The purpose of the present experiment was to assess the categorical perception and role of speech expectation in speech identification by chidren with sensorineural hearing loss. To do this, the category boundary and variability score were measured in normally hearing and hearing-impaired children. Speech identification tasks consisting of 12 natural words [saku-taku-aku], varing in length of initial /s/ portion. Subjects were 21 normally hearing children (8, 10, and 12 years) and 7 (Ave. 11; 6 years) hearing-impaired children. In task 1, categorical perception of different phonemes was demonstrated in all groups. In task 2, where irrelevant stimulus was used, no marked differences were observed among normal groups. Speech identification score by hearing-impaired children was poorer than the results of task 1. Boundaries of phonemecategory shift were dislocated in the hearing-impaired group when compared with results of the normal groups. The results of the category boundary and variability score showed that significant effects of hearing loss and irrelevant stimulus.
MLR and EP from both right and left AI were recorded simultaneously from eleven cats, both awake and after Pentobarbital injection. The profile of Changes in MLR and EP were investigated in three of them. As a result, the latency of P1 of EP from AI, which appears as a positive peak after Auditory Brainstem Response (ABR), was significantly greater till 165 minutes after Pentobarbital injection. Its amplitude was smallest 30 minutes after the injection, then started to increase till it reached maximum between 135 and 165 minutes after the injection. The latency of NA, which appeares as a first negative peak after ABR in MLR, was significantly greater till 165 minutes after Pentobarbital injection, and its amplitude Changed in proportion to that of P1. The amplitude of NA and P1 were correlated significantly. The data suggest that NA of MLR is correlated with the auditory cortex.
Using HPLC, the concentrations of furosemide, one of the organic anions, in the perilymph and endolymph of the guinea pig cochleae were measured after intravenous administration of 100mg/kg of furosemide. We further investigated the furosemide concentrations in the perilymph and endolymph pretreated with the organic anion transport inhibitor, probenecid. In the scala tympani perilymph (STP), a peak concentration of 4.9μg/ml was reached at 15min. after injection of furosemide and gradually declined thereafter. The concentration of furosemide increased slowly and continued to rise gradually in the scala vestibuli perilymph (SVP). In the endolymph, the concentration of furosemide increased slowly for one hour to 1.6μg/ml and gradually declined thereafter. Two hundred mg/kg of probenecid had no effect on the furosemide elimination in the endolymph except the furosemide concentration at 2hr, though the elimination curve of furosemide in STP was drastically changed and became analogous to that in SVP which was unaffected by probenecid. The effect of probenecid in the endolymph was very similar to that in the serum, while the pronounced gradient of the furosemide concentration existed between them. These results suggest that the furosemide is passively transferred from blood to the endolymph with relatively high impenetrability.
Responses of the auditory system to complex tones were summarized. As in the auditory nerve, tuning curve and nonlinearity of the basilar membrane vibration were found. Isolated outer hair cells were also well tuned. Combination tones can be explained by this nonlinearity which comes from the active process. Two-tone suppression found in the auditory nerve was also detected in the receptor potential of the inner hair cells. Phase-locked response to complex tones was visublized by period histograms, which was susceptible to the sound pressre level. “Missing fundamental” is an classical problem of auditory physiology. There are two theories. Temporal theory focuses on the periodic discharge of fibers, and pattdrn theory utilizes the spectral pattern of the complex. Stimulated by artificial vowels, most fibers saturate at high sound pressure level, but formant pattern is preserved in the ALSR neurogram. At the cochlear nucleus, neurons which show strong inhibition may extract the feature of the complex. Central beats and binaural masking suggest that phase infomation is carried to some center concerning binaural audition. Auditory cortical neurons show rather simple feature extraction in contrast to the visual cortex. Whole feature may be represented by the total responses of many cortical neurons.