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.

Open Educational Resources (OER) have been lauded for their ability to reduce student costs and improve equity in higher education. Research examining whether OER provides learning benefits have produced mixed results, with most studies showing null effects. We argue that the common methods used to examine OER efficacy are unlikely to detect positive effects based on predictions of the access hypothesis. The access hypothesis states that OER benefits learning by providing access to critical course materials, and therefore predicts that OER should only benefit students who would not otherwise have access to the materials. Through the use of simulation analysis, we demonstrate that even if there is a learning benefit of OER, standard research methods are unlikely to detect it.

Humans combine the visual information from mouth movements with auditory information from the voice to recognize speech. A common method for assessing multisensory speech perception is the McGurk effect: when presented with particular pairings of incongruent auditory and visual speech syllables (e.g., the auditory speech sounds for “ba” dubbed onto the visual mouth movements for “ga”) individuals perceive a third syllable, distinct from the auditory and visual components. Chinese and American cultures differ in the prevalence of direct facial gaze and in the auditory structure of their languages, raising the possibility of cultural and language-related group differences in the McGurk effect. There is no consensus in the literature about the existence of these group differences, with some studies reporting less McGurk effect in native Mandarin Chinese speakers than in English speakers and others reporting no difference. However, these studies sampled small numbers of participants tested with a small number of stimuli. Therefore, we collected data on the McGurk effect from large samples of Mandarin-speaking individuals from China and English-speaking individuals from the USA (total n = 307) viewing 9 different stimuli. Averaged across participants and stimuli, we found similar frequencies of the McGurk effect between Chinese and American participants (48% vs. 44%). In both groups, we observed a large range of frequencies both across participants (range from 0% to 100%) and stimuli (15% to 83%) with the main effect of culture and language accounting for only 0.3% of the variance in the data. The high variability in the McGurk effect necessitates the use of large sample sizes to accurately estimate group differences.

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We report the unexpected finding that slowing video playback decreases perception of the McGurk effect. This reduction is counter-intuitive because the illusion depends on visual speech influencing the perception of auditory speech, and slowing speech should increase the amount of visual information available to observers. We recorded perceptual data from 110 subjects viewing audiovisual syllables (either McGurk or congruent control stimuli) played back at one of three rates: the rate used by the talker during recording (the natural rate), a slow rate (50% of natural), or a fast rate (200% of natural). We replicated previous studies showing dramatic variability in McGurk susceptibility at the natural rate, ranging from 0–100% across subjects and from 26–76% across the eight McGurk stimuli tested. Relative to the natural rate, slowed playback reduced the frequency of McGurk responses by 11% (79% of subjects showed a reduction) and reduced congruent accuracy by 3% (25% of subjects showed a reduction). Fast playback rate had little effect on McGurk responses or congruent accuracy. To determine whether our results are consistent with Bayesian integration, we constructed a Bayes-optimal model that incorporated two assumptions: individuals combine auditory and visual information according to their reliability, and changing playback rate affects sensory reliability. The model reproduced both our findings of large individual differences and the playback rate effect. This work illustrates that surprises remain in the McGurk effect and that Bayesian integration provides a useful framework for understanding audiovisual speech perception.

This article examines the impact of Zero Cost Textbooks (ZCB) courses on two key factors of students success: pass rates and completion rates. We examine 3 years of data at Houston Community College, ending with the first year of their implementation of a ZCB program. Following the "access hypothesis," we suppose that students who would not otherwise be able to purchase traditional textbooks will have higher pass rates and completion rates in ZCB courses. We use Pell recipient status and ethnicity as proxies for socio-economically disadvantaged students, targeting those populations where the access hypothesis will have the greatest impact. We isolate faculty who taught both ZCB and non-ZCB courses during the period under review and conduct a post-hoc analysis, using mixed effects logistic regression, to identify interactions between student and course characteristics and success metrics. We find that HCC's ZCB program had a statistically significant positive effect on pass rates for all students, but no effect on completion. We find a trend to suggest the ZCB program may improve success among Black students, but only a statistically significant positive effect among Asian students, and no interaction with Pell recipient status. These results are not well-explained by the access hypothesis; they suggest the need for further research.

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