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Biomedical subjects

G B Henning

Publications and source records attributed to G B Henning.

11 recordsLinked to original sources
PubMed1992

Training can improve muscle strength and endurance in 78- to 84-yr-old men.

Nine men, 78-84 yr of age, participated in a dynamometer training program 2-3 times/wk, totaling 25 sessions, using voluntary maximal isometric, concentric, and eccentric right knee-extension actions (30 and 180 degrees/s). Measurements of muscle strength with a Kin-Com dynamometer and simultaneous electromyograms (EMG) were performed of both sides before and after the training period. Muscle biopsies were taken from the right vastus lateralis muscle. The total quadriceps cross-sectional area was measured with computerized tomography. Training led to an increase in maximal torque for concentric (10% at 30 degrees/s) and eccentric (13-19%) actions in the trained leg. The EMG activity increased at maximal eccentric activities. The total cross-sectional quadriceps area of the trained leg increased by 3%, but no changes were recorded in muscle fiber areas in these subjects, who already had large mean fiber areas (5.15 microns 2 x 10(3)). The fatigue index measured from 50 consecutive concentric contractions at 180 degrees/s decreased and the citrate synthase activity increased in all but one subject. The results demonstrate that increased neural activation accompanies an increase in muscle strength at least during eccentric action in already rather active elderly men and that muscle endurance may also be improved with training.

Aged↗
PubMed1991

Binaural amplitude discrimination and the binaural masking-level difference.

Under certain conditions, amplitude discrimination is not a monotonic increasing function of signal-to-noise ratio. The non-monotonicity arises when the tones to be discriminated are presented 180 degrees out-of-phase at the observer's ears and just above their detection 'threshold' in noise that is in-phase at the observer's ears, and with 2-6-dB differences in amplitude.

Acoustic Stimulation↗
PubMed1991

On the effect of interaural phase differences on loudness.

The loudness of four monaurally presented Gaussian shaped, 60-ms tone bursts was matched to that of four similar pulses presented binaurally. The stimuli to be matched were all presented in continuous binaural noise of three levels and, in different experiments, either the monaural or the binaural stimuli were adjusted by the observer. With 250- and 710-Hz tone bursts, there are large differences in loudness that, at low signal-to-noise ratios, depend on the interaural phase conditions in a manner consistent with the changes in masked threshold produced by the phase manipulation; there is little, if any, effect of interaural phase on loudness for 2-kHz signals. The effect of interaural phase on loudness decreases with increasing level but, at 250 Hz, remains measurable some 30-40 dB above masked threshold. The matching function for signals out-of-phase grows in proportion to the level to be matched over the entire range from masked threshold to the highest level used. In contrast, for the in-phase condition, the observers show a step at a level that depends both on frequency and on the observer from proportional growth near thresholds to parallel proportional growth some 6 to 12 dB higher.

Acoustic Stimulation↗
PubMed1990

The effect of a low-frequency masker on loudness.

Intense low-frequency tones produce masking-period patterns in which the masking of a higher-frequency tone burst varies by up to 25 dB over the period of the masker. In this experiment, observers were asked to match the loudness of partially masked test-tone bursts in one ear by adjusting the level of unmasked bursts presented to the other ear. It was found that the variation in masked threshold over the period of the masker also affects loudness matches. This effect on loudness, although it decreases in size with increasing level above masked threshold, persists even 25 dB above masked threshold.

Acoustic Stimulation↗
PubMed1990

The effect of interaural phase on frequency discrimination with broad- and narrow-band maskers.

With both broad-band and narrow-band noise maskers there is a small range of signal-to-noise ratios where, with the maskers in-phase and signals 180 degrees out-of-phase at the ears, detection performance grows with increasing signal-to-noise ratio but frequency discrimination performance does not. The observation may have significant consequences for our understanding of the way in which frequency is coded at low signal-to-noise ratios.

Discrimination, Psychological↗
PubMed1990

The effect of signal duration on frequency discrimination at low signal-to-noise ratios in different conditions of interaural phase.

Frequency discrimination in noise at low signal-to-noise ratios where the signals to be discriminated are equally well detected but only faintly audible is better when the signals are in-phase at the ears than when they are out-of-phase. In spite of the difference in discriminability, however, the form of the dependence of the just-noticeable frequency difference on signal duration is the same in both cases.

Acoustic Stimulation↗
PubMed1989

Some observations on the masking effects of two-dimensional stimuli.

Gratings that differ in orientation by as much as 62.5 deg from that of a signal grating raise the signal's threshold by nearly a log unit. The spatial-frequency tuning of the masking effect reaches a maximum slightly below the spatial frequency of the maskers but far from that of any quadratic distortion product. Further, the location of the peak does not depend much on the relative orientation of the signal and maskers thus making it unlikely that the masking effect can be explained in any simple way by the presence of visual nonlinearities. This illustrates the difficulty of attempting to explain human performance in even relatively simple discrimination experiments with models based on mechanisms tuned for spatial frequency and orientation.

Form Perception↗