title: Human odometer is gait-symmetry specific.
abstract: In 1709, Berkeley hypothesized of the human that distance is measurable by 'the motion of his body, which is perceivable by touch'. To be sufficiently general and reliable, Berkeley's hypothesis must imply that distance measured by legged locomotion approximates actual distance, with the measure invariant to gait, speed and number of steps. We studied blindfolded human participants in a task in which they travelled by legged locomotion from a fixed starting point A to a variable terminus B, and then reproduced, by legged locomotion from B, the A-B distance. The outbound ('measure') and return ('report') gait could be the same or different, with similar or dissimilar step sizes and step frequencies. In five experiments we manipulated bipedal gait according to the primary versus secondary distinction revealed in symmetry group analyses of locomotion patterns. Berkeley's hypothesis held only when the measure and report gaits were of the same symmetry class, indicating that idiothetic distance measurement is gait-symmetry specific. Results suggest that human odometry (and perhaps animal odometry more generally) entails variables that encompass the limbs in coordination, such as global phase, and not variables at the level of the single limb, such as step length and step number, as traditionally assumed.
authors.affiliation: Center for the Ecological Study of Perception and Action , U 20, University of Connecticut, 406 Babbidge Road, Storrs, CT 06269-1020, USA. michael.turvey@uconn.edu
authors.forename: Michael T
authors.initials: MT
authors.lastname: Turvey
authors.forename: Carissa
authors.initials: C
authors.lastname: Romaniak-Gross
authors.forename: Robert W
authors.initials: RW
authors.lastname: Isenhower
authors.forename: Ryan
authors.initials: R
authors.lastname: Arzamarski
authors.forename: Steven
authors.initials: S
authors.lastname: Harrison
authors.forename: Claudia
authors.initials: C
authors.lastname: Carello
mesh_terms: D003237:Connecticut; D004215:Distance Perception / Q000502:physiology*; D005684:Gait / Q000502:physiology*; D006801:Humans; D008124:Locomotion / Q000502:physiology*; D009949:Orientation / Q000502:physiology*; D055815:Young Adult