Joints and their relations as critical features in action discrimination: Evidence from a classification image method

• DOI: 10.1167/15.1.20
• Publication Date: 2015-01-21T04:22:11Z
• Authors: J. J. A. van Boxtel; H. Lu
• Keywords: Feature (linguistics); Similarity (geometry)

Classifying an action as a runner or walker is seemingly effortless process. However, it difficult to determine which features are used with hypothesis-driven research, because biological motion stimuli generally consist of about dozen joints, yielding enormous number potential relationships among them. Here, we develop hypothesis-free approach based on classification image method, using experimental data from relatively few trials (∼1,000 per subject). Employing ambiguous actions morphed between and runner, identified three types that play important roles in discriminating bipedal locomotion presented side view: (a) critical joint feature, supported by the finding similarity movements feet wrists prototypical these joints were most reliably across all participants; (b) structural features, indicated contributions almost other potentially through form-based analysis; (c) relational revealed statistical correlations contributions, specifically relations two feet, wrists/elbow hips. When inverted, only remained significantly influence discrimination responses. continuous depth rotation, associated strongly Using double-pass paradigm, estimated internal noise twice large external noise, consistent previous findings. Overall, our novel design rich set discrimination. The visual system flexibly selects subset depending viewing conditions.