Sources of variance in the audiovisual perception of speech in noise

The sight of a talker’s face dramatically influences the perception of auditory speech. This effect is most commonly observed when subjects are presented audiovisual (AV) stimuli in the presence of acoustic noise. However, the magnitude of the gain in perception that vision adds varies considerably in published work. Here we report data from an ongoing study of individual differences in AV speech perception when English words are presented in an acoustically noisy background. A large set of monosyllablic nouns was presented at 7 signal-to-noise ratios (pink noise) in both AV and auditory-only (AO) presentation modes. The stimuli were divided into 14 blocks of 25 words and each block was equated for spoken frequency using the SUBTLEXus database (Brysbaert and New, 2009). The presentation of the stimulus blocks was counterbalanced across subjects for noise level and presentation. In agreement with Sumby and Pollack (1954), the accuracy of both AO and AV increase monotonically with signal strength with the greatest visual gain being when the auditory signal was weakest. These average results mask considerable variability due to subject (individual differences in auditory and visual perception), stimulus (lexical type, token articulation) and presentation (signal and noise attributes) factors. We will discuss how these sources of variance impede comparisons between studies.