DISCRIMINATION OF COMPLEX PATTERNS - ORIENTATION INFORMATION IS INTEGRATED ACROSS SPATIAL SCALE - SPATIAL-FREQUENCY AND CONTRAST INFORMATION ARE NOT

Real-world objects are complex, containing information at multiple ori entations and spatial scales. It is well established that at initial c ortical stages of processing, local information about an image is sepa rately represented at multiple spatial scales. However, it is not yet established how these early representations are later integrated acros s scale to signal useful information about complex stimulus features, such as edges and textures. In the studies reported here, we investiga te the scale-integration processes involved in distinguishing among co mplex patterns. We use a concurrent-response paradigm in which observe rs simultaneously judge two components of compound gratings that diffe r widely in spatial frequency. In different experiments, each componen t takes one of two slightly different values along the dimensions of s patial frequency, contrast, or orientation. Using analyses developed w ithin the framework of a multivariate extension of signal-detection th eory, we ask how information about the frequency, contrast, or orienta tion of the components is or is not integrated across the two grating components. Our techniques permit us to isolate and identify interacti ons due to excitatory or inhibitory processes from effects due to nois e, and to separately assess any attentional limitations that might occ ur in processing. Results indicate that orientation information is ful ly integrated across spatial scales within a limited orientation band and that decisions are based entirely on the summed information. Infor mation about spatial frequency and contrast is not summed over spatial scale; cross-scale results show sensory independence. However, our re sults suggest that observers cannot simultaneously use information abo ut frequency or contrast when it is presented at different spatial sca les. Our results provide direct evidence for the existence of a higher -level summing circuit tailored to signal information about orientatio n. The properties of this mechanism differ substantially from edge-det ector mechanisms proposed by Marr and others.