Do the neocortical commissures of the mammalian brain facilitate cognitive function? We are trying to find out if bilateral brain function is more efficient when the hemispheres are connected than when they are separated. If interconnection does facilitate function, we will try to determine the nature of the facilitation. We have trained cats bilaterally on a stimulus detection task requiring a high level of performance in response to target stimuli in visual displays which vary over a wide range of complexity and which we change from trial to trial. The task places a premium on the subject's ability to attend; on his accuracy and perceptual speed (stimulus duration thresholds are measured); and his ability to respond appropriately to differences and similarities among stimuli (i.e., to discriminate and generalize). Subjects are trained and tested rigorously before and after surgery (section of anterior commissure, corpus callosum, and hippocampal and habenular commissures) to see if the operation results in a loss of capacity. We also plan to make a careful assessment of each hemisphere's functional capacity. We would like to find out if the significant differences in capacity which we found in an earlier study represent qualitative differences between the hemispheres or simply a nonspecific superiority on one side. If we find a deficit in the above hemisphere-separation study we might expect to find that there is some specialization of the individual hemispheres. Such specialization would mean that for complex tasks the highest level of mediation could only be attained when the two sides complement each other, interacting via the neocortical commissures. If on the other hand, we find that hemisphere separation does not lower functional capacity, it is likely that we will find that the hemispheres are qualitatively similar, with the separate hemispheres supplementing each other in the mediation of complex tasks to yield the bihemispheric (as contrasted with single-hemisphere) superiority we found in earlier studies. Such findings would mean that the 2 brain halves can work simultaneously and independently to quarantee a high level of efficiency of cognitive processing of information.