The different mechanisms of the direct and indirect tilt illusions

Peter Wenderoth*, Syren Johnstone

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    94 Citations (Scopus)


    Both the tilt illusion and aftereffect exhibit indirect effects under certain conditions: these are negative (assimilation) effects which occur with large (70-90 deg) angular separations between test and inducing gratings. They are opposite in direction to the positive, and much larger, contrast effects which occur at smaller (10-15 deg) separations. Evidence from six experiments shows that stimulus manipulations which reduce direct effects have little or no effect on indirect effects and vice versa, suggesting that the two effects have different determinants. It is proposed that direct effects arise from lateral inhibitory interactions between populations of neurones in striate cortex and that indirect effects occur at a higher level, possibly in areas concerned with stimulus-specific interactions beyond the classic receptive field. The implications of the data for theories of the tilt illusion are considered.

    Original languageEnglish
    Pages (from-to)301-312
    Number of pages12
    JournalVision Research
    Issue number2
    Publication statusPublished - 1988


    • Indirect effect
    • Orientation
    • Spatial frequency
    • Tilt illusion
    • Total receptive field


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