Segment interdependency and gaze anchoring during manual two-segment sequences

Abstract

This study examined two-segment pointing movements with various accuracy constraints to test whether there is segment interdependency in saccadic eye movements that accompany manual actions. The other purpose was to examine how planning of movement accuracy and amplitude for the second pointing influences the timing of gaze shift to the second target at the transition between two segments. Participants performed a rapid two-segment pointing task, in which the first segment had two target sizes, and the second segment had two target sizes and two movement distances. The results showed that duration and peak velocity of the initial pointing were influenced by altered kinematic characteristics of the second pointing due to task manipulations of the second segment, revealing segment interdependency in hand movements. In contrast, saccade duration and velocity did not show such segment interdependency. Thus, unlike hand movements, saccades are planned and organized independently for each segment during sequential manual actions. In terms of the timing of gaze shift to the second target, this was delayed when the initial pointing was made to the smaller first target, indicating that gaze anchoring to the initial target is used to verify the pointing termination. Importantly, the gaze shift was delayed when the second pointing was made to the smaller or farther second target. This suggests that visual information of the hand position at the initial target is important for the planning of movement distance and accuracy of the next pointing. Furthermore, timings of gaze shift and pointing initiation to the second target were highly correlated. Thus, at the transition between two segments, gazes and hand movements are highly coupled in time, which allows the sensorimotor system to process visual and proprioceptive information for the verification of pointing termination and planning of the next pointing.

Movement segmentation and visual perturbation increase developmental differences in motor control and learning

“…According to the optimized sub‐movement model, the primary sub‐movement of a rapid aiming movement is under central control, and the secondary sub‐movement relies upon visual feedback (Meyer, Abrams, Kornblum, Wright, & Smith, ). In a two‐segment movement task, vision guides the hand to the target, verifies the movement's completion and prepares the movement to the next target (Rand, ). However, the prefrontal cortex and its connections with the cortical and subcortical regions, which are thought to play essential roles in top–down cognitive control, continue to develop during the first two decades of life (Gogtay et al, ; Hwang et al, ; Mills et al, ; Somerville et al, ).…”

“…It has been observed that changing the difficulty of one movement segment influences the entire movement sequence, which indicates that our central nervous system accounts for the features of both segments in the planning or organisation of a movement sequence (Adam et al, ; Rand et al, ). Moreover, planning of the entire movement sequence becomes more difficult if the first movement segment is more difficult (Rand, ) or if the participants are older (Rand & Stelmach, ). Childhood is a critical period for brain development, but few studies have examined the control and learning of two‐segment movements in children.…”

“…In contrast, children of 7–8 years of age can learn visual–motor mapping, but they make more corrective movements when performing the mirror‐drawing tasks (Julius & Adi‐Japha, ). Visual feedback guides the hand to the target and allows the performer to plan the next target‐pointing movement in the two‐segment movement (Rand, ; Rand & Stelmach, ). However, little is known about the effects of visual perturbation on the control and learning of a two‐segment arm movement from a developmental perspective.…”

Eye-Hand Coordination during Visuomotor Adaptation with Different Rotation Angles: Effects of Terminal Visual Feedback

“…Eye movements were differentiated by using a two-point central-difference algorithm to obtain velocity. Onset and offset of the initial saccade immediately after the target presentation were determined using a threshold criterion of 20 cm/s in the velocity profile [8,11,12]. The results of this automatic procedure were inspected and corrected manually as needed based on visual inspection; 27.7% (onset) and 22.8% (offset) of all analyzed trials were corrected.…”

“…This gaze behavior (called gaze anchoring [10]) is useful to control reaching movement, especially during the homing-in phase, because it places the visual target in fovea as the hand approaches to the target, while temporally removing the added burden of spatial updating for gaze shift [13]. Functionally, it allows for effective use of visual feedback of both the target and the approaching hand to guide and complete a precise reaching movement [11,12,14,15]. …”