Stimulus frequency otoacoustic emissions from guinea pig and human subjects.

Stimulus frequency otoacoustic emissions (SFOAEs) have previously been recorded from human subjects by the suppression of a continuous stimulus tone generated OAE by a second tone (Kemp et al., 1990). This study presents comparative data from guinea pig and human subjects using a similar method. Differences between human and guinea pig responses to suppressor tones of higher frequency than the stimulus tone are reported. The most effective suppressors of the SFOAE in human subjects was found to be a tone of the same or slightly higher frequency than the continuous stimulus tone. In guinea pigs, this stimulus condition was found to be less effective than higher-frequency suppressors. Large phase changes were found in the SFOAE from guinea pigs when higher-frequency suppressors were employed. These were not seen in the human data. Changes in the SFOAE latency from guinea pig ears were also found as the suppressing tone frequency moved above that of the stimulus tone. These level and phase effects, when taken together with latency changes, may be indicative of the differing contributions of stimulus-place generated OAEs and those from more basal elements to the total emission recorded in the meatus in guinea pig. The results are discussed in view of the known species differences in the tuning characteristics at the frequency region studied.