Comparing lateral motion and motion-in-depth with continuous psychophysics
Joan López-Moliner

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Date: Wednesday, 25.01.23 15:20 CET

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Abstract:

Thresholds for motion-in-depth (MID) are often larger than those reported for lateral or fronto-parallel motion, denoting lower sensitivity for MID. Probably this is so because the use of monocular and binocular cues in MID needs the support of extra-retinal signals. However, MID is ubiquitous in many perception-action tasks in which people perform quite well (e.g. catching a fly-ball). Using continuous psychophysics, one study has shown that MID is also impaired based on spatio-temporal properties of the tracking behaviour when compared to lateral motion. The motion in this study consisted of a random-walk, so the use of velocity was not possible. I will present data from two experiments that aimed at comparing position and velocity uncertainties between MID and lateral components of motion. In one experiment, participants had to cancel any perceived motion by tracking the trajectory of a structured cloud of dots with the eye-head system within a VR setting (HTC VivePro @90Hz). The dots underwent an elliptical motion with lateral and depth components. In the second experiment participants had to track a single target that described different trajectories with depth and lateral components in the same immersive environment.

Positional and speed measurement uncertainties were estimated by using a Kalman filter defined according to the stimulus dynamics. Results show that positional uncertainty was only significantly larger for the depth component (10.9 cm) relative to the lateral one (8.7 cm) when participants tracked a single-target but not when they had to cancel the retinal motion. Speed uncertainties, however, were very similar for both motion components in the two experiments. Unlike many previous studies that have reported a clear superiority for lateral motion, the differences are far less clear when uncertainties are estimated by using continuous psychophysics methodology.