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Memory for frequency of occurrence: Intelligence level and retrieval cues
INTELLIGENCE 13, 53-61 (1989)
Memory for Frequency of Occurrence" Intelligence Level and Retrieval Cues PAMELA W O O D L E Y - Z A N T H O S NORMAN R . ELLIS
University of Alabama
The purposes were (a) to assess the effects of the nature of the retrieval cue on frequency processing, (b) to determine the effects of type of stimulus on frequency processing, and (c) to test the Hasher and Zacks (1979, 1984) intelligence invariance criterion for automaticity. Mentally retarded and nonretarded persons judged frequency of occurrence of words and photographs under oral and visual retrieval cue conditions. They saw a study list of one type of stimulus presented on 35-mm slides at a 5-s rate under incidental instructions. Immediately following the study phase, they estimated frequencies (0, 1, 3, 5) under either a visual (original stimulus) retrieval cue or an oral retrieval cue condition. There were no differences between the groups on frequency estimates. There was a stimulus effect with both groups giving more accurate estimates for pictorial stimuli. The oral retrieval cue resulted in less accurate frequency estimates for the nonretarded in the word condition and for the retarded in the picture condition, but these were small effects. Results were discussed in terms of the Hasher and Zacks position on automaticity as well as the Greene (1986) and Begg, Maxwell, Mitterer, and Harris (1986) positions on the nature of frequency processing.
S i n c e the early 1970s c o g n i t i v e d e f i c i e n c i e s in p e r s o n s w i t h low IQ h a v e b e e n a t t r i b u t e d to c o n t r o l p r o c e s s i n g deficits ( e . g . , see D e t t e r m a n , 1979; Ellis, 1970). T h i s b e g s the q u e s t i o n : W h y does a d e q u a t e strategy use fail to d e v e l o p in the m e n t a l l y r e t a r d e d ? H o w e v e r c o n v e n i e n t it m a y be to say that they d o not learn to u s e s t r a t e g i e s , it is also t a u t o l o g i c a l . T o say they do not learn strategies b e c a u s e t h e y h a v e n o s t r a t e g y for l e a r n i n g to use strategies is not a c c e p t a b l e . O n e possible s o u r c e o f the d e f i c i e n c y is the role p l a y e d b y structurally b a s e d c o g n i t i v e m e c h a n i s m s in the d e v e l o p m e n t o f c o n t r o l p r o c e s s i n g . T h e c u r r e n t r e s e a r c h e m p h a s i s o n effortful a n d a u t o m a t i c p r o c e s s i n g p r o v i d e s the c o n c e p t u a l f r a m e w o r k for this study. W h i l e the t e r m s control processing a n d effor(ful processing are o f t e n u s e d i n t e r c h a n g e a b l y , a s i m i l a r t r a n s l a t i o n f r o m This research was supported by Grant HD-15558 to Norman R. Ellis from the National Institute of Child Health and Human Development. Pamela Woodley-Zanthos was a Fellow in the Mental Retardation training program sponsored by Grant HD-07262 from the National Institute of Child Health and Human Development. Special thanks to the Tuscaloosa City Board of Education and Dennis Bryant. Correspondence and requests for reprints should be sent to Pamela Woodley-Zanthos, Department of Psychology, University of Alabama, Tuscaloosa, AL 35487. 53
54
WOODLEY-ZANTHOSAND ELLIS
structural to automatic processing cannot be made. According to Hasher and Zacks (1979), automatic processes operate with or without conscious awareness and do so in spite of a person's intelligence level, age, culture, or educational background. Automatic processes may be either learned or biological; those that are biological are innate, structural, and unaffected by practice, feedback, and intention--variables known to affect effortful processes. Examples of automatically acquired information are frequency of occurrence and spatial location. The present study is one of a series (Ellis & Allison, 1988; Ellis, Katz, & Williams, 1987; Ellis, Palmer, & Reeves, 1988; Meador & Ellis, 1987) directed to understanding the nature of automatic processing in mentally retarded persons and the role such processes play in effortful control processing in these persons. Perhaps the effortful processing deficiency is simply due to reduced attentional capacity. On the other hand, inadequacies in automatic processing may require compensatory allocation of attentional resources to tasks normally processed automatically, thus ostensibly involving deficits in effortful processing only. In any case, it is unlikely that control processing deficiencies in retarded persons are independent of other, even more fundamental, aspects of cognition. Very little is known about automatic processing as it relates to cognitive handicap, and even less about the interrelation of automatic and effortful processing in cognitive handicaps. Previous studies in this series have shown that memory for spatial location (Ellis et al., 1987) and memory for frequency of occurrence (Ellis et al., 1988; Ellis & Allison, 1988) are remembered automatically and equally well by college students and mentally retarded persons. There is one exception. With respect to memory for frequency, Ellis and Allison found superior memory for the frequency of occurrence of pictures, but not words, by college students. The present study is an investigation of the Ellis and Allison finding and an attempt to identify the source of the differences. Ellis and Allison (1988) compared mildly mentally retarded subjects with college students on a frequency task in a study-test paradigm. The stimuli were words, line drawings, photographs, and semantically encoded photographs shown at frequencies of 1,2, 3, and 4. In each condition the stimuli were viewed and named by the subjects; in the semantically encoded photograph condition, subjects also told the use of each item shown. It was anticipated that the retarded subjects would make relatively better use of the more visually enriched stimuli since presumably these stimuli were the more memorable. All subjects gave more accurate frequency estimates for pictures than for words, with the best performance occurring in the semantically encoded photograph condition. In each of the pictorial conditions, the nonretarded estimated frequency significantly more accurately than the retarded, even though the differences were small. However, both groups performed equally well in the word condition. Although the more memorable pictorial stimuli provided an advantage over words for both groups, the advantage was relatively greater for the nonretarded than for the retarded. Ellis and Allison (1988) interpreted the effect for stimulus type as being
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55
consistent with the Greene (1986) and Begg, Maxwell, Mitterer, and Harris (1986) positions that more memorable stimuli are more easily retrieved and then counted. The global results of the Ellis and Allison study also provided some support for the Hasher and Zacks position that memory for frequency is invariant across intelligence levels. But, this had to be qualified since the frequency of pictorial items was not estimated as accurately by the retarded. The current study is an extension of the Ellis and Allison (1988) study. If the nonretarded make better use of more memorable stimuli than do the retarded, it may be that the advantage manifests itself in the differential use of retrieval cues. That is, if the nonretarded encode more attributes of a stimulus, then when the stimulus is re-presented in its original form at test, they have more retrieval cues than the mentally retarded and more enriched memory traces upon which to base frequency estimates. Words, which inherently have fewer memorable details, do not offer an advantage for the nonretarded. To test this hypothesis we manipulated retrieval cues and type of stimuli in a 2 (Groups) x 2 (Stimulus Type) x 2 (Retrieval Cues) design. The stimuli were words and photographs, and retrieval cues were visual or oral. Visual retrieval cues consisted of a re-presentation of the study item at test, and oral retrieval cues were the names of the items. If the nonretarded's advantage in estimating frequency of pictorial items is due to more effective retrieval cues, the oral retrieval cues should tend to equate the groups and allow for a more definitive comparison of frequency estimates between the groups.
METHOD Subjects The subjects were 80 eighth graders from a public middle school. The 40 mentally retarded persons were enrolled in special education classes and had a mean IQ of 66 (SD=6.89) and a mean age of 14.56 years (SD= 11.05 months). The 40 nonretarded attended regular classes and had a mean age of 14.37 years (SD = 10.34 months). Of the retarded subjects, there were 22 males and 18 females, 37 blacks and 3 whites. Twenty-five of the nonretarded participants were female and 15 were male; blacks and whites were equally represented. One retarded and one nonretarded subject were excluded; the retarded subject was unable to read the words, and the nonretarded was inattentive and failed to follow directions during the study phase. All subjects volunteered to participate, and parental permission was obtained prior to testing. Intelligence tests had been administered to all of the retarded subjects within 3 years prior to this study, and scores were obtained from school records. All subjects received T-shirts for participation.
Stimuli and Apparatus The two types of stimuli were AA and A rated nouns from the Thorndike and Lorge (1944) word list, and colored photographs of common objects such as a
56
WOODLEY-ZANTHOS AND ELLIS
car, a bicycle, gloves, etc. There were 80 stimuli in each condition reproduced on 35-mm slides. Twenty-four unique words or pictures were shown, 8 at each frequency of 1, 3, or 5. There were 4 buffer slides at the beginning and 4 at the end of the study list. Eight additional items were used as 0 frequency items in the test list. Items were randomly assigned to position in the study list with the restriction that an item did not occur more than once within any 5-item block. The slides were arranged in a carousel of 80 including the 8 buffer slides. They were presented on a rear projection screen of approximately 205 × 305 mm.
Procedure The 40 subjects from each group were randomly and equally assigned to either the word-oral (WO), word-visual (WV), picture-oral (PO), or picture-visual (PV) condition. Subjects were tested individually. Each slide was exposed for 5 s with a l-s interslide interval. Subjects were told to look at each item and to read the word or name the picture aloud, and that their memory for the items would be tested later. No mention of frequency was made. The test session immediately followed the study phase. Subjects in the visual conditions were shown the 24 slides they had seen in the study phase, plus 8 additional slides (0 frequency) that had not been seen previously. For the oral conditions, the experimenter either said the words or named the pictures that had been seen earlier along with those that represented a 0 frequency. Subjects in all conditions were instructed to say aloud how many times (0, 1, 3, or 5) they had seen the item in the study phase. They were told that all frequencies should be used and that if they did not know how many times they had seen an item, they should guess. At the end of the test session, all retarded subjects were given a brief counting task with either words or pictures on index cards to ensure that they were able to count accurately. All subjects were able to do this task.
RESULTS In order to assess constant error in the frequency estimates--that is, the extent to which the absolute magnitude of estimates agreed with actual frequencies--each subject's 8 estimates of each frequency were averaged, yielding a mean score for each of the four frequencies. Figure 1 presents the results of most interest. An interaction between frequency and retrieval cue, shown in Figure la, F(3,216) = 4.51, p < .01, results from more accurate performance in the visual than oral condition at the higher frequencies. The Frequency × Stimulus interaction depicted in Figure lb, F(3,216) = 13.98, p < .01, is a result of more accurate estimates for pictures than for words, again at the higher frequencies. There is also a third order interaction: IQ Group × Retrieval Cue × Stimulus Type × Frequency, F(3,216) = 3.78, p < .05. Figures lc and ld show that at the higher frequencies the retarded gave the least accurate estimates in the picture/oral
RETRIEVAL IN FREQUENCY
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ACTUALFREQUENCY F I G . 1. Absolute frequency estimates showing the effects of retrieval cue in (a), stimulus type in (b), and stimulus type and retrieval cue effects separately for mentally retarded (MR) in (c) and nonretarded (NR) in (d). (The dotted line is the actual frequency of occurrence.)
condition, while the lowest performance for the nonretarded was in the word/oral condition. There was no overall effect for groups, however, F(3,216) = 1.84. Three dependent variables were used to assess sensitivity to frequency: the regression of estimated on actual frequencies, correlation coefficients between actual and estimated frequencies, and percent correct estimates. Table 1 presents the means and standard deviations for each of these measures. The correlation coefficients were converted to Fisher Z scores and averaged. While all three measures were analyzed, they each led to similar interpretations, and only the slope analysis is described. There was a significant main effect for Stimulus Type F(1,72) = 25.97, p < .001. Both IQ groups demonstrated more sensitivity to frequency for pictures than for words. There was a trend suggesting that visual retrieval cues were better overall than oral cues, (F(1,72) = 3.47; F of 3.98 is needed for significance at .05 level). An IQ Groups × Stimulus Type x Retrieval Cue interaction also approached significance, F(1,72) = 3.90. In view of this marginal F value, separate analyses for each of the IQ groups were completed, and they yielded a significant effect for stimulus type for both groups, F (1,36) = 6.79, p < .05 for the retarded, F(1,36) = 20.90, p < .01 for the nonretarded). Further analyses showed that oral retrieval cues handicapped the
58
WOODLEY-ZANTHOS AND ELLIS TABLE 1
Means and Standard Deviations for the Three Measures of Sensitivity
Group
Measure
Picture Oral
Picture Visual
Word Oral
Word Visual
Slope MR
M SD
.79 .12
.88 .08
.74 .14
.73 .11
NR
M SD
.87 .06
.87 .08
.64 .13
.75 .18
Pearson correlation coefficients transformed to Fisher Z scores MR
M SD
1.46 0.40
1.79 0.60
1.16 0.33
1.12 0.23
NR
M SD
1.70 0.22
1.55 0.29
1.08 0.28
1.34 0.56
% correct MR
M SD
79.36 11.46
82.20 9.79
66.90 11.44
68.44 8.78
NR
M SD
86.25 5.55
82.82 6.13
65.03 12.22
68.76 13.00
MR = mentally retarded. NR = Nonretarded.
retarded persons in the picture condition only and the nonretarded in the word condition only. Though significant, these effects are small and their meaning is equivocal. Frequency estimates were curvilinear for all conditions with a consistent underestimation of the highest frequency, which is to be expected in data such as these. Both groups were more sensitive to frequency for pictures than for words. This is in agreement with Ghatala, Levin, and Wilder (1973), who found more accurate frequency judgments for pictures than words in sixth graders, and with Ellis and Allison (1988), who demonstrated a superiority for pictures over words in a similar frequency task. The IQ groups did not differ significantly in their sensitivity to frequency in any of the conditions. This is consistent with the Hasher and Zacks (1979, 1984) intelligence invariance criterion. It is atso generally supportive of the earlier Ellis and Allison (1988) and Ellis et al. (1988) studies. Ellis and Allison found no intelligence-related differences in the processing of words and only small (but significant) differences for pictures. The Ellis et al. (1988) study found retardednonretarded differences in the accuracy of frequency estimates of words and pictures in an online frequency task. However, as shown by Hockley (1984), in
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59
an online-type frequency task subjects will use strategies in estimating frequency. When Ellis et al. (1988) used a study-test paradigm in order to minimize strategy use, these intelligence-related differences disappeared. There were several differences between the current study and the Ellis and Allison (1988) study. In the present study fewer stimuli were used: 80 as opposed to 150 in the earlier study. It may be that the larger number of stimuli engendered boredom and/or fatigue in the retarded persons, which attenuated their attention to the stimuli in the pictorial conditions as the study phaseprogressed. This may not have occurred in the word condition since, with their weaker reading skills, the retarded, of necessity, may have attended more closely to the words in order to read them. The skilled reader, on the other hand, would have read the words more automatically. This may have resulted in more in-depth encoding of words by the mentally retarded persons. In the current study, with fewer stimuli, attention to the stimuli may have been equated between the groups. Such an interpretation seems inconsistent with the Hasher and Zacks position, which maintains that "minimal attention" to a stimulus is all that is required for an automatic process to work optimally. However, considerable evidence is accruing for a depth of encoding/automatic processing relationship (e.g., see Greene, 1986; Jonides & Naveh-Benjamin, 1987; Rose & Rowe, 1976); that is, instructions that ensure more semantic processing lead to more accurate frequency estimates. Greene interprets this relationship in terms of the memorability of the stimulus; the more memorable stimuli are more deeply encoded and thus more easily retrieved and counted. The current study used less extreme groups for comparison than did the Ellis and Allison (1988) study. Nonretarded age-mates from the same school population as the retarded were used as the comparison group rather than college students. It cannot be assumed that the mean intelligence level of the nonretarded in the present study was equal to that of the college students. But, according to Hasher and Zacks (1979), this should not have affected frequency encoding. In the present study the interaction of IQ Groups x Stimulus Type x Retrieval Cue is interesting. Nonretarded subjects were handicapped by the oral retrieval cue in the word condition, while retarded subjects showed a similar oral retrieval cue disadvantage in the picture condition. Though there was a tendency for the retarded to use more idiosyncratic labels for the pictures (e.g., " r a c k " for coat hanger) and the nonretarded to use more elaboration (e.g., "green Chevrolet" for car), any interpretations drawn from this would be mere conjecture. It may be, for example, that the oral retrieval cues did not serve to equate retrieval differences as effectively as was intended. Differences may also stem from differences in the nature of the academic day for the two groups. A heavy concentration on learning to read is still a daily factor in the lives of special education students. They may be more attentive to oral questions about isolated words than are the nonretarded. In addition, they may be less able to form images when memory for pictures is cued by words than are the nonretarded (Lebrato &
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WOODLEY-ZANTHOS AND ELLIS
Ellis, 1974). These effects are small and should not obscure the fact that the retarded persons were no less sensitive to frequency than nonretarded persons. Mildly retarded persons estimate frequency for both words and pictures as well as do the nonretarded. This agrees with the Hasher and Zacks (1979) intelligence invariance criterion for an automatic process. Frequency judgments for pictures are more accurate than for words, which is consistent with the Begg et al. (1986) and Greene (1986) positions that more memorable stimuli are more easily retrieved and then counted, as opposed to the notion that a frequency attribute is encoded along with other stimulus at-tributes. On the other hand, a more memorable trace might facilitate encoding of frequency; that is, when the stimulus is presented more than once, the subsequent encodings might be improved when the original trace is strong. Oral retrieval cues differentially affected retarded and nonretarded persons depending upon the type of stimuli being cued, but the effect was small. We suspect this derives from the different experiences of these persons. Finally, since retarded persons process frequency information as well as nonretarded persons, this cannot be a source for the retarded persons' deficiencies in effortful processing. In laboratory studies comparing cognitive processes in retarded and nonretarded persons, the retarded invariably prove to be less adequate. If this is not the case, usually the methodology proves to be inadequate or the behavior studied is trivial. That is not the case here. Remembering frequency of occurrence is an important aspect of adaptive behavior (e.g., see Hasher and Zacks, 1984, for a discussion of adaptive aspects of frequency processing), and the methodology seems unflawed. It is refreshing to find that seriously mentally handicapped persons are normal in some important aspects of information processing.
REFERENCES Begg, I., Maxwell, D., Mitterer, J.O., & Harris, G. (1986). Estimate of frequency: Attribute or attribution? Journal of Experimental Psychology: Learning, Memory, and Cognition. 12, 496-508. Detterman, D.K. (1979). Memory in the mentally retarded. In N.R. Ellis (Ed.), Handbook of mental deficiency: Psychological theory and research (2nd ed., pp. 727-760). Hillsdale, NJ: Erlbaum. Ellis, N.R. (1970). Memory processes in retardates and normals. In N.R. Ellis (Ed.), lnternatioaal review of research in mental retardation (Vol. 4) (pp. 1-32). New York: Academic. Ellis, N.R., & Allison, P. (1988). Memory for frequency of occurrence in retarded and nonretarded persons. Intelligence, 12, 61-75. Ellis, N.R., Katz, E., & Williams, J. (1987). Developmental aspects of memory for spatial location. Journal of Experimental Child Psychology, 44, 401-412. Ellis, N.R., Palmer, R.L., & Reeves, C.L. (1988). Developmental and intellectual differences in frequency processing. Developmental Psychology, 24, 38-45. Ghatala, E.S., Levin, J.R., & Wilder, L. (1973). Apparent frequency of words and pictures as a function of pronunciation and imagery. Journal of Verbal Learning and Verbal Behavior, 12, 85-90.
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Greene, R.L. (1986). Effects of intentionality and strategy on memory for frequency. Journal of Experimental Psychology: Learning, Memory and Cognition, 12, 489-495. Hasher, L., & Zacks, R.T. (1979). Automatic and effortful processes in memory. Journal of Experimental Psychology: General, 108, 356-388. Hasher, L., & Zacks, R.T. (1984). Automatic processing of fundamental information. American Psychologist, 39, 1372-1388. Hockley, W.E. (1984). Retrieval of item frequency information in a continuous memory task. Memory and Cognition, 12, 229-242. Jonides, J., & Naveh-Benjamin, M. (1987). Estimating frequency of occurrence. Journal of Experimental Psychology: Learning, Memory, and Cognition, 13, 230-240. Lebrato, M., & Ellis, N.R. (1974). Imagery mediation in paired-associate learning by retarded and normal subjects. American Journal of Mental Deficiency, 78, 704-713. Meador, D., & Ellis, N.R. (1987). Automatic and effortful processing in mentally retarded and nonretarded persons. American Journal of Mental Deficiency, 91, 613-619. Rose, R.J., & Rowe, E.J. (1976). Effects of orienting tasks and spacing of repetitions on frequency judgments. Journal of Experimental Psychology: Human Learning and Memory, 2, 142-152. Thorndike, E.L., & Lorge, I. (1944)~ The teacher's word book of 30,000 words. New York: Columbia University, Teacher's College, Bureau of Publications.
Memory for Frequency of Occurrence" Intelligence Level and Retrieval Cues PAMELA W O O D L E Y - Z A N T H O S NORMAN R . ELLIS
University of Alabama
The purposes were (a) to assess the effects of the nature of the retrieval cue on frequency processing, (b) to determine the effects of type of stimulus on frequency processing, and (c) to test the Hasher and Zacks (1979, 1984) intelligence invariance criterion for automaticity. Mentally retarded and nonretarded persons judged frequency of occurrence of words and photographs under oral and visual retrieval cue conditions. They saw a study list of one type of stimulus presented on 35-mm slides at a 5-s rate under incidental instructions. Immediately following the study phase, they estimated frequencies (0, 1, 3, 5) under either a visual (original stimulus) retrieval cue or an oral retrieval cue condition. There were no differences between the groups on frequency estimates. There was a stimulus effect with both groups giving more accurate estimates for pictorial stimuli. The oral retrieval cue resulted in less accurate frequency estimates for the nonretarded in the word condition and for the retarded in the picture condition, but these were small effects. Results were discussed in terms of the Hasher and Zacks position on automaticity as well as the Greene (1986) and Begg, Maxwell, Mitterer, and Harris (1986) positions on the nature of frequency processing.
S i n c e the early 1970s c o g n i t i v e d e f i c i e n c i e s in p e r s o n s w i t h low IQ h a v e b e e n a t t r i b u t e d to c o n t r o l p r o c e s s i n g deficits ( e . g . , see D e t t e r m a n , 1979; Ellis, 1970). T h i s b e g s the q u e s t i o n : W h y does a d e q u a t e strategy use fail to d e v e l o p in the m e n t a l l y r e t a r d e d ? H o w e v e r c o n v e n i e n t it m a y be to say that they d o not learn to u s e s t r a t e g i e s , it is also t a u t o l o g i c a l . T o say they do not learn strategies b e c a u s e t h e y h a v e n o s t r a t e g y for l e a r n i n g to use strategies is not a c c e p t a b l e . O n e possible s o u r c e o f the d e f i c i e n c y is the role p l a y e d b y structurally b a s e d c o g n i t i v e m e c h a n i s m s in the d e v e l o p m e n t o f c o n t r o l p r o c e s s i n g . T h e c u r r e n t r e s e a r c h e m p h a s i s o n effortful a n d a u t o m a t i c p r o c e s s i n g p r o v i d e s the c o n c e p t u a l f r a m e w o r k for this study. W h i l e the t e r m s control processing a n d effor(ful processing are o f t e n u s e d i n t e r c h a n g e a b l y , a s i m i l a r t r a n s l a t i o n f r o m This research was supported by Grant HD-15558 to Norman R. Ellis from the National Institute of Child Health and Human Development. Pamela Woodley-Zanthos was a Fellow in the Mental Retardation training program sponsored by Grant HD-07262 from the National Institute of Child Health and Human Development. Special thanks to the Tuscaloosa City Board of Education and Dennis Bryant. Correspondence and requests for reprints should be sent to Pamela Woodley-Zanthos, Department of Psychology, University of Alabama, Tuscaloosa, AL 35487. 53
54
WOODLEY-ZANTHOSAND ELLIS
structural to automatic processing cannot be made. According to Hasher and Zacks (1979), automatic processes operate with or without conscious awareness and do so in spite of a person's intelligence level, age, culture, or educational background. Automatic processes may be either learned or biological; those that are biological are innate, structural, and unaffected by practice, feedback, and intention--variables known to affect effortful processes. Examples of automatically acquired information are frequency of occurrence and spatial location. The present study is one of a series (Ellis & Allison, 1988; Ellis, Katz, & Williams, 1987; Ellis, Palmer, & Reeves, 1988; Meador & Ellis, 1987) directed to understanding the nature of automatic processing in mentally retarded persons and the role such processes play in effortful control processing in these persons. Perhaps the effortful processing deficiency is simply due to reduced attentional capacity. On the other hand, inadequacies in automatic processing may require compensatory allocation of attentional resources to tasks normally processed automatically, thus ostensibly involving deficits in effortful processing only. In any case, it is unlikely that control processing deficiencies in retarded persons are independent of other, even more fundamental, aspects of cognition. Very little is known about automatic processing as it relates to cognitive handicap, and even less about the interrelation of automatic and effortful processing in cognitive handicaps. Previous studies in this series have shown that memory for spatial location (Ellis et al., 1987) and memory for frequency of occurrence (Ellis et al., 1988; Ellis & Allison, 1988) are remembered automatically and equally well by college students and mentally retarded persons. There is one exception. With respect to memory for frequency, Ellis and Allison found superior memory for the frequency of occurrence of pictures, but not words, by college students. The present study is an investigation of the Ellis and Allison finding and an attempt to identify the source of the differences. Ellis and Allison (1988) compared mildly mentally retarded subjects with college students on a frequency task in a study-test paradigm. The stimuli were words, line drawings, photographs, and semantically encoded photographs shown at frequencies of 1,2, 3, and 4. In each condition the stimuli were viewed and named by the subjects; in the semantically encoded photograph condition, subjects also told the use of each item shown. It was anticipated that the retarded subjects would make relatively better use of the more visually enriched stimuli since presumably these stimuli were the more memorable. All subjects gave more accurate frequency estimates for pictures than for words, with the best performance occurring in the semantically encoded photograph condition. In each of the pictorial conditions, the nonretarded estimated frequency significantly more accurately than the retarded, even though the differences were small. However, both groups performed equally well in the word condition. Although the more memorable pictorial stimuli provided an advantage over words for both groups, the advantage was relatively greater for the nonretarded than for the retarded. Ellis and Allison (1988) interpreted the effect for stimulus type as being
RETRIEVAL IN FREQUENCY
55
consistent with the Greene (1986) and Begg, Maxwell, Mitterer, and Harris (1986) positions that more memorable stimuli are more easily retrieved and then counted. The global results of the Ellis and Allison study also provided some support for the Hasher and Zacks position that memory for frequency is invariant across intelligence levels. But, this had to be qualified since the frequency of pictorial items was not estimated as accurately by the retarded. The current study is an extension of the Ellis and Allison (1988) study. If the nonretarded make better use of more memorable stimuli than do the retarded, it may be that the advantage manifests itself in the differential use of retrieval cues. That is, if the nonretarded encode more attributes of a stimulus, then when the stimulus is re-presented in its original form at test, they have more retrieval cues than the mentally retarded and more enriched memory traces upon which to base frequency estimates. Words, which inherently have fewer memorable details, do not offer an advantage for the nonretarded. To test this hypothesis we manipulated retrieval cues and type of stimuli in a 2 (Groups) x 2 (Stimulus Type) x 2 (Retrieval Cues) design. The stimuli were words and photographs, and retrieval cues were visual or oral. Visual retrieval cues consisted of a re-presentation of the study item at test, and oral retrieval cues were the names of the items. If the nonretarded's advantage in estimating frequency of pictorial items is due to more effective retrieval cues, the oral retrieval cues should tend to equate the groups and allow for a more definitive comparison of frequency estimates between the groups.
METHOD Subjects The subjects were 80 eighth graders from a public middle school. The 40 mentally retarded persons were enrolled in special education classes and had a mean IQ of 66 (SD=6.89) and a mean age of 14.56 years (SD= 11.05 months). The 40 nonretarded attended regular classes and had a mean age of 14.37 years (SD = 10.34 months). Of the retarded subjects, there were 22 males and 18 females, 37 blacks and 3 whites. Twenty-five of the nonretarded participants were female and 15 were male; blacks and whites were equally represented. One retarded and one nonretarded subject were excluded; the retarded subject was unable to read the words, and the nonretarded was inattentive and failed to follow directions during the study phase. All subjects volunteered to participate, and parental permission was obtained prior to testing. Intelligence tests had been administered to all of the retarded subjects within 3 years prior to this study, and scores were obtained from school records. All subjects received T-shirts for participation.
Stimuli and Apparatus The two types of stimuli were AA and A rated nouns from the Thorndike and Lorge (1944) word list, and colored photographs of common objects such as a
56
WOODLEY-ZANTHOS AND ELLIS
car, a bicycle, gloves, etc. There were 80 stimuli in each condition reproduced on 35-mm slides. Twenty-four unique words or pictures were shown, 8 at each frequency of 1, 3, or 5. There were 4 buffer slides at the beginning and 4 at the end of the study list. Eight additional items were used as 0 frequency items in the test list. Items were randomly assigned to position in the study list with the restriction that an item did not occur more than once within any 5-item block. The slides were arranged in a carousel of 80 including the 8 buffer slides. They were presented on a rear projection screen of approximately 205 × 305 mm.
Procedure The 40 subjects from each group were randomly and equally assigned to either the word-oral (WO), word-visual (WV), picture-oral (PO), or picture-visual (PV) condition. Subjects were tested individually. Each slide was exposed for 5 s with a l-s interslide interval. Subjects were told to look at each item and to read the word or name the picture aloud, and that their memory for the items would be tested later. No mention of frequency was made. The test session immediately followed the study phase. Subjects in the visual conditions were shown the 24 slides they had seen in the study phase, plus 8 additional slides (0 frequency) that had not been seen previously. For the oral conditions, the experimenter either said the words or named the pictures that had been seen earlier along with those that represented a 0 frequency. Subjects in all conditions were instructed to say aloud how many times (0, 1, 3, or 5) they had seen the item in the study phase. They were told that all frequencies should be used and that if they did not know how many times they had seen an item, they should guess. At the end of the test session, all retarded subjects were given a brief counting task with either words or pictures on index cards to ensure that they were able to count accurately. All subjects were able to do this task.
RESULTS In order to assess constant error in the frequency estimates--that is, the extent to which the absolute magnitude of estimates agreed with actual frequencies--each subject's 8 estimates of each frequency were averaged, yielding a mean score for each of the four frequencies. Figure 1 presents the results of most interest. An interaction between frequency and retrieval cue, shown in Figure la, F(3,216) = 4.51, p < .01, results from more accurate performance in the visual than oral condition at the higher frequencies. The Frequency × Stimulus interaction depicted in Figure lb, F(3,216) = 13.98, p < .01, is a result of more accurate estimates for pictures than for words, again at the higher frequencies. There is also a third order interaction: IQ Group × Retrieval Cue × Stimulus Type × Frequency, F(3,216) = 3.78, p < .05. Figures lc and ld show that at the higher frequencies the retarded gave the least accurate estimates in the picture/oral
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ACTUALFREQUENCY F I G . 1. Absolute frequency estimates showing the effects of retrieval cue in (a), stimulus type in (b), and stimulus type and retrieval cue effects separately for mentally retarded (MR) in (c) and nonretarded (NR) in (d). (The dotted line is the actual frequency of occurrence.)
condition, while the lowest performance for the nonretarded was in the word/oral condition. There was no overall effect for groups, however, F(3,216) = 1.84. Three dependent variables were used to assess sensitivity to frequency: the regression of estimated on actual frequencies, correlation coefficients between actual and estimated frequencies, and percent correct estimates. Table 1 presents the means and standard deviations for each of these measures. The correlation coefficients were converted to Fisher Z scores and averaged. While all three measures were analyzed, they each led to similar interpretations, and only the slope analysis is described. There was a significant main effect for Stimulus Type F(1,72) = 25.97, p < .001. Both IQ groups demonstrated more sensitivity to frequency for pictures than for words. There was a trend suggesting that visual retrieval cues were better overall than oral cues, (F(1,72) = 3.47; F of 3.98 is needed for significance at .05 level). An IQ Groups × Stimulus Type x Retrieval Cue interaction also approached significance, F(1,72) = 3.90. In view of this marginal F value, separate analyses for each of the IQ groups were completed, and they yielded a significant effect for stimulus type for both groups, F (1,36) = 6.79, p < .05 for the retarded, F(1,36) = 20.90, p < .01 for the nonretarded). Further analyses showed that oral retrieval cues handicapped the
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WOODLEY-ZANTHOS AND ELLIS TABLE 1
Means and Standard Deviations for the Three Measures of Sensitivity
Group
Measure
Picture Oral
Picture Visual
Word Oral
Word Visual
Slope MR
M SD
.79 .12
.88 .08
.74 .14
.73 .11
NR
M SD
.87 .06
.87 .08
.64 .13
.75 .18
Pearson correlation coefficients transformed to Fisher Z scores MR
M SD
1.46 0.40
1.79 0.60
1.16 0.33
1.12 0.23
NR
M SD
1.70 0.22
1.55 0.29
1.08 0.28
1.34 0.56
% correct MR
M SD
79.36 11.46
82.20 9.79
66.90 11.44
68.44 8.78
NR
M SD
86.25 5.55
82.82 6.13
65.03 12.22
68.76 13.00
MR = mentally retarded. NR = Nonretarded.
retarded persons in the picture condition only and the nonretarded in the word condition only. Though significant, these effects are small and their meaning is equivocal. Frequency estimates were curvilinear for all conditions with a consistent underestimation of the highest frequency, which is to be expected in data such as these. Both groups were more sensitive to frequency for pictures than for words. This is in agreement with Ghatala, Levin, and Wilder (1973), who found more accurate frequency judgments for pictures than words in sixth graders, and with Ellis and Allison (1988), who demonstrated a superiority for pictures over words in a similar frequency task. The IQ groups did not differ significantly in their sensitivity to frequency in any of the conditions. This is consistent with the Hasher and Zacks (1979, 1984) intelligence invariance criterion. It is atso generally supportive of the earlier Ellis and Allison (1988) and Ellis et al. (1988) studies. Ellis and Allison found no intelligence-related differences in the processing of words and only small (but significant) differences for pictures. The Ellis et al. (1988) study found retardednonretarded differences in the accuracy of frequency estimates of words and pictures in an online frequency task. However, as shown by Hockley (1984), in
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an online-type frequency task subjects will use strategies in estimating frequency. When Ellis et al. (1988) used a study-test paradigm in order to minimize strategy use, these intelligence-related differences disappeared. There were several differences between the current study and the Ellis and Allison (1988) study. In the present study fewer stimuli were used: 80 as opposed to 150 in the earlier study. It may be that the larger number of stimuli engendered boredom and/or fatigue in the retarded persons, which attenuated their attention to the stimuli in the pictorial conditions as the study phaseprogressed. This may not have occurred in the word condition since, with their weaker reading skills, the retarded, of necessity, may have attended more closely to the words in order to read them. The skilled reader, on the other hand, would have read the words more automatically. This may have resulted in more in-depth encoding of words by the mentally retarded persons. In the current study, with fewer stimuli, attention to the stimuli may have been equated between the groups. Such an interpretation seems inconsistent with the Hasher and Zacks position, which maintains that "minimal attention" to a stimulus is all that is required for an automatic process to work optimally. However, considerable evidence is accruing for a depth of encoding/automatic processing relationship (e.g., see Greene, 1986; Jonides & Naveh-Benjamin, 1987; Rose & Rowe, 1976); that is, instructions that ensure more semantic processing lead to more accurate frequency estimates. Greene interprets this relationship in terms of the memorability of the stimulus; the more memorable stimuli are more deeply encoded and thus more easily retrieved and counted. The current study used less extreme groups for comparison than did the Ellis and Allison (1988) study. Nonretarded age-mates from the same school population as the retarded were used as the comparison group rather than college students. It cannot be assumed that the mean intelligence level of the nonretarded in the present study was equal to that of the college students. But, according to Hasher and Zacks (1979), this should not have affected frequency encoding. In the present study the interaction of IQ Groups x Stimulus Type x Retrieval Cue is interesting. Nonretarded subjects were handicapped by the oral retrieval cue in the word condition, while retarded subjects showed a similar oral retrieval cue disadvantage in the picture condition. Though there was a tendency for the retarded to use more idiosyncratic labels for the pictures (e.g., " r a c k " for coat hanger) and the nonretarded to use more elaboration (e.g., "green Chevrolet" for car), any interpretations drawn from this would be mere conjecture. It may be, for example, that the oral retrieval cues did not serve to equate retrieval differences as effectively as was intended. Differences may also stem from differences in the nature of the academic day for the two groups. A heavy concentration on learning to read is still a daily factor in the lives of special education students. They may be more attentive to oral questions about isolated words than are the nonretarded. In addition, they may be less able to form images when memory for pictures is cued by words than are the nonretarded (Lebrato &
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WOODLEY-ZANTHOS AND ELLIS
Ellis, 1974). These effects are small and should not obscure the fact that the retarded persons were no less sensitive to frequency than nonretarded persons. Mildly retarded persons estimate frequency for both words and pictures as well as do the nonretarded. This agrees with the Hasher and Zacks (1979) intelligence invariance criterion for an automatic process. Frequency judgments for pictures are more accurate than for words, which is consistent with the Begg et al. (1986) and Greene (1986) positions that more memorable stimuli are more easily retrieved and then counted, as opposed to the notion that a frequency attribute is encoded along with other stimulus at-tributes. On the other hand, a more memorable trace might facilitate encoding of frequency; that is, when the stimulus is presented more than once, the subsequent encodings might be improved when the original trace is strong. Oral retrieval cues differentially affected retarded and nonretarded persons depending upon the type of stimuli being cued, but the effect was small. We suspect this derives from the different experiences of these persons. Finally, since retarded persons process frequency information as well as nonretarded persons, this cannot be a source for the retarded persons' deficiencies in effortful processing. In laboratory studies comparing cognitive processes in retarded and nonretarded persons, the retarded invariably prove to be less adequate. If this is not the case, usually the methodology proves to be inadequate or the behavior studied is trivial. That is not the case here. Remembering frequency of occurrence is an important aspect of adaptive behavior (e.g., see Hasher and Zacks, 1984, for a discussion of adaptive aspects of frequency processing), and the methodology seems unflawed. It is refreshing to find that seriously mentally handicapped persons are normal in some important aspects of information processing.
REFERENCES Begg, I., Maxwell, D., Mitterer, J.O., & Harris, G. (1986). Estimate of frequency: Attribute or attribution? Journal of Experimental Psychology: Learning, Memory, and Cognition. 12, 496-508. Detterman, D.K. (1979). Memory in the mentally retarded. In N.R. Ellis (Ed.), Handbook of mental deficiency: Psychological theory and research (2nd ed., pp. 727-760). Hillsdale, NJ: Erlbaum. Ellis, N.R. (1970). Memory processes in retardates and normals. In N.R. Ellis (Ed.), lnternatioaal review of research in mental retardation (Vol. 4) (pp. 1-32). New York: Academic. Ellis, N.R., & Allison, P. (1988). Memory for frequency of occurrence in retarded and nonretarded persons. Intelligence, 12, 61-75. Ellis, N.R., Katz, E., & Williams, J. (1987). Developmental aspects of memory for spatial location. Journal of Experimental Child Psychology, 44, 401-412. Ellis, N.R., Palmer, R.L., & Reeves, C.L. (1988). Developmental and intellectual differences in frequency processing. Developmental Psychology, 24, 38-45. Ghatala, E.S., Levin, J.R., & Wilder, L. (1973). Apparent frequency of words and pictures as a function of pronunciation and imagery. Journal of Verbal Learning and Verbal Behavior, 12, 85-90.
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Greene, R.L. (1986). Effects of intentionality and strategy on memory for frequency. Journal of Experimental Psychology: Learning, Memory and Cognition, 12, 489-495. Hasher, L., & Zacks, R.T. (1979). Automatic and effortful processes in memory. Journal of Experimental Psychology: General, 108, 356-388. Hasher, L., & Zacks, R.T. (1984). Automatic processing of fundamental information. American Psychologist, 39, 1372-1388. Hockley, W.E. (1984). Retrieval of item frequency information in a continuous memory task. Memory and Cognition, 12, 229-242. Jonides, J., & Naveh-Benjamin, M. (1987). Estimating frequency of occurrence. Journal of Experimental Psychology: Learning, Memory, and Cognition, 13, 230-240. Lebrato, M., & Ellis, N.R. (1974). Imagery mediation in paired-associate learning by retarded and normal subjects. American Journal of Mental Deficiency, 78, 704-713. Meador, D., & Ellis, N.R. (1987). Automatic and effortful processing in mentally retarded and nonretarded persons. American Journal of Mental Deficiency, 91, 613-619. Rose, R.J., & Rowe, E.J. (1976). Effects of orienting tasks and spacing of repetitions on frequency judgments. Journal of Experimental Psychology: Human Learning and Memory, 2, 142-152. Thorndike, E.L., & Lorge, I. (1944)~ The teacher's word book of 30,000 words. New York: Columbia University, Teacher's College, Bureau of Publications.