Oculomotor learning is evident during implicit motor sequence learning

Abstract

Motor sequence learning involves both oculomotor and manual motor systems, yet the role of the oculomotor system in the learning and execution of skilled arm movements remains underexplored. In the current work, the influence of sequence learning on the oculomotor system was investigated by testing 20 healthy adults for 3 days as they practiced an implicit motor learning task, the serial targeting task (STT). The STT contained a repeated sequence, which was interleaved with random sequences. This task was practiced on a KINARM robot that tracked both saccades and reaches. A delayed, 24-h retention test assessed sequence-specific motor learning. Sequence-specific changes across practice and learning were observed for both saccades and reaches; this was demonstrated by faster saccade and arm motor reaction times for the repeated sequence compared to random sequences. Notably, change in the oculomotor system occurred earlier in practice as compared to the manual motor system. Reaches were executed more quickly when led by express saccades (rapid eye movements occurring within 90-120 ms) compared to when they were preceded by regular latency (> 120 ms) saccades early in practice. Our findings highlight distinct yet interconnected functions between oculomotor and manual motor systems associated with implicit motor sequence learning.

Keywords: Implicit motor sequence learning; Motor skill learning; Oculomotor learning; Reaches; Saccades.

Fig. 1

Experimental procedure and task. The STT was practiced in the KINARM over three consecutive days (A). Participants saw only two targets at a time, the target they were currently positioned on, and the target they were required to move to. Participants’ view of their hand was occluded, and they controlled a white cursor to reach to the new target (B). The 8-element repeated sequence followed a unique pattern; numbers and grey circles depicted are for visualization purposes only (C).

Fig. 2

Practice and retention test data. Plots show raw RT means with standard error of the mean for each block, for saccades (A) and reaches (B). Lines connect blocks of practice conducted within each testing session. RET: 24-h retention block.

Fig. 3

Practice data illustrating differences in sequence type by day or block. Plots show estimated marginal means (EMMs) with 95% confidence intervals, as derived from the linear mixed-effects models, reflecting model-based differences in RT between random and repeated sequences across days (A,B), and across blocks for saccades (C) and reaches (D). Asterisks in plots C and D indicate statistically significant difference between sequence types, marking the first instance of sequence-specific change for saccades versus reaches.

Fig. 4

Relationship between saccade and reach RT change scores. RT change scores represent the difference in performance between repeated and random sequences; a larger negative change score indicates greater change in RT for the repeated sequence relative to random sequences. Each dot represents a participant, demonstrating the relationship between saccade and reach RT change scores. Data from the first block of each practice day only were included in the analysis.

Fig. 5

Relationship between saccade type and reach responses. Mean reach RT of all trials in which an express (90–120 ms) or regular latency (> 120 ms) saccade preceded the reach. Data are averaged over blocks for each practice day. Error bars represent standard error of the mean.