Disambiguating the cognitive and adaptive effects of contextual cues of an impending balance perturbation

Contextual cueing advancing the characteristics of an impending balance perturbation has been thought to induce optimized automatic postural responses. In this investigation, we aimed to disambiguate the cognitive and adaptive components of cueing a balance perturbation through the direction sequence of a series of base of support translations. We compared three experimental conditions: (a) block, with one perturbation cueing that the following one would be in the same direction; (b) serial, with one perturbation cueing that the following one would be in the opposite direction; and (c) random, representing a control uncued condition. Participants were instructed about the perturbation sequences. With this arrangement, at the cognitive level there was no directional uncertainty both in the block and serial sequences, while at the non-cognitive level only the block sequence was expected to lead to optimized responses in comparison to the random sequence. Results showed that the block sequence led to the generation of more stable automatic postural responses in comparison to the serial and random sequences, as indicated by lower amplitudes of body sway and lower velocity of center of pressure displacement. Increased balance stability in the block sequence was associated with longer delays of activation onset of leg distal muscles. Comparisons between the serial and random perturbation sequences failed to show any significant differences. These results indicate that optimized postural responses in the block sequence are due to adaptive processes underlying repetitive perturbations over trials rather than to processing of contextual cues at the cognitive level reducing uncertainty about characteristics of an impending perturbation.