Pattern coding of spatial order information in short-term memory

JOURNAL OF VERBAL LEARNING AND VERBAL BEHAVIOR 16, 419-437 (1977)

Pattern Coding of Spatial Order Information in Short-Term Memory ALICE F. HEALY

Yale University and Haskins Laboratories

Three experiments were conducted to extend the finding that, whereas phonemic coding is employed for short-term temporal order recall, coding of temporal-spatial patterns is employed for short-term spatial order recall. In Experiment 1 subjects employed pattern coding for spatial order information even though item information had to be retained as well as spatial order information. In Experiment 2 temporal and spatial order recall were differentially affected by various interpolated tasks; temporal order recall was disrupted by tasks demanding vocalization, whereas spatial order recall was disrupted by tasks demanding processing of spatial information. In Experiment 3 a change in the method of response led subjects to employ pattern coding for temporal order recall without eliminating phonemic coding. Phonemic coding is such a ubiquitous strategy in short-term memory that numerous early researchers (for example, Atkinson & Shriffrin, 1968; Sperling & Speelman, 1970) implied that human adults are limited to phonemic coding for representing information in short-term memory even when the information is presented visually. More recently, a number of researchers have found evidence that adults do not always employ phonemic coding in short-term memory. These more recent studies can be divided into two groups: (a) In one set of studies the evidence for or against phonemic coding comes either from analyses of substitution errors involving phonemically similar items (the Experiment 1 was conducted at the Mathematical Psychology Laboratory of The Rockefeller University, supported in part by PHS Grants Nos. GM 1789 and GM16735. Experiments 2 and 3 were conducted at Yale University, supported in part by PHS Grants Nos. MH26573 and RR07015 to Yale University and NICHD Grant No. HD01994 to Haskins Laboratories. The author is indebted to The Rockefeller University for lending the display apparatus employed for all three experiments, to M. Guyote for helping to conduct Experiments 2 and 3, and to R. Crowder and J. Neely for commenting on earlier versions of this paper. The author also thanks Professor W. K. Estes for helpful comments and suggestions at numerous phases of this research. Copyright © 1977 by Academic Press, Inc. All rights of reproduction in any form reserved. Printed in Great Britain

"confusion effect," Crowder, Note 1) or from comparisons of recall levels between lists o f phonemically similar items and lists of dissimilar items (the "similarity decrement," Crowder, Note 1). In all such studies the present author could find, evidence for alternative coding strategies is provided only for those cases when the subjects neither heard nor articulated the to-be-remembered items. For example, Estes (1973) and Peterson and Johnson (1971) found evidence for alternative coding strategies when they prevented subjects from articulating the names of visually presented to-be-remembered items. Similarly, Conrad (1970) found evidence for alternative coding strategies in a group of deaf subjects for whom earlier studies had shown that forced articulation of the to-be-remembered items depressed recall. (b) The second set of studies provides evidence for alternative coding strategies in the form of differential effects of distractor tasks on different sets of to-be-remembered items. It should be noted that finding such differential effects may suggest that a phonemic coding strategy is employed for one set of items but not for another set; however, such a finding would not necessarily preclude the less interesting possibility that a phonemic coding strategy is 419

ISSN 0o22-5371

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employed for both sets of items but is coupled with different additional strategies for the different sets. In any event, in all such studies the present author could find, different coding strategies were found for different sets of items only when either items presented in different modalities were compared or verbal items were compared to nonverbal items. For example, Sanders and Schroots (1969), den Heyer and Barrett (1971), Meudell (1972), and Salthouse (1974, 1975) found evidence for different types of coding of characters (letters or digits) and spatial positions; Pelligrino, Siegel, and Dhawan (1976) reported different types of coding of pictures and words; Deutsch (1970) reported differential coding of tones and numbers; Margrain (1967), Kroll, Parks, Parkinson, Bieber, and Johnson (1970), Tell (1971), and Elliott and Strawhorn (1976) provided evidence for different types of coding of auditorily and visually presented items; and Brooks (1968) showed that visually presented line diagrams are coded differently from auditorily presented sentences. All of the studies in both of these sets are consistent with the generalization that, whereas nonphonemic coding may be employed for nonverbal items or items presented visually and not articulated, phonemic coding is employed for auditorily presented and/or articulated verbal items. In fact, Healy (1974) has demonstrated that subjects employ phonemic coding for auditorily presented and/or articulated verbal items even when it is a very inemcient coding strategy. The question remains whether subjects are limited to phonemic coding under such circumstances, or, rather, if alternative coding strategies are available under those circumstances as well. This question is one of broad interest since circumstances involving the recall of auditorily presented verbal items are very common indeed. In an attempt to discover a set of conditions in which auditorily presented verbal material is not coded phonemically in shortterm memory, one situation seemed most promising: Subjects would be asked to recall

items in their spatial rather than their temporal order of presentation and spatial and temporal orders would be uncorrelated. Such a situation seemed to be a likely candidate on the basis of studies by O'Connor and Hermelin (1972, 1973) which suggest that temporal order information is mediated by the auditory modality, whereas spatial order information is mediated by the visual modality. Such a situation als0 seemed promising on the basis of the finding by Adams, Thorsheim, and McIntyre (1969) that the effect of phonemic similarity is larger for sequential presentation than for simultaneous presentation of to-beremembered letters. Although a number of investigators have compared short-term memory for temporal and spatial order information (for example, Anderson, 1976; Hitch, 1974; Lundberg & Book, 1969a,b; Mandler & Anderson, 1971; Murdock, 1969; Snodgrass, Burns, & Pirone, Note 2), only one study (Healy, 1975) has provided the necessary set of conditions and analyses in order to test the question at hand. In that study, whereas phonemic coding was found for consonants pronounced aloud by the subject which were to be recalled in their temporal order of presentation, a different form of coding was found for the same items when they were to be recalled according to their spatial order of presentation. This study therefore provided the first evidence of nonphonemic coding of vocalized verbal items. Because of the theoretical importance of this finding, the conditions under which one can obtain such nonphonemic coding should be investigated further. In addition, the nature of the nonphonemic coding strategy merits further investigation. Healy maintained that the alternative coding strategy involved temporalspatial patterns of item presentation. More work is needed to establish firmly this proposal. With these general goals in mind, the present study seeks to answer three more specific questions: (1) The first question is whether or not one can obtain temporal-spatial pattern

421

PATTERN CODING OF SPATIAL ORDER

coding in a spatial order recall situation in which item information is not redundant. Temporal-spatial pattern information alone was sufficient for correct performance in the spatial order recall conditions of Healy (1975) since the same four items were shown on every trial and their temporal order was fixed. In other words, subjects in these conditions could ignore item information since it was redundant. (It should be noted that parallel arguments apply to the temporal order recall conditions of the study by Healy, 1975, but despite this fact the subjects did not seem to employ pattern coding in those conditions.) It could be argued that subjects in the experiments by Healy (1975) chose pattern coding rather than phonemic coding for spatial order recall only because they could ignore item information; that is, the pattern coding observed for spatial order recall might have been artifactually caused by the redundancy of the item information. According to this argument, one should expect to find phonemic coding when item information must be retained along with spatial order information. (2) The evidence provided by Healy (1975) against phonemic coding came largely from analyses of substitution errors. As reviewed above, another potential source of evidence involves differential effects of distractor tasks. The second question, probing for such evidence, is whether or not the coding of temporal order information and the coding of spatial order information are differentially affected by interpolated tasks involving the processing of phonemic and spatial information. If spatial order recall involves the coding of temporalspatial patterns and temporal order recall involves phonemic coding, then spatial order recall but not temporal order recall should be disturbed by an interpolated task involving the processing of spatial information. Furthermore, temporal order recall but not spatial order recall should be disturbed by an interpolated task involving the processing of phonemic information. (3) The third question is whether or not one can obtain coding of

temporal-spatial patterns in temporal order recall when the to-be-remembered items are pronounced by the subjects. Healy (1975) found no evidence for pattern coding in temporal order recall except in the case when phonemic coding was prohibited by forcing the subjects to pronounce irrelevant items rather than the names of the to-be-remembered items as they were presented. Perhaps subjects did not make use of pattern coding under the standard conditions because they failed to attend to the spatial locations of the to-beremembered items. If subjects were forced to attend to such information, they might be led to employ temporal-spatial pattern coding in temporal order recall even when phonemic coding was not prohibited. The three questions outlined here shall be addressed in turn by the three experiments of the present series. EXPERIMENT l

The present experiment was designed to determine whether pattern coding rather than phonemic coding is employed for the shortterm retention of spatial order information when item information is not redundant. Specifically, spatial order recall was tested in a situation where item information was not provided to the subject in advance but rather had to be learned by the subject on each trial along with order information. As in the earlier studies by Healy (1975), temporal and spatial orders were varied independently in order to distinguish between them. In addition, in order to determine whether or not subjects made use of temporal order information even when asked only for spatial order recall, two conditions were compared. In one condition (Alphabetical) the temporal order of the items was redundant and in the other condition (Random) it was not. If subjects made use of temporal order information, as they would if they coded temporal-spatial patterns, performance would be superior in the Alphabetical condition compared to the Random

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condition. The experiment was otherwise designed to be parallel to the one conducted by Bjork and Healy (1974) where item and temporal order information, rather than item and spatial order information, were to be retained. Since the two experiments differ primarily in the type of order information to be retained, one would expect that performance levels would be similar in the two experiments in terms of item recall scoring but might differ in terms of ordered recall scoring. In order to determine whether or not subjects employ phonemic coding in this spatial order recall task, we shall examine the patterns of substitution errors; a predominance of phonemic confusion errors would suggest phonemic coding. In addition, in order to determine whether or not subjects continue to employ temporal-spatial pattern coding for spatial order recall, we shall examine the effects of pattern on recall level; if pattern coding is employed, we should find a significant correlation across conditions in the percentages of correct responses made to each of the temporal-spatial patterns.

Method Subjects. The subjects were 24 male and female young adults who were recruited by advertisements in a New York City newspaper and paid at the rate of $2.50 per hour. There were two conditions with 12 subjects in each condition. The assignment of subjects to conditions was determined by time of arrival for testing. Apparatus. An Iconix Bina-view display device, operated by means of a Digitronics paper-tape reader, was employed for the visual presentation of the stimuli. The screen of the Bina-view included four cells arranged in a horizontal linear array. The four cells defined four different spatial positions, numbered consecutively from left to right. Three clocks were included in the system which timed the stimulus duration at 400 milliseconds per item, the intertrial interval at 16 seconds, and the interstimulus interval at approxi-

mately 2 milliseconds. Each stimulus character was approximately 3.5 centimeters high and 2.2 centimeters wide. Design and materials. The display sequences for a given experimental session were programmed on paper control tapes. Four different 72-trial sequences were prepared; each sequence was shown to six subjects, three of whom saw the sequence from beginning to end, and three of whom saw the last 36 trials first followed by the initial 36 trials. Two of these sequences were in the Alphabetical condition and the remaining two sequences were in the Random condition. A given trial included a four-consonant stimulus followed by a retention interval with either 3, 8, or 18 intervening digits. The four consonants and the digits in a trial were presented successively. Each character was displayed in only one of the four cells of the display screen, while the other three cells were left blank. Each of the four consonants was presented in a different one of the four cells of the screen. The consonants were not necessarily presented from left to right, so that the spatial order of the consonants did not necessarily correspond to the temporal order. Similarly, the cell location where each digit appeared varied from digit to digit; the location was quasirandom with the constraint that two successive digits never appeared in the same cell location. The intervening digits displayed on each trial were randomly selected from the digits 1 to 9 with the constraint that no digit occurred twice in a row. The consonants were drawn from a population of 12 letters employed by Bjork and Healy (1974) including four subsets, two of which are called "confusable" subsets since they contain letters which are phonemically similar to each other, and two of which are called "control" subsets since they contain consonants each of which is assumed to be phonemically similar to no other consonant in the population. The two confusable subsets are: (1) BPV and (2) FSX. The control sub-

PATTERN

CODING

sets are (3) KMR and (4) HLQ. As in the Bjork and Healy experiment, from these four subsets two types of stimuli were constructed: Paired-Context stimuli and All-DifferentContext stimuli. In the Paired-Context stimuli, two of the four consonants are from one of the two confusable subsets and two are from one of the two control subsets. In the All-Different-Context stimuli, each of the four consonants is from a different one of the four subsets. Thus in the Paired-Context stimuli, exactly two letters are phonemically similar, and in the All-Different-Context stimuli, no two letters are phonemically similar. There were equal numbers of stimuli in the Paired Context and in the All-Different Context at each of the three retention intervals. The particular letters comprising each of the 72 stimuli were chosen randomly from within the four subsets except for the constraint that all letters appear equally often in each combination of context type and retention interval. The presentation order of the stimuli was random with the following constraint: In every block of 18 successive stimuli, each combination of context type and retention interval occurred three times. On any given trial, the same letters and digits occurred in each of the four sequences, and the digits occurred in the same temporal and spatial orders in each sequence. However, the temporal and spatial orders of the consonants shown on a given trial varied across sequences. For the two sequences in the Alphabetical condition, the temporal order of the letters on each trial was their alphabetical order, whereas for the two sequences in the R a n d o m condition, the temporal order of the letters on each trial was pseudorandom. The spatial order of the consonants on a given trial in all four sequences was also pseudorandom with three restrictions: (1) Each one of the 24 possible temporal-spatial patterns of consonant presentations (see Figure 1) occurred three times in each sequence, once at each of the three retention intervals. (2) The spatial

423

OF SPATIAL ORDER

Spatial Order I

7

15

19

2

8

14

20

T e m

3

9

15

21

p 0 r a

4

I0

16

22

L

0 r

5

II

17

23

d e r

6

12

18

24

FIG. 1. Temporal-spatial patterns of consonant presentations. The spatial positions are shown horizontally and the temporal positions are shown vertically. For example, in pattern number 7, the subject first sees a consonant in the third cell, then one in the fourth cell, then one in the first cell, and then one in the second cell, order of the consonants on a given trial in a given sequence in the Alphabetical condition was the same as that on the corresponding trialin one of the two sequences in the R a n d o m condition. (3) The temporal-spatial pattern of consonant presentations on a given trial in a given sequence in the Alphabetical condition was the same as that on the corresponding trial in one of the two sequences in the R a n d o m condition. Two different six-trial practice sequences were constructed, one in the Alphabetical condition and one in the R a n d o m condition. The sequences were constructed in a manner similar to the experimental sequences. The spatial orders of the consonants were the same for the two practice sequences, but the consonants on a given trial occurred in

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alphabetical temporal order in the Alphabetical condition and in a, pseudorandom temporal order in the Random condition. Procedure. Subjects were tested individually in hour-long sessions. Each subject was instructed to shadow, or read aloud, each item as it appeared on the screen. At the end of each sequence of consonants and digits, the screen became blank and the subject was given 16 seconds to write down the four consonants in their spatial order on a 3 x 5 card on which four boxes had been printed. The subject was required to fill in every box, but he was not required to fill in the boxes in any particular temporal sequence. Subjects in the Alphabetical condition were told that the temporal order of the consonants would always correspond to their alphabetical order, whereas subjects in the Random condition were given no information about the temporal order of the consonants. Results and Discussion

Two comparisons are of primary concern: (1) the comparison between the level of performance in the present task, involving spatial order recall, and that in the experiment by Bjork and Healy (1974), involving temporal order recall; and (2) the comparison between the Alphabetical and Random conditions of the present experiment, which differ only in that temporal order is redundant in the former but not in the latter condition. The results of the present experiment and the results of the analogous experiment by Bjork and Healy (1974) are summarized in Table 1 in terms of percentages of correct responses by both ordered and item recall scoring. (By ordered recall scoring an item is scored as correct only if both the identity and the serial position of the item were accurate, whereas by item recall scoring an item is scored as correct if the identity was accurate, irrespective of the accuracy of its serial position.) The standard error of the values in the table for the present experiment is 2 % for ordered recall scoring and 1% for item recall scoring, as determined

TABLE 1 PERCENTAGES OF CORRECT RESPONSESAS A FUNCTION OF RETENTION INTERVAL IN THE BJORK AND HEALY (1974) EXPERIMENT AND IN BOTH CONDITIONS OF THE PRESENT EXPERIMENT 1 IN TERMS or ORDERED AND ITEM RECALL SCORING Number of digits Experiment

3

8

18

50 38 62

34 29 38

85 82 83

70 69 66

Ordered recall Present Alphabetical Random Bjork and Healy

62 52 85 Item recall

Present Alphabetical Random Bjork and Healy

96 94 96

by analyses of variance. ~ Clearly, the results of the present experiment are similar to those of the Bjork and Healy (1974) experiment by item recall scoring, whereas they differ markedly by ordered recall scoring. This outcome was expected on the basis of the fact that the item information to be recalled was similar in the two experiments; the experiments differed primarily in the type of order information to be retained. An advantage is seen for the Alphabetical condition where temporal order information is redundant over the Random condition for ordered recall scoring, F(1, 22) = 3.38, p < .05 by a one-tailed test, but not for item recall 1 Here and in all succeeding analyses reported in this paper, the standard error is computed by using the mean square of the appropriate error term from the analysis of variance in the formula S~ = (MS/r) tl2, where r is the number of observations contributing to each mean. When the table presents a breakdown of the data averaged across a within-subjects variable employed in the analysis of variance (for example, when the table averages across retention intervals), then the error mean square chosen is the one for the interaction depicted in the table, and r is equal to the number of subjects contributing an observation to each mean times the number of levels on the averaged factor.

PATTERN CODING OF SPATIAL ORDER

scoring, F(1, 22)< 1.00. The difference for ordered recall scoring suggests that subjects attend to temporal order information when recalling spatial order information, as they would if they were coding information about temporal-spatial patterns for spatial order recall. Confusion errors. The previous analysis indicated that item information was retained as well in the present experiment as in that by Bjork and Healy. Phonemic coding was found to be the basis for representing item information in the Bjork and Healy study. An interesting question is whether or not phonemic coding also provides the basis for representing item information in the present situation, which differs from that of Bjork and Healy in that items are recalled in their spatial rather than their temporal order of presentation. To answer this question an analysis was made of confusion errors involving phonemically similar letters. Responses were classified as confusion errors if the letter incorrectly recalled for a given position on a given trial was from the same consonant subset as the letter presented. These errors involve confusions of phonemically similar letters only in the case of the confusable subsets. The conditional percentages of confusion errors, given that an error was made on a letter from a Paired-Context stimulus, are shown in Table 2 for letters from the confusable and control TABLE2 PERCENTAGES OF ERRORS THAT REFLECT INTRASUBSET CONFUSIONS IN THE PAIRED CONTEXT STIMULI OF EXPERIMENT I BY CONDITION, RETENTION INTERVAL, AND CONFUSABLE VERSUS CONTROL LETTER SUBSET

Number of digits Condition

3

8

18

Alphabetical Confusable Control

30 37

26 35

21 23

Random Confusable Control

33 33

24 30

24 26

15

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subsets as a function of condition and retention interval. The conditional percentages for letters from the confusable subsets were less than or equal to the percentages for letters from the control subsets at each retention interval. These results suggest that phonemic coding was not employed in the present situation. The lack of evidence for phonemic coding is consistent with the previous studies of spatial order recall (Healy, 1975) but contrasts markedly with the previous studies of temporal order recall (see, for example, Bjork & Healy, 1974, Healy, 1974, 1975), where evidence for phonemic coding was found. In light of the observation above that at allretentionintervals item information is retained as well in the present experiment as in the experiment by Bjork and Healy, it appears that some new coding system has been developed by subjects in the present experiment which is just as effective as phonemic coding for the retention of item information. The fact that spatial rather than temporal order recall was required in the present situation may be the reason why subjects are able to develop such an efficient nonphonemic coding strategy since they seem limited to phonemic coding in temporal order recall situations even when phonemic coding is inefficient (Healy, 1974). Serialpositionfunctions. In previous studies of spatial order recall where item information was redundant (Healy, 1975), bow-shaped serial position curves were found for temporal positions. This finding gave support to the possibility that subjects were making use of temporal information even for spatial order recall. Similarly, temporal serial position is an important variable in the present study, F(3, 66)= 28.27, p < .01, and this variable compares favorably in the magnitude of its effect with the variable of spatial serial position, F(3, 66) = 13.57, p < .01. Different serial position functions were found for item and order errors in the experiment by Bjork and Healy (1974). It is of interest to determine whether or not the same

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ALICE F. HEALY TABLE 3

PERCENTAGES OF ORDER AND ITEM ERRORS IN EXPERIMENT 1 BY SPATIAL AND TEMPORAL POSITIONS

Position Position type

1

2

3

4

Spatial Order Item

36 17

41 18

42 17

36 17

Temporal Order Item

31 14

41 19

43 20

39 16

pattern of results occurs in the present experiment where items are recalled in their spatial rather than their temporal order. Serial position functions for the present experiment both for temporal and spatial positions are presented in Table 3 as a function of order and item errors. (If the letter incorrectly recalled for a given position of a given trial had been presented on that trial but in a different position, the response was scored as a transposition, or order, error. If the letter incorrectly recalled for a given position of a given trial had not appeared in any position of that trial, the response was scored as a nontransposition, or item, error.) Analyses of variance yielded 1 ~ as an estimate of the standard error of the entries of Table 3. The data in Table 3 are not separated by condition since this factor did not interact significantly with the factors serial position or error type. Order and item errors are differentially affected by serial position, as evidenced by a significant interaction of serial position and error type, both for temporal positions, F(3, 66)=2.97, p < . 0 5 , and for spatial positions, F(3, 66)= 2.87, p < .05. This observation is consistent with previous findings for temporal order recall that order and item errors showed different serial position functions (Bjork & Healy, 1974; Healy, 1974). Pattern analysis. Previous experiments (Healy, 1975) demonstrated that the temporal-

spatial patterns of consonant presentations (see Figure 1) affected spatial order recall. Healy (1975) demonstrated the effect of temporal-spatial patterns by finding a significant correlation across spatial order recall conditions in the percentages of correct responses made to each of the 24 temporalspatial patterns. Specifically, the percentage of correct responses to a given pattern was computed for a given experimental condition by determining the number of correct responses made to that pattern by all the subjects in that condition. One percentage was computed for each of the 24 patterns. With these 24 percentages for each condition, Pearson productmoment correlation coefficients were calculated comparing the various spatial order recall conditions. The coefficients ranged from 0.57 to 0.81 (p < .01 in each case). A similar pattern analysis was conducted for the present experiment. The percentage of correct responses (with ordered recall scoring) made to each of the 24 patterns in the Alphabetical condition was compared to that in the Random condition; a significant correlation was found, r(22) = 0.79, p < .01. Furthermore, the 24 percentages for each of the present conditions were compared to those from the various spatial order recall conditions of Healy (1975). The correlations ranged from .54 to .89 (p < .01). This analysis indicates that temporal-spatial pattern affects recall in a consistent manner in these various spatial order recall tasks, presumably because in the present experiment, as in the earlier studies, subjects are coding information about temporal-spatial patterns. The analysis above leads to the conclusion that spatial order information is coded in memory in terms of attributes of temporalspatial patterns of letter presentations. It is not clear, however, whether this memory code is basically verbal, visual, or more abstractpropositional. Future research may be able to narrow down these possibilities by changing the memory loads on the visual and verbal systems, for example. (See Scarborough, 1972,

PATTERN CODING OF SPATIAL ORDER

for a description of this experimental technique.) The question also remains of how item information is coded in this experiment since there is no evidence for phonemic coding. Pattern information could not provide the basis for item recall since knowledge of which pattern was shown on a particular trial could not reveal which items were shown. On the basis of these assumptions, when item rather than ordered recall scoring is employed, the correlations among conditions on the percentages of correct responses made at each pattern should not be high. It is possible, however, that the observed high correlations for ordered scoring were not indicative of pattern coding per se but rather indicated the existence of other factors which would have made some patterns more prone to errors than others. In this event high correlations would be expected for item scoring as well as for ordered scoring. In fact, although the two conditions of the present experiment yielded a significant correlation coefficient for item scoring when compared with each other, r(22) = 0.65, p < .01, the correlation coefficients comparing the present conditions (for item scoring) with the spatial order recall conditions of Healy (1975) (necessarily for ordered scoring) range from -0.07 to 0.35, p > .05. Furthermore, the correlation coefficient comparing the 24 percentages for the two scoring methods was not significant for either the Random, r(22)=0.24, p >.05, or the Alphabetical condition, r(22) = 0.37, p > .05. This result indicates that temporal-spatial pattern may influence the percentage of items correctly recalled, but in any event, the pattern information is used differently for coding item information than for coding order information.

427

task. Healy found that interpolated tasks that required the subject to process the spatial characteristics of the intervening items caused the most forgetting. The difficulty of the intervening task seemed to be less important in determining recall performance than the particular processing demands made by the interpolated task. However, the role of difficulty could not be assessed precisely in that situation. Healy suggested that the best way to refute the notion that overall difficulty is the prime determiner of interpolated task effectiveness would be to manipulate the nature of the interpolated task in an experimental situation involving a temporal order recall condition as well as a spatial order recall condition. An interaction between condition and type of interpolated task would provide more convincing evidence that the effectiveness of the interpolated task cannot be attributed solely to task difficulty. (See Clayton & Warren, 1976, for a similar argument.) The present study was designed with such a goal in mind. In particular, two intervening task variables were manipulated in both temporal and spatial order recall. Subjects either read the names or the spatial positions of intervening digits (within-subject manipulation) aloud or silently (between-subject manipulation). It was hypothesized that the nature of the material to be read (names versus positions) would have an influence on spatial order recall, as it did in previous studies (Healy, 1974, Experiment III), but not on temporal order recall. On the other hand, the vocalization variable (aloud versus silent) should be more influential for temporal order recall than for spatial order recall. Specifically, if it is assumed that both temporal order recall and interpolated reading aloud involve the processing of phonemic information, whereas both spatial order recall and interpolated reading of digit positions involve processing of spatial information, EXPERIMENT 2 then temporal order recall should be disrupted In Experiments III and IV of the study by by interpolated reading aloud, and spatial Healy (1975) the nature of the interpolated order recall should be disrupted by intertask was manipulated in a spatial order recall polated reading of digit positions. Two more

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specific predictions also follow from these assumptions: (1) A preponderance of phonemic confusion errors should be found for temporal order recall but not spatial order recall, and the proportion of phonemic confusion errors in temporal order recall should be reduced when the interpolated material is read aloud rather than silently. (2) A consistent effect of temporal-spatial pattern should be found for spatial order recall but not temporal order recall, and this effect should be diminished when the interpolated task involves spatial positions rather than names of digits.

Method Subjects. Sixteen volunteers recruited from posters at colleges in the New Haven area participated as subjects and were paid $2.50 each. There were four conditions with four subjects in each condition: Aloud Temporal Order Recall, Silent Temporal Order Recall, Aloud Spatial Order Recall, and Silent Spatial Order Recall. The assignment of subjects to conditions was determined by time of arrival for testing. Apparatus. The display device employed was the same as in Experiment 1. In addition an electrical device was employed which allowed the subjects to write down the stimuli as they were displayed on the screen without taking their eyes away from the screen. The subjects wrote their responses on a roll of paper tape 7.6 centimeters wide which was advanced underneath a board at the rate of approximately 0.5 centimeters per second. The board had an opening 9.7 x 2.5 centimeters through which the paper tape was exposed. The subject placed his hand on the board so that he could write through the opening onto the paper without having to move his hand or look down at the paper. Design and materials. Eight different 48-trial experimental display sequences were prepared. Each subject was shown two sequences, and each sequence was shown to four different subjects. Four of these sequences were in the

Temporal Order Recall conditions and four were in the Spatial Order Recall conditions. A given trial included a four-consonant stimulus followed by a retention interval with either 3 or 18 intervening digits. As in Experiment 1, each of the four consonants was presented in a different one of the four cells of the screen. Similarly, the cell location where each digit appeared varied from digit to digit; the location was quasirandom with the constraint that across trials there were equal numbers of instances of digit positions 1, 2, 3, and 4, and a given position did not occur twice in immediate succession. The intervening digits displayed on each trial were a pseudorandom selection from the four digits 5, 6, 8, and 9. The order of the positions of the digits on trials 25-48 corresponded to the order of the digits themselves on trials 1-24 with the mapping of positions 1, 2, 3, and 4 to digits 5, 6, 8, and 9, respectively. Similarly, the order of the digits themselves on trials 25-48 correspond to the order of the positions of the digits on trials 1-24. These constraints were imposed to equate the orders of digit names and digit positions as nearly as possible. The same digit sequence was shown to each subject; only the consonants differed across subjects. As in the experiments by Healy (1975), item information was redundant since the same four consonants appeared on each trial of a given display sequence. In a given sequence, each of the 24 temporal-spatial patterns of letter presentations appeared once at each of the two retention intervals and either the temporal or the spatial ordering (depending on the recall condition) of the letters was held constant throughout the 48 trials. The presentation order of the trials was quasirandom with the constraint that in every block of 12 trials each retention interval occurred six times. The consonants were drawn from the population of eight employed by Healy (1975), including the two confusable subsets BP and FS and the two control subsets KM and HL.

PATTERN CODING OF SPATIAL ORDER

As in the experiments by Healy (1975), four of the sequences involved sets of these stimuli in the Paired Context; there were two of these sequences with the letters BKPM and two with FHSL. The other four sequences involved stimuli in the All-Different Context; there were two of these sequences with the letters BKFHand two with PMSL. The two sequences involving a given fourletter string included one sequence in the Temporal Order Recall conditions and one in the Spatial Order Recall conditions. The two sequences in a pair were identical except for the order of the letters on a given trial. The temporal-spatial pattern of letters employed on a given trial in one sequence was the same as that employed in the other sequence, and the constant temporal order of the letters in the Spatial Order Recall conditions was the same as the constant spatial order of the letters in the Temporal Order Recall conditions. The constant orders were BKPM, FHSL, BKFH, and PMSL for the four sequence pairs, respectively. Different permutations of the letters ABCD were shown on six practice trials. Two different sequences of practice trials were employed, differing only in the order of the consonants. One sequence was employed in the Temporal Order Recall conditions and one in the Spatial Order Recall conditions. The constant order was ABCD, and six different temporal-spatial patterns were employed, three at each of the two retention intervals. The orders of digits and digit positions were quasirandom. Procedure. Subjects were tested individually in sessions lasting approximately 75 minutes. Each subject was shown two 48 trial sequences, each paired with a different interpolated task: either reading digit names or reading digit positions. For eight subjects the digit names task was first and for eight subjects the digit positions task was first. The first sequence shown to each subject was always in the Paired Context and the second sequence was always in the All-Different Context. Subjects

429

shown the sequence involving BKPM first were then shown the sequence involving BKFH, and subjects shown FHSL were then shown PMSL. Across subjects in each condition each sequence was equally often employed with a digit name task and a digit position task. Each subject was instructed to shadow, or read aloud, each consonant as it appeared on the screen. Subjects in the Aloud conditions were also instructed to read aloud either the digit positions or digit names (depending on the nature of the interpolated task) as they appeared, but subjects in the Silent conditions were told to read the digit names or positions silently. In addition, all subjects were required to write either the digit positions or digit names (depending on the nature of the interpolated task) on the moving roll of the paper tape, responding to each intervening digit as it occurred. At the end of each sequence of letters and digits, the screen became blank and the subject was given 16 seconds to write down the four consonants in either their temporal order (Temporal Order Recall conditions) or their spatial order (Spatial Order Recall conditions) on a 3 × 5 card on which four boxes had been printed. The subject was required to fill in every box but he was not required to fill in the boxes in any particular temporal sequence. Subjects were informed of the constant spatial order of the letters in the Temporal Order Recall conditions and the constant temporal order in the Spatial Order Recall conditions.

Results and Discussion The results of the present experiment are summarized in Table 4 in terms of percentages of correct responses as a function of condition, retention interval, and interpolated material. The standard error of the entries of Table 4 is 5 ~. There is no difference in overall levels of performance for the two recall conditions, F(1, 12) < 1; however, the retention function for Temporal Order Recall is steeper than that for Spatial Order Recall, F(1, 12)= 8.03,

430

ALICE F. HFALY

TABLE 4 PERCENTAGES OF CORRECT RESPONSESIN EXPERIMENT 2 BY CONDITION, RETENTION INTERVAL~ AND NATURE OF INTERPOLATED MATERIAL

Retention interval

Temporal Aloud Silent

Spatial Aloud Silent

3 Digit name Digit position

67 68

92 93

80 65

77 61

18 Digit name Digit position

42 44

74 58

68 52

63 46

p < .05, as previous research had indicated (Healy, 1975). The effect of the interpolated task variables on recall performance in the two recall conditions is of major concern. The overall effect of interpolated vocalization is not significant, F(1, 12)=2.21, p > . 0 5 , but the interaction of this factor and recall condition is significant, F(1, 12)=4.79, p < .05. Performance in Temporal Order Recall, but not that in Spatial Order Recall, was disturbed by the requirement to read the interpolated matertial aloud. In fact, a crossover of performance levels is obtained; the percentage of correct responses is higher for Temporal Order Recall (79) than for Spatial (62) in the Silent condition, but the percentage is higher for Spatial Order Recall (66) than for Temporal ( 5 5 ) i n the Aloud condition. These results are consistent with the hypothesis that processing of phonemic information is employed for temporal but not spatial order recall. The overall effect of interpolated material is significant; performance was worse for interpolated digit positions than digit names, F(1, 12) = 11.29, p < .01. However, the effect of the nature of the interpolated material is much larger for Spatial Order Recall than for Temporal Order Recall, F(1, 12)=6.06, p < .05. Again a crossover of performance levels is obtained; the percentage of correct responses is higher for Spatial Order Recall

(72) than for Temporal (68) with digit names, but the percentage is higher for Temporal Order Recall (66) than for Spatial (56) with digit positions. (Note that in one condition of Temporal Order Recall, there seemed to be an effect of the nature of the interpolated task: In Silent Temporal Order Recall at the 18-digit retention interval, the percentage of correct responses was higher for the digit name than for the digit position task. However, the relevant four-way interaction was not significant, F(1, 12)< 1.) These results are consistent with the hypothesis that processing of spatial information is employed for spatial but not temporal order recall. Confusion-set errors. The preceding analyses indicate that phonemic coding is employed for temporal but not spatial order recall and that phonemic coding is disrupted by conditions involving reading the interpolated material aloud. Further evidence for this conclusion can be obtained from an analysis of the errors involving phonemic confusions. A confusionset error has been defined by Healy (1975) as the replacement of a letter belonging to one of the confusable subsets with the other member of its subset in the Paired Context and with the letter belonging to the other confusable subset in the All-Different Context. Phonemic coding is indicated by a difference between the percentages of confusion-set errors on phonemically similar letters, always in the Paired Context, and on letters that are not phonemically similar, always in the All-Different Context. The conditional percentages of confusion-set errors, given an error was made on a letter from one of the phonemically confusable subsets, are shown in Table 5 as a function of condition. An analysis of variance yielded 4 ~ as an estimate of the standard error of the means. (Note that Table 5 presents the more reliable pooled group means although, by necessity, the analysis of variance was conducted using the means of the individuals' scores. This convention will be employed throughout this paper.) The conditional percentages of confusion-set errors

PATTERN CODING OF SPATIAL ORDER

TABLE 5 CONDITIONALPERCENTAGESOF CONFUSION-SETERRORS ON PHONEMICALLYSIMILARAND DISSIMILARLETTERS IN EXPERIMENT 2 BY CONDITION

Condition

Letters Similar Dissimilar

Silent Temporal Spatial

58 20

24 27

Aloud Temporal Spatial

43 27

34 30

were higher on the phonemically similar letters than on the dissimilar letters in Temporal but not in Spatial Order Recall, F(1, 12) = 27.63, p < .01, and this effect was more pronounced in the Silent than in the Aloud conditions, F(1, 12) = 5.82, p < .05. These results support the contention that phonemic coding is used only in Temporal Order Recall and is disrupted by the Aloud conditions. Serial position .functions. The results concerning serial position functions for the present experiment essentially replicate those of the previous experiments by Healy (1975). In particular, in both Temporal and Spatial Order Recall, bowed serial position curves occur for temporal positions, whereas flatter curves occur for spatial positions. The;e data will not be reported in further detail here. Pattern analysis. The analyses involving percentages of correct responses indicate that pattern coding is employed for Spatial but not Temporal Order Recall and that pattern coding is disrupted by interpolated tasks requiring the processing of spatial information, such as when subjects write down the spatial positions of the intervening items. Pattern coding is evidenced by a correlation across conditions in the percentages of correct responses on each of the 24 patterns. The percentages of correct responses were computed for each of the 24 patterns separately for each experimental condition and type of interpolated material. The 24 percentages in

431

the Silent Spatial Order Recall condition were compared to those in the Aloud Spatial Order Recall condition for the case when the interpolated material involved digit names. Tl:e correlation was significant, r(22) = .53, p < .01, thereby lending evidence that pattern coding was employed for Spatial Order Recall when the interpolated task involved writing the names of intervening digits. In contrast, the correlation comparing the 24 percentages in the Silent Spatial Order Recall condition to those in the Aloud Spatial Order Recall condition, for the ca~e when the interpolated material involved digit positions, was not statistically reliable, r(22)=.31, p > .05. This result supports the notion that the pattern coding typically employed for Spatial Order Recall is disrupted by an intervening task involving the writing of spatial positions. (Note that Healy, 1975, did report significant correlations for Spatial Order Recall condition~ involving reading aloud spatial positions. Perhaps pattern coding was less disrupted in those tasks than in the present similar tasks because the previous tasks were not as demanding as the present tasks since no writing was required by the subject.) When similar analyses were conducted for the conditions involving Temporal Order Recall, as previous results had indicated, the correlations across conditions were not statistically significant, either for interpolated digit names, r(22) = .18, p > .05, or for interpolated digit positions, r(22)= .30, p > .05. These results are consistent with the conclusion that pattern coding is not employed for Temporal Order Recall. EXPERIMENT3 The aim of the present experiment is to discover whether or not subjects can be induced to employ pattern coding for Temporal Order Recall i n a situation where phonemic coding is not prohibited. The mechanism employed for inducing pattern coding involves a change in the method of recall response which forces the subject to

432

ALICE F. HEALY

attend to the spatial locations of the to-beremembered items. Specifically, subjects are asked to fill in their response on a 4 x 4 matrix of boxes (similar to the grids shown in Figure 1) indicating both the temporal and spatial orders of the items, although, as in previous experiments, the temporal order of the items remains constant in Spatial Order Recall, and the spatial order of the items remains constant in Temporal Order Recall. In essence, this new response method forces the subjects to write down the to-be-recalled letters in their temporal-spatial pattern of presentation. The new response method (Matrix condition) was compared to the standard method (Standard condition) using two groups of subjects from the same populations. As in previous experiments, we shall examine the pattern of phonemic confusion errors in order to determine whether phonemic coding is employed, and we shall examine the correlations across conditions in the percentages of correct responses made to each of the temporal-spatial patterns in order to determine whether or not pattern coding is employed. If phonemic coding is employed for temporal order recall in the Standard condition, and pattern coding is employed in both conditions of spatial order recall and in the Matrix condition of temporal order recall, then we should find a predominance of phonemic confusion errors only for the Standard Temporal Order Recall condition and significant positive correlation coefficients among all conditions except for Standard Temporal Order Recall. The possibility should also be considered that subjects combine phonemic and pattern coding strategies in the Matrix Temporal Order Recall condition. In that event, we would expect to find a predominance of phonemic confusion errors and significant correlation coefficients in Matrix Temporal Order Recall.

students of Yale College who were taking a course in introductory psychology. These subjects received course credit for their participation. The second replication involved 16 volunteers recruited from posters at colleges in the New Haven area. These subjects were paid $2.50 for their participation. Each replication included four conditions with four subjects in each condition: Matrix Temporal Order Recall, Matrix Spatial Order Recall, Standard Temporal Order Recall, and Standard Spatial Order Recall. Within each replication the assignment of subjects to condition was determined by time of arrival for testing. Apparatus. The same device was employed as in the previous experiments. Design and materials. Eight different 72-trial experimental display sequences were employed which were identical to those employed in Experiment I of the study by Healy (1975). Four of the sequences were used for Temporal Order Recall and four were used for Spatial Order Recall. Each sequence was shown to four different subjects, two in one of the Matrix conditions and two in one of the Standard conditions. In all sequences a trial consisted of a four-consonant stimulus followed by a retention interval of either 3, 8, or 18 intervening digits. As in Experiment 2, the same four consonants appeared on each trial of a given display sequence in either a constant temporal order (Spatial Order Recall conditions) or a constant spatial order (Temporal Order Recall conditions). The consonant sets and constant orders employed in the sequences of the present experiment were the same as those employed in the sequences of Experiment 2: BKPM, FHSL, BKFH, and PMSL. Two different six-trial sequences of practice trials, also identical to those employed by Healy (1975, Experiment I), were employed with different permutations of the letters ABCD. Method One sequence, with constant spatial order, was Subjects. The experiment was run in two employed for Temporal Order Recall, and the replications. The first replication involved 16 other sequence, with constant temporal order,

PATTERN CODING OF SPATIAL ORDER

433

was employed for Spatial Order Recall. For letters was held constant and hence was further details of the sequences, see Healy redundant. In both conditions, the subjects were required to fill four boxes with letters but (1975). Procedure. Subjects were tested individually they were not required to fill in the boxes on in hour-long sessions. The subjects were the cards in any particular temporal sequence. instructed to read aloud each item (digit or Subjects in the Temporal Order Recall consonant) as it appeared on the display conditions were told that the spatial order of screen. As in previous experiments, at the end the letters would be constant and were inof each sequence the subjects were given 16 formed of the constant order for their session. seconds to respond. In the Standard condi- Similarly, subjects in the Spatial Order tions subjects responded by writing down the Recall conditions were informed of the confour consonants in their proper order (the stant temporal order of the letters for their temporal order in the Temporal Order Recall session. conditions and the spatial order in the Spatial Order Recall conditions) on 3 × 5 Results and Discussion cards on which four boxes had been printed in The same pattern of results was obtained in a horizontal row. In the matrix conditions the two replications of the experiment. Hence for both Temporal and Spatial Order Recall, in the discussion below, the data from all 32 the subjects responded by writing the con- subjects were combined. The results of the sonants on 4 x 6 cards on which a 4 x 4 present experiment are summarized in Table 6 matrix of boxes was printed. Subjects were to in terms of percentages of correct responses place the letters in the matrix in such a way as as a function of condition and retention interto indicate both the temporal and spatial val. An analysis of variance yielded 3 ~ as an arrangements of the letters, the vertical estimate of the standard error of the means. position in the matrix representing the Performance seems to be worse overall in the temporal position and the horizontal position Matrix conditions than in the Standard conrepresenting the spatial position of a given ditions, but the difference is not statistically letter. More specifically, subjects were asked reliable, F(1, 28)=2.47, p > . 1 0 . Likewise, to write the letter seen first in one of the response condition seems to have a larger positions in the first row, the letter seen second effect on Temporal Order Recall than on in one of the positions in the second row, and Spatial Order Recall, but the interaction is so on. The particular one of the four columns not statistically significant, F(1, 28)< 1. In that the subject was to choose to place a given both sets of response conditions Temporal letter depended on its spatial position in the display. Subjects were instructed to write the TABLE 6 letter that appeared in the left-most cell of the PERCENTAGES OF CORRECT RESPONSES IN EXPERIMENT 3 display screen in the left-most column, the BY CONDITION AND RETENTION INTERVAL letter that appeared in the cell second to the Number of digits left in the column second to the left, and so on. Note that although subjects were asked to Condition 3 8 18 recall both temporal and spatial arrangements of the letters in the Matrix conditions but only Standard Temporal 93 80 70 one of these arrangements in the Standard Spatial 88 86 79 conditions, the amounts of information recalled in the two sets of conditions were Matrix Temporal 82 71 61 essentially identical since in each case either Spatial 87 79 76 the temporal or the spatial arrangement of the

434

ALICE F. HEALY

Order Recall yields a steeper retention function than Spatial Order Recall, F(2, 56) = 5.07, p < .01. The steep retention function found in Temporal Order RecaU had been attributed to phonemic coding by Healy (1975). This reasoning would indicate that subjects continue to employ phonemic coding for Temporal Order Recall even in the Matrix condition of the present experiment. Further evidence for this conclusion can be obtained from an analysis of confusion-set errors (see discussion of Experiment 2 above for a definition of confusion-set errors). Confusion-set errors. The conditional percentages of confusion-set errors given an error was made on a letter from one of the phonemically confusable subsets are shown in Table 7 as a function of condition. An analysis of variance yielded 5 ~o as an estimate of the standard error of the means. The increase in confusion-set errors on phonemically similar letters compared to phonemically dissimilar letters is larger for Temporal Order Recall than Spatial Order Recall, F(1, 2 4 ) = 10.47, p < .01, thereby indicating phonemic coding for Temporal but not Spatial Order Recall. This pattern is more striking for the Standard conditions than for the Matrix conditions but the three-way interaction is not statistically reliable, F(1, 24) = 1.28, p > .10. The results do not rule out the conclusion that subjects employ phonemic coding in Temporal TABLE 7 CONDITIONAL PERCENTAGESOF CONFUSION-SET ERRORS ON PHONEMICALLYSIMILARAND DISSIMILARLETTERS IN EXPERIMENT 3 BY CONDITION

Letters Condition

Similar Dissimilar

Standard Temporal Order Spatial Order

46 11

24 27

Matrix Temporal Order Spatial Order

33 17

31 32

Order Recall even in the Matrix condition. The possibility has not been eliminated, however, that subjects in the Matrix Temporal Order Recall condition employ pattern coding as well as phonemic coding. An analysis which makes reference to the temporal-spatial patterns is necessary to test this possibility. Pattern analysis. An analysis of the effect o f temporal-spatial patterns was performed on the data from the present experiment by computing the percentages of correct responses made on each of the 24 patterns by the subjects in each of the four conditions. The 24 percentages for Temporal Order Recall were compared to the 24 percentages for Spatial Order Recall in both the Matrix and Standard conditions by means of Pearson productmoment correlation coefficients. Although the correlation was not significant for the Standard conditions, r(22)= .06, it was for the Matrix conditions, r(22)= .70, p < .01, and the difference between the two correlation coefficients was significant, z = 2.62, p < .01 (see Hays, 1973). This difference suggests that pattern coding is employed only in Spatial Order Recall in the Standard condition but in both Temporal and Spatial Order Recall in the Matrix condition. This conclusion is further supported by finding a significant correlation coefficient~when. the ~t w o Spatial Order Recall conditions (Matrix and Standard) of the present experiment were compared, r(22)-= .64, p < .01, and a nonsignificant correlation coefficient when the two Temporal Order Recall conditions were compared, r(22) = .31, p > .05. These results indicate that under standard response conditions subjects do not employ pattern coding for Temporal Order Recall, but they can be made to employ such coding by changing the response conditions, although phonemic coding is not eliminated under these conditions. Serialpositionfunctions. The serial position data of the present experiment are comparable to those of Experiment 2 and the experiments by Healy (1975); these data will not be reported here.

PATTERN CODING OF SPATIAL ORDER SUMMARY AND CONCLUSIONS

The present study demonstrates that at least three different types of coding strategies are available to subjects in short-term memory tasks where to-be-remembered letters are vocalized: (1) phonemic coding, (2) temporalspatial pattern coding, and (3) item coding, as yet unspecified in character. A fourth coding strategy is indirectly implicated as well. The present study also indicates the conditions under which these various coding strategies, either alone or in combination, can be obtained. Phonemic coding seems to be limited exclusively to situations involving temporal order recall. Even when item information had to be retained in a spatial order recall task, there was no evidence for phonemic coding in that task (Experiment I). The evidence for or against phonemic coding came in two forms: (1) from analyses of substitution errors and (2) from examination of the effects of different interpolated tasks. Although subjects were likely to substitute a phonemically similar letter for the to-be-remembered letter in temporal order recall, this pattern of substitutions was not found for spatial order recall (Experiments 1-3). In addition, whereas interpolated tasks involving vocalization of the intervening items led to worse performance than similar tasks without vocalization for temporal order recall, the effect of interpolated vocalization was different for spatial order recall (Experiment 2). Temporal-spatial pattern coding was found in all the present conditions of spatial order recall including the condition where subjects were to retain item information as well as spatial order information (Experiment 1). In addition, subjects were found to employ temporal-spatial pattern coding along with phonemic coding in temporal order recall when a new method of response forced them to attend to the spatial locations of the to-beremembered letters (Experiment 3). Evidence for pattern coding was based primarily on the

435

consistent effects across conditions of temporal-spatial pattern on level of performance (Experiments 1-3). Additional support for the coding of temporal-spatial patterns in spatial order recall came from analyses which indicate that subjects code both spatial and temporal information in spatial order recall. Analyses of the effects of interpolated tasks on spatial order recall (Experiment 2) suggest that subjects process spatial information; interpolated tasks requiring subjects to process the spatial positions of intervening items disrupted recall performance to a greate r extent than did similar tasks without the spatial processing demands. Two additional observations suggest that subjects also process temporal information in spatial order recall: (1) Superior performance by ordered recall scoring was observed when temporal order information was redundant than when it varied randomly (Experiment 1) and (2) bowshaped serial position functions were found for temporal positions in spatial order recall (Experiments 1-3). It should be noted that, although pattern coding was found consistently in the spatial order recall tasks of the present series, subjects may find such a coding strategy difficult when the length of the to-be-remembered list of items is long (and hence the number of alternative temporal-spatial patterns is large) and/or when the subjects are shown only difficult temporal-spatial patterns. Such conditions held, for example, in the studies by Mandler and Anderson (1971) and Anderson (1976) where lists including eight or more items were employed and "highly patterned sequences were rejected (Anderson, 1976, p. 389)." The~e authors did not specifically examine the effects of temporal-spatial pattern on recall performance. However, their finding of inferior spatial order recall of words relative to temporal order recall of words suggests that subjects cannot effectively employ pattern coding in their tasks. In addition to pattern coding and phonemic coding, the present study implicates a third

436

ALICE F. HEALY

type of coding strategy employed to retain item information. In Experiment 1, which involved spatial order recall, item information was retained at a level comparable to that found for temporal order recall in the study by Bjork and Healy (1974). However, whereas phonemic coding was found in the study by Bjork and Healy, there was no evidence for phonemic coding in Experiment 1. It also seems unlikely that temporal-spatial pattern coding provided the basis for representing item information since knowledge of which pattern occurred on a given trial could not reveal which items occurred. In fact, the effect of pattern on level of recall was different for item and ordered recall scoring. Furthermore, there was no effect of redundant temporal order by item recall scoring, as there was by ordered recall scoring. Hence, further work is needed to identify the form of coding employed for the short-term retention of item information. Just as Estes (1973) suggested that a visual code may be employed in addition to a phonemic code for temporal order recall, the possibility should be considered that a visual code is employed for storing item information in spatial order recall. Finally, there is indirect evidence for a fourth type of coding strategy which remains even more obscure than the item coding discussed above. In the Random condition of Experiment 1 where temporal order information was not redundant and subjects had to retain both item and spatial order information, knowledge of the temporal-spatial pattern of item presentations and knowledge of the identity of the items occurring on a given trial were not sufficient for correct recall of the items in their proper spatial positions. For example, if the subject knew that B, L, F, and R were the items shown on a given trial and that they were displayed according to temporal-spatial pattern number 14 (see Figure I), he or she would not necessarily know the correct spatial order of the items. The subject needs in addition some kind of information

which links or combines the patteln and item information. Such information is provided in the Alphabetical condition of Experiment 1 by the fact that the temporal order of the items is alphabetical, and such information is provided in the other spatial order recall conditions of this series by the fact that the temporal order of the items is constant. To continue the example above, if the subject knew in addition that the temporal order of the items was their alphabetical order, B FL R, then he would know that the correct spatial order was L B F R. The fact that subjects perform substantially above chance levels in the Random condition of Experiment 1 suggests that they are able to code this additional information along with pattern and item information. In conclusion, the important point to be made by these studies is that subjects are not limited to phonemic coding strategies in short-term memory even for the recall of verbal items which are vocalized. A number of alternative coding strategies, including temporal-spatial pattern coding, are available to subjects, and they employ these strategies in addition to phonemic coding for temporal order recall and instead of phonemic coding for spatial order recall. REFERENCES ADAMS, J. A., THORSHEIM,H. I., & MCINTYRE, J. S, Short-term memory and acoustic similarity. Psychonomic Science, 1969, 5, 77-78. A~DERSON, R. E. Short-term retention of the where and when of pictures and words. Journal of Experimental Psychology: General, 1976, 105, 378~02. ATKINSON,R. C., ~¢ SHIFFRIN,R. M. Human memory: A proposed system and its control processes. In K. W. Spence & J. T. Spence (Eds.), The psycho-

logy of learning and motivation: Advances in research and theory. New York: Academic Press, 1968. Vol. 2, pp. 89-195. BJORK, E. L., ~6 HEALY, A. F. Short-term order and item retention. Journal of Verbal Learning and Verbal Behavior, 1974,13,80-97. BROOKS, L. R. Spatial and verbal components of the act of recall. Canadian Journal of Psychology, 1968, 22, 349-368.

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CLAYTON,K. N., & WARREN,M. W. Methodological

MURDOCK,B. B., Jr. Where or when: Modality effects

problems with the use of the retroactive interference design to infer what is stored. Memory & Cognition, 1976, 4, 237-243. CONRAD, R. Short-term memory processes in the deaf. British Journal of Psychology, 1970, 61, 179-195. DEUTSCH,D. Tones and numbers: Specificity of interference in immediate memory. Science, 1970, 168, 1604-1605. DEN HEYER, K., & BARRET'r,B. Selective loss of visual and verbal information in STM by means of visual and verbal interpolated tasks. Psychonomic Science, 1971,25,100-102. ELLIOTT, L. A., & Sa~AWHORN, R. J. Interference in short-term memory from vocalization: Aural versus visual modality differences. Journal of

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Experimental Psychology: Human Learning and Memory, 1976, 2, 705-711. ESTES, W. K. Phonemic coding and rehearsal in shortterm memory for letter strings. Journal of Verbal Learning and Verbal Behavior, 1973, 12, 360-372. HAYS, W. L. Statistics for the social sciences. New York: Holt, Rinehart & Winston, 1973.2nd Ed. HEALY, A. F. Separating item from order information in short-term memory. Journal of Verbal Learning and Verbal Behavior, 1974,13, 644-655. HEALY, A. F. Coding of temporal-spatial patterns in short-term memory. Journal of Verbal Learning and Verbal Behavior, 1975,14, 481-495. HITCH, G. J. Short-term memory for spatial and temporal information. Quarterly Journal of Experimental Psychology, •974, 26, 503-513. KROLL, N. E. A., PARKS, T., PARKINSON, S. R., BIEBER, S. L., & JOHNSON, A. L. Short-term memory while shadowing: Recall of visually and of aurally presented letters. Journal of Experimental Psychology, 1970, 85, 220-224. LUNDBERG,I., & BOoK,A. Postcued recall of competing spatial and temporal order. Umea Psychological Reports, 1969a, No. 7. LUNDBERG, I., & BOOK, A. Selection of order information from spatio-temporal configurations. Umea Psychological Reports, 1969b, No. 8. MANDLER, G., ~¢ ANDERSON, R. E. Temporal and spatial cues in seriation. Journal of Experimental Psychology, 1971,90,128-135. MARGRAIN,S. A. Short-term memory as a function of input modality. Quarterly Journal of ExperimentalPsychology, 1967, 19, 109-114. MEUDELL,P. R. Short-term visual memory: Comparative effects of two types of distraction on the recall of visually presented verbal and nonverbal material. Journal of Experimental Psychology, 1972, 94,244-247.

O'CONNOR,N., • HERMELIN,B. Seeing and hearing and space and time. Perception andPsyehophysics, 1972,11,4648. O'CONNOR, N., & HERMELIN, B. The spatial or temporal organization of short-term memory.

Quarterly Journal of Experimental Psychology, 1973, 25, 335-343. PELLEGRINO,J. W., SIEGEL,A. W., & DHAWAN,M. Short-term retention of pictures and words as a function of type of distraction and length of delay interval. Memory & Cognition, 1976, 4, 11-15. PETERSON,L. R., & JOHNSON,S. T. Some effects of minimizing articulation on short-term retention.

Journal of Verbal Learning and Verbal Behavior, 1971,10, 346-354. SANDERS, A. F., & SCHROOTS, J. J. F. Cognitive categories and memory span. III. Effects of similarity on recall. Quarterly Journal of Experimental Psychology, 1969, 21, 21-28. SALTHOUSE, T. A. Using selective interference to investigate spatial memory representations. Memory & Cognition, 1974, 2, 749-757. SALTHOUSE,T. A. Simultaneous processing of verbal and spatial information. Memory & Cognition, 1975, 3, 221-225. SCARBOROUGH, D. L. Memory for brief visual displays of symbols. Cognitive Psychology, 1972, 3, 408-429. SPERLING, G., & SeEELMAN,R. G. Acoustic similarity and auditory short-term memory: Experiments and a model. In D. A. Norman (Ed.), Models of human memory. New York: Academic Press, 1970, pp. 151-202. TELL, P. M. Influence of vocalization on short-term memory. Journal of Verbal Learning and Verbal Behavior, 1971,10,149-156.

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Pictures and words and space and time: In search of the elusive interaction. Unpublished manuscript, 1976. (Received August 9,1976)