Perceptual decision making processes are affected by intensity of an acoustic stimulus in an inspection time paradigm


Previously we showed that irrelevant acoustic stimuli could influence the amount of time required for a visual stimulus to be accurately perceived. Participants performed an inspection time (IT) task whereby they identified which leg of a briefly presented (15-135ms) "pi" figure was longer, but on some trials it was accompanied with a tone presented to the left or right ear via headphones. The tone was presented on the same side as the longest leg of the figure (congruent), or opposite (incongruent). At short presentation times congruent auditory stimuli led to an increase in the proportion of correct identifications, whereas incongruent stimuli decreased the proportion of correct responses at these times. It was unclear, however, whether subjects were simply choosing the side where the tone was presented or whether the acoustic stimulus was involuntarily influencing their response. The purpose of the current study was to address this by varying the intensity of the tones. It was hypothesized that if participants were simply choosing the side with the tone, then its intensity (either quiet:60 dB, or loud:85 dB) should not influence decision making. Results showed that on incongruent trials participants were significantly more likely to incorrectly report the longest leg of the pi figure when the acoustic stimulus was loud, as opposed to when it was quiet for the shortest visual presentation time. Because the likelihood of responding to the side of the acoustic stimulus scaled with intensity, these results suggest irrelevant accessory stimuli can subliminally/involuntarily affect perceptual decision making processes.

Acknowledgments: Supported by NSERC and the Ontario Ministry of Research and Innovation.