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Subjects observed and then described continuously repeated twoelement temporal patterns (one of two alternative elements per event) and their component one-element patterns (one element or its nonoccurrence per event). Descriptions could begin at any event in a pattern, since there are as many possible descriptions as events in continuous patterns. Descriptions of one-element patterns revealed two organizing principles: preference for longest gap at the end, or longest run of positive events at the beginning. Variability of pattern organization was low when in a particular pattern these two principles were compatible or when the principles were incompatible but with the gap principle stronger, and increased when the two principles were incompatible and equally strong or the run principle was stronger. The descriptions of two-element patterns showed that one element emerged as 'figure' and the organizing principles for that element determined the perceived organization for the two-element pattern. It was concluded that variability and difficulty of two-element perceptual organization is a function both of figure-ground relations between the two elements and of compatibility of one-element organizing principles. A temporal pattern is a continuously repeating sequence of events. In a two-element pattern a single event is the occurrence of one of two alternative elements in a given unit of time. In a one-element pattern, an event consists of the occurrence or nonoccurrence of a single element. A two-element pattern may be thought of as the interlocking of two one-element patterns, since any two-element pattern can be decomposed into two unique one-element patterns. To illustrate, the two-element pattern XXXOXOO . . . contains XXX'X" ... and "'O'OO .. . as its unique one-element patterns, with the (') indicating the nonoccurrence of an element in the given unit of time. There are as many different possible organizations for a temporal pattern as there are events in the pattern. For example, the twoelement pattern XXO . . . can be organized XXO, XOX, or OXX. Each of these organizations, when repeated continuously, produces patterns which are indistinguishable from each other except in terms Received for publication November 17, 1969. This study was supported by Grant MH-14229 from the National Institute of Mental Health to Yale University. The authors are indebted to Mr. Nigel Cox for help in instrumentation.