THE SOMATOSENSES 21 1 pressure Sensory psychologists speak oftouch and pressure as tWO separate senses. They define ( ん as the sensation Of very light contact Of an ObJect with the skin and 尾材尾 as the sensation produced by more forceful contact. sensatlons Of pressure occur only when the skin is actually moving, which means that the pressure detectors respond only while they are being bent. Just hOW the 1 れ Otion stimulates the neurons IS not known. If you rest your forearm on a table and place a small weight on your skin, you will feel the pressure at first, but eventually you willfeel nothing at a11 , if you keep your arm still. You failto feel the pressure not because your brain lgnores' lncommg stimulation but because your sensory end- lngs actually cease sending impulses tO your brain. studies that have measured the very SIOW, very n11 Ⅱー ute movements Of a weight sinking down intO the Skin have Shown that sensatlons Of pressure cease when the movements stop. With the addition Of another weight 0 Ⅱ top Of the first one, movement and sensatlons Of pressure begin again (Nafe and Wagoner, 1941 ). A person will feel a very heavy weight indefinitely, but the sensatlon is probably one Of pain rather than pressure. sensitivity tO subtle differences in touch and pressure vanes widely across the surface Of the bOdy. The most sensltive regions are the lips and the fin- gertips. The most C0n11 れ on measure Of the tactile discrinunatlon Of a reg10n Of skin is the two-point discrimination threshold. TO determine this measure, the experimenter touches the subJect with one or both legs of a pair dividers and asks the person tO say whether the sensatlon IS coming from one or two points. (See 6.40. ) The farther apart the legs of the dividers must be before the per- son reports feeling tWO separate sensatlons, the lower the sensitivity Of that region Of skin. paln IS a complex sensatlon involving not only intense sensory stimulation but aISO an emo- tional component; a glven sensory input tO the brain might be interpreted as paln ln one sltuatlon and as pleasure ln another. For example, when people are sexually aroused, they become less sensltlve tO many forms Of pain and may even find such intense stlmu- lation pleasurable. physiological evidence suggests that the sensa- tIOn Of pain IS quite different from the emotional reactlon tO pain. opiates such as morphine diminish the sensation Of pain by stimulating OP1ate receptors on neurons in the brain; these neurons blOCk the transm1SS10n Of pain informatlon tO the brain. FIGURE 6.40 The method for determining the two-point discrimination threshold. contrast, S01 れ e tranquilizers (such as valium) depress neural systems that are responsible for the emotional reactlon tO pain but dO not diminish the intensity Of the sensation. Thus, people whO have received a drug like valium will report that they feel the pain Just as much as they did before but that it does れ 0t bother them much. Evidence from surgical procedures alSO supports the distinction between sensatlon and emotlon. Pre- frontallobotomy (a form of brain surgery), like the use Of tranquilizers such as Valium, blocks the Ⅱ 0- tional component Of pain but does not affect the prlmary sensation. Therefore, operatlons tO prefrontal lobotomy (but much less drastic) are sometimes performed tO treat people , hO suffer from chronic pain that cannot be alleviated by other means. Many nOXIOus stimuli elicit t , 0 kinds Ofpain an lmmediate sharp, or "bright,' pain followed by a deep, dull, sometimes throbbing pain. Some stimuli elicit only one Of these t , 0 kinds Of pain. For exam- ple, a pinprick will produce only the superficial "bright" pain, whereas a hard blow from a blunt obJect to a large muscle will produce only the deep, dull pain. Different sets Of axons mediate these tWO types of pain ・ pain—or the fear Of pain— IS one Of the most effective motivators Of human behavior. However, as the father in the openlng vlgnette pointed out tO his child, it alSO serves us well in the れ ormal course Of living. As unpleasant as pam is, we would have diffi- culty survlvlng without it. THE INTERNAL SENSES sensory endings located lnternal organs, bones and JOints, and muscles convey painful, neutral, and

EXPRESSION AND RECOGNITION OF EMOTIONS 457 Just as neutral stimuli can become conditioned rein— forcers and punishers, they aISO tO evoke emotional states. For humans the eliciting stimuli and the れ 0- tIOns they produce can be far removed from each Other in t11 Ⅱ e. AS I already mentioned, we can experl- ence emotlons by remembering things that hap- pened tO us or things ℃ did. ln addition, emotions can be the products ofcognitlve processes. For exam- ple, suppose that someone says something tO you that, 0 Ⅱ the surface, appears to be complimentary. 旺 this event affects your emotional state, it is likely tO dO SO in a POSItive way. But suppose you later think about the remark and realize that it was actually a disguised insult. This realization ーー a product Ofyour ー leads you to become angry ・ cognltlve processes MOSt investlgators believe that humans dO not differ substantially 0n1 most other mammals in their expressions and feelings Of emotion. There are differences, of course, but the differences appear to be less important than the similarities. If you have ever had a dog, you know that it can express fear, anger, happiness, sadness, surprise, shame, and Other れ 0t10 Ⅱ S 1 れ ways that we can recogmze as similar tO ours. However, we dO differ substantially 伝 01 Ⅱ Other animals in the types Of stimuli that can evoke these Ⅱ Ot1011S. For example, an animal may become frightened and embarrassed by the presence 0 信 large group Of strangers, but only humans can become frightened and embarrassed by having to perform in front Of a television camera, because only humans realize that they are confronting an unseen audience. Similarly, only humans can experlence feelings of love and longing while looking at a picture of an absent loved one. ln humans emotlons are often produced by 」 udg- ing the significance Of a particular situation. For ex- ample, after a performance a P1anist may perceive the applause as praise for an outstanding performance, 」 udging it tO be a positive evaluation Of her own worth. She feels pride and satisfaction. ln this case her emotional state is produced by social rein- forcement ーー the expresslon Of approval and admira- tion by other people. However, ifthe pianist believes she has performed poorly, she may 」 udge the ap- plause as mindless enthusiasm ofpeople who have Ⅱ 0 taste or appreclation for muSIC, SO that she feels only contempt. Furthermore, the person whO turned the pages Of the mt1SIC is also present on the stage and thus alSO percelves the applause. However, because he does not evaluate the applause as praise for any- thing he did, he does not experience the emotions A vervet monkey from Kenya with her infant. Maler and the pianist feels. The applause may even make him feel jealous. Clearly, a given set of stimuli does not always elicit the same er れ 0t10n ; in this case the 」 udg- ments made about the significance Of the stimuli determine the emotion the person feels. I dO not want tO imply that 4 〃 human emotlons are the products Of 」 udgments. Emotions can also be triggered much more automatically, as classically conditioned responses. For example, if we are walk- 1 れ g across a street, the sound Of screeching tires will probably produce a surge of adrenaline, a rapidly beating heart, and other signs 0f fear before we have tlme tO assess what is happening. There is nothing innately threatening about the sound Of screeching tires, but we have learned Of its assoclation with fast- movmg cars. LEARNING WHEN TO DISPLAY AN EMOTION A research project by Marler, Seyfarth, and Cheney (summarized by Marler, 1984 ) illustrates the adap- priate stimuli with the appropriate signs Of distress. monkeys and their ability tO learn tO respond to appro- his colleagues studied the development of vervet ゞ第 0 0 1

525 GROUP PROCESSES subJects who were actually watched by other people showed the expected increase in dominant responses. 1 2 spa[qns Åq apecu asuodsa 」一 0 」 Most-rehearsed words SOCIAL LOAFING: SHARE THE LOAD As we 」 ust saw, people usually try harder when other people are watching them. However, when the Other people are co-workers rather than observers, the presence Ofa group sometlmes results in a イ e ( 尾 4 e in effort, or socialloafing. Thus, the whole is often less than the sum of its individual parts. Many years ago, Ringelmann (cited by Dashiell, 1935 ) measured the effort that people made when pulling a rope ⅲ a mock tug-of-war contest agalnst a device that mea- sured the exerted force. presumably, the force ex- erted by eight people pulling together in a simple task would be at least the sum of their individual efforts or even somewhat greater than the sum, be- cause Ofthe phenomenon ofsocial facilitation. HOW- ever, Ringelmann found that the total force exerted was only about half what would be predicted by the simple combination of individual efforts. The sub- Jects exerted less force when they worked ⅲ a group ・ 、åore recent studies have confirmed these results and have extended them tO Other behaviors. For ex- ample, Latané, Williams, and Harkins ( 1979 ) asked sub. 」 ects a10 れ e , in palrs, or 1 れ groups Of SiX tO Shout as loudly as they could. The subjects wore blindfolds and headphones that played a loud noise. Thus, they could not hear the shouting of the other subjects nor could they see or be seen by the other people in their group. When subjects shouted a10 れ e , they made more noise than when they shouted in groups; their group effort was only 82 percent of their individual effort. Several variables determine whether the pres- ence Of a group will produce social facilitation or social loafing. One Of the most important Of them is e 厩品〃 . Williams, Harkins, and Latané ( 1981 ) asked subJects to shout as loud as they could individu- ally or ⅲ groups ・ SubJects who were told that the eqmpment could measure only the total group effort shouted less loudly than those who were told that the eqmpment could measure individual efforts. The latter shouted 」 ust as loudly in groups as they did a10 Ⅱ e. These results suggest that a person's efforts in a group activity are affected by whether or not Other people can observe his or her individual efforts. 旺 they can, social facilitation is likely to occur; if they cannot, then social loafing is likely tO occur. 嶬 can analyze the effect ofidentifiability on effort terms Of reinforcement. ・・ he Ⅱ a Least-rehearsed words Noaudience Audience FIGURE 15.14 Number of responses of most rehearsed and least rehearsed words made by subjects in the presence or absence Of an audience. (Based on data from Zajonc, 日 . B. and Sales, S. M. Journal of Experimental Social Psych010gy, 1966 , 2 , 160 ー 168. ) probability of dominant responses. The experi- menters read aloud a list Of fictitious Turkish words and had subjects pronounce each Ofthem 0n1 one tO sixteen times. Then they asked the subjects tO watch a screen, on which the words would be flashed t00 rapidly to be seen clearly, and to guess which word had been presented. ln fact, the experimenters flashed a meaninglessjumble ofshapes on the screen. SubJects who performed this part of the task alone guessed that they saw many 0f the words they had heard. They were more likely to say the words they had rehearsed more often, but they also chose a good number Of the least practiced ones. Other subjects performed ⅲ the presence of two people who had supposedly asked the experimenter whether they could watch the procedure.With this audience present the subJects tended tO stick with the words they had practiced the most; it was as if their in- creased arousal caused them tO make 0 Ⅱ ly the domi- nant responses. Perhaps they found it harder t0 think of the words they had not rehearsed as often. (See 重 15.14. ) Why does the presence of a group mcrease a person's arousal? One important factor seems tO be whether the subjects perceive the group as observing (and thus evaluating) their performance. Cottrell, Wack, Sekerak, and RittIe ( 1968 ) had their subjects perform a task like the one used by and Sales. During the word-guesslng phase some subJects were tested alone; Others were tested in the presence Of two blindfolded or unblindfolded people. Only the

1 60 CHAPTER 5 DEVELOPMENT Harlow's studies with monkeys have shown that clinging, one of the impor- tant behaviors ln attachment, IS an lnnate tendency and does not have tO be rein- forced by food or warmth. lnfant humans and monkeys are normally afraid ofnovel stimuli, but the presence Of their care- giver ()r cuddly surrogate) provides a se- cure base from which they can explore a れ e ー envlronment. Development also involves the ac- quisition Of SOCial skills. lnteractlon with peers is probably the most important fac- tor ln SOCial development. Research with monkeys has shown that deprivatlon Of contact With peers has even 1 れ ore ser10t1S effects than deprivation of contact with the mother. MORAL DEVELOPMENT The word 川 ora 〃 comes from a Latin word that means "custom. ”、 Moral behavior is behavior that conforms to a generally accepted set ofrules. philos- ophers and theologians have argued about whether good and evil exist 1 Ⅱ any absolute sense, but we need れ Ot concern ourselves With this issue. lnstead, ℃ may accept the fact that morality is extremely useful tO human SOCiety. With very few exceptions (fortunately), by the tlme a person reaches adulthood, he or she has ac- cepted a set ofrules about personal and social behav- ior. These rules vary in different cultures ーー・ even ln different individuals ーー but common themes are present in all ofthem. Let us begin by considering the way a child acquires a concept of morality. The pio- neer in this field, as in cognitive development, was Jean Piaget. PIAGET'S DESCRIPTION OF MORAL DEVELOPMENT Piaget studied the behavior ofchildren from the ages of four to twelve years and interviewed them about their beliefs (Piaget, 1932 ). For example, he co ル fronted them with stories about children who had committed various transgresslons, and he asked them t0 give their oprnions about the guilt of the children in the stories. According to Piaget, the first stage of moral development (ages 5 to 10 years) is called 1 れ oral realism. lt is characterized by 0 化れ作な川 self-centeredness") and blind adherence to rules. Guilt is determined almost solely by the effects a person's behavior has, and れ Ot by his or her inten- tlons. An egocentric child can evaluate events only in terms Of their personal consequences. The child's behavior is not guided by the effects it might have on someone else, because he or She iS not capable Of lmagming himself or herself in the other person's place. Thus, a young child does not consider whether an act is right or wrong but only whether it is likely to have good or bad consequences,personally. Punish- ment is a bad consequence, and the fear Of punish- ment is the only real moral force at this age. A young child 引 so believes that rules come 伝 om parents (or other authority figures, such as older children or God) and that rules cannot be changed. Older children and adults Judge an act by the lntentlons Ofthe actor as well as by the consequences ofthe act. A young child considers only the objective outcomes, not the subjective intent that lay behind the act. For example, Piaget tOld tWO storles, one about John, who accidentally broke 15 cups, and Henry, who broke one cup while trying to do some- thing that was forbidden to him. ・ When a young moral realist is asked which ofthe two children is the naughtiest, the child will say thatJohn is, because he broke 15 cups. The fact that the act was entirely accidental is not taken intO account. As a child matures, he or she becomes somewhat less egocentric and becomes capable 0f empathy; he or she can lmagine hOW another person feels. This shift 伝 om egocentrism means that a child's behavior may be guided not merely by the effects acts have on himselfor herselfbut 引 so by the effects they have on others. Around ten years of age, the child enters the second stage of moral development: morali 0f cooperation. Rules also become 1 れ ore flexible as the child learns that many of them (such as those that govern games) are SOCiaI conventlons that may be altered by mutual consent. KOHLBERG'S DESCRIPTION OF MORAL DEVELOPMENT Piaget's description of moral development has been considerably elaborated by Lawrence Kohlberg. Kohlberg studied somewhat older children (boys be- tween 10 and 17 years of age), and he studied the same bOYS over a course Of several years. He pre- sented the children with stories that presented moral dilemmas. For example, one story described a man called Heinz whose wife was dying of a cancer that

1 85 VISION 8 マ / LO 4 3 pa も 9 も p aq モ theater. lfyou have 」 ust come ⅲ from the bright sun, your eyes d0 not respond well t0 the low level 0f illumination. However, after a few mlnutes you can see rather well ー your eyes have adapted. ln order for light to be detected, the photons must bleach (split) molecules of rhodopsin ()r the other photopigments). ・ When high levels of illumi- nat10n strike the retina, the rate Of regeneratlon Of rhodopsin falls behind the rate of the bleaching pro- cess. With 0 Ⅱ ly a small percentage of the rhodopsin molecules intact, the rods are not very sensltlve tO light. 旺 you enter a dark room after being ⅲ a brightly lit room or ln sunlight, there are t00 few intact rhodopsin molecules for your eyes tO respond immediately to dim light. The probability that a phOton will strike an intact molecule ofrhodopsin is very 10W. However, after a while the regeneratlon Of rhodopsin overcomes the bleaching effects of the energy oflight. The rods become full of unbleached rhodopsin, and a photon passing through a rod is likely to find a target. The eye has undergone dark adaptation. Even before the development ofelectron 1 Ⅱ lcro - scopes, which permitted detailed examination Of rods and cones, psychologists were able t0 demon- strate differences in their functions by studying the process ofdark adaptation. Hecht and Schlaer ( 1938 ) exposed a subJect's eyes tO bright illumination and then completely darkened the room. At varymg lengths of time they tested their subjects and deter- mined the dimmest light that they were able to de- tect. As dark adaptation proceeded, the subjects' eyes became progressively more sensltlve tO light; they could detect fainter and fainter lights. Figure 6.11 shows the results ofthe dark adapta- t10n expenment. Each point on the vertical axis indi- cates the intensity Of light necessary tO produce a sensation. (N ・ Ote that the scale on the vertical axis IS logarithmic; a log value 0f8 is 100 , 000 times greater than a log value of 3. ) The figure shows clearly that the process Of dark adaptation is not れ OOth and contlnuous; a break occurs after about seven mmutes in the dark. (See 6.11. ) The discontinuity in the dark adaptation curve IS called the rod-cone break. The function is really composed Of tWO curves, not one. cones, WhiCh are less sensltive than rods, complete their regeneratlon Of photopigments in five tO seven mmutes. The part ofthe curve before the break represents their activity. Rods are slower tO regenerate rhodopsin, but they are れ IOre sensltlve tO light, SO we see the effect Of their adaptation only after the cones are completely dark- adapted. 5 0 30 35 20 25 Time in dark (minutes) FIGURE 6.1 1 A dark adaptation curve showing a rod-cone break. (From Hecht, S. , and SchIaer, S. JournaI of the OpticaI Society ofAmerica, 1938. 28 , 269 ー 275. ) } ま 0 can ℃ be sure that the break is due tO differences in the rate of dark adaptation of rods and cones and that cones are responsible for the top curve and rods for the bOttom one? A rather simple experl- ment provides the answer. Before I describe it, try tO see whether you can think Of it yourself. Here is a hint: Remember that the fovea contams only cones. The evidence can be obtained in the following way: lfa subject 100kS directly at a small spot oflight, only the fovea (which contains Just cones) will be stimulated. A dark adaptation curve obtained in this way contams only the upper portion. However, if the spot of light appears 0 任 t0 the side, so that it stimulates more peripheral portions Of the retma (where both rods and cones are located), the dark adaptatlon curve contains bOth portions. EYE MOVEMENTS our eyes are never completely at rest, even When our gaze is fixed upon a particular place (the 重れ 四り . Three types 0f movements can be observed: 1. Fast, aimless, 」 ltterlng movements occur, prob- ably similar tO the fine tremors we see 1 Ⅱ our hands and fingers when we attempt t0 keep them still. 2. superlmposed on these random tremors are slow, drifting movements that shift the image on the retlna a distance Of approximately twenty cone widths. 3. These slow drifts are terminated by quick move- ments that bring the image Of the fixation point back to the fovea. Although the small, jerky movements that the eyes make when at rest are random, they appear tO

1 1 5 INSTRUMENTAL CON 団引 ON 爪 G ever you say "Speak!" You get a few pieces 0f 応 0d that the dog likes. Then you attract its attention and say, "Speak! ' ' while wavlng a piece 0 仼 00d in front of it. The dog begins to show S1gns ofexcitement at the sight of the 応 od and finally lets ou い bark. lmmedi- ately, you give it the 応 0d. Then you bring out an- other piece 0ff00d and again say "Speak!" This time the dog probably barks a little sooner. After several trials the dog will bark whenever you said "Speak!" even if れ 0 fOOd iS visible. You dO not reinforce barking whenever lt occurs but only when you first present the stimulus "Speak!" At all other times you lgnore barking or perhaps even scold the dog for barking. ln this way the dog learns tO discriminate between the tWO conditions and to respond appropriately. The com- mand serves as the discrimmatlve stimulus. Our daily behavior is guided by many different kinds of discriminative stimuli. 旺 our telling of funny 」 okes has been reinforced by other people's laughter, we will tell them only when there are other people present; we will not tell jokes in an empty r001 れ . The presence Of Other people serves as the discrinunatlve stimulus for the behavior 0 巧 Oke tell- tloning complement each Other. The pmrmgs ofneutral stimuli with appetitive and averslve stimuli (classical condition- ing) determine which stimuli become conditioned (secondary) reinforcers and punishers. Through the process ofinstru- mental conditioning the contingencles between organism's behavior these stimuli adapt the organlsm's behav- 10r tO 1tS envlronment. Complex re— sponses, which are unlikely tO occur spontaneously, can be reinforced by the methOd Of successlve approximatlons (shaping). Teachers use this process t0 train their students tO perform complex behaviors, and something similar occurs When, in the course Of learmng a skill, we become satisfied only when we detect srgns Of improvement. The Premack principle helps identify reinforcing situations: The opportunity tO perform a more preferred activity can be used tO reinforce the performance Of a less preferred one. STIMULI THAT GUIDE BEHAVIOR SO far in this chapter we have encountered five types Of stimuli: れ一川 20 な 4 れ一川材乢 tO which orienting responses become habituated; 材れ ( 0 れ市行 0 れ al 川材〃 , WhiCh produce unconditional responses; ( 0 れ d 一行 0 れ 4 / 行川″ which through assoclatlon with uncondi- tional stimuli produce conditional responses; 「れ - 丿ら尾ⅲ g 行川乢 which strengthen responses; and 24 れ - なんⅲ g 行ら which suppress responses. Another category Of stimuli ・ - ー市立日川 4 怩ゞ川″・一 - guides responding by indicating that a particular response will be reinforced or punished on that occaslon. l)iscnmmation l)iscrlmrnative indi— cate the nature Of the current contlngency between response and reinforcement ()r punishment). That is, the stimuli say whether responses will be rein- forced or punished, or whether there will be れ 0 con- sequences at all. Every lnstance Of instrumental con- ditiomng involves SO れ sort Of discrinunatlve stimulus. First, let us 100k at a clear-cut example. Suppose you want to teach your dog t0 bark when- The discriminative ability Of animals can Often very practical purposes.

567 CLASS 旧 CATION AND DIAGNOSIS were normal, although some of their fellow patients did, apparently from the fact that they openly took notes. One patlent said, "You're not crazy. You're a 」 ournalist or a professor. You're checking up on the hospital" (Rosenhan, 1973 , p. 252 ). 嶬市 e Ⅱ the pseu- dopatients were released, the diagn0SIS in almost every case was "schizophrenia, ln rer れ 1SSIOn. ' (Re— 川い 0 れ means lessemng ln extent or degree. When these results were published, some people concluded that psychiatric diagnosis was a useless endeavor if it could not distinguish between normal people and schizophrenics. However, a closer exam- ination Of the facts shows that the data dO not war- rant this conclusion. The clinicians ・ ere not re- quired t0 distinguish between 加「 4 / people and people with a mental disorder; they were required t0 detect that some people were 2 化れ市れ tO have symptoms 0f schizophrenia. ln fact, Spitzer ( 1975 ) has shown that on the basis Of the data the clinicians had, Ⅱ 0 other diagnosis would have been justified. He noted that the pseudopatients insisted on admis- SIOn tO the hospitals, which itself is an lmportant symptom ofmental or emotional disturbance. 、 - over, their behavior after admiSS10n was れ Ot , in fact normal; a れ ormal person , ould go tO the nursing station and say, "l'm really not crazy ー I 」 ust pre- tended to be. Now I want to be released. '' The pseu- dopatients remained paSSIVe. Rosenhan's study and Spitzer's crltlcism have stimulated much public discusslon about an impor- tant issue. They also reinforce the value offollowing the scientific method (discussed in Chapter 2 ). should certainly critlclze any tendency Of mental health professionals tO view patients' behavior only ln terms Ofan initial psychiatric diagnosis. However, we should not blame them for making a reasonable diagnosis when a patient lies about symptoms that are almost never found in people whO are not psy- chotic. Because labeling can have bad effects, perhaps we should abandon all attempts to classify and diag- nose 1 e れ tal disorders. However, proper classifica- tion does have advantages for a patient. One advan- tage is that, with few exceptions, the recognition Ofa specific diagnostic category precedes the develop- ment Of successful treatment for that disorder. Treatments for diseases such as diabetes, syphilis, tetanus, and malaria were found only after the dis- orders could be reliably diagnosed. A patient may have a multitude of symptoms; but before the cause of the disorder (and hence its treatment) can be dis- covered, the primary symptoms must be identified. seek admiSS10n as patlents ln var10t1S psychiatric hOS— pitals. To gain admission, they complained of only 0 れ e symptom ー that they heard voices saylng "empty," "hollow," and "thud. " (Hallucinations are symptoms indicative ofschizophrenia. ) A11 other state ments were as true and accurate as th ey could make them, and they did not behave abnormally. Furthermore, after they were admitted, they did not complain Of the V01Ces any 1 Ⅱ ore. ル lost of the volunteers were diagnosed as psy- chOtic. Once they were in the hospitals, Rosenhan said, the staff explained their behavior as sympto- matic Of their mental illness. None Of the mental health professionals realized that the pseudopatients When we observe clearly unusual behavior, we wonder what itS causes are. 4

ancestors had self-awareness—before the brain functions neces- sary fO 「 consciousness evolved. Therefore, the primitive system is not connected with the systems responsible fO 「 con- sciousness; only the new mammalian visual system iS. When we see something with the newer system, we are aware Of what we see. But when your grandfather's remaining visual system —the primitive one—・ detects something, he iS not conscious Of seeing anything, because that system is not connected with those respon- sible fO 「 awareness. コ think ー understand," said Laura. She paused, looking reflective. 'l've never thought Of consciousness as something that you could study scientifically. DO you think your research can find out how it works?' ' 'WeIl, that will probably take a long time, but llike to think my research takes us a few steps in that direction. This chapter explores the nature human self- awareness: knowledge Of our 0 、 eXIStence, behav- ior, perceptions, and thoughts. This is the most com- mon, and probably the most important, meamng of consclousness. ・ / ・ hy are we conscious? } 0 " dO we direct our consclousness frOl れ one event tO another, paymg attentlon tO some stimuli and ignormg others? what is known about the brain functions responsible for consclousness? what iS hypn0SIS can another person really take control Of our 0 , n thoughts and behavior?W ・ hy do we regularly un- dergo the profound alteration in consclousness called sleep? ・第 dO not yet have all the answers tO these questions, but we have made much progress. CONSCIOUSNESS AS A SOCIAL BEHAVIOR Why are we aware of ourselves? what purpose IS served by our ability tO realize the fact that we exist, that events occur, that we are doing things, and that we have memories? If VIew consclousness as an adaptive trait of the human species, the most likely explanation lies in 1tS relation tO commumcatlon. Because Ofour ability tO commumcate, are aware ofourselves. consclousness is a SOCial phenomenon. ConSC10usness IS a prlvate experlence.• per— son can directly experlence only his or her 0 , Ⅱ con- humans conscious—aware Of our own existence. 3

239 PERCEPTION OF SPACE AND MO 引 ON Depth cues 210n0Cu ー a 「 cues Binocular cues Motion parallax Retinal disparity (stereopsis) Pictorial cues Convergence lnterposition Size Perspective Texture Haze FIGURE 7.27 The principal monocular and binocular depth cues. Shading 日 evation ments. PerceiV1ng Where things are and percelvlng what they are doing are obviously important func- t10ns Of the visual system. are turned inward. If it is farther away, they look more nearly straight ahead. Thus, the eyes can be used like range finders; the brain controls the extra- ocular muscles, SO it knows the angle between them, which is related tO the distance between the object and the eyes. (See 7.2 & ) An even more lmportant factor in the perceptlon Of distance is the informatlon provided by retinal disparity. ( D なア 4 日 means "unlikeness" or "dis- similarity. ") Hold up a finger of one hand at arm's length and then hold up a finger of the other hand midway between your nose and the distant finger. 旺 you 100k at one of the fingers, you will see a double image ofthe other one. (Try it. ) Whenever your eyes are pointed toward a particular point, the images Of obJects at different distances will fall 0 Ⅱ different portions Of the retina ln each eye. The amount Of disparity produced by the images of an object on the tWO retlnas provides an lmportant clue about its dis- tance from us. The perception ofdepth 伝 om retinal disparity is called stereopsis. A 立 e 0 立 02e is a device that shows two slightly different pictures, one to each eye. The PICtures are taken by a camera equipped with tWO lenses, located a few inches apart,just as our eyes are. When you 100k through a stereoscope you see a three-dimensional image. An experlment by Julesz ( 1965 ) demonstrated that retinal disparity is what produces the effect of depth. Using a computer, he produced two displays of randomly positioned dots in which the location of some dots differed slightly. 旺 some of the dots in one of the displays were dis- placed slightly to the right or the left, the two dis- PERCEPTION OF DISTANCE ・ We perceive distance by means Of two kinds ofcues: binocular ("two-eye") and monocular ("one-eye"). Only animals with eyes 0 れ the front of the head (such as primates, cats, and some birds) can obtain binocular cues; animals with eyes on the side Oftheir heads (such as rabbits and fish) can obtain only mon- ocular cues, because the visual fields Of their eyes dO not overlap. one Of the 1 れ 0 Ⅱ ocular cues involves movement and thus must be experlenced in the natu- ral envlronment or ln a 1 Ⅱ 0t10n PICture. The Other 1 れ 0 れ ocular cues can be represented in a drawing or a photograph. ln fact, most 0f these cues were 0r1g1- nally discovered by artists and only later studied by psychologists. Artists wanted tO represent the world realistically, and they studied their visual envlron- ments tO identify the features that indicated distance Of ObJects from the viewer. Art historians can show us the evidence Of their discovenes. Figure 7.27 shows the ten most important sources Of distance cues ( C010r terms). (see ー′に 7.27. ) Binocular Cues An important cue about distance is supplied by convergence. Recall 伝 om Chapter 6 that the eyes make conjugate movements SO that both 100k at ()o れ (n) the same point ofthe visual scene. lfan ObJect is very close tO your face, your eyes

183 、ゞ The German astronomer J0hannes Kepler ( 1571 ー 1630 ) was the first scientist tO suggest that the retina of the eye was responsible for ViSion. Kepler iS shown discussing hiS astronomi- cal observations with his sponsor, Emperor Rud01ph Ⅲ . こご ganglion cell that recewes information 伝 01 Ⅱ SO many rods is sensitive to very low levels oflight; a small quantity oflight falling 0 Ⅱ many rods can thus effec- tively stimulate the ganglion cell on which their informatlon converges. ROdS are therefore responsl— ble for our sensitivity to very dim light but provide poor actllty. TRANSDUCTION OF LIGHT BY PHOTORECEPTORS Although light-sensitive sensory organs have evolved independently in a wide variety of animals fror れ insects tO fish tO mammals ーー the chemistry IS essentially the same in all species: A molecule de- rived 伝 01 Ⅱ vltamin A is the central ingredient in the transduction Of the energy Oflight intO neural activ- ity. (Carrots are said tO be good for vision because they contain a substance that the bOdy easily converts to vitamin A. ) ln the absence oflight this molecule is attached tO another molecule, a protein. The tWO molecules together form a photopigment. The photoreceptors Of the human eye contain four kinds of photopigments (one for rods and three for cones), but their basic mechanism is the same. When a phO- ton (a particle oflight) strikes a photopigment, the photoplgment splits apart 1ntO its tWO constltuent molecules. This event starts the process Of transduc- tion. The splitting of the photopigment causes a series ofchemical reactlons that stimulate the phOtO- receptor and cause lt tO send a message tO the bipolar cell with which it forms a synapse. The bipolar cell sends a message to the ganglion cell, which then sends one on to the brain. (See 愈 6.10. ) lntact photoplgments have a charactenstic C010r. For example, rhodopsin, the photopigment ofrods, synapses. BiPOlar cells transmit this informatlon tO the ganglion cells, neurons whose axons travel across the retlna and through the opt1C nerves. Thus, visual informatlon passes through a three-cell chain to the brain: photoreceptor → bipolar cell → ganglion cell → brain. A single photoreceptor responds only t0 light that reaches its lmmediate vicinity, but a ganglion cell can recelve information 伝 01 Ⅱ many different photoreceptors. The retlna aISO contams neurons that interconnect bOth adjacent photoreceptors adjacent ganglion cells. (See 重 6.9. ) The exis tence Of this neural circtlltry indicates that son ・ kinds ofinformation processlng are performed in th retlna. The human retlna contalns two general types Of photoreceptors: 125 million rods and 6 million cones, so called because oftheir shapes. The fovem a small pit in the back of the retina approximately 1 millimeter in diameter, contalns only cones. (Refer tO 重 6.6. ) Because most cones are connected tO only one ganglion cell apiece, the fovea is responsible for our finest, most detailed vision.When we lOOk at a P01nt ln our visual field, ℃ move our eyes SO that the image of that point falls directly upon the cone- packed fovea. Thus, the fovea provides us with our greatest visual acuity. ( 月 c 材″ア derives 伝 om the Latin 4 ( リ meamng 'needle. '' ・ e use the same concept when we say that someone has "sharp eyes"; we mean he or she can see extremely small details. ) Cones are alSO responsible for our ability tO see COlors, a topic discussed later in this chapter. Farther away 伝 om the fovea the number 0f cones decreases and the number ofrods increases.Up to 100 rods may converge on a single ganglioncell. A