Assessing automaticity in audiovisual speech integration: evidence from the speeded classification task

The McGurk effect is usually presented as an example of fast, automatic, multisensory integration. We report a series of experiments designed to directly assess these claims. We used a syllabic version of the speeded classification paradigm, whereby response latencies to the first (target) syllable of spoken word-like stimuli are slowed down when the second (irrelevant) syllable varies from trial to trial. This interference effect is interpreted as a failure of selective attention to filter out the irrelevant syllable. In Experiment 1 we reproduced the syllabic interference effect with bimodal stimuli containing auditory as well as visual lip movement information, thus confirming the generalizability of the phenomenon. In subsequent experiments we were able to produce (Experiment 2) and to eliminate (Experiment 3) syllabic interference by introducing 'illusory' (McGurk) audiovisual stimuli in the irrelevant syllable, suggesting that audiovisual integration occurs prior to attentional selection in this paradigm.