Psychoacoustic evaluation of present prostheses.

A battery of psychoacoustic tests, designed to specify auditory discriminations possible with present, single-channel auditory prostheses, was administered successfully to 12 of the 13 subjects. While no subject was able to perform all discriminations required by this battery of tests, there was no discrimination that at least one subject did not perform successfully. The typical subject could 1) discriminate intensity differences within normal limits for frequencies below 1000 Hz; 2) discriminate frequency differences quite normally at 125 and 250 Hz, but not at all at 1000 or 2000 Hz; 3) discriminate differences in signal duration, temporal patterning (rhythm), and spectrum (e.g., tone vs narrow-band noise); and 4) discriminate between pairs of synthesized vowel-like sounds. The results of masking experiments could only be interpreted in terms of intensity discrimination. Several subjects were able to relate stimulus intensity to loudness for low-frequency sounds; and they could relate stimulus frequency to pitch for signals below 25 Hz. The intelligibility of the subjects' speech was found to improve when their prostheses were activated.