The Effect of Continuous and Discretized Presentations of Concurrent Augmented Visual Biofeedback on Postural Control in Quiet Stance

Abstract

The purpose of this study was to evaluate the effect of a continuous and a discretized Visual Biofeedback (VBF) on balance performance in upright stance. The coordinates of the Centre of Pressure (CoP), extracted from a force plate, were processed in real-time to implement the two VBFs, administered to two groups of 12 healthy participants. In the first group, a representation of the CoP was continuously shown, while in the second group, the discretized VBF was provided at an irregular frequency (that depended on the subject's performance) by displaying one out of a set of five different emoticons, each corresponding to a specific area covered by the current position of the CoP. In the first case, participants were asked to maintain a white spot within a given square area, whereas in the second case they were asked to keep the smiling emoticon on. Trials with no VBF were administered as control. The effect of the two VBFs on balance was studied through classical postural parameters and a subset of stabilogram diffusion coefficients. To quantify the amount of time spent in stable conditions, the percentage of time during which the CoP was inside the stability area was calculated. Both VBFs improved balance maintainance as compared to the absence of any VBF. As compared to the continuous VBF, in the discretized VBF a significant decrease of sway path, diffusion and Hurst coefficients was found. These results seem to indicate that a discretized VBF favours a more natural postural behaviour by promoting a natural intermittent postural control strategy.

Fig 1. Modality of VBF presentation.

(A) VBF_CoP presentation: the black square represents the force plate, the red square represents the area of stability, and the white spot represents the current position of the CoP. During tasks the spot moves in real time on the screen. (B) VBF_emoticon presentation: one out of five different emoticons appears in the centre of the screen. A smiling emoticon (3) appears if the participant stays in the stability area; if the CoP coordinates exceed the boundaries of the stability area, one out of a set of four sad emoticons is displayed. In particular: if the CoP exceeds the boundaries in the ML direction, the sad emoticon tilts 30° to the left (1) or to the right (2) hand side; if the CoP exceeds the boundaries in the AP direction, the sad emoticon is magnified (4) or reduced (5).

Fig 2. VBF_CoP-VBF_emoticon comparison.

Mean ± standard deviation for SP, Mpf_AP, diffusion and Hurst coefficients in the two tasks (VBF_CoP and VBF_emoticon). ANOVA result for Task Type are also reported (** p<0.01, ***p<0.001).