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High speed memory scanning in mental retardates: Evidence for a central processing deficit
JOURNAL
OF EXPERIMENTAL
CHILD
PSYCHOLOGY
17, 452-459
(1974)
Hig.h Speed Memory Scanning in Mental Retardates: Evidence for a Central Processing Deficit1j2 GILBERT Herbert
H. Lehman
College,
ROBERT Bergen
,J. HARRIS City
E.
Community
University
of New
York
FLEER College
Third-grade, high-school, and adult normal subjects and two diagnostic categories of educable mental retardates (cultural familials and encephalopathies) were tested in a Sternberg-type “memory scanning” recognition task. All five groups showed the characteristic linear increase in correct reaction time as the number of items in the memorized set increased. The slopes of the linear functions, however, were streper for the two retardate samples than for the normal samples, suggesting a central processing deficit which could not be attribut,ed to a lag in devrlopment.
Sternberg (1966) found that when a subject decides whether or not a visually presented item has appeared in a previously memorized short list, reaction time for correct responses is an increasing linear function of the number of items in the list or the “set size.” The parallel linearity of reaction time functions for “yes” and “no” responses in this task leads t’o a model of high speed memory scanning that utilizes an item by item LLserial-exhaustive” search process. According to Sternberg, when the subject is presented with a test item, it is compared with the memory representation of every item in the set in a serial manner. The search is exhaustive because even after a match is obtained, all remaining items in memory are searched before a response is selected. The speed of the hypothesized scanning process is 2530 items per second for normal subjects as evidenced by the obtained slopes of the linear functions and thus is not to be confused with overt or subvocal rehearsal which proceeds at a 1 Subjects were tested while both authors were at the Department of Psychology. New York State Institute for Research in Mental Retardation. Requests for reprints should be addressed to G. J. Harris, Department of Psychology, H. H. Lehman College, CUNY, Bronx, N. Y. 10468. ‘The authors express their thanks to the Reverend Mother Mary, Principal of St. Rita’s School, Staten Island, N. Y., and to Sister Maureen, Guidance Counselor at Countess Moore High School, Staten Island, N. Y., for their cooperation in providing normal subjects. 452 Copyright @ 1974 by Academic Press, Inc. All rights of reproduction in any form reserved.
MEMORY
SCANNING
IN
RETARDATES
453
much slower rate (Landauer, 1964). The reaction time for “yes” responses as a function of the serial position of the test item in the memorized sequence has been viewed as an additional empirical test of the serial-exhaustive model of scanning. If the sequence is searched exhaustively before a response is selected, then the serial position of the test item should have no effect on reaction time since it is only the size of the set which is the crucial determinant of reaction time. Consideration of the information processing aspects of the model yields subprocesses which contribute additive components to the total reaction time (Sternberg, 1969). Since the dependent variable is measured from the presentation of the test item to the completion of the motor response, X must (a) perceive the test item, (b) scan the memorized set, and (c) select and execute the response. It should be noted that the amount of processing necessary in the perception and response processing components remains the same regardless of the number of items in the memorized set for a given trial. Only the scanning subprocess is affected by the variation in set size. Thus, the intercept of the obtained function can be considered an estimate of the time taken for peripheral (i.e., perceptual and response) processing while the memory scanning rate, as estimated by the slope of the function, can be considered a central process (Smith, 1968). A developmental investigation of the memory scanning paradigm has shown that the slope, but not the intercept, of the linear function relating set size to reaction time is constant for kindergarten, fourth-grade, and college-age subjects (Hoving, Morin & Konick, 1970) indicating that although perceptual and/or response processes develop added efficiency within these age limits, the memory scanning rate remains unchanged. Anders, Fozard, and Lillyquist (1972)) comparing 20-year-old, 38-yearold, and 68-year-old groups in a memory scanning task, found that the subprocesses inferred from both slope and intercept values showed decreases in efficiency with age. Kirsner (1972)) using subjects from 10-60 years of age, showed, however, that relative to perceptual and response processes, memory scanning time is insensitive to age differences. The present study seeks to investigate first whether the serial exhaustive model holds up for educable mental retardates, and if so, whether the constant scanning rate, found from kindergarten age through at least young adults, is also found in retardates. METHOD Design One between-subjects variable and two within-subjects variables were manipulated in a 5 X 4 X 2 experimental design. Five groups of Ss
454
HARRIS
AND
FLEER
(third-grade, high-school, and adult normals; cultural familial and encephalopathy-diagnosed educable mental retardates) constituted the between-subjects variable, while the number of items in the memorized set was varied from one to four as a within-subjects factor. The second within-subjects variable was whether or not the test item was present in the memorized set. Subjects Each of the five groups contained 10 male Ss. The mean and standard deviation for chronological age (CA) for each group as well as the mean and standard deviation of mental age (MA) and intelligence quotient (IQ) for the two retardate samples is presented m Table 1. The MAs and IQs for the retardates were based on the administration of the StanfordBinet, the Wechsler Intelligence Scale for Children, or the Wechsler Intelligence Scale for Adults. The third-grade sample was selected from average classes based on reading scores so that it was considered an MA match for both retardate samples. The high-school sample was similarly selected as a CA match. Both the cultural familial and encephalopathy Ss were selected from their respective populations at Willowbrook State School, Staten Island, N. Y. Diagnoses of the organic sample contained encephalopathies due to prenatal injury, mechanical injury at birth, and anoxemia at birth. Ma.terials and Procedure Each S was tested at each of two sessions two weeks apart. Each session consisted of 96 trials, the first 16 of which were considered practice and not scored. Each trial consisted of a sequence of from one to four nonrepeating digits from the set 0123456789 followed by a test digit. In half
ME:ANS AND STANDAHD MENTAL AGE (MA),
TABLE 1 DEVIATIONS (SO) FOR CHRONOLOGICAL AGE (CA), AND INTELLIGENCE QUOTIENT (IQ) OF SUBJECTS CA (Yrs.-MO.)
Mental retardate samples Cultural familials (N = 10) Encephalopathies (iS’ = 10) Normal samples Third grade (N = 10) High school (N = 10) Adults (A’ = 10)
MA (Yrs.-Mo.) -____-__
Mean
SD
16-1 16-5
l-1 l-3
8-6 16-1 24-11
o-4 o-11 2-2
IQ
-
Mean
SD
Mean
SD
s-3 x-4
O-S O-6
55.5 57.8
4.4 3.8
MEMORY
SCANNING
IN
RETARDATES
455
of the 80 test trials in each session, the test item had been present in the sequence (‘Lyes” response required) while in the other half it had not (“no” response required). Twenty test trials at each sequence length were randomized to make up the 80 trials. For the trials in which a LLyes” response was required, the serial position in the sequence of the test item was distributed as evenly as possible aross each set size. The S sat at a small desk upon which rested two reaction-time keys 4 in. apart and was instructed to place his index fingers on the keys. For half the Ss in each group the preferred hand key was designated as the “yes” response while for the other half the preferred hand key was designated as the “no” response. The experimenter (E) said “ready” immediately before presenting S the sequence to be remembered on each trial. From one to four digits were shown at a rate of 1.5 SW per item using a Kodak Carousel Projector which was programmed by an eight-bank Lafayette Timer. Two blank slides, following the slide containing the last sequence item, indicated to S the end of the sequence. Following the second blank, the test item was presented. The S was instructed to press the appropriate key to signify whether or not the test item had appeared in the sequence. The Ss were told to respond as fast as possible without making any errors. The reaction time, from the onset of the test item to the subject’s pressing of a response key, was recorded by a Hickock electronic counter/printer which recorded which of the two keys was pressed as well as the reaction time on each trial. The Ss were given a 1-min rest after each eight trials and a 5-min break at the midpoint of each session. RESULTS
The percentage of trials on which Ss pressed the wrong key (i.e., errors) is shown for each group at each set size and for each session in Ta,ble 2. An analysis of variance on the number of errors ‘per session collapsed across set size showed a significant interaction between Sessions and Groups (F(4,45) = 6.52, p < .Ol) as well as main effects of Groups (F(4,45) = 3.88, p < .Ol) and of Sessions (F(1,45) = 45.29, p < .Ol). Subsequent tests of the simple effects of the groups variable showed that although the groups differed in number of errors for Session 1 (F(4,45) = 11.16, p < .Ol), there was no significant difference for Session 2. A Newman-Keuls analysis showed that for Session 1, the two retardate samples made more errors than did the three normal samples (CY= .Ol). The dependent variable of primary interest was correct reaction time and not number of errors, but it was felt important that the different samples be equal in terms of error rate so that differences in reaction time could not be attributed to error differences. Thus, correct reaction time analyses below considered the data from Session 2 only.3 The median reaction time for correct responses was computed separately
11.5 4.0 3.0 1.5
8.5 4.0 3.0 2.5
MA) CA)
Retardate encephalopathies Normal third grade (equal Normal high school (equal Normal adult
8.5
2
10.5
cultural
1
familials
Retardate
.~
Session 3
14.0 5.0 3.5 4.5
11.9 11.9 4.5 3.3 3.0
13.5 5.0 3.5 3.5
All
16.5
4
TABLE 2 OF ERRONEOUS 1 set size
12.0
PERCENTAGE
1
4.5 2. 0 2.0 2.5
3.0
RESPONSICS
.5 5 :i 5 3 .5 5.0
2.0 5.0
5.5
3
2 set, size
6.0 3.0
5 0
2
Session
3.0 4.0
6.0 4.5
10.0
4
2.6 4.1
0- .5 3 8
5.9
All
3 !s #
$ u
ti
MEMORY
SCANNING
IN
SET
FIG. 1. Combined reaction size. A. Normal-adult (RT MR-CF (RT = 422 + 66s). Grd. (RT = 688 + 428).
time for “yes” = 306 + 418). D. MR-Enceph.
457
RETARDATES
SIZE (9
and “no” responses as a function of set B. Normal-HS. (RT = 395 + 42s). C. (RT = 563 + 1115). E. Normal-3rd
for “yes” and “no” responses at each set size for each S. Although “no” responses were consistently longer than “yes” responses (F( 1,45) = 29.48, p < .Ol), this effect did not interact with groups or set size.4 The lack of any interaction between the “yes”-%o” and Set Size variables indicates that the “yes” and “no” functions for each group were parallel. Since the data yielded linear functions as well, the slopes of the “yes” and “no” functions for any one group were equal. Thus, each S’s “yes” and [‘no” responses were combined and the median at each set size was computed. The equation of the best fitting straight line for each S was determined as were the equations of the mean data for each group which is shown in Fig. 1. The group equations accounted for more than 98% of the total variance of the combined data for each group. An analysis of variance was performed on the slopes of the best fitting functions for each S. The results showed a significant difference between groups (F(4,45) = 10.13, p < .Ol). A subsequent Newman-Keuls analysis showed that the mean slopes for the three normal samples were significantly smaller than those of the two retardate samples and also that the ‘Subsequent analysis of Session 1 reaction time data yielded ences from that of Session 2. *Sternberg (1969) has pointed out that the serial exhaustive predicts equal slopes for “yes” and “no” functions but makes their relative intercepts.
no important scanning model no predictions
differonly as to
458
HARRIS
AND
FLEER
encephalopathy sample yielded a significantly steeper slope than did the cultural familials (N = .Ol). An analysis of variance on the intercepts of the individual functions also showed a significant difference between groups (F(4,45) = 12.99, p < .Ol) as can be seen in Fig. 1. A Newman-Keuls analysis (N = .Ol) showed that the third-grade sample had the largest intercept. In addition, the intercept of the encephalopathy sample was significantly larger than the remaining three sample intercepts and, finally, the adult normals yielded a smaller intercept than that of both the retardate cultural familials and the high-school normals, the latter two not differing from each other. Analysis of the effect of serial position of the test item on reaction time did not show any differences for any of the five groups.
The results indicate that the same information processing model which is supported by the data of the normal ‘3s also fits that of the retardates. The parallel linearity of the “yes” and ‘Lno” functions relating set size to reaction time and also the lack of serial-position effects on reaction time for all five samples in the present study provided support for Sternberg’s (1966) serial-exhaustive high speed scanning model in normal subjects as well as extending it to two diagnostic classifications of retardates. This suggests that, at least for the memory recognition task reported, retardates process information in the same qualitative manner as do normals. However, differences in the magnitudes of the slopes and the intercepts of the best fitting straight-line functions between retardates and normals indicated that the retardates were less efficient than normals in the central processing (i.e., memory scanning) aspects of the task. The slopes of the three normal groups did not differ from each other although the mean age of these groups varied from 8-24 years. Thus, the steeper slopes or slower memory scanning rate of the retardate samples cannot be interpreted as a developmental decrement but rather some kind of permanent deficiency in central processing can be hypothesized. The even steeper slope of the encephalopathy sample compared with that of the cultural familials indicates that brain damage, or at least the diagnosis of it, is positively correlated with the amount of this central processing deficit. Not unexpectedly, the three normal samples show a trend of decreasing intercepts with age indicating that throughout t,he age range sampled, the speed of peripheral processing (i.e., perception and response) increases. The cultural familials showed the same intercept value as did the CA control group, which amplifies the finding that the locus of the performance difference between retardates and normals is in the central processing aspects of the task. That the encephalopathy sample was slower in inter-
MEMORY
SCANNING
IN
459
RETARDATES
cept time than both the cultural familials and the CA controls and almost as slow as the MA controls indicates that peripheral processing deficiency, as well as central processing deficiency, is positively related to the diagnosis of organicity in mental retardates. The retardate deficiency in memory scanning rate obtained in the present study is compatible with two recently presented empirical relationships. Spitz (1973)) in a review of the retardate memory literature, showed that the memory span or channel capacity for educable retardates is about 3-4 items rather than the 5-7 items found with normals (Miller, 1956; Spitz, 1972). Cavanagh (1972) has found a strong reciprocal relationship between central processing rate in memory scanning experiments and memory span capacity across widely varying types of stimulus materials with normal subjects. For example, memory scanning tasks using digits have yielded processing rates of about 35 msec per item. Subjects in memory span studies using digits have recalled about 7.7 items. On the other hand, when geometrical shapes have been employed as stimuli, processing rates have been about 50 msec per item while memory span capacity has been about 5.3 items. This finding, that slower scanning rate (clearly a central process) and decreased memory span capacity are correlated, supports the notion that short-term memory performance deficits in educable mental retardates, commonly found in memory span tasks, are central rather than peripheral. REFERENCES
ANDERS, T. R., FOZARD,J. L., & LILLYQUIST, T. D. The effects of age upon retrival from short-term memory. Developmental Psychology, 1972, 6, 214-217. CAVANAGH, J. P. Relation between the immediate memory span and the memory search rate. Psychological Review, 1972, 6,525-530. HOVIN~, K. L., MORIN, R. E., & KONICK, D. S. Recognition reaction time and size of the memory set: a developmental study. Psychonomic Science, 1970, 21, 247-248.
KIRSNER, K. Developmental Journal
of Psychology,
changes in short-term
recognition
memory.
British
1972,63,
10%117. speech. Perceptual
LANDAUER, T. Rate of implicit and Motor Skills, 1962, 15, 646. MILLER, G. A. The magical number seven, plus or minus two: some limits on our capacity for processing information. PsychoZogicaZ Review, 1956, 63, 81-97. SMITH, E. E. Choice reaction time: an analysis of the major theoretical positions. Psychological
Bulletin,
1968, 69, 77-110.
SPITZ, H. H. Note on immediate memory for digits: invariance over the years. Psychological Bulletin, 1972, 78, 183-185. SPITZ, H. H. The channel capacity of educable mental retardates. In D. K. Routh (Ed.), The Experimental psychology of mental retardation. Chicago: Aldine, 1973. Pp. 133-156. STERNBERG,S. High-speed scanning in human memory. Science, 1966, 153, 652-654. STERNBERG,S. The discovery of stages: extensions of Donders’ method. Acta Psychologica,
1969,
30, 276315.
OF EXPERIMENTAL
CHILD
PSYCHOLOGY
17, 452-459
(1974)
Hig.h Speed Memory Scanning in Mental Retardates: Evidence for a Central Processing Deficit1j2 GILBERT Herbert
H. Lehman
College,
ROBERT Bergen
,J. HARRIS City
E.
Community
University
of New
York
FLEER College
Third-grade, high-school, and adult normal subjects and two diagnostic categories of educable mental retardates (cultural familials and encephalopathies) were tested in a Sternberg-type “memory scanning” recognition task. All five groups showed the characteristic linear increase in correct reaction time as the number of items in the memorized set increased. The slopes of the linear functions, however, were streper for the two retardate samples than for the normal samples, suggesting a central processing deficit which could not be attribut,ed to a lag in devrlopment.
Sternberg (1966) found that when a subject decides whether or not a visually presented item has appeared in a previously memorized short list, reaction time for correct responses is an increasing linear function of the number of items in the list or the “set size.” The parallel linearity of reaction time functions for “yes” and “no” responses in this task leads t’o a model of high speed memory scanning that utilizes an item by item LLserial-exhaustive” search process. According to Sternberg, when the subject is presented with a test item, it is compared with the memory representation of every item in the set in a serial manner. The search is exhaustive because even after a match is obtained, all remaining items in memory are searched before a response is selected. The speed of the hypothesized scanning process is 2530 items per second for normal subjects as evidenced by the obtained slopes of the linear functions and thus is not to be confused with overt or subvocal rehearsal which proceeds at a 1 Subjects were tested while both authors were at the Department of Psychology. New York State Institute for Research in Mental Retardation. Requests for reprints should be addressed to G. J. Harris, Department of Psychology, H. H. Lehman College, CUNY, Bronx, N. Y. 10468. ‘The authors express their thanks to the Reverend Mother Mary, Principal of St. Rita’s School, Staten Island, N. Y., and to Sister Maureen, Guidance Counselor at Countess Moore High School, Staten Island, N. Y., for their cooperation in providing normal subjects. 452 Copyright @ 1974 by Academic Press, Inc. All rights of reproduction in any form reserved.
MEMORY
SCANNING
IN
RETARDATES
453
much slower rate (Landauer, 1964). The reaction time for “yes” responses as a function of the serial position of the test item in the memorized sequence has been viewed as an additional empirical test of the serial-exhaustive model of scanning. If the sequence is searched exhaustively before a response is selected, then the serial position of the test item should have no effect on reaction time since it is only the size of the set which is the crucial determinant of reaction time. Consideration of the information processing aspects of the model yields subprocesses which contribute additive components to the total reaction time (Sternberg, 1969). Since the dependent variable is measured from the presentation of the test item to the completion of the motor response, X must (a) perceive the test item, (b) scan the memorized set, and (c) select and execute the response. It should be noted that the amount of processing necessary in the perception and response processing components remains the same regardless of the number of items in the memorized set for a given trial. Only the scanning subprocess is affected by the variation in set size. Thus, the intercept of the obtained function can be considered an estimate of the time taken for peripheral (i.e., perceptual and response) processing while the memory scanning rate, as estimated by the slope of the function, can be considered a central process (Smith, 1968). A developmental investigation of the memory scanning paradigm has shown that the slope, but not the intercept, of the linear function relating set size to reaction time is constant for kindergarten, fourth-grade, and college-age subjects (Hoving, Morin & Konick, 1970) indicating that although perceptual and/or response processes develop added efficiency within these age limits, the memory scanning rate remains unchanged. Anders, Fozard, and Lillyquist (1972)) comparing 20-year-old, 38-yearold, and 68-year-old groups in a memory scanning task, found that the subprocesses inferred from both slope and intercept values showed decreases in efficiency with age. Kirsner (1972)) using subjects from 10-60 years of age, showed, however, that relative to perceptual and response processes, memory scanning time is insensitive to age differences. The present study seeks to investigate first whether the serial exhaustive model holds up for educable mental retardates, and if so, whether the constant scanning rate, found from kindergarten age through at least young adults, is also found in retardates. METHOD Design One between-subjects variable and two within-subjects variables were manipulated in a 5 X 4 X 2 experimental design. Five groups of Ss
454
HARRIS
AND
FLEER
(third-grade, high-school, and adult normals; cultural familial and encephalopathy-diagnosed educable mental retardates) constituted the between-subjects variable, while the number of items in the memorized set was varied from one to four as a within-subjects factor. The second within-subjects variable was whether or not the test item was present in the memorized set. Subjects Each of the five groups contained 10 male Ss. The mean and standard deviation for chronological age (CA) for each group as well as the mean and standard deviation of mental age (MA) and intelligence quotient (IQ) for the two retardate samples is presented m Table 1. The MAs and IQs for the retardates were based on the administration of the StanfordBinet, the Wechsler Intelligence Scale for Children, or the Wechsler Intelligence Scale for Adults. The third-grade sample was selected from average classes based on reading scores so that it was considered an MA match for both retardate samples. The high-school sample was similarly selected as a CA match. Both the cultural familial and encephalopathy Ss were selected from their respective populations at Willowbrook State School, Staten Island, N. Y. Diagnoses of the organic sample contained encephalopathies due to prenatal injury, mechanical injury at birth, and anoxemia at birth. Ma.terials and Procedure Each S was tested at each of two sessions two weeks apart. Each session consisted of 96 trials, the first 16 of which were considered practice and not scored. Each trial consisted of a sequence of from one to four nonrepeating digits from the set 0123456789 followed by a test digit. In half
ME:ANS AND STANDAHD MENTAL AGE (MA),
TABLE 1 DEVIATIONS (SO) FOR CHRONOLOGICAL AGE (CA), AND INTELLIGENCE QUOTIENT (IQ) OF SUBJECTS CA (Yrs.-MO.)
Mental retardate samples Cultural familials (N = 10) Encephalopathies (iS’ = 10) Normal samples Third grade (N = 10) High school (N = 10) Adults (A’ = 10)
MA (Yrs.-Mo.) -____-__
Mean
SD
16-1 16-5
l-1 l-3
8-6 16-1 24-11
o-4 o-11 2-2
IQ
-
Mean
SD
Mean
SD
s-3 x-4
O-S O-6
55.5 57.8
4.4 3.8
MEMORY
SCANNING
IN
RETARDATES
455
of the 80 test trials in each session, the test item had been present in the sequence (‘Lyes” response required) while in the other half it had not (“no” response required). Twenty test trials at each sequence length were randomized to make up the 80 trials. For the trials in which a LLyes” response was required, the serial position in the sequence of the test item was distributed as evenly as possible aross each set size. The S sat at a small desk upon which rested two reaction-time keys 4 in. apart and was instructed to place his index fingers on the keys. For half the Ss in each group the preferred hand key was designated as the “yes” response while for the other half the preferred hand key was designated as the “no” response. The experimenter (E) said “ready” immediately before presenting S the sequence to be remembered on each trial. From one to four digits were shown at a rate of 1.5 SW per item using a Kodak Carousel Projector which was programmed by an eight-bank Lafayette Timer. Two blank slides, following the slide containing the last sequence item, indicated to S the end of the sequence. Following the second blank, the test item was presented. The S was instructed to press the appropriate key to signify whether or not the test item had appeared in the sequence. The Ss were told to respond as fast as possible without making any errors. The reaction time, from the onset of the test item to the subject’s pressing of a response key, was recorded by a Hickock electronic counter/printer which recorded which of the two keys was pressed as well as the reaction time on each trial. The Ss were given a 1-min rest after each eight trials and a 5-min break at the midpoint of each session. RESULTS
The percentage of trials on which Ss pressed the wrong key (i.e., errors) is shown for each group at each set size and for each session in Ta,ble 2. An analysis of variance on the number of errors ‘per session collapsed across set size showed a significant interaction between Sessions and Groups (F(4,45) = 6.52, p < .Ol) as well as main effects of Groups (F(4,45) = 3.88, p < .Ol) and of Sessions (F(1,45) = 45.29, p < .Ol). Subsequent tests of the simple effects of the groups variable showed that although the groups differed in number of errors for Session 1 (F(4,45) = 11.16, p < .Ol), there was no significant difference for Session 2. A Newman-Keuls analysis showed that for Session 1, the two retardate samples made more errors than did the three normal samples (CY= .Ol). The dependent variable of primary interest was correct reaction time and not number of errors, but it was felt important that the different samples be equal in terms of error rate so that differences in reaction time could not be attributed to error differences. Thus, correct reaction time analyses below considered the data from Session 2 only.3 The median reaction time for correct responses was computed separately
11.5 4.0 3.0 1.5
8.5 4.0 3.0 2.5
MA) CA)
Retardate encephalopathies Normal third grade (equal Normal high school (equal Normal adult
8.5
2
10.5
cultural
1
familials
Retardate
.~
Session 3
14.0 5.0 3.5 4.5
11.9 11.9 4.5 3.3 3.0
13.5 5.0 3.5 3.5
All
16.5
4
TABLE 2 OF ERRONEOUS 1 set size
12.0
PERCENTAGE
1
4.5 2. 0 2.0 2.5
3.0
RESPONSICS
.5 5 :i 5 3 .5 5.0
2.0 5.0
5.5
3
2 set, size
6.0 3.0
5 0
2
Session
3.0 4.0
6.0 4.5
10.0
4
2.6 4.1
0- .5 3 8
5.9
All
3 !s #
$ u
ti
MEMORY
SCANNING
IN
SET
FIG. 1. Combined reaction size. A. Normal-adult (RT MR-CF (RT = 422 + 66s). Grd. (RT = 688 + 428).
time for “yes” = 306 + 418). D. MR-Enceph.
457
RETARDATES
SIZE (9
and “no” responses as a function of set B. Normal-HS. (RT = 395 + 42s). C. (RT = 563 + 1115). E. Normal-3rd
for “yes” and “no” responses at each set size for each S. Although “no” responses were consistently longer than “yes” responses (F( 1,45) = 29.48, p < .Ol), this effect did not interact with groups or set size.4 The lack of any interaction between the “yes”-%o” and Set Size variables indicates that the “yes” and “no” functions for each group were parallel. Since the data yielded linear functions as well, the slopes of the “yes” and “no” functions for any one group were equal. Thus, each S’s “yes” and [‘no” responses were combined and the median at each set size was computed. The equation of the best fitting straight line for each S was determined as were the equations of the mean data for each group which is shown in Fig. 1. The group equations accounted for more than 98% of the total variance of the combined data for each group. An analysis of variance was performed on the slopes of the best fitting functions for each S. The results showed a significant difference between groups (F(4,45) = 10.13, p < .Ol). A subsequent Newman-Keuls analysis showed that the mean slopes for the three normal samples were significantly smaller than those of the two retardate samples and also that the ‘Subsequent analysis of Session 1 reaction time data yielded ences from that of Session 2. *Sternberg (1969) has pointed out that the serial exhaustive predicts equal slopes for “yes” and “no” functions but makes their relative intercepts.
no important scanning model no predictions
differonly as to
458
HARRIS
AND
FLEER
encephalopathy sample yielded a significantly steeper slope than did the cultural familials (N = .Ol). An analysis of variance on the intercepts of the individual functions also showed a significant difference between groups (F(4,45) = 12.99, p < .Ol) as can be seen in Fig. 1. A Newman-Keuls analysis (N = .Ol) showed that the third-grade sample had the largest intercept. In addition, the intercept of the encephalopathy sample was significantly larger than the remaining three sample intercepts and, finally, the adult normals yielded a smaller intercept than that of both the retardate cultural familials and the high-school normals, the latter two not differing from each other. Analysis of the effect of serial position of the test item on reaction time did not show any differences for any of the five groups.
The results indicate that the same information processing model which is supported by the data of the normal ‘3s also fits that of the retardates. The parallel linearity of the “yes” and ‘Lno” functions relating set size to reaction time and also the lack of serial-position effects on reaction time for all five samples in the present study provided support for Sternberg’s (1966) serial-exhaustive high speed scanning model in normal subjects as well as extending it to two diagnostic classifications of retardates. This suggests that, at least for the memory recognition task reported, retardates process information in the same qualitative manner as do normals. However, differences in the magnitudes of the slopes and the intercepts of the best fitting straight-line functions between retardates and normals indicated that the retardates were less efficient than normals in the central processing (i.e., memory scanning) aspects of the task. The slopes of the three normal groups did not differ from each other although the mean age of these groups varied from 8-24 years. Thus, the steeper slopes or slower memory scanning rate of the retardate samples cannot be interpreted as a developmental decrement but rather some kind of permanent deficiency in central processing can be hypothesized. The even steeper slope of the encephalopathy sample compared with that of the cultural familials indicates that brain damage, or at least the diagnosis of it, is positively correlated with the amount of this central processing deficit. Not unexpectedly, the three normal samples show a trend of decreasing intercepts with age indicating that throughout t,he age range sampled, the speed of peripheral processing (i.e., perception and response) increases. The cultural familials showed the same intercept value as did the CA control group, which amplifies the finding that the locus of the performance difference between retardates and normals is in the central processing aspects of the task. That the encephalopathy sample was slower in inter-
MEMORY
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cept time than both the cultural familials and the CA controls and almost as slow as the MA controls indicates that peripheral processing deficiency, as well as central processing deficiency, is positively related to the diagnosis of organicity in mental retardates. The retardate deficiency in memory scanning rate obtained in the present study is compatible with two recently presented empirical relationships. Spitz (1973)) in a review of the retardate memory literature, showed that the memory span or channel capacity for educable retardates is about 3-4 items rather than the 5-7 items found with normals (Miller, 1956; Spitz, 1972). Cavanagh (1972) has found a strong reciprocal relationship between central processing rate in memory scanning experiments and memory span capacity across widely varying types of stimulus materials with normal subjects. For example, memory scanning tasks using digits have yielded processing rates of about 35 msec per item. Subjects in memory span studies using digits have recalled about 7.7 items. On the other hand, when geometrical shapes have been employed as stimuli, processing rates have been about 50 msec per item while memory span capacity has been about 5.3 items. This finding, that slower scanning rate (clearly a central process) and decreased memory span capacity are correlated, supports the notion that short-term memory performance deficits in educable mental retardates, commonly found in memory span tasks, are central rather than peripheral. REFERENCES
ANDERS, T. R., FOZARD,J. L., & LILLYQUIST, T. D. The effects of age upon retrival from short-term memory. Developmental Psychology, 1972, 6, 214-217. CAVANAGH, J. P. Relation between the immediate memory span and the memory search rate. Psychological Review, 1972, 6,525-530. HOVIN~, K. L., MORIN, R. E., & KONICK, D. S. Recognition reaction time and size of the memory set: a developmental study. Psychonomic Science, 1970, 21, 247-248.
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SPITZ, H. H. Note on immediate memory for digits: invariance over the years. Psychological Bulletin, 1972, 78, 183-185. SPITZ, H. H. The channel capacity of educable mental retardates. In D. K. Routh (Ed.), The Experimental psychology of mental retardation. Chicago: Aldine, 1973. Pp. 133-156. STERNBERG,S. High-speed scanning in human memory. Science, 1966, 153, 652-654. STERNBERG,S. The discovery of stages: extensions of Donders’ method. Acta Psychologica,
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