Abstract
When we walk in place with our eyes closed after a few minutes of walking on a treadmill, we experience an unintentional forward body displacement (drift), called the sensory-motor aftereffect. Initially, this effect was thought to be due to the mismatch experienced during treadmill walking between the visual (absence of optic flow signaling body steadiness) and proprioceptive (muscle spindles firing signaling body displacement) information. Recently, the persistence of this effect has been shown even in the absence of vision, suggesting that other information, such as the sound of steps, could play a role. To test this hypothesis, six cochlear-implanted individuals were recruited and their forward drift was measured before (Control phase) and after (Post Exercise phase) walking on a treadmill while having their cochlear system turned on and turned off. The relevance in testing cochlear-implanted individuals was that when their system is turned off, they perceive total silence, even eliminating the sounds normally obtained from bone conduction. Results showed the absence of the aftereffect when the system was turned off, underlining the fundamental role played by sounds in the control of action and breaking new ground in the use of interactive sound feedback in motor learning and motor development.
Highlights
The Surface factor unveiled a higher forward drift for the Natural Footstep Sound (NFS) compared to the SS; considering Phase, the ANOVA showed a higher value for the PE phase compared to the C phase
The interaction between Experimental Condition and Phase showed a higher value in PE compared to C only in the Cochlear Implant on (CIon) condition, and a higher value for CIon compared to Cochlear Implant off (CIoff) in the PE phase
Our results strongly sustain the reliance on auditory feedback: when the cochlear system was turned off, there was no presence of a sensory-motor aftereffect
Summary
During the past 20 years, the sensory-motor aftereffect after walking on a treadmill has been widely studied as a motor consequence resulting from a mismatch of information among the senses (Anstis, 1995; Durgin and Pelah, 1999; Durgin et al, 2005; Zanetti and Schieppati, 2007; Philbeck et al, 2008). Sensory information coming from the muscle spindles, in addition to tactile and vestibular receptors, combine to create a memory for these recent actions, which diverges from the information shared by the neural circuits responsible for the integration of afferent stimuli (Van Der Kooij et al, 1999) This mismatch of information leads to a perceptuo-motor re-calibration that can be seen as a forward displacement of the center of pressure while standing on a force plate (Zanetti and Schieppati, 2007), as a forward drift during walking in place (Anstis, 1995), or as an overshoot of a previously seen target (Rieser et al, 1995; Durgin et al, 2005). On the contrary, when the cochlear system was turned off, we expected no change in the amount of forward displacement between the pre- and post-treadmill phases
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