Search

Nearly perfect speech recognition was observed under conditions of greatly reduced spectral information. Temporal envelopes of speech were extracted from broad frequency bands and were used to modulate noises of the same bandwidths. This manipulation preserved temporal envelope cues in each band but restricted the listener to severely degraded information on the distribution of spectral energy. The identification of consonants, vowels, and words in simple sentences improved markedly as the number of bands increased; high speech recognition performance was obtained with only three bands of modulated noise. Thus, the presentation of a dynamic temporal pattern in only a few broad spectral regions is sufficient for the recognition of speech.

Two distinct physiological mechanisms underlying loudness sensation were inferred from electric stimulation of the human auditory nerve and brainstem. In contrast to a power function relating loudness and stimulus intensity in acoustic hearing, loudness in electric stimulation of the auditory nerve depends on stimulus frequency. Loudness is an exponential function of electric amplitude for high frequencies and is a power function for low frequencies. A frequency-dependent, two-stage model is suggested to explain the loudness function, in which the first stage of processing is performed by a mechanical mechanism in the cochlea for high-frequency stimuli and by a neural mechanism in the cochlear nucleus for low-frequency stimuli.