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At least 631 records · Page 35Linked to original sources
PubMed1983

Shared characteristics of stereopsis and the purely binocular process.

Wolfe and Held (1981) Vision Res. 21, 1755-1759 demonstrated the existence in the human visual system of a purely binocular process. A purely binocular process is defined as a process that responds only to binocular stimulation and not to stimulation of either eye alone. In this paper, some of the characteristics of the purely binocular process are investigated. We find: (1) the process is less sensitive to high spatial frequencies than is the visual system as a whole. (2) It is insensitive to stimuli near the detection threshold for the visual system as a whole. (3) It makes a greater contribution to the appearance of vertically oriented stimuli than to the appearance of horizontally oriented stimuli. (4) The function of the purely binocular process can be disrupted by blurring the image in one eye (artificial anisometropia). Each of these properties of the purely binocular process is similar to the known characteristics of stereopsis. This suggests that the purely binocular process is a necessary stage in stereopsis.

Adaptation, Ocular↗
PubMed1983

Texture changes versus size changes as stimuli for motion in depth.

As an object approaches the eye, its retinal image size grows larger and its surface texture appears to grow coarser. We compare these two visual correlates of motion in their effectiveness as stimuli for motion in depth. In some experiments texture and object size both expanded or both contracted; in other experiments the two stimuli were pitted against each other. When texture and size change as for a rigid, nonrotating real world object an untextured square can be a more effective stimulus for motion in depth than the same square with texture. On way of describing this finding is to calculate the departure from linear summation of texture and size contributions. The departure is greatest when texture is static, being even greater than when texture changes in the opposite direction to size.

Adaptation, Ocular↗
PubMed1984

Movement adaptation in the peripheral retina.

With strict fixation, the eye quickly adapts to moving periodic stimuli presented to the peripheral retina. A slowly spinning sector disk, 7 degrees in diameter, will rapidly appear to slow down and come to a standstill (within 5-25 sec). The time required for this full motion adaptation decreases with (a) increasing retinal eccentricity (30-70 degrees); (b) increasing number of sectors (16-60); and (c) decreasing speed of rotation (0.3-0.5 rev/sec). After the standstill, the disk fades from view in much the same way as a stationary stimulus (Troxler effect). A spinning disk presented to the temporal retina appears to stop about 2.5 times faster than a disk presented to the nasal side. Adapting one eye reduces the time of adaptation for the other eye by 70%. If an aperiodic sector disk is used, no standstill is perceived.

Adaptation, Ocular↗
PubMed1984

Interocular transfer of a chromatic frequency shift: temporal constraints.

Interocular transfer of a chromatic version of the Blakemore and Sutton (1969) [Science 166, 245-247] spatial frequency shift is not obtained with long steady (3000 msec) test presentation, but does occur when the test is brief (400 msec) or flickering. By contrast, interocular transfer of achromatic spatial frequency adaptation occurs with long steady tests as well as with brief or flickering tests.

Adaptation, Ocular↗
PubMed1985

Separate detectors for simple and complex grating patterns?

Grating having two sinusoidal components show a periodic variation in contrast which is visible as a "beat" pattern. The spatial frequency of the beat is the difference between the frequencies of the two components. Thresholds for a number of detection and discrimination tasks were measured using beat patterns of 1 c/deg (with components of 9 and 10 c/deg), and gratings of 1 and 10 c/deg. Temporal modulation at 6 Hz lowered detection thresholds for 1 c/deg gratings, but not for beats or 10 c/deg gratings. The effect of contrast on the range of temporal frequencies over which direction of movement can be discriminated differs for the three types of pattern: beats resemble neither low nor high spatial frequency gratings. Low and (for 2 of 3 observers) high spatial frequency gratings, but not beat patterns, are susceptible to a movement after effect induced by a low spatial-frequency grating. Beat patterns induce little or no movement after effect. We conclude that beat patterns are not detected by the same mechanisms that detect simple gratings.

Figural Aftereffect↗
PubMed1985

The low level motion system has both chromatic and luminance inputs.

Adaptation to moving isoluminant gratings induces a motion after-effect (MAE). Isoluminant gratings are less effective at inducing and at nulling MAEs than are luminance gratings. These results are consistent with a low-level motion detection system which operates on signals from mechanisms which show both spatial and chromatic opponency.

Adaptation, Ocular↗
PubMed1985

Adaptation to apparent motion.

A spot alternating between two positions can produce apparent motion (AM). Following prolonged inspection, the AM degenerates into flicker. This adaptation effect was found to depend on spacing and timing; the probability of seeing motion during a 30-sec inspection period declined linearly with log spatial separation (over a range from 0.1 to 1 deg), and with log alternation rate (over a range from 2 to 4.5 Hz). Cross-adaptation, in which subjects were adapted to one alternation rate and tested at another, showed that low alternation rates gave stronger motion signals than high rates did. Adaptation to real motion (RM) strongly suppressed AM, which suggests that AM must be stimulating the same neural pathways as RM. Flickering spots (i.e. in-phase flicker) produced less adaptation than did a spot alternating between two positions (i.e. counterphase flicker), so the adapting mechanism must be responding to relative temporal phase. Embedding the adapting spots in configurations of other spots, which altered the pattern of perceived adapting motion without altering the local retinal stimulation, minimized the adaption, so the adapting mechanism must be responding to the path of seen motion. Adaptation can be used to measure the strength of AM and shows that AM is strongest for small separations, low alternation rates and high luminance contrast.

Adaptation, Ocular↗