TIME PERCEPTION

experience or awareness of the passage of time. The human experience of change is complex. One primary element clearly is that of a succession of events, but distinguishable events are separated by more or less lengthy intervals that are called durations. Thus, sequence and duration are fundamental aspects of what is perceived in change. Manifestly, duration is relative to the events people isolate in the sequences through which they live: the duration of a kiss, of a meal, of a trip. A given interval always can be subdivided into a sequential chain delimiting briefer durations, as with the regular units that provide empirical measures of time: the second, the day, the year. Indeed, human experience is not simply that of one single series of events, but of a plurality of overlapping changes. The duration of a radio program, for example, can combine with that of a breakfast, both being inserted within the longer period of an ocean voyage. Humans seem to be unable to live without some concept of time. Ancient philosophies sought to relate the concept of time to some objective reality to which it would correspond. Ren Descartes (15961650) inaugurated a critical era of philosophy by stressing the ancient problem of the origin of ideas, including the idea of time. Immanuel Kant (17241804), providing a radical answer to the epistemological problem of time, wrote that we do not appreciate time objectively as a physical thing; that it is simply a pure form of sensible intuition. Other philosophers of the 18th and 19th centuries sought to explain the notion of time as arising from association and memory of successive perceptions. A move to empirical psychology emerged with the growth of research on the introspective data of experience. From about mid-19th century, under the influence of the psychophysical notions of Gustav Theodor Fechner, psychologists conducted experiments to study the relationship between time as perceived and time as measured in physics. Their work with adults gradually spread to the study of children and of animals. The psychologists then broadened their investigations of time to cover all forms of adaptation to sequence and duration. experience or awareness of the passage of time. Time is the dimension of change, and time perception, then, is the capacity to interpret changes in sensory (and bodily) stimuli with respect to their temporal relationsmost basically, their order in time and the amount of time between them. Since about the middle of the 19th century, the study of time perception has been conducted empirically, with psychologists examining how and why a person's sense of the length of a period of time can differ from a precise measurement. Two features of temporality are central to time perception: sequence and duration. A sense that one event follows another in a fairly stable sequence is developed by conditioning. The perception of duration falls into two classes. Animals can judge not only the duration between two events (called an empty duration) but also the duration of a single event, as delimited by its start and its finish (called a full duration). Perception, strictly speaking, always occurs in the present: an individual cannot reach forward or backward in time to perceive future or past events but can only perceive what is happening now. For the purposes of measuring time, the present is supposed to have no duration. However, the present as experienced in perception does have a brief but definite duration. That is, one can take in some change in an event in one act of perception, without having to refer to memory. The length of this perceptual moment of the present can vary, depending on the nature of and organization between the events involved. There are also lower and upper limits to the amount of time that can be perceived as a single duration. Within these limits, the perception of duration can vary according to the structure of the stimulus and the sense involved. At the lower limit the ear is more sensitive than the eyei.e., it is better able to detect that a stimulus has length and is not merely instantaneous. Above a limit, about two seconds for both ear and eye, the duration of the stimulus is no longer directly perceived but must be judged with the aid of memory. Durations can be estimated with reference to a task being done, but here both the nature of the task and the actor's attitude toward it become important factors. A continuous burst of activity seems to take less time than does an activity that proceeds by fits and starts, but a task for which the actor is not highly motivated will seem to last longer than it actually does. The ability to estimate durations has been found to vary with age, with children being generally less accurate than adults, theoretically because children are not yet familiar enough with various activities to use them as guides for estimates of duration. The physiological bases of time perception are still only poorly understood. Additional reading Paul Fraisse, The Psychology of Time (1963, reprinted 1975; originally published in French, 1957), provides the most complete synthesis of the psychological works on time. The collective works edited by J.T. Fraser, The Voices of Time, 2nd ed. (1981); and R. Fisher, Interdisciplinary Perspectives of Time, Annals of the New York Academy of Sciences, vol. 138, article 2 (1967), present the most varied aspects of the problem of time, ranging from religious conceptions to scientific data from physics and biology. Erwin Bnning, The Physiological Clock: Circadian Rhythms and Biological Chronometry, trans. from German, rev. 3rd ed. (1973), provides a very sound study of the problems of the temporal regulation of organisms. The point of view of genetic epistemology is developed by Jean Piaget, The Child's Conception of Time (1969; originally published in French, 1946). Louis Jolyon West The Editors of the Encyclopdia Britannica