Abstract

The scintillating grid illusion is an intriguing stimulus consisting of a grey grid on a black background, with white discs at the grid intersections. Most viewers perceive illusory “scintillating” black discs within the physical white discs, especially at non-fixated locations. Here, we report for the first time that this scintillation percept is stronger when the stimulus is viewed binocularly than when it is presented to only one eye. Further experiments indicate that this is not simply because two monocular percepts combine linearly, but involves a specifically cyclopean contribution (Schrauf & Spillmann, 2000). However, the scintillation percept does not depend on the absolute disparity of the stimulus relative to the screen. In an intriguing twist, although the basic illusion shows more scintillation when viewed binocularly, when the illusion is weakened by shifting the discs away from the grid intersections, scintillation becomes stronger with monocular viewing.

Highlights

  • 1 Introduction The scintillating grid illusion (Schrauf, Lingelbach, & Wist, 1997) is a variant of the Hermann grid in which white discs are placed at the intersections (Figure 1)

  • This creates a powerful illusion of black spots flashing inside the white discs, in peripheral vision and during saccadic eye movements (Schrauf, Wist, & Ehrenstein, 2000)

  • Stimulus code was written in Matlab using the Psychophysics Toolbox (Brainard, 1997; Kleiner, Brainard, & Pelli, 2007; Pelli, 1997)

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Summary

Introduction

The scintillating grid illusion (Schrauf, Lingelbach, & Wist, 1997) is a variant of the Hermann grid in which white discs are placed at the intersections (Figure 1) This creates a powerful illusion of black spots flashing inside the white discs, in peripheral vision and during saccadic eye movements (Schrauf, Wist, & Ehrenstein, 2000). The scintillating effect requires the white discs to have at least twice the luminance of the grey grid, and is best when the disc luminance is around 10 times that of the grid and 100 times that of the black background (Schrauf et al, 1997) It depends on orientation, being strongest when the gridlines are vertical/ horizontal as, and weakest when the entire pattern is rotated through 45° (De Lafuente & Ruiz, 2004). This has not been replicated, with other workers reporting that this dichoptic version of the grid produces binocular rivalry (Troscianko, 1982)

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