Abstract
Studying illusions provides insight into the way the brain processes information. The Müller-Lyer Illusion (MLI) is a classical geometrical illusion of size, in which perceived line length is decreased by arrowheads and increased by arrowtails. Many theories have been put forward to explain the MLI, such as misapplied size constancy scaling, the statistics of image-source relationships and the filtering properties of signal processing in primary visual areas. Artificial models of the ventral visual processing stream allow us to isolate factors hypothesised to cause the illusion and test how these affect classification performance. We trained a feed-forward feature hierarchical model, HMAX, to perform a dual category line length judgment task (short versus long) with over 90% accuracy. We then tested the system in its ability to judge relative line lengths for images in a control set versus images that induce the MLI in humans. Results from the computational model show an overall illusory effect similar to that experienced by human subjects. No natural images were used for training, implying that misapplied size constancy and image-source statistics are not necessary factors for generating the illusion. A post-hoc analysis of response weights within a representative trained network ruled out the possibility that the illusion is caused by a reliance on information at low spatial frequencies. Our results suggest that the MLI can be produced using only feed-forward, neurophysiological connections.
Highlights
Visual illusions have the potential to offer great insight into our visual perception
Experiment III: Illusion Strength Affected by Angle The results shown in Experiment II demonstrate errors consistent with an illusory effect; they do not provide a detailed picture of classification performance using HMAX for control versus illusory data
We devised a set of experiments to measure the classification performance for an ML stimulus versus a control, in a biologically plausible model of object recognition
Summary
Visual illusions have the potential to offer great insight into our visual perception. Illusions have been extensively studied by psychologists, as a method of deducing the assumptions that the brain makes and how we process visual information. One classical illusion known to induce misjudgement, is the Muller-Lyer Illusion (MLI). In the MLI, the perceived length of a line is affected by arrowheads or arrowtails placed at the ends of the line [1]. The line appears elongated in the arrowtails and contracted with arrowheads (see Fig. 1A). Behavioural studies have shown that the strength of the illusion is correlated with factors including shaft length [2,3], fin angle [4] and inspection time [5,6]
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