Evaluating the articulation index for auditory-visual consonant recognition.

Adequacy of the ANSI standard for calculating the articulation index (AI) [ANSI S3.5-1969 (R1986)] was evaluated by measuring auditory (A), visual (V), and auditory-visual (AV) consonant recognition under a variety of bandpass-filtered speech conditions. Contrary to ANSI predictions, filter conditions having the same auditory AI did not necessarily result in the same auditory-visual AI. Low-frequency bands of speech tended to provide more benefit to AV consonant recognition than high-frequency bands. Analyses of the auditory error patterns produced by the different filter conditions showed a strong negative correlation between the degree of A and V redundancy and the amount of benefit obtained when A and V cues were combined. These data indicate that the ANSI auditory-visual AI procedure is inadequate for predicting AV consonant recognition performance under conditions of severe spectral shaping.