Binocular information in the control of prehensile movements in multiple-object scenes

Recent evidence suggests that the visual control of prehension may be less dependent on binocular information than has previously been thought. Studies investigating this question, however, have generally only examined reaches to single objects presented in isolation, even though natural prehensile movements are typically directed at objects in cluttered scenes which contain many objects. The present study was designed, therefore, to assess the contribution of binocular information to the control of prehensile movements in multiple-object scenes. Subjects reached for and grasped objects presented either in isolation or in the presence of one, two or four additional 'flanking' objects, under binocular and monocular viewing conditions. So that the role of binocular information could be clearly determined, subjects made reaches both in the absence of a visible scene around the target objects (self-illuminated objects presented in the dark) and under normal ambient lighting conditions. Analysis of kinematic parameters indicated that the removal of binocular information did not significantly affect many of the major indices of the transport component, including peak wrist velocity. However, peak grip apertures increased and subjects spent more time in the final slow phase of movement, prior to grasping the object, during monocularly guided reaches. The dissociation between effects of binocular versus monocular viewing on transport and grasp parameters was observed irrespective of the presence of flanking objects. These results therefore further question the view that binocular vision is pre-eminent in the control of natural prehensile movements.     

Binocular cues and the control of prehension

The present study was designed to assess the importance of binocular information (i.e. binocular disparity and angle of convergence) in the control of prehension. Previous studies which have addressed this question have typically used the same experimental manipulation: comparing prehensile movements executed either under binocular conditions to those executed when one eye was occluded (monocular). However this may not be the correct comparison as in addition to depriving the subject of binocular depth cues. it also deprives the subject of any visual information in one eye. Therefore we determined the prehensile performance when the subject viewed the target object and scene with either (i) two different views (binocular), (ii) two identical views (bi-ocular), or (iii) one view only (monocular). Overall, the qualitative and quantitative performance in the bi-ocular and monocular control conditions was very similar on all the main measures (and different from the performance in the binocular condition). We conclude that the deficits in performance observed found for 'monocular' reaches should be attributed to the lack of local depth information specified by the binocular cues. In addition we speculate that convergence angle and binocular disparity, although involved in both the pre-movement and movement-execution phases of the reach, the cues may be weighted differently in both phases of a prehension movement depending on the behavioural strategy involved.     

Quality of Visual Cue Affects Visual Reweighting in Quiet Standing

Sensory reweighting is a characteristic of postural control functioning adopted to accommodate environmental changes. The use of mono or binocular cues induces visual reduction/increment of moving room influences on postural sway, suggesting a visual reweighting due to the quality of available sensory cues. Because in our previous study visual conditions were set before each trial, participants could adjust the weight of the different sensory systems in an anticipatory manner based upon the reduction in quality of the visual information. Nevertheless, in daily situations this adjustment is a dynamical process and occurs during ongoing movement. The purpose of this study was to examine the effect of visual transitions in the coupling between visual information and body sway in two different distances from the front wall of a moving room. Eleven young adults stood upright inside of a moving room in two distances (75 and 150 cm) wearing a liquid crystal lenses goggles, which allow individual lenses transition from opaque to transparent and vice-versa. Participants stood still during five minutes for each trial and the lenses status changed every one minute (no vision to binocular vision, no vision to monocular vision, binocular vision to monocular vision, and vice-versa). Results showed that farther distance and monocular vision reduced the effect of visual manipulation on postural sway. The effect of visual transition was condition dependent, with a stronger effect when transitions involved binocular vision than monocular vision. Based upon these results, we conclude that the increased distance from the front wall of the room reduced the effect of visual manipulation on postural sway and that sensory reweighting is stimulus quality dependent, with binocular vision producing a much stronger down/up-weighting than monocular vision.     

The role of binocular information in the 'on-line' control of prehension

Binocular visual information may be involved in the selection of appropriate motor programs before a reach is executed or it may be involved during the movement-execution phase in order to monitor and guide the hand to the target object. Here we introduced binocular information after 0%, 25%, 50% or 75% of the movement-execution phase and determined its effects on the kinematic indices of prehensile movements made to objects of different sizes placed at different distances. Kinematic indices linked to the transport component, such as peak velocity and time-to-peak velocity, were unaffected by the presence of binocular cues whereas later occurring indices, such as peak grip aperture and time in the slow phase, were significantly affected. Although the magnitude of the peak grip was affected by the presence of binocular cues, the time at which it occurred did not change. This pattern of results suggest that the visuo-motor control of prehensile movements utilises both feedforward and feedback strategies and that binocular cues are particularly important for the fine manual adjustments typical of the latter.     

Depth resolution in the pigeon

Summary Pigeons possess a binocular visual field and a retinal region of higher cellular density pointing to the center of this overlap. These features and the precision of pecking behavior suggest that in this lateral-eyed bird cues other than monocular ones might participate in depth judgements.Pigeons were trained with an operant procedure to discriminate between luminous points differing in depth which appeared to the observer as floating in the dark. The accuracy of depth judgements was found to be a function of the ratio between the interstimulus distance and the mean eyes-to-stimulus distance. In a first test (experiment I) no external binocular disparity cues were available, the animal only seeing one luminous point at a time (near or far). In a second test (experiment II) where binocular disparity cues were available, the animal having this time to discriminate a pair of points placed at equal depth from a pair placed at unequal depths, only one pair being visible at a time, depth resolution did not improve. This suggests that, at least within the range of distances explored, the pigeon has no stereoscopic vision. Notwithstanding this, binocular cues do play a role, since when tests were done comparing binocular with monocular viewing (experiment III), monocular depth resolution was significantly worse.     

Depth generalization from stereo to motion parallax in the owl

Although many sources of three-dimensional information have been isolated and demonstrated to contribute independently, to depth vision in animal studies, it is not clear whether these distinct cues are perceived to be perceptually equivalent. Such ability is observed in humans and would seem to be advantageous for animals as well in coping with the often co-varying (or ambiguous) information about the layout of physical space. We introduce the expression primary-depth-cue equivalence to refer to the ability to perceive mutually consistent information about differences in depth from either stereopsis or motion-parallax. We found that owls trained to detect relative depth as a perceptual category (objects versus holes) when specified by binocular disparity alone (stereopsis), immediately transferred this discrimination to novel stimuli where the equivalent depth categories were available only through differences in motion information produced by head movements (observer-produced motion-parallax). Motion-parallax discrimination did occur under monocular viewing conditions and reliable performance depended heavily on the amplitude of side-to-side head movements. The presence of primary-depth-cue equivalence in the visual system of the owl provides further conformation of the hypothesis that neural systems evolved to detect differences in either disparity or motion information are likely to share similar processing mechanisms.     

Visual cortical responses to the input from the amblyopic eye are suppressed during binocular viewing

Amblyopia is a visual disorder caused by an anomalous early visual experience. It has been suggested that suppression of the visual input from the weaker eye might be a primary underlying mechanism of the amblyopic syndrome. However, it is still an unresolved question to what extent neural responses to the visual information coming from the amblyopic eye are suppressed during binocular viewing. To address this question we measured event-related potentials (ERP) to foveal face stimuli in amblyopic patients, both in monocular and binocular viewing conditions. The results revealed no difference in the amplitude and latency of early components of the ERP responses between the binocular and fellow eye stimulation. On the other hand, early ERP components were reduced and delayed in the case of monocular stimulation of the amblyopic eye as compared to the fellow eye stimulation or to binocular viewing. The magnitude of the amblyopic effect measured on the ERP amplitudes was comparable to that found on the fMRI responses in the fusiform face area using the same face stimuli and task conditions. Our findings showing that the amblyopic effects present on the early ERP components in the case of monocular stimulation are not manifested in the ERP responses during binocular viewing suggest that input from the amblyopic eye is completely suppressed already at the earliest stages of visual cortical processing when stimuli are viewed by both eyes.     

The effect of binocular and monocular viewing conditions on performance of rats in the Morris water maze

The visually guided behaviour in the Morris water maze (using distal extramaze cues for navigation to a small invisible platform in a large pool of opaque water) was analyzed by comparing monocular and binocular performance of hooded rats in various versions of this task. A dish-shaped metal foil occluder connected to a carrier fixed to the frontal bones was used to restrict vision to one eye. Acquisition of the water maze task with one eye occluded proceeded at the same rate as with both eyes open. There was no difference in the transfer from binocular to monocular and from monocular to binocular viewing. Retrieval of the monocularly acquired habit was equally efficient with the same as with the contralateral eye. Similar results were obtained in naive and overtrained rats. In the working memory version of the task, rats received a single acquisition trial with a new position of the escape platform followed after a delay of 2, 5, 20 or 40 min by a single retrieval trial. Performance deteriorated with increasing delay faster under interocular transfer conditions then when the same eye was used in both trials. No signs of ocular dominance were found in this task. It is concluded that successful place learning is little affected by monocular or binocular viewing conditions, but that monocular impairment becomes apparent when the difficulty of the task is increased.     

The role of cutaneous feedback for anticipatory grip force adjustments during object movements and externally imposed variation of the direction of gravity

Grip force adjustments to changes of object loading induced by external changes of the direction of gravity during discrete arm movements with a grasped object were analyzed during normal and anesthetized finger sensibility. Two subjects were seated upright in a rotatable chair and rotated backwards into a horizontal position during discrete movements with a hand-held instrumented object. The movement direction varied from vertical to horizontal inducing corresponding changes in the direction of gravity, but the orientation of the movement in relation to the body remained unaffected. During discrete vertical movements a maximum of load force occurs early in upward and late in downward movements; during horizontal movements two load force peaks result from both acceleratory and deceleratory phases of the movement. During performance with normal finger sensibility grip force was modulated in parallel with fluctuations of load force during vertical and horizontal movements. The grip force profile adopted to the varying load force profile during the transition from the vertical to the horizontal position. The maximum grip force occurred at the same time of maximum load force irrespective of the movement plane. During both subjects' first experience of digital anesthesia the object slipped from the grasp during rotation to the horizontal plane. During the following trials with anesthetized fingers subjects substantially increased their grip forces, resulting in elevated force ratios between maximum grip and load force. However, grip force was still modulated with the movement-induced load fluctuations and maximum grip force coincided with maximum load force during vertical and horizontal movements. This implies that the elevated force ratio between maximum grip and load force does not alter the feedforward system of grip force control. Cutaneous afferent information from the grasping digits seems to be important for the economic scaling of the grip force magnitude according to the actual loading conditions and for reactive grip force adjustments in response to load perturbations. However, it plays a subordinate role for the precise anticipatory temporal coupling between grip and load forces during voluntary object manipulation.     

The role of cutaneous feedback for anticipatory grip force adjustments during object movements and externally imposed variation of the direction of gravity

Grip force adjustments to changes of object loading induced by external changes of the direction of gravity during discrete arm movements with a grasped object were analyzed during normal and anesthetized finger sensibility. Two subjects were seated upright in a rotatable chair and rotated backwards into a horizontal position during discrete movements with a hand-held instrumented object. The movement direction varied from vertical to horizontal inducing corresponding changes in the direction of gravity, but the orientation of the movement in relation to the body remained unaffected. During discrete vertical movements a maximum of load force occurs early in upward and late in downward movements; during horizontal movements two load force peaks result from both acceleratory and deceleratory phases of the movement. During performance with normal finger sensibility grip force was modulated in parallel with fluctuations of load force during vertical and horizontal movements. The grip force profile adopted to the varying load force profile during the transition from the vertical to the horizontal position. The maximum grip force occurred at the same time of maximum load force irrespective of the movement plane. During both subjects' first experience of digital anesthesia the object slipped from the grasp during rotation to the horizontal plane. During the following trials with anesthetized fingers subjects substantially increased their grip forces, resulting in elevated force ratios between maximum grip and load force. However, grip force was still modulated with the movement-induced load fluctuations and maximum grip force coincided with maximum load force during vertical and horizontal movements. This implies that the elevated force ratio between maximum grip and load force does not alter the feedforward system of grip force control. Cutaneous afferent information from the grasping digits seems to be important for the economic scaling of the grip force magnitude according to the actual loading conditions and for reactive grip force adjustments in response to load perturbations. However, it plays a subordinate role for the precise anticipatory temporal coupling between grip and load forces during voluntary object manipulation.     

Binocular single vision and perceptual processing.

Stimuli with small binocular disparities are seen as single, despite their differing visual directions for the two eyes. Such stimuli also yield stereopsis, but stereopsis and single vision can be dissociated. The occurrence of binocular single vision depends not only on the disparities of individual stimulus elements, but also on the geometrical relation of different parts of the pattern presented to each eye. A pair of vertical bars with opposite binocular disparities is seen as single if the pair is moderately widely spaced but not if it is narrow. Vertical alignment and identity in length of such bars also increase the occurrence of double vision. It is argued that these effects reflect the extraction of features of the monocular patterns, with these detected monocular features determining the binocular percept. Single and double vision of bars differing in orientation can be similarly analysed. The occurrence of relatively elaborate processing of monocular signals does not exclude the possibility that binocular interaction can occur between signals that have not been so processed. Multiple sites or types of binocular interaction are likely.     

正常及异常双眼视觉的视动震颤（OKN）反应特性研究

为探讨不同双眼视觉状态下ＯＫＮ反应的特性,对正常人和不同类型的双眼视觉异常者的单眼鼻向及颞向ＯＫＮ反应进行了研究。实验发现：单眼视觉抑制者表现出鼻向与颞向ＯＫＮ反应不对称特性;两眼皆因视剥夺造成双眼视觉异常者主要以ＯＫＮ眼动增益降低为特点;双眼视觉正常者鼻、颞向ＯＫＮ反应是对称的。结果表明：单眼ＯＫＮ眼动反应的不对称特性及增益改变对探讨双眼视觉异常机制有重要意义,为视皮层双眼细胞异常导致单眼ＯＫＮ不对称的假设提供了支持性证据,并对弱视早期诊断及其分类有重要价值。     

Extrapolating and interpolating surfaces in depth

Random-dot stereograms were generated with a blank area placed in part of the right-hand image so making a patchwork of monocular and binocular areas. The perceived depth and shape of the monocular region, where depth was not explicitly marked, depended in part on the depth and surface orientation of adjacent binocular areas. Thus a monocular rectangle flanked by two binocular rectangles which were placed in different fronto-parallel planes was seen as a sloping surface spanning the depth between the binocular regions, and, under some conditions, the gradient of a sloping binocular plane extended into a neighbouring monocular area. Division of the monocular region into two by textural discontinuities or discontinuities of motion sometimes altered the shape of the extrapolated surface. Often, though, the shape was unchanged by such discontinuities implying that both two- and three-dimensional features are used to segment a scene into separate surfaces. Pictorial cues also contribute to the shape and apparent depth of the monocular surface. For instance, when subjects viewed a display consisting of portions of a cube of which two ends were shown stereoscopically and one side monocularly, the monocular side was seen in three dimensions filling the gap between the ends. When stereo cues were pitted against pictorial cues, sometimes pictorial cues and sometimes stereo cues dominated, and sometimes the surface contained sharp discontinuities enabling both to be accommodated.     

Relating Lateralization of Eye Use to Body Motion in the Avoidance Behavior of the Chameleon (Chamaeleo chameleon)

Lateralization is mostly analyzed for single traits, but seldom for two or more traits while performing a given task (e.g. object manipulation). We examined lateralization in eye use and in body motion that co-occur during avoidance behaviour of the common chameleon, Chamaeleo chameleon. A chameleon facing a moving threat smoothly repositions its body on the side of its perch distal to the threat, to minimize its visual exposure. We previously demonstrated that during the response (i) eye use and body motion were, each, lateralized at the tested group level (N = 26), (ii) in body motion, we observed two similar-sized sub-groups, one exhibiting a greater reduction in body exposure to threat approaching from the left and one – to threat approaching from the right (left- and right-biased subgroups), (iii) the left-biased sub-group exhibited weak lateralization of body exposure under binocular threat viewing and none under monocular viewing while the right-biased sub-group exhibited strong lateralization under both monocular and binocular threat viewing. In avoidance, how is eye use related to body motion at the entire group and at the sub-group levels? We demonstrate that (i) in the left-biased sub-group, eye use is not lateralized, (ii) in the right-biased sub-group, eye use is lateralized under binocular, but not monocular viewing of the threat, (iii) the dominance of the right-biased sub-group determines the lateralization of the entire group tested. We conclude that in chameleons, patterns of lateralization of visual function and body motion are inter-related at a subtle level. Presently, the patterns cannot be compared with humans'' or related to the unique visual system of chameleons, with highly independent eye movements, complete optic nerve decussation and relatively few inter-hemispheric commissures. We present a model to explain the possible inter-hemispheric differences in dominance in chameleons'' visual control of body motion during avoidance.     

Plasticity of monocular and binocular vision following cerebral blindness: evoked potential evidence

Using monocular and dynamic random dot correlogram (DRDC) stimuli, sequential visual evoked potentials changes were demonstrated in 2 patients following cerebral blindness. The recovery of binocular vision was delayed in comparison to the recovery of monocular vision. The results are not due to simple acuity impairment or convergence deficiency, and thus provide evidence for the vulnerability of postsynaptic cortical mechanisms of human binocular vision.     

The effect of sensory uncertainty due to amblyopia (lazy eye) on the planning and execution of visually-guided 3D reaching movements

Background

Impairment of spatiotemporal visual processing in amblyopia has been studied extensively, but its effects on visuomotor tasks have rarely been examined. Here, we investigate how visual deficits in amblyopia affect motor planning and online control of visually-guided, unconstrained reaching movements.

Methods

Thirteen patients with mild amblyopia, 13 with severe amblyopia and 13 visually-normal participants were recruited. Participants reached and touched a visual target during binocular and monocular viewing. Motor planning was assessed by examining spatial variability of the trajectory at 50–100 ms after movement onset. Online control was assessed by examining the endpoint variability and by calculating the coefficient of determination (R²) which correlates the spatial position of the limb during the movement to endpoint position.

Results

Patients with amblyopia had reduced precision of the motor plan in all viewing conditions as evidenced by increased variability of the reach early in the trajectory. Endpoint precision was comparable between patients with mild amblyopia and control participants. Patients with severe amblyopia had reduced endpoint precision along azimuth and elevation during amblyopic eye viewing only, and along the depth axis in all viewing conditions. In addition, they had significantly higher R² values at 70% of movement time along the elevation and depth axes during amblyopic eye viewing.

Conclusion

Sensory uncertainty due to amblyopia leads to reduced precision of the motor plan. The ability to implement online corrections depends on the severity of the visual deficit, viewing condition, and the axis of the reaching movement. Patients with mild amblyopia used online control effectively to compensate for the reduced precision of the motor plan. In contrast, patients with severe amblyopia were not able to use online control as effectively to amend the limb trajectory especially along the depth axis, which could be due to their abnormal stereopsis.     

Lateralized visual behavior in bottlenose dolphins (Tursiops truncatus) performing audio-visual tasks: the right visual field advantage

Analyzing cerebral asymmetries in various species helps in understanding brain organization. The left and right sides of the brain (lateralization) are involved in different cognitive and sensory functions. This study focuses on dolphin visual lateralization as expressed by spontaneous eye preference when performing a complex cognitive task; we examine lateralization when processing different visual stimuli displayed on an underwater touch-screen (two-dimensional figures, three-dimensional figures and dolphin/human video sequences). Three female bottlenose dolphins (Tursiops truncatus) were submitted to a 2-, 3- or 4-, choice visual/auditory discrimination problem, without any food reward: the subjects had to correctly match visual and acoustic stimuli together. In order to visualize and to touch the underwater target, the dolphins had to come close to the touch-screen and to position themselves using monocular vision (left or right eye) and/or binocular naso-ventral vision. The results showed an ability to associate simple visual forms and auditory information using an underwater touch-screen. Moreover, the subjects showed a spontaneous tendency to use monocular vision. Contrary to previous findings, our results did not clearly demonstrate right eye preference in spontaneous choice. However, the individuals' scores of correct answers were correlated with right eye vision, demonstrating the advantage of this visual field in visual information processing and suggesting a left hemispheric dominance. We also demonstrated that the nature of the presented visual stimulus does not seem to have any influence on the animals' monocular vision choice.     

Left hemispheric advantage for numerical abilities in the bottlenose dolphin

In a two-choice discrimination paradigm, a bottlenose dolphin discriminated relational dimensions between visual numerosity stimuli under monocular viewing conditions. After prior binocular acquisition of the task, two monocular test series with different number stimuli were conducted. In accordance with recent studies on visual lateralization in the bottlenose dolphin, our results revealed an overall advantage of the right visual field. Due to the complete decussation of the optic nerve fibers, this suggests a specialization of the left hemisphere for analysing relational features between stimuli as required in tests for numerical abilities. These processes are typically right hemisphere-based in other mammals (including humans) and birds. The present data provide further evidence for a general right visual field advantage in bottlenose dolphins for visual information processing. It is thus assumed that dolphins possess a unique functional architecture of their cerebral asymmetries.     

Visually targeted reaching in horse-head grasshoppers

Visually targeted reaching to a specific object is a demanding neuronal task requiring the translation of the location of the object from a two-dimensionsal set of retinotopic coordinates to a motor pattern that guides a limb to that point in three-dimensional space. This sensorimotor transformation has been intensively studied in mammals, but was not previously thought to occur in animals with smaller nervous systems such as insects. We studied horse-head grasshoppers (Orthoptera: Proscopididae) crossing gaps and found that visual inputs are sufficient for them to target their forelimbs to a foothold on the opposite side of the gap. High-speed video analysis showed that these reaches were targeted accurately and directly to footholds at different locations within the visual field through changes in forelimb trajectory and body position, and did not involve stereotyped searching movements. The proscopids estimated distant locations using peering to generate motion parallax, a monocular distance cue, but appeared to use binocular visual cues to estimate the distance of nearby footholds. Following occlusion of regions of binocular overlap, the proscopids resorted to peering to target reaches even to nearby locations. Monocular cues were sufficient for accurate targeting of the ipsilateral but not the contralateral forelimb. Thus, proscopids are capable not only of the sensorimotor transformations necessary for visually targeted reaching with their forelimbs but also of flexibly using different visual cues to target reaches.     

Perceived surface slant is systematically biased in the actively-generated optic flow

Humans make systematic errors in the 3D interpretation of the optic flow in both passive and active vision. These systematic distortions can be predicted by a biologically-inspired model which disregards self-motion information resulting from head movements (Caudek, Fantoni, & Domini 2011). Here, we tested two predictions of this model: (1) A plane that is stationary in an earth-fixed reference frame will be perceived as changing its slant if the movement of the observer's head causes a variation of the optic flow; (2) a surface that rotates in an earth-fixed reference frame will be perceived to be stationary, if the surface rotation is appropriately yoked to the head movement so as to generate a variation of the surface slant but not of the optic flow. Both predictions were corroborated by two experiments in which observers judged the perceived slant of a random-dot planar surface during egomotion. We found qualitatively similar biases for monocular and binocular viewing of the simulated surfaces, although, in principle, the simultaneous presence of disparity and motion cues allows for a veridical recovery of surface slant.