Raymond S. Karlovich

Acoustic reflex and critical bandwidth

The threshold of the acoustic reflex was measured with an electroacoustic impedance bridge in six subjects with normal hearing sensitivity. Reflex thresholds were measured as a function of the bandwidth (1, 10, 30, 100, 300, 1155, 2042 Hz) of an acoustic stimulus centered around 1 kHz, and also for broad‐band noise (5780‐Hz bandwidth). Acoustic‐reflex thresholds were relatively constant for bandwidths between 1 and 300 Hz, and became progressively lower as the bandwidth increased (1155, 2042, 5780 Hz). The data support the idea that there is a critical‐band mechanism operating for elicitation of the acoustic reflex, and that the critical bandwidth for the acoustic reflex at 1 kHz is substantially wider than that observed in psychophysical studies.

Comments on the Relations between Auditory Fatigue and Iris Pigmentation

It has been reported that subjects with highly pigmented irises (brown) experience significantly less temporary threshold shift (TTS) than subjects with less pigmented irises (blue), and that those with green-gray pigmentation display intermediate amounts of TTS. TOTA and BOCCI noted the high correlation between the melanin content in the stria vascularis and that found in the pigmentation of the iris; they attributed their TTS differences across eye colour to the protective effects of melanin. TTS data are reported in this paper as a function of eye colour for exposure stimulus parameters almost identical to those used by TOTA and BOCCI (1 000 HZ at 110 dB SPL for 3 min). The present results do not support the hypothesis that individuals with highly pigmented irises (brown-eyed) are more resistant to auditory fatigue than those with less pigmentation of the iris (blue-eyed). Median TTS at 20 sec post-exposure among brown, green-gray, and blue iris categories did not differ by more than 1.8 dB, and the median TTS at 2 min post-exposure among those iris categories did not differ by more than 0.2 dB.

Remote masking generated by high-frequency two-tone complexes.

Auditory masking generated by two-tone complexes centered around 7 000 Hz was measured in 10 young adults with normal hearing sensitivity as a function of the frequency separation (deltaf) and SPL of the maskers components. Remote masking (1) was evident for test signals in the frequency region corresponding to the maskers deltaf; (2) increased with masker SPL, but at a rate less than that usually observed when lower frequency bands of noise are used as maskers, and (3) was relatively constant in magnitude for a given SPL as a function of the maskers deltaf. The masking produced in low-frequency regions by high-frequency two-tone complexes adds support to the hypothesis that remote masking is primarily a result of aural distortion.

AUDITORILY PACED KEYTAPPING PERFORMANCE DURING SYNCHRONOUS, DECREASED, AND DELAYED VISUAL FEEDBACK

20 young adult female Ss tapped on a tapping key to low, mid, and high sensation-level pure-tone auditory-pacing stimuli while being exposed to synchronous visual-feedback, delayed visual-feedback, and decreased sensory-feedback conditions. The stroboscopic visual-feedback stimulus was judged to be as bright as the mid-sensation-level auditory stimulus was loud in a preliminary cross-modality matching study. The dependent variables evaluated were tapping error, temporal deviation of the taps from the onset of the pacing stimuli, and tap duration. Few tapping errors occurred under any of the conditions which indicated that the auditory sensory modality is effective in regulating motor performance even when temporally distorted visual feedback is associated with the performance. Tapping deviation data strongly suggested that the relative perceptual magnitudes between the auditory pacing stimuli and the delayed visual-feedback stimulus are important factors in determining the speed of motor response. Tap durations were greater during decreased sensory-feedback and delayed visual-feedback conditions than during synchronous visual-feedback conditions, and it was speculated that these changes occurred due to an increase in tactual and kinesthetic feedback employed by Ss to counterbalance the distorted and decreased sensory feedbacks.

Effect of Contralateral Noise on Speech Detection and Speech Reception Thresholds

Speech detection thresholds (SDT) and speech reception thresholds (SRT) for spondee words were obtained on 20 normal hearing listeners while white or speech noise making was presented to the contralateral ear. Each masker was presented continously or pulsed simultaneously with the onset of each spondee word. Several masker sensation levels (SL) of 30, 40, 50, 60, 70, and 80 dB were employed, and the amount of masking (threshold shift) was determined for each condition. Small but consistent SDT and SRT shifts were apparent at low masker SLs (30 dB). FOR 60-80 DB masker SLs, the shifts were about 3.5 dB for each 10-dB increase in the masker. The greater threshold shifts at the higher masker SLs may have resulted from transcranial conduction and/or activation of the acoustic reflex. The pulsed masker condition had more of an effected on the SDT than on the SRT; SDT shifts were consistently larger for each masker SL when the masker was pulsed compared to continuous presentation. Overall, the average threshold shifts ranged from about 1 to 11 dB as the masker SL was increased from 30 to 80 dB. These data suggest that central masking is operating for masker SLs below 60 dB; for higher masker SLs, the increased threshold shifts probably result from a combination of central masking, transcranial conduction, and acoustic stapedius reflex action. The clinical implications of central masking are also discussed.

Auditory thresholds during stroboscopic visual stimulation.

Twelve experienced subjects participated in a Bekesy‐type tracking procedure and obtained their thresholds for a 25‐ and a 300‐msec duration 1‐kHz pulsing auditory stimulus in the absence and presence of time‐locked stroboscopic visual stimulation. Six subjects obtained their thresholds in quiet, and the remainder tracked threshold in the presence of white noise. The data indicated that psychophysical sensory interaction between the auditory and visual systems does not occur when auditory thresholds are assessed in the presence of visual stimulation. Auditory thresholds were neither facilitated nor inhibited. These generalizations applied whether thresholds were obtained for short‐ or long‐duration auditory stimuli in quiet or in the presence of a masking stimulus. Similar results were obtained for attenuator pen excursion size. A hypothesis is presented suggesting that the potential for psychophysical sensory interaction to occur between the visual and auditory modalities may increase as the magnitudes o...

Application of the TTS Paradigm for Assessing Sound Transmission in the Auditory System during Speech Production

Ten male and 10 female subjects were exposed to a 100 dB SPL 1000‐Hz fatigue stimulus for 3 min. During the exposure time, the subjects repeatedly produced a voiced vowel, a whispered vowel, or performed a nonvoiced articulatory gesture representing a vowel without whispering. Pre‐ and postexposure thresholds were tracked with a Bekesy‐type procedure for a stimulus 12 oct above the fatigue frequency. Temporary threshold shift (TTS) in males and females following voiced /ɑ/ and /i/ vowel conditions was significantly less than that observed for corresponding whispered or nonvoiced conditions at each postexposure recovery time measured. The magnitude of these differences ranged from 9 dB at 10 sec to 4 dB at 3 min of recovery. The results strongly indicate that voiced vowel production impedes transmission and hence reduces the energy delivered to the cochlea from a 1000‐Hz fatigue stimulis, as evidenced by the reduced TTS magnitudes associated with this condition. Two potential mechanisms are proposed to acc...

Auditory thresholds during visual stimulation as a function of signal bandwidth.

A Beḱsy‐type tracking procedure was employed with eight male subjects to obtain auditory thresholds for pulsing wide‐band. low‐band, mid‐band, and high‐band noise during nonvisual and visual stimulation periods. Thresholds and attenuator pen‐excursion sizes obtained for each bandwidth auditory stimulus were not significantly different between nonvisual and visual condition. The data indicated that psychophysical sensory interaction between the auditory and visual systems did not occur for the stimulus used, that is, auditory thresholds were neither facilitated nor inhibited during presentation of a time‐locked stroboscopic visual stimulus.

Sensory Interaction: Perception of Loudness During Visual Stimulation

Eight subjects engaged in an alternate binaural loudness balance (ABLB) task utilizing the method of adjustment to explore the perception of loudness of a 300‐msec‐duration 1‐kHz auditory stimulus at 20 dB and 50 dB SLs. Conditions utilized were no visual stimulation during ABLB, visual stimulation in synchrony with the standard auditory stimulus during ABLB, and visual stimulation in sychrony with the comparison auditory stimulus during ABLB. The visual stimulus was a short‐duration stroboscopic light flash. The data indicated that sensory interaction in terms of visual facilitation of auditory loudness does occur and is more apparent at higher rather than lower SLs. The comparison stimulus was adjusted to a higher SL when the visual stimulus was associated with the standard auditory stimulus than when the visual stimulus was associated with the comparison auditory stimulus. The magnitude of this statistically significant difference was approximately 7 dB and implies that information presented to the v...

Auditory Fatigue during Articulation: Preliminary Observations

Four subjects were exposed to a high‐SL pure‐tone fatigue stimulus for 3 min. During exposure, the subjects read a passage aloud during one session and they read the same passage silently during another session. The reading‐aloud condition produced consistently greater TTS than the reading‐silently condition for the entire 3 min of recovery measured. The data are interpreted in terms of impedance changes in the ear caused by vocal articulation. The results also may be germane to the contradictory literature concerned with the idea of a central factor in auditory fatigue.