How does visuospatial attention modulate motor preparation during gait initiation?

Gait initiation is an automatized motor program that is preceded by anticipatory postural adjustments (APAs). These adjustments create the propulsive forces required to reach the steady-state gait at the end of the first step and can be studied by the displacement of the centre of pressure. The objective of this study was to demonstrate that APAs can be modulated by visuospatial attentional processes prior to motor execution. An adaptation of the Posner paradigm was used to assess attention during step initiation. Twelve healthy subjects performed a gait initiation task under three conditions: a no-cue condition (the control experiment), a double-cue condition (alerting attention) and a single-cue condition (orienting attention). The kinetic and kinematic parameters of the APAs and step initiation were recorded. The time to step initiation was significantly shorter in the alerting condition than in the control condition. This effect was associated with the earlier occurrence of APAs. Orienting condition also had an effect and was associated with the modulation of APA errors (defined as a contralateral shift of the CoP on the cue side before corrective shifting to the target side). Behavioural measurements (such as postural preparation of step initiation) may reflect the interaction between attention and locomotion. Our results show that the different components of attention each have a specific influence on step initiation parameters.