|Series| Feedback Techniques
What is Lissajous Feeback?
All forms of feedback within coordinated rhythmic movement (CRM) are used to guide learning. Lissajous feedback is no different to other forms of feedback in this regard. It is, however, fundamentally different in how it achieves this goal.
Central to the technique is the use of a Lissajous figure (hence the name). A Lissajous figure is a continuous, 2-dimensional plot of the relative motions of the two limbs. The right arm follows the abscissa (representing X-axis/horizontal-axis on the Lissajous figure) and the left arm follows the ordinate (representing Y-axis/vertical-axis on the Lissajous figure).
What does Lissajous feedback look like in practice?
In-phase or 0° motions produce a straight line extending from the lower left portion of the monitor toward the upper right portion.
Anti-Phase or 180° motions produce a straight line extending from the lower right portion of the monitor toward the upper left portion.
A 45° pattern produces an ellipse extending from the lower left to the upper right.
A 135° pattern produces an ellipse extending from the lower right to the upper left.
A 90° pattern produces a circle.
What do these shapes mean?
In order to understand what these shapes mean, we must understand how they are used. Their use is twofold. For one, they inform the participants in real time of how well they are performing the task (that is, the particular variety of movement, i.e. 90°). Secondly, they provide the platform on which the data is collected and ultimately analysed to assess production.
Informing participants in real time of how well they are performing is continuous feedback. Lissajous figures are used to achieve this by presenting the template shape in conjunction with a participant controlled dot, and having the participant trace the required shape with the dot. Accurate tracing results in the accurate production of the required phase. For example, if a participant was tasked to produce 90°, the participant would be presented with the outline of a circle on a screen (Fig. 5). Their task would be to move the apparatus (typically two joysticks, one in each hand) in order to trace that shape. How well they produce the rhythmic movement corresponds to how well they trace the circle.
This tracing is informative to the participant in real time. The participant is able to use the visual information available (the shape of the figure and the position of the dot) to adjust the movements to more accurately trace the lissajous figure. This tracing data is recorded and used to assess production.
So, what do these shapes mean? Independent of context, they don’t mean a sausage. However, in the context of CRM they are one variety of continuous feedback and a way to tackle data assessment.
How is Lissajous Feedback Unique?
In the opening paragraph I stated that lissajous feedback is fundamentally different to other forms of CRM feedback in how it guides learning. This requires some proper attention, so I will assign a separate post to cover this topic.