Terrestrial-passage theory: Failing a test

Charles F. Reed, Elizabeth A. Krupinski

Research output: Contribution to journalArticlepeer-review


Terrestrial-passage theory proposes that the 'moon' and 'sky' illusions occur because observers learn to expect an elevation-dependent transformation of visual angle. The transformation accompanies daily movement through ordinary environments of fixed-altitude objects. Celestial objects display the same visual angle at all elevations, and hence are necessarily non-conforming with the ordinary transformation. On hypothesis, observers should target angular sizes to appear greater at elevation than at horizon. However, in a sample of forty-eight observers there was no significant difference between the perceived angular size of a constellation of stars at horizon and that predicted for a specific elevation. Occurrence of the illusion was not restricted to those observers who expected angular expansion. These findings fail to support the terrestrial-passage theory of the illusion.

Original languageEnglish (US)
Pages (from-to)740-747
Number of pages8
Issue number5
StatePublished - 2009

ASJC Scopus subject areas

  • Experimental and Cognitive Psychology
  • Ophthalmology
  • Sensory Systems
  • Artificial Intelligence


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