Visual orientation and motion discrimination uncertainty as a function of postural stability
Poster Presentation

Ciara Brien
Psychology, University College Dublin

Danielle Gaynor
Psychology, University College Dublin

Stuart Smith
Psychology, University College Dublin

Oliver Kannape
Psychology, UCD

     Abstract ID Number: 47
     Full text: Not available
     Last modified: May 30, 2007

Abstract
Perception of one’s orientation with respect to the environment is naturally multisensory with inputs from visual, vestibular, auditory and proprioceptive modalities. Internal estimates of body orientation based upon multisensory static (e.g. visual vertical) and dynamic (e.g. optic flow) orientation cues are then used in the control of posture. Most psychophysical studies of visual perceptual performance reported in the literature have been conducted with observers statically oriented, usually with respect to gravitational vertical. Using the Rod and Frame Test, Bray et al (2004) showed an improvement in perception of visual vertical during a postural challenge task (beam balancing). In a series of experiments we demonstrate how perceptual uncertainty in visual orientation and optic flow discrimination tasks is significantly modulated during trials when postural stability and proprioceptive information is altered (sitting, standing and air mattress balancing). Using 2AFC method of constant stimuli and fitting the resulting psychometric data with the Matlab toolbox, psychofit (Wichman and Hill, 2001), we quantified perceptual uncertainty by the standard deviation of the cumulative Gaussian fit. Our data extends the previous findings of Bray et al (2004) to off-vertical orientation judgments and perception of visual motion. We discuss our data in terms of MLE models of multisensory integration.