- Email: [email protected]
Presentation rate and the serial-position effect of immediate serial recall
JOURNAL
OF VERBAL
LEARNING
Presentation
AND
Rate
VERBAL
BEHAVIOR
7, 608-612 (1968)
and the Serial-Position Serial Recall1
Effect
of Immediate
JOHN C. JAHNKE Miami University, Oxford, Ohio 45056 This study examined the effects of rate of presentation on the serial organization of lists of words near and beyond span-length. The Ss were instructed for the serial (ordered) recall of the lists. Recall was better at slower rates of presentation, but the improvement in recall at the slower rates did not extend to terminal items of a list. Slower rates were found to increase the size of the initial span and to facilitate the ordering of items in recall as requested. Emphasis was placed on both order of presentation and order of recall as determiners of serialposition effects.
Murdock (1962) and Glanzer and Cunitz (1966; Exp. I) have examined the effects of presentation rate on the serial-position effect of immediate free recall. In these studies lists of 20 words were presented at rates ranging from l-9 set/word. Recency was stronger than primacy, and slower rates were found to improve recall of all items but the last few of a list. Posner (1964) examined the effects of presentation rate on immediate memory when constraint was placed upon the order of recall. In his study lists of 8 digits were presented at rates of .625 and 2 set/digit, and order of recall was controlled by instructing Ss for reversed recall (items recalled in order 5-8 followed by 14) and serial recall (items to be ordered in recall as in presentation). Overall performance and the serial-position effect were relatively uninfluenced by rate when recall was in reversed order. Overall performance was better at the faster rate when recall
was in serial order, and the faster rate appeared to benefit the recall of all items but the last one. Posner (1964) suggested that faster rates are likely to facilitate recall when items are recalled in the order in which they are presented, although this finding may be restricted to materials which are easily encoded (see Posner, 1963, pp. 334-335). The present study seeks to provide further information on the effects of presentation rate on the serial organization of short-term memory. An attempt is made to examine the influence of rate on the immediate recall of lists of words both near and beyond spanlength when order of recall is constrained to the order of presentation.
METHOD Subjects. The Ss were 48 male students enrolled in the introductory psychology course at Miami University. Participation in experiments was in partial fulfillment of course requirements. None of the .Sshad participated in experiments on memory in which the * This research was supported by Public Healrh stimuli were lists of words. Service Grant MH 12343-01 from the National Materials and Procedure. The materials and proInstitute of Mental Health. Preparation of the report cedure were similar to those of an earlier study (Jahnke, was facilitated by Contract 33(615)-2224 with the 1965). In both that and the present study, Ss were Aerospace Medical Laboratories, Engineering Psy- presented lists of 6, 10, and 15 words for immediate chology Research, Wright-Patterson Air Force Base, recall. In the present study Ss were given five, rather Ohio. Appreciation is gratefully expressed to James H. than four, lists at each of the three lengths of list, and Davis and Ronald A. Hoppe, who read critically earlier there was a total of 12 different orders of presentation drafts of this paper and to Gary Schneider, who of the lists. In each block of three successive trials collected the data and contributed to their analysis. (lists) Ss received one list of each of the three lengths. 608
609
PRESENTATION RATE AND RECALL Each length of list occurred equally frequently at each stage of practice. The words of the lists were of Thorndike-Lorge (1944) frequency of4549 per million in order to keep the average word-frequencies of the different lists essentially constant. The Ss were assigned at random to one of four conditions of rate of presentation (l/2, 1,2, and 4 secjitem), except for the restriction that N = 12 in each of the four conditions. The stimulus lists were presented by a memory drum. As each word appeared in the drum, it was spoken aloud by S. Asterisks marked the beginning and end of each list. The Ss were given explicit instructions for serial recall, including an illustrative example which used digits as the to-be-remembered materials. Recalls were given orally to E, who recorded the items in the order in which they were recalled. The Ss were instructed to say “blank” to indicate omitted words. Recall was accomplished during an intertrial interval of approximately 45 sec.
p < .05, respectively. Corresponding values for the items-recalled measure were also significant, F(3,44) = 5.57, p < .Ol ; F(2,88) = 8.98, p < .Ol; and F(6, 88) = 3.78, pc .Ol, respectively. The interaction term of the first analysis may be interpreted as showing that percentage recalled drops more slowly with increases in list-length at the slower rates than at the faster rates. The corresponding term of the second analysis shows, as noted above, the decrease in number of items recalled as listlength increased for all but the 4-set conditions. Serial-position curves for each experimental condition are shown in Fig. 1. For the 6- and IO-word conditions, shown in the two upper panels of Fig. 1, primacy effects were greater than those of recency at all presentation rates. For the 15-word conditions, primacy was also greater than recency for the slow (2- and 4-set) rate conditions, although bowing was much diminished for the 4-set condition. For the fast (l/2- and 1-set) rate conditions, on the other hand, primacy effects were much reduced at this list-length and were weaker than those of recency. All panels of Fig. 1 show that the effect of a slower rate was primarily to improve recall of items early in the list. Such a finding hints that, at the slower rates, Ss were able to recall a larger number of initial items consecutively without error. To check on this possibility, initial and terminal spans were computed for each condition. Initial and terminal spans were defined, as by Waugh (1960), as the mean number of items recalled before the first failure to recall from the beginning, or the end, of a series, respectively,
RESULTS
Mean percentage of recall and mean number of items recalled are shown in Table 1 for each experimental condition. For the present analysis, an item was scored correct regardless of whether or not it was given in proper serial position. Table 1 shows that mean percentage of recall increased as presentation rate and list-length decreased. These relations held also for mean number of items recalled, except for the 4-set rate conditions, for which performance increased as list-length increased. Analyses of variance of the data from which this table was derived were computed separately for each of the two response measures. For the percentage-recalled measure, the effects of rate, list-length, and their interaction were significant, F(3, 44) = 4.16, p < .05 ; F(2,88) = 669.46,~ < .Ol;andF(6,88) = 2.46, TABLE MEAN
PERCENTAGE
RECALLED
6-Word lists
M% MX 21
1
AND MEAN
NUMBER
OF ITEMS RECALLED
IO-Word lists
15-Word lists
l/2
1
2
4
l/2
1
2
4
l/2
1
2
4
80.83 4.85
80.00 4.80
85.28 5.12
83.89 5.03
41.67 4.17
41.83 4.18
46.67 4.67
52.17 5.22
22.67 3 40
27.00 4.05
27.89 4.18
37.11 5.57
610
JAHNKE
‘100 r .d
ioor
, 12
Y stt:
1
.5
SEC
5 a.
. . . . . . . . . . . 1.0
SEC
I !i
-----
2.0
SEC
-v-*-e
4.0
SEC
12
3
4
5
6
7 SERIAL
FIG.
1. Serial-position
8
9
, 3
10
11
, 5
12
1 6
13
I 7
14
I 8
I 9
, 10
15
POSITION
curves for each experimental
except in those instances in which all items of a list were recalled. In such cases, half the items were assigned to the initial span and half to the terminal span. (All such instances but one occurred in the 6-word conditions.) The mean lengths of these spans are shown in Table 2. The data for each of the list-length conditions show a regular increase in the length of the initial span as rate decreases. There is a somewhat less marked and less regular tendency for the length of the terminal span to decrease as rate decreases. Table 2 also shows that initial and terminal spans decrease as list-length increases. Analyses of variance of the data on which Table 2 is based were performed separately for each list-length condition. These analyses
I 4
condition.
showed that, for the 6-word conditions, initial spans were significantly longer than terminal spans, F(1, 44) = 85.59, p -C .Ol. Neither the effect of rate nor its interaction with span were significant, F < 1 and F(3,44) 7 1.32, respectively, p > .05. For the lo-word conditions also, initial spans were longer than terminal spans, F( 1, 44) = 10.63, p < .Ol, and performance was better at the slower rates, F(3, 44) = 5.63, p -C .Ol. The interaction between rate and span was significant: initial spans increased with decreases in presentation rate, while terminal spans remained essentially constant at all rates, F(3, 44) = 6.10, p -c .Ol. For the 15-word conditions, there was no significant main effect of span, F-C 1. Again performance was better at the slower rates,
PRESENTATION
RATE
F(3,44) = 3.47, p < .05, and again there was a
significant interaction: initial spans increased and terminal spans decreased as rate decreased, F(3,44) = 20.24, p < .Ol. These analyses show that the size of the initial span increases regularly as presentation rate decreases and support the conjecture that variations in rate allow S to distribute his rehearsal in different ways at different rates. In the present instance, it may be presumed that rehearsal of initial items is more effective at the slower rates (cf. Cooper and Pantle, 1967). Order of Recall. It was a major intent of the
present study to observe the effects of pre-
AND
611
RECALL
consistently able to initiate recall with items from the beginning of the list. Present data do not indicate whether Ss were unwilling or were unable to begin recall uniformly with first items. The fact that Ss did begin recall as requested except for the longer lists at the faster rates provides some evidence that the latter supposition is correct. Further, Wickelgren (1965) has shown retroactive inhibition of the short-term recall of a target set of consonants which was followed by an interpolated set of acoustically similar consonants. The possibility suggests itself that the inability of Ss to begin recall with initial items in the present study is a retroactive effect induced by
TABLE 2 INITIAL AND TERMINAL SPANS FOR EACHEXPERIMENTAL CONDITION
lo-Word lists
6-Word lists
l/2 set 1 set 2sec 4 set
15-Word lists
Initial span
Terminal span
Initial span
Terminal span
Initial span
Terminal span
2.77 2.90 3.12 3.25
1.90 1.75 1.73 1.68
1.08 1.15 2.05 2.38
1.27 1.25 1.03 P.28
.40 .57 1.17 2.10
1.45 1.08 .63 .73
sentation rate when order of recall was constrained to the order of presentation. To gather information on the degree to which this constraint was effected, counts were made for each experimental condition separately of the number of times (out of a total of 60 possible) that Ss began their recalls with initial items of a string (Item 1, Item 2, or an extralist intrusion followed by either Item 1 or Item 2). For the four rate conditions, given in order of decreasing rate, these frequencies were 60, 58, 60, and 60, for the 6-word conditions. Corresponding frequencies for the lo-word conditions were 42, 40, 52, and 51; for the 15-word conditions, 18, 23, 43, and 51. These data show that, except for the shortest lists, only at the two slower rates were Ss rather
subsequent items in the longer lists and that, for this reason, Ss were unable to recall as requested. In any event, it may be noted that present methods were not completely successful in constraining uniformly the order in which items were actually recalled. Simply to instruct Ss for the immediate serial recall of word lists may be rather ineffective in this regard. DISCUSSION
The present results have several implications. First, it will be remembered that the association of faster rates with better ordered recall (Posner, 1964) was not found here. Ordered recall may be a necessary, but not sufficient, condition for the facilitation of
612
JAHNKE
recall by faster rates of presentation. Second, the present findings taken in conjunction with those of Deese (1957), Murdock (1963), and Tulving and Arbuckle (1963, 1966), indicate that order of recall may have a substantial influence on trace-strength and, therefore, on both the level of short-term recall and on which items are recalled. Future studies of serialposition effects should benefit to the degree that they are able to constrain order of recall. Methods such as those of partial recall (e.g., Anderson, 1960) and recognition memory (e.g., Wickelgren and Norman, 1966) may afford greater control of order of recall and, therefore, of the contribution of this variable to the over-all serial-position effect. Third, the present results suggest generally the difficulties of assessing, or controlling, order of recall-regardless of the kind of recall procedure utilized. For example, it is unlikely that when Ss are given the opportunity to recall items in any order they wish, they will all do so in the same order under all conditions and at all stages of practice (cf. Postman and Phillips, 1965). Studies of serial-position effects of free recall, therefore, may suffer a confounding owing to the uncontrolled effects of order of recall. For such reasons, some caution in the interpretation of studies in which order of recall is unknown or uncontrolled is warranted until the seriousness of such confounding is known. Recall of items of a series seems to be a function of order of presentation and order of recall, both of which differentially determine retention intervals for individual items and also afford differential opportunities for the operation of retroactive and proactive interference. Fourth, it will be remembered that Ss appeared to be unable to order as requested their recalls of the longer lists, particularly at the faster rates. If so, there is reason to suggest that trace-strength deter-
mines, as well as is determined by, order of recall. REFERENCES ANDERSON, N. S. Poststimulus cuing in immediate memory. J. exp. Psychol., 1960,60,216-221. COOPER,E. H., AND PANTLE, A. J. The total-time hypothesis in verbal learning. Psychof. Bull., 1967, 68, 221-234. DEESE, J. Serial organization in the recall of disconnected items. Psychol. Rep., 1957,3, 577-587. GLANZER, M., AND Cur~rrz, A. Two storage mechanisms in free recall. J. oerb. Learn. verb. Behav., 1966,5,351-360. JAHNKE, J. C. Supplementary report: Primacy and recency effects in serial-position curves of immediate recal1.J. exp. PsychoI., 1965,70,130-132. MURDOCK, B. B. JR. The serial-position effect of free recall. J. exp. Psychol., 1962,64,482-488. MURDOCK, B. B., JR. Interpolated recall in short-term memory. J. exp. Psychol., 1963,66,525-532. POSNER,M. I. Immediate memory in sequential tasks. Psychol. Bull., 1963,60,333-349. POSNER,M. I. Rate of presentation and order of recall in immediate memory. Brit. J. Psycho& 1964,55, 303-306. POSTMAN,L., AND PHILLIPS, L. W. Short-term temporal changes in free recall. Quart. J. exp. Psychol., 1965,17,132-138. THORNDIKE, E. L., AND LORGE, I. The teacher’s word book of 30,000 words. New York: Bureau of Publications, Teachers College, Columbia University, 1944. TULVING, E., AND ARBUCKLE, T. Y. Sources of intratrial interference in immediate recall of paired associates. J. verb. Learn. verb. Behuv., 1963, 1, 321-334. TULVING, E., AND ARBUCKLE, T. Y. Input and output interference in short-term associative memory. J. exp. Psychol., 1966,72,145-l 50. WAUGH, N. C. Serial position and memory-span. Amer. J. Psychof., 1960,73,68-79. WICKELGREN, W. A., AND NORMAN, D. A. Strength models and serial position in short-term memory. J. math. Psychol., 1966,3,316-347. WICKELGREN,W. A. Acousticsimilarityand retroactive interference in short-term memory. J. verb. Leurn. verb. Behuv., 1965,4,53-61. (Received May 15,1967)
OF VERBAL
LEARNING
Presentation
AND
Rate
VERBAL
BEHAVIOR
7, 608-612 (1968)
and the Serial-Position Serial Recall1
Effect
of Immediate
JOHN C. JAHNKE Miami University, Oxford, Ohio 45056 This study examined the effects of rate of presentation on the serial organization of lists of words near and beyond span-length. The Ss were instructed for the serial (ordered) recall of the lists. Recall was better at slower rates of presentation, but the improvement in recall at the slower rates did not extend to terminal items of a list. Slower rates were found to increase the size of the initial span and to facilitate the ordering of items in recall as requested. Emphasis was placed on both order of presentation and order of recall as determiners of serialposition effects.
Murdock (1962) and Glanzer and Cunitz (1966; Exp. I) have examined the effects of presentation rate on the serial-position effect of immediate free recall. In these studies lists of 20 words were presented at rates ranging from l-9 set/word. Recency was stronger than primacy, and slower rates were found to improve recall of all items but the last few of a list. Posner (1964) examined the effects of presentation rate on immediate memory when constraint was placed upon the order of recall. In his study lists of 8 digits were presented at rates of .625 and 2 set/digit, and order of recall was controlled by instructing Ss for reversed recall (items recalled in order 5-8 followed by 14) and serial recall (items to be ordered in recall as in presentation). Overall performance and the serial-position effect were relatively uninfluenced by rate when recall was in reversed order. Overall performance was better at the faster rate when recall
was in serial order, and the faster rate appeared to benefit the recall of all items but the last one. Posner (1964) suggested that faster rates are likely to facilitate recall when items are recalled in the order in which they are presented, although this finding may be restricted to materials which are easily encoded (see Posner, 1963, pp. 334-335). The present study seeks to provide further information on the effects of presentation rate on the serial organization of short-term memory. An attempt is made to examine the influence of rate on the immediate recall of lists of words both near and beyond spanlength when order of recall is constrained to the order of presentation.
METHOD Subjects. The Ss were 48 male students enrolled in the introductory psychology course at Miami University. Participation in experiments was in partial fulfillment of course requirements. None of the .Sshad participated in experiments on memory in which the * This research was supported by Public Healrh stimuli were lists of words. Service Grant MH 12343-01 from the National Materials and Procedure. The materials and proInstitute of Mental Health. Preparation of the report cedure were similar to those of an earlier study (Jahnke, was facilitated by Contract 33(615)-2224 with the 1965). In both that and the present study, Ss were Aerospace Medical Laboratories, Engineering Psy- presented lists of 6, 10, and 15 words for immediate chology Research, Wright-Patterson Air Force Base, recall. In the present study Ss were given five, rather Ohio. Appreciation is gratefully expressed to James H. than four, lists at each of the three lengths of list, and Davis and Ronald A. Hoppe, who read critically earlier there was a total of 12 different orders of presentation drafts of this paper and to Gary Schneider, who of the lists. In each block of three successive trials collected the data and contributed to their analysis. (lists) Ss received one list of each of the three lengths. 608
609
PRESENTATION RATE AND RECALL Each length of list occurred equally frequently at each stage of practice. The words of the lists were of Thorndike-Lorge (1944) frequency of4549 per million in order to keep the average word-frequencies of the different lists essentially constant. The Ss were assigned at random to one of four conditions of rate of presentation (l/2, 1,2, and 4 secjitem), except for the restriction that N = 12 in each of the four conditions. The stimulus lists were presented by a memory drum. As each word appeared in the drum, it was spoken aloud by S. Asterisks marked the beginning and end of each list. The Ss were given explicit instructions for serial recall, including an illustrative example which used digits as the to-be-remembered materials. Recalls were given orally to E, who recorded the items in the order in which they were recalled. The Ss were instructed to say “blank” to indicate omitted words. Recall was accomplished during an intertrial interval of approximately 45 sec.
p < .05, respectively. Corresponding values for the items-recalled measure were also significant, F(3,44) = 5.57, p < .Ol ; F(2,88) = 8.98, p < .Ol; and F(6, 88) = 3.78, pc .Ol, respectively. The interaction term of the first analysis may be interpreted as showing that percentage recalled drops more slowly with increases in list-length at the slower rates than at the faster rates. The corresponding term of the second analysis shows, as noted above, the decrease in number of items recalled as listlength increased for all but the 4-set conditions. Serial-position curves for each experimental condition are shown in Fig. 1. For the 6- and IO-word conditions, shown in the two upper panels of Fig. 1, primacy effects were greater than those of recency at all presentation rates. For the 15-word conditions, primacy was also greater than recency for the slow (2- and 4-set) rate conditions, although bowing was much diminished for the 4-set condition. For the fast (l/2- and 1-set) rate conditions, on the other hand, primacy effects were much reduced at this list-length and were weaker than those of recency. All panels of Fig. 1 show that the effect of a slower rate was primarily to improve recall of items early in the list. Such a finding hints that, at the slower rates, Ss were able to recall a larger number of initial items consecutively without error. To check on this possibility, initial and terminal spans were computed for each condition. Initial and terminal spans were defined, as by Waugh (1960), as the mean number of items recalled before the first failure to recall from the beginning, or the end, of a series, respectively,
RESULTS
Mean percentage of recall and mean number of items recalled are shown in Table 1 for each experimental condition. For the present analysis, an item was scored correct regardless of whether or not it was given in proper serial position. Table 1 shows that mean percentage of recall increased as presentation rate and list-length decreased. These relations held also for mean number of items recalled, except for the 4-set rate conditions, for which performance increased as list-length increased. Analyses of variance of the data from which this table was derived were computed separately for each of the two response measures. For the percentage-recalled measure, the effects of rate, list-length, and their interaction were significant, F(3, 44) = 4.16, p < .05 ; F(2,88) = 669.46,~ < .Ol;andF(6,88) = 2.46, TABLE MEAN
PERCENTAGE
RECALLED
6-Word lists
M% MX 21
1
AND MEAN
NUMBER
OF ITEMS RECALLED
IO-Word lists
15-Word lists
l/2
1
2
4
l/2
1
2
4
l/2
1
2
4
80.83 4.85
80.00 4.80
85.28 5.12
83.89 5.03
41.67 4.17
41.83 4.18
46.67 4.67
52.17 5.22
22.67 3 40
27.00 4.05
27.89 4.18
37.11 5.57
610
JAHNKE
‘100 r .d
ioor
, 12
Y stt:
1
.5
SEC
5 a.
. . . . . . . . . . . 1.0
SEC
I !i
-----
2.0
SEC
-v-*-e
4.0
SEC
12
3
4
5
6
7 SERIAL
FIG.
1. Serial-position
8
9
, 3
10
11
, 5
12
1 6
13
I 7
14
I 8
I 9
, 10
15
POSITION
curves for each experimental
except in those instances in which all items of a list were recalled. In such cases, half the items were assigned to the initial span and half to the terminal span. (All such instances but one occurred in the 6-word conditions.) The mean lengths of these spans are shown in Table 2. The data for each of the list-length conditions show a regular increase in the length of the initial span as rate decreases. There is a somewhat less marked and less regular tendency for the length of the terminal span to decrease as rate decreases. Table 2 also shows that initial and terminal spans decrease as list-length increases. Analyses of variance of the data on which Table 2 is based were performed separately for each list-length condition. These analyses
I 4
condition.
showed that, for the 6-word conditions, initial spans were significantly longer than terminal spans, F(1, 44) = 85.59, p -C .Ol. Neither the effect of rate nor its interaction with span were significant, F < 1 and F(3,44) 7 1.32, respectively, p > .05. For the lo-word conditions also, initial spans were longer than terminal spans, F( 1, 44) = 10.63, p < .Ol, and performance was better at the slower rates, F(3, 44) = 5.63, p -C .Ol. The interaction between rate and span was significant: initial spans increased with decreases in presentation rate, while terminal spans remained essentially constant at all rates, F(3, 44) = 6.10, p -c .Ol. For the 15-word conditions, there was no significant main effect of span, F-C 1. Again performance was better at the slower rates,
PRESENTATION
RATE
F(3,44) = 3.47, p < .05, and again there was a
significant interaction: initial spans increased and terminal spans decreased as rate decreased, F(3,44) = 20.24, p < .Ol. These analyses show that the size of the initial span increases regularly as presentation rate decreases and support the conjecture that variations in rate allow S to distribute his rehearsal in different ways at different rates. In the present instance, it may be presumed that rehearsal of initial items is more effective at the slower rates (cf. Cooper and Pantle, 1967). Order of Recall. It was a major intent of the
present study to observe the effects of pre-
AND
611
RECALL
consistently able to initiate recall with items from the beginning of the list. Present data do not indicate whether Ss were unwilling or were unable to begin recall uniformly with first items. The fact that Ss did begin recall as requested except for the longer lists at the faster rates provides some evidence that the latter supposition is correct. Further, Wickelgren (1965) has shown retroactive inhibition of the short-term recall of a target set of consonants which was followed by an interpolated set of acoustically similar consonants. The possibility suggests itself that the inability of Ss to begin recall with initial items in the present study is a retroactive effect induced by
TABLE 2 INITIAL AND TERMINAL SPANS FOR EACHEXPERIMENTAL CONDITION
lo-Word lists
6-Word lists
l/2 set 1 set 2sec 4 set
15-Word lists
Initial span
Terminal span
Initial span
Terminal span
Initial span
Terminal span
2.77 2.90 3.12 3.25
1.90 1.75 1.73 1.68
1.08 1.15 2.05 2.38
1.27 1.25 1.03 P.28
.40 .57 1.17 2.10
1.45 1.08 .63 .73
sentation rate when order of recall was constrained to the order of presentation. To gather information on the degree to which this constraint was effected, counts were made for each experimental condition separately of the number of times (out of a total of 60 possible) that Ss began their recalls with initial items of a string (Item 1, Item 2, or an extralist intrusion followed by either Item 1 or Item 2). For the four rate conditions, given in order of decreasing rate, these frequencies were 60, 58, 60, and 60, for the 6-word conditions. Corresponding frequencies for the lo-word conditions were 42, 40, 52, and 51; for the 15-word conditions, 18, 23, 43, and 51. These data show that, except for the shortest lists, only at the two slower rates were Ss rather
subsequent items in the longer lists and that, for this reason, Ss were unable to recall as requested. In any event, it may be noted that present methods were not completely successful in constraining uniformly the order in which items were actually recalled. Simply to instruct Ss for the immediate serial recall of word lists may be rather ineffective in this regard. DISCUSSION
The present results have several implications. First, it will be remembered that the association of faster rates with better ordered recall (Posner, 1964) was not found here. Ordered recall may be a necessary, but not sufficient, condition for the facilitation of
612
JAHNKE
recall by faster rates of presentation. Second, the present findings taken in conjunction with those of Deese (1957), Murdock (1963), and Tulving and Arbuckle (1963, 1966), indicate that order of recall may have a substantial influence on trace-strength and, therefore, on both the level of short-term recall and on which items are recalled. Future studies of serialposition effects should benefit to the degree that they are able to constrain order of recall. Methods such as those of partial recall (e.g., Anderson, 1960) and recognition memory (e.g., Wickelgren and Norman, 1966) may afford greater control of order of recall and, therefore, of the contribution of this variable to the over-all serial-position effect. Third, the present results suggest generally the difficulties of assessing, or controlling, order of recall-regardless of the kind of recall procedure utilized. For example, it is unlikely that when Ss are given the opportunity to recall items in any order they wish, they will all do so in the same order under all conditions and at all stages of practice (cf. Postman and Phillips, 1965). Studies of serial-position effects of free recall, therefore, may suffer a confounding owing to the uncontrolled effects of order of recall. For such reasons, some caution in the interpretation of studies in which order of recall is unknown or uncontrolled is warranted until the seriousness of such confounding is known. Recall of items of a series seems to be a function of order of presentation and order of recall, both of which differentially determine retention intervals for individual items and also afford differential opportunities for the operation of retroactive and proactive interference. Fourth, it will be remembered that Ss appeared to be unable to order as requested their recalls of the longer lists, particularly at the faster rates. If so, there is reason to suggest that trace-strength deter-
mines, as well as is determined by, order of recall. REFERENCES ANDERSON, N. S. Poststimulus cuing in immediate memory. J. exp. Psychol., 1960,60,216-221. COOPER,E. H., AND PANTLE, A. J. The total-time hypothesis in verbal learning. Psychof. Bull., 1967, 68, 221-234. DEESE, J. Serial organization in the recall of disconnected items. Psychol. Rep., 1957,3, 577-587. GLANZER, M., AND Cur~rrz, A. Two storage mechanisms in free recall. J. oerb. Learn. verb. Behav., 1966,5,351-360. JAHNKE, J. C. Supplementary report: Primacy and recency effects in serial-position curves of immediate recal1.J. exp. PsychoI., 1965,70,130-132. MURDOCK, B. B. JR. The serial-position effect of free recall. J. exp. Psychol., 1962,64,482-488. MURDOCK, B. B., JR. Interpolated recall in short-term memory. J. exp. Psychol., 1963,66,525-532. POSNER,M. I. Immediate memory in sequential tasks. Psychol. Bull., 1963,60,333-349. POSNER,M. I. Rate of presentation and order of recall in immediate memory. Brit. J. Psycho& 1964,55, 303-306. POSTMAN,L., AND PHILLIPS, L. W. Short-term temporal changes in free recall. Quart. J. exp. Psychol., 1965,17,132-138. THORNDIKE, E. L., AND LORGE, I. The teacher’s word book of 30,000 words. New York: Bureau of Publications, Teachers College, Columbia University, 1944. TULVING, E., AND ARBUCKLE, T. Y. Sources of intratrial interference in immediate recall of paired associates. J. verb. Learn. verb. Behuv., 1963, 1, 321-334. TULVING, E., AND ARBUCKLE, T. Y. Input and output interference in short-term associative memory. J. exp. Psychol., 1966,72,145-l 50. WAUGH, N. C. Serial position and memory-span. Amer. J. Psychof., 1960,73,68-79. WICKELGREN, W. A., AND NORMAN, D. A. Strength models and serial position in short-term memory. J. math. Psychol., 1966,3,316-347. WICKELGREN,W. A. Acousticsimilarityand retroactive interference in short-term memory. J. verb. Leurn. verb. Behuv., 1965,4,53-61. (Received May 15,1967)