Interaction between first- and second-order orientation channels revealed by the tilt illusion

Psychophysics and computational modelling

Stuart Smith*, Colin W G Clifford, Peter Wenderoth

*Corresponding author for this work

Research output: Contribution to journalArticle

22 Citations (Scopus)


This paper examines the interaction between first- and second-order contours in the orientation domain. Using the simultaneous tilt illusion (TI), we show that the apparent rotation of a vertical test grating away from that of a surrounding inducing grating (repulsion effect) occurs when both the inducing and test grating are either first- or second-order. Furthermore, a significant repulsion effect is obtained when a first-order inducing grating surrounds a second-order test. If lateral inhibitory interactions between populations of orientation selective neurons provides a plausible explanation for orientation repulsion effects [Blakemore, C. B. Carpenter, R. H. S. & Georgeson, M. A. (1970) Nature, 228, 37-39], it is likely that the cue-invariant mechanisms that encodes the orientation of first- and second-order contours also exhibit inhibitory interactions. A two-channel computational model of orientation encoding is presented where one channel encodes only first-order stimuli while the second channel encodes both first- and second-order contours. In addition to predicting the orientation repulsion effects we observed, the model also provides a functional account of orientation attraction effects in terms of the responses of populations of orientation-tuned neurons.

Original languageEnglish
Pages (from-to)1057-1071
Number of pages15
JournalVision Research
Issue number8
Publication statusPublished - 2001


  • First-order
  • Orientation coding
  • Second-order interaction
  • Tilt illusion

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