Many comparisons involve sequentially presented stimuli, as perforce the case in comparisons of temporal intervals. Interactions of such stimuli are as inevitable as the spatial interactions that yield color and brightness contrast. A memory-trace theory of perception (TToP) is developed and applied to time perception. Duration is estimated based on the memorial strength of the stimuli that signal the initiation of an interval at the time of its termination. Memorial persistence depends on modality and character of the signals, which condition the response to them. When the constant difference limen on the memorial continuum is back-translated to the temporal one it yields a generalized Weber function. Memory traces interact as a function of generalization gradients: Memories of stimuli that are similar enough are aggregated—feature-bound—some veridically, others as illusory conjunctions. The resulting representations may then be judged in a discrimination paradigm, or translated back to the physical domain as reproductions of the intervals. The presentation of a standard stimulus affects the perception of the comparison stimulus, warping the ruler by which it is measured. Complementary effects are predicted for discrimination and adjustment paradigms. Thus configured, the TToP accounts for multiple special effects, variously referred to as distortions, anomalies, and illusions, that are observed with classical psychophysical methods: Scalar and nonscalar timing, modality effects, time-order errors, masking, time warping, lengthening, and Vierordt’s law. Similar processes affect the perception of nontemporal stimuli whenever they are presented in sequential proximity to one another.