Perception of spasmodic dysphonia speech in background noise.

The purpose of this investigation was to judge whether the Lombard effect, a characteristic change in the acoustical properties of speech produced in noise, existed in adductor spasmodic dysphonia speech, and if so, whether the effect added to or detracted from speaker intelligibility. Intelligibility, as described by Duffy, is the extent to which the acoustic signal produced by a speaker is understood by a listener based on the auditory signal alone. Four speakers with adductor spasmodic dysphonia provided speech samples consisting of low probability sentences from the Speech Perception in Noise test to use as stimuli. The speakers were first tape-recorded as they read the sentences in a quiet speaking condition and were later tape-recorded as they read the same sentences while exposed to background noise. The listeners used as subjects in this study were 50 undergraduate university students. The results of the statistical analysis indicated a significant difference between the intelligibility of the speech recorded in the quiet versus noise conditions (F(1,49) = 57.80, p < or = .001). It was concluded that a deleterious Lombard effect existed for the adductor spasmodic dysphonia speaker group, with the premise that the activation of a Lombard effect in such patients may detract from their overall speech intelligibility.