Comparison of two single-channel vibrotactile aids for the hearing-impaired.

Two commercially available single-channel vibrotactile aids, designed to transmit information about acoustic stimuli to persons who cannot perceive such stimuli through conventional amplification, were compared in a number of tasks with the same subjects. Both devices employed a vibratory transducer worn on the wrist. One device represented characteristics of the envelope of the waveform by using it to modulate the amplitude of a 250-Hz carrier vibration (an amplitude-modulated, or AM, signal). The other device presented and amplitude-modulated a broad-band signal whose spectral characteristics preserved information about the signal. Subjects performed several tasks. On some tasks (sound detection, environmental sound identification, syllable rhythm and stress categorization) information about the envelope of the stimulus was expected to be sufficient for good performance. On others (speech sound recognition) additional information about the spectral fine structure of the signal spectrum was anticipated to be required for good performance. Results indicated that the subjects performed comparably with both devices on all tasks, suggesting that they did not make use of the spectral information available in the more complex signal.