Postural control during the Stroop test in dyslexic and non dyslexic teenagers.

Zoï Kapoula,Emilie Demule,Caroline Fauvel,Eric Matheron,Maria-Pia Bucci

doi:10.1371/journal.pone.0019272

Abstract

Postural control in quiet stance although simple still requires some cognitive resources; dual cognitive tasks influence further postural control. The present study examines whether or not dyslexic teenagers experience postural instability when performing a Stroop dual task for which their performances are known to be poor. Fifteen dyslexics and twelve non-dyslexics (14 to 17 years old) were recruited from the same school. They were asked to perform three tasks: (1) fixate a target, (2) perform an interference Stroop test (naming the colour or the word rather than reading the word), (3) performing flexibility Stroop task: the subject performed the interference task as in (2) except when the word was in a box, in which case he had to read the word. Postural performances were measured with a force platform. The results showed a main task effect on the variance of speed of body sway only: such variance was higher in the flexibility task than for the other two tasks. No group effect was found for any of the parameters of posture (surface, mediolateral and anteroposterior sway, variance of speed). Further wavelet analysis in the time-frequency domain revealed an increase in the spectral power of the medium frequency range believed to be related to cerebellum control; an accompanying increase in the cancellation time of the high frequency band related to reflexive loops occurred for non-dyslexics only. These effects occurred for the flexibility task and could be due to its high cognitive difficulty. Dyslexics displayed shorter cancellation time for the medium frequency band for all tasks, suggesting less efficient cerebellar control, perhaps of eye fixation and attention influencing body sway. We conclude that there is no evidence for a primary posture deficit in 15 year old teenagers who come from the general population and who were recruited in schools.

Highlights

Postural control in quiet stance involves continuous multisensory central integration of visual, vestibular and proprioceptive inputs in order to produce motor commands controlling the body’s position in space
Postural results Means and standard errors are shown in Table 1: for each group of subjects (Dyslexics and Controls) and for the 27 subjects together, and for each condition (FT, Stroop interference task (SIT), Stroop flexibility task (SFT)); all postural parameters are shown, i.e. the surface of the center of pressure (CoP) excursions, SDx, SDy, the variance of speed, PII, and PI and canceling time (CT) for each plane for each frequency bands (0.05–0.50 Hz, 0.50–1.50 Hz and 1.50–10.00 Hz)
Effects of task There was a main effect of the task only on the variance of speed (F(2,50) = 3.90; p = .024), and on two parameters elaborated from the wavelet transform, the power indices for the second frequency band (PIx2, F(2,50) = 3.90; p = .025) and the canceling time of the third frequency band (CTx3, F(2,50) = 3.62; p = .032) on the mediolateral sway

Summary

Introduction

Postural control in quiet stance involves continuous multisensory central integration of visual, vestibular and proprioceptive inputs in order to produce motor commands controlling the body’s position in space. It is a simple task, body control still requires some cognitive resources. Many studies used double tasks contributing greatly to the field of postural control [1,2]. It has been showed, in adults or elderly, that the cognitive task influences postural control [2,3,4,5,6]. Various models have been proposed to explain such interaction: for instance the model of competition or sharing the attention resource system, the model of non-linear interaction between different tasks and the model of priority task [7,8]

Methods

Results

Conclusion