This is an excerpt from Neurophysiological Basis of Motor Control-3rd Edition by Mark L. Latash & Tarkeshwar Singh.
Intercepting and catching a moving projectile are fundamental motor skills that require precise timing and coordination between the eye and the hand. The moving projectile is tracked with smooth-pursuit eye movements, and then the limb is directed toward the point of impending collision. The main difference between reaching and interception movements is that in contrast to saccadic eye movements that are made during reaching, interception movements primarily engage smooth-pursuit eye movements. Tracking moving objects enables continuous high-acuity vision, but smooth-pursuit eye movements are limited to a maximum speed of 80º/s to 100º/s (Meyer et al., 1985). Thus, for stimuli that move faster than that speed, the oculomotor system launches catch-up saccades to compensate for position and velocity errors.
During catching or interception action in sports, players track the moving object with a combination of eye and head movements until the hand is aligned with the moving object at the point of interception (reviewed in Fooken et al. 2021). Often there is a short phase of smooth tracking observed right before the ball is intercepted, suggesting that keeping the eye on the object is important for accurate prediction of object motion (Hayhoe et al. 2012; Land and McLeod 2000). If the eye movements are constrained (e.g., when participants are asked to fixate at a point instead of freely pursuing the moving projectile), their performance is degraded. The most likely explanation for this is that object speed during visual fixation is overestimated, leading to interception movements ahead of the moving object.
It is currently also believed that the nervous system uses efference copies of oculomotor commands associated with smooth-pursuit eye movements to make predictions about object motion and coordinating eye and hand movements for interception. The reliance on both retinal projections of the object image and the extraretinal oculomotor signals might be more important for smooth eye–hand coordination when the object motion is more unpredictable (e.g., intercepting a curving soccer kick or catching a fly) (see figure 30.6).
The studies on manual interception with human participants and primates have highlighted the important role played by the MT/MST and FEF areas and the parietal cortex in the precise spatiotemporal coordination of both eye and limb movements (Merchant et al. 2004, 2006; Zago et al. 2009). Lesions in the parietal cortex, FEF, and MT/MST cause deficits in smooth-pursuit eye movements (Dursteler and Wurtz 1988; Heide et al. 1996) and consequently in eye–hand coordination.
MT and MST project to the premotor cortex, especially the FEF and the dorsal premotor cortex. These projections likely are involved in continuous transformation of motion signals from a projectile into motor commands to move the limb to the right location in space to make contact with the projectile. Simultaneously, the nervous system also prepares a postural response to absorb the projectile’s momentum.
Evidence for the transformation of motion signals to continuous modification of limb posture has come from a study by Selen and colleagues (Selen et al. 2012). In their experiment, participants viewed a dynamic random dot display and indicated their decision about the direction of the dot movement by moving a handle to one of two targets. The random dot (figure 30.1) display engages neural area MT/MST, which is also involved in tracking moving objects. The experimenters perturbed the arm at random times during decision formation. The long-latency reflex gains of the M3 component (also see chapter 18) were modulated by the strength and duration of motion of the random dots, reflecting the accumulated evidence in support of the evolving decision. Their results support the existence of a sensorimotor process that continuously transforms motion signals for limb motor control. Furthermore, this suggests that the motor system might continuously set the referent joint configurations for catching movements based on the sensory output from area MT/MST.