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PubMed1999

Macaque inferior temporal neurons are selective for disparity-defined three-dimensional shapes.

Real-world objects are three-dimensional (3D). Yet, it is unknown whether the neurons of the inferior temporal cortex, which is critical for object recognition, are selective for the 3D shape of objects. We tested for such selectivity by comparing responses to stereo-defined curved 3D shapes derived from identical pairs of monocular images. More than one-third of macaque inferior temporal neurons were selective for 3D shape. In the vast majority of those neurons, this selectivity depended on the global binocular disparity gradient and not on the local disparity. Thus, inferior temporal cortex processes not only two-dimensional but also 3D shape information.

Animals↗

PubMed1996

Selectivity of the parietal visual neurones in 3D orientation of surface of stereoscopic stimuli.

We identified a group of neurones in the posterior parietal cortex of the monkey that responded preferentially to a flat stimulus in a particular orientation on a 3D computer graphics display. We designated these neurones surface-orientation selective (SOS) neurones since they showed tuning to the 3D orientation of the surface. Almost all of the SOS neurones were sensitive to binocular disparity and their responses increased with the width or length of the stimulus, but the responses of only some of them decreased with increasing thickness of the stimulus. These results suggest that SOS neurones extract surface orientation signals from the binocular disparity signals and play an important role in the perception of 3D shape and the visual guidance of hand movement.

Animals↗

PubMedDate not supplied

Eliminating disparities: empowering health promotion within preventive medicine.

The estimated 800,000 U.S. deaths in 1990 related to behavioral decisions challenge physicians to better assist behavioral change through expanded health promotion activities. Based on the format guidelines of this special issue, this brief paper first examines the current and optimal roles of health promotion within Preventive Medicine, including five physician roles for improving modifiable public health-risk behavior burdens: (1) preventive services clinician, (2) health promotion researcher, (3) educator-communicator, (4) systems manager, and (5) health promotion advocate. After presenting a new vision statement, this paper proceeds to discuss the opportunities and barriers, including system, clinician-office, and patient factors, to attaining this new vision of empowering health promotion within Preventive Medicine. Finally, all physicians are invited to engage in a threefold strategic plan for change through at least one of five action items: (1) health promotion advocacy, (2) health promotion research, (3) public communication, (4) protocol dissemination and implementation, and (5) Preventive Medicine training.

Communication↗

PubMedDate not supplied

A new VEP system for studying binocular single vision in human infants.

Visual evoked potentials (VEPs), that provide unequivocal objective evidence of cortical binocularity have been recorded from adults and young infants using a new VEP system developed for this purpose. The system uses alternating field stereoscopy (AFS) to present separate visual stimuli to each eye. With this system, the binocular image pairs to the right and left eyes alternate at a high rate on a single video monitor. The subject wears spectacles incorporating light-scattering liquid crystal lenses which alternate electronically between opaque and clear modes in synchrony with the video monitor. To detect cortical binocularity, the system analyzes VEP activity mathematically and identifies significant responses at test frequencies reflecting binocular cortical interactions exclusively. Three types of binocular stimuli were presented: (1) dynamic random dot correlograms (correlograms); (2) dynamic random dot stereograms (stereograms); and (3) dichoptic checkerboard stimuli. The correlograms are generated when moving random dot patterns presented to each eye alternate between two phases, correlated and anticorrelated. With the stereograms, portions of random dot patterns presented to each eye are shifted horizontally relative to each other at a fixed rate, alternately producing crossed and uncrossed binocular disparities. Subjectively, these patterns appear to shift in depth. Dichoptic checkerboard stimuli are regular checkerboard patterns which reverse at different rates (frequencies) for each eye. Binocular VEPs are generated due to cortical interactions at the difference (beat) frequency. Using this VEP system, we have recorded binocular VEPs from 10 normal adults and more than 40 infant subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1997

Residual binocular interactions in the striate cortex of monkeys reared with abnormal binocular vision.

We investigated the nature of residual binocular interactions in the striate cortex (V1) of monkey models for the two most common causes of visual dysfunction in young children, specifically anisometropia and strabismus. Infant rhesus monkeys were raised wearing either anisometropic spectacle lenses that optically defocused one eye or ophthalmic prisms that optically produced diplopia and binocular confusion. Earlier psychophysical investigations had demonstrated that all subjects exhibited permanent binocular vision deficits and, in some cases, amblyopia. When the monkeys were adults, the responses of individual V1 neurons were studied with the use of microelectrode recording techniques while the animals were anesthetized and paralyzed. The manner in which the signals from the two eyes were combined in individual cells was investigated by dichoptically stimulating both eyes simultaneously with drifting sine wave gratings. In both lens- and prism-reared monkeys, fewer neurons had balanced ocular dominances and greater numbers of neurons were excited by only one eye. However, many neurons that appeared to be monocular exhibited clear binocular interactions during dichoptic stimulation. For the surviving binocular neurons, the maximum binocular response amplitudes were lower than normal; fewer neurons, particularly complex cells, were sensitive to relative interocular spatial phase disparities; and the remaining disparity-sensitive neurons exhibited lower degrees of binocular interaction. In prism-reared monkeys, an unusually high proportion of complex cells exhibited binocular suppression during dichoptic stimulation. Binocular contrast summation experiments showed that for both cooperative and antagonistic binocular interactions, contrast signals from the two eyes were combined by individual neurons in a normal linear fashion in both lens- and prism-reared monkeys. The observed binocular deficits appear to reflect a reduction in functional inputs from one eye and/or spatial imprecision in the monocular receptive fields rather than an aberrant form of binocular interaction. In the prism-reared monkeys, the predominance of suppression suggests that inhibitory connections were, however, less susceptible to diplopia and confusion than excitatory connections. Overall, there were many parallels between V1 physiology in our monkey models and the residual vision of humans with anisometropia or strabismus.

Animals↗

PubMed2000

A Fraser illusion without local cues?

In the well-known Fraser illusion, a line composed of tilted elements itself appears tilted. The standard explanation of this illusion has been that the global orientation of the line is in some way influenced by the local orientation of the elements. The illusion was recreated using a texture composed of collinear Gabor stimuli, which were vertical. There was no local tilt. The illusory tilt was produced by gradually shifting the phase of the successive Gabors along each line. Although the 2D Fourier transform of this global pattern peaks at off-vertical orientations, the local energy of the patches is predominantly vertical. How does the visual system nevertheless pick up this global information? This can be explained by elongated linear filters, or a phase-tuned second-stage mechanism. We examined the first theory using a stereoscopic demonstration. When lines of opposite tilt are presented in the two eyes, they combine binocularly to produce stereoscopic slant. We tested whether the illusory tilts in the phase-shifted Gabors texture give stereoscopic slant, when opposite tilts are presented to the two eyes. They do not. Instead, stereoscopic depth is dominated by the local phase-disparity of the individual patches. This indicates that the illusion is not present at the stage of linear filters, which are input to stereo, but must involve second-stage interactions or collators.

Cues↗

PubMed1989

Ocular vergence under natural conditions. II. Gaze shifts between real targets differing in distance and direction.

Horizontal binocular eye movements of three subjects were recorded with the scleral sensor coil--revolving magnetic field technique during voluntary shifts of gaze between pairs of stationary, real, continuously visible targets. The target pairs were located either along the median plane (requiring symmetrical vergence), or on either side of the median plane (requiring asymmetrical vergence). Symmetrical vergence was primarily smooth, but it was often assisted by small, disjunctive saccades. Peak vergence speeds were very high; they increased from about 50 degrees s-1 for vergence changes of 5 degrees to between 150 and 200 degrees s-1 for vergence changes of 34 degrees. Differences between convergence and divergence were idiosyncratic. Asymmetrical vergence, requiring a vergence of 11 degrees combined with a version of 45 degrees, was largely saccadic. Unequal saccades mediated virtually all (95%) of the vergence required in the divergent direction, whereas 75% of the vergence required in the convergent direction was mediated by unequal saccades, with the remaining convergence mediated by smooth vergence, following completion of the saccades. Peak divergence speeds during these saccades were very high (180 degrees s-1 for a change of vergence of 11 degrees); much faster than the smooth, symmetrical vergence change of comparable size (14 degrees). Peak convergent saccadic speeds were about 20% lower. This difference in peak speed was caused by an initial, transient divergence, observed at the beginning of all horizontal saccades. The waveform of disjunctive saccades did not have the same shape as the waveform of conjugate saccades of similar size. The smaller saccade of the disjunctive pair was stretched out in time so as to have the same duration as its larger, companion saccade. These results permitted the conclusion that the subsystems controlling saccades and vergence are not independent. Vergence responses were relatively slow and incomplete with monocular viewing, which excluded disparity as a cue. Monocularly stimulated vergence decreased as a function of the increasing presbyopia of our three subjects. Subjects were able to generate some vergence in darkness towards previously seen and remembered targets. Such responses, however, were slow, irregular and evanescent. In conclusion, vergence shifts between targets, which provided all natural cues to distance, were fast and accurate; they appeared adequate to provide effective binocular vision under natural conditions. This result could not have been expected on the basis of previous observations, all of which had been made with severely reduced cues to depth.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1998

Stereoscopic and contrast-defined motion in human vision.

There is considerable evidence for the existence of a specialized mechanism in human vision for detecting moving contrast modulations and some evidence for a mechanism for detecting moving stereoscopic depth modulations. It is unclear whether a single second-order motion mechanism detects both types of stimulus or whether they are detected separately. We show that sensitivity to stereo-defined motion resembles that to contrast-defined motion in two important ways. First, when a missing-fundamental disparity waveform is moved in steps of 0.25 cycles, its perceived direction tends to reverse. This is a property of both luminance-defined and contrast-defined motion and is consistent with independent detection of motion at different spatial scales. Second, thresholds for detecting the direction of a smoothly drifting sinusoidal disparity modulation are much higher than those for detecting its orientation. This is a property of contrast-modulated gratings but not luminance-modulated gratings, for which the two thresholds are normally identical. The results suggest that stereo-defined and contrast-defined motion stimuli are detected either by a common mechanism or by separate mechanisms sharing a common principle of operation.

Depth Perception↗

PubMed2006

Crossed-uncrossed difference (CUD) in a new light: anatomy of the negative CUD in Poffenberger's paradigm.

Crossed Uncrossed Differentials (CUDs) have long been used as surrogate for the interhemispheric transfer time (IHTT). Evidence is presented that macular vision is the province of the major hemisphere, wherein all commands are initiated regardless of the laterality of the effectors of such commands. Using clinical and time-resolved data it is shown also that the above arrangement (i.e. neural handedness) corresponds to the subject's behavioral avowed (avowed, self-declared) handedness only in a statistical sense; with a substantial minority of humanity displaying a disparity of neural and behavioral handedness. Evidence is provided that the negative CUD in previously reported studies was a reflection of such incongruity in those subjects studied. Thus, to lateralize the command center it is sufficient to determine the reaction time of two symmetrically located effectors on the body. The side with longer reaction time is ipsilateral to the major hemisphere, with the difference of the two sides commensurate to transcallosal IHTT.

Brain↗

PubMed1989

Binocular depth reversals despite familiarity cues.

Stereoscopic depth can be reversed by interchanging the left- and right-eye views (pseudoscopy) when abstract stereograms are used, but not when stereograms contain natural objects or scenes. This resistance to reversal of depth has traditionally been attributed to familiarity with the shape of objects and the presence of monocular depth cues. However, when texture disparity is neutralized by making the texture perspective of surfaces identical for both eyes, even a highly familiar object, like a monocularly recognizable human face, appears as concave (nose pointing inwards) when viewed pseudoscopically.

Cognition↗

PubMed2000

[Effects of different types of disparity cues on the response of axis-orientation selective cells in the monkey parietal cortex].

PURPOSE: To specify the cues for the discrimination of orientation in depth in axis orientation selective (AOS) neurons. METHODS: We analyzed the responses of AOS neurons in the monkey caudal intraparietal sulcus (cIPS) region using binocular disparity stimuli generated by stereoscopic 3 D computer graphics. RESULTS: Most AOS neurons (20/27) were sensitive to binocular disparity and showed tuning to the orientation of a slit in the sagittal plane with orientation disparity cues. For 12 neurons we also used an array of discs or dots instead of slits to eliminate orientation disparity. Half of the neurons (6/12) responded better to the slits than to the discs or dots, suggesting that they were sensitive to orientation disparity. Five neurons (5/12) responded equally well to the discs or dots suggesting that they were more sensitive to the gradient of horizontal disparity than to the orientation disparity. CONCLUSION: Both orientation disparity and disparity gradient were likely to be integrated in the cIPS area to represent axis orientation of an object in space.

Animals↗

PubMed1986

Selective losses in binocular vision in anisometropic amblyopes.

Human anisometropic amblyopes typically exhibit reduced contrast sensitivity in the amblyopic eye, especially at higher spatial frequencies. We determined whether this spatial frequency selective loss in contrast sensitivity is accompanied by selective losses in binocular function. Binocular summation (the improvement in one eye's detection performance produced by a subthreshold pattern presented to the fellow eye) was measured at several spatial frequencies. Normal observers exhibited equivalent binouclar summation at all spatial frequencies, whereas all anisometropic amblyopes exhibited normal summation at low spatial frequencies but none at high spatial frequencies. Stereoacuity (minimum resolvable disparity) was also measured as a function of spatial frequency. For normal observers, stereoacuity was best at the highest spatial frequency; for anisometropes stereoacuity was normal at low spatial frequencies, subnormal at intermediate spatial frequencies, and unmeasurable at higher spatial frequencies. Anisometropia may represent a form of selective binocular deprivation that affects neural mechanisms underlying binocular summation and stereopsis.

Adult↗

PubMed1998

Neuronal responsiveness to three-dimensional motion in cat posteromedial lateral suprasylvian cortex.

The neuronal responsiveness to three-dimensional (3D) motion in cat posteromedial lateral suprasylvian (PMLS) cortex was studied using a computer-controlled, stereoscopic 3D graphic display capable of reproducing the major visual cues for natural 3D motion, including motion disparity, size, texture, and shading changes. The animals were anesthetized with nitrous oxide supplemented with alphaxalone, and paralysis prevented eye movement. Systematic investigation of neuronal responsiveness to 3D motions in 26 different directions revealed that more than half of the PMLS cells were selectively responsive to approaching (AP cells, 112 of 271) or recessive motion (RC cells, 64 of 271). The remaining cells were selectively responsive to frontoparallel motion (FP cells, 49 of 271) or nonselectively responsive to motion in multiple directions (NS cells, 46 of 271). The dependency on these visual cues was investigated as a reduction in the response amplitude or the response selectivity for the removal of a single cue from the motion stimuli containing the full visual cues. The AP and RC cells showed a strong dependency on the motion disparity cue, moderate dependency on the size cue, and weak dependency on the texture and shading cues. The FP cells showed no dependency on those visual cues. The cue dependency analysis indicated the existence of nonlinear interactions between those visual cues. Comparison of the responses to a combination of the motion disparity and size cues with the summed responses to each of the individual cues revealed that the responses to the combined cues are roughly predicted as a linear sum between the preferred responses. This comparison also showed nonlinear summation between the nonpreferred responses, i.e., responses to the combined cues were smaller than the summed responses. A similar quasilinear summation of the preferred responses between the two eyes and a nonlinear summation of the nonpreferred responses were found in the AP and RC cells for the motion disparity stimulus. All of these observations indicate that quasilinear and nonlinear interactions of the responses to various stimulus elements underlie the 3D motion responsiveness of the PMLS cells.

Animals↗

PubMed1994

Contrast thresholds for stereoscopic depth identification with isoluminant and isochromatic stimuli.

Contrast thresholds for stereoscopic depth identification (crossed or uncrossed) were measured as a function of disparity using isoluminant (red-green) and isochromatic (yellow-black) 0.5 c/deg Gabor patches. For the purposes of comparison stimulus contrasts were scaled by their respective detection thresholds. The detection thresholds employed were computed from the monocular detection thresholds of the stereo half-images, based on the assumption that simultaneous detection of these half-images in each eye was a sufficient condition for stereopsis. It was found that the disparity tuning of both chromatic and luminance mechanisms was similar, with a performance peak for a binocular phase disparity of 50-120 deg. However, more contrast was required, relative to detection threshold, for the chromatic patterns to evoke a sensation of stereoscopic depth. These results suggest that stereopsis in the absence of luminance cues is supported by a less-contrast-sensitive analogue of the system that supports stereopsis in the presence of luminance cues. The results are also consistent with there being a lower density of disparity-selective mechanisms in the chromatic pathway. The implications of these data for previous studies of stereopsis at isoluminance is discussed.

Calibration↗

PubMed1997

Medial rectus fadenoperation for esotropia only at near fixation.

PURPOSE: The patient with a large esodeviation at near and a minimal if any deviation at distance who is unable to discontinue bifocal wear or demonstrates a decrease in binocular function presents a difficult therapeutic dilemma to the strabismologist. The medial rectus fadenoperation has been proposed as a method of reducing the accommodative convergence/accommodation (AC/A) ratio and may be a reasonable approach to correct a deviation that is present only at near fixation. We examined our results with this type of operation in these difficult patients. METHODS: A review of consecutive patients who underwent a bilateral medial rectus fadenoperation (no recession) for high AC/A ratio esotropia with a significant esodeviation only at near was performed. Preoperative and postoperative motility and sensory status were evaluated. RESULTS: Sixteen patients meeting the criteria were identified. The preoperative mean distance deviation was 8.8 PD of esodeviation and the mean near deviation was 33 PD of esodeviation. The mean AC/A ratio (by the gradient method) preoperatively was 7.4 PD/D. The average age at surgery was 8 years. Six (38%) had undergone prior strabismus surgery. Average follow-up was 36 months (range 12 to 98 months). Postoperatively the mean distance deviation was 3.2 PD of esodeviation and the mean near deviation was 10.3 PD of esodeviation. The mean decrease in the near deviation was 22.8 PD. The mean postoperative AC/A ratio was 2.9. Ninety-five percent of the patients normalized their AC/A ratios and 70% attained 400 arc-sec of stereopsis postoperatively (vs 44% preoperatively. The majority of patients (86%) were able to maintain satisfactory near ocular alignment without bifocals. CONCLUSIONS: The fadenoperation appears to be useful in this patient population by reducing the distance-near disparity and the AC/A ratio, by decreasing the necessity for bifocal wear, and by improving binocular function at near.

Accommodation, Ocular↗

PubMed2000

Cue combination in the motion correspondence problem.

Image motion is a primary source of visual information about the world. However, before this information can be used the visual system must determine the spatio-temporal displacements of the features in the dynamic retinal image, which originate from objects moving in space. This is known as the motion correspondence problem. We investigated whether cross-cue matching constraints contribute to the solution of this problem, which would be consistent with physiological reports that many directionally selective cells in the visual cortex also respond to additional visual cues. We measured the maximum displacement limit (Dmax) for two-frame apparent motion sequences. Dmax increases as the number of elements in such sequences decreases. However, in our displays the total number of elements was kept constant while the number of a subset of elements, defined by a difference in contrast polarity, binocular disparity or colour, was varied. Dmax increased as the number of elements distinguished by a particular cue was decreased. Dmax was affected by contrast polarity for all observers, but only some observers were influenced by binocular disparity and others by colour information. These results demonstrate that the human visual system exploits local, cross-cue matching constraints in the solution of the motion correspondence problem.

Color↗

PubMed2001

The physiology of stereopsis.

Binocular disparity provides the visual system with information concerning the three-dimensional layout of the environment. Recent physiological studies in the primary visual cortex provide a successful account of the mechanisms by which single neurons are able to signal disparity. This work also reveals that additional processing is required to make explicit the types of signal required for depth perception (such as the ability to match features correctly between the two monocular images). Some of these signals, such as those encoding relative disparity, are found in extrastriate cortex. Several other lines of evidence also suggest that the link between perception and neuronal activity is stronger in extrastriate cortex (especially MT) than in the primary visual cortex.

Animals↗

PubMed1987

Binocular anomalies and reading problems.

This paper reviews and evaluates the research literature on the relationship of binocular anomalies to reading problems. The weight of the evidence supports a positive relationship between certain binocular anomalies and reading problems. The evidence is positive for exophoria at near, fusional vergence reserves, aniseikonia, anisometropia, convergence insufficiency, and fixation disparity. There is some weak positive evidence for esophoria at near and mixed evidence for stereopsis. The evidence on lateral phorias at distance is negative.

Aniseikonia↗