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Compulsory averaging of crowded orientation signals in human vision

Abstract

A shape can be more difficult to identify when other shapes are near it. For example, when several grating patches are viewed parafoveally, observers are unable to report the orientation of the central patch. This phenomenon, known as 'crowding,' has historically been confused with lateral masking, in which one stimulus attenuates signals generated by another stimulus. Here we show that despite their inability to report the orientation of an individual patch, observers can reliably estimate the average orientation, demonstrating that the local orientation signals are combined rather than lost. Our results imply that crowding is distinct from ordinary masking, and is perhaps related to texture perception. Under crowded conditions, the orientation signals in primary visual cortex are pooled before they reach consciousness.

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Figure 1: Examples of experimental stimuli.
Figure 2: Orientation thresholds for classifying targets as clockwise or counterclockwise.
Figure 3: Results of foveal presentation (experiment 6).
Figure 4: Effect of distractor tilt.

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Acknowledgements

This work was supported by a grant from the Engineering and Physical Sciences Research Council (EPSRC) of Great Britain. The experiments were carried out at the Institute of Cognitive Neuroscience, University College London.

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Correspondence to Michael Morgan.

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Parkes, L., Lund, J., Angelucci, A. et al. Compulsory averaging of crowded orientation signals in human vision. Nat Neurosci 4, 739–744 (2001). https://doi.org/10.1038/89532

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