Dissociable processes for orientation discrimination learning and contextual illusion magnitude.

Charlotte Elizabeth Holmes Wilks,Geraint Rees,Dietrich Samuel Schwarzkopf

doi:10.1371/journal.pone.0103121

Charlotte Elizabeth Holmes Wilks, Geraint Rees + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0103121

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Abstract

Previous research suggests an inverse relationship between human orientation discrimination sensitivity and tilt illusion magnitude. To test whether these perceptual functions are inherently linked, we measured both orientation discrimination sensitivity and the magnitude of the tilt illusion before and after participants had been trained for three days on an orientation discrimination task. Discrimination sensitivity improved with training and this improvement remained one month after the initial learning. However, tilt illusion magnitude remained unchanged before and after orientation training, at either trained or untrained orientations. Our results suggest that orientation discrimination sensitivity and illusion magnitude are not inherently linked. They also provide further evidence that, at least for the training periods we employed, perceptual learning of orientation discrimination may involve high-level processes.

Highlights

Visual illusions dissociate a physical stimulus from its subjectively perceived quality
We examined a potential inherent trade-off between orientation discrimination sensitivity and the strength of the tilt illusion
In both experiments we showed that training for three days improved orientation discrimination ability at the trained orientations

Summary

Introduction

Visual illusions dissociate a physical stimulus from its subjectively perceived quality. Individuals who are better at discriminating orientation exhibit weaker illusion magnitudes and have greater V1 surface areas. That is, when the surface area of V1 is larger, intra-cortical connections may be weaker because there are physical constraints on their length and/or the speed of transmission This would reduce the effect of contextual interactions and reduce illusion strength. Since orientation is encoded in an orderly map comprising homogeneous orientation domains [7,8,9], it is possible that such domains are wider, and locally more homogenous, in individuals with larger V1 This would predict finer orientation selectivity on average and could result in greater discrimination ability

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