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At least 523 records · Page 29Linked to original sources
PubMed1996

Adaptive changes in saccade amplitude: oculocentric or orbitocentric mapping?

The saccadic system rapidly adjusts the amplitude of refixation movements to visual targets when abnormal postsaccadic errors occur. This is called rapid saccadic adaptation. It is not yet clear whether this form of adaptation produces changes related to oculocentric mechanisms, such as retinal error or motor error, or orbitocentric mechanisms, such as eye or gaze position. These experiments were designed to test whether rapid saccadic adaptation was orbitocentric, oculocentric, or both by creating a precise sensory motor mismatch between the visual target and the required saccade. Measurements were made to determine adaptive changes as function of (1) saccade direction; (2) eye position; and (3) saccade amplitude. Changes were found to be amplitude- and direction-specific but changes were generalized across a broad range of orbital positions. Two conditions of adaptation: increasing and decreasing amplitude, produced quantitatively similar results, indicating that similar mechanisms underlie both processes. Thus, these data support the view that changes during rapid saccadic adaptation are organized principally in a retina-referenced (oculocentric) map, but only broadly, if at all, in a head-referenced (orbitocentric) map. The changes are consistent with a mechanism represented in a spatial mapping of either retinal or motor error.

Adaptation, Ocular↗
PubMed2004

Laser in situ keratomileusis for high hyperopia in awake, autofixating pediatric and adolescent patients with fully or partially accommodative esotropia.

PURPOSE: To establish the safety and efficacy of laser in situ keratomileusis (LASIK) in pediatric and adolescent patients with bilateral visual acuity of 20/30 or better and accommodative or partially accommodative esotropia. SETTING: Department of Ophthalmology and Visual Science, University of Texas-Houston Medical School, Houston, Texas, USA. METHODS: The study comprised 30 eyes of 15 consecutive patients with accommodative or partially accommodative esotropia who met eligibility requirements and had bilateral LASIK using the Alcon Summit Autonomous LADARVision excimer laser to correct a refractive error after January 2001. All patients were awake and autofixating during the procedure. RESULTS: The mean age of the patients was 13.9 years (range 9.1 to 18.8 years) and the mean refractive error, +5.35 diopters (D) (range +3.75 to +8.50 D) with anisometropia of 2.0 D or less. The mean follow-up was 15.7 months (range 9.5 to 22.5 months). No intraoperative complications were encountered. The percentage of undercorrection [100% -[(treatment achieved/treatment attempted) x 100%]] [mean 34% +/- 17% (SD), coefficient of variation (SD/mean) 0.50, range 5% to 58%] was higher than expected. Seven patients (47%) required enhancement due to undercorrection of hyperopia with diplopia (6 patients) or astigmatism with decreased visual acuity (1 patient). In this small series, no patient lost best corrected visual acuity or stereo acuity. CONCLUSION: Laser in situ keratomileusis can safely and effectively reduce refractive error in this group of patients; however, patient selection is extremely critical and enhancement was required in almost half the patients.

Accommodation, Ocular↗
PubMed2004

Effects of spatial arrangement of visual stimulus on inverted self-motion perception induced by the foreground motion: examination of OKN-suppression hypothesis.

Our previous study revealed that a slowly moving foreground, which is presented in front of a fast-moving orthogonal background, can induce self-motion perception in the same direction as its motion (inverted vection; Vis. Res. 40 (2000) 2915). The present study shows that inverted vection becomes stronger in the conditions where the foreground stimulus is presented in the central area of observer's visual field and the observer's eyes converge on the same depth plane. These stimulus conditions are consistent with the one where the foreground can induce observer's optokinetic nystagmus more effectively, and therefore, the results of this study support our hypothesis in that mis-registered eye-movement information caused by the suppression of optokinetic nystagmus induced by the foreground motion is a critical factor in perceiving inverted vection.

Adult↗
PubMed2005

Selective attention and cyclopean motion processing.

The effect of diverted selective attention on the induction of the cyclopean motion aftereffect (aftereffect induced from dynamic disparity information) was investigated. The luminance motion aftereffect was examined for comparison. During diverted-attention trials, observers ignored background adapting motion and performed a low-load or high-load rapid serial visual presentation (RSVP) task presented in the center of the motion display. Baseline motion aftereffects were obtained with no diverted attention. The results showed that the cyclopean motion aftereffect, similar to the luminance motion aftereffect, declined only modestly under diverted-attention conditions. Selective attention appears to play a modest role in the visual processing of cyclopean motion.

Adaptation, Ocular↗
PubMed1997

Extraretinal eye position signals determine perceived target location when they conflict with visual cues.

To examine the role of extraretinal eye position information (EEPI) in visual perception of target location in normal room illumination, subjects participated in experiments in which EEPI was manipulated using the eye press maneuver with either monocular or binocular viewing. The viewing condition and eye press caused EEPI and retinal information about target location to conflict. Pointing responses in eye press trials were all in the direction of EEPI showing that EEPI is the dominant source of information in egocentric visual space perception. In binocular viewing, version and vergence occur in response to the eye press to maintain fusion and EEPI based on these movements also determine perceived location. An unanticipated finding was that the eye press was variable in its effectiveness in rotating the eye, which contributed to large variability in pointing errors and suggested the method would be a poor choice for future work.

Adult↗
PubMed1987

Apparent motion in depth resulting from changing size and changing vergence.

Two experiments are reported in which the effect of combining stimuli of changing size and changing vergence on the perception of motion in depth was examined. Changing size and changing vergence corresponded to in-phase or anti-phase sinusoidal motions of an outline circle, with different amplitudes. In-phase stimuli had approximately additive effects on the estimated peak-to-peak amplitude of apparent motion in depth. Anti-phase stimuli did not cancel each other; apparent motion was in-phase with one or the other stimulus. When apparent motion was in-phase with one stimulus, there was only a limited influence of the other stimulus. The results are discussed with regard to a model proposed by Regan and Beverley for the combination of changing size and changing disparity.

Adult↗
PubMed1993

Apparent motion perception: the contribution of the binocular and monocular systems. An improved test based on motion aftereffects.

Research concerning the perception of apparent motion is not easy to conduct: it is hard to obtain quantitative results that can be easily interpreted. A solution to this problem is the use of motion aftereffects (MAEs). Adapting subjects to a specific type of motion leads to apparent motion in the opposite direction when the stimulus is removed. However, subjects are aware of the change in stimulus conditions. A new dynamic test stimulus is proposed in order to avoid artefacts introduced by the awareness of the conditions by the subject. A model, derived from earlier observations, is described which includes contributions from monocular and binocular systems. Results from an experiment in which the dynamic test stimulus was used show that they do not necessarily reproduce the results obtained with a static test stimulus. Central monocular systems are added to the model to account for this discrepancy. The 'pooling hypothesis', which states that the MAE is a weighted mean of the processes involved, permits the estimation of the weights of the individual subsystems. The results of the experiments are explained in terms of this hypothesis by the new model.

Adaptation, Ocular↗
PubMed1995

Cortical representation of visual three-dimensional space.

Perception of real depth includes information on stereopsis and distance. How both interact in the visual pathway was the subject of a study performed on the behaving monkey. Neurons in the primary visual cortex (area V1) have their activity, visual and/or spontaneous, modulated by the viewing distance. Disparity selectivity may be present or better expressed at a given viewing distance. This modulation is independent of the visual pattern. The use of prisms shows that vergence is implicated in this phenomenon. Consequently, extraretinal signals related to ocular motility have access to area V1. Among them, proprioceptive signals from the eye muscles have been shown to be involved in visual cortical function and in the development of depth perception. It is possible that the same signals may also be involved in the distance modulation shown in V1 neurons, but this remains to be examined. A possible specialisation of disparity-selective cells in different cortical areas is discussed.

Animals↗
PubMed1996

Relations between individual differences in oculomotor resting states and visual inspection performance.

Individual differences in the oculomotor resting states (dark vergence and dark focus) have previously been linked to subjective and visual consequences of near visual work. The present experiment investigated whether these resting states are related also to performance on a near visual inspection task. Dark vergence and dark focus were measured in 38 students before and after they spent 40 min searching for a target letter among distractor letters on a video display terminal at a distance of 20 cm. Subjects with relatively near dark vergence positions performed the inspection task significantly more quickly than subjects with relatively far dark vergence positions. Also, subjects who showed a relatively large inward shift in dark vergence tended to perform quickly. Inspection performance was not related to individual differences in dark focus. These results extend existing oculomotor theory and suggest that the performance of visual inspectors is maximized when the mismatch between the task distance and their dark vergence posture is minimized.

Accommodation, Ocular↗
PubMed1982

Congenital esotropia--a documented case report.

Criteria for defining congenital esotropia and its cure are related to a documented case history. A congenitally esotropic child had strabismus surgery at age 13 months. At 11 years of age the had 20 delta of left exotropia. One year of vision training enabled her to achieve some stereopsis but she retained a small angle asotropia whenever the controlled her exophoric tendency.

Accommodation, Ocular↗
PubMed1983

Zone of zero-associated phoria in patients with convergence insufficiency.

The zone of zero-associated phoria (ZZAP) was determined for patients with convergence insufficiency. The ZZAP for these patients differs from that of asymptomatic patients. It is concluded that the ZZAP may be used as a supplemental test to help the clinician detect convergence insufficiency and possibly other binocular deficiencies.

Accommodation, Ocular↗