Binocular advantage for prehension movements performed in visually enriched environments requiring visual search

Targeted reaching with monocular depth information and haptic feedback: Comparing between monocular patients and normally sighted observers

Monocular blindness impairs visual depth perception, yet patients seldom report difficulties in targeted actions like reaching, walking, or driving. We hypothesized that by utilizing monocular depth information and calibrating actions with haptic feedback, monocular patients can perceive egocentric distance and perform targeted actions. We compared targeted reaching in monocular patients, monocular-viewing, and binocular-viewing normal controls. Sixty observers reached either a far or a near target, calibrating reaches to the near target with accurate or false feedback while leaving reaches to the far target uncalibrated. Reaching accuracy and precision were analyzed. Results indicated no difference in reaching accuracy between monocular patients and normal controls; all groups initially underestimated distances before until calibration. Monocular patients responded to calibration sensitively, achieving accuracy in calibrated reaches and generalizing this effect to uncalibrated distances. Thus, with monocular depth information and haptic feedback, monocular patients could perceive distance and accomplish targeted reaching.

The role of binocular vision in the control and development of visually guided upper limb movements

Vision provides a key sensory input for the performance of fine motor skills, which are fundamentally important to daily life activities, as well as skilled occupational and recreational performance. Binocular visual function is a crucial aspect of vision that requires the ability to combine inputs from both eyes into a unified percept. Summation and fusion are two aspects of binocular processing associated with performance advantages, including more efficient visuomotor control of upper limb movements. This paper uses the multiple processes model of limb control to explore how binocular viewing could facilitate the planning and execution of prehension movements in adults and typically developing children. Insight into the contribution of binocularity to visuomotor control also comes from examining motor performance in individuals with amblyopia, a condition characterized by reduced visual acuity and poor binocular function. Overall, research in this field has advanced our understanding of the role of binocular vision in the development and performance of visuomotor skills, the first step towards developing assessment tools and targeted rehabilitation for children with neurodevelopment disorders at risk of poor visuomotor outcomes. This article is part of a discussion meeting issue 'New approaches to 3D vision'.

Binocular Viewing Facilitates Size Constancy for Grasping and Manual Estimation

A prerequisite for efficient prehension is the ability to estimate an object’s distance and size. While most studies demonstrate that binocular viewing is associated with a more efficient grasp programming and execution compared to monocular viewing, the factors contributing to this advantage are not fully understood. Here, we examined how binocular vision facilitates grasp scaling using two tasks: prehension and manual size estimation. Participants (n = 30) were asked to either reach and grasp an object or to provide an estimate of an object’s size using their thumb and index finger. The objects were cylinders with a diameter of 0.5, 1.0, or 1.5 cm placed at three distances along the midline (40, 42, or 44 cm). Results from a linear regression analysis relating grip aperture to object size revealed that grip scaling during monocular viewing was reduced similarly for both grasping and estimation tasks. Additional analysis revealed that participants adopted a larger safety margin for grasping during monocular compared to binocular viewing, suggesting that monocular depth cues do not provide sufficient information about an object’s properties, which consequently leads to a less efficient grasp execution.

Stereopsis contributes to the predictive control of grip forces during prehension

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.

The effect of three-dimensional visualisation on performance in endoscopic sinus surgery: A clinical training study using surgical navigation for movement analysis in a randomised crossover design

OBJECTIVES

Endoscopic imaging techniques and endoscopic endonasal surgery (EES) expertise have evolved rapidly. Only few studies have assessed the effect of three-dimensional (3D) endoscopy on endoscopic sinus surgery (ESS). The present study aimed to objectively and subjectively assess the additional value of 3D high-definition (HD) endoscopy in ESS.

DESIGN

A randomized crossover study of endoscopic surgery performance, using five ESS tasks of varying complexity, performed on Thiel embalmed human specimens.

SETTING

Simulated surgical environment.

PARTICIPANTS

Thirty participants, inexperienced in ESS.

MAIN OUTCOME MEASURES

Performance was assessed using video imaging, surgical navigation and questionnaires. Main outcome measures were as follows: efficiency (defined by time to task completion), distance covered inside the nose, average velocity towards target, accuracy (measured by error rate), and subjective assessment of endoscope characteristics.

RESULTS

During ESS tasks, both efficiency and accuracy did not differ significantly between 2D HD and 3D HD endoscopy. Subjectively, imaging characteristics of the 3D HD endoscope were rated significantly better.

CONCLUSIONS

ESS performance of inexperienced participants was not significantly improved by the use of 3D HD endoscopy during ESS tasks, although imaging characteristics of the 3D HD endoscope were rated significantly better. Surgical field characteristics and surgical techniques are likely to influence any additional value of 3D HD endoscopy.

Some binocular advantages for planning reach, but not grasp, components of prehension

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.

Reading ability of children treated for amblyopia

Previous studies have reported compromised reading ability in children with amblyopia. Standardized psychoeducational test norms have not been used; therefore, the practical consequences of poor reading ability, such as eligibility for reading supports at school, have not been assessed. Furthermore, several studies have used atypical reading conditions such as monocular or distant viewing. It is also not clear how amblyopia treatment impacts reading ability. Thus, the goal of this study was to use standardized tests to compare binocular reading performance in children treated for amblyopia to that of a large normative sample, as well as to the types of control groups used in previous studies. Children treated for strabismic or anisometropic amblyopia (N = 14) were compared to children treated for strabismus without amblyopia (N = 12) and to children with healthy vision (N = 39). Visual acuity, stereoacuity, interocular suppression, intellectual functioning, oral single-word reading (TOWRE-2), and oral paragraph reading (GORT-5) were assessed. The control group showed significantly higher single-word reading accuracy than the amblyopia and strabismus groups. However, mean performance for all groups was within the average range of the normative sample. While mean scores were in the average range, six children (four amblyopia, two strabismus) performed below average on the single-word reading task; four of these children also showed below average paragraph reading. Reading scores were not correlated with visual acuity in the patient groups. The results raise the possibility that both strabismus and amblyopia can disrupt reading ability, even following successful treatment, to an extent that might benefit from reading supports at school.

The role of somatosensory input in target localization during binocular and monocular viewing while performing a high precision reaching and placement task

Binocular vision provides the most accurate and precise depth information; however, many people have impairments in binocular visual function. It is possible that other sensory inputs could be used to obtain reliable depth information when binocular vision is not available. However, it is currently unknown whether depth information from another modality improves target localization in depth during action execution. Therefore, the goal of this study was to assess whether somatosensory input improves target localization during the performance of a precision placement task. Visually normal young adults (n = 15) performed a bead threading task during binocular and monocular viewing in two experimental conditions where needle location was specified by 1) vision only, or 2) vision and somatosensory input, which was provided by the non-dominant limb. Performance on the task was assessed using spatial and temporal kinematic measures. In accordance with the hypothesis, results showed that the interval spent placing the bead on the needle was significantly shorter during monocular viewing when somatosensory input was available in comparison to a vision only condition. In contrast, results showed no evidence to support that somatosensory input about the needle location affects trajectory control. These findings demonstrate that the central nervous system relies predominately on visual input during reach execution, however, somatosensory input can be used to facilitate the performance of the precision placement task.

Stereopsis: are we assessing it in enough depth?

The assessment of stereoacuity is an integral part of the ophthalmic assessment, with the responses used to inform clinical management decisions. Stereoacuity impacts on many aspects of life, but there are discrepancies reported where people without measurable stereoacuity report appreciating 3-D vision. This could be due, in part, to the presentation of the stimuli. A literature review was undertaken to evaluate current assessment techniques, how they relate to patient outcomes, identify the limitations of current tests and discuss how they could be improved. Recent evidence has been collated on currently available tests, used commonly within vision clinics, with normative data provided allowing responses to the tests to be interpreted. The relevance of the results is evaluated in relation to a range of outcomes, where a reduced level of stereopsis has a negative impact on the ability of an individual to perform many tasks, and can lead to an increase in difficulty interacting in the world. Current tests are limited in the aspects of stereoacuity they assess and their ability to precisely measure stereopsis. The world is not static, yet clinical tests are limited to measuring static stereoacuity, even though higher grades of depth perception can be identified in the presence of changing depth. Presentation methods of stereoacuity tests have remained similar over time, with a limited number of disparity levels assessed. New assessment methods are becoming available that include automated staircase testing to present multiple levels of disparity using digital technology. Current clinical tests are limited in their presentation, and are poor at detecting/measuring stereoacuity in those with limited stereopsis. Given the relevance of the stereoacuity measurement to management choices and functional outcomes, new testing methods would be beneficial to fully assess stereoacuity, both static and dynamic.

Evaluation of the Leap Motion Controller during the performance of visually-guided upper limb movements

Kinematic analysis of upper limb reaching provides insight into the central nervous system control of movements. Until recently, kinematic examination of motor control has been limited to studies conducted in traditional research laboratories because motion capture equipment used for data collection is not easily portable and expensive. A recently developed markerless system, the Leap Motion Controller (LMC), is a portable and inexpensive tracking device that allows recording of 3D hand and finger position. The main goal of this study was to assess the concurrent reliability and validity of the LMC as compared to the Optotrak, a criterion-standard motion capture system, for measures of temporal accuracy and peak velocity during the performance of upper limb, visually-guided movements. In experiment 1, 14 participants executed aiming movements to visual targets presented on a computer monitor. Bland-Altman analysis was conducted to assess the validity and limits of agreement for measures of temporal accuracy (movement time, duration of deceleration interval), peak velocity, and spatial accuracy (endpoint accuracy). In addition, a one-sample t-test was used to test the hypothesis that the error difference between measures obtained from Optotrak and LMC is zero. In experiment 2, 15 participants performed a Fitts’ type aiming task in order to assess whether the LMC is capable of assessing a well-known speed-accuracy trade-off relationship. Experiment 3 assessed the temporal coordination pattern during the performance of a sequence consisting of a reaching, grasping, and placement task in 15 participants. Results from the t-test showed that the error difference in temporal measures was significantly different from zero. Based on the results from the 3 experiments, the average temporal error in movement time was 40±44 ms, and the error in peak velocity was 0.024±0.103 m/s. The limits of agreement between the LMC and Optotrak for spatial accuracy measures ranged between 2–5 cm. Although the LMC system is a low-cost, highly portable system, which could facilitate collection of kinematic data outside of the traditional laboratory settings, the temporal and spatial errors may limit the use of the device in some settings.

Object-Tool-Actor Interaction: Object Information Drives Intended Action

Tool use is typically explored via actor-tool interactions. However, the target-object (that which is being acted on) may influence perceived action possibilities and thereby guide action. Three different tool-target-object pairings were tested (Experiment 1). The hammering action demonstrated the greatest sensitivity and therefore subsequently used to further investigate target-object pairings. The hammer was removed as an option and instructions were provided using pictorial (Experiment 2), written (Experiment 3), and both pictorial and written formats (Experiment 4). The designed tool is chosen when available (Experiment 1) and when removed as a choice (i.e., the hammer), participants perform the same action associated with the designed tool (i.e., hammering) regardless of instruction method (Experiments 2, 3, and 4).

Contribution of binocular vision to the performance of complex manipulation tasks in 5-13years old visually-normal children

Individual studies have shown that visuomotor coordination and aspects of binocular vision, such as stereoacuity and dynamic vergence control, continue to improve in normally developing children between birth and early teenage years. However, no study has systematically addressed the relationship between the development of binocular vision and fine manipulation skills. Thus, the aim of this cross-sectional study was to characterize performance of complex manipulation tasks during binocular and monocular viewing. Fifty-two children, between 5 and 13years old, performed 2 manipulation tasks: peg-board and bead-threading under randomized viewing conditions. Results showed that binocular viewing was associated with a significantly greater improvement in performance on the bead-threading task in comparison to the peg-board task and the youngest children showed the greatest decrement in task performance under the monocular viewing condition when performing the bead-threading task. Thus, the role of binocular vision in performance of fine manipulation skills is both task- and age-dependent. These findings have implications for assessment of visuomotor skills in children with abnormal binocular vision, which occurs in 2-3% of otherwise typically developing children.