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Biomedical subjects

J Hohnsbein

Publications and source records attributed to J Hohnsbein.

46 records · Page 3Linked to original sources
PubMed1988

Perceptual latencies are shorter for motion towards the fovea than for motion away.

Subjects had to align a brief test flash with a peripheral steady reference target during ocular pursuit, or with a moving reference target during steady eye fixation. The performance was determined by the direction of movement, of the reference target image on the retina--towards or away from fovea. The data are explained by the hypothesis that the passage of a retinal locus by a moving target image is experienced faster when the image moves foveopetally, regardless of whether the passage is caused by real target movement or by ocular pursuit.

Adult↗
PubMed1988

Dynamic auditory localization: perceived position of a moving sound source.

Experiments are presented in which a sound source was moved at 15.2 cm/s over a horizontal path of 60 cm length, positioned at a 57 cm distance in front of the observer, symmetrically relative to the median plane. The subjects had to localize the sound at different moments of time. The sound source was predominantly mislocated in the direction of the movement; the mislocation increased at the end of the movement by up to 10-11 deg. In another condition the sound source was localized when it was stationary. In this case the mislocation was directed towards the median plane. The differences between the static and dynamic auditory localization are discussed.

Auditory Perception↗
PubMed1987

Tonic contraction of canine gastric muscle during long-lasting calcium removal and its dependence on magnesium.

1. Tonic contractions induced by acetylcholine (ACh) in canine gastric fundus preparations were shown to persist during long-lasting exposure to Ca2+-free solution containing EGTA (1 mmol/l). These EGTA-resistant contractions amounted to up to more than 50% of maximal ACh-control responses in physiological salt solution. They could be evoked repeatedly for more than 20 h without reduction in size, each contraction lasting as long as ACh was present. 2. During prolonged exposure to Ca2+-free solution at normal Mg2+ concentration ([Mg2+]O = 1.2 mmol/l), the preparations exhibited a slowly developing contracture (elevation of the baseline of contraction), which was particularly pronounced in strips taken from the circular layer of the muscular wall (44% of control ACh-maximum after 4 h in Ca2+-free solution). Contracture could be suppressed either by increasing [Mg2+]O to 6-10 mmol/l or by depolarizing the cell membrane (replacement of external Na+ by K+). However, contracture also developed if, at physiological [Na+]O and [K+]O, [Mg2+]O was further increased to 50 mmol/l. 3. The combined effects of [Mg2+]O and membrane potential suggest that contracture is caused by a gain of Mg2+ by the cells. This conclusion is based on the assumption that (a) the cytoplasmic Mg2+ concentration is determined by the transmembrane electrochemical gradient acting on Mg2+, the magnesium permeability of the cell membrane (PMg) and an active extrusion mechanism, and that (b) Ca2+ removal leads to an increase of PMg which is (partly) prevented by an appropriate increase of [Mg2+]O. 4. 45Ca efflux experiments, performed at [Mg2+]O = 10 mmol/l to avoid interference of ACh responses with contracture, showed that the cellular 45Ca content decreased from some 200 mumol/kg wet wt. to less than 10 mumol/kg wet wt. within 10-20 h in Ca2+-free solution. Activations by ACh did not produce any detectable increase in 45Ca efflux. 5. The calcium ionophore A23187 (10(-5) mol/l), applied in order to increase the calcium permeability of the cell membrane, did not reduce the EGTA-resistant contractions. 6. Experimental procedures conducted to replace calcium within intracellular stores by strontium or barium did not affect the EGTA-resistant ACh response. However, prior uptake of manganese by the cells had an amplifying effect. 7. Caffeine (30 mmol/l) failed to produce contraction in Ca2+-free solution, whereas ACh evoked contractile responses, both in the presence of and after application of caffeine.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1985

Dynamic visual capture: apparent auditory motion induced by a moving visual target.

Apparent motion of a sound source can be induced by a moving visual target. The direction of the perceived motion of the sound source is the same as that of the visual target, but the subjective velocity of the sound source is 25-50% of that of the visual target measured under the same conditions. Eye tracking of the light target tends to enhance the apparent motion of the sound, but is not a prerequisite for its occurrence. The findings are discussed in connection with the 'visual capture' or 'ventriloquism' effect.

Adult↗
PubMed1985

Differentiation of the action potential in the smooth muscle of canine gastric antrum using calcium-inhibitory drugs.

Electrical and mechanical activity were recorded simultaneously in smooth muscle preparations from the antrum region of canine stomach by means of a single sucrose gap technique (SGT). The SGT was optimized to permit stable recording from multicellular smooth muscle preparations over several hours of electrical and mechanical activity with little disturbance of their normal properties. Acetylcholine (ACh, 10(-8) to 10(-6) M) induced or augmented dose-dependently the electrical and mechanical activity. The plateau of the action potential complex was elevated by ACh, while the contraction was increased in linear correlation to the magnitude of the plateau component. In spontaneously active (or in ACh-stimulated) preparations TEA (5 to 20 mM) magnified the plateau component, induced or strengthened spikes on the plateau ('secondary spikes'), and induced or strengthened phasic contractions. Nifedipine (10(-6) M) abolished secondary spikes, part of the plateau component of the action potential, and suppressed mechanical activity. The complex action potential of canine gastric antrum can be differentiated into (a) a basic action potential, consisting of an initial, primary spike and a plateau depolarization; this basic action potential is resistant to nifedipine and does not trigger any mechanical activity; and (b) a nifedipine-sensitive component (calcium component), which consists of an augmentation of the plateau depolarization and of secondary spikes, and which is responsible for the initiation of mechanical activity.

Acetylcholine↗
PubMed1982

Pacemaker process of ureteral peristalsis in multicalyceal kidneys.

The mechanical activity of isolated strips from different areas of the pyeloureteral system was investigated in 10 pigs: calyx, renal pelvis, pyeloureteral junction and ureter. Additionally, electrical activity was measured in some pyeloureteral preparations using the sucrose-gap technique. Regular spontaneous activity with an average frequency of 9.5/min was recorded in calyceal strips, decreasing to 5.4/min in renal pelvis, 5.7/min in pyeloureteral preparations and to 1.2/min in ureteral preparations. The activity of renal pelvis, pyeloureteral and ureteral preparations was less regular, and bursts of fast activity (near 10/min) could be observed in all these preparations. The membrane potential of pyeloureteral strips showed spontaneous generator oscillations of about 10/min. Variations in the pattern of ureteral peristalsis are due to different coupling ratios of membrane potential oscillations to contractions. Adrenaline (10(-5) mol/l) increased the frequency of the oscillations and enhanced their manifestation in the mechanical recordings, whereas tetraethylammonium (5-20 mmol/l) only increased the coupling ratio. The following concept for the generation of ureteral peristalsis in multicalyceal kidneys is developed: several (primary) oscillators exist in the calyces; in the pyeloureteral junction a (secondary) pacemaker exists which has an intrinsic frequency similar to that of the calyceal pacemakers; both processes cooperate in the generation of ureteral peristalsis.

Animals↗
PubMedDate not supplied

Improved amplitude evaluation of the frequency following response (FFR).

Three methods were combined to improve the evaluation of the amplitude of the frequency following response (FFR) in unfavorable signal-to-noise conditions. The first step was the application of a time-multiplex averager to reduce noise variance between amplitude values to be compared. The second step was the evaluation of amplitude in the frequency domain by means of a digital triangle filter. The third step was the correction of raw FFR amplitudes by an algorithm that takes into account several noise values.

Electrophysiology↗