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Levels of processing and memory in mentally retarded and nonretarded persons
INTELLIGENCE 10, 1-8 (1986)
Levels of Processing and Memory in Mentally Retarded and Nonretarded Persons* BRUCE
D. BOYD AND NORMAN
R. ELLIS
The University of Alabama
Individual differences in memory were examined from the levels of processing perspective. Mentally retarded persons were expected to be more superficial processors. The recall of nonretarded and two IQ levels of retarded young adults was compared following the presentation of pictorial stimuli with either a shallow processing, deep processing, or control orienting task. Shallow processing was induced by directing subjects to name the colors of the pictures. In the deep processing condition, subjects were told to say what the pictured object was used for. In the control condition, they were directed to look at the pictures. The stimuli were presented as an incidental learning task. Encoding condition was a between-subjects variable. Nonretarded subjects remembered more overall than did the two retarded groups, which did not differ. At each intelligence level, more stimuli were remembered in the deep processing condition than in the shallow condition. There was no interaction of intelligence level with encoding condition. The hypothesis that retarded persons process at a more superficial level was not supported. A "spread of encoding" deficit in retarded persons is favored to explain the recall differences obtained in this experiment.
The levels of processing (LOP) approach to the study of memory (Craik & Lockhart, 1972; Jacoby & Craik, 1979; Lockhart, Craik, & Jacoby, 1976) may provide an explanation for individual differences in memory performance. The LOP model asserts that memorability is dependent upon the level at which a tobe-remembered stimulus is processed. Processing at a superficial level only would lead to a less memorable trace. Persons of low intelligence, such as the mentally retarded, perform less well on many memory tasks (Detterman, 1979) probably as a result of processing more superficially than the nonretarded. If deeper processing relies on an associative network, it follows that an impoverished associative network hinders deeper processing. A person cannot
*This research was supported by Grant HD 15558 from the National Institute of Child Health and Human Development, Public Health Service. Also, the first author was a predoctoral trainee supported by Grant HD 07262 from NICHD during the course of this research. A doctoral dissertation, by the first author, submitted to the University of Alabama, is based on data reported in this paper. A version of this paper was presented at the Gatlinburg Conference, March 1984. Correspondence and requests for reprints should be sent to Bruce D. Boyd, Fairview Training Center, 2250 Strong Road S.E., Salem, OR 97310.
2
BOYD AND ELLIS
encode a stimulus in terms of attributes with which he or she is not familiar. Further, if a stimulus is not richly encoded, it is unlikely to add to the network of information in memory. Thus, a deficiency perpetuates itself. Evidence regarding differential use of levels of processing by retarded and nonretarded persons comes from elaborative mediation studies. What Craik and Lockhart would call orienting tasks are more often called elaboration strategies in the mental retardation and developmental literatures. By 1974 it was established that retarded persons can utilize mediation, the degree of effectiveness being related to IQ and MA, but in ordinary circumstances they do not do so (Borkowski & Wanschura, 1974). This supports the notion of a production deficiency (Flavell, Beach, & Chinsky, 1966). A study by Rohwer, Raines, Eoff, & Wagner (1977, Exp. 3), using nonretarded adolescents, demonstrated that persons who were either younger or had lesser paired-associate (PA) learning ability do not elaborate spontaneously. Both the age and ability differences suggest an analog for a retarded-nonretarded comparison. The experimental tasks in mediation and elaboration studies are similar to the types of encoding tasks used in LOP studies. Using traditional LOP tasks, Weiss, Robinson, and Hastie (1977) found a developmental trend in the use of deep processing by nonretarded children. Deep processing was more effective than shallower levels only for older children. Engle and Nagle (1979, Exp. 2) showed the same age trend within a sample of retarded children. Two studies, one with CA-matched subjects and the other MA-matched, have compared retarded and nonretarded subjects on LOP tasks (McFarland & Sandy, 1982, Exp. 1; Schultz, 1983). In both, deep processing was superior but there was no interaction of processing level with intelligence level. In both studies, however, a recognition test was used. Recognition testing is less dependent than recall on the reconstruction that Lockhart et al. (1976) say is the major mechanism of both recall and recognition. Since recall relies more heavily on reconstruction of encoded events, a recall test may have been more sensitive to differences in processing level between subject groups. These studies tend to suggest that retarded persons rely more on shallower levels of processing than do the nonretarded, but the evidence is hardly conclusive. Retarded-nonretarded comparisons have not been made using mature, CA-matched subjects with recall as the dependent variable. The following experiment compared recall by retarded and nonretarded persons with encoding level varied from shallow to deep.
METHOD Subjects The 129 retarded subjects were recruited from high schools and from a sheltered workshop. Of these, 21 were excluded for various reasons. The remaining 108
LEVELS OF PROCESSING AND MEMORY
3
retarded subjects (87 students and 21 workshop clients) were divided at the median IQ in order to form high and low retarded groups. Subjects within each of these groups were assigned at random to one of the three encoding conditions. Table 1 shows the means and SDs of the IQs of the retarded subjects for each encoding condition. Of the 21 workshop clients, 18 fell in the low retarded sample. They, also, were assigned randomly to encoding condition and were represented equally in the three conditions. The mean IQ of the low retarded workshop clients did not differ from that of the low retarded high school students (56.7 vs. 57.0, respectively). The workshop clients were, however, older, having a mean CA of 29.0 (SD = 8.1) years, in contrast to a mean CA of 17.3 (SD = 0.9) years for the students within the low retarded group. The workshop clients only were paid minimum wage for their participation. The 70 nonretarded subjects were undergraduate students. Sixteen students •were excluded when posttest interviews revealed that they suspected that they would be asked to recall the stimuli. (No retarded subjects suspected this.) Only nonretarded subjects in the control condition suspected. Their recall was greater than that of retained subjects in the control condition (46.7 vs. 41.5%, respectively), t(32) = 3.49, p < .002. These subjects were awarded course credit for their participation.
Materials The stimuli were 36 35-mm slides of colored photographs of common objects such as an umbrella, cookies, a telephone, sofa, kite, or a train. The photographs were of single, actual objects, against either a natural background (e.g., a cow in an empty field) or a pastel background. Each stimulus contained at least three colors. The slides were rear-projected onto a 32 × 36 cm plexiglass screen. Subjects were seated approximately 200 cm in front of the screen. The projected image was approximately 20 x 20 cm.
TABLE ! Means and SDs of the IQs of the Retarded Subjects Encoding Condition Intelligence Level High Retarded M SD Low Retarded M SD
Shallow
Control
Deep
70.9a 2.8
68.8 6.0
70.1 4.4
56.9 5.2
55.7 5.8
58.0 5.6
an = 18 for each encoding condition at each intelligence level.
4
BOYD AND ELLIS
Procedure The picture presentation order was rerandomized after every third subject within an intelligence level. Each presentation order occurred equally often in all encoding conditions and intelligence levels. In order to disguise the intent to test memory for pictures, each subject was presented a digit span task before and after presentation of the pictures. They were told that this was a number memory task that would be given twice and that during a waiting period between presentations he or she would be shown some pictures and asked questions about them. The digit span task required subjects to repeat strings of digits read by the experimenter. Digit strings of increasing length were read until the subject failed three consecutive attempts to reproduce strings of the same length. This took 90 to 120 s to perform. Immediately prior to the presentation of the pictures, subjects in the shallow processing condition were told, "Tell me all the colors in these pictures." For the deep processing condition, subjects were instructed to "Tell me what each of these is used for." In the control condition they were told to "Look at all of these pictures." Each picture was presented for 5s. Five minutes following the presentation of the pictures, subjects were unexpectedly asked to recall the pictures. A correct response was the object name. In order to obtain some estimate of subjects' associative network, following the recall test, those in the control condition were given a word association test. Using the method of Noble (1952), 10 of the pictures were shown 1 at a time and the subject was asked, "What word does (picture name) make you think of?." The question was repeated after each response within 60 s. The repetition of the question was intended to prevent free association. The slides were originally selected randomly. Thereafter, the same 10 slides in the same order were used for each control subject.
RESULTS Mean percent recall for each group under each condition is shown in Figure 1. The datum was percentage of stimuli recalled for each subject. A 3 x 3 ANOVA (intelligence level × encoding condition) was performed on these data. The analysis yielded significant main effects for both intelligence level, F(2, 153) = 28.44, p < .0001, and encoding condition, F(I, 153) --- 32.64, p < .0001. The nonretarded subjects remembered more than did the high retarded subjects, F(1, 102) = 27.80, p < .001. The recall difference between the two retarded groups approached significance, F(1, 102) -- 3.02, p < .09. The deep processing condition produced greater recall than the control condition, F(I, 102) = 11.46, p < .002, and the control condition produced greater than the shallow processing condition, F(1, 102) = 21.96, p < .0001. There were no significant interactions.
LEVELS OF PROCESSINGAND MEMORY
5
60
Itu nnO 0 Iz
uJ
50,
.....
NMR HIMR LOMR
40'
30
(3
nInn Q.
---"
20,
01
_o,:........ I:::::"':":='"" ot
•
!
I
I
Shallow
Control
Deep
ENCODING CONDITION FIG. l. Percentrecall at five-minutedelay under three encodingconditionsfor three levels of intelligence. The datum in the word association study was the number of word associates given to a picture by each control subject. A one-way ANOVA comparing intelligence levels was performed on these data. There was a main effect for intelligence level, F(2, 51) = 27.03, p < .0001. The nonretarded subjects gave more associates to the stimuli than did the high retarded subjects, t(34) = 5.78, p < .001, or the low retarded, t(34) = 6.82, p > .001. The two retarded groups did not differ, t(34) = 1.05, p < .05. DISCUSSION We predicted that deep processing would yield greater recall than shallow processing, regardless of intelligence level, and this prediction was supported. The response of the retarded subjects to the encoding conditions was similar to that of the nonretarded. The superiority of deep over shallow encoding was about equal for all intelligence levels. The induced processing conditions also related similarly to the control condition in each intelligence level. At each level, deep processing improved performance over what is typically seen in an incidental memory situation, while shallow processing depressed it. The main hypothesis was that recall differences between nonretarded and retarded persons are a result of shallower processing by the retarded. Evidence for this assertion would be an interaction between encoding conditions and intelligence levels. If a difference in processing level is a cause of recall dif-
6
BOYD AND ELLIS
ferences, then the retarded subjects in this experiment should have been helped more than the nonretarded by induced deep processing and handicapped less by the induced shallow processing. No such interaction was evident. Recall in the shallow condidion by the nonretarded subjects was not depressed to the level of the retarded in the shallow condition, nor was the level of the retarded subjects in the deep condition elevated to that of the nonretarded in the deep condition. The results of the supplemental study may provide an explanation. The pictures elicited fewer associates from the long-term memory of retarded persons than from the nonretarded. An examination of the responses suggests that the memory of the retarded persons is also less elaborate and complex. For instance, for the picture of a glass mixing bowl, the retarded subjects simply listed the possible contents of the bowl (e.g., cereal, peas, etc,) more often than did the nonretarded subjects. The nonretarded subjects, in contrast, were more likely to give responses representing a variety of aspects of the object, such as its function, its composition, or other objects similar in some way. Also, they were somewhat more likely to give category names (e.g., food) as well as exemplars (e.g., cookie dough). To the bowl, nonretarded subjects responded, for example, " f o o d , " "cookie dough," "glass," " p o t , " " c o o k , " "stir," "wash," and "pantry." The responses of the college students tended to include personal associations to the stimuli more than did those of the retarded subjects. The college students might name friends the picture makes them think of, or events involving themselves and the pictured object. Thus, the responses of the retarded, while only rarely structural (e.g., color, size) and indicating some use of the deeper levels of memory, showed a network of associations both smaller and less complex than that of the nonretarded. This makes deep processing less useful to the retarded than to the nonretarded in producing a distinctive trace. The hypothesis that retarded-nonretarded recall differences are due to shallower processing was not supported. An alternate hypothesis is that the retarded are processing at the same level as the nonretarded, but are not elaborating as much within that processing level. The associates given by the retarded subjects were more semantic than structural or acoustic, but not as numerous or elaborate as those given by the nonretarded. It is possible that there were differences in spread of encoding (elaboration within a level) (Lockhart et al., 1976) operating to produce the retarded-nonretarded differences within the three conditions. In the deep condition, for example, both the nonretarded and retarded encoded in terms of function, but the nonretarded had more function-related associates to bring to the encoding. A spread of encoding deficit may not be the only alternate hypothesis. Such an explanation is attenuated somewhat by the equal superiority of nonretarded recall over retarded recall in both the deep and shallow conditions. An argument could be made that greater spread of encoding would be expected in the deep condition. Since few structural associates were elicited in the supplemental study, a comparison between nonretarded and retarded of the richness of their
LEVELS OF PROCESSING AND MEMORY
7
memory at the shallow level cannot be made. A further post-hoc explanation is that the nonretarded employed a superior retrieval strategy. Both the LOP approach and the encoding specificity principle (Tulving & Thompson, 1973) suggest that retrieval effectiveness is determined by encoding events. Nevertheless, a superior nonretarded retrieval strategy, independent of encoding, is not contradicted by the data of this experiment. Caruso and Detterman (1983) have said that retarded and nonretarded persons process information in highly similar ways. For both retarded and nonretarded subjects they correlated match-to-sample decision ti~mes with stimulus attributes such as symmetry and complexity. The stimuli were black and white, 4 x 4 square matrices with various patterns of filled cells. The correlations for the retarded group were very close to those for the nonretarded. The main retardednonretarded differences were that the retarded were slower and made more errors. Otherwise, the stimuli appeared to be processed in a similar manner. In the present experiment, retarded and nonretarded subjects seemed to process information in a similar manner, i.e., differences between these subjects are best described as quantitative. The retarded person has a more impoverished long-term memory, and therefore, the processing of new stimuli is affected. A less distinctive, less elaborate trace is produced as a result. The trace is less likely to be integrated into long-term memory so the information stored grows only slowly. This, in turn, hinders future processing and the circle is complete.
REFERENCES Borkowski, J. G., & Wanschura, P. B. (1974). Mediation processes in the retarded. In N. R. Ellis (Ed.), International review of research in mental retardation (Vol. 7). New York: Academic Press. Caruso, D. R., & Detterman, D. K. (1983). Stimulus encoding by mentally retarded and nonretarded adults. American Journal of Mental Deficiency, 87, 649-655. Craik, F. I. M., & Lockhart, R. S. (1972). Levels of processing: A framework for memory research. Journal of Verbal Learning and Verbal Behavior, 11, 671-684. Detterman, D. K. (1979). Memory in the mentally retarded. In N. R. Ellis (Ed.), Handbook of mental deficiency: Psychological theory and research (2nd Ed.). HiUsdale, NJ: Erlbaum. Engle, R. W., & Nagle, R. J. (1979). Strategy training and semantic encoding in mildly retarded children. Intelligence, 3, 17-30. Flavell, J. H., Beach, D. R., & Chinsky, J. M. (1966). Spontaneous verbal rehearsal in memory task as a function of age. Child Development, 37, 283-299. Jacoby, L. L., & Craik, F. I. M. (1979). Effects of elaboration of processing at encoding and retrieval: Trace distinctiveness and recovery of initial context. In L. S. Cermak & F. I. M. Craik (Eds.), Levels of processing in human memory. Hillsdale, NJ: Erlbaum. Lockhart, R. S., Craik, F. I. M., & Jaeoby, L. L. (1976). Depth of processing, recognition and recall: Some aspects of a general memory system. In J. Brown (Ed.), Recall and recognition. London: Wiley. McFarland, C. E., Jr., & Sandy, J. T. (1982). Automatic and conscious processing in retarded and nonretarded adolescents. Journal of Experimental Child Psychology, 33, 20-38. Noble, C. E. (1952). An analysis of meaning. Psychological Review, 59, 421-430.
8
BOYD AND ELLIS
Rohwer, W. D., Jr., Raines, J. M., Eoff, J., & Wagner, M. (1977). The development ofelaborative propensity during adolescence. Journal of Experimental ChiM Psychology, 23, 472-492. Schultz, E. E. (1983). Depth of processing by mentally retarded and MA-matched nonretarded individuals. American Journal of Mental Deficiency, 88, 307-313. Tulving, E., & Thompson, D. M. (1973). Encoding specificity and retrieval processes in episodic memory. Psychological Review, 80, 352-373. Weiss, S. L., Robinson, G., & Hastie, R. (1977). The relationship of depth of processing to free recall in second and fourth graders. Developmental Psychology, 13, 525-526.
Levels of Processing and Memory in Mentally Retarded and Nonretarded Persons* BRUCE
D. BOYD AND NORMAN
R. ELLIS
The University of Alabama
Individual differences in memory were examined from the levels of processing perspective. Mentally retarded persons were expected to be more superficial processors. The recall of nonretarded and two IQ levels of retarded young adults was compared following the presentation of pictorial stimuli with either a shallow processing, deep processing, or control orienting task. Shallow processing was induced by directing subjects to name the colors of the pictures. In the deep processing condition, subjects were told to say what the pictured object was used for. In the control condition, they were directed to look at the pictures. The stimuli were presented as an incidental learning task. Encoding condition was a between-subjects variable. Nonretarded subjects remembered more overall than did the two retarded groups, which did not differ. At each intelligence level, more stimuli were remembered in the deep processing condition than in the shallow condition. There was no interaction of intelligence level with encoding condition. The hypothesis that retarded persons process at a more superficial level was not supported. A "spread of encoding" deficit in retarded persons is favored to explain the recall differences obtained in this experiment.
The levels of processing (LOP) approach to the study of memory (Craik & Lockhart, 1972; Jacoby & Craik, 1979; Lockhart, Craik, & Jacoby, 1976) may provide an explanation for individual differences in memory performance. The LOP model asserts that memorability is dependent upon the level at which a tobe-remembered stimulus is processed. Processing at a superficial level only would lead to a less memorable trace. Persons of low intelligence, such as the mentally retarded, perform less well on many memory tasks (Detterman, 1979) probably as a result of processing more superficially than the nonretarded. If deeper processing relies on an associative network, it follows that an impoverished associative network hinders deeper processing. A person cannot
*This research was supported by Grant HD 15558 from the National Institute of Child Health and Human Development, Public Health Service. Also, the first author was a predoctoral trainee supported by Grant HD 07262 from NICHD during the course of this research. A doctoral dissertation, by the first author, submitted to the University of Alabama, is based on data reported in this paper. A version of this paper was presented at the Gatlinburg Conference, March 1984. Correspondence and requests for reprints should be sent to Bruce D. Boyd, Fairview Training Center, 2250 Strong Road S.E., Salem, OR 97310.
2
BOYD AND ELLIS
encode a stimulus in terms of attributes with which he or she is not familiar. Further, if a stimulus is not richly encoded, it is unlikely to add to the network of information in memory. Thus, a deficiency perpetuates itself. Evidence regarding differential use of levels of processing by retarded and nonretarded persons comes from elaborative mediation studies. What Craik and Lockhart would call orienting tasks are more often called elaboration strategies in the mental retardation and developmental literatures. By 1974 it was established that retarded persons can utilize mediation, the degree of effectiveness being related to IQ and MA, but in ordinary circumstances they do not do so (Borkowski & Wanschura, 1974). This supports the notion of a production deficiency (Flavell, Beach, & Chinsky, 1966). A study by Rohwer, Raines, Eoff, & Wagner (1977, Exp. 3), using nonretarded adolescents, demonstrated that persons who were either younger or had lesser paired-associate (PA) learning ability do not elaborate spontaneously. Both the age and ability differences suggest an analog for a retarded-nonretarded comparison. The experimental tasks in mediation and elaboration studies are similar to the types of encoding tasks used in LOP studies. Using traditional LOP tasks, Weiss, Robinson, and Hastie (1977) found a developmental trend in the use of deep processing by nonretarded children. Deep processing was more effective than shallower levels only for older children. Engle and Nagle (1979, Exp. 2) showed the same age trend within a sample of retarded children. Two studies, one with CA-matched subjects and the other MA-matched, have compared retarded and nonretarded subjects on LOP tasks (McFarland & Sandy, 1982, Exp. 1; Schultz, 1983). In both, deep processing was superior but there was no interaction of processing level with intelligence level. In both studies, however, a recognition test was used. Recognition testing is less dependent than recall on the reconstruction that Lockhart et al. (1976) say is the major mechanism of both recall and recognition. Since recall relies more heavily on reconstruction of encoded events, a recall test may have been more sensitive to differences in processing level between subject groups. These studies tend to suggest that retarded persons rely more on shallower levels of processing than do the nonretarded, but the evidence is hardly conclusive. Retarded-nonretarded comparisons have not been made using mature, CA-matched subjects with recall as the dependent variable. The following experiment compared recall by retarded and nonretarded persons with encoding level varied from shallow to deep.
METHOD Subjects The 129 retarded subjects were recruited from high schools and from a sheltered workshop. Of these, 21 were excluded for various reasons. The remaining 108
LEVELS OF PROCESSING AND MEMORY
3
retarded subjects (87 students and 21 workshop clients) were divided at the median IQ in order to form high and low retarded groups. Subjects within each of these groups were assigned at random to one of the three encoding conditions. Table 1 shows the means and SDs of the IQs of the retarded subjects for each encoding condition. Of the 21 workshop clients, 18 fell in the low retarded sample. They, also, were assigned randomly to encoding condition and were represented equally in the three conditions. The mean IQ of the low retarded workshop clients did not differ from that of the low retarded high school students (56.7 vs. 57.0, respectively). The workshop clients were, however, older, having a mean CA of 29.0 (SD = 8.1) years, in contrast to a mean CA of 17.3 (SD = 0.9) years for the students within the low retarded group. The workshop clients only were paid minimum wage for their participation. The 70 nonretarded subjects were undergraduate students. Sixteen students •were excluded when posttest interviews revealed that they suspected that they would be asked to recall the stimuli. (No retarded subjects suspected this.) Only nonretarded subjects in the control condition suspected. Their recall was greater than that of retained subjects in the control condition (46.7 vs. 41.5%, respectively), t(32) = 3.49, p < .002. These subjects were awarded course credit for their participation.
Materials The stimuli were 36 35-mm slides of colored photographs of common objects such as an umbrella, cookies, a telephone, sofa, kite, or a train. The photographs were of single, actual objects, against either a natural background (e.g., a cow in an empty field) or a pastel background. Each stimulus contained at least three colors. The slides were rear-projected onto a 32 × 36 cm plexiglass screen. Subjects were seated approximately 200 cm in front of the screen. The projected image was approximately 20 x 20 cm.
TABLE ! Means and SDs of the IQs of the Retarded Subjects Encoding Condition Intelligence Level High Retarded M SD Low Retarded M SD
Shallow
Control
Deep
70.9a 2.8
68.8 6.0
70.1 4.4
56.9 5.2
55.7 5.8
58.0 5.6
an = 18 for each encoding condition at each intelligence level.
4
BOYD AND ELLIS
Procedure The picture presentation order was rerandomized after every third subject within an intelligence level. Each presentation order occurred equally often in all encoding conditions and intelligence levels. In order to disguise the intent to test memory for pictures, each subject was presented a digit span task before and after presentation of the pictures. They were told that this was a number memory task that would be given twice and that during a waiting period between presentations he or she would be shown some pictures and asked questions about them. The digit span task required subjects to repeat strings of digits read by the experimenter. Digit strings of increasing length were read until the subject failed three consecutive attempts to reproduce strings of the same length. This took 90 to 120 s to perform. Immediately prior to the presentation of the pictures, subjects in the shallow processing condition were told, "Tell me all the colors in these pictures." For the deep processing condition, subjects were instructed to "Tell me what each of these is used for." In the control condition they were told to "Look at all of these pictures." Each picture was presented for 5s. Five minutes following the presentation of the pictures, subjects were unexpectedly asked to recall the pictures. A correct response was the object name. In order to obtain some estimate of subjects' associative network, following the recall test, those in the control condition were given a word association test. Using the method of Noble (1952), 10 of the pictures were shown 1 at a time and the subject was asked, "What word does (picture name) make you think of?." The question was repeated after each response within 60 s. The repetition of the question was intended to prevent free association. The slides were originally selected randomly. Thereafter, the same 10 slides in the same order were used for each control subject.
RESULTS Mean percent recall for each group under each condition is shown in Figure 1. The datum was percentage of stimuli recalled for each subject. A 3 x 3 ANOVA (intelligence level × encoding condition) was performed on these data. The analysis yielded significant main effects for both intelligence level, F(2, 153) = 28.44, p < .0001, and encoding condition, F(I, 153) --- 32.64, p < .0001. The nonretarded subjects remembered more than did the high retarded subjects, F(1, 102) = 27.80, p < .001. The recall difference between the two retarded groups approached significance, F(1, 102) -- 3.02, p < .09. The deep processing condition produced greater recall than the control condition, F(I, 102) = 11.46, p < .002, and the control condition produced greater than the shallow processing condition, F(1, 102) = 21.96, p < .0001. There were no significant interactions.
LEVELS OF PROCESSINGAND MEMORY
5
60
Itu nnO 0 Iz
uJ
50,
.....
NMR HIMR LOMR
40'
30
(3
nInn Q.
---"
20,
01
_o,:........ I:::::"':":='"" ot
•
!
I
I
Shallow
Control
Deep
ENCODING CONDITION FIG. l. Percentrecall at five-minutedelay under three encodingconditionsfor three levels of intelligence. The datum in the word association study was the number of word associates given to a picture by each control subject. A one-way ANOVA comparing intelligence levels was performed on these data. There was a main effect for intelligence level, F(2, 51) = 27.03, p < .0001. The nonretarded subjects gave more associates to the stimuli than did the high retarded subjects, t(34) = 5.78, p < .001, or the low retarded, t(34) = 6.82, p > .001. The two retarded groups did not differ, t(34) = 1.05, p < .05. DISCUSSION We predicted that deep processing would yield greater recall than shallow processing, regardless of intelligence level, and this prediction was supported. The response of the retarded subjects to the encoding conditions was similar to that of the nonretarded. The superiority of deep over shallow encoding was about equal for all intelligence levels. The induced processing conditions also related similarly to the control condition in each intelligence level. At each level, deep processing improved performance over what is typically seen in an incidental memory situation, while shallow processing depressed it. The main hypothesis was that recall differences between nonretarded and retarded persons are a result of shallower processing by the retarded. Evidence for this assertion would be an interaction between encoding conditions and intelligence levels. If a difference in processing level is a cause of recall dif-
6
BOYD AND ELLIS
ferences, then the retarded subjects in this experiment should have been helped more than the nonretarded by induced deep processing and handicapped less by the induced shallow processing. No such interaction was evident. Recall in the shallow condidion by the nonretarded subjects was not depressed to the level of the retarded in the shallow condition, nor was the level of the retarded subjects in the deep condition elevated to that of the nonretarded in the deep condition. The results of the supplemental study may provide an explanation. The pictures elicited fewer associates from the long-term memory of retarded persons than from the nonretarded. An examination of the responses suggests that the memory of the retarded persons is also less elaborate and complex. For instance, for the picture of a glass mixing bowl, the retarded subjects simply listed the possible contents of the bowl (e.g., cereal, peas, etc,) more often than did the nonretarded subjects. The nonretarded subjects, in contrast, were more likely to give responses representing a variety of aspects of the object, such as its function, its composition, or other objects similar in some way. Also, they were somewhat more likely to give category names (e.g., food) as well as exemplars (e.g., cookie dough). To the bowl, nonretarded subjects responded, for example, " f o o d , " "cookie dough," "glass," " p o t , " " c o o k , " "stir," "wash," and "pantry." The responses of the college students tended to include personal associations to the stimuli more than did those of the retarded subjects. The college students might name friends the picture makes them think of, or events involving themselves and the pictured object. Thus, the responses of the retarded, while only rarely structural (e.g., color, size) and indicating some use of the deeper levels of memory, showed a network of associations both smaller and less complex than that of the nonretarded. This makes deep processing less useful to the retarded than to the nonretarded in producing a distinctive trace. The hypothesis that retarded-nonretarded recall differences are due to shallower processing was not supported. An alternate hypothesis is that the retarded are processing at the same level as the nonretarded, but are not elaborating as much within that processing level. The associates given by the retarded subjects were more semantic than structural or acoustic, but not as numerous or elaborate as those given by the nonretarded. It is possible that there were differences in spread of encoding (elaboration within a level) (Lockhart et al., 1976) operating to produce the retarded-nonretarded differences within the three conditions. In the deep condition, for example, both the nonretarded and retarded encoded in terms of function, but the nonretarded had more function-related associates to bring to the encoding. A spread of encoding deficit may not be the only alternate hypothesis. Such an explanation is attenuated somewhat by the equal superiority of nonretarded recall over retarded recall in both the deep and shallow conditions. An argument could be made that greater spread of encoding would be expected in the deep condition. Since few structural associates were elicited in the supplemental study, a comparison between nonretarded and retarded of the richness of their
LEVELS OF PROCESSING AND MEMORY
7
memory at the shallow level cannot be made. A further post-hoc explanation is that the nonretarded employed a superior retrieval strategy. Both the LOP approach and the encoding specificity principle (Tulving & Thompson, 1973) suggest that retrieval effectiveness is determined by encoding events. Nevertheless, a superior nonretarded retrieval strategy, independent of encoding, is not contradicted by the data of this experiment. Caruso and Detterman (1983) have said that retarded and nonretarded persons process information in highly similar ways. For both retarded and nonretarded subjects they correlated match-to-sample decision ti~mes with stimulus attributes such as symmetry and complexity. The stimuli were black and white, 4 x 4 square matrices with various patterns of filled cells. The correlations for the retarded group were very close to those for the nonretarded. The main retardednonretarded differences were that the retarded were slower and made more errors. Otherwise, the stimuli appeared to be processed in a similar manner. In the present experiment, retarded and nonretarded subjects seemed to process information in a similar manner, i.e., differences between these subjects are best described as quantitative. The retarded person has a more impoverished long-term memory, and therefore, the processing of new stimuli is affected. A less distinctive, less elaborate trace is produced as a result. The trace is less likely to be integrated into long-term memory so the information stored grows only slowly. This, in turn, hinders future processing and the circle is complete.
REFERENCES Borkowski, J. G., & Wanschura, P. B. (1974). Mediation processes in the retarded. In N. R. Ellis (Ed.), International review of research in mental retardation (Vol. 7). New York: Academic Press. Caruso, D. R., & Detterman, D. K. (1983). Stimulus encoding by mentally retarded and nonretarded adults. American Journal of Mental Deficiency, 87, 649-655. Craik, F. I. M., & Lockhart, R. S. (1972). Levels of processing: A framework for memory research. Journal of Verbal Learning and Verbal Behavior, 11, 671-684. Detterman, D. K. (1979). Memory in the mentally retarded. In N. R. Ellis (Ed.), Handbook of mental deficiency: Psychological theory and research (2nd Ed.). HiUsdale, NJ: Erlbaum. Engle, R. W., & Nagle, R. J. (1979). Strategy training and semantic encoding in mildly retarded children. Intelligence, 3, 17-30. Flavell, J. H., Beach, D. R., & Chinsky, J. M. (1966). Spontaneous verbal rehearsal in memory task as a function of age. Child Development, 37, 283-299. Jacoby, L. L., & Craik, F. I. M. (1979). Effects of elaboration of processing at encoding and retrieval: Trace distinctiveness and recovery of initial context. In L. S. Cermak & F. I. M. Craik (Eds.), Levels of processing in human memory. Hillsdale, NJ: Erlbaum. Lockhart, R. S., Craik, F. I. M., & Jaeoby, L. L. (1976). Depth of processing, recognition and recall: Some aspects of a general memory system. In J. Brown (Ed.), Recall and recognition. London: Wiley. McFarland, C. E., Jr., & Sandy, J. T. (1982). Automatic and conscious processing in retarded and nonretarded adolescents. Journal of Experimental Child Psychology, 33, 20-38. Noble, C. E. (1952). An analysis of meaning. Psychological Review, 59, 421-430.
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Rohwer, W. D., Jr., Raines, J. M., Eoff, J., & Wagner, M. (1977). The development ofelaborative propensity during adolescence. Journal of Experimental ChiM Psychology, 23, 472-492. Schultz, E. E. (1983). Depth of processing by mentally retarded and MA-matched nonretarded individuals. American Journal of Mental Deficiency, 88, 307-313. Tulving, E., & Thompson, D. M. (1973). Encoding specificity and retrieval processes in episodic memory. Psychological Review, 80, 352-373. Weiss, S. L., Robinson, G., & Hastie, R. (1977). The relationship of depth of processing to free recall in second and fourth graders. Developmental Psychology, 13, 525-526.