Academic journal article Perception and Psychophysics

Stopping Eye and Hand Movements: Are the Processes Independent?

Academic journal article Perception and Psychophysics

Stopping Eye and Hand Movements: Are the Processes Independent?

Article excerpt

To explore how eye and hand movements are controlled in a stop task, we introduced effector uncertainty by instructing subjects to initiate and occasionally inhibit eye, hand, or eye + hand movements in response to a color-coded foveal or tone-coded auditory stop signal. Regardless of stop signal modality, stop signal reaction time was shorter for eye movements than for hand movements, but notably did not vary with knowledge about which movement to cancel. Most errors on eye + hand stopping trials were combined eye + hand movements. The probability and latency of signal respond eye and hand movements corresponded to predictions of Logan and Cowan's (1984) race model applied to each effector independently.

Many studies have detailed the linkage between movements fof the eyes and hands. Reaction times (RTs) of eyes and hands covary under various circumstances (Biguer, Jeannerod & Prablanc, 1982; Fischer & Rogal, 1 986; Fisk & Goodale, 1 985; Gielen, van den Heuvel, & van Gisbergen, 1984; Gribble, Everling, Ford & Mattar, 2002; Herman, Herman, & Maulucci, 1981; Hodgson, Muller, & O'Leary, 1995; Lunenburger & Hoffmann, 2003; Lunenburger, Kutz, & Hoffmann, 2000; Neggers & Bekkering, 2000; Sailer, Eggert, Ditterich, & Straube 2000). Even saccade dynamics can be affected by limb kinetics (van Donkelaar, Siu, & Walterschied, 2004; Snyder, Calton, Dickinson, & Lawrence, 2002; Tipper, Howard, & Paul, 2001). For example, movements of the eyes and hands to opposite locations are delayed relative to movements to the same location (Fisk & Goodale, 1985), and saccades are produced with shorter reaction times when produced with an arm movement (Lunenburger et al., 2000; Snyder et al., 2002). Further, saccades directed away from the endpoint of a pointing movement are delayed until the end of the arm movement (Neggers & Bekkering, 2000). Neurophysiological evidence has suggested a linkage as well. In particular, neural activity in the superior colliculus associated with saccade production is modulated by limb position (Stuphorn, Hoffmann, & Miller, 1999), and neural activity in posterior parietal cortex associated with limb movements is modulated by eye position (Snyder, 2000). Overall, the data have been interpreted to indicate a general facilitation of coordinated movements of eyes with hands.

Another critical aspect of motor control is the withholding of a movement, for control over movements is the hallmark of voluntary behavior. This ability can be probed by the countermanding, or stop signal, task. This is an RT task where an imperative stop signal is infrequently presented which instructs subjects to cancel the planned movement (Hanes & Schall, 1995; Lappin & Erikson, 1966; Logan, 1994). Logan and Cowan (1984) showed that performance on this task could be accounted for by a race between stochastic processes that generate (GO process) or inhibit (STOP process) the movement. This race model predicts the probability and latency of errors of commission and provides an estimate of stop signal reaction time (SSRT), the time needed to cancel the planned movement.

A previous study found that saccadic eye movements stop sooner than hand movements but did not examine the coordination of stopping between the eyes and hands (Logan & Irwin, 2000). Here we ask, given the evidence that the eyes and hand move together, do they stop together? Specifically, are partially prepared eye and hand movements inhibited independently or together? We measured performance in both blocked and interleaved trials in which subjects were instructed to make an eye movement alone, a hand movement alone, or a combined eye + hand movement toward an eccentric target. On a minority of trials, subjects had to cancel their previously planned eye movement, hand movement, or coordinated eye + hand movement if a stop signal occurred. In the blocked condition, subjects knew in advance which effector (eye, hand, eye + hand) to stop; in the interleaved condition, subjects were cued by the color of a visual stop signal (Experiment 1) or the tone of an acoustic stop signal (Experiment 2) which effector to stop. …

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