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Biomedical subjects

O Bock

Publications and source records attributed to O Bock.

At least 73 records · Page 4Linked to original sources
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↗
PubMed1982

Non-linear interaction of the vestibular and the eye tracking system in man.

Oculomotor control in man was investigated during passive, sinusoidal, whole-body rotation under a conflict between the vestibulo-ocular reflex (VOR) and the eye tracking system (ETS), as to the appropriate direction of compensatory eye movements. ETS predominated at stimulus frequencies below 0.8 Hz, and VOR above 1.5 Hz. In the intermediate frequency range the dominance repeatedly flipped between ETS and VOR, suggesting that the interaction of the two systems is not linear, but rather governed by a switch.

Eye Movements↗
PubMed1980

Air versus water caloric test.

The air caloric test is favoured because of the advantage of higher convenience for patient and operator and its applicability in situations where water is contradicted. We examined 20 normal subjects with air (60 s, 12 min, 45 degrees/29 degrees C) and 25 with water (30 s, 30 cm3, 44 degrees/30 degrees C) caloric test. Additionally, we evaluated the influence of flow rate and irrigating 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--close to the tympanic membrane appeared to be essential to achieve reliable results in air caloric test. Furthermore, measurements of the actual temperature should be done at the irrigation tip delivery in every air caloric test. The lower heat capacity of air, turbulences near the tympanic membrane and air aspired from the environment are the main reasons of more distinct temperature drops in the air caloric test. We observed a significant (P less than 0.05) difference between maximum slow phase velocity in air (11.5 degrees C/s) and water (19.5 degrees C/s) irrigation. The relative standard deviation was markedly higher for air irrigations. Therefore, in spite of the advantages of the air caloric test, the disadvantage of a higher variability, even when using a sophisticated technique, has to be considered.

Adult↗
PubMed1980

[The reproducibility of A. G. Lauritzen's registrations].

The reproducibility of the positional relationship of mandible models in the Dentatus Articulator was studied. Based on the method of A.G. Lauritzen, the articulator is oriented on a hinge axis. The registration procedure was carried out by two subjects on three patients (5 times each). The deviations in the hinge axis point against a value of zero (initial measurement) were then determined with a face-bow. TMJ and SAM face-bows were used for these controls. The deviations from the mean value of the hinge axis point determined in the articulator were within the range of +/- 3 mm in the sagittal and vertical directions. The results tend to indicate that experience, routine, and knowledge of the varioius possibilities of error are necessary if the registration is to be accurate.

Dental Articulators↗
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↗