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When we catch a moving object in mid-flight, our eyes and hands are directed toward the object. Yet, the functional role of eye movements in guiding interceptive hand movements is not yet well understood. This review synthesizes emergent views on the importance of eye movements during manual interception with an emphasis on laboratory studies published since 2015. We discuss the role of eye movements in forming visual predictions about a moving object, and for enhancing the accuracy of interceptive hand movements through feedforward (extraretinal) and feedback (retinal) signals. We conclude by proposing a framework that defines the role of human eye movements for manual interception accuracy as a function of visual certainty and object motion predictability.

Patients with central vision loss (CVL) typically adopt eccentric viewing strategies using a preferred retinal locus (PRL) in peripheral retina. Clinically, the PRL is defined monocularly as the area of peripheral retina used to fixate small stimuli. It is not clear if this fixational PRL describes the same portion of peripheral retina used during dynamic binocular eye–hand coordination tasks. We studied this question with four participants each with a unique CVL history. Using a scanning laser ophthalmoscope, we measured participants’ monocular visual fields and the location and stability of their fixational PRLs. Participants’ monocular and binocular visual fields were also evaluated using a computer monitor and eye tracker. Lastly, eye–hand coordination was tested over several trials where participants pointed to and touched a small target on a touchscreen monitor. Trials were blocked and carried out monocularly and binocularly, with a target appearing at 5° or 15° from screen center, in one of 8 locations. During pointing, our participants often exhibited long movement durations, an increased number of eye movements and impaired accuracy, especially in monocular conditions. However, these compensatory changes in behavior did not consistently worsen when loci beyond the fixational PRL were used. While fixational PRL size, location and fixation stability provide a necessary description of behavior, they are not sufficient to capture the pointing PRL used in this task. Generally, patients use a larger portion of peripheral retina than one might expect from measures of the fixational PRL alone, when pointing to a salient target without time constraints. While the fixational and pointing PRLs often overlap, the fixational PRL does not predict the large area of peripheral retina that can be used.

Adults with a history of unilateral amblyopia and abnormal binocularity have a range of visual deficits, with some of the 'higher' levels ones generalizing to their dominant (non-amblyopic) eye and linked to widespread binocular cortical network dysfunctions. Our interests are in how these problems also impact on their hand action control in real-world situations. We investigated whether eye-hand coordination deficits, known to exist in amblyopia when goal objects are presented under full-lighting and at high contrast, are exacerbated under low object-background contrast or in dim lighting/low visibility conditions. Hand movement parameters were recorded and quantified in 13 amblyopia and 13 control subjects while they reached-to-precision grasp objects using both eyes together or just their dominant or amblyopic/non-dominant eye alone under these 3 task conditions. Compared to controls, the amblyopia subjects spent significantly longer in preparing their movements, in the initial (planned) periods of their reach and grasp and in applying their grip, while making more reach and grasp errors under all 3 views and tasks. Deficits in planning and controlling the grasp were also selectively accentuated in the low contrast condition, but with no evidence of relatively worse performance under low environmental illumination. We suggest that the dysfunctions in amblyopia are associated with generalized difficulties in obtaining reliable visual evidence about the target's 3D properties during movement planning and in selecting and guiding the proper course of action, especially when segregating the object from background is more challenging.

We investigated the precision of binocular gaze control while observers performed a high-precision manual movement, which involved hitting a target hole in a plate with a hand-held needle. Binocular eye movements and the 3D-position of the needle tip were tracked. In general the observers oriented their gaze to the target before they reached it with the needle. The amplitude of microsaccades scaled with the distance of the needle tip. We did not find evidence for the coordination of version and vergence during microsaccades which could be expected if those movements displaced gaze between the needle and the target hole. In a control experiment observers executed small saccades between marks on a slanted plane. Even when the observers executed saccades as small as the microsaccades in the needle experiment, we observed a coordinated displacement of the point of gaze on the horizontal and depth axis. Our results show that the characteristics of eye movements such as the frequency and amplitude of microsaccades are adapted online to the task demands. However, a coordinated control of version and vergence in small saccades is only observed if a movement of gaze on a slanted trajectory is explicitly instructed.

The contribution of binocular vision to the performance of reaching and grasping movements has been examined previously using single reach-to-grasp movements. However, most of our daily activities consist of more complex action sequences, which require precise temporal linking between the gaze behaviour and manual action phases. Many previous studies found a stereotypical hand-eye coordination pattern, such that the eyes move prior to the reach initiation. Moving the eyes to the target object provides information about its features and location, which can facilitate the predictive control of reaching and grasping. This temporal coordination pattern has been established for the performance of sequential movements performed during binocular viewing. Here we manipulated viewing condition and examined the temporal hand-eye coordination pattern during the performance of a sequential reaching, grasping, and placement task. Fifteen participants were tested on a sequencing task while eye and hand movements were recorded binocularly using a video-based eyetracker and a motion capture system. Our results showed that monocular viewing disrupted the temporal coordination between the eyes and the hand during the place-to-reach transition phase. Specifically, the gaze shift was delayed during monocular compared to binocular viewing. The shift in gaze behaviour may be due to increased uncertainty associated with the performance of the placement task because of increased vergence error during monocular viewing, which was evident in all participants. These findings provide insight into the role of binocular vision in predictive control of sequential reaching and grasping movements.

In animals with specialized foveae, eye position has a direct influence over the acquisition of detailed visual information. At the same time, eye movements executed during natural behaviors are closely linked with motor actions. In this study, we investigated patterns of eye movements during a simple visual discrimination task. Three rhesus monkeys learned to recognize images of real world objects with no explicit constraints on eye position. Analysis of the monkeys’ eye movements showed that although the endpoint of the initial saccade depended on the particular visual stimulus, the trajectory of the first saccades also reliably predicted the manual response associated with that stimulus. We thus observed that initial saccades executed in a recognition task reflect both perceptual and motor aspects of a visual task. This pattern of eye movements emerged spontaneously in all three animals tested despite the fact that saccades were never explicitly rewarded. As the average saccade latency was under 200 ms, object specific learned associations must have exerted their influence over the initial saccade even earlier, providing a novel temporal marker for the rapidity of visual recognition processes. Taken together, these results suggest that caution should be exercised when interpreting the meaning of oculomotor patterns observed during perceptual tasks, as these blur the line between perceptual processing and motor preparation.

Task influence has long been known to play a major role in the way our eyes scan a scene. Yet most studies focus either on visual search or on sequences of active tasks in complex real world scenarios. Few studies have contrasted the distribution of eye fixations during viewing and grasping objects. Here we address how attention is deployed when different actions are planned on objects, in contrast to when the same objects are categorized. In this respect, we are particularly interested in the role every fixation plays in the unfolding dynamics of action control. We conducted an eye-tracking experiment in which participants were shown images of real-world objects. Subjects were either to assign the displayed objects to one of two classes (categorization task), to mimic lifting (lifting task), or to mimic opening the object (opening task). Results suggest that even on simplified, two dimensional displays the eyes reveal the participant’s intentions in an anticipatory fashion. For the active tasks, already the second saccade after stimulus onset was directed towards the central region between the two locations where the thumb and the rest of the fingers would be placed. An analysis of saliency at fixation locations showed that fixations in active tasks have higher correspondence with salient features than fixations in the passive task. We suggest that attention flexibly coordinates visual selection for information retrieval and motor planning, working as a gateway between three components, linking the task (action), the object (target), and the effector (hand) in an effective way.

Ocular dominance is the tendency to prefer visual input from one eye to the other [e.g. Porac, C. & Coren, S. (1976). The dominant eye. Psychological Bulletin 83 (5), 880–897]. In standard sighting tests, most people consistently fall into either the left- or right eye-dominant category [Miles, W. R. (1930). Ocular dominance in human adults. Journal of General Psychology 3 , 412–420]. Here we show this static concept to be flawed, being based on the limited results of sighting with gaze pointed straight ahead. In a reach–grasp task for targets within the binocular visual field, subjects switched between left and right eye dominance depending on horizontal gaze angle. On average, ocular dominance switched at gaze angles of only 15.5° off center.

Reaching towards a visual object in the absence of visual referents relies on a chain of information, from the sensory signals encoding the object's image on the retina, to the motor signals driving the hand. One link in this chain is an extraretinal eye position signal (EEPS), which specifies the position of the eye in the head. EEPS must be updated in precise coordination with the eye's rapidly changing position, or perisaccadic visual targets will be mislocalized. There have been conflicting reports about the existence and nature of mislocalizations associated with saccades. We measured perisaccadic visual localization by presenting brief (250 microseconds), bright (6000 cd/m2), binocular, gaze-point (foveal) probe flashes in an otherwise dark field to normal human subjects instructed to point to them with an unseen hand. Saccade and fixation targets were auditory, making intravisual comparison impossible. Saccades, elicited randomly to left and right of straight ahead, had a mean magnitude of 8.9 deg. Control trials, employing only non-perisaccadic probes and providing feedback of pointing errors, were randomly interspersed, to monitor and control drift of hand-eye coordination. On average, localization began to shift for probes presented 2 msec after the eye began to move, reaching a stable post-saccadic value with time constant tau = 71 msec. A second experiment was similar, except that viewing was monocular, and probes were presented randomly, at gaze (on fovea), 6 deg left of gaze (right of fovea) and 6 deg right of gaze (left of fovea). The main analysis treated saccades larger than 8 deg: their mean magnitude was 12.9 deg. Flashes left of gaze were relocalized faster (tau = 65 msec) than flashes right of gaze (tau = 129 msec) around the time of leftward saccades. In contrast, flashes right of gaze were relocalized faster (tau = 62 msec) than flashes left of gaze (tau = 90 msec) around the time of rightward saccades. Time constant was independent of saccade size. Updating began for probes presented within 4 msec of the beginning of saccades, and was not a function of saccade or flash direction. Thus, there were no systematic mislocalizations of probes presented before eye movement, and large mislocalizations of probes presented during and after. Mislocalizations were, on average, always in the direction opposite the saccade, and were maximal (about half the magnitude of the completed saccade) near the end of the saccade. Stable post-saccadic localization was not achieved until about 100-300 msec after completion of a saccade; EEPS was updated slowly, compared to eye position itself. The visual field was not remapped uniformly: the side that would normally contain the target of a visually evoked saccade (and usually the target of a corrective saccade), was updated with a shorter time constant.

Monocular eye-hand coordination was tested in a pointing experiment in the central and peripheral visual field of each eye of strabismic and anisometropic amblyopes, strabismic alternators and normal controls. In the normal controls, pointing was accurate in the central visual field. Towards the periphery, normal observers showed a varying amount of undershoot as well as increasing uncertainty. The pointing pattern was similar in the two eyes of these subjects. Increased uncertainty of pointing responses was found in most amblyopic eyes as compared to the dominant eyes. Three strabismic amblyopes and one strabismic alternator also had systematic pointing errors (i.e. systematic differences between pointing under the control of the dominant as compared to the nondominant eye). The pointing pattern was not uniform across the visual field in some of the Strabismics, but was composed of areas of larger and smaller pointing errors. Larger pointing errors (i.e. larger differences between the dominant and nondominant eyes) were usually found in the central visual field. These errors were not closely related to the angle of squint. The clinical history of the strabismics seems to be an important factor for the occurrence of pointing errors.

When a peripheral visual stimulus is briefly presented in an empty surround, and an observer is required, after a delay of a few seconds, to point toward the remembered location of that target, the responses are strongly influenced by eye orientation at the time of pointing. Remembered locations, as indicated in total darkness, are typically more precise (more reproducible across trials) when the subject's eyes are aimed toward the target before pointing, than when initial fixation (straight ahead) is maintained during pointing. Furthermore, when the eyes are aimed toward the target, the indicated directions are usually biased toward less eccentric locations than those indicated with eyes aimed straight ahead. These differences in scatter and in bias arise regardless of whether the eye movement toward target location, which precedes pointing, is made while the target is visible or occurs thereafter in total darkness, thus demonstrating that non-visual stimuli associated with eye orientation affect the spatial memory used by the skeletal muscle system.

This article reviews the past 25 years of research on eye movements (1986–2011). Emphasis is on three oculomotor behaviors: gaze control, smooth pursuit and saccades, and on their interactions with vision. Focus over the past 25 years has remained on the fundamental and classical questions: What are the mechanisms that keep gaze stable with either stationary or moving targets? How does the motion of the image on the retina affect vision? Where do we look – and why – when performing a complex task? How can the world appear clear and stable despite continual movements of the eyes? The past 25 years of investigation of these questions has seen progress and transformations at all levels due to new approaches (behavioral, neural and theoretical) aimed at studying how eye movements cope with real-world visual and cognitive demands. The work has led to a better understanding of how prediction, learning and attention work with sensory signals to contribute to the effective operation of eye movements in visually rich environments.