Relative performance of single-channel and multichannel tactile aids for speech perception.

Although the results from a number of studies of the performance of multichannel tactile aids for speech perception have suggested that such devices might provide more benefit to hearing-impaired persons than single-channel tactile aids (3,4), recent studies involving direct comparisons of multichannel and single-channel vibrotactile aids (5,6) indicated otherwise. In fact, for some types of speech information, such as rhythm and stress perception, single-channel aids were shown to be superior. The present study attempted to address this apparent discrepancy by comparing the performance of two single-channel devices with two multichannel devices in a variety of speech perception tasks including both single-item and connected speech stimuli. Results indicated that the two classes of tactile device performed similarly in rhythm and stress perception, but that the multichannel aids in many cases showed better performance for tasks in which the identification of fine-structure phoneme information was required (both single-item and connected speech). Results are discussed in terms of the possibility that the performance of a specific multichannel tactile aid cannot be considered indicative of all devices of the same class.

Evaluation of two multichannel tactile aids for the hearing impaired.

Two multichannel tactile devices for the hearing impaired were compared in speech perception tasks of varying levels of complexity. Both devices implemented the "vocoder" principle in their stimulus processing: One device had a 16-element linear vibratory array worn on the forearm and displayed activity in 16 overlapping frequency channels; the other device delivered tactile stimulation to a linear array of 16 electrodes worn on the abdomen. Subjects were tested in several phoneme discrimination tasks, ranging from discrimination of pairs of words differing in only one phoneme under tactile aid alone conditions to identification of stimuli in a larger set under tactile aid alone, lipreading alone, and lipreading plus tactile aid conditions. Results showed both devices to be better transmitters of manner and voicing features of articulation than of place features, when tested in single-item tasks. No systematic differences in performance with the two devices were observed. However, in a connected discourse tracking task, the vibrotactile vocoder in conjunction with lipreading yielded much greater improvements over lipreading alone than did the electrotactile vocoder. One possible explanation for this difference in performance, the inclusion of a noise suppression circuit in the electrotactile aid, was evaluated, but did not appear to account for the differences observed. Results are discussed in terms of additional differences between the two devices that may influence performance.