Kaoru Ashihara

Hearing thresholds for pure tones above 16kHz

Hearing thresholds for pure tones between 16 and 30 kHz were measured by an adaptive method. The maximum presentation level at the entrance of the outer ear was about 110 dB SPL. To prevent the listeners from detecting subharmonic distortions in the lower frequencies, pink noise was presented as a masker. Even at 28 kHz, threshold values were obtained from 3 out of 32 ears. No thresholds were obtained for 30 kHz tone. Between 20 and 28 kHz, the threshold tended to increase rather gradually, whereas it increased abruptly between 16 and 20 kHz.

Ultrasonic binaural echo perception of object's texture by human echolocation

Echolocating bats use frequency-modulated (FM) and/or constant-frequency (CF) sound for ultrasonic sensing depending on the situation during flight. We investigated discrimination ability of object’s texture for sighted subjects to understand acoustic clues for texture recognition in human echolocation. FM and CF ultrasonic echoes from six objects with different materials and surface structures were acquired by a 1/7-size miniature dummy head for presentation of 1/7-times pitch converted binaural audible sounds to listeners through headphones. In the results, averaged rate of correct answer in the case of extremely different surface condition (i.e., acrylic board versus artificial grass) was more than 90% while one in the slightly different surface condition (i.e., acrylic board versus foamed polystyrene) was under 40%. Furthermore, the rate of correct answers in the CF sound condition was approximately 13% lower than one in the FM sound condition. The correlation diagram among targets by multidimensional...

Effects of auditory information on self-motion perception during simultaneous presentation of visual shearing motion

Recent studies have found that self-motion perception induced by simultaneous presentation of visual and auditory motion is facilitated when the directions of visual and auditory motion stimuli are identical. They did not, however, examine possible contributions of auditory motion information for determining direction of self-motion perception. To examine this, a visual stimulus projected on a hemisphere screen and an auditory stimulus presented through headphones were presented separately or simultaneously, depending on experimental conditions. The participant continuously indicated the direction and strength of self-motion during the 130-s experimental trial. When the visual stimulus with a horizontal shearing rotation and the auditory stimulus with a horizontal one-directional rotation were presented simultaneously, the duration and strength of self-motion perceived in the opposite direction of the auditory rotation stimulus were significantly longer and stronger than those perceived in the same direction of the auditory rotation stimulus. However, the auditory stimulus alone could not sufficiently induce self-motion perception, and if it did, its direction was not consistent within each experimental trial. We concluded that auditory motion information can determine perceived direction of self-motion during simultaneous presentation of visual and auditory motion information, at least when visual stimuli moved in opposing directions (around the yaw-axis). We speculate that the contribution of auditory information depends on the plausibility and information balance of visual and auditory information.

Human echolocation system using a miniature dummy head

To promote understanding of sonar mechanisms in bats, we propose a novel tool that makes echolocation available for humans. In this method, ultrasonic echoes are captured by a miniature dummy head so that they can be converted to binaural audible sounds using time expansion.In order to examine the effectiveness of this technique, perceptual listening tests were conducted on human listeners with normal hearing.The sounds (white noise with frequencies between 5 and 90 kHz with 0.7-s duration, including 0.05-s rise/fall time) were recorded at a distance of 1m from a loudspeaker using two condenser microphones that were placed in the ear canals of a 1/7 size miniature dummy head. The recorded ultrasounds were 1/7-times pitch converted, and then were presented to the listener through headphones. As a result, the listeners perceived correct directions of the pitch converted sounds which were recorded using the miniature dummy head, although front-back error was occasionally observed. When the miniature dummy he...

Capturing spatial audio information by using a miniature head simulator

A conventional dummy head or a microphone array with a number of microphones has been used to record spatial audio information. We propose an audio capture system called “Miniature head simulator” that consists of a microphone system and a signal processor. Instead of using a conventional dummy head, a small microphone system that consists of three omni-directional microphones is used to capture acoustic signals. The signals are then encoded to a custom data format and transmitted online. The transmitted data can be decoded and reproduced as binaural signals. Because of its size and weight, the conventional dummy head has been used exclusively for the research purpose. A miniature head simulator can provide much more convenient tools to record spatial audio information. Since it deals with only three channels of audio stream, data can be processed with relatively low computational cost. By using a miniature head simulator, spatial audio information can be streamed to the browser or even to the smartphones...

An attempt to measure the hearing thresholds for high‐frequency sounds by using the auditory brain‐stem response

Recently, devices using high‐power ultrasounds are increasing. However, influences of high level ultrasounds on human are not fully understood. Psychophysical studies show that the hearing thresholds exceed 80 dB SPL at a frequency above 20 kHz. It is reported that high frequency sounds above 20 kHz affect activities in the human nervous system. In order to examine whether the peripheral auditory system can be activated by high‐frequency sounds, an attempt is made to measure the auditory brainstem response (ABR) for the frequency range between 4 and 20 kHz. In preliminary experiments, the ABR was measured for a tone pip with the center frequency of 14 kHz. However, the ABR was not clearly observed above 16 kHz. The thresholds determined by the ABR were approximately 40 dB larger than the psychophysical thresholds. The ABR was evoked by low‐frequency components of the tone pip at the high presentation levels.

Threshold of hearing for pure tones between 16 and 30 kHz

Hearing thresholds for pure tones were obtained at 2‐kHz intervals between 16 and 30 kHz in an anechoic chamber. Measured 50 cm from the sound source, the maximum presentation sound pressure level ranged from 105 to 112 dB depending on the frequency. To prevent the listener from detecting the quantization noise or subharmonic distortions at low frequencies, a pink noise was added as a masker. Using a 3‐down 1‐up transformed up‐down method, thresholds were obtained at 26 kHz for 10 out of 32 ears. Even at 28 kHz threshold values were obtained for 3 ears, but none were observed for a tone at 30 kHz. Above 24 kHz, the thresholds always exceeded 90 dB SPL. Between 16 and 20 kHz thresholds increased abruptly, whereas above 20 kHz the threshold increase was more gradual.

Detection of a tonal stimulus masked by a complex with coherent or incoherent frequency modulation

The purpose of this study is to investigate if coherent frequency modulation by itself can induce auditory streaming when there are no harmonicity cues. A signal tone was presented with a complex of tones whose frequency fluctuated. To separate the effects of frequency modulation from those of harmonicity, components of the masker were not spaced by a fixed frequency distance but by a critical bandwidth. The detection threshold of the signal was tested in two conditions. In the first, called the coherent condition, all components of the masker were modulated coherently. In the second, incoherent condition, the masker was divided into two parts, the on‐signal part and the flanking part. The on‐signal part was the bandpass filter of the complex that was centered on the signal frequency and the flanking part was the rest of it. To make the modulation incoherent, the flanking part was moved forward or backward by half a cycle of modulation. The signal was detected with less difficulty in the coherent conditio...