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Biomedical subjects

G B Henning

Publications and source records attributed to G B Henning.

At least 37 records · Page 2Linked 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↗
PubMed1988

Spatial-frequency tuning as a function of temporal frequency and stimulus motion.

Spatial-frequency tuning at two different spatial frequencies was determined by measuring the detectability of a signal grating that was made difficult to see by low- or high-pass visual noise. The signals were vertical sinusoidal gratings of different spatial frequencies. The detectability of the signal was measured in two-alternative forced-choice tasks with different temporal envelopes: (1) a slowly changing raised-cosine (Hanning) window, (2) a rectangularly gated 2-Hz counterphase flickering envelope, and (3) a rectangularly gated 10-Hz counterphase flickering envelope. Additional measurements were made using drifting stimuli with the signal and noise drifting in the same or in opposite directions. The temporal envelopes were chosen because they have different effects on the contrast-sensitivity function and it was desired to know how temporal factors affect the spatial-frequency tuning of the relatively narrowly tuned channels thought to underlie contrast sensitivity. The results show that, for counterphase flickering stimuli, spatial-frequency tuning does not depend on temporal envelopes applied identically to the signal and to the masking noise. A similar picture emerges at slow (2.7-deg/sec) but not at fast (10.9-deg/sec) drift rates.

Contrast Sensitivity↗
PubMed1988

Direction-of-motion discrimination with complex patterns: further observations.

Moving one component of a stimulus comprising two sinusoidal gratings of the same orientation sometimes results in mistaken judgments of the direction of motion. If the component with the higher spatial frequency moves and the stimulus is presented briefly, observers report motion in the direction opposite that which actually occurs. The illusory, or backward, motion appears whether the movement producing it occurs smoothly or as a discrete jump at the midpoint of the stimulus presentation. At durations at which motion appears reversed, smooth and discrete motion are indistinguishable. Measurement of the speed of the illusory motion by a cancellation technique permits comparison with results from classical induced-motion paradigms; the classical effect, obtained with spatially separated components, is smaller but in the same direction as the errors in perceived direction of motion that we measure. We suggest that the errors in judging the direction of motion may result from interactions among motion detectors tuned to the different spatial-frequency components of the stimulus.

Discrimination, Psychological↗
PubMed1987

Errors in direction-of-motion discrimination with complex stimuli.

The direction of apparent motion in a complex pattern comprising a static 1-cycle/degree (c/deg) grating and a moving 3-c/deg grating changes with stimulus duration. At durations longer than about 150 msec, motion is seen almost veridically; the motion of the 3-c/deg grating, which is seen correctly, merely induces in the 1-c/deg grating a weak apparent motion in the opposite direction. At shorter durations, however, the only motion seen is in the opposite direction from that which, in fact, occurs. The reversed apparent motion is both compelling and consistent; it is reported both by naive and by experienced observers, and, although it only occurs for certain ranges of spatial frequency, contrast and duration, the ranges are substantial. The reversal appears to be almost independent of the temporal frequency and the spatial phase of the stimulus; it occurs both for discrete and for continuous motion. It seems likely that the apparent motion with short duration stimuli reveals properties of local visual movement detection previously unknown and difficult to account for within the framework of current models of motion perception.

Discrimination, Psychological↗
PubMed1986

Muscle morphology, enzymatic activity, and muscle strength in elderly men: a follow-up study.

A follow-up study of muscle strength, muscle morphology, and enzymatic activity in 23 men, 73-83 years of age, was performed 7 years after the first investigation. With the exception of two men treated for congestive heart failure and four treated for hypertension, all were apparently clinically healthy and none had functional locomotor disturbances. Body weight was reduced by 2% and body cell mass by 6%, whereas the quadriceps muscle strength decreased 10%-22% over the 7-year period. Fiber composition in the vastus lateralis did not change significantly, and there was no significant difference between the biopsies from the biceps brachii and vastus lateralis. In the vastus lateralis, there was a reduction in fast-twitch fiber areas, which were smaller than in the biceps brachii (not studied at the previous investigation). There were also more histopathologic changes in the vastus lateralis than in the biceps brachii. The enzymatic activities of lactate dehydrogenase and myokinase, which were studied on both occasions in the vastus lateralis, did not change, and the activities of the other measured enzymes indicated a maintained metabolic capacity at high age. Oxidative enzymatic activities were higher in the vastus lateralis, and glycolytic enzymatic activities were higher in the biceps brachii, which could partly be explained by differences in relative fiber areas.

Aged↗
PubMed1985

The four factors leading to binaural masking-level differences.

A simple extension of the Webster-Jeffress model is presented together with its predictions for the effects of various stimulus parameters on the size of binaural masking-level differences (BMLDs). The four factors leading to BMLDs (just-noticeable differences (JNDs), temporal effects in simultaneous masking, binaural interaction, and temporal effects in non-simultaneous masking) are described, new measurements of the effect of signal duration on the detectability of interaural delay are presented, and the high degree of correlation between observers' sensitivity to changes in level and their sensitivity to changes in interaural delay is demonstrated. A number of examples illustrating where knowledge of JNDs for level and interaural delay and their joint dependence on certain stimulus parameters are sufficient to predict BMLDs are discussed.

Auditory Perception↗
PubMed1984

Effects of the bandwidth and level of noise and of the duration of the signal on binaural masking-level differences.

An investigation of the effects of the level and bandwidth of the masking noise and of the effect of test-tone duration on binaural masking-level differences (BMLDs) has been carried out using the standard Békésy audiometric techniques. The BMLDs increase in magnitude with increasing masker level, reach a shallow maximum at bandwidths of the masker near 30 Hz, and scarcely differ for signal durations of 20 and 200 ms. Most of these data are consistent with previously reported results and are to be used in related studies with the same observers.

Auditory Threshold↗
PubMed1984

Binaural masking-level differences with tones masked by noises of various bandwidths and levels.

Binaural masking-level differences (BMLDs) were measured for tones at frequencies below and above masking noises centred on 250 Hz, having 10, 31.6 or 100 Hz bandwidths and either 40 or 60 dB spectral density levels. The BMLD drops rapidly when masker and signal have no frequency components in common. The magnitude of the decrease in the BMLD is not merely a result of the reduced masking effect and is not to be predicted by the models of Durlach [2] or Schenkel [12].

Auditory Threshold↗
PubMed1984

Binaural masking-level differences with tonal maskers.

The thresholds for monaural and binaural 250-Hz test tones masked by a 250-Hz sinusoidal masker were measured as a function of the duration of the test tone. The signal and masker were presented either in-phase or in-quadrature. Next, the just-noticeable degree of amplitude modulation (AM) and just-noticeable modulation index for frequency modulation (FM) were measured as a function of the rate of modulation. Both sets of results suggest that monaural and binaural time constants have similar values (near 100 ms) and that the hearing system does not seem particularly 'sluggish' with the paradigms we used. In a second series of experiments, we again measured the masking of a tone by a tone of the same frequency. Long duration signals were used and we manipulated the phases of the masker and the signal. In order to interpret the results we require no more than the individual just-noticeable difference in level (monaurally about 1 dB) and the just-noticeable interaural time delay (about 100 microseconds at our signal frequency).

Acoustic Stimulation↗