Question Details

Answered: - Describe ALL the dependent variables for the designated

Describe ALL the dependent variables for the designated experiment:

  • Provide an operational definition
  • Name?the?units??it?was?measured?in

Identify all the main effects and interactions (if the design is factorial). Make sure you state the main effect for EACH independent variable you named in (5):

  • Provide the statistical statement (t- or F-statement)

Identify all the main effects and interactions (if the design is factorial). Make sure you state the main effect for EACH independent variable you named in (5):

  • Provide the statistical statement (t- or F-statement)
  • Explain each statement in plain English
  • Explain each statement in plain English


  • 5.???????? Describe ALL the independent variables for the designated experiment:
  • Name each variable
  • List its levels
  • State?the?statistical?test(s)?that?was/were??used?to?analyze?the?data

Use Figure 1 on p. 653 and create a similar figure (in EXCEL, then copy and paste) to predict reaction time latencies for a memory set of seven items for a probe present and a probe absent response.? Describe the difference. (One-two paragraphs).

  • If there are more than one independent variable, state the factorial design

High-Speed Scanning in Human Memory


Author(s): Saul Sternberg


Source: Science, New Series, Vol. 153, No. 3736 (Aug. 5, 1966), pp. 652-654


Published by: American Association for the Advancement of Science


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References and Notes


the typical range of stimulation levels


and onvironments of the species; per1. J. H. Bruell, Amer. Zoologist 4, 125 (1964).


2. D. S. Falconer, Introduction to Quantitative


haps it would be most relevanlt for


Genetics (Ronald Press, New YorlQ, 1960).




evolution of behaviotr.


The sec3. G. Lindzey, D. T. Lykken, H. D. Winston, J.


Abnormal Social Psychol. 61, 7 (1960); G.


ond approach, however, enables sysLindzey, H. D. Winston, M. Manosevitz, J.


Com . Physiol. Psychol. 56, 622 (1963).




tematic analysis of the influence of


P. L. Broadhurst, in Experimentsin Personvarious environmentsand test situations 4. ality, vol. 1, Psychogeneticsand Psychopharmacology, H. J. Eysenck, Ed. (Routledge and


on behavior of the species.


Kegan Paul,


The existence of intleractions


between 5. J. H. Bruell,London, 1960). Behavior, F L.


in Roots of


Bliss, Ed. (Harper, New York, 1962), p. 48.


variables does Inot imply that general


6. A longer, more detailed paper describing the


statements cannot be made about gecomplete study, including diallel cross and


correlation analyses and a discussion of


netic, age, or environmentalfactors per


specific gamete, treatment, and sex cffects is


se. SigniScant main effects may still be


in preparation.


Psychol. Repts.


the primary concern of the investigator 7. N. D. Henderson, Physiol. Psychol. 15, 579


(1964); J. Comp.


59, 439


and may frequlentlyemerge. The valu!e




8. Among previously undisturbed mice, mode of


of such results increases considerably,


inheritance interacts with sex, and dominance


appears within sexes. This finding is consisthowever, if it is known that the effect


ant with the results of J. H. Bruell: "Mode of


occurs over a wide range of conditions


inheritance of emotional defecation in mice,'>




and if the investigator is aware of spe9. N. D. Henderson, J. Comp. Physiol. Psychol.


cific interactions.


57, 284 (1964); ibid. 59, 439 (1965).


10. G. W. Meier, ibid. 58, 418


NORMAN HENDERSON11. Research supported by NSF (1964).GB 1863. I






Department of Psychology,


thanlQR. L. Collins for helpful comments.


Oberlin College, Oberlin, Ohio


4 May 1966





was pulled, a feedback light informed


the subject whether his response had


been correct. The trial ended with his


attempt to recall the series in order. For,


every value of s, positive and negative


responses were required with equal frequency. Each digit in the series occurred as a test stimulus with probability (2s)- and each of the remain1,


ing digits occurred with probability






Each subject had 24 practice trials


and 144 test trials. Feedback and payoffs were designed to encourage subjects to respond as rapidly as possible


while maintaining a low error-rate.


The eight subjects whose data are presented pulled the wrong lever on 1.3


percent of the test trials (5). Recall


was imperfect on 1.4 percent of the


trials. The low error-rates justify the


assumption that on a typical trial the


series of symbols in memory was the


same as the series of symbols presented.


Results are shown in Fig. 1. Linear


regression accounts for 99.4 percent of


High-Speed Scanning in Human Memory


the variance of the overall mean reAbstract. When sabjects judge whether a test symbol is contained in a short sponse-latencies (6). The slope of the


nqemorized seqaence of synqbols, their mean reaction-time increases linearly fitted line is 37.9 + 3.8 msec per symwith the length of the sequence. The linearity and slope of the function imply bol (7); its zero intercept is 397.2 +


the existence of an internal serial-comparison process whose average rate is


19.3 msec. Lines fitted separatelyto the


between 25 and 30 symbols per second


mean latencies of positive and negative


responses differ in slope by 9.6 + 2.3


How is symbolic information re- the information is retrieved. Of pal:- msec per symbol. The difference is


trieved from recent memory? The study ticular interest in the study of retrieval attributable primarily to the fact that


of short-term tn-emory(1) has revealed is the effect of the number of elements for s = 1, positive responses were 50.0


some of the determinantsof failures to in memory on the response latency. + 20.1 msec faster than negative reremember, but has provided little in- The subject first memorizes a short sponses. Lines fitted to the data for


sight into error-free performance and series of symbols. He is then shown a


2 sc


6 differ in slope by an inthe retrieval processes that underlie it. test stimulus, and is required to decide significant 3.1 + 3.2 msec per symbol.


One reason for the neglect of .retrieval whether or not it is one of the symbols


The latency of a response depends,


mechanisms may be th.e implicit as- in memory. If the subject decides in part, on the relative frequency with


sumption that a short time after several affirmativelyhe pulls one lever, making which it is required (8). For this reaitems have been memorized, they can a positive response; otherwise he makes son the frequenciles of positive and


be immediately and simultaneously a negative response by pulling the other negative resplonsesand, more generally,


available for expression in recall or in lever. ][nthis paradigm it is the identity the resp!onse entropy (8), wlere held


other responses, rather than having to of the symbols in the series, but not constant for all values of s in experibe retrieved first. Tn another vocabu- their order, that is relevant to the ment 1. However, the test-stimulus


lary (2), this is to assume the equiva- binary response. The response latency entropy (predictability) was permitted


lence of the "span of immediate mem- is defined as the time from the onset to co-vary with s.


ory" (the number of items that can be of the test stimulus to the occurrence


Both response and test-stimulus enrecalled without error) and the "mo- of the response.


tropies were controlled in experiment


mentary capacity of consciousness"


Because they are well learned and 2, in which the retrieval process was


(the number of items immediately highly discriminable, the ten digits studied by an alternative method simiavailable). The experiments reported were used as stimuli. On each trial of


lar to that used in more conventional


h.ere (3) show that the assumption is experiment 1, the subject (4) saw a ran- experiments on choice-reaction time.


dom series of from one to six different In experiment 1, the set of symbols




Underlying the paradigm of these digits displayed singly at a fixed locus


associated with the positive respolnse


experiments is the supposition that if for 1.2 seconds eache The length, s, of


changed from trial to trial. In conthe selection of a response requires the the series varied at random from trial trast to this varied-set procedure, a


use of information that is in memory, to trial. There followed a 2.0-second fixed-set procedure was used in experithe latency of the response will reveal delay, a warning signal, and then the ment 2. In each of three parts of the


something about the process by which test digit. As soon as one of the levers session, a set of digits for which the








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positive response was required (the


positive set ) was announced to the


subject (4); there followed 60 practice


trials and 120 test trials based on this


set. The suibjec;tknew that on cach


trial any of the ten digits could appear as the test stimulus, and that for


all the digits not in the positive set


(the negative set) the negative response


was required. Each subject worked


with nonintersecting positive sets of


size s = 1, 2, and 4, whose composition was varied from subject to subject.


Stimulus and response entropies were


both held constant while s was varied,


by means of specially constructedpopulations of test stimuli. Let xl, Y1,Y2,zls


. . ., z and wl, . . ., W3 represerlt


the ten digits. Their relative frequencies in the popullation were xl, 4/15;


each y, 2/15; each z, 1/15; and each


w, 1/15. The three sequences of test


stimuli presented to a subje!ctwere obtained by random permutation of


the fixed population and assignment


of xl, the Yi, or the zi to the positive


response. Thus, the population of test


stimuli, their sequential properties, and


the relative frequency of positive responses (4/15) were the same in all


conditions (9).


A trial consisted of a warning signal,


the test digit, the subject'sresponse, and


a feedback light. Between a response


and the next test digit, 3.7 seconds


elapsed. As in experiment 1, feedback


and payoffs were designed to encourage


speed without sacrificeof accuracy. The


six subjects whose data are presented


pulled the wrong lever on 1.0 percent


of the test trials (5).


The results, shown in Fig. 2, closely


resemble those of experiment 1. A


positive set in experiment 2 apparently


played the same role as a series of


symibols presented in experiment 1,


both correspondingto a set of symbols


stored in memory and used in the


selection of a response. As in experiment 1, linear regression accounts for


99.4 percent of the variance of the


overall mean response-latencies (6).


The slope of 38.3 + 6.1 msec per


symbol is indistinguishable from that


in experiment 1; the zero intercept


is 369.4 + 10.1 msec. In experiment 2, the relation between latencies


of positive and negative responses when


s - 1 is not exceptional. Lines fitted


separately to latencies of the two kinds


of response differ in slope by an insignificant 1.6 + 3.0 msec per symbol.


The linearity of the latency functions




































J 500-









z -































































Fig. 1. Relation between resplonse latency


and the number of symbols in memory, s,


in experiment 1. Mean latencies, over


eight sulbjects,of positive responses (filled


circles) and negative responses (open


circles). About 95 observations per point.


For each s, overall mean (heavy bar) and


estimates of + ff are indicated (6). Solid


lline was fitted by least squares to overall


means. Upper bound for parallel process


(broken curve).



suggests that the time between test


stimulus and response is occupied, in


part, by a serial-comparison(scanning)


process. An internal representation of


the test stimulus is compared successively to the symbols in memory, each


comparison resulting in either a match


or a mismatch. The time from tlhe beginning of one comparison to the beginning of the next (the comparison time)


has th!esame mean value for successive


comparisons. A positive response is



























, 600-

































+38.3 s












































































Fig. 2. Relation between response latency


and the size of the positive set, s, in experiment 2. Mean latencies, over six subjects, of positive responses (filled circles)


and negative responses ( open circles) .


About 200 (positive) or 500 (negative)


observations per point. For each s, overall





mean (heavy bar) and esltimates + ff


are indicated (6). Solid line was fitted


by least squaresto overall means. Upper


bound for parallelprocess(brokencurve).



made if there has been a match, and a


negative response otherwise.


On trials requiring negative responses, s comparisons must be made.


If positive responses were initiated as


soon as a matichhad occurred (as in a


self-terminatingsearch), the mean number of comparisons on positive trials


would be (s + 1)/2 rather than s. The


latency function for positive responses


would then have half the slope of the


function for negative responses. The


equality of the observed slopes shows,


instead, that the scanning process is


exhaustive: even when a match has


occurred, scanning continues through


the entire series. This may appear


surprising, as it suggests nonoptimality. One can, however, conceive


of systems in which a self-terminating


search would be inefficient. For example, if the determination of whether


or not a match had occurred were a


slow operation that could not occur


concurrently with scanning, self-termination would entail a long interruption in the scan after each comparison.


On the basis of the exhaustive-scanning theory, the zero intercept of the


latency function is interpreted as the


sum of the times taken by motor response, formation of the test-stimulus


representation, and other unknown


processes whose durations are independent of the number of symbols in


memory. The slope of the latency


function represents thenean comparison-time. The two experiments, then,


provide a measure of the speed of


purely internal events, independent of


the times taken by sensory and motor


operations.The average rate of between


25 and 30 symbols per second is about


four times as high as the maximum rate


of "subvocal speech" when the words


are the names of digits (11). This difference suggests that the silent rehearsal


(12) reported by subjects in both experiments should probably not be identified with high-speed scanning, but


should be thought of as a separateprocess whose function is to maintain the


memory that is to be scanned.


In view of the substantial agreement


in results of the two experiments, one


diSerence in procedure merits particular emphasis. A response in experiment 1 was the first and only response


based on a particularseries, made about


three seconds after the series had been


presented. In contrast, the positive set


on which a response was based in experiment 2 had been used on an average of 120 previous trials. Evidently,



5 AUGUST 1966






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tive set



(n s)



had no ef3ect on the



either practice in scanning a particular series nor lengthening of the time


it has been stored in-memory need increase the rate at which it is scanned.


In accounting for human performance in other tasks that appear to involve multiple comparisons, theorists


have occasionally proposed that the


comparisons are carried out in parallel


rather than serially (13, 14). (This


perhaps corresponds to the assumption


mentioned earlier that the momentary


capacity of consciousness is several


items rather than only one. Are the


present data inconsistent with such a


proposal? Parallel comparisons that begin and also end simultaneously(14) are


excluded because the mean latency has


been shown to increase with s. A process irl which multiple comparisons begin simultaneously is more difficult to


excltlde if the comparison times are in?


dependent, their distribution has nonzero variance, and the response is initiated when the slowest comparison


ends. A linear increase in mean latency


cannot alone be taken as conclusive


earidenceagainst such a process. The


magnitude of the latency increase that


would result from a parallel process is


bounded ahove, however (15); it is


possible to apply the bound to these


data (]6). This was done for the negative responsesin both experiments,with


the results shcown the broken curves




in Figs. 1 and 2. Evidently, the increase


in response latency with s is too great


to be attributed to a parallel process


with independent comparison times


(17) .


Other experiments provide added


support for the scanning theory (16).


Two of the findings are noted here: (i)


variation in Ithe size, n, of the nega-



.09 (experiment 2), suggesting true intersubject differences in slope; the population


distribution of slopes has an estimated standard deviation of 8.0 msec per symbol


W. R. Garner, Uncertaintyand Structure as


Psychological Concepts (Wiley, New York,


1962) .


Bell Telephone Laboratories,


9. A result of this procedure is that other


factors in choice-reaction time were also conMurray Hill, New Jersey


trolled : stimulus discriminability (10);


information transmitted (8); and information reReferences and Notes


duced, M. I. Posner, Psychol. Rel^. 71, 491


(1964); P. M. Fitts and I. Biederman, J. Exp.


1. A. W. Melton, J. Verbal Learning Ve7*ba1


Psychol. 69, 408 (1965).


Behavior 2, 1 ( 1963 .




10. R. N. Shepard and J. J Chang, J. Exp.


2. G. A. Miller, Psychology, the Science of


Psychol. 65, 94 ( 1963); M. Stone, PsychoMental Life ( Harper and Row, New York,


metrika 25, 251 ( 1960) .


1962), p. 47.


11 T. K. Landauer, Percept. Mot. Skills 15, 646


3. These experiments were first reported by S.




Sternberg, "Retrieval from recent memory: 12. D. E. Broadbent, Perception and CommllSome reaction-timeexperimentsand a search


nication (Pergamon, New York, 1958), p. 225.


theory," paper presented at a meeting of the


13. L. S. Christie and R. D. Luce, Bull. Math.


PsychonomicSociety, BrynMawr,August 1963.


Biophys. 18, 89 (1956); A. Rapoport, Be4. Subjects were undergraduatesat the UniverhalnioralSci. 4, 299 ( 1959) .


sity of Pennsylvania.


14 U. Neisser, Amer. J. Psychol. 76, 376 (1963);


5. These trials were, excluded from the analysis.


Sci. Amer. 210, 94 ( 1964) .


Three other subjects in experiment1 (twol in


15. H. O. Hartley and H. A. David, Ann. Math.


experiment2) were reiected because they exStat. 25, 85 ( 1954) .


ceeded an error criterion. Their latency data, 16. S. Sternberg, in preparation


which are not presented, resembled those of


17.- Exponentially distributed parallel comparisons


the other subjects.


(13) and other interesting theories of multi^


6. For both experiments the data subjected to


ple comparisons (lE) lead to a latency funcanalysis of variance were, for each subjecty


tion that is approximately linear in log s.


the mean latency for each value of s. So


Deviations of the overall means from such a


that inferences might be drawn about tlle


function are significant (P < .03) in both


population of subjects, individual diiderences




in mean and in linear-regressionslope were 18. A. T. Welford, Ergonomics 3, 189 (1960).


treated as "random eidects." Where quan- 19. I. Pollack, J. Verbal Learning Verbal Betities are stated in the form a + bJ b is an


havior 2, 159 ( 1963); D. E. Broadbent and


estimate of the standard error of a. Such


M. Gregory,


estimates were usually calculated by usirlg 20. Supported in Nature 193, 1315 (1962).


part by NSF grant GB-1172 to


variance components derived from the analthe University of Pennsylvania. I thank D. L.


ysis of variance.


Scarborough for assistance, and J. A. Deutsch,


7. The analyses oXf


variancefor both experitnents


R. Gnanadesikan, and C. L. Mallows for


provided a means of testing the significance


helpful discussions.





corrected; and (v) until the response


to one stimulus is completed the next


stimulus cannot be viewed.







diiderencesamong individual slopes. Significance levels are .07 (experiment 1) and



25 May 1966






Anxiety Levels in Dreams: Relation to Changes in


Plasma Free Fatty Acids



Abstract. Blood samples for determination of plasma free fatty acids were


obtained throughout the night by means of an indwelling catheter. The first


sample was drawn at the onset of rapid eye movements ancl cz second after 15


minutes of these movements. Subjects were then awakened and asked to relate


their dreams; a third sample was drawn 15 to 25 minutes later. Anxiety scores


derived from 20 dreams of nine subjects had significant positive correlations


with changes in f ree f atty acids occurring during REM sleep. No statistically


significant relation was found between anxiety and the changes in free fatty


acids occurring from the time just before awakening to ]5 to 25 minutes


mean latency, indicating that stimulus later. Presumably, anxiety in dreams triggers the release of catecholamines into


confusahility (10, 18) cannot account the circulation, and these catecholamines mobilize proportional amounts of


for the results of experiments 1 and 2; free fatty acids from body fat.


(ii) variation in the size of a responseirrelearant


memory load had no ef3




A previous study of the relation of


Nine paid volunteer male subjects,


on the latency function, implying that emotions and blood lipids during the ranging in ages from 19 to 25, were


the increase in latency reflects the du- waking state revealed a significantposi- asked to sleep overnight in a dream


ration of retrieval and not merely the tive correlation between low levels of laboratory, arranged to appear as a


exigencies of retention.


arousal of anxiety, as determined from hospital room. Subjects slept 1 or 2


The generality of the high-speed a 5-minute period of free associative nights in the laboratcory


but were not


scanning process has yet to be deter- speech (1), and concentrations of free given preliminary periods in which to


mined, but there are several features fatty acids (FFA) in plasma. No essen- become accustomed to sleeping in this


of experiments 1 and 2 that should be tial correlation was found in this study room. They were told that we were intaken into account in any comparison between hostility and concentrations of arestigating


sleep, dreams, and changes


with other binary classification tasks FFA. The positive correlation between in body chemistry. Subjects were in(14, 19): (i) at least one of the classes anxiety levels and FFA raised the ques- structed not to eat after their evening


is small; (ii) class members are as- tion whether a similar relation might meal at 6:00 p.m. and to report to the


signed arbitrarily; (iii ) relatively little occur while subjects are in a dream laboratory at 11:00 p.m. At !this time


practice is provided; (iv) high ac- state. Our study was undertaken to ex- a venipuncture was performed in the


curacy is required and errors cannot be plore such a possibility.


left antecubitalvein with a No. 18 thin654






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