title: Drifting while stepping in place in old adults: Association of self-motion perception with reference frame reliance and ground optic flow sensitivity.
abstract: Optic flow provides visual self-motion information and is shown to modulate gait and provoke postural reactions. We have previously reported an increased reliance on the visual, as opposed to the somatosensory-based egocentric, frame of reference (FoR) for spatial orientation with age. In this study, we evaluated FoR reliance for self-motion perception with respect to the ground surface. We examined how effects of ground optic flow direction on posture may be enhanced by an intermittent podal contact with the ground, and reliance on the visual FoR and aging. Young, middle-aged and old adults stood quietly (QS) or stepped in place (SIP) for 30s under static stimulation, approaching and receding optic flow on the ground and a control condition. We calculated center of pressure (COP) translation and optic flow sensitivity was defined as the ratio of COP translation velocity over absolute optic flow velocity: the visual self-motion quotient (VSQ). COP translation was more influenced by receding flow during QS and by approaching flow during SIP. In addition, old adults drifted forward while SIP without any imposed visual stimulation. Approaching flow limited this natural drift and receding flow enhanced it, as indicated by the VSQ. The VSQ appears to be a motor index of reliance on the visual FoR during SIP and is associated with greater reliance on the visual and reduced reliance on the egocentric FoR. Exploitation of the egocentric FoR for self-motion perception with respect to the ground surface is compromised by age and associated with greater sensitivity to optic flow.
authors.affiliation: CIAMS, Université Paris-Sud, Université Paris-Saclay, Orsay, France; CIAMS, Université d'Orléans, Orléans, France; Vision Sciences Department, Essilor International R&D, Paris, France. Electronic address: cpagathos@gmail.com.
authors.forename: Catherine P
authors.initials: CP
authors.lastname: Agathos
authors.affiliation: Vision Sciences Department, Essilor International R&D, Paris, France.
authors.forename: Delphine
authors.initials: D
authors.lastname: Bernardin
authors.affiliation: Vision Sciences Department, Essilor International R&D, Paris, France.
authors.forename: Konogan
authors.initials: K
authors.lastname: Baranton
authors.affiliation: LNC UMR 7291, Aix-Marseille Univ, CNRS, Marseille, France; FR 3512, Aix-Marseille Univ, CNRS, Marseille, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Assaiante
authors.affiliation: CIAMS, Université Paris-Sud, Université Paris-Saclay, Orsay, France; CIAMS, Université d'Orléans, Orléans, France.
authors.forename: Brice
authors.initials: B
authors.lastname: Isableu
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009039:Motion Perception; D057849:Optic Flow; D012649:Self Concept; D016138:Walking; D055815:Young Adult
keywords: aging; frames of reference; ground surface; optic flow; self-motion perception; stepping in place