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PubMed1975

The relation between discrimination and sensitivity in the perception of motion in depth.

1. Binocular discrimination of the direction of a target's motion in depth was measured in terms of the smallest angular difference in direction that could be detected with a probability 50% better than chance. Directional discrimination was measured for targets moving along 16 different trajectories directed to the left and right of the nose. 2. The relative velocities of the retinal images in the left and right eyes gave a sensitive cue to the direction of the target's motion in depth. 3. The direction of motion was bets discriminated when the target moved along a line directed close to the nose. A change in direction of only 0.2 degrees from this direction of motion could be detected. Discrimination showed two other maxima, one on each side of the central maximum. Discrimination fell to about 0.6-0.8 degrees when the target's direction was changed by only 6 degrees to either side of the nose. 4. The curve of sensitivity to movement in depth had a generally inverse shape to the directional discrimination curve: sensitivity was minimal for trajectories directed near the nose and increased for trajectories directed so as to miss the head. 5. The directional discrimination curve can be related to the sensitivity curves of the four postulated neural mechanisms tuned to different directions of motion in depth; there are three discrimination maxima and, correspondingly, three trajectories for which the slopes of adjacent sensitivity curves differ maximally. This suggests that binocular psychophysical judgements of the direction along which a target moves in depth are to some extent mediated by neural mechanisms that compare (e.g. subtract) the outputs of directionally tuned movement detectors. One function of such neural comparators might be to enhance psychophysical sensitivity to the direction along which a target moves in depth, and thus to provide a physiological basis for precisely judging whether or not an object will hit the head. 6. We suggest that the neural basis for judging the direction of moving objects has an analogy in colour vision where opponent-colour mechanisms enhance sensitivity to wave-length differences in such a way that wave-lengths are more easily discriminated in those parts of the spectrum where the slopes of the pigment action spectra differ maximally.

Adaptation, Ocular↗
PubMed2005

Parents' leisure: the impact of raising a child with Down syndrome.

A healthy and productive life depends upon the balance between work, leisure, and activities of daily living. Gaining or regaining that balance is a core concept within occupational therapy. Raising a child with special needs is one factor that challenges parents in achieving a balance. The purpose of this research was to describe factors that affect the leisure occupations of these parents. A qualitative approach was used in which in-depth interviews and the adapted Barth Time Construction were administered to four married couples that were raising children with Down syndrome who were between seven and nine years of age. Data was examined through content analysis. Results indicated that the parents of children with Down syndrome had limitations in time available for leisure, changes in types of leisure engaged in, and an increase in planning for leisure activities. Despite overall satisfaction with the manner in which they allocated their time, parents frequently noted the potential benefits of incorporating more leisure into their daily lives. Limitations of the study include type and size of sample.

Adult↗
PubMed1983

On the relation of stereoacuity to interocular transfer of the motion and the tilt aftereffects.

Interocular transfer of both the motion and the tilt aftereffect were tested in 43 subjects with varying degrees of stereopsis, ranging from normal to stereoblind. Although there was an overall tendency for transfer to diminish with decreasing stereovision, stereoblind subjects always showed some transfer of the tilt aftereffect, and sometimes also of the motion aftereffect, while some subjects with normal stereothresholds had greatly reduced or no interocular transfer. No quantitative correlation between stereothresholds and amount of transfer could be found. The results indicate that there is no simple relationship between interocular transfer, stereopsis and cortical binocularity, as had been suggested previously.

Adaptation, Ocular↗
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↗
PubMed1986

On the gekko pupil and Scheiner's disc.

The four pinhole apertures of the constricted gekko pupil are an adaptation for decreasing the depth of field of the eye, while decreasing the total light flux to the retina. This may be useful for distance estimation at high light levels.

Animals↗
PubMed1987

Human binocular interaction: towards a neural model.

A new model for binocular processing is described. (i) In the bilateral either-eye channel, summation of the excitatory monocular responses is preceded by partial, reciprocal inhibition between each eye's responses. (ii) In the fused channel, the response is binocular, purely excitatory, multiplicative. (iii) The net binocular response of the system is a sum of the outputs of (i) and (ii). The model contains no independent monocular contributions to the net binocular response. All stimuli on corresponding retinal loci are processed in the either-eye channel; in addition, the fused channel responds to stimuli that are near 0-phase interocularly. The model is sufficiently general to account for binocular performance at the differential luminance threshold and in suprathreshold contrast matching, and it also offers a novel explanation for interocular transfer of adaptation. Plausibility of the model is briefly considered with regard to visual neurophysiology.

Adaptation, Ocular↗
PubMed1992

Disparity tuning in mechanisms of human stereopsis.

The change in sensitivity across some stimulus dimension which follows adaptation to a particular stimulus can reveal a great deal about the tuning characteristics of underlying sensory/perceptual mechanisms. In this study, a psychophysical adaptation paradigm was employed to characterize the disparity tuning of perceptual mechanisms involved in stereopsis. The stimulus was a dynamic random-dot stereogram (DRDS) portraying a surface which varied in interocular correlation (IOC) and retinal disparity. Adaptation to a fully correlated DRDS surface produced an elevation in IOC threshold over a relatively narrow range of disparities, with maximum effect at the disparity of the adapting stimulus. The width of these disparity tuning functions varied from 5 arc min for adaptation at the horopter to 20 arc min for adaptation at 20 arc min disparity. Frequently, IOC sensitivity was enhanced for disparities on either side of the adapted disparity, suggesting that an opponent center-surround organization operates at an early level of disparity processing. A model of underlying channel structure consistent with these data is presented.

Adaptation, Ocular↗
PubMed1994

Properties of the stereoscopic (cyclopean) motion aftereffect.

Across four experiments, this study investigated properties of the stereoscopic motion aftereffect (adaptation from moving retinal disparity information). The results showed that stereoscopic motion can induce an adaptation aftereffect across a wide range of conditions and observers, provided that the duration of adaptation is sufficiently long and a perceptually salient test pattern is viewed. Motion adaptation was found to transfer between the stereoscopic and luminance domains [replicating a previous report by Fox, Patterson and Lehmkuhle (1982) Investigative Ophthalmology and Visual Science (Suppl.), 22, 144], suggesting that motion perception from stereoscopic (second-order) and luminance (first-order) attributes is mediated by a common neural substrate.

Adaptation, Ocular↗
PubMed1996

Enduring stereoscopic motion aftereffects induced by prolonged adaptation.

This study investigated the effects of prolonged adaptation on the recovery of the stereoscopic motion aftereffect (adaptation induced by moving binocular disparity information). The adapting and test stimuli were stereoscopic grating patterns created from disparity, embedded in dynamic random-dot stereograms. Motion aftereffects induced by luminance stimuli were included in the study for comparison. Adaptation duration was either 1, 2, 4, 8, 16, 32 or 64 min and the duration of the ensuing aftereffect was the variable of interest. The results showed that aftereffect duration was proportional to the square root of adaptation duration for both stereoscopic and luminance stimuli; on log-log axes, the relation between aftereffect duration and adaptation duration was a power law with the slope near 0.5 in both cases. For both kinds of stimuli, there was no sign of adaptation saturation even at the longest adaptation duration.

Adaptation, Ocular↗
PubMed1997

Direction-selective coding of stereoscopic (cyclopean) motion.

This study employed a selective adaptation paradigm and investigated thresholds for direction discrimination of translational stereoscopic motion (moving binocular disparity information). The stimuli were moving arrays of randomly positioned stereoscopic discs created from disparity embedded in dynamic random-element stereograms. When discrimination thresholds were measured across a range of base directions following adaptation in a fixed direction, discrimination thresholds were maximally elevated 20-30 deg away from adaptation and reduced in the same direction as adaptation. These results are consistent with a distributed-channel model of direction coding and indicate that the direction of stereoscopic motion is encoded by adaptable direction-selective mechanisms similar to those proposed for luminance-defined motion.

Adaptation, Ocular↗
PubMed1999

The stereoscopic (cyclopean) motion aftereffect is selective for spatial frequency and orientation of disparity modulation.

Across two experiments, this study investigated the spatial frequency tuning and orientation tuning (both in the disparity domain) of the stereoscopic (cyclopean) motion aftereffect. In Experiment 1, observers adapted to a moving stereoscopic grating of a given cyclopean spatial frequency and tested for the motion aftereffect with a static grating of the same or different spatial frequency. Robust motion aftereffects were induced only when the spatial frequency of the adapt and test stimuli was the same. In Experiment 2, observers adapted to a moving stereoscopic grating of a given cyclopean orientation and tested for the motion aftereffect with a static grating of the same or different orientation. Robust motion aftereffects were induced only when the orientation of the adapt and test stimuli was the same. Together, these results suggest that the stereoscopic motion aftereffect is tuned for cyclopean spatial frequency and orientation which, in turn, suggest that the stereoscopic motion aftereffect is mediated by low-level oriented spatial-frequency mechanisms.

Adaptation, Physiological↗
PubMed2000

Cross-domain adaptation reveals that a common mechanism computes stereoscopic (cyclopean) and luminance plaid motion.

Across three experiments, this study investigated the visual processing of moving stereoscopic plaid patterns (plaids created with cyclopean components defined by moving binocular disparity embedded in a dynamic random-dot stereogram). Results showed that adaptation to a moving stereoscopic plaid or its components affected the perceived coherence of a luminance test plaid, and vice versa. Cross-domain adaptation suggests that stereoscopic and luminance motion signals feed into a common pattern-motion mechanism, consistent with the idea that stereoscopic motion signals are computed early in the motion processing stream.

Adaptation, Ocular↗