Eye-hand coordination during a double-step task: evidence for a common stochastic accumulator

Abstract

Many studies of reaching and pointing have shown significant spatial and temporal correlations between eye and hand movements. Nevertheless, it remains unclear whether these correlations are incidental, arising from common inputs (independent model); whether these correlations represent an interaction between otherwise independent eye and hand systems (interactive model); or whether these correlations arise from a single dedicated eye-hand system (common command model). Subjects were instructed to redirect gaze and pointing movements in a double-step task in an attempt to decouple eye-hand movements and causally distinguish between the three architectures. We used a drift-diffusion framework in the context of a race model, which has been previously used to explain redirect behavior for eye and hand movements separately, to predict the pattern of eye-hand decoupling. We found that the common command architecture could best explain the observed frequency of different eye and hand response patterns to the target step. A common stochastic accumulator for eye-hand coordination also predicts comparable variances, despite significant difference in the means of the eye and hand reaction time (RT) distributions, which we tested. Consistent with this prediction, we observed that the variances of the eye and hand RTs were similar, despite much larger hand RTs (∼90 ms). Moreover, changes in mean eye RTs, which also increased eye RT variance, produced a similar increase in mean and variance of the associated hand RT. Taken together, these data suggest that a dedicated circuit underlies coordinated eye-hand planning.

Contrasting effects of exogenous cueing on saccades and reaches

“…These findings are consistent with previous research suggesting both effector-dependent andindependent movement planning processes. As mentioned in the introduction, a number of studies have shown strong correlations between initiation times of the eye and the hand, consistent with a shared movement planning stage (Biguer, Jeannerod, & Prablanc, 1982;Bekkering et al, 1995;Gopal & Murthy, 2015;Lee et al, 2014;Neggers & Bekkering, 1999;Sailer et al, 2000;Suzuki, Izawa, Takahashi, & Yamazaki, 2008;Tao, Khan, & Blohm, 2018). An effector-independent stage reflecting shared outcomes for different effectors has been suggested previously in terms of a shared target selection stage for both the eye and the hand (Song & McPeek, 2009).…”

An independent race model involving an abort and re‐plan strategy explains reach redirecting movements during planning and execution

“…The stochastic independence of the GO and STOP processes can be tested qualitatively by comparing cumulative RT distributions of step error trials and no‐step trials (Boucher et al ., ; Kapoor & Murthy, ; Gopal & Murthy, ). If we assume an independent race model, it predicts an ordering of cumulative RT distributions for step errors and no‐step trials; the distributions would have a common minimum and diverge at longer TSDs, with the error distribution to the left of the no‐step RT distribution.…”

“…Subjects were monetarily rewarded for their participation and for every correct trial to keep them motivated to do the task. Part of the data (eight of 24 subjects) was already used elsewhere (Gopal & Murthy, ; Gopal et al ., ) for another purpose and was added to the dataset to further substantiate the generality of the results.…”

“…If the target shift appears early enough, subjects compensate for the shift in the target location by making movements to the second target location (Becker & Jürgens, ). Although the double‐step task has been extensively studied to understand various aspects of oculomotor control (Ray et al ., ; Camalier et al ., ; Ramakrishnan et al ., ), it is only relatively recently that efforts have been directed to understand the computational and neural mechanisms that underlie the ability to redirect reach movements (Mirabella et al ., , ; Gopal & Murthy, ; Gopal et al ., ; Jana et al ., ).…”

Abnormalities of Eye–Hand Coordination in Patients with Writer’s Cramp: Possible Role of the Cerebellum

“… 31 However, since we did not calculate the latency of the hand movements from the display of the visual target, it is not possible to determine whether this increased latency is a result of a delay in initiating the saccade or a delay in initiating the hand movement or both. Gopal and Murthy 32 in their study on latency of the saccades and hand motor system have documented the existence of a dedicated circuit for the EHC. Since there was a failure in reduction of saccadic latency in patients with WC during EHC, we propose that there may be an involvement of this circuit in WC patients.…”