Crowding: a cortical constraint on object recognition

Research output: Contribution to journalReview articlepeer-review


The external world is mapped retinotopically onto the primary visual cortex (V1). We show here that objects in the world, unless they are very dissimilar, can be recognized only if they are sufficiently separated in visual cortex: specifically, in V1, at least 6 mm apart in the radial direction (increasing eccentricity) or 1 mm apart in the circumferential direction (equal eccentricity). Objects closer together than this critical spacing are perceived as an unidentifiable jumble. This is called 'crowding'. It severely limits visual processing, including speed of reading and searching. The conclusion about visual cortex rests on three findings. First, psychophysically, the necessary 'critical' spacing, in the visual field, is proportional to (roughly half) the eccentricity of the objects. Second, the critical spacing is independent of the size and kind of object. Third, anatomically, the representation of the visual field on the cortical surface is such that the position in V1 (and several other areas) is the logarithm of eccentricity in the visual field. Furthermore, we show that much of this can be accounted for by supposing that each 'combining field', defined by the critical spacing measurements, is implemented by a fixed number of cortical neurons.{A textbox is presented}.

Original languageEnglish (US)
Pages (from-to)445-451
Number of pages7
JournalCurrent Opinion in Neurobiology
Issue number4
StatePublished - Aug 2008

ASJC Scopus subject areas

  • General Neuroscience


Dive into the research topics of 'Crowding: a cortical constraint on object recognition'. Together they form a unique fingerprint.

Cite this