Transcript Bimanual interference during on-line control to

Bimanual interference during on-line control to
symbolically- vs. directly-cued target locations
Jarrod Blinch, Brendan Cameron, Melanie Lam, Silvia Hua, Melissa Cory, Romeo Chua
School of Human Kinetics, University of British Columbia
[email protected]
Background
Results
The study of bimanual coordination has found many constraints on our actions. For
example, in the reaction time (RT) paradigm (Spijkers, Heuer, Kleinsorge, & van der
Loo, 1997), participants simultaneously reached for a short or long target with each
hand. When the targets were symbolically cued, with letters S and L for short and long
movements, there was a RT cost for asymmetric movements (right hand short, left hand
long or vice versa, which is cued by S L or L S) compared to symmetric movements (S
S or L L). When the targets were directly cued by illuminating the targets, the cost was
abolished (Diedrichsen, Hazeltine, Kennerley, & Ivry, 2001).
All participants successfully made on-line corrections to symbolically- or directly-cued
target locations. Figure 2 illustrates the mean trajectories of a representative participant
making directly- or symbolically-cued on-line correction to the left target box with the left
hand. The time to respond to a target perturbation was significantly longer for symbolic
cues than direct cues (Figure 3). The effect of the perturbation on the unperturbed
hand was determined by comparing the lateral position of the unperturbed hand to
control trials. We observed significantly larger mean lateral deviation in the position of
the unperturbed hand in the symbolic compared to the direct condition (Figure 4).
In a similar target jump paradigm (Diedrichsen, Nambisan, Kennerley, & Ivry, 2004),
participants simultaneously reached for two targets. On-line corrections were directly
cued by having one of the targets jump to the left or right. These corrections were
accomplished with asymmetric movements of the hands. Like the directly-cued
movements in the RT paradigm, there was minimal bimanual interference with only a
small, transient perturbation in the trajectory of the unperturbed hand. The advantages
afforded by direct cuing are presumed to be due to the facilitation of response selection
processes (RT paradigm) and to vision-dependent, automatic corrections (target jump
paradigm).
Purpose
We compared symbolically- and directly-cued on-line corrections in a bimanual
reaching task. We anticipated greater interference for symbolically-cued than for
directly-cued corrections, as seen for asymmetric movements in the RT paradigm.
Symbolic
Direct
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Mean Lateral Position (mm)
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Mean Lateral Position (mm)
Figure 2. Mean trajectories of a representative participant for control (black), direct (red), and
symbolic (blue) conditions. Means were calculated from trials with normalized displacement.
The outside, dotted lines depict standard deviations from the mean trajectories.
Methods
500
Correction Latency (ms)
Ten participants made bimanual reaching movements with a movement time goal of
500 ms. The trajectories of the hands were recorded with an Optotrak with a sample
frequency of 500 Hz. Vision of the hands was available at the start of every trial to
orient the participant, but it was removed during movements to prevent vision-based online corrections. A fixation point was used to prevent eye movements from affecting the
trajectories (Figure 1a). All movements were cued by having a target number 8 appear
in the middle target box for each hand (Figure 1b). This ensured the same information
processing occurred up to movement onset.
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Direct
Symbolic
Target Perturbation
Figure 3. Time to respond to target perturbations for directly- and symbolically-cued
corrections.
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Left
Symbolic
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Mean Lateral Position (mm)
Figure 1. Stimulus progression for each type of trial. The fixation point appears in the middle
of the target boxes for the left and right hands (a). A target number 8 appears in the middle
target box for each hand as the movement cue (b). In control trials, an on-line correction is
not required and the participant simply reaches to the original targets (c). Both the direct (d)
and symbolic (e) cues shown above require an on-line correction of the right hand to the right
target box. The red lines represent the trajectories of the hands.
Mean Lateral Position (mm)
Direct
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Diedrichsen, J., Hazeltine, E., Kennerley, S., & Ivry, R.B. (2001). Moving to directly cued
locations abolishes spatial interference during bimanual actions. Psychological Science,
12, 493-498.
Diedrichsen, J., Nambisan, R., Kennerley, S.T., & Ivry, R.B. (2004). Independent on-line
control of the two hands during bimanual reaching. European Journal of Neuroscience,
19, 1643-1652.
Spijkers, W., Heuer, H., Kleinsorge, T., & van der Loo, H. (1997). Preparation of bimanual
movements with same and different amplitudes: Specification interference as revealed by
reaction time. Acta Psychologica, 96 , 207–227.
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Percentage of Movement
At movement onset for 50% of the trails, an on-line correction was directly or
symbolically cued by a target jump (Figure 1d) or target identity change (Figure 1e),
respectively. For directly-cued on-line corrections, the target 8 would jump to the left or
right target box and the participant would reach to the new target location (Figure 1d).
If the right target changed to a rightward facing E (Figure 1e), then the right hand (the
perturbed hand) would make an on-line correction to the right target box. A leftward
facing E was used for corrections to the left target box. We examined the effects of the
target perturbation on the unperturbed hand when only one hand was required to
change direction by comparing the lateral deviation to control trials.
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Percentage of Movement
Figure 4. Mean lateral position of the right, unperturbed hand by the percentage of movement.
Directly-cued on-line corrections are on the left graph and symbolically-cued corrections are on
the right. The position of the unperturbed hand is shown when the correction of the left,
perturbed hand is right (red), left (blue), or control (black). Filled points are significantly
different from control; vertical lines depict standard deviations of the means.
Conclusions
The time to respond to symbolic cues was longer than direct cues as they rely on
vision-dependent, voluntary processes rather than automatic processes. We anticipated
greater interference for symbolically-cued than for directly-cued corrections.
Symbolically-cued on-line corrections did result in larger lateral deviations in the
unperturbed hand compared to directly-cued corrections. However, the influence of
symbolic cues on the degree of interference was less than what might be expected
based on RT costs for asymmetric bimanual movements.
Funding from NSERC supported this experiment.