Anisotropy in judging the absolute direction of motion

Gunter Loffler, Harry S. Orbach

Research output: Contribution to journalArticlepeer-review

31 Citations (Scopus)


The angular dependence of precision measurements is well established as the oblique effect in motion perception. Recently, it has been shown that the visual system also exhibits anisotropic behaviour with respect to accuracy of the absolute direction of motion of random dot fields. This study aimed to investigate whether this angular dependent, directional bias is a general phenomenon of motion perception. Our results demonstrate, for single translating tilted lines viewed foveally, an extraordinary illusion with perceptual deviations of up to 35° from veridical. Not only is the magnitude of these deviations substantially larger than that for random dots, but the general pattern of the illusion is also different from that found for dot fields. Significant differences in the bias, as a function of line tilt and line length, suggest that the illusion does not result from fixed inaccuracies of the visual system in the computation of direction of motion. Potential sources for these large biases are motion integration mechanisms. These were also found to be anisotropic. The anisotropic nature and the surprisingly large magnitude of the effect make it a necessary consideration in analyses of motion experiments and in modelling studies.

Original languageEnglish
Pages (from-to)3677-3692
Number of pages16
JournalVision Research
Issue number27
Publication statusPublished - 1 Nov 2001


  • psychophysics
  • illusions
  • vision sciences
  • motion
  • anisotropy


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