Scale dependence and channel switching in letter identification

Ipek Oruç, Michael S. Landy

Research output: Contribution to journalArticlepeer-review


Letters are broadband visual stimuli with information useful for discrimination over a wide range of spatial frequencies. Yet, recent evidence suggests that observers use only a single, fixed spatial-frequency channel to identify letters and that the scale of that channel, in units of letter size, is determined by the size of the letter (scale dependence). We report two letter-identification experiments using critical-band masking. With sufficiently high-amplitude, low- or high-pass masking noise, observers switched to a different range of spatial frequencies for the task. Thus, letter channels are not fixed for a given letter size. When an additional white-noise masker was added to the stimulus to flatten the contrast-sensitivity function, the letter channel used by the observer still depended on letter size, further supporting the hypothesis that letter identification is scale dependent.

Original languageEnglish (US)
Article number4
JournalJournal of vision
Issue number9
StatePublished - Aug 13 2009


  • Channel switching
  • Critical-band masking
  • Equivalent input noise
  • Ideal observer
  • Letter channels
  • Letter identification
  • Scale invariance

ASJC Scopus subject areas

  • Ophthalmology
  • Sensory Systems


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