Emerging Themes in Cognitive Development

,

I

Mark L. Howe

• -----------

Robert Pasnak

Editors

Emerging Themes in Cognitive Development Volume I: Foundations

With 36 Illustrations

Springer-Verlag New York Berlin Heidelberg London Paris Tokyo Hong Kong Barcelona Budapest

2 The Ontogeny of Inhibition Mechanisms: A Renewed Approach to Cognitive Development

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KATHERINE KIPP HARNISHFEGER AND DAVID

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BJORKLUND

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A major focus of developmental researchers has concerned the isolation of the mechanisms behind age-related improvements in cognition. Work­ ing memory capacity, metacognitive abilities, strategies, and knowledge base have all been touted as important causative agents in children's thinking (e.g., Bjorklund, 1990; Schneider & Pressley, 1989). Meanwhile, although inhibition processes enjoyed a role in early theories of cognition and development (Luria, 1961; Underwood, 1957), inhibition has been neglected, in part, because it has not appeared to be compatible with the computer metaphor of cognition (Bjork, 1989; Dempster, this volume). Currently, the developmental significance of inhibitory processing is garnering renewed support from such diverse areas as memory develop­ ment (Bjorklund & Harnishfeger, 1990), object permanence in infancy (Diamond, 1988), and discourse processing in the aged (Hasher & Zacks, 1989). It is time to reexamine inhibition as a central mechanism in accounts of cognitive development. In an earlier paper (Bjorklund & Harnishfeger, 1990), we outlined a developmental theory of inefficient inhibition. We proposed that, with age, children are increasingly able to keep task-irrelevant information out of working memory. Younger children's poor inhibitory mechanisms result in less efficient cognitive processing because working memory space is consumed with irrelevant information, leaving less mental space avail­ able for other aspects of processing. We proposed this theory in response to recent attacks on the resources hypothesis of cognitive development (Brainerd & Reyna, 1989, 1990; Howe & Rabinowitz, 1990; Stanovich, 1990). Basically, the resources hypothesis holds that developmental dif­ ferences in cognitive functioning are due to differences in children's efficiency in allocating their limited mental resources; this efficiency improves with experience, knowledge, and maturation (Bjorklund & Harnishfeger, 1990; Case, 1985). A model of inefficient inhibition main­ tains many of the explanatory powers of the resources hypothesis and provides a broader context in which a new framework of cognitive devel­ opment can be formulated (Bjorklund & Harnishfeger, 1990). 28

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tlso been investigated in velopment of the verbal young children were told 10US kinds of visual and .s was varied, and in some ·balize as well as perform !In researchers have con­ 19u1ation as occurring in about 1.5 and 5.5 years, Ir own behavior through , control their behavior ter is verbal self-control reveals that speech has functions. The initiative nd at early stages speech

t, immediate instructions , instructions that are in ze the ball") will neither ally intensify the child's )r response at this stage is 'ouch your knee" (Luria, (in Luria, 1961) demon­ oor inhibitory function of ~ to a red light and not ..ith fairly good inhibition red to say "Press" when to the green light, their this condition, the chil­

2. Inhibition

31

dren squeezed the bulb both when saying "Press" and when saying "Don't press." Luria's work suggests that verbal self-regulation reaches mature function sometime after 4.5 to 5.5 years.

Response Inhibition The process of inhibiting motor responses continues to be of interest in older children. Constantini and Hoving (1973a) defined response inhibition as "the ability to slow down, delay, or withhold a previously learned or preferred response" (p. 484). Various tasks have been used to assess behavioral response inhibition in children, such as the Draw-a­ Line Slowly Test and the Reel-up-Slowly Test, both of which require motoric control. Response inhibition has been found to increase with age (Constantini & Hoving, 1973a), to correlate with IQ (Maccoby, Dowley, Hagen, & Degerman, 1965), to be influenced by overt and covert self­ instructions (Meichenbaum & Goodman, 1969), and to improve with training (Constantini & Hoving, 1973b). The ability to inhibit motor impulsivity may be a composite of an immediate response inhibition function and a more sustained inhibition or attention function that occurs over protracted delay periods. For example, Masters and Binger (1978) distinguished between interruption of an ongoing activity and maintenance of action suppression (such as in a delay of gratification paradigm), and found developmental improvements in both processes. Similarly, Olson (1989) has proposed that "by the onset of the early school-age period, two different subtypes of impUlsivity may exist: a 'cognitive' dimension indexing ability to inhibit overt be­ haviors in highly structured task situations and a 'delay' dimension indexing compliance with social expectations for 'correct' behavior" (p. 182). Logan and his colleagues have looked more closely at the immediate inhibition of motor behaviors (Logan & Cowan, 1984; Schachar & Logan, 1990). They proposed that young children's poor inhibitory control may be caused by inefficient response inhibition, which is demonstrated by "impulsive behaviors such as responding before the task is understood, answering before sufficient information is available, allowing attention to be captured by irrelevant stimuli (I.e., distractibility), or failing to correct obviously inappropriate responses" (Schachar & Logan, 1990, p. 710). To assess inhibitory control, Logan developed the stop-signal test, per­ formance on which is independent of IQ, metacognition, and motivation (Logan, Cowan, & Davis, 1984; Logan & Cowan, 1984). The stop-signal paradigm consists of a primary task that engages the subject's attention, such as a forced-choice letter discrimination task. On one-quarter of the primary-task trials, an auditory signal is presented and the subject is to inhibit his or her response to the primary task when this signal is heard.

32

Katherine Kipp Harnishfeger and David F. Bjorklund

Logan and his colleagues have been primarily interested in the inhibi­ tion of action (Logan & Cowan, 1984; Logan et al., 1984). In one study, Schachar and Logan (1990) looked for developmental and individual differences in inhibition functions among normal and disabled children. Differences in inhibition between second grade children and adults were not significant, although they did find poorer inhibitory performance in hyperactive than normal children. This suggests that the mechanism of inhibitory control of a motor response may be developed by the second grade. In this section we havebriefty reviewed research demonstrating the progressive development of the inhibitory control of motor behavior. Inhibition of action begins to come under control in infancy and becomes more and more refined through the early childhood years. Although the inhibitory function of simple actions may be mature by age 7 years, variations in task and response requirements continue to tax inhibitory processes throughout childhood.

Inhibition of External Distractors One of the most important cognitive functions of inhibition is its role in selective attention. At any given moment, we are capable of receiving an almost infinite array of stimuli. In order to function effectively, we need to be able to select from that array the critical stimulus and ignore the other irrelevant, distracting stimuli. Our ability to do this is a central cognitive skill and, as such, has been the focus of a large body of research (see reviews by Davies, Jones, & Taylor, 1984, and Lane & Pearson, 1982). Several investigators have demonstrated that inhibitory processes operate in selective attention performance (e.g., Neill, 1977; Tipper, 1985; Tipper & Cranston, 1985). For example, Tipper has demonstrated a "negative priming" effect in a Stroop task. The Stroop task is a selective attention test in which the subject's task is to name the color of the ink of a series of words, which are themselves color names. The test has long been used as a measure of selective attention and interference. In Tipper's paradigm, performance in the standard Stroop condition is compared with a negative-priming condition, in which the color to be named on trial n is identical to the color word on trial n-l. The color word on trial n-1 was an irrelevant stimulus and thus should have been ignored. Tipper found that adults' performance was impaired in these conditions, compared to the standard Stroop conditions. This supports the idea that ignored stimuli (the color word on trial n-1) are actively inhibited, and so when those words subsequently become target stimuli, processing is impaired (Tipper, 1985; Tipper & Cranston, 1985).

There has been a great ( selective attention abilities ing ability has been dem(] speeded classification (Stru ing (Hagen & Hale, 1973; (Doyle, 1973), and Stroop Lane and Pearson (1982 developmental improveme of older children'S ability reaches meaning. Rather, that multiple stimuli are p target stimuli are selected stimuli are actively inhibit~ that developmental impro maintain inhibition of im and the ability to inhibit i task processing (Doyle, 1~ Another hypothesis su performance after repeal occurs as a result of habit children may be more effi. 1984; Lorch & Horn, 19 some children were given Lorch and Horn found showed less interference Furthermore, younger ch benefitted more from tl through sixth-graders). L facilitation afforded by e and practice) may contrit ments in selective attenti 1975, for similar views). Tipper, Bourque, And tributions of habituatiol changes in selective attenl interested in determininl each contributed indepel (a) children (second-grac tion than adults; (b) ne was significant for the a. was significant for both Flaugher, 1977; Hale & that habituation and inhi opmental patterns: the al

)fklund

, interested in the inhibi­ aI., 1984). In one study, )pmental and individual ill and disabled children. children and adults were lhibitory performance in s that the mechanism of developed by the second earch demonstrating the trol of motor behavior. ,I in infancy and becomes nod years. Although the mature by age 7 years, :mtinue to tax inhibitory

)f inhibition is its role in e capable of receiving an tion effectively, we need stimulus and ignore the f to do this is a central f a large body of research I, and Lane & Pearson,

1at inhibitory processes g., Neill, 1977; Tipper, ipper has demonstrated a Stroop task is a selective . name the color of the olor names. The test has ion and interference. In U'd Stroop condition is 1 which the color to be on trial n-l. The color i thus should have been ~ was impaired in these onditions. This supports 'n trial n-1) are actively y become target stimuli, ;ranston, 1985).

2. Inhibition

33

There has been a great deal of research examining the development of selective attention abilities. Generally, a developmental trend of increas­ ing ability has been demonstrated for selective attention tasks such as speeded classification (Strutt, Anderson, & Well, 1975), incidental learn­ ing (Hagen & Hale, 1973; Hagen & Stanovich, 1977), selective listening (Doyle, 1973), and Stroop tests (Comalli, Wapner, & Werner, 1962). Lane and Pearson (1982), in their review of the literature, argue that developmental improvements in selective attention are not a function of older children's ability to filter out irrelevant information before it reaches meaning. Rather, in concordance with Tipper's work, it appears that multiple stimuli are processed for meaning in parallel, and then the target stimuli are selected into a limited-capacity system as the distractor stimuli are actively inhibited (see also Duncan, 1980). Others have argued that developmental improvements are the result of improved ability to maintain inhibition of irrelevant information (Hale & Alderman, 1978) and the ability to inhibit intrusions of irrelevant information in primary­ task processing (Doyle, 1973). Another hypothesis suggests that facilitation of selective attention performance after repeated exposure to the same distracting stimuli occurs as a result of habituation to the repeated stimulus, and that older children may be more efficient in this process (Lorch, Anderson, & Well, 1984; Lorch & Horn, 1986). In a speeded classification task in which some children were given prior exposure to irrelevant, distracting stimuli, Lorch and Horn found that children given preexposure and practice showed less interference than those who did not receive preexposure. Furthermore, younger children (kindergartners through second-graders) benefitted more from the preexposure than older children (fourth­ through sixth-graders). Lorch and Horn suggested that such short-term facilitation afforded by efficient habituation (i.e., through preexposure and practice) may contribute significantly to the developmental improve­ ments in selective attention (see Jeffrey, 1968, and Wright & Vlietstra, 1975, for similar views). Tipper, Bourque, Anderson, and Brehaut (1989) examined the con­ tributions of habituation and inhibition processes to developmental changes in selective attention in a Stroop paradigm. They were specifically interested in determining whether habituation and inhibition processes each contributed independently to selective attention. They found that (a) children (second-graders) were more distracted in the Stroop condi­ tion than adults; (b) negative priming, a demonstration of inhibition, was significant for the adults, but not the children; and (c) habituation was significant for both groups, but larger for the children (cf. Hale & Flaugher, 1977; Hale & Stevenson, 1974). These results demonstrated that habituation and inhibition are dissociated and show different devel­ opmental patterns: the automatic processing of stimuli and habituation to

34

Katherine Kipp Harnishfeger and David F. Bjorklund

repeated stimuli develop rapidly and are functional by second grade, whereas the inhibitory mechanism is not firmly established until sometime later. Tipper et a1. concluded that "the greater distractability of children in certain situations may be due in part to the underutilization of this inhibitory mechanism" (p. 353). In summary, children become increasingly efficient at establishing and maintaining selective attention with age. Although processes of inhibition and habituation both contribute to efficient selective attention, develop­ mental improvements in inhibition most likely are responsible for the developmental trends seen in selective attention performance.

Inhibition of Internal Distractors In addition to the inhibition of inappropriate motor behaviors and of distracting stimuli in the environment, efficient inhibition requires the inhibition of internal distractors. This is a central concept in current theories of attention. For example, Posner and Friedrich (1986) discuss the activation and inhibition processes of a limited capacity, semantic network system. In semantic network models, knowledge is represented by an expanded body of nodes, corresponding to units of knowledge such as words or concepts. The nodes are connected by links, representing the various relationships among the concepts. Executing a cognitive task via this network occurs through the spreading activation of nodes and links. Processing within such a network requires both the excitation and inhibi­ tion of links. For the system to operate effectively, task-relevant links and nodes must be activated, while task-irrelevant links and nodes must remain unactivated. In many cases, NON-activation translates into an active process of inhibition. Some theories of attention propose that spreading activation is an automatic process that occurs upon presenta­ tion of a stimulus, whereas inhibition of activation occurs later, and may be a slower, more conscious process (Neely, 1977; Posner & Friedrich, 1986).

Lexical Ambiguity One avenue to investigating inhibitory processes that work on internal distractors is the study of lexical ambiguity. When we encounter a polysemous word such as scale, we must have some process to select the correct meaning of the word for the particular context. Current research has converged in support of an exhaustive-access model of lexical ambiguity (Onifer & Swinney, 1981; Seidenberg, Tanenhaus, Leiman, & Bienkowski, 1982; Swinney, Zurif, & Nicol, 1989). The model proposes that immediately after the presentation of a polysemous word, all meanings of the word are automatically accessed. The initial access is

followed by a decision s is selected. Finally, the a Research investigating generally supported tho courses for the automa (Simpson & Lorsbach, 1 an automatic spreading early and operate effici. years). A subsequent, 0 ing is thought to emerg· depending on the task). Swinney and Prather I lexical ambiguity proces: examine which meaning biasing sentence context the child hears the sen tel in the park). Swinneyan( all meanings of the ambi accessed the dominant n tion for the subordinate mammal) for the 4-year-o biased to prime for that m lying in the park). Swinney and Prather Sl the younger children havil the various meanings of Nicol, 1989). According t< of the younger children t( is due to a slower word-: that if processing had b syllables, the younger chi of all meanings. An in second-, fourth-, and six Foster, 1986). Simpson al offset and target onset in saw the targets 150, 300, experiment suggested th: ings of the homographs. actively attending to the by facilitation for domim associates, whereas the facilitation for both dOl 7SOmsec after prime off all meanings and had re younger children had or

j

2, Inhibition

by second grade, hed until sometime ;tability of children ~rutilization of this

at establishing and cesses of inhibition attention, develop­ 'esponsible for the rmance.

behaviors and of )ition requires the :oncept in current rich (1986) discuss capacity, semantic dge is represented of knowledge such s, representing the cognitive task via If nodes and links. :itation and inhibi­ -relevant links and and nodes must translates into an tion propose that rs upon presenta­ Irs later, and may sner & Friedrich,

work on internal we encounter a process to select :ontext. Current ~ccess model of ~rg, Tanenhaus, 989). The model )lysemous word, ! initial access is

35

followed by a decision stage, when the contextually appropriate meaning is selected. Finally, the alternative, inappropriate meanings are suppressed. Research investigating developmental differences in lexical access has generally supported the idea that there are different developmental courses for the automatic and conscious components of lexical access (Simpson & Lorsbach, 1983; West & Stanovich, 1978). The initial phase, an automatic spreading activation process, is thought to reach maturity early and operate efficiently in very young children (as early as age 4 years). A subsequent, conscious allocation phase of attentional process­ ing is thought to emerge later in development (by fifth or sixth grade, depending on the task). Swinney and Prather (1989) investigated developmental differences in lexical ambiguity processing. They used a cross-modal priming task to examine which meanings of polysemous words are activated within a biasing sentence context (e.g., which meanings of bat are activated when the child hears the sentence: The baseball player picked up the bat lying in the park). Swinney and Prather found that 5-year-old children accessed all meanings of the ambiguous words, whereas 4-year-old children only accessed the dominant meanings of the words. There was no facilita­ tion for the subordinate meanings of polysemous words (e.g., bat the mammal) for the 4-year-old children, even when the sentence context was biased to prime for that meaning (e.g., The birdwatcher picked up the bat lying in the park). Swinney and Prather suggested that these findings may be a result of the younger children having a protracted rise time for exhaustive access of the various meanings of the ambiguous words (cf. Swinney, Zurif, & Nicol, 1989). According to the protracted rise time hypothesis, the failure of the younger children to activate all meanings of the polysemous words is due to a slower word-access process. Swinney and Prather suggested that if processing had been tapped downstream, perhaps after a few syllables, the younger children may have demonstrated exhaustive access of all meanings. An investigation of lexical ambiguity processing in secondo, fourth-, and sixth-graders supports this hypothesis (Simpson & Foster, 1986). Simpson and Foster varied the time interval between prime offset and target onset in a task similar to Swinney and Prather's. Children saw the targets 150, 300, or 750 msec after the primes. Results from this experiment suggested that all the children initially accessed both mean­ ings of the homographs. However, by 750msec the older children were actively attending to the dominant meanings of the words, as evidenced by facilitation for dominant associates and by interference for subordinate associates, whereas the second- and fourth-graders continued to show facilitation for both dominant and subordinate associates. That is, by 750msec after prime offset the older children had exhaustively accessed all meanings and had restricted activation to the dominant meaning; the younger children had only reached the phase of exhaustive activation of

36

Katherine Kipp Harnishfeger and David F. Bjorklund

all meanings by that time. This experiment was interpreted as supporting the two-process theory of ambiguity processing in which initial activation is followed by inhibition of irrelevant, or subordinate, meanings. Further, the data suggested that the inhibitory aspect of this process reaches maturity at a later age than the activation aspect. Age-related dfferences in lexical processing can be accounted for by the poorer inhibitory processing of young children. The studies reviewed in this section have demonstrated that younger children are competent and efficient in an initial automatic activation stage of processing. Young children are inefficient, however, in the subsequent suppression of context-irrelevant meanings. Although it is possible that the inhibition stage of processing would occur further downstream than these investiga­ tions monitored, this possibility is unlikely, as Simpson and Lorsbach (1983) failed to find inhibition of irrelevant information in young children even after 2,OOOmsec.

Discourse Processing Hasher and Zacks (1989) have examined adult developmental trends in discourse processing and have proposed that inefficient inhibition may account for deficits in performance among the aged. In a study examining inferences made during the reading of a discourse passage, young and old adults read passages that either maintained the meaning of the passage inferred in the early sentences (expected versions) or that altered the meaning of the passage so that the initial inferences were invalidated by the end of the passage (unexpected versions) (V. Hamm, cited in Hasher & Zacks, 1989). As the adults were reading the passages, they were periodically presented with a single word that they were to judge as either consistent or inconsistent with their current understanding of the passage. Hamm found that, although older adults did maintain the correct inference at the end of both the expected and unexpected versions (as demon­ strated by their consistency ratings), they were also likely to maintain the incorrect inference at the end of the unexpected versions. That is, the older adults maintained erroneous and irrelevant information in working memory, along with the correct information, for longer periods than young adults. Hasher and Zacks interpreted these results as evidence for the reduced efficiency of inhibitory processes in the aged. Their model of discourse processing posits that when inhibition is not effective, irrelevant information will be entered into and maintained in working memory. This will result in cross-talk among competing messages and difficulties in the retrieval of relevant information, which will seriously impair the process­ ing of discourse. Several others lines of research have suggested that adults may suffer from increasingly less efficient inhibitory processes with age. For example, interference on the Stoop task has been found to increase with age (Cohn, Dustman, & Bradford, 1984; Comalli et aI., 1962). The elderly

have also been found intrusions in free reca 1987).

Memory

Recent models of mem limited mental resoufCi improvements in mem( & Schneider, 1990). I developmental improv and development of I inefficient inh~bition n block the activation efficiently during cog information becomes a poses a problem bec memory. With space bt remains for the storagf fore, task performan( inefficient. There is some evide deleterious influence 0 tions demonstrated th. was proactive interfen previously remember€ improvements in resi~ mented and may contl memory (cf., Dempst€ Another consistent I errors and intrusions children will have mOl to the memory task. recognitions and intr Townsend, and Lawtc memory for prose pa~ more intrusions of il than older children. S investigated the hypo implicit associations a errors to their own w

A Study of Inefficient

We found evidence 1 reanalysis of data fr' kindergarten, third-, .

Bjorklund

as !nterpreted as supporting Ig In which initial activation rdinate, meanings. Further, :ct of this process reaches ecl. can be accounted for by the n. The studies reviewed in ;hildren are competent and tage of processing. Young ubsequent suppression of )()ssible that the inhibition tream than these investiga­ as Simpson and Lorsbach ormation in young children

[t developmental trends in inefficient inhibition may aged. In a study examining rse passage, young and old le meaning of the passage sions) or that altered the :ences were invalidated by V. Hamm, cited in Hasher the passages, they were ley were to judge as either 'erstanding of the passage. ntain the correct inference ~ted versions (as demon­ also likely to maintain the :ed versions. That is, the It information in working for longer periods than se results as evidence for the aged. Their model of s not effective, irrelevant in working memory. This ses and difficulties in the )usly impair the processd that adults may suffer

s with age. For example,

d to increase with age

. aI., 1962). The elderly

2. Inhibition

37

have also been found to make more false-recognition errors and more intrusions in free recall (Rankin & Kausler, 1979; Stine & Wingfield, 1987).

Memory Recent models of memory have emphasized the roles of knowledge base, limited mental resources, and strategies in accounting for developmental improvements in memory performance (e.g., Bjorklund, Muir-Broaddus, & Schneider, 1990). In an extension of this model, we proposed that developmental improvements in inhibition are central to the operation and development of memory (Bjorklund & Harnishfeger, 1990). This inefficient inhibition model posits that young children are not able to block the activation of task-irrelevant information and associations efficiently during cognitive processing. Consequently, task-irrelevant information becomes activated and maintained in working memory. This poses a problem because of the limited-capacity nature of working memory. With space being consumed by off-task activations, less capacity remains for the storage and retrieval of task-relevant information. There­ fore, task performance will suffer whenever inhibition processes are inefficient. There is some evidence in the developmental literature pointing to the deleterious influence of inefficient inhibition on memory. Early investiga­ tions demonstrated that one source of problem for memory performance was proactive interference, the interruption of a current memory task by previously remembered materials (Underwood, 1957). Developmental improvements in resistance to proactive interference have been docu­ mented and may contribute generally to developmental improvements in memory (cf., Dempster, 1985, 1989). Another consistent line of evidence concerns children's false recognition errors and intrusions in memory tasks. The theory proposes that young children will have more activations of information that is not directly tied to the memory task. This information may be demonstrated by false recognitions and intrusions. In support of this, Brown, Smiley, Day, Townsend, and Lawton (1977) examined developmental improvements in memory for prose passages and found that younger children made many more intrusions of irrelevant information during memory performance than older children. Similarly, Shepard, Cohen, Gold and Orbino (1976) investigated the hypothesis that false recognition errors are promoted by implicit associations and found that children made more false recognition errors to their own word associations than to those of their peers. A Study of Inefficient Inhibition in Memory We found evidence for inefficient inhibition during a memory task in a

reanalysis of data from a cued recall experiment with nursery school, kindergarten, third-, and sixth-grade children (Bjorklund & Harnishfeger,

38

Katherine Kipp Harnishfeger and David F. Bjorklund TABLE

50

2.1. Cue and target words for cued recall experiment.

Cue type

Cue word

Target word

Category

Furniture Weapons Listen Throw Teach Like

Bed Knife Ear Ball Peach Bike

Function Acoustic

0/.

40

n

a

p P

30

r

0

p

20

r i

a t

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1990). The task involved the presentation of words to be remembered, along with a cue that was given at presentation and at recall. The targets and cues were related in one of three ways: categorically, functionally, or acoustically (see Table 2.1). At recall, children were given cues and asked to give one response to each cue. To examine children's failures to keep off-task information from interfering with the task, we measured the proportion of intrusions (Le., words recalled that were not on the list) in the child's recall. The rate of instrusions decreased with age, with the nursery school and kindergarten children making a significantly higher percentage of intrusions than the third- and sixth-graders (see Fig. 2.1).

25r-~--------------------------------------------~

20

15

10

o~------~~------~---------~--------~--------~

Nursery

Kindergarten

Third

Sixth

Grade 2.1. Percentage of intrusions in cued recall for nursery school, kindergarten, third-, and sixth-grade children.

FIGURE

10

0

Nursery

Ki

FIGURE 2.2. Percentage of inap school, kindergarten, third-, and

The inefficient inhibition h dren will have more intrusiOi intrusions will be task-irrele intrusion as task-appropriat' intrusions were defined as wo: were related to the cue in I experiment (i.e., categorical, child received the cue word ball, blow would be an apI (or any other nonword) Wl inappropriate intrusions to inappropriate) was compute variance. The analysis was s sequent Bonferroni t tests ill more inappropriate intrusion older children (see Fig. 2.2 inefficient inhibition hypoth, better able to keep irreleva reducing the number of inapJ As a further test of the ine intrusion effects in a free-rl secondo, and 32 fourth-gradl lists of 16 words that were c each word was categorical(

md

2. Inhibition 50

experiment. Target word Bed

Knife

Ear

Ball

Peach

Bike

39

%

40

n

a

p p

30

--._--._.

r 0

p r i

20

t

10

a

to be remembered, at recall. The targets :ally, functionally, or given cues and asked 'en's failures to keep ~, we measured the re not on the list) in I with age, with the , significantly higher ders (see Fig. 2.1).

-

Sixth

for nursery school,

e

0

Nursery

Kindergarten

Third

Sixth

Grade 2.2. Percentage of inappropriate intrusions in cued recall for nursery school, kindergarten, third-, and sixth-grade children.

FIGURE

The inefficient inhibition hypothesis predicts not only that young chil­ dren will have more intrusions in recall, but more specifically, that their intrusions will be task-irrelevant. To examine this, we classified each intrusion as task-appropriate or task-inappropriate. Task-appropriate intrusions were defined as words recalled that were not on the list but that were related to the cue in one of the three relationships used in the experiment (Le., categorical, functional, or acoustic). For example, if the child received the cue word throw, to which the correct target word is ball, blow would be an appropriate intrusion, whereas needle or zow (or any other nonword) would be inappropriate. The proportion of inappropriate intrusions to total number of intrusions (appropriate + inappropriate) was computed and entered into a one-way analysis of variance. The analysis was significant, F(3, 60) = 5.74, P < 0.01. Sub­ sequent Bonferroni t tests indicated that the younger children produced more inappropriate intrusions, relative to appropriate intrusions, than the older children (see Fig. 2.2). These findings were consistent with the inefficient inhibition hypothesis, suggesting that, with age, children are better able to keep irrelevant information from working memory, thus reducing the number of inappropriate responses made to a specific probe. As a further test of the inefficient inhibition hypothesis, we investigated intrusion effects in a free-recall paradigm. Thirty-two kindergarten, 32 secondo, and 32 fourth-grade children attempted immediate free-recall of lists of 16 words that were categorically and acoustically related. That is, each word was categorically related to one word in the list and was

40

Katherine Kipp Harnishfeger and David F. Bjorklund TABLE

Categorical order Eagle Parrot Red Blue Four Two Head Knees Dolly Ball Collie Beagle Peas Carrot Door Wall

12

2.2. Word list used for free recall experiment. Acoustic order

10 Eagle Beagle Red Head Four Door Knees Peas Dolly Collie Parrot Carrot Wall Ball Blue Two

%

8

n t r u

6

s i

0

4

n

s

-,-_.---­

2

0

I

Kinder

FIGURE 2.3. Percentage of fourth-grade children.

acoustically related to another list item. We manipulated the salience of the relation dimension for the children by emphasizing either the categorical or acoustic relations through word order (see Table 2.2). An analysis of the proportion of intrusions in recall indicated that intrusions decreased with age (F(2, 85) = 7.72, p < 0.001) between the kindergarten and second-grade children, with no difference in intrusion rates between second- and fourth-graders (see Fig. 2.3). The absolute levels of intrusions were lower in this experiment than in the cued-recall experiment, which is most likely due to the differences in the tasks. In this experiment, the children spontaneously produced the free-recall stream, whereas in the cued-recall experiment, the children were exposed to a probe prior to each recall attempt. This presentation of the cue may cause to reactivate the cue word and so intrusions in recall may reflect either inhibition failures during presentation (which are stored and remembered at recall), or failure to inhibit the spreading activation to the cue during recalL If inefficient inhibition affects processing at all stages, then the exposure to cues during recall would likely add this additional burden to the young children's poor inhibitory functioning. To investigate the appropriateness of the intrusions made by the children, we again classified the intrusions as appropriate or inappro­ priate. Because there were so few intrusions in the second and fourth grades, we performed the appropriateness analysis collapsing across the upper two grades, yielding an older and a younger group. This analysis again revealed a higher percentage of inappropriate intrusions in the younger children's recall (61 %) than the older children's recall (26%): F(l, 31) = 4.99, P < 0.05.

In summary, the ineft dren's failure to inhibi detrimentally impacts th we found that children n that the intrusions older those made by younger

Individual DiffereI

Although this chapter short note on individual number of different are; of inhibition in account his colleagues (1979; Jo that an inhibitory failUl ness may be responsib: disorders suffered by empirical support (e.g., Inefficient inhibition hyperactivity (deHaas, Lufi, Cohen, & Parish­ & Young, 1984) has fo deficits of sustained a

2. Inhibition

orklund 12

experiment. ~coustic

41

order

Eagle

Beagle

Red

Head

Four

Door

Knees

Peas

Dolly

Collie

Parrot

Carrot

Wall

Ball

Blue

Two

manipulated the salience emphasizing either the rder (see Table 2.2). in recall indicated that p < 0.001) between the 10 difference in intrusion Fig. 2.3). The absolute nt than in the cued-recall differences in the tasks. produced the free-recall he children were exposed :sentation of the cue may ons in recall may reflect (which are stored and )reading activation to the processing at all stages, ikely add this additional lllctioning. intrusions made by the appropriate or in appro­ I the second and fourth 'sis collapsing across the ger group. This analysis priate intrusions in the children's recall (26%):

10

%

8 n t

r

u

6

S

i

0

4

n

s

2

0

Kindergarten

Second

Fourth

Grade 2.3. Percentage of intrusions in free recall for kindergarten, secondo, and fourth-grade children.

FIGURE

r

In summary, the inefficient inhibition model proposes that young chil­ dren's failure to inhibit the activation of task-irrelevant information detrimentally impacts their cognitive task performance. In support of this, we found that children make fewer intrusions in their recall with age, and that the intrusions older children do make are more task-appropriate than those made by younger children.

Individual Differences in Inhibitory Functioning Although this chapter specifically addresses developmental function, a short note on individual differences is warranted. Research investigating a number of different areas of individual differences has implicated the role of inhibition in accounting for those differences. For example, Frith and his colleagues (1979; Joseph, Frith, & Waddington, 1979) have proposed that an inhibitory failure to limit and control the contents of conscious­ ness may be responsible for the hallucinations, delusions, and thought disorders suffered by schizophrenics. This model has received some empirical support (e.g., Bullen & Hemsley, 1987). Inefficient inhibition appears to be a central deficit in disorders of hyperactivity (deHaas, 1986; Gorenstein, Mammato, & Sandy, 1989; Luft, Cohen, & Parish-Plass, 1990). For example, deHaas (1986; deHaas & Young, 1984) has found that hyperative children suffer primarily from deficits of sustained attention and inhibition of impulsive behaviors.

42

Katherine Kipp Harnishfeger and David F. Bjorklund

Similarly, several researchers (e.g., Kelly, Best, & Kirk, 1989; Lazarus, Ludwig, & Aberson, 1984) have found that the idea of inhibitory deficits is consistent with reading and learning disabled children's difficulties with selective attention to primary aspects of tasks, difficulties with sustained attention, and inhibiting routinized responses. Thus, inhibitory deficits appear to play an important role in individual differences in cognitive function, further supporting the idea that inhibition may also contribute to age changes in children's memory and cognitive processesing in general.

Conclusion: Inefficient Inhibition and Development With age children become increasingly able to inhibit aspects of their motor behavior, attention, and thought processes. In infancy, there is a struggle between the inhibition of prepotent motor responses and infants' intentional control of their behavior (e.g., Diamond, 1988). Throughout childhood, children continue to have difficulties with the inhibition of impulsive or perseverative motor actions. Development occurs in an outward-in direction, with commands from adults directing inhibition first, followed by the child's own, overt, self-directions, and finally with the child being able to control both the inhibition and initiation of behavior covertly (e.g., Luria, 1961). Inhibition is a basic function in cognition as well. Children must be able to control their attention within a realm of unending distractions from without and within. Numerous studies have documented children's increasing abilities to ignore external dis tractors and maintain attention to the task at hand (e.g., Lane & Pearson, 1982). These studies have demonstrated that, with age, children become more efficient in the inhibition of impulsive attentional shifts as well as the maintenance of inhibitory control over longer periods of time. Furthermore, the central role of inhibition, rather than habituation or some other process, in the development of attentional maintenance has been empirically demon­ strated (e.g., Tipper et al., 1989). Finally, recent evidence is accumulat­ ing that suggests that inhibition of internal associations or activations is a process that becomes more efficient with age and that contributes significantly to cognitive function. With respect to cognition, we propose that changes in children's ability to keep inappropriate information out of working memory is a major factor influencing cognitive development (e.g., Bjorklund & Harnishfeger, 1990). Evidence from research on lexical decisions (e.g., Simpson & Foster, 1986; Swinney & Prather, 1989), discourse processing (e.g., Hasher & Zacks, 1989), and memory (reported herein) illustrates devel­ opmental differences in the suppression of task-irrelevant information­ with age, children are increasingly able to keep inappropriate information

out of working memo memory and uses some could better be used for children do not necessa various aspects of a tas information in working I limited resources to the There are a number processes. As children I with a particular doma relevant information m Harnishfeger & BjorkiUl is an increased ability t( Siegler (1988) has prol solving and word-identil strategy is that of direCl 8, or the meaning of th alternative answers ma: 3 + 5 = ? problem, pOl alternative reaches a c retrieved. If none of t fall-back strategy to s problems, phonologica experience retrieving 1 becomes higher and th lower. We further pro retrieving correct altel answer, but also stren! There is also clear changes in inhibitory I lobes as the location Diamond (1985, 1988) underlies the AB err< been found in monke task between 2 and L adult monkeys, howel much like 7- to 9-mo trials, they fail to seal search where it had I Goldman-Rakic, 198'i performance on the J synaptic density in t subsequently die) (G frontal lobe synaptic age, a period when 11

F. Bjorklund

Best, & Kirk, 1989; Lazarus, t the idea of inhibitory deficits

bled children's difficulties with sks, difficulties with sustained lseS. Thus, inhibitory deficits idual differences in cognitive nhibition may also contribute ;nitive processesing in general.

and Development Ie to inhibit aspects of their )cesses. In infancy, there is a : motor responses and infants' Diamond, 1988). Throughout :;ulties with the inhibition of Development occurs in an n adults directing inhibition If-directions, and finally with inhibition and initiation of n as well. Children must be dm of unending distractions have documented children's ors and maintain attention to 1982). These studies have :ome more efficient in the well as the maintenance of e. Furthermore, the central or some other process, in las been empirically demon­ cent evidence is accumulat­ associations or activations h age and that contributes :hanges in children's ability Irking memory is a major Bjorklund & Harnishfeger, :cisions (e.g., Simpson & iscourse processing (e.g., ::I herein) illustrates devel­ {-irrelevant information­ inappropriate information

2. Inhibition

43

out of working memory. Task-irrelevant information clogs working memory and uses some of the limited mental space (or resources) that could better be used for other aspects of task processing. Thus, with age, children do not necessarily have more mental resources to allocate to various aspects of a task, but have less competing (and inappropriate) information in working memory, permitting them to devote more of their limited resources to the task-relevant operations and information. There are a number of factors that influence changes in inhibitory processes. As children become more experienced with a specific task or with a particular domain of knowledge, they process task- or domain­ relevant information more quickly (e.g., Bjorklund, 1987; Case, 1985; Harnishfeger & Bjorklund, 1990). Accompanying the processing advantage is an increased ability to inhibit irrelevant task information. For example, Siegler (1988) has proposed a model of children's arithmetic problem­ solving and word-identification strategies. In this model, the most efficient strategy is that of direct fact retrieval (e.g., just "knowing" that 3 + 5 =: 8, or the meaning of the word dog). For any particular problem, several alternative answers may be activated in long-term memory (e.g., for the 3 + 5 == ? problem, potential alternatives may be 7, 8, and 9). When one alternative reaches a critical level of activation, that answer is directly retrieved. If none of the alternatives reach that level, children use a fall-back strategy to solve the problem (e.g., counting for arithmetic problems, phonological analysis for word identification). With repeated experience retrieving the correct answer, activation of that alternative becomes higher and the activation of the incorrect alternatives becomes lower. We further propose, following Case (1985), that experience with retrieving correct alternatives not only increases the activation of that answer, but also strengthens the inhibition of alternative responses. There is also clear evidence of a biological basis to developmental changes in inhibitory mechanisms. Numerous sources point to the frontal lobes as the location of important inhibitory processing. For example, Diamond (1985, 1988) has proposed that immaturity of the frontal lobes underlies the AS error seen in infants. Evidence in support of this has been found in monkeys, who typically solve the AB object permanence task between 2 and 4 months of age. Damage to the frontal cortex of adult monkeys, however, causes them to make the AB error, performing much like 7- to 9-month-old human infants do; on delays during the B trials, they fail to search where the object was recently hidden but rather search where it had been hidden on the immediately previous trial (see Goldman-Rakic, 1987). In monkeys, the period associated with improved performance on the AB task corresponds to the time when there is excess synaptic density in the frontal area of the brain (many of these cells subsequently die) (Goldman-Rakic, 1987). The corresponding period of frontal lobe synaptic excess in humans is between 8 months and 2 years of age, a period when major cognitive changes occur (Huttenlocher, 1979).

44

Katherine Kipp Harnishfeger and David F. Bjorklund

Other evidence of a link between frontal lobe development and inhibitory processes can be found in the timing of myelinization of the brain. The frontal cortex is the last brain area to be fully myelinized, with degree of myelinization being related to cognitive accomplishments from infancy through adolescence (Lecours, 1975; Yakovlev & Lecours, 1967). Moreover, a host of cognitive deficits have been associated with brain damage to the frontal area, with patients showing impairments in a wide range of tasks that require suppression of prepotent responses (see Dempster, this volume; Goldman-Rakic, 1987). Finally, frontal lobe dysfunction has been proposed to underlie the inhibitory deficits of hyperactive (Gorenstein et al., 1989; Chelune, Ferguson, Koon, & Dickey, 1986) and reading disabled children (Kelly et aI., 1989). We propose a general theory of development with inhibition playing a central role. With age, children become more efficient inhibitors, and this affects many aspects of their behavior and cognition. Efficient inhibition allows children to guide their motor behavior, to direct and sustain their attention in the face of distraction, and to monitor and control their own cognitive processes. Furthermore, we propose that inhibition mechanisms affect cognitive development through their interaction with limited mental resources. With age, task-irrelevant information is increasingly screened out from working memory, affording children greater functional mental resources, which translates into enhanced performance. The ontogeny of inhibition is influenced both by experience and maturationally paced factors. We believe that inhibition will be increasingly found to be a powerful explanatory mechanism for cognitive development. Acknowledgements. We thank the students and staff of Coral Sunset Elementary School and Henderson University School for their coopera­ tion in the execution of the memory experiment, and Thomas R. Coyle and Cherie Everett for help in conducting the memory experiment. We also thank Elizabeth Ashley, William S. Cassel and Wolfgang Schneider for comments on earlier drafts of this chapter. Correspondence should be sent to Katherine Kipp Harnishfeger at the Department of Psychology, University of Georgia, Athens, GA, 30602, or David F. Bjorklund at the Department of Psychology, Florida Atlantic University, Boca Raton, FL, 33431.

References Bjork, R.A. (1989). Retrieval inhibition as an adaptive mechanism in human memory. In !LL. Roediger, III, & F.LM. Craik (Eds.), Varieties of memory and consciousness. Hillsdale, Nl: Erlbaum. Bjorklund, D.F. (1987). How age changes in knowledge base contribute to the development of children's memory: An interpretive review. Developmental Review, 7,93-103.

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