title: Tilt psychophysics measured in nonhuman primates.
abstract: A method to measure tilt psychophysics in nonhuman primates has been developed and tested. Two rhesus monkeys were trained to orient a light bar parallel to the direction of gravity by rotating a small steering wheel attached to the primate chair. After adequate training, they performed this task during motion paradigms that rotated the gravitoinertial force (GIF) in the roll plane. The animals accurately aligned the light bar with the direction of gravity during and following roll tilts. Subtle aspects of perceived roll tilt previously recorded in human subjects were also observed in the monkeys. During centrifugation and linear translation, an interaural inertial force rotates the GIF in the roll plane. Similar to humans, the animals' perceived direction of gravity shifted toward alignment with the GIF during these paradigms, and the dynamics of these shifts demonstrated an interaction between the otolith afferents that transduce the GIF and rotational cues from the semicircular canals. Finally, optokinetic roll stimulation induced an illusion of roll tilt that was dependent on head orientation, similar to results described in human subjects. Taken together, these findings validate the methodology employed to measure tilt psychophysics; the monkeys' responses were qualitatively similar to those described in human subjects and also recapitulated subtle aspects of the perceptual response observed in humans. This new methodology sets the stage for innovative experimental approaches that will help to elucidate the neural mechanisms underlying the perception of spatial orientation.
authors.affiliation: Department of Otology and Laryngology, Harvard Medical School, Jenks Vestibular Physiology Laboratory, Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston MA 02114, USA. Richard_lewis@meei.harvard.edu
authors.forename: Richard F
authors.initials: RF
authors.lastname: Lewis
authors.forename: Csilla
authors.initials: C
authors.lastname: Haburcakova
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Merfeld
mesh_terms: D000818:Animals; D008253:Macaca mulatta; D017120:Nystagmus, Optokinetic / Q000502:physiology; D010775:Photic Stimulation; D011187:Posture