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At least 613 records · Page 34Linked to original sources
PubMed2006

[Flexibility of adaptation of vestibule-ocular reflex in human beings].

Vestibulo-ocular reflex (VOR) makes images remain relatively stable on the retina. To keep appropriate performance and minimize image slip throughout life, VOR is subject to long-term adaptive regulation by visual input. It has been reported that adaptive changes in VOR gain (eye velocity/head velocity) are evoked either by fitting subjects with magnifying, miniaturizing, or reversing spectacles during normal behavior or by moving a large visual field in or out of phase relative to the subject's head movement. These feature frequency-selectivity. We studied the flexibility of adaptive gain change in VOR required by a horizontal visual-vestibular mismatch in earth vertical axis rotation (EVAR), including adaptive gain change from EVA to off-vertical axis rotation (OVAR) and other velocities. The visual-vestibular mismatch was made by oscillating subjects in EVAR for 30 minutes at 0.3 Hz with the peak velocity of 30 deg/s and 60 deg/s, synchronized with both in-phase (gain decrease: x 0 experiment) and out-of-phase (gain increase: x 2 experiment) sinusoidal rotation of white-black stripe patterns. Subjects were 19 healthy adult volunteers with no history of neurological symptoms. Horizontal and vertical eye positions were recorded by bitemporal DC-coupled electrooculography. In the x 2 adaptation experiment with 0.3 Hz at the peak velocity of 30 deg/s, the percent change in gain (post-pre/ pre) was 110% at the same stimulation and 100% at 40 deg/s in EVA. In the x 0 adaptation experiment with 0.3 Hz at the peak velocity of 30 deg/s, the percent change in gain was -50% at the same stimulation in EVA. In the x 2 adaptation experiment with 0.3 Hz at the peak velocity of 60 deg/s, the percent change in gain was 66% at the same stimulation in EVA, 30% at the same stimulation in nose-up position, and 74% at the same stimulation in nose-down position. In the x 0 adaptation experiment with 0.3 Hz at the peak velocity of 60 deg/s, the percent change in gain was -34% at the same stimulation in EVA. No change in VOR gain was observed at other peak velocities. These results suggest that VOR adaptation depends frequency and maximum angular head velocity, and this characteristic is observed in OVAR.

Adaptation, Ocular↗
PubMed1985

Role of the primate flocculus in adaptation of the vestibulo-ocular reflex.

Neuronal events associated with adaptation of the horizontal vestibulo-ocular reflex (HVOR) induced by sustained vestibular-visual mismatching were investigated in the primate flocculus. The floccular area related to the HVOR (H-zone) was identified by electrical micro-stimulation which induced ipsilaterally directed horizontal eye movement. It was thus found that Purkinje cells in the H-zone consistently changed their simple spike responses to head rotation in parallel with the adaptive HVOR gain change. This was demonstrated by observing the change of simple spike firing of Purkinje cells during adaptation of HVOR either in a population study or an individual study. Since similar changes occurred even after bilateral lesioning of vestibular nuclei had extinguished the HVOR, these changes appear to represent vestibular, but not eye velocity, mossy fiber responsiveness. The complex spike discharge, on the other hand, modulated during vestibular-visual stimulation with a reciprocal pattern to the adaptive changes in the simple spike discharge. These results are consistent with the hypothesis that the flocculus Purkinje cells adaptively control the HVOR through their simple spike activity under influences of retinal error signals conveyed by visual climbing fiber pathways.

Adaptation, Physiological↗
PubMed1972

Electrical stimulation of the human eye in different adaptational states.

1. Experiments are described in which the phosphene produced by passing alternating current of frequency 100 Hz through the eye is matched with a patch of light having the same apparent size.2. Matches of this type have been made against different background light intensities, and at various times after a strong retinal bleach.3. To match the phosphene under particular conditions of this type, it is found that the patch must be set some 1.5 log td brighter than its own threshold under the same conditions. Exceptions to this rule occur with very bright backgrounds, or very soon after bleaching.4. The increment threshold for a small spot of light on the phosphene in the dark is some 0.5 log td higher than for the same spot on a patch of light matched in appearance to the phosphene under the same conditions.5. The process linking electrical stimulation of the eye to firing of fibres in the optic nerve is deduced to be substantially unaffected by the state of adaptation of the eye, save perhaps in the exceptional conditions described in (3).6. It is therefore argued that this phosphene is the result of stimulation both of the retinal visual pathways lying central to the variable-gain element commonly accepted to explain the facts of dark adaptation, and also of the input to this element that is supposed to alter its gain.

Adaptation, Ocular↗
PubMed1991

Accommodative hysteresis. Fundamental asymmetry in decay rate after near and far focusing.

The resting level of accommodation, or dark focus (DF), was compared before and after subjects maintained 8-min of clear focus on targets either at the far point (FP) of accommodation or at an equivalent dioptric distance on the near side of the DF. Although both conditions showed significant shifts in tonic accommodation in the direction of their respective fixation targets, only after near fixation was the shift maintained in darkness for 24-min postfixation. After FP viewing the aftereffect decayed in darkness with a significant linear trend (P less than 0.05). Thus, maintaining focus on a near target is more likely to induce an enduring adaptive shift in tonic accommodation than is far-target viewing, for reasons associated with the systems controlling far and near accommodation, respectively. Additional analyses provided further evidence that the degree of separation of the target from the DF is a highly significant factor controlling individual differences in initial adaptation levels.

Accommodation, Ocular↗
PubMed2000

Effects of adaptation of vestibulo-ocular reflex function on manual target localization.

The goal of the present study was to determine if adaptive modulation of vestibulo-ocular reflex (VOR) function is associated with commensurate alterations in manual target localization. To measure the effects of adapted VOR on manual responses we developed the Vestibular-Contingent Pointing Test (VCP). In the VCP test, subjects pointed to a remembered target following passive whole body rotation in the dark. In the first experiment, subjects performed VCP before and after wearing 0.5X minifying lenses that adaptively attenuate horizontal VOR gain. Results showed that adaptive reduction in horizontal VOR gain was accompanied by a commensurate change in VCP performance. In the second experiment, bilaterally labyrinthine deficient (LD) subjects were tested to confirm that vestibular cues were central to the spatial coding of both eye and hand movements during VCP. LD subjects performed significantly worse than normal subjects. These results demonstrate that adaptive change in VOR can lead to alterations in manual target localization.

Adaptation, Physiological↗