No correlations between the magnitude of visual illusions

In cognition, audition and somatosensation, performance correlates strongly between different tasks suggesting the existence of common factors. Surprisingly, this does not hold true for vision. For example, Vernier acuity and Gabor detection correlate very weakly (r2 = 0.003). Here, we show similar results for visual illusions. 143 participants, aged from 8 to 81 were tested for illusion magnitude using the method of adjustment in six visual illusions. Correlations of illusion strength were very low and mostly non-significant. For example, the correlation between the Ebbinghaus and the Ponzo illusion was r2 = 0.07, i.e., the two illusions have only 7% of variance in common. Results for males and females were similar. Our null results are supported by good test-retest reliability and a Bayesian analysis. Our results suggest that, contrary to cognition, audition and somatosensation, there is no general factor for vision