Time Perception

[Publishers are always concerned about the number of pages in a book, so to pare down an earlier edition of the text, this section was removed. It's now a bit dated, but I'll make an effort to update it when the smoke clears a bit.]

            Perhaps you have an uneasy feeling as you begin to read about time perception.  Color perception, shape perception, and distance perception all refer to tangible attributes.  Even loudness, pitch, and motion perception seem reasonably concrete.  But time perception?  The topic refers to something invisible and fleeting.  We have seen how photoreceptors register information about light and hair cells register information about sound, yet no receptor registers information about the passage of time.  And consider the stimulus for time perception.  A square or a red patch exists, yet as Fraisse (1984) points out, "Duration has no existence in and of itself" (p.  2).
            Although invisible and fleeting, time is an essential variable in perception.  The timing of the stimuli must be precisely correct for backward masking to occur, for example.  The timing of the two stimuli in stroboscopic movement studies must be equally precise; the phenomenon is lost if the interval between the two stimuli is too long or too short.  Careful regulation of the interval length can produce the impression of an object moving through space or — by extending the interval by less than one tenth of a second — the impression of movement unaccompanied by an object (phi movement).  A sound that arrives at one ear a small fraction of a second after it arrives at the other ear provides us with information about the location of the sound source.  Virtually every experiment in perception specifies how long a stimulus was exposed to observers, how long observers were allowed to dark adapt, the number of cycles that a sound wave completes in 1 second, or some other characteristic related to time.
            However, until now, time has been on the periphery of our discussion.  Now we'll make it our central issue.  Block (1990) has identified four factors that provide a context within which psychological time is perceived: characteristics of the time experiencer, time-related behaviors and judgments, contents of a time period, and activities during a time period.  We will adopt Block's framework, and discuss each of the four factors.  Although we will consider each factor separately, Block stresses the interrelationships among the four factors; changes in one factor are likely to induce changes among the other factors.

Characteristics of the Time Experiencer

            In The Hitchhiker's Guide to the Galaxy, Douglas Adams (1979) satirizes the foibles of modern people, including our obsession with digital wristwatches.  Keeping track of the passage of time is certainly important to many people, but the level of concern varies among cultural groups and even among people of a single culture (Levine, 1988; 1990).  The pace with which people lead their lives certainly indicates the extent to which their actions are in keeping with the Latin phrase "Tempus fugit" ("time flies"). 
            In developing objective measures of the importance of time to people in various American cities, Robert V. Levine (1990) and his colleagues made use of four measures: the speed with which bank tellers made change, the talking speed of postal clerks, the walking speed of pedestrians, and the proportion of pedestrians wearing wristwatches.  Levine found that the Northeastern United States is more fast-paced than the Western United States.  For instance, the three fastest-paced cities surveyed were Boston, Buffalo, and New York.  The three slowest-paced cities surveyed were Shreveport, Sacramento, and Los Angeles.  Furthermore, there was a moderate correlation between the pace of life and the rate of death from heart disease.  Because of the correlational nature of the study, one cannot conclude that a faster pace of life leads to an increase in heart attacks.  Nonetheless, the results are intriguingly consistent with our beliefs about the relationship between stress and heart disease.
            Without a timepiece, or even conscious awareness, people perceive the passage of time.  For instance, many of us believe that we can go to sleep without an alarm and wake up at a predetermined time.  In fact, the evidence suggests that although more people can perform such a feat than should happen by chance, a relatively small proportion of us possess this particular ability (Campbell, 1990) .  Nonetheless, virtually everyone is aware of the passage of time, and can estimate its passage with some accuracy.  The means by which organisms perform this task, however, remains something of a mystery. 
            Many organisms, including humans, appear to organize their lives around the light/dark cycle of a typical day.  The behavioral patterns that emerge are referred to as circadian rhythms because they are organized around a period of approximately one day (in Latin circa means approximately and dies means day).  The adaptive advantages of using external cues from the environment are apparent.  If an organism could use sun-position cues, for example, to keep track of the passage of time, then it could tell that a flower's nectar was likely to have been replenished or that prey are likely to return to drink from a river.  As a result, if you feed an animal at a regular time, it will begin to salivate in anticipation of food at the appropriate time, even if no other feeding cues are present (Campbell, 1990) .
            External cues, such as the sunrise, serve to trigger circadian rhythms, which then continue without additional external input (Block, 1990) .  In the absence of continuous time-of-day cues, many internal states exhibit circadian rhythmicity, including hormonal levels and body temperature.  Such circadian rhythms are the product of an internal clock of some sort.  Research suggests that this biological clock might well be located in a brain structure near the optic chiasm (Block, 1990).  The nearness of the biological clock to the visual pathway illustrates the importance of light as a trigger mechanism.
            Imagine what would happen if you were to live for a long while in a cave or a room with only artificial light and no clocks.  In the interest of research on time perception and circadian rhythms, several people have lived under just such conditions.  The length of their "day" becomes elongated, and is often roughly 25 hours long.  Further, when asked to estimate the length of an hour by pressing a button with the passage of each hour, the typical subjective hour is longer than an actual hour.  People's estimates are also widely variable, suggesting that judgments of these durations are extremely imprecise.  In Scott S. Campbell's (1990) terms, estimation of these longer durations is characterized by both sluggishness and sloppiness.
            Time perception might well be influenced by physiological state, knowledge, personality, and other factors.  For instance, there is some evidence that a person with a high fever shortened her estimates of a 1-sec interval and that a person who lived in a cold cave lengthened his time estimates.  The evidence for the contribution of metabolic rate to time perception is weak, but would be consistent with a biological clock.  The fact that knowledge and experience also play a role (Theme 4), however, argues that there is a cognitive component in time perception.  Alberto Montare (1985; 1988) has found that providing feedback to people about the accuracy of their time estimations increases the accuracy of subsequent judgments.  Montare did not find gender differences, suggesting that time perception might be equivalent among men and women.
            Overall, then, the research suggests that people have a biological clock that regulates various internal circadian rhythms.  However, because of the sloppiness and sluggishness of that regulation, and because of the effects of experience, it is unlikely that our perception of time is due solely to this same clock. 

Time-Related Behaviors and Judgments

            We've already mentioned some ways in which researchers have assessed people's perception of time.  Dan Zakay (1990) provides several examples of methodological differences and the ways in which they might influence judgments of time.  It is important to discuss these various measures because, as Fraisse (1984) emphasizes, "Results are neither comparable nor homogeneous across methodologies" (p.  10).  We will now discuss four classes of measures, or dependent variables, used by researchers in studying time perception: estimation, production, reproduction, and comparison (Zakay, 1990). 
            There are several variants of the estimation procedure.  First, participants in the study could simply estimate time passage in some standard units of time such as seconds or minutes.  A duration could be presented, and immediately after the time period, participants would estimate time passage.  Time estimation could also be assessed using the some of the psychophysical methods discussed in Chapter 2.  For instance, rather than estimating the number of minutes or seconds that had passed, participants could assign a number value or a line length to match their impression of the duration.  Finally, an estimation might be made with a rating scale.  For example, the two ends of the rating scale might be labeled "short time interval" and "long time interval."  Alternately, the ends might be labeled "time passed quickly" and "time passed slowly" (e.g., Joubert, 1984).
            A second class of dependent variable involves time production.  Participants could be told to press a button and release it, for example, when they thought that 2 minutes had passed.  This procedure can be used to explore time perception in both humans and other organisms (Wearden & McShane, 1988).  A third class of dependent variable requires participants to reproduce a given time period.  The experimenter could present a time interval of a certain duration, perhaps 2 minutes, without telling the participants the number of minutes that had passed.  The participants would then be asked to match the duration of the interval presented previously.
            Finally, a comparison procedure might be used.  One procedure would be to present two different durations and ask a person to identify which of the two was longer.  The two-alternative forced choice method could also be used.  Using this method, two different durations could be presented (A and B) and then a duration (X) could be presented and the observer asked to label the final duration (X) as either A or B.
            The estimation and reproduction approaches can be applied in experimental situations in which participants expect to make time judgments or are surprised by being asked to make time judgments.  For example, Brown and Stubbs (1988) asked some undergraduates to listen to several musical selections and to pay close attention to the selections because of a subsequent questionnaire; no mention was made of duration.  Other undergraduates were asked to remove their watches and to listen to the same selections in an effort to estimate their durations.  Just as Montare found that feedback about accuracy improves timing judgments, Brown and Stubbs found that people are more accurate when they know that they will be judging duration.
            Studies of time typically involve levels of time in the independent variable.  We have already seen that some studies require people to judge the duration of fairly long time periods, such as hours.  In other research, such as that of Montare (1985; 1988), much shorter durations are used (4 or 12 secs).  Generally, people tend to overestimate brief intervals and underestimate longer intervals (Zakay, 1990).  Further, researchers believe that longer intervals — beyond 5 secs — involve memory (Fraisse, 1984).

• Consistent with the results reported above, Crystal (2006) argues that time is not perceived in a linear fashion. That is, one minute will not appear to be one sixtieth of an hour. Moreover, there is not a simple linear translation of perceived time into actual time. Crystal discusses the multiple-oscillator theory of timing, the broadcast theory of timing, and the stochastic counting cascades approach -- all of which are consistent with nonlinear representation of time.

Contents of a Time Period

            Events that occur during the interval being judged have a major influence on duration estimation.  For example, stimulus intensity is important.  Fraisse (1984) concludes that more intense sounds and lights are judged longer than less intense stimuli.  This phenomenon is particularly true for vision. 
            Stimulus complexity also influences duration estimation.  Poynter and Homa (1983) presented flashing lights, which flashed on and off in either a simple, regular pattern or a more complex, irregular pattern.  Using the reproduction technique of duration estimation, participants provided longer estimates for the more complex patterns.  Furthermore, when participants look at a display of dots, the perceived duration depends upon the number of dots and the velocity with which the dots are rotated.  The greater the number of dots (Mo, 1975) or the faster the speed of rotation (Tayama, Nakamura & Aiba, 1987), the longer the time interval seems to be.  
            Duration estimates also depend upon whether the interval is segmented or unsegmented.  Poynter (1983) prepared two kinds of tape recordings.  Both consisted of 27 nouns and the names of 3 U.S.  presidents, and each recording lasted 170 seconds.  However, in the unsegmented recording, all 3 presidents' names appeared first, followed by the 27 nouns.  In the segmented recording the three presidents' names appeared in positions 10, 20, and 27, thereby creating three segments, or parts, in the recording.  Poynter found that the unsegmented recording was judged to be shorter than the segmented recording.
            Recall the filled space-open space illusion.  Do you think that a duration will seem longer if it is filled or empty?  Ornstein (1969) proposed that a filled interval should appear to be longer, and some data support his position.  As we'll discuss in the next section, the activities with which a person fills a time period are also thought to influence time perception.  However, there are other data that suggest that filled intervals are not always perceived as being longer.  Jones and Boltz (1989) argue that the expectancies created by the information filling an interval are more important than the absolute quantity of information filling the interval.  For instance, songs that ended unexpectedly early were judged to be shorter in duration.  So time perception is influenced by several higher-level processes, including expectations, consistent with Theme 4.
            Most studies of time perception don't specifically involve auditory stimuli, but it is clearly the case that time is crucial for audition.  In fact, durations that would not be perceived by our visual system have profound implications for our auditory system.  You might assume, therefore, that the perceived duration of auditory stimuli would differ from the duration of visual stimuli.  However, Schab and Crowder (1989) found little or no difference in the accuracy of judgments of intervals greater than 1 sec that were presented visually or auditorily.
            Music represents one type of auditory stimulus for which timing is crucial (Jones, 1990).  The timing with which the notes are played determines the tempo, or overall pace of the piece of music (slow or fast).  Just as Andrea Halpern (1989) found that people had good memories for the typical pitch of familiar songs, she also found that people remember the tempos of familiar songs, although they were tolerant of both faster and slower tempos (Halpern, 1988).
            Musicians can maintain identical tempos and still change the internal temporal organization of a song, called meter or rhythm.  If you've heard the same melody played as rock and reggae or jazz, then you know the importance of rhythm.  Even the melody itself is strongly determined by timing.  The melodies of two of the songs of The Music Man — "Seventy-Six Trombones" and "Goodnight My Someone" — are composed of virtually identical notes played with substantial timing differences, such that the two songs do not sound at all similar.
            Notice, then, that stimulus characteristics can have an important influence on duration estimates.  A time period is judged longer if it is intense, complex, or segmented.  A time period marked by auditory stimuli is judged no more accurately than a time period marked by visual stimuli.  Some evidence suggests that a filled time period is perceived as longer than an empty time period, although it appears that this might well be due to expectations derived from the information filling the time period.

Activities During a Time Period

            The activities of the person during the time interval being judged typically interact with the contents of the duration, making the distinction between these two areas somewhat arbitrary.  Generally, you can think of the activities of the observer as requiring greater or lesser amounts of cognitive effort.  Often the contents of the duration produce these differing attentional demands.  Some stimuli require more cognitive processing, and we may judge time on the basis of the amount of cognitive "work" required of a person during an interval (Luce, 1984).  The important factor, apparently, is not the complexity of particular stimuli presented, but the complexity of the task in which a person is engaged (Block, 1990).
            For instance, one study asked people to estimate time passage, in number of seconds, for a tone sounded while they were performing another task (Tsao, Wittlieb, Miller & Wang, 1983).  When the other task was extremely demanding, they were more likely to underestimate time.  For example, a 63-second interval was estimated as 38 seconds when the other task was extremely demanding, in contrast to 49 seconds when people were performing no other task.
            Rather than use different competing tasks, Brown and West (1990) had people perform simultaneous duration judgments.  The letters A, B, C, and D could appear in one of the four corners of a computer screen for durations between 6 and 16 seconds.  Each letter would be on the screen for a different duration, and each would start and stop at different times.  People who were asked to keep track of all four letters were much less accurate in their time estimates than people asked to keep track of only one letter, providing further evidence for the position that timing performance is disrupted with increasing attentional demands.
            Two proverbs emphasize the impact of a person's activities on time perception.  You've heard the proverb, "A watched pot never boils."  This saying has inspired several studies to determine whether people overestimate time when they are waiting for an event.  Cahoon and Edmonds (1980) told participants in their study that the experiment would start after a delay; the experimenter said he would return later.  One group was told to call the experimenter when the water in a glass coffee pot started to boil, whereas a control group did not receive these instructions.  In both cases the experimenter returned 4 minutes later and asked the participants to estimate how long he had been gone.  The duration estimates were significantly longer for participants in the "watched-pot" group.  Note that these results are consistent with the hypothesis that filled time intervals appear to be longer than equal unfilled intervals.
            Contrast these results with another proverb, "Time goes quickly when you're having fun."  This proverb suggests that filled time intervals can appear to be shorter than unfilled intervals — if the task is a pleasant one.  
            Thayer and Schiff (1975) asked female participants to estimate duration in a neutral condition and then in an experimental condition in which they gazed at another person.  This other person was either smiling or scowling.  The duration of the interval was either 12 or 36 seconds, and participants were asked to reproduce the time interval on a masked stopwatch.  The time estimates were significantly longer when the face was scowling than when it was smiling. 
            Thayer and Schiff studied perceived duration when the contents were pleasant or unpleasant, but what about the duration spent waiting for a pleasant or unpleasant event?  Does the time spent waiting for the trip to the dentist appear to be shorter or longer than the time spent waiting for a vacation trip?  Edmonds, Cahoon, and Bridges (1981) found that the duration spent waiting for a positive experience appeared longer than the duration spent waiting for a negative experience.
            The activities in which a person is engaged also interact with the type of study being conducted.  As Block (1990) says, "Experienced duration depends on variables such as the amount of attention to temporal information, whereas remembered duration involves contextual changes in memory" (p. 30).  Thus, you might expect the activities of an experiencer of time to be more of a factor when the person knows that they are going to have to judge the duration of a forthcoming interval.
            So the perception of time is a complex process involving several interrelated factors.  As a means of organizing the information on time perception, we have chosen to focus on the framework proposed by Block (1990).  Our brief review of the field suggests that individual differences are substantial in time perception, and that characteristics of the person judging time intervals has an impact on time perception.  How a researcher chooses to design a time perception study also appears to have an impact.  The structure of the central task in which people are engaged, as well as any peripheral tasks they have to perform, seem to have an impact on time perception.  Further, in keeping with Theme 4 of this text, our sense of time certainly involves higher-order processes, as indicated by the importance of learning and attentional demands. 

Summary: Time Perception

1. Four factors appear to influence time perception: characteristics of the time experiencer, time-related behaviors and judgments, contents of a time period, and activities during a time period.
2. Time is of greater concern to different cultures and different groups within the same culture.  Nonetheless, all people have a number of internal processes that follow circadian rhythms, suggesting the presence of an internal biological clock.
3.  In time perception research, one might choose a dependent variable from among several options: (a) time estimation, using common units (mins, secs), magnitude estimation, or rating scales; (b) time production; (c) time reproduction; and, (d) comparisons of time intervals.
4.  The contents of a time period influence duration estimates; a time period is judged longer if it is intense, complex, and segmented.  Some evidence suggests that a filled time period is perceived as longer than an empty time period, although it appears that this might well be due to expectations derived from the information filling the time period.
5.  Activities of the participants influence duration estimates; a time period is judged less accurately if people are performing other tasks simultaneously.   Time appears to pass more quickly if people are waiting for an unpleasant event, or if the situation in which they are engaged is pleasant.


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More Recent Material

Scientific American (Sept. 2002) issue focuses on time, with an article by Antonio Damasio, "Remembering when" (66-73) and by Carol Ezzell, " Clocking cultures" (74-75). [Apparently re-issued with changes in 2006 as a "Special Edition"]