Kazuhito Ito

Perception Mechanisms of Bone-Conducted Ultrasound Assessed by Acoustic Characteristics in the External Auditory Meatus

Acoustic fields/vibrations in the external auditory meatus (ear canal) and tympanic membrane (TM) under bone-conducted ultrasonic stimulation were measured to elucidate the contributions of the osseotympanic and inertial routes to bone-conducted ultrasonic (BCU) perception. Evidence showing nonlinear distortions, especially the generation of audible subharmonics in the outer and middle ear, was examined. In the results, we did not find any audible signals corresponding to the subjective pitch of a BCU tone in the acoustic fields for the auditory meatus and TM vibrations. This suggests that nonlinear distortions in the osseotympanic and inertial routes do not contribute to bone-conducted ultrasonic perception. Specific properties of perception may be related to mechanisms in the cochlea or afferent neural pathway.

Assessment of Linearity of Bone-Conducted Ultrasound Transmission in the Human Head

We investigated the linearity of bone-conducted ultrasound transmission through a living human head. The frequency response functions and the coherence functions of head vibration at different signal levels were examined. Vibrations in the heads of six subjects were measured using a small accelerometer in the ear canal under bone-conducted tone stimulation from audible high frequencies to ultrasonic frequencies. Stepped sine signals from 10 to 45 kHz in 0.5 kHz steps at two different signal levels were used. The signal levels were set to the levels corresponding to 5 and 10 dB sensation level (SL) at 30 kHz in each subject. The result suggests that the head vibration increases almost linearly across an audible to ultrasonic frequency range and there was no significant difference in nonlinear behavior between the audible and ultrasonic sound transmissions.

Psychophysical Boundary for Categorization of Voiced–Voiceless Stop Consonants in Native Japanese Speakers

Purpose The purpose of this study was to investigate the psychophysical boundary used for categorization of voiced-voiceless stop consonants in native Japanese speakers. Method Twelve native Japanese speakers participated in the experiment. The stimuli were synthetic stop consonant-vowel stimuli varying in voice onset time (VOT) with manipulation of the amplitude of the initial noise portion and the first formant (F1) frequency of the periodic portion. There were 3 tasks, namely, speech identification to either /d/ or /t/, detection of the noise portion, and simultaneity judgment of onsets of the noise and periodic portions. Results The VOT boundaries of /d/-/t/ were close to the shortest VOT values that allowed for detection of the noise portion but not to those for perceived nonsimultaneity of the noise and periodic portions. The slopes of noise detection functions along VOT were as sharp as those of voiced-voiceless identification functions. In addition, the effects of manipulating the amplitude of the noise portion and the F1 frequency of the periodic portion on the detection of the noise portion were similar to those on voiced-voiceless identification. Conclusion The psychophysical boundary of perception of the initial noise portion masked by the following periodic portion may be used for voiced-voiceless categorization by Japanese speakers.

Study on interactions between voicing production and perception using auditory feedback paradigm

A previous study reported that perturbed auditory feedback affected voicing production [Mitsuya, MacDonald, and Munhall (2014). J. Acoust. Soc. Am., 135, 2986-2994]. In this study, we investigated whether perturbed auditory feedback would also affect voicing perception. Eighteen native Japanese speakers participated in the experiment. Half of the participants performed an auditory feedback task in which a syllable sound /da/ was presented simultaneously with the participant’s utterance of /ta/. The other participants did a passive listening task in which participants heard a syllable sound /da/ without the utterance. Before and after each task, participants performed a /da/-/ta/ speech production task and a speech identification task of / da/-/ta/ continuum varying in voice-onset time (VOT). Results showed that perturbed auditory feedback lengthened the VOT of /ta/ production, whereas passive listening did not affect voicing production. Regarding voicing perception, passive listening shortened the VOT boundary of /da/-/ta/, which may be due to selective adaptation. On the other hand, perturbed auditory feedback did not vary the boundary. One interpretation of these results is that the effects of voicing production modulation on voicing perception can be cancelled out by selective adaptation, which may have occurred by listening to a syllable sound /da/ during auditory feedback task.A previous study reported that perturbed auditory feedback affected voicing production [Mitsuya, MacDonald, and Munhall (2014). J. Acoust. Soc. Am., 135, 2986-2994]. In this study, we investigated whether perturbed auditory feedback would also affect voicing perception. Eighteen native Japanese speakers participated in the experiment. Half of the participants performed an auditory feedback task in which a syllable sound /da/ was presented simultaneously with the participant’s utterance of /ta/. The other participants did a passive listening task in which participants heard a syllable sound /da/ without the utterance. Before and after each task, participants performed a /da/-/ta/ speech production task and a speech identification task of / da/-/ta/ continuum varying in voice-onset time (VOT). Results showed that perturbed auditory feedback lengthened the VOT of /ta/ production, whereas passive listening did not affect voicing production. Regarding voicing perception, passive listening shortened the VOT bou...

Development of bone-conduction mobile phones: Assessment of hearing mechanisms by measuring psychological characteristics and acoustical properties in the outer ear canal

We have been developing novel mobile phones using bone conduction, with flat-panel loudspeakers that convey speech sound by vibrating the pinna. In bone conduction via the pinna, i.e., pinna conduction, it is thought that speech sounds are conveyed via both air- and bone-conduction pathways. To obtain useful information for further development of bone-conduction mobile phones, peripheral mechanisms of the pinna conduction need to be clarified. In this study, hearing thresholds, sound field in the outer ear canals, and vibrations of the inner wall of the outer ear canals were measured while normal-hearing participants used pinna-conduction mobile phones. Thresholds decreased linearly as contact pressure increased below 1 kHz, but contact pressure did not affect thresholds above 2 kHz. Additionally, sound fields in the ipsilateral ear canal showed similar results. These results indicate that there is a considerable degree of bone-conduction components from the pinna to the inner ear, which only allow sounds below 1 kHz through. Because similar characteristics were observed in the threshold and the sound field in the outer ear canal, we suggest that osseotympanic emission, sound emission into the ear canal from the inner wall, and air conduction via external auditory foramen are the dominant components of pinna conduction. However, in the vibration measurement, differences between the ipsi- and contra-lateral responses were smaller than the sound field measurement. The smaller inter-lateral differences of the vibration in the outer ear canal suggest the existence of a significant amount of bone-conduction components that directly reach the middle or inner ear. Although the amount of such bone-conduction components does not seem sufficient for pinna.

Within- and between-frequency gap duration discrimination as a function of the standard duration

It is well known that individuals exhibit worse performance during between-frequency gap detection than during within-frequency gap detection. A similar performance difference is also found between within- and between-frequency gap duration discrimination involving undetectably short standard durations. This is reasonable because such discrimination could be considered to be a variant of gap detection. However, because of the paucity of existing data, it is unclear whether frequency differences affects gap discrimination tasks involving longer standard durations. In this study, we measured within- and between-frequency discrimination thresholds in the presence of various standard durations from 1 to 100 ms. As a result, it was shown that the within-frequency thresholds were significantly lower than the between-frequency thresholds when a standard duration of 1-ms was employed, whereas there were no significant differences between them when the standard duration was >50 ms. This implies that the within- an...

Relationship between the frequency asymmetry of across-frequency gap detection and the temporal asymmetry of cochlear responses

Gap detection is often used to estimate the temporal resolution of the human auditory system. Gap detection performance becomes worse when the frequency difference between the leading and trailing markers that delimit a silent gap gets larger. In addition, the across-frequency gap detection threshold is not always constant when the presentation order of the two markers is altered, even if the frequency difference remains unchanged. We suspect that these inconsistencies in gap detection performance are partly caused by cochlear delay; i.e., low frequency signals reach the responding areas of the cochlea later than higher frequency signals. To examine whether across-frequency gap detection thresholds increase when the leading marker is higher in frequency than the trailing marker, as would be expected if the above mentioned hypothesis is correct, we conducted across-frequency gap detection tasks by altering the presentation order of the two markers (marker frequency: from 250 to 8000 Hz). The gap detection ...

Relationship between voicing perception and auditory brainstem responses to stop consonants

A number of psychophysical studies have suggested that auditory temporal resolution is related to the voicing boundaries of stop consonants. For example, hearing-impaired listeners with poor temporal resolution have difficulty perceiving voiceless stop consonants. However, there is little neurophysiological evidence for the existence of a relationship between voicing boundaries and auditory temporal resolution. The auditory brainstem response (ABR) is suited to investigations of this relationship because it has proved useful in assessments of auditory temporal processing and speech processing. We conducted a speech identification task using synthesized /da/-/ta/ stimuli in which we varied the voice onset time from 3 to 15 ms in 2 ms steps. There were two types of /da/-/ta/ stimuli whose aspiration noise exhibited high or low power. ABR were measured for the some stimuli across voicing boundaries. The aspiration noises with higher power displayed shorter voicing boundaries and longer peak-to-peak latency b...

Self-demodulation of amplitude-modulated signal components in amplitude-modulated bone-conducted ultrasonic hearing

A novel hearing aid system utilizing amplitude-modulated bone-conducted ultrasound (AM-BCU) is being developed for use by profoundly deaf people. However, there is a lack of research on the acoustic aspects of AM-BCU hearing. In this study, acoustic fields in the ear canal under AM-BCU stimulation were examined with respect to the self-demodulation effect of amplitude-modulated signal components generated in the ear canal. We found self-demodulated signals with an audible sound pressure level related to the amplitude-modulated signal components of bone-conducted ultrasonic stimulation. In addition, the increases in the self-demodulated signal levels at low frequencies in the ear canal after occluding the ear canal opening, i.e., the positive occlusion effect, indicate the existence of a pathway by which the self-demodulated signals pass through the aural cartilage and soft tissue, and radiate into the ear canal.

Characterization of human head vibration with bone-conducted ultrasonic stimulation

A novel hearing aid system based on bone-conducted ultrasonic (BCU) hearing is being developed for use by profoundly deaf people. However, the perception mechanisms involved in BCU hearing remain unclear. In this study, the way in which the mechanical frequency characteristics of human head vibration under BCU stimulation contribute to the hearing process was considered and examined in terms of the effects of the elasticity of the surface tissue that was in contact with a bone conduction vibrator. The results suggest that head vibration under BCU stimulation has low-pass filter-type characteristics with a cut-off frequency of between 30 and 40 kHz, which is attributed to the effects of the elasticity of living human skin. However, the issue of the psychoacoustic characteristics of the BCU hearing process not necessarily reflecting the mechanical frequency characteristics of head vibration remains.