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Results for “visual feedback”

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PubMed1979

Jerk nystagmus: some new findings.

Eye movements in a subject with jerk nystagmus were recorded during a variety of tracking tasks using a photoelectric method. New findings included ability to reduce nystagmus amplitude and frequency when instructed "to hold the eye steady" rather than "to fixate" in the presence of a visible target, changes in nystagmus characteristics and visual acuity as a function of head position which related to overall retinal-image motion, marked variability of nystagmus especially during reading, and necessity of a prolonged period of visual feedback for generation of nystagmus to approach a "steady-state" level. Clinical implications of these findings are discussed, including use of the "hold" command during ophthalmoscopy in patients with nystagmus.

Adult↗

PubMed2002

Spectral decomposition of variability in synchronization and continuation tapping: comparisons between auditory and visual pacing and feedback conditions.

Spectral analysis was applied to study the variability in human rhythmic synchronization to a visual, auditory or combined auditory-visual metronome of about 2 Hz, as well as the variability in continuation tapping at the same rate with or without visual or auditory feedback. In synchronization, variability was larger in the visual condition than in the auditory and combined conditions, but only below frequencies of about 0.3 Hz. Thus, there seem to be at least two sources of variability in synchronization, one being modality-independent and limited to intervals shorter than 3 s, and the other being modality-dependent and evident as slow "drift", especially in the visual task. In continuation tapping, variability did not depend reliably on the presence or modality of feedback. However, spectral analysis revealed a change in the temporal structure of variability around 0.08 Hz (a period of about 12 s or 24 taps), which roughly agrees with earlier findings reported in the literature.

Adult↗

PubMed1998

Gaze stabilization during dynamic posturography in normal and vestibulopathic humans.

Dynamic posturography by measurement of center of pressure (COP) is a widely employed technique for evaluating the vestibular system. However, the relationship of COP motion to vestibulo-ocular reflex (VOR) function and image stability on the retina has not been determined previously. To assess these relationships, we report gaze, head, and trunk stability during dynamic posturography in 11 normal volunteers, 7 subjects with unilateral vestibular lesions, and 3 subjects with bilateral vestibular lesions. Posturographic tasks consisted of standing still and standing on a platform that was sliding (0.2 Hz), tilting (0.1 Hz), or covered with a foam cushion 6 cm thick while tilting (0.1 Hz). Each perturbation was imposed in the anterior-posterior and repeated in the medial-lateral direction, in both light and darkness. Subjects viewed (or in darkness remembered) a target located 50, 100, or 500 cm distant. COP, angular eye position, and angular and linear orbit and trunk positions were measured using magnetic search coils and flux gate magnetometer sensors. With the target visible, the velocity of image motion on the retina was on average always less than 1 degree/s, well within the range consistent with high visual acuity. In darkness, gaze velocity increased for normal and vestibulopathic subjects. During tilt, vestibulopathic subjects had a significantly greater gaze velocity than controls. Gain of the angular VOR (eye velocity/head velocity) was significantly lower in darkness than in light and in vestibulopathic as compared to control subjects. Gain of the VOR was significantly correlated with gaze instability, but variation in VOR gain accounted for only 20-40% of the variance. In darkness, the velocity of the COP was significantly greater in vestibulopathic than control subjects for every condition tested. In light, this difference was small and often not significant. Although spectral analysis of the COP indicated frequencies above 1 Hz that were not observed in motion of the trunk and orbit, root mean square (RMS) velocities of the trunk and orbit in the horizontal plane were higher in darkness and in vestibulopathic subjects, mirroring COP findings. Only in vestibulopathic subjects tested in darkness was there a correlation between COP velocity and gaze velocity; COP velocity was otherwise uncorrelated with gaze. Gaze velocity was greater with near than with distant targets. Vertical VOR gain was higher with near targets. No other significant effects of target distance were found. Head movement strategy, VOR gain, and COP were all unaffected by target proximity. These data show that gaze velocity measurements during dynamic posturography in darkness are sensitive to vestibular loss. With a visible target, both COP and gaze stability of vestibulopathic subjects are difficult to distinguish from normal. During visual feedback, it is likely that image stabilization over the range of frequencies tested is achieved through better head stability and through visual tracking, allowing vestibulopathic subjects to maintain adequate visual acuity.

Adult↗

PubMed1977

The effect of chronic anxiety level upon self control of heart rate.

A sample of 90 subjects were rated on the IPAT anxiety scale and 5 subjects (3 male and 2 female) per group were selected from each of the high and low anxiety categories. All subjects were naive participants in heart rate biofeedback sessions utilising analogue visual feedback. Following a heart rate baseline (no feedback) session, all subjects were required to raise their heart rate and lower their heart rate in two separate trials, a visual "target" criteria being provided. The data collected consisted of a resting baseline heart rate value, mean heart rate increase, and mean heart decrease values expressed as beats per minute. Results indicated a marked ability for highly anxious subjects to self-induce heart rate increases only and for low anxious subjects to decrease their heart rate only.

Anxiety↗

PubMed1978

Visual calibration of posture in normal and motor retarded Down's syndrome infants.

Infants with Down's syndrome are delayed in achieving motor milestones. When they first sit unsupported a discrepancy between visual and mechanical-vestibular indices of postural stability is less disruptive of their balance than in normal infants. Yet when they first stand unsupported, the same discrepancy disrupts balance more in these infants than in the normal infants. The effect of discrepant visual feedback also differs systematically as a function of the infants' experience of the posture. Monitoring posture in relation to a stable visual surround appears to be fundamental to the normal development of motor control.

Child Development↗

PubMed1975

Feedback versus motor programming in the control of aimed movements.

In the Fitts paradigm the subject moves a stylus to the left or right of an initial rest position to reach targets that vary in size and in distance from the initial position. The classic finding for relatively long movements is that movement time, measured from leaving the initial position until contact with the target, depends on both distance and target size according to a relationship known as "Fitts' law." By contrast, reaction time, measured from the signal to move until the stylus leaves the initial position, is independent of these parameters. While replicating these results for long movements, the present data show a different pattern for very short movements, for which Fitts' law no longer holds and for which reaction time increases as the size of the target is decreased. These findings were interpreted as implying that long movements are under feedback control, whereas short movements are predominately programmed and ballistic. This conclusion was supported by the additional finding that elimination of visual feedback was more disruptive to the long than to the short movements.

Adolescent↗

PubMed1993

Reference systems for coding spatial information in normal subjects and a deafferented patient.

To produce accurate goal-directed arm movements, subjects must determine the precise location of target object. Position of extracorporeal objects can be determined using: (a) an egocentric frame of reference, in which the target is localized in relation to the position of the body; and/or (b) an allocentric system, in which target position is determined in relation to stable visual landmarks surrounding the target (Bridgeman 1989; Paillard 1991). The present experiment was based on the premise that (a) the presence of a structured visual environment enables the use of an allocentric frame of reference, and (b) the sole presence of a visual target within a homogeneous background forces the registration of the target location by an egocentric system. Normal subjects and a deafferented patient (i.e., with an impaired egocentric system) pointed to visual targets presented in both visual environments to evaluate the efficiency of the two reference systems. For normals, the visual environment conditions did not affect pointing accuracy. However, kinematic parameters were affected by the presence or absence of a structured visual surrounding. For the deafferented patient, the presence of a structured visual environment permitted a decrease in spatial errors when compared with the unstructured surrounding condition (for movements with or without visual feedback of the trajectory). Overall, results support the existence of an egocentric and an allocentric reference system capable of organizing extracorporeal space during arm movements directed toward visual targets.

Adult↗

PubMed2004

Deficits in rapid adjustments of movements according to task constraints in Parkinson's disease.

The role of the basal ganglia in the adaptive control of movement was investigated by unexpectedly perturbing movements in 8 patients with Parkinson's disease (PD) tested off medication and in 6 aged-matched healthy subjects. Subjects performed two movement components simultaneously and without visual feedback: touching the nose with the finger while leaning the trunk forward. Subjects wore a harness connected to an electromagnet, which was attached to a wall. The trunk movement was mechanically blocked in randomly selected trials by engaging the electromagnet. While healthy subjects performed the task equally well in both conditions, PD subjects' hand movements significantly deteriorated in trunk-perturbed compared to trunk-free trials. Deteriorated hand movements were characterized by segmented hand paths, unsmooth velocity profiles, and prolonged movement times. This finding indicated that the relatively local trunk perturbation had a global effect on the hand movement of PD subjects, necessitating them to reinitiate, after some delay, their arm movement in perturbed trials. Thus, the basal ganglia may be a critical node in brain networks mediating the flexibility of responses to altered motor states.

Adaptation, Physiological↗

PubMed1980

[Effects of vision on tonic vibration response of a muscle or its antagonists in normal man (author's transl)].

In normal man, a vibratory stimulus applied to tendon of arm muscles can induce either a tonic motor response in the vibrated muscle or in its antagonists depending upon presence or absence of visual feedback from arm (perception of position vrs. perception of an illusive motion). Spinal motor effects of inputs from muscle spindle afferents elicited by vibration can be modified by the perceptive events experienced by the subject.

Feedback↗

PubMed2006

Long-lasting aftereffect of a single prism adaptation: shifts in vision and proprioception are independent.

After a single adaptation session to prisms with gradually incremented shift magnitude, the prism adaptation aftereffect was measured by open loop mid-sagittal pointing (O) to a visual target without visual feedback. This aftereffect corresponded to the summation of the shift in proprioception, measured by straight ahead pointing without vision (S), and the visual straight ahead judgement (V), measured by verbal stopping of an LED moving from two opposite directions. However, the measurement of the aftereffects made over a period of 7 days revealed significantly different decay curves in V, O and S. Surprisingly the S shift was still present up to 7 days after the training, while V had returned to the original level by 2 h, which was the first measurement after subjects returned to a normal visual environment. O had returned to pre-test level after 1 day. After 3 days Wilkinson's (J Exp Psychol 89:250-257, 1971) additive hypothesis (O=S-V) no longer fit the data. Rather "O=Pl-V", where Pl (Pr) is the shift in proprioception measured by passive lateral arm movements from left (right), fitted better during the whole 7 days of aftereffect in our study. Therefore, the aftereffect of our strong prism adaptation revealed, firstly, that classical open loop pointing consisted of aftereffect shifts equal to the summation of the shifts in the two passively measurable aftereffect components, vision (V) and proprioception (Pl), rather than with active straight ahead pointing (S). Secondly, the decay of the shift in visual perception and in passively measurable proprioception is independent. The former decays fast, and the latter decays slowly with two separate waves. Thirdly, we suggest that the use of visual perception-dependent spatial codes for visual-manual transformation and the vision-independent internal egocentric reference frame are mutually exclusive. We proposed a model to explain these possible mechanisms.

Adaptation, Physiological↗

PubMed1999

Pointing to remembered visual targets after active one-step self-displacements within reaching space.

We studied pointing movements to remembered visual targets in a completely darkened room with and without self-made step movements in order to investigate in which coordinate system and to what extent target representations relative to the body are updated for self-induced egomotion. A small red-light-emitting diode on the fingertip provided visual feedback about fingertip position at all times. We asked subjects to make pointing movements that started 2 s after disappearance of a visual target. In this interval of 2 s the subject did or did not make a step. The pointing errors without a step showed that subjects undershot faraway targets in a systematic way, whereas they sometimes overshot nearby targets. We found that the step causes larger pointing errors both in amplitude and direction with a bias in the direction of the step. We explored three different versions of a descriptive model in which polar coordinates were used to describe the pointing movement, and in which either Cartesian or polar coordinates were used to update target position relative to the shoulder for the step. The results suggest that incorporation of the step displacement in the new target position relative to the subject is done in a Cartesian frame of reference. Moreover, the amplitude of the step displacement tends to be underestimated by subjects.

Adult↗

PubMed2005

The effects of blurring vision on medio-lateral balance during stepping up or down to a new level in the elderly.

Visual impairment is an important risk factor for falls, but relatively little is known about how it affects stair negotiation. The present study determined how medio-lateral (ML) dynamics of stepping and single limb support stability when stepping up or down to a new level were affected by blurring the vision of healthy elderly subjects. Twelve elderly subjects (72.3 +/- 4.2 years) were analysed performing single steps up and single steps down to a new level (7.2, 14.4 and 21.6 cm). Stepping dynamics were assessed by determining the ML ground reaction force (GRF) impulse, lateral position of the centre of mass (CM) relative to the supporting foot (average horizontal ML distance between CM and CP during single support) and movement time. Stability was determined as the rms fluctuation in ML position of the centre of pressure (CP) during single support. Differences between optimal and blurred visual conditions were analysed using a random effects model. Duration of double and single support, and the ML GRF impulse were significantly greater when vision was blurred, while the average CM-CP ML distance and ML stability was reduced. ML stability decreased with increasing step height and was further decreased when stepping down than when stepping up. These findings indicate that ML balance during stepping up and down was significantly affected by blurring vision. In particular, single limb support stability was considerably reduced, especially so during stepping down. The findings highlight the importance of accurate visual feedback in the precise control of stepping dynamics when stepping up or down to a new level, and suggest that correcting common visual problems, such as uncorrected refractive errors and cataract may be an important intervention strategy in improving how the elderly negotiate stairs.

Aged↗

PubMed2000

Can a motion-blind patient reach for moving objects?

It has been claimed that the visual brain is organized in two separate processing streams for spatial vision: one for perception and one for action. To determine whether motion vision is also divided into vision for action and for perception we examined the interceptive behaviour of the motion-blind patient LM. The task for LM and three age-matched control subjects was to reach-and-grasp for an object that moved away. Three experiments were conducted to examine the effects on perfomance of target speed (Expt 1), observation time (Expt 2) and visual feedback (Expt 3). As LM is only able to reach for objects which move at 0.5 m/s or less, her performance is inferior to that of controls who can reach for objects moving at 1.0 m/s, but it is better than would be expected from her performance in psychophysical experiments on her motion vision. Kinematic analysis of LM's reaching movements showed that she adapted the speed of her moving hand to the speed of the target but only when full vision was available. In contrast to normal subjects, LM required long observation times and vision of her moving hand to produce successful reaching responses. Thus, the impairment of both perception and action in LM suggests that the motion area MT/V5 is located at an early stage of the extrastriate hierarchy and provides input to both the perception and the action processing streams.

Aged↗

PubMed1978

Effects of electromyographic feedback training on motor control in spastic cerebral palsy.

Electromyographic feedback training may play a special role in increasing active range of motion in spastic cerebral palsied individuals. The effects of electromyographic feedback training were documented on four persons with spastic diplegic cerebral palsy within a single subject design. Subjects received immediate auditory and visual feedback twice daily during ten consecutive days. Electromyographic feedback training resulted in increases in the active range of motion of the ankle joint of from 20 percent to 500 percent in the limbs trained during the first five days with electromyographic feedback and of from 33 percent to 450 percent in the limbs trained in the last five days. The acquired active range of motion was maintained by two of the subjects over intervals of from four to nine weeks.

Adolescent↗

PubMed1999

Evidence for an eye-centered spherical representation of the visuomotor map.

During visually guided movement, visual coordinates of target location must be transformed into coordinates appropriate for movement. To investigate the representation of this visuomotor coordinate transformation, we examined changes in pointing behavior induced by a local visuomotor remapping. The visual feedback of finger position was limited to one location within the workspace, at which a discrepancy was introduced between the actual and visually perceived finger position. This remapping induced a change in pointing that extended over the entire workspace and was best captured by a spherical coordinate system centered near the eyes.

Adult↗

PubMedDate not supplied

Eye-head coordination toward auditory and visual targets in humans.

Eye-head coordination during gaze orientation toward auditory targets in total darkness has been examined in human subjects. The findings have been compared, for the same subjects, with those obtained by using visual targets. The use of auditory targets when investigating eye-head coordination has some advantages with respect to the more common use of visual targets: (i) more eccentric target positions can be presented to the subject; (ii) visual feedback is excluded during the execution of gaze displacement; (iii) complex patterns of saccadic responses can be elicited. This last aspect is particularly interesting for examining the coupling between the eyes and the head displacements. The experimental findings indicate that during gaze orientation toward a visual or an auditory target the central nervous system adopts the same strategy of using both the saccadic mechanism and the head motor plant. In spite of a common strategy, qualitative and quantitative parameters of the resulting eye-head coordination are slightly different, depending on the nature of the target. The findings relating to patterns of eye-head coordination seem to indicate a dissociation between the eyes and the head, which receive different motor commands independently generated from the gaze error signal. The experimental findings reported in this paper have been summarized in a model of the gaze control system that makes use of a gaze feedback hypothesis through the central reconstruction of the eye and head positions.

Adult↗

PubMed1976

Feedback-aided self-regulation of skin temperature with a single feedback locus. I. Acquisition and reversal training.

A technique has been developed that enables most humans to establish rapid self-regulatory control of their own skin temperature when provided with immediate visual feedback information concerning variations in local skin temperature. Training took place during 15-min periods within 45-min sessions. Clear evidence of learning was usually manifested within 4 sessions. After acquisition occurred, mean change per session was approximately 2.2 degrees F, ranging up to 6.5 degrees F. Training was continued with some subjects who were taught to alter temperature in opposite directions during successive periods on the same day. After practice, these subjects routinely displayed ranges of 9-14 degrees F within 15 min.

Adolescent↗

PubMed1989

[A microcomputer system of biotechnical feedback].

A microcomputer system has been constructed and developed for biofeedback research and clinical biofeedback training. Hardware and software enable on-line data acquisition, storage and real-time analysis with visual feedback of chosen parameters, while changes in other physiological variables are recorded and monitored. The software handles control of experimental sessions, data reduction, statistics, data base management and output document forming. Computer analysis of pulse transit time biofeedback training with multiple cardiovascular monitoring in experimental and clinical setting outlined contributions of sympathetic and parasympathetic influences on observed patterns of cardiovascular modifications.

Biofeedback, Psychology↗