Elsevier

Consciousness and Cognition

Volume 18, Issue 3, September 2009, Pages 646-652
Consciousness and Cognition

Cognitive constraint on the ‘automatic pilot’ for the hand: Movement intention influences the hand’s susceptibility to involuntary online corrections

https://doi.org/10.1016/j.concog.2009.04.008Get rights and content

Abstract

Research suggests that the reaching hand automatically deviates toward a target that changes location (jumps) during the reach. In the current study, we investigated whether movement intention can influence the target jump’s impact on the hand. We compared the degree of trajectory deviation to a jumped target under three instruction conditions: (1) GO, in which participants were told to go to the target if it jumped, (2) STOP, in which participants were told to immediately stop their movement if the target jumped, and (3) IGNORE, in which participants were told to ignore the target if it jumped and to continue to its initial location. We observed a reduced response to the jump in the IGNORE condition relative to the other conditions, suggesting that the response to the jump is contingent on the jump being a task-relevant event.

Introduction

Daily life involves many decisions about what objects to use and how to use them to accomplish higher level goals. To make a pot of tea, for instance, we must select and act upon the kettle, the tea bag, and the pot in the right sequence and at the right time. But if we wished to alter this sequence, we could easily do so (though the quality of the tea might suffer). However, it may not be as easy to alter the individual movements that link each event in the sequence as it is to alter the sequence itself. Once we have selected the tea bag and decided to reach for it, our conscious mind may have little control over the reach until it is done. Milner and Goodale, 1995, Goodale and Milner, 2004 have suggested, based primarily on neurological patient work, that the visual processing that underlies object identification is separate from that which serves movement control and, furthermore, that the former is consciously accessible, while the latter is not. Pisella et al. (2000) have shown that even if we intend to stop our movement when the target of our reach changes location, our movement will follow the target. These lines of evidence suggest that while conscious intention influences object selection, it has little impact on the control of an unfolding action. Our study further investigates the link between conscious intention and online control. Are there conditions under which intention might influence an unfolding movement?

In Pisella et al.’s (2000) study, participants were instructed to make rapid aiming movements to a target that could jump to a new location at movement onset. In one condition participants were told to stop their movement midflight if the target jumped. The results showed that for movements ranging from 200 to 300 ms in duration, participants’ hands followed the target and touched down at the new location on a significant number of trials. This led the researchers to suggest that rapid movements are under the control of an ‘automatic pilot’. This research was extended by Cressman, Franks, Enns, and Chua (2006) to show that even when participants successfully stopped their movement midflight, the hand had already begun to deviate towards the target location. Day and Lyon (2000) showed a similar effect when, rather than instructing participants to stop when a target moved, they instructed participants to point in the direction opposite to that of the target’s motion (i.e., to ‘anti-point’). In their task, the hand initially deviated toward the target’s new location before being re-directed to the instructed location.

These studies suggest that a reach is under the control of its intended target for at least the first 200–300 ms of the movement: if the target moves, our hand will too. However, in each of these previous studies the target jump constituted a signal that was explicitly relevant to the performance of the task. The instructions indicated that when the target moved, the participant should either stop their movement (Cressman et al., 2006, Pisella et al., 2000) or initiate a new movement in the opposite direction (Day & Lyon, 2000). This leaves the possibility that, were the target jump a signal that was irrelevant to the performance of the task, the participant may be able to diminish its impact on the hand.

Research on visual attention suggests that task demands (e.g. ‘look for a red target’ vs. ‘look for a target onset’) influence the ability of visual onsets to capture attention, such that a visual onset will fail to involuntarily grab attention if one is searching for a red target (Folk, Remington, & Johnston, 1992). Thus, a seemingly ‘automatic’ perceptual process like the exogenous capture of attention can be influenced by the perceiver’s perceptual intentions. Here we investigate whether action processing might be influenced by action intentions in an analogous way. Specifically, we test whether the intention to ignore a target jump reduces the extent to which the jump dictates the trajectory of the movement.

We compared the degree of online correction to a target jump in three conditions: (1) Participants were instructed to go to the target’s new location, (2) participants were instructed to stop their movement as soon as the target jumped, and (3) participants were told to ignore the target jump and continue to the target’s initial location. We hypothesized that automatic trajectory modifications would be reduced in the 3rd case relative to the other two conditions.

Section snippets

Participants

Ten right-handed University of British Columbia students (1 male, 9 female; ages 18–24) participated in the study. Participants were paid $25 for a 2.5 h commitment. All participants gave informed consent, and the study was conducted according to the ethical guidelines of the university.

Apparatus and procedure

Participants sat with their head in a chin rest, their eyes approximately 60 cm from the display surface. The upper layer of this surface was a Plexiglas sheet, and light-emitting diodes (LEDs) were set below the

Online response to the target jump

We were particularly interested in the effect of the participant’s intentions (manipulated by instruction) on the ability of the target jump to influence the unfolding movement. To quantify this effect, we measured the number of times that the reaching hand deviated significantly towards the jumped target’s new location (T2) (Cressman et al., 2006). First we calculated mean hand trajectories on stationary target trials for a given participant and plotted a two standard deviation (SD) bandwidth

Discussion

We hypothesized that action intention would reduce online responding to a target jump if the intention reduced the relevance of the target jump to the task. The results, which showed reduced responding to the target jump in the IGNORE relative to the GO and STOP conditions, support this hypothesis. The comparison between the IGNORE and STOP conditions is particularly relevant to this hypothesis, because in both cases participants do not intend to go to the target, but in the STOP condition the

Conclusion

We have shown that the effect of unpredictable target jumps on the online control of the reaching hand depends on the intentions of the participant. When the target jump is relevant to the performance of the task, the hand is more susceptible to being captured by the jumping target. We suggest that a conscious intention to ignore a target jump pre-sets the visuomotor system to inhibit a response to this jump rather than globally down-regulating the online control of the reach, though we hope

Acknowledgments

This research was supported by a NSERC Discovery Grant awarded to R.C. We thank Dr. James Danckert and an anonymous reviewer for helpful comments on the manuscript.

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