Recognizing and Responding to Repetition

Suppose a man who was born and raised in 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—except, perhaps, for the inconvenience it causes on his commute to work.

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 behav-ior. 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 (Thompson, 2009). In the fol-lowing sections, 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.

Another common way to study habituation uses the orienting response, an organism’s natural reaction to a novel stimulus or to 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 rats’ 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 an elaborate response to every 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 habitu-ated 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.

(b) Orienting response in infants Figure 3.1 Habituation

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

[(a) Adapted from Davis, 1980; (b) adapted from Malcuit et al., 1996.]

B E H A V I O R A L P R O C E S S E S

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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 experi-ences, 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 other causes of decreased behavioral responding to repetition is by disrupting the repetition of experienced events, as described below.

Stimulus Specificity and Dishabituation

An important feature of habituation is that habituation to one event doesn’t cause habituation 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 respond-ing provides evidence of habituation to the first visual stimulus because if the baby was simply falling asleep, it should not matter what visual stimulus 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 simi-lar the image, the less the fixation time will increase. This phenomenon, called stimulus generalization, is observed in all forms of learning; we discuss generaliza-tion in greater detail in Chapter 6.

In some cases, presenting a novel stimulus after multiple presentations of a familiar stimulus can actually lead to recovery of the habituated 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 introduced into a sequence of otherwise monotonous repeti-tions but 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 stimulus is indeed the result of habituation and not some other factor like fatigue.

All organisms that show habituation also show dishabituation. In the labora-tory, 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 dishabitu-ation of sexual responding is sometimes referred to as the Coolidge effect, after

From The New Yorker Collection, 2008. Bruce Eric Kaplan from cartoonbank.com.

“Sometimes I get so bored with myself I can barely make it to ‘doodle-do.’”

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” above for more on habituation and dishabituation of human sexual responses.)

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

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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 sexu-ally explicit photos. Such studies have shown that if the same arousing photos are presented repeatedly, human males respond less strongly, just like other ani-mals (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 usu-ally do not become as aroused as their male counterparts when viewing sexu-ally 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 managed 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 habitu-ation is that it seems to happen without conscious awareness. For example, male students in a sexual habituation experi-ment often show habituation 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 impercep-tible decreases in arousal might be a factor in promiscuity and infidelity, 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 rela-tionship deal with the scourge of sexual habituation? Prolonged abstinence could lead to spontaneous recovery of inter-est. Another option is to introduce 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 rela-tionship, a trip to Tahiti might be just what the doctor ordered!

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