A Role for Cortical Crosstalk in the Binding Problem: Stimulus-driven Correlations that Link Color, Form, and Motion Vincent A. Billock1and Brian H. Tsou2 Abstract &The putative independence of cortical mechanisms for color, form, and motion raises the binding problem—how isneural activity coordinated to create unified and correctly segmented percepts? Binding could be guided by stimulus-driven correlations between mechanisms, but the nature ofthese correlations is largely unexplored and no one has(intentionally) studied effects on binding if this joint informa-tion is compromised. Here, we develop a theoretical frame-work which: (1) describes crosstalk-generated correlationsbetween cortical mechanisms for color, achromatic form, and motion, which arise from retinogeniculate encoding; (2) showshow these correlations can facilitate synchronization, segmen-tation, and binding; (3) provides a basis for understanding perceptual oddities and binding failures that occur forequiluminant and stabilized images. These ideas can be testedby measuring both perceptual events and neural activity while achromatic border contrast or stabilized image velocity is manipulated. & INTRODUCTION How does the brain coordinate the activity of visual mechanisms to create unified percepts? There are twoparticularly important aspects to this binding problem(see Treisman, 1996 for a review of all aspects)—thebinding of different parts of the same image and thebinding of different image features (e. g., form, color, and motion). Part-and feature-binding are closely related because each feature class contributes to the segmenta-tion of images from backgrounds (Regan, 2000). Thisarticle is not a theory of binding, nor is it a theory ofmotion, color, and luminance defined form—on whichvast literatures already exist. Rather, we create a frame-work in which binding and its perceptual attributes maybe better understood. Towards this end, we tackle some key questions that are too seldom addressed in binding studies: (1) Just how independent are putatively inde-pendent cortical mechanisms for color, achromatic form,and motion, and what is the nature of any crosstalkbetween them? (2) How could crosstalk between thesemechanisms contribute to binding? (3) If ordinary visionis a resounding binding success, what would a catastroph-ic part-binding failure look like (feature-binding failures are called illusory conjunctions; Treisman, 1996), and under what conditions would binding failures occur?Background on Parallel Perceptual Mechanisms and Binding Theory Ample physiological and psychophysical evidence sug-gest that human vision is mediated by multiple mecha-nisms, each responding to selective combinations ofimage attributes (color, spatial frequency, orientation,motion, etc. ; for reviews see Regan, 2000; Zeki, 1993). This parallel processing—although crucial to under-standing visual detection and appearance—raises a bind-ing problem: How are unified and correctly segmented percepts created from the activity of putatively indepen-dent, spatially separated c ortical mechanisms? One theory is that binding stems from coordination of mech-anisms responding to an image (von der Malsburg, 1981,1995). Electrophysiological studies show coordinated g-band (generally 30-90 Hz) oscillations between cells inthe same and different orientation columns of the same cortical area, in different cortical areas, and in different hemispheres (for review and debates, see Gray, 1999;Shadlen & Movshon, 1999; Singer, 1999; Singer & Gray,1995). Recently, a series of compelling studies have tiedspecific g-band EEG activity in humans to specific per-cepts (Gruber, Mu ¨ller, & Keil, 2002; Tallon-Baudry & Bertrand, 1999). This impressive corpus of work onbinding and neural synchronization compels us to ad-dress a key question: What information governs binding? In principle, a sufficien tly potent coupling could synchronize any two neurons' activity, but indiscrimi-1General Dynamics,2U. S. Air Force Research Laboratory D2004 Massachusetts Institute of Technology Journal of Cognitive Neuroscience 16:6, pp. 1036-1048