Volume 7, Number 2, Article 12, Pages 1-9 doi:10.1167/7.2.12 http://journalofvision.org/7/2/12/ ISSN 1534-7362
Crowding and surround suppression: Not to be confused
Yury Petrov
Psychology Department, Northeastern University, Boston, MA, USA
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Ariella V. Popple
School of Optometry and Helen Wills Neuroscience Institute, UC Berkeley, Berkeley, CA, USA
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Suzanne P. McKee
Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA
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Abstract

Crowding and surround suppression share many similarities, which suggests the possibility of a common mechanism. Despite decades of research, there has been little effort to compare the two phenomena in a consistent fashion. A recent study by D. M. Levi, S. Hariharan, and S. A. Klein (2002) argues that the two are unrelated because crowding effects can be much stronger than suppression effects. Here we report experiments in which the same Gabor target was used both for orientation identification (crowding) and contrast detection (suppression) tasks. In agreement with early crowding studies (e.g., H. Bouma, 1973) we found, that an outward mask is much more effective than an inward mask for the orientation identification task. Notably, no such anisotropy was observed for the contrast detection task, commonly used to measure surround suppression. The anisotropic masking, which defines crowding, is observed only at fine scales (roughly within an octave of the acuity limit), whereas surround suppression is observed at all scales. Our results demonstrate that surround suppression and crowding are indeed two distinct phenomena. We used this characteristic anisotropy to show that a popular crowding paradigm in which target contrast is varied to measure crowding is confounding it with surround suppression. Surround suppression apparently dominates at low contrasts, which would explain some of the reported similarities between the two phenomena.

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History
Received July 15, 2006; published April 25, 2007
Citation
Petrov, Y., Popple, A. V., & McKee, S. P. (2007). Crowding and surround suppression: Not to be confused. Journal of Vision, 7(2):12, 1-9, http://journalofvision.org/7/2/12/, doi:10.1167/7.2.12.
Keywords
crowding, surround suppression, anisotropy
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