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Biomedical subjects

T Ifukube

Publications and source records attributed to T Ifukube.

At least 19 recordsLinked to original sources
PubMed1996

A portable digital speech-rate converter for hearing impairment.

A real-time hand-sized portable device that slows speech speed without changing the pitch is proposed for hearing impairment. By using this device, people can listen to fast speech at a comfortable speed. A combination of solid-state memory recording and real-time digital signal processing with a single chip processor enables this unique function. A simplified pitchsynchronous, time-scale-modification algorithm is proposed to minimize the complexity of the DSP operation. Unlike the traditional algorithm, this dynamic-processing algorithm reduces distortion even when the expansion rate is only just above 1. Seven out of 10 elderly hearing-impaired listeners showed improvement in a sentence recognition test when using speech-rate conversion with the largest expansion rate, although no improvement was observed in a word recognition test. Some subjects who showed large improvement had limited auditory temporal resolution, but the correlation was not significant. The results suggest that, unlike conventional hearing aids, this device can be used to overcome the deterioration of auditory ability by improving the transfer of information from short-term (echoic) memory into a more stable memory trace in the human auditory system.

Audiometry, Speech↗
PubMed1996

Objective method to determine the contribution of the great toe to standing balance and preliminary observations of age-related effects.

The purpose of this study was to examine the relationship between toe pressure and tactile sensitivity in the great toe and to describe two newly developed measurements of postural stability. The subjects of the study were 21 healthy volunteers. The subjects were divided into two age groups, the young group (mean 21.0 +/- 1.6 years, 7 males and 6 females), and the elderly group (mean 71.4 +/- 2.8 years, 4 males and 4 females). The methods and materials used for the first experiment (balance test): The instrument for measuring standing balance was a force plate. Data were analyzed to provide two main variables: 1) body sway index (SI: mm) and 2) toe pressure (%BW/cm2). The subjects were asked to stand in a relaxed posture for 20 s. The variables of body sway were measured in four conditions: normal surface with eyes open or closed, and soft surface with eyes open or closed. Second experiment (tactile sense test): This experiment utilized a new system which was developed for measuring the tactile sensation. The tactile threshold value was measured with the subject seated in a chair, the back supported, and the hips and knees flexed at 90 degrees. The contactor pulled and pushed the toe longitudinally along its axis at a constant velocity of 1 mm/s. There were significant differences between the young and elderly groups in the tactile sense of the great toe (p < .001). No significant difference between age groups was found for postural sway while the subjects stood on the normal surface with eyes open; however, when they stood on the soft surface with their eyes open and closed, the elderly showed significantly more sway (p < 0.01) than the young. Moreover, the maximal great toe pressure in the elderly group was significantly greater than that in the young group. The results suggest that the reduced tactile sense, deprivation of visual information, and toe pressure weakness are all important factors associated with postural instability.

Adult↗
PubMed1996

Proposal of a new auditory nerve stimulation method for cochlear prosthesis.

The stimulation electrodes of cochlear implants are covered by a lymph liquid with high electrical conductivity, which causes the transmitted information to be reduced by channel interaction. Even if this problem were solved, the stimulation regions may be discrete; therefore, there may be regions in which the electrode array cannot stimulate selectively. To solve these problems, we proposed a new auditory nerve stimulation method which we call the tripolar electrode stimulation method for cochlear implants. Our method stimulates using 3 adjacent electrodes selected from among the electrodes of the electrode array. The center electrode receives the currents emitted from the electrodes on both sides. We conducted animal experiments using this method. On the basis of the results we obtained, we concluded that our method may succeed in narrowing the stimulation region and continuously moving the stimulation site.

Animals↗
PubMed1996

An experience of the usage of electrical tinnitus suppressor.

An electrical tinnitus suppressor based on the use of an extracochlear stimulator has been developed at Hokkaido University, Sapporo, Japan, and was implanted in 2 male and 2 female patients. Tinnitus improved in all patients because the auditory nerve was able to be stimulated at home whenever patients wanted treatment. Additional benefits reported after electrical stimulation of the cochlea included sound sleep, relaxation in all cases, and improved hearing acuity in Cases 1, 2, and 4. Minimal temporary complications, including habituation and ear drum perforation, were observed.

Adult↗
PubMed1996

Analysis of toe pressures under the foot while dynamic standing on one foot in healthy subjects.

Dynamic balance is a crucial element in performing many activities of daily living. The one-leg stance test is a valuable test for balance impairment. The aim of the present study was to assess the relationships between body sway and toe pressure for dynamic balance test of one-leg standing on a perturbation platform. The subjects were 15 volunteers (six males and nine females, age = 21.1 +/- 1.8 years). The instrument used for evaluation of balance was the Balance System, whose software provides information on the subject's stance balance through calculation of two main variables: 1) body sway parameters (cm) and 2) peak pressure (percent of body weight/cm2) under the toes. The Balance System includes actuators which move the foot platform back and forth (+/- 40 mm perturbation at 0.25 Hz) at an average velocity of 20 mm/sec. The subjects were asked to balance on each leg for 20 seconds. The trials were repeated on the opposite foot after 5 minutes of rest. The dynamic postural control induced by low frequency perturbation in the anterior/posterior direction used the ankle strategy. Body sway was more significantly correlated with the peak anterior/posterior sway component than with lateral sway (p < 0.01). The peak pressure value of the great toe was significantly greater (p < 0.01) than the sum of the peak values of the other four toes for both sides. The study indicates the importance of the strength of the toes and somatosensory information from the sole and ankle during the dynamic one-foot standing balance as goals in rehabilitation for poor balance.

Adult↗
PubMed1994

A study of electrical promontory stimulation in tinnitus patients.

Electrical promontory stimulation relieved tinnitus in 74 (57.4%) of 129 ears (112 patients). There was no significant difference in etiology of tinnitus, age, average audiogram, or tinnitus frequency between patients who responded to electrical stimulation and those who did not. Most patients who did not respond to the initial stimulation trial did not respond to the subsequent trials, suggesting that the initial response to treatment predicts the subsequent response. Patients who did not respond to repetitive treatment were supposed to be under severe stress.

Adolescent↗
PubMed1994

Neural responses to electrical stimulation of the cochlea in guinea pigs.

A special bridge circuit was constructed to compensate stimulus artifact to determine the effects of an alternating current (AC) in the range of 3 to 20 kHz and direct current (DC) stimulation on the activity of cochlear nerve fibers. When AC and DC stimulation of the same fiber were compared, a greater current intensity was required to change the spike rate with AC stimulation than DC stimulation. While positive DC stimulation reduced activity, negative DC stimulation increased the spike rate. AC stimuli excited fibers in a manner similar to that observed with negative DC stimulation. Thresholds increased with stimulus frequency, suggesting that the effects of AC stimulation on the discharge rate are independent of the CF (characteristic frequency) of a fiber. The effects of short-time AC and DC stimulation on cochlear fiber activity lasted only during the stimulation, and the spontaneous activity did not significantly differ before and after electrical stimulation.

Animals↗
PubMed1994

[Electroconduction system for implantable tinnitus suppressor].

The purpose of this study was to introduce the electroconduction system for an implantable tinnitus suppressor. This system is a modification of the extracochlear implant system, which was developed at Hokkaido University. This system consists of a stimulator and two coils. One of the coils is implanted inside the temporal bone and its size, including the current limiter, is 9 mm long, 6.4 mm wide and 6 mm thick. Another is contained in the plastic case which is used for hearing aids. The efficacy of conduction depends on the wave frequency. The most effective frequency was about 30 kHz. The maximum current required to relieve tinnitus is 100 microA when using this system. The heat emitted from the coil inside the case is so minimal at an intensity of 100 microA as to be negligible systemically. The electromagnetic coupling system works well for more than 4 months in saline.

Cochlear Implants↗
PubMed1994

[A tinnitus case with an implanted electrical tinnitus suppressor].

An electrical tinnitus suppressor, which was developed at Hokkaido University, was implanted in a female tinnitus patient. She had suffered from bilateral chronic otitis media and her bilateral hearing was seriously impaired. The electrical tinnitus suppressor consists of a stimulator, a coil inside the plastic hearing aid case and an implanted coil in the mastoid. The auditory nerve is stimulated at home twice. Using the system, her hearing ability and emotion improved in addition to tinnitus suppression. Her hearing level and tinnitus also improved in the ear contralateral to the stimulated side.

Cochlear Implants↗
PubMed1992

Recording eye movement during stepping in place with a CCD (charge-coupled device) imagesensor.

A new system for recording eye movements using a charge-coupled device (CCD) imagesensor in a video camera, in which less than 0.5 degree of horizontal and vertical eye movements can be recorded, was applied in 7 subjects. Eye movements were recorded while they stepped in place. We observed 5 normal subjects, a patient with horizontal and vertical oscillopsia during walking, and one with a chronic limp. In the normal adults, the amplitude of vertical eye movement was less than 0.5 degree, and the horizontal eye movement was less than 2 degrees. The mean amplitude of horizontal and vertical eye movements in the subject who limped was larger than that of normal subjects. The patient who complained of vertical oscillopsia during walking showed the largest amplitude of vertical eye movement among any subject tested. The vertical oscillopsia in the patient was due to the largest amplitude of vertical eye movement. This system for recording eye movements will be useful in analyzing the mechanism of gaze fixation during walking.

Adult↗
PubMed1992

[A comparison of time resolution among auditory, tactile and promontory electrical stimulation--superiority of cochlear implants as human communication aids].

Our previous reports showed that second formant information, using a speech coding method, could be transmitted through an electrode on the promontory. However, second formant information can also be transmitted by tactile stimulation. Therefore, to find out whether electrical stimulation of the auditory nerve would be superior to tactile stimulation for our speech coding method, the time resolutions of the two modes of stimulation were compared. The results showed that the time resolution of electrical promontory stimulation was three times better than the time resolution of tactile stimulation of the finger. This indicates that electrical stimulation of the auditory nerve is much better for our speech coding method than tactile stimulation of the finger.

Cochlea↗
PubMed1991

A blind mobility aid modeled after echolocation of bats.

A new model of a mobility aid for the blind was designed using microprocessor and ultrasonic devices. This mobility aid was evaluated based on psychophysical experiments. In this model, a downswept FM ultrasound signal is emitted from a transmitting array with broad directional characteristics in order to detect obstacles. The ultrasound reflections from the obstacles are picked up by a two-channel receiver. The frequency of the emitted ultrasound is swept from 70 to 40 kHz within 1 ms, so it has almost the same characteristics as the ultrasound a bat produces for echolocation. The frequency of the reflected ultrasound wave is down converted by about 50:1 by using a microcomputer with A/D and D/A converters. These audible waves are then presented binaurally through earphones. In this method obstacles may be perceived as localized sound images corresponding to the direction and the size of the obstacles. From the results of psychophysical experiments, it was found that downswept FM ultrasound was superior for the recognition of small obstacles compared to other ultrasonic schemes. With it a blind person can recognize a 1-mm-diameter wire. It was also proved that the blind could discriminate between several obstacles at the same time without any virtual images. This mobility aid, modeled after the bat's echolocation system, is very effective at detecting small obstacles placed in front of the head.

Animals↗
PubMed1989

Discrimination of synthetic vowels by using tactile vocoder and a comparison to that of an eight-channel cochlear implant.

A vowel discrimination test using a tactual vocoder was administered and the results were compared to that of an eight-channel cochlear implant. Both the tactile vocoder and the cochlear implant divided the speech signals into 16 frequency components using band-pass filters and lateral inhibition circuits. In the tactile vocoder, these 16 components were converted into a vibration with 200 Hz frequency and applied to a 3 x 16 element vibrator array using bimorph piezoelectric elements. The vibratory patterns were sensed on the fingertip. In the cochlear implant, the 16 components were reduced to eight current stimulation signals, consisting of biphasic pulses with 200 Hz frequency, which were applied to an eight-channel electrode array implanted in the scala tympani. The electrode array passed through the round window into the scala tympani to a depth of 23 mm. These psychophysical experiments investigate the ability of human subjects to discriminate synthetic vowels as a function of the number of channels employed. The results suggested that an eight-channel and a 16-channel tactile vocoder provided essentially the same discrimination scores. However, the ability to discriminate synthetic vowels decreased rapidly when less than eight channels were employed. The ability of an eight-channel tactile vocoder is expected to be better than that of the eight-channel cochlear implant because it is supposed that vowel discrimination is degraded by a phenomenon known as "current spreading" in the case of cochlear stimulation. However, the comparison between the two devices was not done on the cochlear implant subject.

Adult↗