An ecological analysis of binocular vision

Summary Underlying the classic binocularity problems of singleness and three-dimensionality is a theory that the stimulus for binocular vision constitutes two two-dimensional images and metric differences between parts of those images. This characterization of the stimulus is criticized here and in its stead an ecologically-based characterization is presented wherein a binocular transformational invariant is shown to specify absolute (body-scaled) size, shape, and distance. The transformation is characterized as a rotation and its specificity to distance assumes a constant interocular distance and either homogeneously textured or extended surfaces. Four experiments demonstrate perceivers' abilities to detect this information and report (verbally or by reaching) the absolute distances of surfaces in stereograms. A fifth experiment revealed that accurate performance did not depend on oculomotor information. The assumptions of texture extent and distribution and constant interocular distance and their possible violations were discussed. A sixth experiment demonstrated that violations of interocular distance are absorbed by surface shapes. The existence and detection of a binocular rotation dissolves the putative problems of singleness and stereopsis, indicates that the importance of having two frontal eyes is for perception of absolute distance, and reformulates the problems for an algorithmic (physiological) theory of vision.     

The locus of perceived equidistance in binocular vision

Empirical studies of the locus of perceived equidistance in binocular vision have revealed a characteristic change of its form, depending on absolute distance. This result is commonly taken to indicate influence of vergence-related binocular information, a conclusion that is by no means exclusively dictated by the data. Heller (1997) has suggested an alternative theoretical account that is based on the idea of independently combining the outcome of monocular input transformations without any form of binocular interaction. This article provides an experimental test of the structural assumption lying at the core of the axiomatic foundation of Heller's theory. I test the so-called Reidemeister condition under reduced cue conditions in two settings for each of 7 subjects. The results provide strong evidence for the validity of the Reidemeister condition and thus challenge the view that the locus of perceived equidistance depends on vergence-related binocular information. The discussion of the factors contributing to the monocular input transformations emphasizes the role of the optical properties of the eyes.     

Amodal completion and the perception of depth without binocular correspondence

Half-occlusions and illusory contours have recently been used to show that depth can be perceived in the absence of binocular correspondence and that there is more to stereopsis than solving the correspondence problem. In the present study we show a new way for depth to be assigned in the absence of binocular correspondence, namely amodal completion. Although an occluder removed all possibility of direct binocular matching, subjects consistently assigned the correct depth (convexity or concavity) to partially occluded 'folded cards' stimuli. Our results highlight the importance of more global, surface-based processes in stereopsis.     

Selective adaptation of monocular and binocular neurons in human vision

Psychophysical techniques were used to examine how subpopulations of visual neurons varying in their ocular dominance interacted in determining performance on a visual task. Using an asymmetric alternating adaptation of the left and right eyes, we manipulated the sensitivity of monocularly driven neurons while keeping the sensitivity of binocularly driven neurons constant. Relative threshold elevations were measured in the left eye, right eye, and both eyes of five observers following different ratios of alternating adaptation. It was found that whereas monocularly measured aftereffects varied monotonically as a function of the adaptation duration of the measured eye, the magnitude of the binocularly measured aftereffect remained constant regardless of how the adaptation was divided between the two eyes. This suggests that neurons differing in their ocular dominance pool their activity in determining sensitivity to a test target.     

Monocular and binocular vision in the control of goal-directed movement

In the present research the authors examined the time course of binocular integration in goal-directed aiming and grasping. With liquid-crystal goggles, the authors manipulated vision independently to the right and left eyes of 10 students during movement preparation and movement execution. Contrary to earlier findings reported in catching experiments (I. Olivier, D. J. Weeks, K. L. Ricker, J. Lyons, & D. Elliott, 1998), neither a temporal nor a spatial binocular advantage was obtained in 1 grasping and 2 aiming studies. That result suggests that, at least in some circumstances, monocular vision is sufficient for the precise control of limb movements. In a final aiming experiment involving 3-dimensional spatial variability and no trial-to-trial visual feedback about performance, binocular vision was associated with greater spatial accuracy. Binocular superiority appeared to be most pronounced when participants were unable to adjust their limb control strategy or procedure on the basis of terminal feedback about performance.     

Three- to eight-month-old infants' catching under monocular and binocular vision

We report a cross-sectional and a longitudinal experiment that examined developmental changes in the relative contribution of monocular and binocular variables in the guidance of interceptive arm movements. Three- to eight-month-old infants were observed while presented with differently sized balls that approached frontally with a constant velocity under both monocular and binocular viewing conditions. Movement onset indicated that with age infants increasingly came to rely on binocular variables in controlling the timing of the interceptive arm movements. That is, from 7 to 8 months of age movement onset was independent from object size under binocular but not under monocular viewing. In contrast, binocular viewing enhanced the spatial accuracy of the interceptive arm movements at all ages. We concluded that attunement to binocular information is a key process in infants' gaining adaptive control of goal-directed arm movements. However, interceptive arm movements entail the formation of multiple on-line couplings between optic and movement variables, each of which appears to develop at its own pace.     

Measurement of visual aftereffects and inferences about binocular mechanisms in human vision

There is conflicting evidence concerning the characteristics of binocular channels in the human visual system with respect to the existence of a 'pure' binocular channel that responds only to simultaneous stimulation of both eyes. Four experiments were conducted to resolve these discrepancies and to evaluate the evidence for the existence of such an exclusive binocular channel. In the first three studies, tilt aftereffects were measured after monocular adaptation. The relative sizes of the direct, interocularly transferred, and binocular aftereffects were not influenced by the configuration of the adapting pattern (experiment 1), or by the eye used for adaptation (experiment 2). There were also consistent interobserver differences in the relative sizes of the aftereffect seen after monocular adaptation (experiment 3). Taken together, these data raise questions about the appropriateness of a monocular adaptation paradigm for evaluating the presence of a pure binocular channel in observers with normal binocular vision. In experiment 4, in which the paradigm of alternating monocular adaptation was used, data were obtained that are consistent with the presence of a pure binocular channel.     

Fragmentation of monocular afterimages in individuals with and without normal binocular vision

Monocular afterimages of a vertical line were generated in each eye of binocularly normal individuals and of those lacking binocular single vision or stereopsis as a consequence of childhood strabismus. Fragmentations and disappearances of the afterimages occurred less frequently in the strabismic than in the normal subjects; they were also less frequent in the dominant (nonamblyopic) eyes of the strabismics than in their amblyopic eyes. The afterimages remained visible for longer when presented to the dominant eyes of the strabismic subjects, and a similar effect was found between the sighting dominant and nondominant eyes of normal subjects.     

Dark vergence in human infants: implications for the development of binocular vision

The resting position of binocular alignment in 1- to 4-month-olds, 6- to 18-month-olds, and adults was estimated by obtaining photographic measures of interpupillary distance in total darkness. The mean dark vergence position in the adult group corresponded to a distance of approximately 100 cm, similar to a previous estimate of 120 cm (Owens and Leibowitz 1976). The mean dark vergence position in the group of 1- to 4-month-olds was approximately 25 cm and in the group of 6- to 18-month-olds was approximately 50 cm. These near dark vergence positions in infants provide strong evidence that inaccuracies in binocular fixation during early infancy are not the result of a divergence bias. The developmental implications of dark vergence, accommodative vergence, and fusional vergence for the control of binocular alignment and distance perception during infancy are discussed.     

Cross-modal interaction between vision and touch: the role of synesthetic correspondence

At each moment, we experience a melange of information arriving at several senses, and often we focus on inputs from one modality and 'reject' inputs from another. Does input from a rejected sensory modality modulate one's ability to make decisions about information from a selected one? When the modalities are vision and hearing, the answer is "yes", suggesting that vision and hearing interact. In the present study, we asked whether similar interactions characterize vision and touch. As with vision and hearing, results obtained in a selective attention task show cross-modal interactions between vision and touch that depend on the synesthetic relationship between the stimulus combinations. These results imply that similar mechanisms may govern cross-modal interactions across sensory modalities.     

Prevalence and reporting of near-point binocular convergence and acuity vision deficits in potential research participants

Visual abilities at near-point distances of 200 self-reported normal vision college students were assessed. Results show that normal visual functioning with no deficits is the exception. The most common visual deficits observed involved binocular lateral posture and fusion convergence deficits. Binocular and monocular acuity deficits also had high prevalence rates, although not as prevalent as the binocular convergence deficits. In addition, 1,340 articles published in four major journals from the years 1997-2004 were examined to ascertain the extent to which authors report the visual capabilities of their participants. Reporting of research participant visual abilities by authors using visual stimuli in experiments appears to be lacking. The results are discussed in terms of the potential impact that visual deficits may have on results obtained in experiments in which visual stimuli are used and the importance of reporting the visual assessment tests and procedures used to assess the visual abilities of potential participants.     

Haploscopic colour mixtures with and without contours in subjects with normal and disturbed binocular vision

Binocular mixtures of equiluminous components of different wavelengths were matched with additive monoptic mixtures of the same components. After a satisfactory match had been achieved, the luminance of each colour in the monoptic mixture was measured photometrically. After presentation of an orthogonal grating superimposed on the colour shown to one eye, the colour matching was repeated. The grating induced a strong dominance of the colour with which it was combined. Yet the uncontoured colour was not entirely suppressed, but contributed to the binocular colour to various degrees. In three subjects with anisometropic amblyopia in one eye the colour presented to the amblyopic eye contributed little or nothing to the haploscopic colour mixture, depending on the degree of amblyopia. This diminished contribution could not be enhanced by a grid. In three cases with strabismic amblyopia and in one case with strabismus alternans no haploscopic colour mixture effects could be demonstrated. The observations are discussed in the context of neurophysiological findings in the visual system of primates, and it is suggested that colour and contour are not transmitted through independent channels from the retina to the cortex.     

视觉正常的自闭症儿童双眼注视点间距的特点及其意义

视网膜上物象对应的外在注视点之间的距离, 即双眼注视点间距(distance of binoculars point of regard, DBPR)在自闭症谱系障碍(autism spectrum disorders, ASD)个体上存在异常的表现, 而ASD个体伴随较高的斜视发病率, 可能会对其双眼注视点间距产生影响。研究采用正弦曲线平滑追踪任务范式, 探索视觉正常的ASD儿童在动态刺激加工过程中DBPR的鉴别意义。结果发现, ASD儿童DBPR过大且具有跨任务类型的稳定性, 且与斜视无关。DBPR在大振幅、快速度的条件下具有优良的鉴别力, 并与自闭症行为量表总分以及感知觉维度显著正相关。结果表明, 双眼注视点间距具有良好的鉴别价值。