Although inadequacies in quantifying personality traits and difficulties in studying estimates of time spans exceeding a few seconds have hampered scientific study, simple observation reveals marked individual differences in the ability to estimate time. Sex differences have not been reliably established, but the influence of age is well known. Experimental data indicate that children use the same criteria as do adults, but give more variable estimates of duration. One reason for this seems to be that they are less able to compensate for differences in the nature of a task or in personal motivation; also they are inexperienced in making inferences based on the volume of work they have accomplished. Elderly people tend to find time shorter, probably since they are likely to notice long-accustomed changes less frequently.

Children are as accurate as adults in reproducing various series of metronome clicks that last about two seconds or less. But estimates of longer intervals require processes for organizing experience that develop only with age, and very young children seem to depend only on limited criteria: “It lasts because it’s longer; because there’s more of it; because it goes faster.” According to Jean Piaget, estimates based on more or less explicit comparison with standard units of duration imply concrete cognitive operations that are developed only after about the age of seven or eight. Adolescents typically construct more sophisticated notions of time abstracted from such concrete experimental data.

Physiological effects: drugs

The precision with which time is perceived has not been found to be related to heart rate or to electroencephalographic data. It has been shown, however, that perception of time as in clapping or counting accelerates or decelerates with the rise and fall of body temperature. The precise metabolic basis for such temperature effects awaits further study.

Ethical considerations sharply limit the dosage level of drugs employed for experiments on human beings. Understanding of the interactions between drug effects and personality traits in studies of time estimation is, therefore, quite incomplete. Within the dosage ranges investigated, however, stimulating drugs (e.g., thyroxine, caffeine, amphetamines) produce overestimates of duration, while depressants and anesthetics (e.g., barbiturates, nitrous oxide) promote underestimates. Under the influence of hallucinogens (e.g., marijuana, mescaline, LSD), subjects tend to estimate absolute duration as very long. In addition, a marijuana user may underestimate the speed of a motor vehicle, increasing the chances of accident.

Sensory deprivation and hypnosis

Relatively complete sensory deprivation (such as may be experienced, for example, by persons undergoing prolonged stays in experimental isolation chambers) compresses the experience of time to the point that short or long intervals (from about a minute to a day) seem to pass about twice as fast as usual. Time spent under these unpleasant conditions paradoxically seems shorter than normal time. Thus, the 58 objective days of a subject’s first stay in a cave were underestimated as 33 days.

Under hypnosis, durations ordinarily are estimated at least as precisely as ever. Time distortion, however, can be readily induced among hypnotized subjects by simple suggestion. Such a subject, for example, may be exposed to two clicks that delimit an objective, 10-second interval but be told that it lasts 10 minutes. On being asked to count objects for 10 minutes, he may report having counted several hundreds without difficulty over what the experimenter’s stopwatch shows to have been 10 seconds.