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A quantitative method is developed for assessing the quality of pattern information in imagery, using the magnitude of color aftereffects as an objective index. Subjects were given instructions to project imagined bar patterns of particular width and orientation onto adapting color fields, in such a manner as to simulate standard conditions for establishing the McCollough effect. Our control procedures indicate that the resulting orientation-specific complementary color aftereffects cannot be attributed to the conditioning of particular directions of eye scanning movements to color processing during adaptation, or to other possible sources of experimental bias. Furthermore, subjects who rated themselves prior to the adaptation procedure as having relatively vivid imagery showed significantly larger aftereffects than those who reported having relatively low imagery. These results not only provide an important confirmation of our earlier finding that imagination can replace physical pattern information in the formation of basic color-feature associations in the human visual system, but also demonstrate that these aftereffects can provide a practical measure of the fidelity of pattern representation in visual images.In a recent study (Finke & Schmidt, 1977), we reported that instructions to imagine horizontally and vertically oriented bar patterns onto an alternating sequence of two complementary, homogeneous fields of color physically presented, and paired in such a manner as to simulate standard adaptation conditions used to produce the McCollough effect (McCollough, 1965), resulted in the presence of weak orientationspecific complementary color aftereffects. Since pattern imagination had replaced the physical presence of pattern information during adaptation exposure tc the color fields, the existence of pattern-contingent color aftereffects upon subsequent viewing of achromatic patterned test fields provided a challenge to traditional models for explaining the process of colorpattern association in the human visual system, models which typically assume the exclusive operation of highly specialized neural analyzing mechanisms (e.g.,

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