Hierarchical control of two-dimensional gaze saccades

Abstract

Coordinating the movements of different body parts is a challenging process for the central nervous system because of several problems. Four of these main difficulties are: first, moving one part can move others; second, the parts can have different dynamics; third, some parts can have different motor goals; and fourth, some parts may be perturbed by outside forces. Here, we propose a novel approach for the control of linked systems with feedback loops for each part. The proximal parts have separate goals, but critically the most distal part has only the common goal. We apply this new control policy to eye-head coordination in two-dimensions, specifically head-unrestrained gaze saccades. Paradoxically, the hierarchical structure has controllers for the gaze and the head, but not for the eye (the most distal part). Our simulations demonstrate that the proposed control structure reproduces much of the published empirical data about gaze movements, e.g., it compensates for perturbations, accurately reaches goals for gaze and head from arbitrary initial positions, simulates the nine relationships of the head-unrestrained main sequence, and reproduces observations from lesion and single-unit recording experiments. We conclude by showing how our model can be easily extended to control structures with more linked segments, such as the control of coordinated eye on head on trunk movements.

What stops a saccade?

“…tongue, head, trunk and limb) [63]. These movements become dysarthric or dysmetric during cerebellar disease [64].…”

“…These movements become dysarthric or dysmetric during cerebellar disease [64]. It is reasonable to assume that they all share a similar dual-pathway structure with saccades; one part of the brain encodes the movement goal and initiates the movement (a feed-forward pathway), and a parallel cerebellar pathway keeps track of the movement's displacement and stops it on target (a feedback pathway) [63,65].…”

Spatial transformations between superior colliculus visual and motor response fields during head‐unrestrained gaze shifts

“…A crucial aspect of gaze control is the decomposition of target position into separate commands for gaze (or the eye) vs. the head (Daye et al ., ). Unlike our previous study (DeSouza et al ., ), here we were able to distinguish whether the motor activity of SC neurons is coding for movement vectors, or final positions of eye or head, as opposed to gaze models (dE, dH, Eh, and Hs, respectively) as opposed to gaze models.…”

“…For example, large head position and movement modulations have been observed in the SC in experiments that deliberately dissociated eye and head displacement and/or used very large excursions in head position. These responses may reflect other aspects of SC organization (Gandhi & Katnani, ; Monteon et al ., ; Daye et al ., ). Thus, to be conservative, our current results should only be interpreted in the context of centre‐out movements and their contribution to the spatial organization of visual and motor receptive fields in the SC.…”

Sustained sensorimotor control as intermittent decisions about prediction errors: computational framework and application to ground vehicle steering

“…2008; Daye et al. 2014). Overall, these motor-level accounts suggest that the kinematic motor primitives considered in the present framework are not truly ballistic, in the sense that there is a closed control loop to support their successful motor completion.…”