Motion in depth cued by chromatic interocular velocity differences and changing disparity Alex Wade Jeffrey Jordan Milena Kaestner Priyav Shah Department of Psychology University of York, UK

CD IOVD Rushbass, C., & Westheimer, G. (1961).

CD IOVD Disparity computed first Disparity computed second (Nefs, O’Hare & Harris, 2010, Shioiri, S., Saisho, H., & Yaguchi, H. (2000) )

Color Isoluminant color not a strong cue to motion or depth. But pure chromatic signals can drive both motion and depth perception at high contrasts Does performance on CD and IOVD detection depend on stimulus chromaticity?

Stimuli Random dot stereograms, + and – contrasts Randomized each 6 frames -> CD Moving, anticorrelated dots -> IOVD/CD Moving, decorrelated dots -> pure IOVD Coherence thresholds compared across all experiments Individual dots at 2x detection threshold. Isoluminance determined from minimum motion

Mirror stereoscope CRT Mirror Participant Screen OPL=1m

Pure CD (100% coherence) Dot FWHM: 0.15deg. Aperture diameter: 4deg

Pure IOVD

Pure IOVD * * * *

Methods OSX Mac / Psykinematix N=12 Thresholds estimated using a Bayesian adaptive paradigm Contrast detection thresholds and isoluminance from separate experiments (2AFC, minimum motion), same display. Subjects indicated polarity of stereomotion sine wave over 1s: average disparity=0

Methods IOVD, CD motion amplitude equiv to 19cm around fixation at 100cm * 38cm * *

Results CD vs IOVD coherence thresholds

Coherence thresholds ** Points: All types yield real thresholds. aIOVD t’holds higher than CD, not sig diff from dIOVD.

Chromatic stimuli K.R. Dobkins, Neuron, Vol. 25, 15–18, January, 2000

Chromatic stimuli

Chromatic stimuli

Chromatic stimuli

Both IOVD and CD are detectable at isoluminance Achromatic thresholds

Interaction between color and stim type: For CD, advantage to L-M Interaction between color and stim type: For CD, advantage to L-M. For IOVD, advantage to S

Cross-channel noise masking Do CD, IOVD systems treat chromatic channels independently? …or are signal, noise pooled across channels before detection?

Detection thresholds are independent of noise chromaticity

Color calibration? Estimated luminance signal in both S-cone and L-M stimuli <0.5% contrast Subjects perform at chance at this contrast level for achromatic tasks Cross-channel masking (S/Lum and L-M/Lum) not significantly different to within-channel masking.

Conclusion IOVD and CD stereomotion systems can be compared using RDK coherence thresholds Achromatic CD thresholds are 2/3 those of IOVD Chromatic IOVD and CD thresholds measured reliably The advantage of CD over IOVD is reduced at isoluminance and for S-cone system. Both mechanisms appear to pool signals across chromatic and achromatic channels.

Thanks Steve Shevell Milena Kaestner Doug Taylor