Motion Perception During Variable-Radius Swing Motion in Darkness

• Published in: Journal of neurophysiology Vol. 102; no. 4; pp. 2232 - 2244
• Main Authors: Rader, A. A, Oman, C. M, Merfeld, D. M
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01.10.2009; American Physiological Society
• Subjects: Adult; Darkness; Female; Humans; Least-Squares Analysis; Linear Models; Male; Middle Aged; Movement; Perception; Proprioception; Psychophysics; Regression Analysis; Rotation; Young Adult
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00116.2009

1 Man Vehicle Lab, Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge; and 2 Jenks Vestibular Research Laboratory, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts Submitted 9 February 2009; accepted in final form 11 July 2009 ABSTRACT Using a variable-radius roll swing motion paradigm, we examined the influence of interaural ( y -axis) and dorsoventral ( z -axis) force modulation on perceived tilt and translation by measuring perception of horizontal translation, roll tilt, and distance from center of rotation (radius) at 0.45 and 0.8 Hz using standard magnitude estimation techniques (primarily verbal reports) in darkness. Results show that motion perception was significantly influenced by both y- and z -axis forces. During constant radius trials, subjects' perceptions of tilt and translation were generally almost veridical. By selectively pairing radius (1.22 and 0.38 m) and frequency (0.45 and 0.8 Hz, respectively), the y -axis acceleration could be tailored in opposition to gravity so that the combined y -axis gravitoinertial force (GIF) variation at the subject's ears was reduced to 0.035 m/s 2 – in effect, the y -axis GIF was "nulled" below putative perceptual threshold levels. With y -axis force nulling, subjects overestimated their tilt angle and underestimated their horizontal translation and radius. For some y -axis nulling trials, a radial linear acceleration at twice the tilt frequency (0.25 m/s 2 at 0.9 Hz, 0.13 m/s 2 at 1.6 Hz) was simultaneously applied to reduce the z -axis force variations caused by centripetal acceleration and by changes in the z -axis component of gravity during tilt. For other trials, the phase of this radial linear acceleration was altered to double the magnitude of the z -axis force variations. z -axis force nulling further increased the perceived tilt angle and further decreased perceived horizontal translation and radius relative to the y -axis nulling trials, while z -axis force doubling had the opposite effect. Subject reports were remarkably geometrically consistent; an observer model-based analysis suggests that perception was influenced by knowledge of swing geometry. Address for reprint requests and other correspondence: D. Merfeld, Jenks Vestibular Physiology Lab, Massachusetts Eye and Ear Infirmary, Rm 421, 243 Charles St., Boston, MA 02114 (E-mail: dan_merfeld{at}meei.harvard.edu ).