Global form perception: interactions between luminance and texture information

Purpose: This experiment reports the independence of first- and second-orde r processing mechanisms in form perception, Methods: Symmetrical dot patterns were created using either luminance-incre ment dots (luminance above background), or texture-defined dots (average lu minance equal to background),The proportion of luminance increment or textu re dots defining each pattern was varied among fields of noise dots of the same type to determine symmetry detection thresholds. Results: Differences in detection thresholds were found between luminance- and texture-defined patterns. Further; symmetry detection thresholds for lu minance-increment dot patterns were resistant to noise defined by dots of o pposite contrast polarity (luminance-decrement dots) or texture, while text ure-defined patterns were resistant to neither texture nor luminance-decrem ent noise. Conclusions: These data suggest that symmetry perception, along with other types of form perception, use both first- and second-order processing mecha nisms,The data are compatible with a second-order system that includes a ne gative half-wave rectifying non-linearity.