Recognizing and Responding to Repetition

suppose a man who was born and raised on the Caribbean island of Jamaica has never seen snow. If he moves to Buffalo, new york, he will probably be excited and fascinated by his first snowfall. But a man of the same age who has grown up in Buffalo will react to the same snowfall very differently. for him, snow is recognizable, common, nothing to write home about—something he accepts and lives with on a daily basis.

everything is novel the first time it happens to you. even the most ordinary events only become mundane after repeated exposures. through repetition, you may learn not to respond to a particular event, even if—like the Jamaican in the snow—you originally responded with great excitement. this kind of learning, habituation, is formally defined as a decrease in the strength or occurrence of a behavior after repeated exposure to the stimulus that produces the behavior. habituation is sometimes described as the simplest or most basic kind of learning. nevertheless, experimental studies conducted over the last 100 years have yet to reveal exactly how habituation works (rankin et al., 2009; thompson, 2009). In the following discussions, we describe some of what researchers have discovered about habituation and its underlying mechanisms.

The Process of Habituation

you’ve experienced habituation if you’ve ever moved to a new home. possibly, the first night or two, you had trouble getting to sleep because of the strange noises outside your window (whether wailing police sirens or chirping crickets).

But after a few nights, you probably were no longer awakened by the noises and slept until morning.

In the laboratory, researchers examine simpler examples of habituation that they can describe in terms of a single easily controlled stimulus and a single easily measurable response. one such response is the acoustic startle reflex, which is a defensive response to a loud, unexpected noise. when a rat in an experimental chamber is startled by a loud noise, it jumps, much as you might jump if someone sneaked up behind you and yelled in your ear. If the same noise is presented over and over again, every minute or so, the rat’s startle response declines (figure 3.1a), just as your responsiveness to noises would decrease after moving into a new home; if the process goes on long enough, the rat may cease to startle altogether. at this point, the rat’s startle response has habituated to the loud noise.

habituation. A decrease in the strength or occurrence of a behavior after repeated exposure to the stimulus that produces that behavior.

acoustic startle reflex. A defensive response (such as jumping or freezing) to a startling stimulus (such as a loud noise).

another common way to study habituation uses the orienting response, an organism’s natural reaction to sensing a novel stimulus or an important event.

for example, if a checkerboard pattern (or any other unfamiliar visual stimulus) is presented to an infant, the infant’s orienting response is to turn her head and look at it for a few seconds before shifting her gaze elsewhere. If the checker-board is removed for 10 seconds and then redisplayed, the infant will respond again—but for a shorter time than on the first presentation (figure 3.1b). the duration of staring, called fixation time, decreases with repeated presentations of the stimulus, in a manner very much like the habituation of a rat’s startle response (malcuit, Bastien, & pomerleau, 1996).

normally, habituation is advantageous for an organism. through habitu-ation to familiar stimuli, the individual avoids wasting time and energy on unnecessary responses to each repeated event. But habituation carries risks. a deer that has gotten used to the sound of gunshots is a deer whose head may end up as a hunter’s trophy. a poker player whose responses become habituated to the excitement of winning a small pot may start to play for larger and larger stakes, putting his finances at risk. the dangers of habituation are immortalized in the story of the boy who cried wolf. In this folk tale, the boy plays practical jokes on his neighbors, calling them to come save him from an imaginary wolf;

eventually the villagers learn there is no reason to respond when he calls. Later, a real wolf attacks, but the villagers ignore the boy’s cries, and no one comes to save him.

this might seem like a case in which the villagers just learned that the boy was unreliable. think, however, about situations in which you have heard a fire or car alarm go off repeatedly for no apparent reason. each time the alarm goes off, you will become more skeptical, and at the same time your orienting or startle response will likely decrease. anytime your response decreases with repeated experiences, there is a good chance that habituation is occurring. of course, it is also possible that you are simply falling asleep, especially if the alarm is going off at night. one way researchers are able to distinguish habituation from fatigue and other causes of decreased behavioral responding to repetition is by disrupting the repetition of experienced events, as described below.

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(a) Startle in rats

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(b) Orienting response in infants Figure 3.1 Habituation

(a) The acoustic startle response in rats declines with repeated presentation of a loud auditory stimulus. (b) The time infants spend looking at a visual stimulus declines with repeated presentation of the stimulus.

(a) Data from Davis, 1980; (b) Data from Malcuit et al., 1996.

orienting response. An organism’s innate reaction to a novel stimulus.

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Stimulus Specificity and Dishabituation an important feature of habituation is that habitua-tion to one event doesn’t cause habituahabitua-tion to every other stimulus in the same sensory modality. In other words, habituation is stimulus specific (thompson

& spencer, 1966). after a baby’s orienting response to one visual stimulus (say, a donut shape) has decreased after several repetitions, the baby will still show a strong orienting response to a new visual stimulus (say, a cross shape). this renewal of responding provides evidence of habituation to the first visual stimulus, because if the baby was simply falling asleep, it should not matter what visual stimu-lus appears. Interestingly, a baby’s fixation time when shown a “new” image depends on how similar that image is to the one that was repeatedly experienced.

the more similar the image, the less the fixation time will increase. this phenomenon, called stimulus generalization, is observed in all forms of learning; we discuss generalization in greater detail in Chapter 6.

In some cases, presenting a novel stimulus after multiple presentations have caused habituation to an earlier stimulus can actually lead to recovery of the response to the familiar stimulus. for example, a baby shown a donut shape many times may show little interest the twentieth time it is presented. If, however, the baby is briefly shown a live kitten after the nineteenth repetition of the donut, the baby is likely to respond to the twentieth presentation of a donut shape as if it were a novel image, showing

a much longer fixation time than in the kitten-free scenario. this renewal of responding after a new stimulus has been presented is called dishabituation.

dishabituation often occurs when an arousing stimulus (like a kitten) is intro-duced into a sequence of otherwise monotonous repetitions, but it can also accompany less eventful changes. simply adding motion to a familiar stimulus can lead to dishabituation, as demonstrated when adults start waving toys around in front of an infant who seems uninterested. dishabituation provides another useful way of demonstrating that the absence of responding to a repeated stimu-lus is indeed the result of habituation and not some other factor like fatigue.

all organisms that show habituation also show dishabituation. In the laboratory, a male rat will mate with an unfamiliar female many times over a period of a few hours but eventually reaches a point at which the mating stops. If the now-familiar female is replaced with a new female, however, the male rat will rush to mate some more. this dishabituation of the mating response shows that habituation occurred with the first partner rather than the rat’s merely running out of energy or interest in sex (dewsbury, 1981; fisher, 1962). the dishabituation of sexual responding is sometimes referred to as the Coolidge effect, after an anecdote involving president Coolidge. while touring a poultry farm, the story goes, the president and his wife were informed that a single rooster could mate dozens of times in a single day.

“ha,” said mrs. Coolidge. “tell that to mr. Coolidge.” the president then asked the tour guide whether the rooster was always required to mate with the same female. told that it was not, the president reportedly remarked, “ha—tell that to mrs. Coolidge.” (see “Learning and memory in everyday Life” on page 77 for information on habituation and dishabituation of human sexual responses.)

Is habituation an inevitable conse-quence of long-term relationships?

Read on…

Andrew Evans/CartoonStock

dishabituation. A renewal of a response, previously habituated, that occurs when the organism is presented with a novel stimulus.

Factors Influencing the Rate and Duration of Habituation how rapidly a response habituates and how long the decrease in responding lasts depend on several factors, including how startling the stimulus is, the number of times it is experienced, and the length of time between repeated exposures. It is relatively easy to get used to the feeling of the tag in the back of your shirt—most people can learn to ignore this stimulus relatively quickly. In fact, at this point you probably would have to make an effort to notice that the tag is even there. It would probably take you longer to get used to the feeling of a spider crawling on the back of your neck—or you might never get used to that at all, even after many repeated experiences. In general, the less arousing an event is, the more rapidly a response to that event will habituate. whenever habituation does occur, larger decreases in responding are seen after earlier repetitions than after later exposures (see figure 3.1). In other words, the big-gest changes in responding are seen when one is first becoming familiar with a stimulus. this pattern is seen for many kinds of learning and will be discussed in greater detail in Chapters 4 and 8.

animals given sessions of multiple exposures to stimuli in which the expo-sures are separated by short intervals will typically show habituation after fewer exposures than animals given sessions in which the same number of exposures are more spread out over time (rankin & Broster, 1992; thompson & spencer, 1966): more rapid repetition of a stimulus generally leads to more rapid habitu-ation. exposures that are repeated close together in time are called massed, whereas exposures that are spread out over time are called spaced. If your goal is to habituate your response to some repeated stimulus as rapidly as possible, your best bet is to find a way to make that stimulus as nonarousing as possible, to expose yourself to closely spaced repetitions of that stimulus, and to repeat the process frequently (as you do when you wear shirts with tags in the back).

the effects of habituation may last for a few minutes or several hours and under some circumstances may last a day or more. But they generally do not last forever and are especially likely to dissipate if the stimulus is absent for a while.

habituation that goes away in seconds or minutes is called short-term habitua-tion; habituation that lasts longer is called long-term habituation (rankin et al., 2009). If a rat has gotten used to a loud noise and then goes through a period of an hour or so in which the noise does not occur, the rat is likely to startle anew when the noise is played again, a process called spontaneous recovery (referred to in the box on page 77). In spontaneous recovery, a stimulus-evoked response that has been weakened by habituation increases in strength or reappears after a period of no stimulus presentation. the factors that determine how quickly an individual’s response habituates also affect how long the effects of habituation last. animals that experience massed exposures to a stimulus learn to ignore that stimulus faster than animals given spaced exposures, but if they are retested after a relatively long break, the animals given massed exposures are also more likely to show spontaneous recovery. when exposures are spaced in time, it takes lon-ger for responding to habituate, but once habituation occurs, it lasts for a lonlon-ger time (gatchel, 1975; pedreira, romano, tomsic, Lozada, & maldonado, 1998).

this finding makes intuitive sense, because animals that have gotten used to the intermittent occurrence of a stimulus should find the recurrence of the stim-ulus after a long interval to be familiar. as a student reading this chapter, you are easily able to detect that repetition is occurring, even when that repetition occurs after moderately long intervals. If your repeated experiences are spread out over time, the likelihood is greater that you will continue to recognize repeating events farther into the future. so, if you want habituation to last for

spontaneous recovery.

Reappearance (or increase in strength) of a previously habituated response after a short period of no stimulus presentation.

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as long as possible, your best bet is to repeatedly expose yourself to the relevant stimulus after longer and longer stretches of time.

although spontaneous recovery might seem to suggest that habituation is a temporary effect, habituation effects accumulate over time. so, if an infant is shown a donut shape 20 times during a single session, her orienting response to that image will likely habituate. If a day or two later the infant is shown the donut shape again, spontaneous recovery will probably have occurred, and the infant’s fixation time will be as long as if the image were completely novel.

however, this time it may only take eight trials before the infant’s orienting response becomes habituated: the effects of repeated experiences have been potentiated by the prior repetitions. this shows that the effects of earlier repeated experiences have not simply faded away. furthermore, the mecha-nisms underlying habituation continue to change with repeated exposures, even when behavioral responses are no longer changing. for instance, a rat exposed to a loud sound many times might stop showing any indication that it even hears the sound—its response has decreased to the point at which there no longer is a response. nevertheless, if the sound continues to be repeated many times after this point, the amount of time required before spontaneous recovery occurs will increase. In this case, the learning associated with repeated exposures is latent, because there are no observable changes in the rat’s behav-ior associated with the increased number of repetitions. the additional effects of repeated exposures after behavioral responding to a stimulus has ceased are only evident when subsequent tests show delayed spontaneous recovery (thompson & spencer, 1966).

A

It’s easier to study dishabituation of sexual responding in rats than in humans. Most human research has instead focused on sexual arousal in male undergraduate volunteers during the viewing of sexually explicit photos. Such studies have shown that if the same arousing photos are presented repeatedly, human males respond less strongly, just like other animals (Koukounas

& Over, 2001; Plaud, Gaither, Henderson, & Devitt, 1997).

Relatively few studies of habituation of sexual arousal have been conducted in women. One problem is that women usually do not become as aroused as their male counterparts when view-ing sexually explicit photos. Obviously, it is hard for researchers to measure decreases in an arousal response if they can’t reli-ably elicit arousal to begin with. But in studies that have man-aged to solve this problem, habituation to sexual arousal seems to occur to a lesser degree in female undergraduates than in male undergraduates (Laan & Everaerd, 1995; Youn, 2006).

An interesting aspect of sexual habituation is that it seems to happen without conscious awareness. For example, male students in a sexual habituation experiment often show habitu-ation within a single session, responding less and less to the same sexually explicit photo as the session goes on—but they also show habituation across sessions, responding less and less each day of a multi-day experiment (Plaud et al., 1997).

Under these circumstances, participants often report that they were aware that their arousal was decreasing within a single session, but they seemed to be unaware that their arousal also decreased across sessions. Such continuous but imperceptible decreases in arousal might be a factor in promiscuity and infi-delity, which not only threaten stable relationships but may contribute to the spread of sexually transmitted diseases (Plaud et al., 1997).

How can someone in a long-term relationship deal with the scourge of sexual habituation? Prolonged abstinence could lead to spontaneous recovery of interest. Another option is to intro-duce novel stimuli to bring about dishabituation—for example, staging romantic interludes or trying a different technique. So the next time you’re feeling bored with an old relationship, a trip to Tahiti might be just what the doctor ordered!

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