Abstract

Motion at constant speed in the world maps into retinal motion very differently for lateral motion and motion in depth. The former is close to linear, for the latter, constant speed objects accelerate on the retina as they approach. Motion in depth is frequently studied using speeds that are constant on the retina, and are thus not consistent with real-world constant motion. Our aim here was to test whether this matters: are we more sensitive to real-world motion? We measured speed change discrimination for objects undergoing accelerating retinal motion in depth (consistent with constant real-world speed), and constant retinal motion in depth (consistent with real-world deceleration). Our stimuli contained both looming and binocular disparity cues to motion in depth. We used a speed change discrimination task to obtain thresholds for conditions with and without binocular and looming motion in depth cues. We found that speed change discrimination thresholds were similar for accelerating retinal speed and constant retinal speed and were notably poor compared to classic speed discrimination thresholds. We conclude that the ecologically valid retinal acceleration in our stimuli neither helps, nor hinders, our ability to make judgements in a speed change discrimination task.

Highlights

  • The perception of motion is crucial for human vision: do we live in a world where important objects move, but we move ourselves

  • We hypothesized that the visual system might be more sensitive to changes in constant world speeds, which accelerate on the retina, than to changes in constant retinal speeds

  • Our results show no significant difference between constant world speed and constant retinal speed conditions, as demonstrated by our World vs. Retina comparison

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Summary

Introduction

The perception of motion is crucial for human vision: do we live in a world where important objects move, but we move ourselves. Human perception of the motion around us has been studied in great detail. From this we know our visual system performs specific processing of motion speed and direction (for a recent review, see [1]). Because the retina can be thought of as a two-dimensional array, the vast majority of this work has been on motion constrained to the two dimensions that specify the fronto-parallel plane. It is essential to understand motion in both two and three dimensions, and to understand the differences between them

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