The relationship of speech-sound discrimination to the development of ear asymmetries in grade-school children

The relationship between ear asymmetry and speech-sound discrimination performance was examined for 364 Ss from ages 7-8, 9-10, and 11-12. Subjects were administered the Goldman-Fristoe-Woodcock Test of Auditory Discrimination and a single-pair-per— trial dichotic recognition task. The dichotic stimuli consisted of CVC nonsense syllables differing in medial vowel or initial stop consonant. For analysis of the dichotic recognition scores, a 3x3x2x2 between-within-subjects analysis of variance design was used, the between factors being age and level of discrimination ability, and the within factors being type of stimulus material and ear of presentation. Both speech-sound discrimination and ear asymmetry were found to increase with age. Increases in left-ear advantage for vowel-varied material with increases in asymmetry was found to be due to decreasing right-ear recognition of vowel-varied stimuli. These results were discussed in terms of a unilateral dominance specific for speech as opposed to a bilateral dominance for both speech and nonspeech material. Therefore the common assumption of a specialization in the right hemisphere for functions involved in left-ear advantages is considered to be inaccurate. In general, a positive relationship was found between the degree of ear asymmetry and speech-sound discrimination ability. To describe the relationship more adequately however, it was necessary to take into account the direction of ear asymmetry obtained for vowel-varied material. This asymmetry-direction factor was interpreted as reflecting the ability of subjects to use the nonencoded attributes of the speech signal. Inferior functioning with respect to this factor was found to result in a marked decrement in speech-sound discrimination performance and in a negative relationship between ear asymmetry and speech-sound discrimination. The influence of this factor was more evident in the younger age groups than it was in the 11-12 age group. The implications of the results were discussed with reference to the reading process and the development of remedial reading programs.Arts, Faculty ofPsychology, Department ofGraduat