The systematic scientific investigation of human perception began over 130 years ago, yet relatively little is known about how we identify complex patterns. A major reason for this is that historically, most perceptual research focused on the more basic processes involved in the detection and discrimination of simple stimuli. This work progressed in a connectionist fashion, attempting to clarify fundamental mechanisms in depth before addressing the more complex problems of pattern recognition and classification. This extensive and impressive research effort built a firm basis from which to speculate about these issues. What seemed lacking, however, was an overall characterization of the recognition problem - a broad theoretical structure to direct future research in this area. Consequently, our primary objective in this volume, originally published in 1981, was not only to review existing contributions to our understanding of classification and recognition, but to project fruitful areas and directions for future research as well. The book covers four areas: complex visual patterns; complex auditory patterns; multi-dimensional perceptual spaces; theoretical pattern recognition.