In Experiments 1 and 2, cebus monkeys matched element comparison stimuli to either element or color-form compound samples, with retention intervals ranging from ,5 to 32 sec. In both experiments, performance on compound sample trials was substantially below performance on element sample trials at the .5-sec delay, and the retention gradients were essentially parallel. These results were viewed as supporting the generalization-decrement rather than the shared-attention interpretation of how animals process compound samples. Experiment 3 employed form-form rather th'an color-form compounds and obtained the same results with simultaneous matching and delays ranging to 128 sec. Experiment 4 verified the findings of Experiment 3 for both form-form and color-form compounds and showed that as predicted by the generalization-decrement view, when the compound sample served as the correct comparison stimulus, performance was closely comparable to that achieved on element trials. The present results, taken in conjunction with earlier work with pigeons, suggest that pigeons and monkeys do not readily abstract the elements of a compound sample, which seems at odds with the pigeon's reported ability to rapidly form concepts based on natural and artificial categories.In an interesting series of experiments, sion (red vs. green, or vertical vs. horizontal Maki and his associates investigated shared lines), matching behavior was poorer than attention in the pigeon in the context of when the sample stimulus consisted of a sinmatching to sample with element and com-gle element (e.g., red or vertical lines). This pound sample stimuli (Maki & Leith, 1973; difference in performance, which survived Maki & Leuin, 1972; Maki, Riley, & Leith, extensive training with compound and ele-1976). The major result of these studies was ment samples, can be interpreted in a numthat when presented with a compound sam-ber of ways. That favored by Maki and his pie stimulus (e.g., vertical lines superinv associates is that when presented with a composed on a red background) followed by a pound sample of relatively brief duration, choice between the elements of one dimen-the bird must share its attention between the , two available elements and, due to a limited This research, based in part on a master's thesis and information-processing system, neither ele-PhD dissertation of j. K. Cox, was supported by grants ment is processed to the same degree as when from the National Science Foundation. j t occurs alone. These investigators ruled out D'&e^ the mor « ? b y ious and Parsimonious expla-