Biomedical subjects

O Bock

Publications and source records attributed to O Bock.

At least 19 recordsLinked to original sources

PubMed1992

Adaptation of aimed arm movements to sensorimotor discordance: evidence for direction-independent gain control.

Human subjects pointed, without sight of their arm, at visual targets presented on a mirror-viewed monitor screen. During the adaptation period of each experiment, the position of the pointing fingertip was continuously recorded and displayed on the screen along with the targets. This visual feedback was not always veridical; rather, it was manipulated to require a gradual modification of the pointing response gain throughout the adaptation period. No visual feedback at all was available during the pre- and postadaptation periods of each experiment. The adaptive effect was determined as difference between pre- and postadaptation gains. In Expt. A, visual feedback during the adaptation period prescribed a gradual reduction of the horizontal response gain without specifying the gain for other directions; the adaptive effect was found to generalize uniformly to all movement directions. Expt. B1 prescribed a reduction of the horizontal, and an unchanged vertical gain component: in spite of this differential requirement, the adaptive effect was again uniform for all directions. Expt. B2 prescribed a reduction of the horizontal, and an increase of the vertical gain component: we found a reduced gain for all directions, with a mild direction-dependence in the magnitude of the adaptive effect. In a modified version of Expt. B2, no intermanual transfer of the adaptive effect was found. Expt. C1-3 prescribed gain reduction for target directions within 15, 30, or 45 degrees around the horizontal, and gain increase for all other directions: we found little or no adaptive effects under such conditions. From the above findings, we concluded that the adapted system controls movement gain largely independent of movement direction. This mechanism responds readily to requirements for gain reduction, but not gain increase. No evidence for an organization of the arm motor system in direction-selective channels was found, in contrast to findings on the saccadic control system in a paradigm similar to our Expt. A8. This discrepancy supports the view that arm and eye movements are controlled by distinct mechanisms.

Adaptation, Psychological↗

PubMed1992

Motor control prior to movement onset: preparatory mechanisms for pointing at visual targets.

The present study investigated the mechanisms involved in the preparation of pointing movements in humans. We provided visual precues on the location of the upcoming target, and registered the effect of these precues on the reaction time (RT = interval between target appearance and movement onset). Generally, precues were found to reduce RT, suggesting that some aspects of the preparatory process have been advanced in time. In Exp. 1, precues fully specified the direction required for the upcoming movement while indicating only a range of movement amplitudes; in Exp. 2, precues fully specified the amplitude and indicated a range of directions. In both experiments, RT was shorter than in control trials without precues, and gradually increased with the size of the precued amplitude or direction range. This result suggests that the preparation of either parameter is possible without knowing the precise value of the other, i.e. amplitude and direction are not prepared in a fixed order. Furthermore, our results are consistent with the view that movement preparation includes a progressive contraction of the precued range towards the final value. The speed of this process can be estimated as 0.31 cm/ms for amplitude, and 1.7 deg/ms for direction ranges. In Exp. 3 and 4, precues indicated both amplitude and direction as ranges only. The size of the amplitude range was held constant while the size of the direction range was varied (Exp. 3), or vice versa (Exp. 4). Under these conditions, RT increased with the size of the varied range.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Accuracy of aimed arm movements in changed gravity.

We studied the accuracy of aimed arm movements in normal gravity, and during the hypergravity (hyper-G) and microgravity (micro-G) episodes of KC-135 parabolic flights. Subjects pointed at mirror-viewed targets without sight of their arm, and final pointing position was measured by a digitizing pad. Compared with the normal gravity (normal-G) baseline, subjects pointed consistently higher in hyper-G, and still higher in micro-G. Results were not different if subjects viewed targets only during normal-G and pointed at their memorized position under changed gravity (changed-G); this suggests that the "elevator illusion" played a minor role in our study. The observed impairments were attributed to degraded proprioceptive feedback and/or inappropriate motor programs in changed-G. Pointing accuracy improved movement-to-movement but not parabola-to-parabola, indicating that prolonged exposure is needed for sustained adaptation.

Aerospace Medicine↗

PubMed1990

Load compensation in human goal-directed arm movements.

We analysed the execution of multijoint pointing movements in humans while weight or spring loads were applied to the pointing hand. Visual feedback on arm and hand position was excluded. Movement paths, final positions, and normalized velocity profiles were found to be load-independent, except for the very first movement after a load change. With increasing size of a weight load movement velocity decreased, and movement duration increased by the same factor, i.e. the velocity profiles were rescaled in magnitude and time. In contrast, under a spring load movement velocity and duration were not different from no-load controls. These findings led us to propose a new hypothesis on load compensation by the motor system. We suggest that an important controlled variable is a fictional force acting externally on the hand, and that the inertia- and gravity-related components of this force are controlled separately; then, loads are compensated by time scaling of the inertia-related, and magnitude scaling of the gravity-related component. The predictions of this hypothesis regarding movement paths and velocities under weight and spring loads are in good quantitative agreement with our experimental data. When specifically asked to do so, our subjects were able to generate velocity profiles under a weight load that were not different from those under no-load conditions, which suggests that alternative control strategies are available when needed.

Biomechanical Phenomena↗

PubMed1990

Control of arm movements in a 2-dimensional pointing task.

The present study analyses in humans the control principles of sequential, unpracticed pointing movements in a 2-dimensional space. Our data reveal that variable pointing errors add up within such sequences. This finding supports the hypothesis that movement amplitude rather than position is the controlled variable of the investigated movements.

Attention↗

PubMed1990

Dynamic properties of human goal-directed arm movements.

In the present study, the velocity of pointing movements towards visual targets was analyzed. In accordance with the literature, tangential velocity was found to exhibit rather smooth, single-peaked profiles. In contrast, however, the profiles of the velocity components in the Cartesian coordinates of space were conspicuously multi-peaked, and suggestive of sums of a smooth curve and an oscillation. Oscillation frequency was 4-6 Hz, and its amplitude 200-600 mm/s; the phase shift between horizontal and vertical oscillation was about 180 degrees. The oscillation remained unaltered when the external load of the arm, the size of the visual target, or the required movement direction were changed. The relationship between the present findings and previously documented rhythmic properties of motor control is discussed, and it is concluded that the oscillations may have been generated by neural circuits with inherent oscillatory properties.

Acceleration↗

PubMed1989

Interaction of visual and non-visual signals in the initiation of smooth pursuit eye movements in primates.

The initiation of smooth pursuit eye movements (PEM) by visual and non-visual signals was analysed in humans and monkeys. While PEM latency ranged around 150 ms when a purely visual target was provided, it often dropped to about 0 ms, or even became negative, when target movement was coupled to the subject's arm; this suggests that signals about the intention to move the arm can be evaluated for PEM control. Eye movements always started in the visually correct direction, independent of the sign of coupling between arm and target; from this we conclude that intentional signals are not mere triggers, but also convey directional information. Short-latency PEM trials were intermixed with those characterized by normal latencies, which often resulted in bimodal latency distributions; this suggests that visual and intentional signals compete for the control of PEM.

Animals↗

PubMed1987

A head-mounted device for measurement of pointing to visual targets without seeing the pointing arm.

A mobile, head-mounted device is introduced, which allows the presentation of visual targets and the measurement of pointing movements to these targets in visual open loop (i.e. blind pointing without seeing the pointing arm). This microcomputer-controlled, easy-to-operate device offers a variety of applications both in basic research and for clinical diagnosis in ophthalmology, neurology, and otolaryngology.

Arm↗

PubMed1987

Information processing in goal-directed movements.

Sensory-motor interaction in pointing at visual targets without sight of the pointing arm was evaluated in human subjects, using information theory. Equations were derived to determine transformation in channels with amplitude-continuous output signals, which overcome the problems involved in dividing the output into discrete bins. The equations were applied to calculate transinformation in our pointing experiment, and to predict transinformation under a variety of different experimental conditions. The results apply also to other systems that can be regarded as channels with similar properties.

Feedback↗

PubMed1987

Coordination of arm and eye movements in tracking of sinusoidally moving targets.

Human subjects tracked sinusoidally moving visual targets with arm and eyes, in absence of visual feedback of the arm. The resulting frequency responses indicated that predictive mechanisms are involved both in arm and in eye tracking, and that the respective upper frequency limits are similar. Most importantly, substantial differences between arm and eye performance were observed: At low frequencies the gain of arm, but not of eye movement was consistently smaller than 0 dB. At higher frequencies arm, but not eye gain exhibited a marked amplitude non-linearity. The intra-trial gain and phase variability of arm movement was not correlated with the respective variability of eye movement. The reaction times to sudden changes of target parameters could be considerably different for arm and eye, and their inter-trial variability was not, or only marginally, correlated. Taken together, these findings strongly suggest that the mechanisms controlling predictive arm and eye movements in our experiment are organized to a major part in independent, parallel channels. The results are discussed with reference to a simple scheme of eye-arm coordination.

Electrooculography↗

PubMed1986

Goal-directed arm movements in absence of visual guidance: evidence for amplitude rather than position control.

The control of pointing arm movements in the absence of visual guidance was investigated in unpracticed human subjects. The right arm grasped a lever which restricted the movement of the right index fingertip to a horizontal arc, centered between the axes of eye rotation. A horizontal panel directly above the arm prevented visual feedback of the movement. Visual stimuli were presented in discrete positions just above panel and fingertip. A flag provided visual feedback on fingertip position before each pointing movement (Exp. A and B), or before a movement sequence (Exp. C). When subjects pointed from straight ahead to eccentric stimulus positions (Exp. A), systematic and variable pointing errors were observed; both kinds of errors increased with stimulus eccentricity. When subjects pointed from 30 deg left to stimuli located further right (Exp. B), errors increased with stimulus position to the right. Taken together, these findings suggest that pointing accuracy depends not primarily on stimulus position, but rather on required movement amplitude. When subjects performed sequences of unidirectional movements (Exp. C), systematic and variable errors increased within the sequence. A quantitative analysis revealed that this increase can be best described as an accumulation of successive pointing errors. We conclude that both findings, error increase with amplitude, and accumulation of successive errors, when considered together strongly support the hypothesis that amplitude, rather than final position, is the controlled variable of the investigated movements.

Arm↗

PubMed1986

Contribution of retinal versus extraretinal signals towards visual localization in goal-directed movements.

In human subjects, we investigated the accuracy of goal-directed arm movements performed without sight of the arm; errors of target localization and of motor control thus remained uncorrected by visual feedback, and became manifest as pointing errors. Target position was provided either as retinal eccentricity or as eye position. By comparing the results to those obtained previously with combined retinal plus extraretinal position cues, the relative contribution of the two signals towards visual localization could be studied. When target position was provided by retinal signals, pointing responses revealed an over-estimation of retinal eccentricity which was of similar size for all eccentricities tested, and was independent of gaze direction. These findings were interpreted as a magnification effect of perifoveal retinal areas. When target position was provided as eye position, pointing was characterized by a substantial inter-, and intra-subject variability, suggesting that the accuracy of localization by extraretinal signals is rather limited. In light of these two qualitatively different deficits, possible mechanisms are discussed how the two signals may interact towards a more veridical visual localization.

Arm↗

PubMed1986

Visual localization after strabismus surgery is compatible with the "outflow" theory.

Strabismic patients pointed at visual targets, presented monocularly, without sight of the pointing arm. After surgical rotation of one eye in the orbit the pointing responses were shifted by a similar amount in the opposite direction in 13 out of 14 patients; this outcome corresponds to the predictions of the outflow theory of visual localization. Occasional differences between predicted and actual response shifts can be attributed to the well-known ambiguity of localization in strabismics.

Humans↗

PubMed1979

Vestibular adaptation to long-term stimuli.

Experimental procedures are described which respectively enlarge stimulus duration in vestibular peracceleratory tests, and allow to rule out direct thermal effects on the vestibular nerve during long term calorisations. First experimental results indicate that time course of nystagmus during prolonged stimulations differs markedly in rotational and caloric tests. Whereas there is a distinct decline of response during rotation (in accordance to the predictions of current mathematical models), in caloric tests nystagmus reaches a steady state level, maintained for at least 15 min.

Adaptation, Physiological↗

PubMed1979

The influence of pneumatization of mastoid bone on caloric nystagmus response. A clinical study and a mathematical model.

Pursuing the problem whether and why the pneumatization of mastoid bone has any influence on caloric nystagmus, we examined 15 large or extensively (L.P.) and 15 poorly (P.P.) pneumatized subjects. Following water irrigation (44 degrees and 30 degrees C, 30 sec) we checked the parameters maximum SPV, max. frequency, latency, duration and time of max. response by ENG recordings. Both groups differed significantly for all parameters except duration (p less than 0.001). On comparing these findings with an earlier proposed model (Bock & Bromm, 1977) we could show a good correspondence for the P.P. group by doubling the parameter 'thermal diffusivity of mastoid bone'. An even better correspondence could be found by diminishing the parameter 'coefficient of temperature changes by perfusion'. The theoretical and practical implications and conclusions of our findings are discussed.

Caloric Tests↗

PubMed1979

[Uses of the occlusal registration instrument (ORI)].

By means of the occlusal recording instrument (ORI), jaw models can be measured three-dimensionally and filed with respect to axes and skull. In clinical trials evaluated with the ORI, it was shown that the position of the maxilla in the skull can be transferred to the articulator with great accuracy. Suggestions are given for improvements to refine the method of measurement. If the third point of reference is also tattooed, the accuracy of the transference of the face-bow is considerably increased. Under these conditions the apparatus is suitable for checking the accuracy of the transference of the face-bow and for photographic documentation.

Dental Articulators↗

PubMed1979

[How useful is the intersaccadic interval analysis of vestibular nystagmus for clinical diagnostic (author's transl)].

The intersaccadic interval analysis of vestibular nystagmus was proposed by Cheng et al. in 1974. This method gives a statistical and sequential description of intersaccadic intervals. Until now there were no reports concerning the clinical diagnostic relevance of this method in vestibular disturbancies. Therefore, we checked 8 normal probands and 7 patients (3 peripheral, 3 central vestibular lesions, one congenital nystagmus). Compared to common nystagmus parameters like maximum speed of slow phase or minimum frequency normal probands showed a relatively high variability, as well as the patients - excluding congenital nystagmus. The maximum of intersaccadic intervals of the latter was very marked between 0,9 and 1,0 seconds. In the other cases the normally monomodal distributed maxima were between 0,2 and 0,6 sec. A multimodal distribution, as described by Cheng et al. in 1974, were to be found very seldomly. The comparison of intersaccadic interval analysis with the common nystagmus parameters showed, that in clinical diagnostic this method should not be too necessary. However, regarding scientific research - including mathematical models of vestibular nystagmus - the intersaccadic interval analysis could be useful.

Caloric Tests↗

PubMed1979

[Air caloric test: as useful as the water caloric test (author's transl)].

Twenty normal probands were examined by us with air (60 sec, 121/min, 45 degrees/29 degrees C) and 25 with water (30 sec, 30 cm3, 44 degrees/30 degrees C) caloric test. Additionally we evaluated the influence of flow rate and tip position on the temperature near the tympanic membrane during the irrigation, using a polyacryl copy of the external auditory canal. A high flow rate and a reproducible tip position very near to the tympanic membrane during the irrigation appeared to be essential to achieve reliable results in air caloric test. Measurements of the actual temperatur should be done therefore at the irrigation tip delivery in every caloric test with air. Lower heat capacity of air, air jamming near the tympanic membrane and heat losses through the meatus wall are the main reasons of more distinct temperature drops and a higher variability in air caloric test, than in the common caloric test with water. Therefore, the air caloric test as a reliable instrument should be reserved for those cases, were water is contradicted.

Air↗