The contribution of linear perspective cues and texture gradients in the perceptual rescaling of stimuli inside a Ponzo illusion corridor.

Gizem Y Yildiz,Philippe A Chouinard,Christine Kettle,Irene Sperandio,Magdalena Ewa Król

doi:10.1371/journal.pone.0223583

Gizem Y Yildiz, Philippe A Chouinard + Show 3 more

Open Access

https://doi.org/10.1371/journal.pone.0223583

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Journal: PloS one	Publication Date: Oct 10, 2019
Citations: 11	License type: CC BY 4.0

Affiliation: La Trobe University, University of East Anglia

Abstract

We examined the influence of linear perspective cues and texture gradients in the perceptual rescaling of stimuli over a highly-salient Ponzo illusion of a corridor. We performed two experiments using the Method of Constant Stimuli where participants judged the size of one of two rings. In experiment 1, one ring was presented in the upper visual-field at the end of the corridor and the other in the lower visual-field at the front of the corridor. The perceived size of the top and bottom rings changed as a function of the availability of linear perspective and textures. In experiment 2, only one ring was presented either at the top or the bottom of the image. The perceived size of the top but not the bottom ring changed as a function of the availability of linear perspective and textures. In both experiments, the effects of the cues were additive. Perceptual rescaling was also stronger for the top compared to the bottom ring. Additional eye-tracking revealed that participants tended to gaze more in the upper than the lower visual-field. These findings indicate that top-down mechanisms provide an important contribution to the Ponzo illusion. Nonetheless, additional maximum likelihood estimation analyses revealed that linear perspective fulfilled a greater contribution in experiment 2, which is suggestive of a bottom-up mechanism. We conclude that both top-down and bottom-up mechanisms play important roles. However, the former seems to fulfil a more prominent role when both stimuli are presented in the image.

Highlights

If two objects at different distances subtend the same visual angle on the retina the object located at the furthest distance is physically larger as a proportion of distance from the other in a manner obeying Euclidian geometry [1]
One sample t-tests revealed that the top standard ring was perceived larger than its physical size across all backgrounds with pictorial depth cues while the bottom standard ring was perceived smaller than its physical size when it was presented with linear perspective cues only (p = .016)
The present study investigated the effects of linear perspective cues and texture gradients in the perceptual rescaling of stimuli over a Ponzo-like illusory display of a hallway

Summary

Introduction

If two objects at different distances subtend the same visual angle on the retina the object located at the furthest distance is physically larger as a proportion of distance from the other in a manner obeying Euclidian geometry [1]. The visual system estimates greater depth when two lines on the retina converge closer together. Another important pictorial depth cue is texture gradient. The visual system estimates greater depth where texture gradients are smaller. Artists apply this knowledge to create illusory depth on a 2D image to trick us in perceiving depth and size differences [5]

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