Effects of facial paralysis and audiovisual information on stop place identification

This study investigated how listeners' perceptions of bilabial and lingua-alveolar voiced stops in auditory (A) and audiovisual (AV) presentation modes were influenced by articulatory function in a girl with bilateral facial paralysis (BFP) and a girl with normal facial movement (NFM). The Fuzzy Logic Model of Perception (FLMP) was used to make predictions about listeners' identifications of stop place based on assumptions about the nature (clear, ambiguous, or conflicting) of the A or AV cues produced by each child during /b/ and /d/ CV syllables. As predicted, (a) listeners' identification scores for NFM were very high and reliable, regardless of presentation mode or stop place, (b) listeners' identification scores for BFP were high for lingua-alveolar place, regardless of presentation mode, but more variable and less reliable than for NFM; significantly lower (overall at a chance level) for bilabial place in the A mode; and lowest for bilabial place in the AV mode. Conflicting visual cues for stop place for BFP's productions of /bV/ syllables influenced listeners' perceptions, resulting in most of her bilabial syllables being misidentified in the AV mode. F2 locus equations for each child's /bV/ and /dV/ syllables showed patterns similar to those reported by previous investigators, but with less differentiation between stop place for BFP than NFM. These acoustic results corresponded to the perceptual results obtained. (That is, when presented with only auditory information, on average, listeners perceived BFP's target /b/ syllables to be near the boundary between /b/ and /d/.)