The effects of enhanced visual feedback on human synchronization.
Tanja Ceux1, Martinus Buekers1 and Gilles Montagne2
Departement of Kinesiology, Katholieke Universiteit Leuven, Belgium
2
UMR Mouvement et Perception, Université de la Méditerranée et CNRS, Marseille,
France
1
Introduction:
Very often actions have to be performed demanding a complex spatial and temporal organization of
the movement as such as well as an appropriate imbedding into the environmental spatio-temporal
constraints. Actually, performance outcome in a cyclical synchronization task appears to be strongly
influenced by the strength of the perception-action coupling (Buekers, Bogaerts, Swinnen & Helsen,
2000). In the present experiment the coupling strength issue is examined more closely as we modify
the spatial and spatio-temporal characteristics of the synchronization task. We achieve this by (a)
enhancing visual feedback and (b) changing the spatial organization of the task. In particular, (a) the
provision of enhanced visual online control of the arm movement will strengthen the perception-action
link while (b) providing an orthogonal spatial organization of the task was anticipated to weaken the
coupling between perception and action.
Methods:
Participants (N=18) were seated comfortably on a chair behind a table in a darkened room. The right
forearm had to be put on a lever that could freely rotate in the horizontal plane. A shaft encoder was
connected to the axis of the lever to record its position (accuracy of 0.02°) at a rate of 500Hz. The
visual signal, displayed as a green rectangle (0.25cm X 0.20cm), was visualized on the white colored
wall in front of the participants using a LCD-projector. The visual target was moving sinusoidal at a
frequency of 0.67Hz. A red laser-pointer light, mounted on the lever and displayed as a dot at the same
height as the center of the horizontal moving visual signal, was employed to provide direct visible
information of the arm movement in the feedback conditions. All participants performed six
conditions, consisting of 10 blocks of 15 cycles each, representing three synchronization modes
(horizontal in-phase, horizontal anti-phase and orthogonal condition) and two feedback conditions (no
feedback and feedback). Participants had to synchronize their horizontal arm movements (required
amplitude of 49°) with the spatio-temporal characteristics of the horizontally (in-phase condition, i.e.,
arm and visual signal moved in the same direction and anti-phase condition, i.e., arm moving in the
opposite direction) or vertically moving visual signal (orthogonal condition, i.e., subjects had to move
to the right when the target traveled down). In this latter condition, the middle of the vertical trajectory
of the visual target was corresponding to the middle of the required horizontal arm movement. The
spatial parameter of movement amplitude and the spatio-temporal variables of mean (continuous)
relative phase and the within-subject variability of relative phase were computed.
Results:
In the no feedback condition, the results of amplitude exhibited a performance decrease from the
horizontal in-phase to the horizontal anti-phase and finally the orthogonal condition (Figure 1). The
synchronization performance in this latter condition also deteriorated as compared to both horizontal
conditions for the mean relative phase. On the other hand in the feedback condition, the amplitude was
not influenced since the presence of continuous visual online control of the arm movement engendered
an equal performance level for the three synchronization modes. Conversely, the relative phase of the
horizontal in-phase condition felt down to the level of the vertical condition.
1
70
65
60
56
60
8.0 48
8
47
47
50
7.0
40
6
5.2
30
4
Amplitude (°)
Relative Phase (°)
10
20
2
1.5
1.5
1.2
0
10
0
In-phase
Anti-phase Orthogonal
In-phase
No feedback
Anti-phase Orthogonal
Feedback
Figure 1: Movement amplitudes and relative phase for the different synchronization conditions.
Conclusions:
The results of the present experiment demonstrate that visual online information of the action is an
important mediator for the synchronization of an arm movement to an external event. Interestingly,
this feedback effect is not only task-specific (Magill, 1993; Wishart, Lee, Cunningham & Murdoch,
2002), but also parameter-specific since the spatial and spatio-temporal characteristics are affected
differently. Apparently, the availability of feedback provoked the use of different strategies to cope
with the constraints of this synchronization task. Actually, the participants appeared literally to
“chase” the target in the horizontal in-phase condition when feedback of the arm movement was
available instead of keeping up with the visual signal. On the other hand, the strategy implying the use
of specific spatio-temporal anchor points appears more suitable for the horizontal anti-phase and
vertical condition where subjects tend to concentrate on synchronizing their arm movement at both
reversal positions (Byblow, Chua & Goodman, 1995).
References
Buekers, M.J., Bogaerts, H.E., Swinnen, S.P. & Helsen, W.F. (2000). The synchronization
of human arm movements to external events. Neuroscience Letters, 290, 181-184.
Byblow, W.D., Chua, R. & Goodman, D. (1995). Asymmetries in coupling dynamics of
perception and action. Journal of Motor Behavior, 27, 123-137.
Magill, R.A. (1993). Augmented feedback in skill acquisition. In R.N. Singer, M. Murphey
and L.K. Tennant (Eds.), Handbook of research on sport psychology (pp. 193-212).
New York: Macmillan.
Wishart, L.R ., Lee, T.D., Cunningham, S.J. & Murdoch, J.E. (2002). Age-related
differences and the role of augmented visual feedback in learning a bimanual
coordination pattern. Acta Psychologica, 110, 247-263.
2