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Binocular viewing is associated with a superior prehensile performance, which is particularly evident in the latter part of the reach as the hand approaches and makes contact with the target object. However, the visuomotor mechanisms through which binocular vision serves prehension are not fully understood. This study assessed the role of stereopsis in the predictive control of grasping by measuring grip force. Twenty participants performed a precision reach-to-grasp task in four viewing conditions: binocular, monocular, and with reduced stereoacuity (200 arc sec, > 400 arc sec). Monocular, compared to binocular viewing, was associated with a fourfold increase in grasp errors, a 56% increase in grasp duration, 22% decrease in grip force at 50 ms following grasp initiation, and the time of peak force occurred 40% later after grasp initiation (all p < 0.05). Grasp performance was also disrupted when viewing with reduced stereoacuity. Notably, grip force at the time of object lift-off was comparable between all viewing conditions. These results demonstrate that binocular stereopsis contributes to the efficient programming of grip forces. Specifically, stereopsis may provide important sensory information that enables the central nervous system to engage in predictive control of grasping. [ABSTRACT FROM AUTHOR]

We investigated monocular information for the continuous online guidance of reaches-to-grasp and present a dynamical control model thereof. We defined an information variable using optical texture projected from a support surface (i.e. a table) over which the participants reached-to-grasp target objects sitting on the table surface at different distances. Using either binocular or monocular vision in the dark, participants rapidly reached-to-grasp a phosphorescent square target object with visibly phosphorescent thumb and index finger. Targets were one of three sizes. The target either sat flat on the support surface or was suspended a few centimeters above the surface at a slant. The later condition perturbed the visible relation of the target to the support surface. The support surface was either invisible in the dark or covered with a visible phosphorescent checkerboard texture. Reach-to-grasp trajectories were recorded and Maximum Grasp Apertures (MGA), Movement Times (MT), Time of MGA (TMGA), and Time of Peak Velocities (TPV) were analyzed. These measures were selected as most indicative of the participant's certainty about the relation of hand to target object during the reaches. The findings were that, in general, especially monocular reaches were less certain (slower, earlier TMGA and TPV) than binocular reaches except with the target flat on the visible support surface where performance with monocular and binocular vision was equivalent. The hypothesized information was the difference in image width of optical texture (equivalent to density of optical texture) at the hand versus the target. A control dynamic equation was formulated representing proportional rate control of the reaches-to-grasp (akin to the model using binocular disparity formulated by Anderson and Bingham (Exp Brain Res 205: 291–306, 2010). Simulations were performed and presented using this model. Simulated performance was compared to actual performance and found to replicate it. To our knowledge, this is the first study of monocular information used for continuous online guidance of reaches-to-grasp, complete with a control dynamic model. [ABSTRACT FROM AUTHOR]

Proficient (fast, accurate, precise) hand actions for reaching-to-grasp 3D objects are known to benefit significantly from the use of binocular vision compared to one eye alone. We examined whether these binocular advantages derive from increased reliability in encoding the goal object's properties for feedforward planning of prehension movements or from enhanced feedback mediating their online control. Adult participants reached for, precision grasped and lifted cylindrical table-top objects (two sizes, 2 distances) using binocular vision or only their dominant/sighting eye or their non-dominant eye to program and fully execute their movements or using each of the three viewing conditions only to plan their reach-to-grasp during a 1 s preview, with vision occluded just before movement onset. Various kinematic measures of reaching and grasping proficiency, including corrective error rates, were quantified and compared by view, feedback and object type. Some significant benefits of binocular over monocular vision when they were just available for pre-movement planning were retained for the reach regardless of target distance, including higher peak velocities, straighter paths and shorter low velocity approach times, although these latter were contaminated by more velocity corrections and by poorer coordination with object contact. By contrast, virtually all binocular advantages for grasping, including improvements in peak grip aperture scaling, the accuracy and precision of digit placements at object contact and shorter grip application times preceding the lift, were eliminated with no feedback available, outcomes that were influenced by the object's size. We argue that vergence cues can improve the reliability of binocular internal representations of object distance for the feedforward programming of hand transport, whereas the major benefits of binocular vision for enhancing grasping performance derive exclusively from its continuous presence online. [ABSTRACT FROM AUTHOR]

Sensorimotor coupling in healthy humans is demonstrated by the higher accuracy of visually tracking intrinsically—rather than extrinsically—generated hand movements in the fronto-parallel plane. It is unknown whether this coupling also facilitates vergence eye movements for tracking objects in depth, or can overcome symmetric or asymmetric binocular visual impairments. Human observers were therefore asked to track with their gaze a target moving horizontally or in depth. The movement of the target was either directly controlled by the observer’s hand or followed hand movements executed by the observer in a previous trial. Visual impairments were simulated by blurring stimuli independently in each eye. Accuracy was higher for self-generated movements in all conditions, demonstrating that motor signals are employed by the oculomotor system to improve the accuracy of vergence as well as horizontal eye movements. Asymmetric monocular blur affected horizontal tracking less than symmetric binocular blur, but impaired tracking in depth as much as binocular blur. There was a critical blur level up to which pursuit and vergence eye movements maintained tracking accuracy independent of blur level. Hand–eye coordination may therefore help compensate for functional deficits associated with eye disease and may be employed to augment visual impairment rehabilitation. [ABSTRACT FROM AUTHOR]

Binocular vision is often assumed to make a specific, critical contribution to online visual control of grasping by providing precise information about the separation between digits and object. This account overlooks the 'viewing geometry' typically encountered in grasping, however. Separation of hand and object is rarely aligned precisely with the line of sight (the visual depth dimension), and analysis of the raw signals suggests that, for most other viewing angles, binocular feedback is less precise than monocular feedback. Thus, online grasp control relying selectively on binocular feedback would not be robust to natural changes in viewing geometry. Alternatively, sensory integration theory suggests that different signals contribute according to their relative precision, in which case the role of binocular feedback should depend on viewing geometry, rather than being 'hard-wired'. We manipulated viewing geometry, and assessed the role of binocular feedback by measuring the effects on grasping of occluding one eye at movement onset. Loss of binocular feedback resulted in a significantly less extended final slow-movement phase when hand and object were separated primarily in the frontoparallel plane (where binocular information is relatively imprecise), compared to when they were separated primarily along the line of sight (where binocular information is relatively precise). Consistent with sensory integration theory, this suggests the role of binocular (and monocular) vision in online grasp control is not a fixed, 'architectural' property of the visuo-motor system, but arises instead from the interaction of viewer and situation, allowing robust online control across natural variations in viewing geometry. [ABSTRACT FROM AUTHOR]

Recent neurophysiological and behavioral studies have established that the saccadic amplitudes performed during combined saccade-vergence movements are unequal in the two eyes. These studies have not established, however, how the saccadic amplitude of each eye is determined. Our goal here is to fill this lacuna. We use three well-known metric attributes of saccadic movements as constraints and argue that the only quantitative model that obeys these constraints is one where each eye's saccadic amplitude is given by a weighted average of the target's locations in the two retinas. However, this theoretical result does not establish whether the weights in the weighted averaging operation are constant or whether they vary for different targets. To test the simpler of these two possibilities, namely the one of constant weights, we recorded combined saccade-vergence movements performed by human subjects. Our analysis of these movements shows that a constant-weights weighted averaging model provides an excellent description of their saccadic amplitudes. Overall, then, our conclusions are: (1) the two eyes' saccadic amplitudes are determined by weighted averages of the target's locations in the two retinas; (2) for targets within the oculomotor range of natural viewing, which was the range in our experiments, a weighted averaging model that uses constant weights accounts superbly for these saccadic amplitudes. We suggest that the weighted averaging operation that determines saccadic amplitudes is a by-product of a process whose purpose is to yoke the two eyes together. We provide a model explaining how this yoking may be achieved. [ABSTRACT FROM AUTHOR]

Saccadic and manual reactions to a peripherally presented target are facilitated by removing a central fixation stimulus shortly before a target onset (the gap effect). The present study examined the effects of removal of a visible and invisible fixation point on the saccadic gap effect and the manual gap effect. Participants were required to fixate a central fixation point and respond to a peripherally presented target as quickly and accurately as possible by making a saccade (Experiment 1) or pressing a corresponding key (Experiment 2). The fixation point was dichoptically presented, and visibility was manipulated by using binocular rivalry and continuous flash suppression technique. In both saccade and key-press tasks, removing the visible fixation strongly quickened the responses. Furthermore, the invisible fixation, which remained on the display but suppressed, significantly delayed the saccadic response. Contrarily, the invisible fixation had no effect on the manual task. These results indicate that partially different processes mediate the saccadic gap effect and the manual gap effect. In particular, unconscious processes might modulate an oculomotor-specific component of the saccadic gap effect, presumably via subcortical mechanisms. [ABSTRACT FROM AUTHOR]

Saccadic peak velocities during monocular and binocular presentation were tested. While the main sequence linear increase in peak velocities as a function of saccade amplitude is well documented, our results provide demonstrations of violations of the main sequence. Peak velocities during monocular presentation were considerably higher toward temporal than nasal stimuli. This nasal-temporal asymmetry (NTA) was not explained by amplitude differences and was most pronounced for the lowest amplitudes tested, decreasing with increased amplitude. Under binocular presentation, this NTA was much smaller. While the exact reasons for this difference in peak velocities between hemifields are unclear at present, we propose that anatomical NTAs result in stronger signals from the nasal, than temporal retina leading to higher peak velocities into the temporal visual hemifield. NTAs in peak velocity are consistent with NTAs in attentional choice and in attentional function, which might also be explained by anatomical NTA. [ABSTRACT FROM AUTHOR]

This study investigated the importance of binocular vision to foot placement accuracy when stepping onto a floor-based target during gait initiation. Starting from stationary, participants placed alternate feet onto targets sequentially positioned along a straight travel path with the added constraint that the initial target (target 1) could move in the medio-lateral (M-L) direction. Repeated trials when target 1 remained stationary or moved laterally at the instant of lead-limb toe-off (TO) or 200 ms after TO (early swing) were undertaken under binocular and monocular viewing. Catch trials when target 1 shifted medially were also undertaken. Foot-reach kinematics, foot trajectory corrections and foot placement accuracy for the step onto target 1 were determined via 3D motion analyses. Peak foot-reach velocity and initial foot-reach duration were unaffected by vision condition but terminal foot-reach duration was prolonged under monocular conditions ( p = 0.002). Foot trajectory alteration onsets were unaffected by vision condition, but onsets occurred sooner when the target shifted in early swing compared to at TO ( p = 0.033). M-L foot placement accuracy decreased ( p = 0.025) and variability increased ( p = 0.05) under monocular conditions, particularly when stepping onto the moving target. There was no difference between vision conditions in A-P foot placement accuracy. Results indicate that monocular vision provides sufficient information to determine stepping distance and correctly transport the foot towards the target but binocular vision is required to attain a precise M-L foot placement; particularly so when stepping onto a moving target. These findings are in agreement with those found in the reaching and grasping literature, indicating that binocular vision is important for end-point precision. [ABSTRACT FROM AUTHOR]

Translational motion induces retinal image slip which varies with object distance. The brain must know binocular eye position in real time in order to scale eye movements so as to minimize retinal slip. Two potential sources of eye position information are orbital proprioception and an internal representation of eye position derived from central ocular motor signals. To examine the role of orbital proprioceptive information, the position of the left eye was perturbed by microstimulation of the left abducens nerve during translational motion to the right or left along the interaural axis in two rhesus macaques. Microstimulation rotated the eye laterally, activating eye muscle proprioceptors, while keeping central motor commands undisturbed. We found that microstimulation-induced eye position changes did not affect the translational VOR in the abductive (lateral rectus) direction, but it did influence the responses in the adductive (medial rectus) direction. Our findings demonstrate that proprioceptive inputs appear to be involved in the TVOR responses at least during ipsilateral head movements and proprioceptive influences on the TVOR may involve vergence-related signals to the oculomotor nucleus. However, internal representation of eye position, derived from central ocular motor signals, likely plays the dominant role in providing eye position information for scaling eye movements during translational motion, particularly in the abducent direction. [ABSTRACT FROM AUTHOR]

We provide a solution to a major problem in visually guided reaching. Research has shown that binocular vision plays an important role in the online visual guidance of reaching, but the visual information and strategy used to guide a reach remains unknown. We propose a new theory of visual guidance of reaching including a new information variable, τ (relative disparity τ), and a novel control strategy that allows actors to guide their reach trajectories visually by maintaining a constant proportion between τ and its rate of change. The dynamical model couples the information to the reaching movement to generate trajectories characteristic of human reaching. We tested the theory in two experiments in which participants reached under conditions of darkness to guide a visible point either on a sliding apparatus or on their finger to a point-light target in depth. Slider apparatus controlled for a simple mapping from visual to proprioceptive space. When reaching with their finger, participants were forced, by perturbation of visual information used for feedforward control, to use online control with only binocular disparity-based information for guidance. Statistical analyses of trajectories strongly supported the theory. Simulations of the model were compared statistically to actual reaching trajectories. The results supported the theory, showing that τ provides a source of information for the control of visually guided reaching and that participants use this information in a proportional rate control strategy. [ABSTRACT FROM AUTHOR]

The role of binocular vision in grasping has frequently been assessed by measuring the effects on grasp kinematics of covering one eye. These studies have typically used three or fewer objects presented at three or fewer distances, raising the possibility that participants learn the properties of the stimulus set. If so, even relatively poor visual information may be sufficient to identify which object/distance configuration is presented on a given trial, in effect providing an additional source of depth information. Here we show that the availability of this uncontrolled cue leads to an underestimate of the effects of removing binocular information, and therefore to an overestimate of the effectiveness of the remaining cues. We measured the effects of removing binocular cues on visually open-loop grasps using (1) a conventional small stimulus-set, and (2) a large, pseudo-randomised stimulus set, which could not be learned. Removing binocular cues resulted in a significant change in grip aperture scaling in both conditions: peak grip apertures were larger (when reaching to small objects), and scaled less with increases in object size. However, this effect was significantly larger with the randomised stimulus set. These results confirm that binocular information makes a significant contribution to grasp planning. Moreover, they suggest that learned stimulus information can contribute to grasping in typical experiments, and so the contribution of information from binocular vision (and from other depth cues) may not have been measured accurately. [ABSTRACT FROM AUTHOR]

Accurate distance perception depends on the processing and integration of a variety of monocular and binocular cues. Dorsal stream lesions can impair this process, but details of this neurocognitive relationship remain unclear. Here, we tested a patient with bilateral occipitoparietal damage and severely impaired stereopsis. We addressed four related questions: (1) Can distance and size perception survive limitations in perceiving monocular and binocular cues? (2) Are egocentric (self-referential) and allocentric (object-referential) distance judgments similarly impaired? (3) Are distance measurements equally impaired in peripersonal and extrapersonal space? (4) Are size judgments possible when distance processing is impaired? The results demonstrate that the patient’s lesions impaired both her distance and size perception, but not uniformly. Her performance when using an egocentric reference frame was more impaired than her performance when using an allocentric reference frame. Likewise, her distance judgments in peripersonal space were more impaired than those in extrapersonal space. The patient showed partial preservation in size processing of novel objects even when familiar size cues were removed. [ABSTRACT FROM AUTHOR]

We studied the effects of paralytic strabismus on visual behaviour and binocularity of cortical visual mechanisms by immobilization of one eye in adult cats. Visual discrimination abilities of the immobilized eye were significantly diminished despite extensive training with one or both eyes. The deficits are not caused by the immobilization itself but appear to reflect an adaptive mechanism to deal with double vision. The deficits with the immobilized eye persisted even after section of the optic chiasm, which effectively removes the direct cortical competition of the two eyes. Single-cell electrophysiological recordings showed that cortical cellular responses are modified by the immobilization, with loss of binocularity in some cells and shifting of receptive fields of other cells that continued to respond to both eyes. [ABSTRACT FROM AUTHOR]

We have recently developed a new motion display in which the monocular and dichoptic motion components move in opposite directions (Hayashi et al. ). In the present paper, we estimated the difference between the integration times required to detect the dichoptic motion and monocular motion by changing the duration of the stimulus. The results showed that monocular motion perception becomes more dominant as the stimulus duration becomes shorter, indicating that the detection of dichoptic motion is relatively slow process that requires a longer integration time compared with the process used to detect monocular motion. [ABSTRACT FROM AUTHOR]

Even though there have been extensive investigations of the temporal integration limits of binocular vision in perceptual tasks, relatively little is known about temporal integration limits during the completion of visuomotor tasks. To assess the temporal integration limits of binocular disparity within the action domain, accuracy of reach kinematics in a reaching and grasping task under continuous binocular and monocular viewing conditions were compared with those obtained under alternating monocular viewing conditions with interocular delays ranging from 14 to 58 ms. Even the shortest of the interocular delays resulted in larger grip apertures than those in the continuous monocular and binocular viewing conditions. The short temporal integration interval of stereovision obtained in this study cannot be accounted for by differential visual feedback in the binocular and interocular delay conditions, nor is it likely to be a consequence of visual disruption due to the interocular delays. Our findings suggest that the visuomotor system has little tolerance to interocular delay. [ABSTRACT FROM AUTHOR]

When the eyes follow a target that is moving directly towards the head they make a vergence eye movement. Accurate perception of the target’s motion requires adequate compensation for the movements of the eyes. The experiments in this paper address the issue of how well the visual system compensates for vergence eye movements when viewing moving targets. We show that there are small but consistent biases across observers: When the eyes follow a target that is moving in depth, it is typically perceived as slower than when the eyes are kept stationary. We also analysed the eye movements that were made by observers. We found that there are considerable differences between observers and between trials, but we did not find evidence that the gains and phase lags of the eye movements were related to psychophysical performance. [ABSTRACT FROM AUTHOR]

Theoretical considerations suggest that binocular information should provide advantages, compared to monocular viewing, for the planning and execution of natural reaching and grasping actions, but empirical support for this is quite equivocal. We have examined these predictions on a simple prehension task in which normal subjects reached, grasped and lifted isolated cylindrical household objects (two sizes, four locations) in a well-lit environment, using binocular vision or with one eye occluded. Various kinematic measures reflecting the programming and on-line control of the movements were quantified, in combination with analyses of different types of error occurring in the velocity, spatial path and grip aperture profiles of each trial. There was little consistent effect of viewing condition on the early phase of the reach, up to and including the peak deceleration, but all other aspects of performance were superior under binocular control. Subjects adopted a cautious approach when binocular information was unavailable: they extended the end phase of the reach and pre-shaped their hand with a wider grip aperture further away from the object. Despite these precautions, initial grip application was poorly coordinated with target contact and was inaccurately scaled to the objects’ dimensions, with the subsequent post-contact phase of the grasp significantly more prolonged, error-prone and variable compared to binocular performance. These effects were obtained in two separate experiments in which the participants’ performed the task under randomized or more predictable (blocked) viewing conditions. Our data suggest that binocular vision offers particular advantages for controlling the terminal reach and the grasp. We argue that these benefits derive from binocular disparity processing linked to changes in relative hand–target distance, and that this depth information is independently used to regulate the progress of the approaching hand and to guide the digits to the (pre-selected) contact points on the object, thereby ensuring that the grip is securely applied. [ABSTRACT FROM AUTHOR]

Do relative binocular disparities guide our movements in depth? In order to find out we asked subjects to move a ‘cursor’ to a target within a simulated horizontal plane at eye height. They did so by moving a computer mouse. We determined how quickly subjects responded to the target jumping in depth. We found that it took subjects about 200 ms to respond to changes in binocular disparity. Subjects responded just as quickly if the cursor was temporarily only visible to one eye near the time that the target jumped in depth, and less vigorously, though just as quickly, if the cursor jumped rather than the target, so the fastest binocular responses cannot be based directly on the relative retinal disparity between the target and the cursor. Subjects reacted faster to changes in the target’s height in the visual field than to changes in binocular disparity, but did not react faster to changes in image size. These results suggest that binocular vision mainly improves people’s everyday movements by giving them a better sense of the distances of relevant objects, rather than by relative retinal disparities being used to directly guide the movement. We propose that relative disparities only guide parts of very slow movements that require extreme precision. [ABSTRACT FROM AUTHOR]

Previous research has suggested that binocular vision plays an important role in prehension. It has been shown that removing binocular vision affects (negatively) both the planning and on-line control of prehension. It has been suggested that the adverse impact of removing binocular vision is because monocular viewing results in an underestimation of target distance in visuomotor tasks. This suggestion is based on the observation that the kinematics of prehension are altered when viewing monocularly. We argue that it is not possible to draw unambiguous conclusions regarding the accuracy of distance perception from these data. In experiment 1, we found data that contradict the idea that a consistent visuomotor underestimation of target distance is an inevitable consequence of monocular viewing. Our data did show, however, that positional variance increases under monocular viewing. We provide an alternative explanation for the kinematic changes found when binocular vision is removed. Our account is based on the changes in movement kinematics that occur when end-point variance is altered following the removal of binocular vision. We suggest that the removal of binocular vision leads to greater perceptual uncertainty (e.g. less precise stimulus cues), resulting in changes in the kinematics of the movement (longer duration movements). Our alternative account reconciles some differences within the research literature. We conducted a series of experiments to explore further the issue of when binocular information is advantageous in prehension. Three subsequent experiments were employed which varied binocular/monocular viewing in selectively lit conditions. Experiment 2 explored the differences in prehension measured between monocular and binocular viewing in a full cue environment with a continuous view of the target object. Experiment 3 required participants to reach, under a monocular or binocular view, for a continuously visible self-illuminated target object in an otherwise dark room. In Experiment 3, the participant could neither see the target object nor the reaching hand following initiation of the prehension movement. Our results suggest that binocular vision contributes to prehension by providing additional information (cues) to the nervous system. These cues appear to be weighted differentially according to the particular constellation of stimulus cues available to the participants when reaching to grasp. One constant advantage of a binocular view appears to be the provision of on-line information regarding the position of the hand relative to the target. In reduced cue conditions (i.e. where a view of the target object is lost following initiation of the movement), binocular information regarding target location appears to be particularly useful in the initial programming of reach distance. Our results are a step towards establishing the specific contributions that binocular vision makes to the control of prehension. [ABSTRACT FROM AUTHOR]

Over what region of space are horizontal disparities integrated to form the stimulus for vergence? The vergence system might be expected to respond to disparities within a small area of interest to bring them into the range of precise stereoscopic processing. However, the literature suggests that disparities are integrated over a fairly large parafoveal area. We report the results of six experiments designed to explore the spatial characteristics of the stimulus for vergence. Binocular eye movements were recorded using magnetic search coils. Each dichoptic display consisted of a central target stimulus that the subject attempted to fuse, and a competing stimulus with conflicting disparity. In some conditions the target was stationary, providing a fixation stimulus. In other conditions, the disparity of the target changed to provide a vergence-tracking stimulus. The target and competing stimulus were combined in a variety of conditions including those in which (1) a transparent textured-disc target was superimposed on a competing textured background, (2) a textured-disc target filled the centre of a competing annular background, and (3) a small target was presented within the centre of a competing annular background of various inner diameters. In some conditions the target and competing stimulus were separated in stereoscopic depth. The results are consistent with a disparity integration area with a diameter of about 5°. Stimuli beyond this integration area can drive vergence in their own right, but they do not appear to be summed or averaged with a central stimulus to form a combined disparity signal. A competing stimulus had less effect on vergence when separated from the target by a disparity pedestal. As a result, we propose that it may be more useful to think in terms of an integration volume for vergence rather than a two-dimensional retinal integration area. [ABSTRACT FROM AUTHOR]

Peak velocity, duration and accuracy of eye movements (saccade, vergence and combined saccade–vergence eye movements) were investigated in fourteen normal children (4.5 to 12 years of age) and ten normal adults (22 to 44 years of age). Horizontal movements from both eyes were recorded simultaneously by the oculometer, a photoelectric device. Peak velocity of all eye movements, saccades, and vergence (convergence and divergence), attains adult levels by the age of 4.5 years and there is no significant change over the age range studied (4.5 to 44 years). Vergence duration is longer only in young children (below 8 years of age). The reciprocal interaction between saccade and vergence during combined movements known in adults, i.e. acceleration of the vergence by the saccade (increase of velocity and decrease of duration) and deceleration of the saccade by the vergence (decrease of velocity and increase of duration) was found to be similar in children. The accuracy of eye movements is good on average for both saccades and vergence by the age of 4.5 years, and does not change with age; an exception is the variability of saccade amplitude, which is higher in children less than 8 years old. Taken together, the results indicate early maturation of brainstem structures controlling spatio-temporal aspects of saccades, vergence and their interaction. [ABSTRACT FROM AUTHOR]

Using functional magnetic resonance imaging (fMRI), we explored the binocular interactions occurring when subjects viewed dichoptically presented checkerboard stimuli. A flickering radial checkerboard was presented to each eye of the subject, while T2*-weighted images were acquired over the visual cortex with gradient-echo, echoplanar sequences. We compared responses in striate and extrastriate visual cortex under four conditions: both eyes were stimulated at the same time (binocular condition), each eye was stimulated in alternation (monocular condition) or first the one eye then the other eye was stimulated (left eye first – right eye trailing, or vice versa). The results indicate that only the striate area, in and near the calcarine fissure, shows significant differences for these stimulation conditions. These differences are not evident in more remote extrastriate or associational visual areas, although the BOLD response in the stimulation-rest comparison was robust. These results suggest that the effect could be related to inhibitory interactions across ocular dominance columns in striate visual cortex. [ABSTRACT FROM AUTHOR]

Eccentric sinusoidal rotation with the nose facing out or in leads to gain modulation of the vestibulo-ocular reflex (VOR), which is a result of an interaction between angular and translational VOR. There are conflicting reports with regard to the type of interaction. Combined angular and translational VOR during eccentric sinusoidal rotations over a wide range of target distances (12–180 cm), eccentricities (centric, 30 and 50 cm nose-out and nose-in eccentric) and frequencies (0.1–4 Hz) were studied in macaque monkeys trained to fixate earth-stationary light-emitting diode (LED) targets while binocular eye positions were measured using magnetic search coils. The monkeys were also exposed to sudden unpredictable position steps with peak accelerations of 500°/s2 using similar eccentricities and target distances. VOR gain enhancement during nose-out eccentric sinusoidal rotation was almost compensatory when the target was visible and was independent of stimulus frequency. Mean responses were still close to ideal when the target was extinguished; however, individual data showed increased variability. Sensitivities of the translational portion of the combined VOR were compensatory. These sensitivities were clearly reduced during nose-in eccentric sinusoidal rotation. Thus, especially for close targets at 4 Hz combined VOR was not compensatory, independent of target visibility. VOR elicited by sudden position steps showed a sequential response: (1) purely angular VOR (up to 40–45 ms); (2) additional translational VOR that was not modulated by target distance (45–65 ms); and (3) translational VOR weighted for target location (>65 ms). We conclude that angular and translational VOR have different latencies during transient accelerations and interact differently during agonistic (nose-out) and antagonistic stimulation (nose-in). [ABSTRACT FROM AUTHOR]

To determine whether dynamic visual acuity (DVA) during head rotations on the stationary body can lateralize unilateral vestibular deafferentation and detect non-labyrinthine compensation mechanisms, 15 normal and 11 subjects with unilateral vestibular deafferentation underwent manually imposed and self-generated transient yaw head rotations during measurement of binocular DVA. DVA was measured by a four-alternative, forced choice, staircase procedure with optotype presentation only when head velocity exceeded thresholds of 50° or 75°/s. Eye and head movements were recorded using search coils to characterize ocular motor strategies. During directionally unpredictable, manually imposed contralesional rotation, unilaterally deafferented subjects had decreases in DVA from the static condition of 0.36±0.22 and 0.47±0.53 log of the minimum angle resolvable (logMAR, mean ± SD), respectively, for 50° and 75°/s thresholds, not significantly greater than those of normal subjects (0.26±0.13 and 0.36±0.14, P>0.05). However, during manually imposed ipsilesional rotation, vestibulopathic subjects had decreases in DVA of 0.66±0.36 and 1.08±0.47 logMAR, significantly greater than during contralesional rotation (P<0.01). The DVA reduction difference for the ipsi- and contralesional directions was less during self-generated than during manually imposed head rotations. The directional difference for manually administered head rotations yielded a robust diagnostic measure with essentially no overlap in performance with normal subjects. Diagnostic performance for DVA during self-generated head rotation was poorer. Recordings of eye and head movements made using search coils during DVA testing confirmed a deficient vestibulo-ocular reflex (VOR) during ipsilesional rotation, with most unilaterally vestibulopathic subjects employing predictive smooth eye movements and vestibular catch-up saccades. Measurement of DVA during transient head rotation on the body thus reliably can detect and lateralize vestibular pathology and compensatory mechanisms. Extravestibular mechanisms for compensation appear more effective during self-generated than manually imposed head rotations. [ABSTRACT FROM AUTHOR]

Although the contribution of binocular vision to reach-to-grasp movements has been extensively studied, it has been largely ignored in locomotion. The aim of these studies was to explore the role of binocular vision during the approach phase and step over the obstacle and the contribution of head movements to acquisition of depth information under monocular vision. Binocular and monocular vision was manipulated in different phases using either an eye patch or liquid crystal glasses. Head movement relative to the trunk was restricted in the first experiment by a modified Ferno Universal Head Immobilizer attached to a rigid board strapped to the participant's back. Whole body kinematics were collected by placing infrared diodes on anatomical landmarks and using an Optotrak imaging system. Several measures related to head and limb movement were analyzed. Three major findings emerged from these studies. First, binocular vision is important for the acquisition of accurate information about the surrounding environment: accuracy but not precision of limb elevation over the obstacle was adversely affected when binocular vision was unavailable. Second, motion parallax due to self-motion provides the most critical depth information and it can be used to partially compensate for the loss of binocular vision. Although head movement is not essential to augment depth information, it is important for reorientation of the visual field to obtain the necessary information about the moving limbs when visual field is suddenly limited under monocular vision. Third, step over the obstacle is pre-planned based on visual information acquired during the approach phase: changes in visual condition during the adaptive step do not influence the limb trajectory. Collectively these three studies provide unique insights into the contribution of binocular vision during adaptive locomotion. [ABSTRACT FROM AUTHOR]

We evaluated the human binocular response to roll motion in the dark and during visual fixation with horizontal convergence. Six normal human subjects were exposed to manually driven, whole-body rotation about an earth-vertical, naso-occipital axis, under two conditions: (I) oscillation at 0.4 Hz (peak velocity 69±3.8°/s) in the dark, and whilst fixating an axial light-emitting diode at 48 cm ('near') and at 206 cm ('far'); (II) constant velocity rotation (56.5±3.1°/s) for 40 s, clockwise and counter-clockwise, in the dark, and sudden stops. Eye and head movements were monitored using scleral search coils. In head-fixed, angular velocity coordinates roll motion always evoked conjugate ocular torsion, with small conjugate horizontal and disconjugate vertical components. The resultant binocular eye responses were rotations about convergent axes. During oscillation with target fixation the convergence of the rotation axes was larger than that predicted by target geometry, producing disconjugate oscillations of vertical gaze about the target ('skewing'). Fast-phase eye movements were primarily resetting rotations about the same convergent rotation axes as the slow phases, but the small vertical velocity components had oscillatory, asymmetrical profiles. In response to velocity steps the slow-phase eye velocity decayed exponentially with time constants of 4.5±1.5 s for the torsional component and 5.8±1.9 s for the 'vertical vergence' component (right eye–left eye recordings). We conclude that in normal human subjects dynamic vertical canal stimulation with horizontal gaze convergence evokes rotation of the eyes about convergent axes and a small skewing of the eyes. [ABSTRACT FROM AUTHOR]

We measured the gain and phase of horizontal and vertical vergences of five subjects as a function of stimulus area and position. Vergence eye movements were recorded by the scleral search coil method as subjects observed dichoptic displays oscillating in antiphase either from side to side or up and down with a peak-to-peak magnitude of 0.5° at either 0.1 Hz or 1.0 Hz. The stimulus was a central textured disc with diameter ranging from 0.75° to 65°, or a peripheral annulus with outer diameter 65° and inner diameter ranging from 5° to 45°. The remaining field was black. For horizontal vergence at both stimulus frequencies, gain and the phase lag were about the same for a 0.75° stimulus as for a 65° central stimulus. For vertical vergence, mean gain increased and mean phase lag decreased with increasing diameter of the central stimulus up to approximately 20°. Thus, the stimulus integration area is much smaller for horizontal vergence than for vertical vergence. The integration area for vertical vergence is similar to that for cyclovergence, as revealed in a previous study. For both types of vergence, response gains were higher and phase lags smaller at 0.1 Hz than at 1.0 Hz. Also, gain decreased and phase lag increased with increasing occlusion of the central region of the stimulus. Vergence gain was significantly higher for a 45° central disc than for a peripheral annulus with the same area. Thus, the central retina has more power to evoke horizontal or vertical vergence than the same area in the periphery. We compare the results with similar data for cyclovergence and discuss their ecological implications. [ABSTRACT FROM AUTHOR]

Ocular vergence movements were measured with a scleral coil technique under stabilized viewing conditions for disparity. Crossed disparity steps, ranging between 0.25 and 10 deg, of three different targets were imposed. Ocular vergence responses consisted of converging movements with an initially constant velocity. This velocity increased with the magnitude of disparity up to about 4 deg and decreased for larger disparities. For disparities up to 2 deg the responses saturated at the limit of convergence. For larger disparities responses were transient, i.e. after large converging movements the angle of convergence gradually declined to about its initial value. For disparities larger than 5 deg amplitudes of the transient responses decreased and occasionally responses were completely absent. The transient character of responses was apparently due to adaptation of the vergence system to a specific disparity, since responses to different disparities could still be induced. Probing of the vergence system with two successive disparity steps of different magnitudes showed that adaptation was selective for a limited range of disparities around the adapting disparity stimulus. Stabilized disparity pulses with durations ranging from 100 to 800 ms induced ocular vergence movements following the time integral of disparity rather than momentary disparity. This indicated that the part of the vergence system sensitive to disparity has mainly integrative properties for large as well as small disparities. Stimulation with trains of shortlasting disparity pulses showed that adaptation also occurred under normal viewing conditions. They further revealed that adaptation is erased during a short period after each blink. [ABSTRACT FROM AUTHOR]

Using the classical mapping technique, the spatio-tectal visual organization in frogs (Rana esculenta) was investigated taking special interest in the previously described existence of a 'systematic disparity' between the two monocular receptive fields of rostral binocular tectal points. The existence of such a disparity was extended to the whole binocular visual field and its sign (crossed or uncrossed disparity) was studied both in paralyzed and anesthetized animals. It was proved however that this disparity phenomenon was not 'systematic', but depended mainly on the experimental methodology. Its physiological significance is discussed. [ABSTRACT FROM AUTHOR]

Fusional vergence ranges were behaviorally determined for two rhesus monkeys and two human subjects using random dot stereograms as stimuli. The subject performed a two-alternative forced choice form discrimination of discretely presented stimuli and the fusional vergence stimulus was changed during the intertrial intervals. The fusional vergence measurements for the monkey were similar to those for the human subjects. [ABSTRACT FROM AUTHOR]

Results of psychophysical experiments are reported showing that synchrony, appropriate relative placement, and absence of standing disparity are important conditions to be met by members of a target configuration if they are to participate in the cooperative neural processes leading to the best disparity discrimination. Consecutive binocular presentation of the members of a stereo target decreases stereoacuity by a factor of about 10, and a step disparity displacement of a single line target needs to be larger still to be detected as a depth stimulus. A standing disparity of even one minute of arc at least doubles the disparity discrimination threshold. It is postulated that a differencing mechanism operates on the depth signal of individual features; the temporal and spatial optima of target presentation for stereoscopic acuity outline the character of the concerned operations. [ABSTRACT FROM AUTHOR]

Cats were raised under conditions of daily alternating monocular exposure, so that each eye received normal input, but the animals were never allowed to use both eyes simultaneously. With single cell recording techniques it could be shown that this led to a severe disturbance of the normal binocularity of cortical neurons. The cats were trained by operant techniques in a two-choice box to discriminate with each eye non-retinotopic stimulus pairs. To test the ability to combine binocular signals it was tested whether the learned discrimination would transfer to red/green colored stimuli which were viewed dichoptically through appropriately colored contact lenses. The arrangement was such that the positive stimulus could be distinguished from the negative stimuli only when the signals from both eyes were combined and used simultaneously. All cats showed immediate transfer, from the monocularly learned discrimination task to the dichoptic paradigm. This indicates that the presence of a normal population of binocular cortical cells in area 17 is not a prerequisite for the ability to use binocular cues for the solution of a pattern discrimination task. [ABSTRACT FROM AUTHOR]

Using standard electrophysiological techniques, 130 neurons were recorded from the binocular region of the paralysed, unanesthetised rabbit's visual cortex. Their receptive fields were categorised into 5 major classes: stationary, motion sensitive, direction selective, double-direction selective and indefinite. The majority of the preferred directions of all direction and double direction selective receptive fields were located within±10° of horizontal or vertical. Of the 130 neurons studied, 104 (79%) were binocular and 50% of these binocular neurons had non-identical receptive fields on the two retinae. The dominance distribution for these binocular neurons revealed a strong tendency toward contralateral dominance, and no ipsilateral monocular neurons were found. The retinal locations of the receptive fields of these binocular neurons extended from 51° to 84° posterior to the optic disc. The ranges of relative horizontal and vertical 'disparity' were calculated for all well-defined binocular receptive fields and found to be 24.5° and 21°, respectively. No evidence of 'columnar organisation' was seen for the visual cortex of the rabbit. These data are contrasted to similar data on the binocular visual system of the cat, and are also interpreted as evidence of the need for interactions among large populations of neurons within the visual cortex of the rabbit. [ABSTRACT FROM AUTHOR]

Normal human subjects were tested for their ability to discriminate the orientation of a square plaque tilted in depth, using two different tasks: a grasping task and a perceptual matching task. Both tasks were given under separate monocular and binocular conditions. Accuracy of performance was measured by use of an opto-electronic motion analysis system, which computed the hand orientation (specifically, a line joining the tips of the thumb and index finger) as the hand either approached the target during grasping or was used to match the target. In all cases there was a very strong statistical coupling between hand orientation and target orientation, irrespective of viewing conditions. However, the matching data differed from the grasping data in showing a consistent curvature in the hand-target relationship, whereby the rate of change of hand orientation as a function of object orientation was smaller for oblique orientations than for those near the horizontal or vertical. The results are interpreted as reflecting the operation of two different mechanisms for analysing orientation in depth: a visuomotor system (assumed to be located primarily in the dorsal cortical visual stream) and a perceptual system (assumed to be located in the ventral stream). It may be that the requirements of visuomotor control dictate a primary need for absolute orientation coding, whereas those of perception dictate a need for more categorical coding. [ABSTRACT FROM AUTHOR]

Previous studies have reported that the visual form agnosic D.F. is able to use information about visual targets for the control of motor acts, but has great difficulty in using the same visual information for perceptual report. This intact visuomotor performance may be mediated by relatively intact parieto-frontal cortical mechanisms. The present study investigated the ability of D.F. to use binocular and monocular information about the orientation of an object in the depth plane for perceptual and visuomotor purposes. A square plaque was presented at seven different orientations in depth to D.F. and to three age- and sex-matched control subjects. Subjects were required to reach out and grasp the plaque using a precision grip (index finger and thumb) under binocular and monocular viewing conditions, and in separate trials to match the orientation of a hand-held plaque to the perceived orientation of the target object, also under both binocular and monocular conditions. D.F.'s performance in grasping trials was found to be normal under binocular conditions, but was substantially worsened by removal of binocular vision. She was severely impaired at matching the orientation of the test square, although under binocular conditions her performance rose clearly above chance. The data suggest that the separation of cortical processing for visuomotor and visual perceptual purposes also applies, at least in part, to information about the orientation in depth of an object. The impaired performance under monocular viewing conditions on the visuomotor task is in agreement with recent physiological data and suggests that posterior parietal systems depend critically on binocular input for the processing of orientation in depth when ventral-stream information is unavailable. [ABSTRACT FROM AUTHOR]

In frogs, each lobe of the midbrain optic tectum receives two spatially aligned maps of binocular visual space, one through each eye. The map from the contralateral eye is the product of direct retinal input to the tectum, while that from the ipsilateral eye is mediated by a commissural system of connections that relays binocular visual information from one tectal lobe to the other. In Xenopus laevis, dark-reared from early life, the visuotectal map through the ipsilateral eye exhibits significant signs of disorder indicating that the normal development of the underlying 'intertectal' system involves experience-dependent processes. Here we investigate the potential of this system for recovery from such deprivation-induced disruption. Three groups of animals were first dark-reared from embryonic stages until 3 months, 12 months or 2 years after metamorphosis. These short-, medium-and long-term periods of visual deprivation are associated with a progressive disturbance of the intertectal system (Grant and Keating 1989b). The animals then experienced 12-18 months in a normal visual environment, before an electrophysiological mapping experiment was carried out to reveal the status of their intertectal system. Quantitative analyses of the visuotopic order in the ipsilateral visuotectal map and of its spatial alignment with the map derived from the contralateral eye revealed that these features were completely normal in all 3 experimental groups. It is concluded that defects present in the intertectal system of dark-reared Xenopus can be repaired by subsequent visual experience, and that the reparative capacity is not limited either by the animal's age or by the existing degree of prior disruption. [ABSTRACT FROM AUTHOR]

Binocular visual responses can be recorded in two regions of the superficial layers of the superior colliculus of the opossum. The direct binocular region (DBR) represents the binocular portion of the contralateral hemifield whereas the rostral pole (RP) represents the binocular portion of the ipsilateral hemifield. In the present study single units from both of these regions were tested with binocular and monocular stimulation. Most cells in both regions showed response facilitation when both eyes were simultaneously stimulated and, when tested with different binocular disparities, most cells showed broadly-tuned disparity selectivity. DBR units usually preferred disparities near zero whereas RP units had a wider range of preferred disparities, with a tendency toward positive (crossed) values. This data indicates that the superior colliculus of the opossum could provide a neural substrate for a coarse analysis of depth and also might help control vergence eye movements. The different ranges of disparity selectivity of DBR and RP are consistent with the previously reported monocular receptive-field data and suggest that DBR and RP analyze different depths of the 3-dimensional visual scene. [ABSTRACT FROM AUTHOR]

The concept of corresponding retinal points was examined in terms of the binocular receptive fields of neurons in Area 17 of the cerebral cortex of the cat. Only a proportion of the binocular receptive field pairs can be accurately superimposed at the one time in a given plane. The fields which are not corresponding are said to show receptive field disparity. The attempt has been made to establish, on a quantitative basis, the parameters of the receptive field disparities that occur within 5° of the visual axis. A new method was used for defining the zero (vertical) meridian. Very effective paralysis of the extraocular muscles was achieved and the very small residual eye movements that occurred were regularly monitored so that corrections could be applied to the plotted positions of the receptive field pairs. The distribution of the receptive field disparities about the position of maximal correspondence has a range of about ±1.2° (S.D. 0.6°) in both the horizontal and vertical directions for fields in the vicinity of the visual axis. Panum's fusional area may represent the extent to which receptive fields in the one eye, all with the same visual direction, are linked to fellow members of a pair in the other eye over a range of receptive field disparities. A naso-temporal overlap of receptive fields occurs which is probably little if any more than can be accounted for on the basis of the disparity of receptive fields lying along the zero (vertical) meridian. When the extraocular muscles are paralyzed the eyes diverge and the binocular receptive field pairs are separated on the tangent screen. The distribution of the horizontal and vertical separations of the receptive field pairs have been examined. [ABSTRACT FROM AUTHOR]