (Faul et al, 2007) to conduct a power analysis, to obtain .80 power to detect Cohen's d effect size of 0.415 for a two-tailed paired t test, at the standard .05 alpha error probability.…”

“…Using the sound-induced flash illusions also affords comparisons with recent reports that dividing attentional labour increases susceptibility to the fission illusion (Wahn et al, 2020). In their study, the tasks were divided across sensory modalities: the participant was asked to count the number of flashes, either with a confederate counting the number of beeps, or alone.…”

“…Taken together with previous studies (Heed et al, 2010;Wahn et al, 2017) where participants were better able to ignore distracting visual stimuli in multisensory tasks, the authors suggest that the presence of another person may act as a visual distractor so that visual information presented on the screen is attended to a lesser extent. Depending on the task, this effect would improve performance when the participant had to ignore visual information during a tactile (Heed et al, 2010) or auditory (Wahn et al, 2017) localization task, and worsen performance when participants had to count visual targets and ignore auditory distractors (Wahn et al, 2020). There is no previous indication, to our knowledge, of whether a similar or opposite effect would be observed in a joint attention manipulation, where both participants in a pair are required to attend and respond to the same modal target.…”