Variability and stability in the McGurk effect: contributions of participants, stimuli, time, and response type

Abstract

In the McGurk effect, pairing incongruent auditory and visual syllables produces a percept different from the component syllables. Although it is a popular assay of audiovisual speech integration, little is known about the distribution of responses to the McGurk effect in the population. In our first experiment, we measured McGurk perception using 12 different McGurk stimuli in a sample of 165 English-speaking adults, 40 of whom were retested following a one-year interval. We observed dramatic differences both in how frequently different individuals perceived the illusion (from 0 % to 100 %) and in how frequently the illusion was perceived across different stimuli (17 % to 58 %). For individual stimuli, the distributions of response frequencies deviated strongly from normality, with 77 % of participants almost never or almost always perceiving the effect (≤10 % or ≥90 %). This deviation suggests that the mean response frequency, the most commonly reported measure of the McGurk effect, is a poor measure of individual participants’ responses, and that the assumptions made by parametric statistical tests are invalid. Despite the substantial variability across individuals and stimuli, there was little change in the frequency of the effect between initial testing and a one-year retest (mean change in frequency = 2 %; test–retest correlation, r = 0.91). In a second experiment, we replicated our findings of high variability using eight new McGurk stimuli and tested the effects of open-choice versus forced-choice responding. Forced-choice responding resulted in an estimated 18 % greater frequency of the McGurk effect but similar levels of interindividual variability. Our results highlight the importance of examining individual differences in McGurk perception instead of relying on summary statistics averaged across a population. However, individual variability in the McGurk effect does not preclude its use as a stable measure of audiovisual integration.

Dissociable Effects of Aging and Mild Cognitive Impairment on Bottom-Up Audiovisual Integration

“…Accuracy rates were calculated for the congruent, auditory-alone, and visual-alone stimulus conditions, and differences in accuracy rates across groups and across conditions within each group were assessed using appropriate nonparametric tests given concerns about violations of the normality and homogeneity of variance assumptions underlying parametric tests for these data [63]. Visual bias (the McGurk effect) in each of the incongruent conditions was defined as the percentage of trials in which participants made either a visual or combination response.…”

“…The strength of the McGurk effect (i.e., the likelihood that incongruent visual speech information influences the perception of auditory speech information) varies considerably across different audiovisual combinations, due primarily to the differences in the relative perceptual reliability of the auditory and visual components of the McGurk stimuli [63,64]. Strong McGurk stimuli occur when the visual component is more reliable than the auditory component and is therefore given greater weight in the integration process, thereby facilitating integration of the visual input with the auditory input to create a strong McGurk effect.…”

Published estimates of group differences in multisensory integration are inflated

“…Using empirical data and simulations, we show that high within-group variability, coupled with routine use of small sample sizes, leads to a proliferation of inflated estimates of group differences in multisensory integration. Our results explain why recent studies have failed to replicate the large reported differences between cultures(15), genders (13), and children with developmental disorders (16). Studies of multisensory integration must increase sample sizes by an order of magnitude to produce accurate and reliable estimates of group differences.…”

“…As a behavioral assay, susceptibility to the McGurk effect has been used to argue for important differences in multisensory integration between genders(5), in atypical human development(4, 6), across the lifespan(7), in mental health disorders (8,9), and between cultural/linguistic groups (10)(11)(12). Amidst the enthusiasm for using the McGurk effect to study such between-group differences, recent work has highlighted large within-group variability in susceptibility to the illusion using relatively homogeneous subject pools (13,14). However, most studies of the McGurk effect test a relatively small number of participants, with only a single published study reporting a group size of greater than 100 (15).…”

Increased Response to Altered Auditory Feedback in Dyslexia: A Weaker Sensorimotor Magnet Implied in the Phonological Deficit

“…This variability in response is certainly not unique to speech perception-production interaction. For instance, the McGurk effect, a traditional measure of audiovisual integration and well known in the DD field, shows a dramatic diversity of responses both across individuals and across used stimuli (Mallick, Magnotti, & Beauchamp, 2015).…”