Compound action potentials (CAPS), synchronized potentials by firings of many fibers in the auditory nerve, are thought to represent temporal information related to sound coding in the cochlea. In the present study, CAPs in nine guinea-pig cochleae evoked by speech sounds were examined by electrocochleography. CAPS were evoked at (1) onset of voiceless stop consonants [p], [k], [t], and voiced stops [b] in every cases, (2) onsets of voiced stops [d], [g] in some cases and (3) onset of semi vowels [w] in some cases. CAPs were not observed at other consonants or semi vowel [y], and seldom observed at the onset of vowels in consonant-vowel syllables.
It is concluded that some inf ormations which are important for speech recognition such as the onset of stop consonants is coded as temporal information, synchronized firing of auditory nerve fibers, in the cochlea.