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At least 613 records · Page 34Linked to original sources
PubMed1999

Effects of smooth pursuit eye movement on ocular responses to sudden background motion in humans.

We studied the effects of horizontal smooth pursuit on the ocular tracking responses to brief perturbations of a textured background in humans. When the subject was fixating a stationary spot, a brief perturbation (60 degrees/s, 40 ms) of the background in any one of four directions (right, left, up, down) elicited a small tracking response. When the subject was pursuing a target moving against the stationary background, the same background perturbation elicited a larger response when in the same direction as the pursuit, but a smaller response when its direction was opposite to the pursuit; the response to vertical background perturbations was also enhanced during pursuit. When the subject was pursuing while the target and background were moving together, the same background perturbations elicited the larger responses regardless of their direction. These results indicate that the sensitivity to background motion is increased during smooth pursuit. However, when pursuit is executed against a stationary background--the usual situation in everyday life--the system is selectively insensitive to the reafferent visual input associated with pursuit, thereby reducing the potentially adverse effect of the background on pursuit performance.

Adult↗
PubMed2001

The effect of perceived length on visuomotor localization.

PURPOSE: The purpose of this experiment was to study visuomotor localization in the presence of either a horizontal array of equally spaced dots or a thin horizontal line. METHODS: Pointing behavior was used to assess directional localization. In experiment 1, subjects were made myopic using a contact lens and then corrected with a spectacle lens. Subjects were tested in the presence and absence of a regularly spaced, horizontal array of dots with and without the contact lens/spectacle combination. In experiment 2, subjects wore the contact lens/spectacle in all cases. Some subjects were tested in the presence and then in the absence of a regularly spaced, horizontal array of dots while the order of conditions was reversed for other subjects. In experiments 3 and 4, subjects were tested without the contact lens/spectacle combination. In experiment 3, subjects were tested in the absence and then in the presence of a regularly spaced, horizontal arrays of dots. In experiment 4, subjects were tested in the absence and then in the presence of a thin horizontal line. RESULTS: In experiment 1, in the absence of the array of dots, subjects undershot targets with the contact lens/spectacle combination. When the array was present, pointing with the contact lens/spectacle combination was accurate. In experiment 2, subjects undershot targets in the absence of the array of dots if this condition was performed first. If the array was present in the initial condition, the pointing undershoot in the second condition (array absent) was reduced. In all cases, the pointing undershoot was reduced in the presence of the array. In experiments 3 and 4, a pointing overshoot was found in the presence of an array of dots or a thin line. CONCLUSIONS: It is concluded that extraretinal eye position information is not the primary determinant of visuomotor localization in the presence of a horizontal contour. The overshoot produced by a horizontal contour may be related to a length illusion brought about by spatial filtering in the visual system or inaccurate distance judgments.

Accommodation, Ocular↗
PubMed2002

Refractive compensation to optical defocus depends on the temporal profile of luminance modulation of the environment.

The refractive state of hatchling chicks rapidly compensates to applied optical defocus through alteration in eye growth. The mechanism is capable of sensing whether the plane of focus lies in front of or behind the photoreceptors, however, its nature and site of action within the retina are unknown. We attempted to create an imbalance in the adaptation of the retinal ON and OFF mechanisms previously implicated in refractive control through pharmacological interventions, by rearing chicks from 4 to 9 days of age with a monocular +10 D, 0 D or -10 D lens, in an environment illuminated by a moving or stationary plaid of luminance gradients. When the plaid moved in one direction a local Fast-ON sawtooth luminance modulation was produced, while plaid motion in the other direction resulted in a Fast-OFF sawtooth modulation. Significantly reduced refractive compensation accompanied +10 D lens/Fast-OFF and -10 D lens/Fast-ON rearing, but not for the other conditions. Thus the refractive compensation mechanism depends on the nature of the temporal contrast of the environment, suggesting a relationship between the sign of defocus and the state of adaptation of the retinal ON and OFF subsystems.

Adaptation, Ocular↗
PubMed1975

Marked accommodation, retinal stretch, monocular space perception and retinal receptor orientation.

In recent years we have come to recognize that retinal receptors are probably aligned with the center of the exit pupil of the eye. It becomes crucial to define those factors influencing and determining photoreceptor alignment. Here, the effect of retinal stretch associated with marked accommodation has been considered. Assuming that a sense of direction is associated with a given retinal locus, we have used a classical monocular bisection test technique in order to see if marked accommodation altered bisection settings. Substantial changes in bisection settings were found when testing in the region of the posterior pole. These could be localized most probably in the retina and choroid. In separate studies, the effect of anterior retinal stretch upon cone receptor orientation in the region of the fovea was evaluated. Marked accommodation caused a transient nasal displacement of the peak of the Stiles-Crawford directional sensitivity function. These studies suggest that the posterior pole of the eye is routinely subject to stresses and strains. This point is of clinical significance. Our studies suggest that the presence of the blind spot influences the magnitude of change of measured parameters. We have only begun the important task of evaluating the nature of recovery processes following marked accommodation. Lastly, in order to obtain the necessary responses, we have had to train our young observers to voluntarily utilize nearly their entire accommodative capability.

Accommodation, Ocular↗
PubMed1975

Complex binocular interaction and other effects in the visual evoked response.

One article dealing with some of the research on binocular interaction effects being carried out in our laboratory has appeared previously in this Journal (White and Bonelli). In that study, it was found that the amplitude of the visually evoked cortical potential (VER) produced by patterned stimuli viewed with both eyes was directly related to the quality of the retina image. Furthermore, the degree of binocular summation shown by the VERs was also related to image quality, with marked summation occurring when sharply focused patterns were presented but much less evidence of it when the patterns were blurred. In that study the retinal images were reasonably similar, since the degree of blur desired was produced by placing ophthalmic lenses of equal strength before the two eyes. The next situation we decided to test was that in which the images presented to the two eyes were not of the same quality. This paper will deal briefly with some work we have done on that topic, and will also present some other examples of work dealing with binocular interaction and related topics.

Accommodation, Ocular↗
PubMed1979

The relationship between convergence insufficiency and school achievement.

Schoolchildren (735) between the ages of 7 and 14 were examined for convergence ability. Nine percent had an objective near point of convergence of more than 10 cm and 10% had a subjective near point of convergence of more than 10 cm. The recovery point was greater than 15 cm for 9% of the subjects when measured objectively and 12% subjectively. The sample was analyzed with regard to age, sex, and IQ. There was no significant difference between children who showed convergence insufficiency and those who did not with regard to school results in their mother tongue and in their grade point average.

Accommodation, Ocular↗
PubMed1984

Effect of a concurrent counting task on dynamic visual accommodation.

The visual accommodation of four male subjects was selectively recorded over a 3-day period using an objective, continuously recording, infrared optometer to determine the effects of a concurrent counting task on their ability to accommodate to a sinusoidally changing focus stimulus ranging from 0.0 to 3.0 D. There was an increase in their steady-state errors in the direction of negative accommodation of from 0.25 to 0.50 D, but the magnitude of the steady-state error induced by the concurrent task did not change over the three sine wave frequencies used (0.1, 0.2 and 0.4 Hz). The results are discussed in terms of an accommodative "lag" model of sympathetic-parasympathetic arousal induced by superimposing an extraneous mental task.

Accommodation, Ocular↗
PubMed1989

The effect of high frequency flicker on accommodation.

Monocular accommodation was measured by a laser optometer while two subjects viewed a letter matrix target illuminated by steady or intermittent (300, 100, 50 and 25 Hz) light and presented at a number of optical distances (0.5, 1.5, 2.5, 3.5 and 4.5 D). At certain rates of intermittent illumination, both above (50 Hz) and below (25 Hz) flicker fusion, an increased accommodation response was found. This increase occurred at all optical distances, except for the distance closest to each subject's dark focus, and resulted in a more accurate accommodation response for one subject, and a less accurate one for the other. Furthermore, for both subjects, evidence of an increase in the amplitude of the fluctuations in accommodation at 50 and 25 Hz was found for the higher stimulus levels. The implications of these findings for the control of accommodation and for practical problems of visual performance in the environment, such as visual discomfort associated with fluorescent lighting and intermittently illuminated visual display units, are discussed.

Accommodation, Ocular↗
PubMed1995

Microfluctuations of steady-state accommodation and the cardiopulmonary system.

The relationship between variations in steady-state accommodation (microfluctuations) and rhythmic cycles in cardiopulmonary system was investigated. As previously reported, vascular pulse frequency was consistently correlated with the high frequency component of steady-state accommodation microfluctuations. In a new finding, respiration rate and an associated cycle in the instantaneous pulse rate also showed a correlation with a low frequency component of the accommodation power spectra. This apparent coherence between respiration frequency and an accommodation low frequency component was maintained during rapid breathing and was evident at the expected frequency during regulated breathing patterns. This association may reflect the direct influence of the autonomic nervous system upon the ciliary muscle or may be caused by the modulation of intraocular pulse by the autonomic nervous system.

Accommodation, Ocular↗