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Related Experiment Videos

Crowding and eccentricity determine reading rate.

Denis G Pelli1, Katharine A Tillman, Jeremy Freeman

  • 1Psychology and Neural Science, New York University, New York, NY, USA. denis.pelli@nyu.edu

Journal of Vision
|January 26, 2008
PubMed
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Reading speed is determined by the number of letters readable without crowding, not letter size. This visual span explains reading rate variations across different text conditions.

Area of Science:

  • Visual perception
  • Reading science
  • Cognitive psychology

Background:

  • Bouma's law of crowding explains limited visual processing in the visual periphery.
  • Reading involves discrete eye fixations, with a limited "visual span" per fixation.
  • The factors limiting this visual span remain incompletely understood.

Purpose of the Study:

  • To determine if the visual span is equivalent to the uncrowded span predicted by Bouma's law.
  • To investigate the relationship between the uncrowded span and reading rate.
  • To explain the parameters of the reading rate curve (critical print size and maximum reading rate).

Main Methods:

  • Measured rapid serial visual presentation (RSVP) reading rate for text (ordered and scrambled) at various sizes and spacings.

Related Experiment Videos

  • Utilized a "silent substitution" technique to measure the uncrowded span during reading.
  • Assessed critical spacing for letter identification and its relation to reading span.

    • Main Results:

    • The visual span is directly proportional to the uncrowded span.
    • Reading rate is proportional to the uncrowded span at each vertical eccentricity.
    • Crowding, not letter size (acuity), limits reading for well-corrected observers under adequate lighting.
    • Critical spacing for letter identification predicts both critical spacing and span for reading.

    Conclusions:

    • Bouma's law of crowding and Legge's conjecture on visual span unify to explain reading rate variations.
    • The uncrowded span model accurately predicts the reading rate curve's shape and parameters.
    • Reading is consistently limited by crowding across various viewing conditions and text types.