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Abstract

Twelve normal-hearing subjects (21 to 33 years of age) listened to sentences in the presence of an eight-talker babble background noise in three signal-to-noise (S:N) conditions: 0, -3, -6 dB S:N. Each sentence was one of nine different syntactic complexity types. Subjects were asked to perform an Object Manipulation Task (OMT) by acting out who did what to whom in the sentences by using toy animals. Each subject's manipulations were coded as correct or incorrect; the incorrect manipulations were subdivided into three error categories: syntactic violations, lexical substitutions, and omissions. The latency of each manipulation was measured. The present study investigated the effect of the S:N conditions and the syntactic complexity on accuracy of comprehension and latency of response. Also, the number and types of errors that occurred as S:N conditions became more adverse were examined. It was found that more complex sentences were not comprehended as accurately as less complex sentences and the more complex sentences took more time to act out. The pattern of the relative number of errors across sentence types were similar across S:N conditions, though fewer sentences were comprehended correctly in the -6 dB S:N condition. It was also found that, in general, syntactic-type errors increased as the S:N condition became more adverse. It was shown that similar errors were made in the present study as were made by aphasic patients (Caplan, Baker, and Dehaut, 1985) and by normal young subjects who were perceptually stressed with a visual presentation of sentences at an increased speed (Miyake, Carpenter, and Just, 1994). The results obtained in the present study were used to evaluate the idea that working memory capacity may limit a listener's ability to comprehend.