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Michael D. Melnick, Duje Tadin; The strength of contextual modulation does not correlate across visual sub-modalities. Journal of Vision 2012;12(9):1300. doi: 10.1167/12.9.1300.
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Typically the way that a visual feature is perceived depends on the surrounding spatial context. For example, in the well-known Ebbinghaus illusion, a circle surrounded by larger circles appears smaller. Similarly, the presence of a high-contrast background decreases the apparent contrast of smaller foreground features. Given qualitative similarities among various contextual surround effects (e.g., the effects tend to be repulsive), it might seem intuitive that these processes are related. It is unknown, however, whether contextual modulation processes across visual sub-modalities are independent, or at least in part share a common underlying mechanism. We addressed this question using an individual differences approach.
METHODS: A contextual modulation battery was administered to 89 subjects: control subjects (N=17), older adults (N=35) and psychiatric patients (N=37). The context battery included six tasks that assessed surround modulations in luminance, contrast, orientation, motion (2X) and size domains. Staircases were used to measure the amount of surround modulation by adaptively adjusting the relevant dimension of a center target so that it matched a context-free reference target.
RESULTS: Robust contextual effects were observed across all tasks and all subject groups, as evidenced by pronounced misperception of center stimulus features. To test for the existence of a common underlying mechanism, we correlated the magnitudes of contextual modulation across different tasks (separately for each group). A common mechanism would predict that a weaker contextual modulation on one task would predict weaker contextual modulation on other tasks. However, we found no significant (uncorrected) correlations for the control group. One significant correlation was found for each special population group (p=0.03), but these should be considerably unreliable given the number of comparisons. Pooled analysis also found no effects.
CONCLUSION: We find that strength of contextual modulation does not correlate across visual sub-modalities, suggesting an absence of a common underlying mechanism.
Meeting abstract presented at VSS 2012
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