Stimulus-driven attention modulates the release of anticipatory postural adjustments during step initiation

Step initiation can be modified by environmental stimulations, suggesting the involvement of stimulus-driven attention. Therefore, we assessed the influence of attentional status during step preparation.

Fourteen healthy, young subjects were presented with an auditory oddball paradigm in which an infrequent "target" stimulus was presented among frequent "standard" stimuli. An imperative visual "Go" signal for step initiation was presented 1.4s after the auditory stimulus. Both the P300 event-related potential (associated with the auditory attention task) and the trajectory of the centre of pressure (associated with step initiation) were recorded.

When presented before the visual "Go" signal, the auditory stimuli prompted the early release of low-amplitude anticipatory postural adjustments, not followed by step execution. They occurred twice as frequently in the "target" condition as they did in the "standard" condition. P300 component was greater after presentation of the target stimulus than after presentation of the standard stimulus.

Stimulus-driven attention can modify the release of anticipatory postural adjustments.

The cortical integration of an auditory stimulus (as evidenced by the P300 component) in a subject conditioned to initiate gait appears to release postural adjustments via two different attentional mechanisms: an "alerting effect" and an "orienting effect".