Fractality of Body Movements Predicts Perception of Affordances: Evidence From Stand-On-Ability Judgments About Slopes

• Published in: Journal of experimental psychology. Human perception and performance 2018-06, Vol.44 (6), p.836-841
• Main Authors: Hajnal, Alen, Clark, Joseph D, Doyon, Jonathan K, Kelty-Stephen, Damian G
• Format: Article
• Language: English
• Subjects: Adult; Body movement; Court decisions; Deviation; Fractals; Head Movements - physiology; Human; Humans; Information systems; Judgment - physiology; Metacognition - physiology; Motion Perception; Motor Activity - physiology; Movement; Perception; Perceptions; Posture; Psychology; Space Perception - physiology; Standard deviation; Test Construction; Variability; Visual Perception; Visual Perception - physiology; Width; Young Adult
• ISSN: 0096-1523; 1939-1277
• DOI: 10.1037/xhp0000510

We recorded head motion with one wireless marker attached to the back of the head during quiet stance as participants visually inspected a sloped ramp in order to perceive whether they might be able to stand on the surface. Participants responded with "yes" or "no" without attempting to stand on the ramp. As has been found in dynamic touch (Palatinus, Kelty-Stephen, Kinsella-Shaw, Carello, & Turvey, 2014), we hypothesized that multiscale fluctuation patterns in bodily movement during visual observation would predict perceptual judgments. Mixed-effects logistic regression predicted binary affordance judgments as a function of geographical slant angle, head-motion standard deviation, and multifractal spectrum width (Ihlen, 2012). Multifractal spectrum width was the strongest predictor of affordance judgments. Specifically, increased spectrum width predicted decreased odds of a "yes" answer. Interestingly, standard deviation was not a significant predictor, reinforcing our prediction that traditional measures of variability fail to account for what fractal measures of multiscale interactions can predict about information pickup in perception-action systems. Public Significance Statement Perception of action possibilities informs everyday action such as judging whether a sloped ground surface affords standing upright. This study demonstrated that the link between perception and action is established through subtle postural movement patterns that predict perceptual responses. This is evidence that perception and action are part of the same integrated system that guides behavior.