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At least 739 records · Page 41Linked to original sources
PubMed1982

Effects of stimulus vergence on mean accommodation response, microfluctuations of accommodation and optical quality of the human eye.

This study was carried out on three observers by means of a highly sensitive infra-red optometer, the principle of which is recalled, associated with other measurement techniques. We found the accommodative "resting position" to coincide with minimum astigmatic ocular aberration, but not necessarily with maximum ocular optical quality, as suggested by Johnson. The amplitude of accommodation microfluctuations appears to vary in opposite directions with ocular optical quality; this result agrees with previous findings of Arnulf et al. The power spectrum of accommodation micrfluctuations we recorded ranged in frequency from 0 to 6 Hz. A relative activity maximum appears in the 1 to 6 Hz bandwidth for the "resting position" or the optimal quality position. We used Toates' s accommodation model as a frame of reference to interpret these results.

Accommodation, Ocular↗
PubMed1982

Velocity blindness during shearing motion.

When two subjects lie at different distances from a moving observer, there is a velocity step at the occluding boundary of the nearer object. When the differential motion is tangential to the boundary, the effect is as if a shearing is taking place. If all texture cues are removed by using similar random dot patterns on each side of the boundary, then 20% of the population cannot use this differential motion to locate the boundary when it is presented to the parafovea. These observers are thus abnormally insensitive to the differential rate of texture flow at boundaries undergoing shearing motion. As no such population differences were observed for differential motion perpendicular to the occluding boundary (occluding motion), we infer that independent mechanisms process shearing and occluding motion.

Adolescent↗
PubMed1986

Areas of spatial interaction for a hyperacuity stimulus.

We report that the ability to detect a small vernier offset (less than 5 sec of arc in many individuals) between two small spots of light separated by a narrow gap can be disrupted by presenting additional targets in close proximity to the vernier stimulus. A rectangular background of light, centered on the vernier stimulus, elevates offset threshold by a factor of two when the total width of the background is 3-4 min arc. Backgrounds narrower or wider than 3-4 min have less or no effect on vernier threshold. These areas of spatial interaction extend to either side of a vertically-oriented vernier stimulus, or above and below a horizontally-oriented stimulus, and their extent is dependent upon the gap size of the two-dot stimulus. The effect of the presence of the background on vernier threshold cannot be accounted for by spatial interval cues nor by changes in the visibility of the stimulus. Two alternative interpretations of the results are presented to develop a description of the underlying mechanisms which produce hyperacuity spatial interactions.

Distance Perception↗
PubMed1986

The rhino-optical phenomenon: ocular parallax and the visible field beyond the nose.

One of the consequences of the noncoincidence of the nodal point and the center of rotation of the eye is the disappearance of targets near the limit of the nasal visual field when the monocular gaze is directed towards them. This ocular parallax phenomenon, which we measured in six adult subjects, is discussed in terms of its usefulness in demonstrating ocular parallax in a classroom situation. Also, a possible laboratory exercise is suggested.

Distance Perception↗
PubMed1987

Dioptric and non-dioptric stimuli for accommodation: target size alone and with blur and chromatic aberration.

The frequency response of the accommodative system (0.05-1 Hz) was determined for various combinations of stimuli: changing target size was presented alone, together with defocus blur, and with both defocus blur and chromatic aberration. A high-speed infrared optometer monitored accommodation while the subject viewed the target in a Badal optometer. Target size was varied sinusoidally and blur was provided by moving the target towards and away from the subject at the same frequency. Chromatic aberration was controlled by using either monochromatic (590 nm) or white (3300 K) light. The target was presented under open-loop conditions when size was the only stimulus. We find that besides the conventional dioptric stimuli, changes in target size that result in changes in apparent distance can have substantial effects on accommodation.

Accommodation, Ocular↗