The relative timing between eye and hand in rapid sequential pointing is affected by time pressure, but not by advance knowledge

Eye-hand coordination during sequential reaching to uncertain targets: the effect of task difficulty, target width, movement amplitude, and task scaling

When making reciprocal hand movements between two fixed/known targets, Fitts' law states that movement time (MT) is a linear function of the index of difficulty (ID) set by the ratio between movement amplitude (A) and target width (W). Crucially ID also impacts eye-hand coordination. However, because known/fixed targets limit the usefulness of eye movements, and because hand dynamics changes drastically with ID (either continuous or discrete), we reexamined this issue using a variant of the Fitts task in which the next target position was assigned randomly and unveiled only when the ongoing target was reached. Practically, hand and eye movements were recorded in participants (N = 25) who had to successively reach 12 circular targets of width W (0.3, 0.6, or 1.2 cm) separated by an amplitude A (5, 10, or 20 cm), allowing to examine IDs ranging from 2.36 to 6.08 bits. Introducing target uncertainty did not alleviate the linear relationship between MT and ID (R2 = 0.99), neither the impact of ID on hand kinematics. Importantly, the influence of ID on eye-hand coordination persisted. Notably, by cross-correlating eye and hand signals, we show a trade-off between its temporal and spatial aspects. Finally, we found that eye-hand coordination was influenced to a larger extent by A than W, making it prone to task scaling effects (differences in AW combinations resulting in similar ID). Altogether these results reinforce the critical role of task difficulty on eye-hand coordination and the need to simultaneously consider its temporal and spatial aspects.

Perception-action coupling during discriminative interceptive actions

Introduction

Interception is a complex task that requires the integration of perception and action under temporal constraints. Decision-making about whether to respond to moving stimuli involved in discriminative responses may further increase the cognitive load imposed on the performer, influencing perception-action coupling during interception. This study investigated the effects of discriminative response requirements on eye and hand movements, the coupling of perception and action, and the accuracy of responses during interceptive actions.

Methods

Twelve right-handed male participants performed interceptive actions to stimuli moving at three velocities (0.53 m/s, 0.66 m/s, 0.88 m/s) in discriminative (target-specific) and non-discriminative (target non-specific) conditions. While the non-discriminative condition required participants to respond to presented stimuli in all trials, the discriminative condition required them to respond to the stimulus moving toward a pre-defined target area.

Results

Timing errors were greater in the discriminative condition than the non-discriminative condition, and increased with increasing stimulus velocity. Both reaction and movement times decreased with increasing stimulus velocity, and the reaction times were longer in the discriminative condition than the non-discriminative condition. Variables representing the temporal aspects of interceptive actions, including saccadic latency, saccadic frequency, gaze duration, and temporal coupling of gaze and stimulus decreased with increasing stimulus velocity. Compared to the non-discriminative condition, saccadic frequency was higher, gaze duration was shorter, and the temporal coupling of gaze and stimulus was longer in the discriminative condition. Variables representing the spatial aspects of responses, including radial error, gaze error, and the spatial couplings of gaze and hand, however, remained unaffected by task conditions.

Conclusion

These findings suggest that decision-making about whether to respond to moving stimuli may impair the temporal accuracy of responses by delaying perception-action coupling without severe influences on the spatial coupling of eye and hand during interceptive actions.

Gaze control during reaching is flexibly modulated to optimize task outcome

When reaching for an object with the hand, the gaze is usually directed at the target. In a laboratory setting, fixation is strongly maintained at the reach target until the reaching is completed, a phenomenon known as "gaze anchoring." While conventional accounts of such tight eye-hand coordination have often emphasized the internal synergetic linkage between both motor systems, more recent optimal control theories regard motor coordination as the adaptive solution to task requirements. We here investigated to what degree gaze control during reaching is modulated by task demands. We adopted a gaze-anchoring paradigm in which participants had to reach for a target location. During the reach, they additionally had to make a saccadic eye movement to a salient visual cue presented at locations other than the target. We manipulated the task demands by independently changing reward contingencies for saccade reaction time (RT) and reaching accuracy. On average, both saccade RTs and reach error varied systematically with reward condition, with reach accuracy improving when the saccade was delayed. The distribution of the saccade RTs showed two types of eye movements: fast saccades with short RTs, and voluntary saccade with longer RTs. Increased reward for high reach accuracy reduced the probability of fast saccades but left their latency unchanged. The results suggest that gaze anchoring acts through a suppression of fast saccades, a mechanism that can be adaptively adjusted to the current task demands.NEW & NOTEWORTHY During visually guided reaching, our eyes usually fixate the target and saccades elsewhere are delayed ("gaze anchoring"). We here show that the degree of gaze anchoring is flexibly modulated by the reward contingencies of saccade latency and reach accuracy. Reach error became larger when saccades occurred earlier. These results suggest that early saccades are costly for reaching and the brain modulates inhibitory online coordination from the hand to the eye system depending on task requirements.

An exploratory study of gaze behaviour in young adults with developmental coordination disorder

Developmental Coordination Disorder (DCD) is characterized by substantial difficulties with motor coordination to the extent that it has a clear impact on the daily functioning of those who suffer from the disorder. Laboratory-based research indicated impaired oculomotor control in individuals with DCD. However, it is not clear how these oculomotor problems contribute to control and coordination in daily tasks. This study explored differences and similarities in gaze behaviour during reading and cup stacking between young adults with DCD and their matched typically developing counterparts (TD; aged 20-23 years). Gaze behaviour was recorded using eye-tracking, and hand movements were registered using a digital camera. Results of the reading tasks demonstrated similar behaviour between the groups, apart from a lower number of characters recorded per fixation in the DCD group. In cup stacking, the individuals with DCD were slower than their counterparts when three cups had to be displaced to a central target using the dominant hand. The gaze strategy of individuals with DCD involved systematic fixations on the cup or target prior to the hand movement to that cup or target, whereas these alternating saccades between cup and target were less obvious in the TD group. In the bimanual stacking task, where a pyramid of six cups had to be built on a central target using both hands, both groups mainly fixated the central target for the whole duration of the task, without distinct differences in gaze behaviour and duration of performance between individuals with and those without DCD. In conclusion, gaze behaviour of young adults with DCD shows differences from that of their typically developing counterparts that may be related to underlying oculomotor deficits in some but not all daily tasks.