A catch-up illusion arising from a distance-dependent perception bias in judging relative movement

Tobias Meilinger,Stephan Schwan,Bärbel Garsoffky

doi:10.1038/s41598-017-17158-8

Abstract

The perception of relative target movement from a dynamic observer is an unexamined psychological three body problem. To test the applicability of explanations for two moving bodies participants repeatedly judged the relative movements of two runners chasing each other in video clips displayed on a stationary screen. The chased person always ran at 3 m/s with an observer camera following or leading at 4.5, 3, 1.5 or 0 m/s. We harmonized the chaser speed in an adaptive staircase to determine the point of subjective equal movement speed between runners and observed (i) an underestimation of chaser speed if the runners moved towards the viewer, and (ii) an overestimation of chaser speed if the runners moved away from the viewer, leading to a catch-up illusion in case of equidistant runners. The bias was independent of the richness of available self-movement cues. Results are inconsistent with computing individual speeds, relying on constant visual angles, expansion rates, occlusions, or relative distances but are consistent with inducing the impression of relative movement through perceptually compressing and enlarging inter-runner distance. This mechanism should be considered when predicting human behavior in complex situations with multiple objects moving in depth such as driving or team sports.

Highlights

How do moving observers perceive the relative movement between two objects? Despite its everyday relevance, this perceptual three-body problem is largely unexplored
When the runners were overall receding from the observer, slower chaser speeds were perceived as being fast as the chased
We have shown that such movements are perceived veridically for movements in the frontal plane but biased for overall visual movements away from or towards an observer

Summary

Introduction

How do moving observers perceive the relative movement between two objects? Despite its everyday relevance, this perceptual three-body problem is largely unexplored. Humans may not derive relative movement from spatial variables (i.e., perceived distances and velocities) of each object, but rely on visual field parameters, which has been demonstrated for various tasks such as breaking[8], catching[9], or self-movement perception[10]. For segments along the sagittal (viewing) axis, visual angle changes are typically not fully compensated; distances are compressed[14,15,16,17,18,19,20,21], that is, perceived as shorter compared to vertically or transversally oriented segments at the same depth The size of A will determine the required speed reduction

Methods

Results

Conclusion