IDENTIFICATION AND DISCRIMINATION OF NORMAL AND DEFECTIVE /S/ BY /S/-MISARTICULATING AND NORMAL CHILDREN

KIM ARTHUR WILCOX, Purdue University

Abstract

A review of relevant literature shows a controversy regarding the ability of misarticulating children to perceive speech. While many authors claim that misarticulators have normal speech perception abilities, many others do not. Past research, however, has been plagued by three major problems: (1) poor subject selection and description procedures. (2) the existence of phonemic differences in the stimuli used, and (3) utilization of stimuli not necessarily related to the subject population's production deficits. Two rather well-defined groups of misarticulators are dentalizing and lateralizing lispers. So by using various /s/ allophones as stimuli in both an identification and a discrimination task it seemed that a more accurate investigation of the existence any subtle perceptual deficits might be made. It was also thought that by utilizing the categorical perception paradigm, information about how the specific /s/ allophones are processed might also be gathered. Hence, the major objectives of the present study were to compare the performance of adults, normally articulating children, dental lispers, and lateral lispers on two speech perception tasks; and to determine how various /s/ allophones are perceived by different listeners. Ten normal speaking children, ten dentalizers, ten lateralizers, and ten certified Speech-Language-Pathologists served as subjects. The subjects first identified as "correct" or "incorrect" 136 /s/ tokens. These tokens had been spliced from the sentence repetitions of dentalizers, lateralizers, and normally articulating children. At a later session, subjects judged 252 (376 for the adults) pairs of /s/ fricative noise pieces as "same" or "different". The fricative noises had been produced by six children, two of which had a dental lisp, two of which had a lateral lisp, and two of which and normal articulation. These pieces were combined in all possible pairs and then randomized for presentation. In addition, the interstimulus-interval on the discrimination tape was varied from 0.5 sec to 1.0 sec to 3.0 sec in a counterbalanced order. The criterion measure for both tasks was percent correct judgements. Statistical analysis of the identification task results indicated that the adult subjects performed better than the three groups of children, but the children did not perform differently from each other. In addition, items produced by the dentalizing speakers were generally the most difficult to correctly judge. The identification task utilized stimuli from thirteen different phonetic contexts, analysis indicated that those /s/'s in a / t(INT)/ context were easiest to identify, next easiest were intervocalic contexts, and the most difficult cases were /s/-blends. Results from the discrimination task also indicated no differences between the three groups of child listeners in perceptual ability, but again there was evidence of superior performance by the adult subjects. The relationship of the two elements of the stimulus pair had no apparent effect upon discrimination. That is, identical pairs, different pairs of the same production type, and different pairs of different production types, were all discriminated with equal effectiveness. This result was persistent even when performance was degraded by increasing the ISI. The findings were taken to indicate that the speech perception abilities of children may not be as acute as sophisticated adult listeners; but relative to normal speaking children, /s/-misarticulators perceive normal and defective /s/ allophones in a similar fashion. In addition, given the apparent lack of importance of group labelling for different /s/-allophones; it was concluded that these three types of allophones all belong to one phonetic category.

Degree

Ph.D.

Subject Area

Speech therapy

COinS