Journal ol Experimental Psychology. 1974, Vol. 102, No. 1, 121-124. RETRIEVAL OF SUPERORDINATES AND SUBORDINATES. ELIZABETH F. LOFTUS 2.
Journal ol Experimental Psychology 1974, Vol. 102, No. 1, 121-124
RETRIEVAL OF SUPERORDINATES AND SUBORDINATES ELIZABETH F. LOFTUS 2
MARTIN BOLTON
University of Washington
New School for Social Research
Semantic memory retrieval was investigated in 2 experiments. In the first experiment, 5s were shown a category name and asked to respond with a word belonging to the category (for one block of trials) or a class to which the category name belonged (for another block of trials). Subjects produced a category member faster than they produced a superordinate. For example, they produced an instance of the category CAR faster than they produced a superordinate such as vehicle. The time taken to retrieve a superordinate was strongly related to the category's hierarchical position, while the time taken to retrieve an instance was not so related. In the second experiment, 5s produced free associates to categories differing in hierarchical level. More subordinates were given for all but the lowest level categories. The data argue against the notion that the superset is the most accessible property of a category or concept.
The present article deals with relations of class inclusion, relations which have been of interest at least since Aristotle's time. Knowledge of these inclusion relations is knowledge that we have learned some time ago and know very well; it forms a part of our semantic memory. Whenever we make a subordinate or superordinate response, as when we assert that (a) an example of a dog is a collie, or (b) the class to which collies belong is "dogs," we manifest our knowledge of inclusion relations. Class inclusion relations have become central in many current theories of memory. In the network model of Rumelhart, Lindsay, and Norman (1972), for example, a statement such as "A car is a vehicle" is represented as 2 nodes, one corresponding to "car" and the other to "vehicle," and a relation between them, the "isa" relation. One question that arises is what directional effects in information retrieval exist as a consequence of these inclusion relations? For example, given the stimulus word CAR, is it easier to retrieve a superordinate response, such as vehicle, object, or thing, or it is easier to retrieve an instance, such as Ford, Buick, or Ferrari? Miller (1969) claims that "a superordi1
The authors are grateful to Sif Wiksten for her assistance in data analysis. * Requests for reprints should be sent to Elizabeth F. Loftus, Department of Psychology, University of Washington, Seattle, Washington 98195.
nate response will be much stronger (more frequent and probably faster) than a subordinate response [p. 231]." He points to results from word association tests to support his claim. For example, the results of a reclassification of the data of Kent and Rosanoff (1910) indicated that 7.6% of all the responses given were superordinate and only 1.6% were subordinate (Woodrow & Lowell, 1916). From this evidence, Miller concluded that the subordinate-superordinate direction of association is stronger than the superordinate-subordinate direction. Collins and Quillian (1972) seem to be in agreement with Miller, as they say "in many cases the superset is the most accessible property of a concept. . . . In contrast, the instances of a concept are not easily accessible properties in general [p. 320]." Rather than trust "indirect" data from word association tests to settle the matter of directionality, an experiment was performed in which & were shown a word on each trial and were asked to name an instance (for one block of trials) or a superordinate (for another block of trials). The 5s were timed while they produced their responses. EXPERIMENT I Method Subjects. The 5s were 22 students at the New School for Social Research. Each 5 took part in one experimental session that lasted 30 min.
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ELIZABETH F. LOFTUS AND MARTIN BOLTON TABLE 1 MEDIAN REACTION TIME (IN SEC.) TAKEN TO RETRIEVE A SUPERORDINATE AND A SUBORDINATE FOR TWENTY SETS OF NESTED CATEGORIES Level 1 category
Level 2 category
Name
Superordinate
Subordinate
Name
Superordinate
Subordinate
CLOTHING SCHOOL ACTIVITY SPORT FOOD VEHICLE TYPE OF BUILDING CITY TITLE PLANT POLITICIAN SCIENCE MINERAL BEVERAGE STONE* TYPE OF MONEY GEOMETRIC SHAPE ANIMAL WORD FURNITURE
2.61 2.25 4.61 1.86 2.74 3.S8 2.65 2.58 3.37 2.54 3.03 3.51 4.06 2.23 3.45 2.61 2.62 2.31 2.28 5.78
1.54 1.67 1.71 1.42 1.99 1.30 1.89 1.19 1.92 2.14 1.88 1.59 2.79 1.50 3.49 1.59 1.54 1.30 1.73 1.35
FOOTWEAR COLLEGE CRIME WATERSPORT VEGETABLE CAR RELIGIOUS BUILDING U.S. CITY MILITARY TITLE TREE PRESIDENT NATURAL SCIENCE METAL SOFT DRINK
2.10 1.93 3.80 3.00 1.95 1.92 2.82 3.08 3.79 2.01 2.05 3.61 2.97 2.30 1.66 1.44 2.04 1.40 2.02 1.44
1.37 1.48
1.75 1.74 1.78 1.72 1.50 1.65 1.76 1.59 1.41 2.05 1.43 1.62 1.60 1.48 2.18 1.72 2.46 2.23
M
3.08
1.72
2.29
1.72
a
GEM
COIN8 TRIANGLE" DOG" NOUN" CHAIR"
Categories for which production of superordinates was faster than production of instances.
Materials. Twenty pairs of nested category names were constructed. For each pair of categories, the Superordinate category (Level 1) included everything that belonged in the subordinate category (Level 2). The nested categories used are presented in Table 1. The category names were printed on 5 X 8 in. index cards, with one category per card. Each S received 2 random permutations of the 40 cards. Half of the 5s named superordinates on the first 40 trials, and subordinates on the last 40 trials. The reverse arrangement held for the remaining 5s. Procedure. Each S was told that we were conducting a study on how memory works, that he would see items consisting of single words, and that he was to respond with a word that was a Superordinate (subordinate) of the stimulus word. He was given examples and told to respond as quickly as possible, but to avoid errors. The S sat in front of a screen in which there was a window covered by half-silvered glass. The index card containing the stimulus was placed in a dark enclosure behind the mirror and was presented by illuminating the enclosure. A microphone was placed in front of 5 and he responded by speaking into it. A trial consisted of the following events. As a card with the item printed in large type was placed in the darkened enclosure behind the half-silvered mirror, E said "Ready," and pressed a button that illuminated the stimulus. The 5's verbal response activated a voice key that stopped the clock and
terminated the trial. If S did not respond within 10 sec., the trial was terminated. A warm-up period of 10 trials, using stimuli different from those used for the experimental trials, preceded each block of experimental trials.
Results Only correct responses (96%) to the 20 pairs of nested categories are included in the following analyses. For each of the nested pairs, one category is more inclusive (higher in the semantic hierarchy) than the other. For example, VEHICLE includes more instances than CAR; in some sense, CAR is lower in the hierarchy than VEHICLE. We designated the higher category "Level 1" and the lower category "Level 2," and we computed a Level 1 and Level 2 median reaction time (RT) for each 5 for each of the 2 types of responses (subordinate and Superordinate). A 2 X 2 repeated measures analysis of variance indicated that the speed of producing a subordinate was significantly faster than the speed of producing a Superordinate, F (1, 21) = 46.46, p < .01. All 22 5s showed this effect. Furthermore,
RETRIEVAL OF SUPERORDINATES AND SUBORDINATES there was a significant effect of hierarchical position of a category on the time taken to respond, F (1, 21) = 9.86, p < .01. The interaction was also significant, F (1, 21) = 12.94, p < .01, indicating that the mean time taken to produce a superordinate was influenced by category level, while the time to produce a subordinate was not so influenced. Median RTs were computed for subordinate and superordinate responses to each of the 40 categories and are presented in Table 1. For 32 stimulus words, 5s produced a subordinate faster than he produced a superordinate; for 6 stimuli, the reverse result occurred. Discussion The finding that subordinates are produced more quickly than superordinates is inconsistent with Miller's (1969) and Collins and Quillian's (1972) intuitions that a superordinate is more accessible than a subordinate. On the other hand, Woodworth and Wells (1911) found that S produces superordinates faster than he produces subordinates, which is, of course, opposite to our own result. To reconcile their data with the present results, we must examine the Woodworth and Wells procedure more closely. In their experiment, 13 5s named superordinates of 20 stimulus words (for example, Ss produced a superordinate for OAK and for CABBAGE, etc.) and they named subordinates of 20 different words (for example, TREE and VEGETABLE). A comparison of the average time taken for the 2 types of responses indicated a shorter RT for naming superordinates. Although the present procedure is sounder than that of Woodworth and Wells (1911) in that we use the same stimulus words for the production of both superordinates and subordinates, the discrepancy between the 2 studies must be explained. A closer examination of the Woodworth and Wells stimulus words indicated that at least 12 of the words in the "name a superordinate" test were themselves instances of the words in the "name a subordinate" test. For example, 5s were required to name a superordinate of OAK, CABBAGE, and PENNY, but to name subordinates of TREE, VEGETABLE, and COIN. Not only were the words for which 5s produced superordinates lower in any assumed hierarchical structure than the words for the
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"subordinate test," but these words were lower than the words we used in Experiment I. Thus, the words for which Woodworth and Wells' 5s produced superordinates would constitute, in our terminology, a "Level 3." These observations suggested the possibility that the discrepancy between the Woodworth and Wells study and the present study was due to item differences (specifically in hierarchical level) between the 2 studies. To test this possibility, Experiment II was designed. EXPERIMENT II Method Subjects. The 5s were 22 college students, none of whom had participated in Experiment I. Materials. The 20 pairs of nested categories shown in Table 1 were used. In addition, a group of Level 3 categories was created by selecting one subordinate for each of the Level 2 categories. So, for example, for the pair FOOD-VEGETABLE, we selected the stimulus LETTUCE. Each 5 was presented a random permutation of the 60 unique categories. Procedure. The 5s were told that we were conducting an experiment on free association. They were told that they would see a series of 60 stimulus words, and after seeing each word, they were to write down the first word that it made them think of.
Results A simple count was made of all response words which were superordinate and those which were subordinate. In case of any doubt, the simple question "Does one of these words belong to the class of things named by the other word?" would usually solve the problem. This technique has been used successfully by Peters (1952). In Figure 1, the mean numbers of these 2 types of responses are presented separately for the 3 levels of stimulus words. A 2 (response type) X 3 (hierarchical level) X 22 (Ss) analysis of variance indicated that more subordinates than superordinates were given, F (1, 21) = 43.90, p < .01, Also significant were hierarchical level F (2, 42) = 32.94, p < .01, and the Level X Response Type interaction, F (2, 42) = 170.37, £ < .01. A 2 (response type) X 3 (levels) X 20 (category triplet) analysis of variance gave identical results, namely, significant response type, level, and interaction effects.
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ELIZABETH F. LOFTUS AND MARTIN BOLTON —I
SUBORDINATE
—I
SUPEROROINATE
FIGURE 1. Mean number of subordinate and superordinate responses given in Experiment II.
GENERAL DISCUSSION Whether or not the superordinate or subordinate is the stronger depends on the level of the stimulus word in the semantic hierarchy. At Levels 1 and 2, more subordinates are given as free associates (Experiment II) and subordinate responses are given faster (Experiment I). At the lowest level, Level 3, more superordinates are given as free associations, and presumably superordinate responses would be given faster. At this level, 5s appear to have few (if any) subordinate responses available. The reader can verify this fact by attempting to produce some instances of CABBAGE or PENNY. Subordinate responses are unlikely as free associates, but, if forced, S might reply with red cabbage or copper penny. Responses are highly idiosyncratic and correct single-word responses rarely occur. The finding in Experiment I that the mean time taken to produce a subordinate when given a Level 1 category was not different from the time taken to produce a subordinate to a Level 2 category replicates an earlier study of Loftus, Freedman, and Loftus (1970), which showed that the RT taken to retrieve a member of a given category was not significantly different from the RT taken to retrieve a member of a superset of that category. Hierarchical position of a category does, however, affect the speed of producing super-
ordinates. The RT taken to produce a superordinate of a Level 2 category such as CAR was faster than the RT taken to produce a superordinate of a Level 1 category such as VEHICLE. Thus, the more specific a word is, the faster 5s can produce a superordinate for that word. In fact, an examination of the 6 categories listed in Table 1 for which production of superordinates was faster than production of instances reveals that S of the categories are the lower member of their respective nested pair. Thus, not only do some Level 2 (or specific) categories have a readily accessible superordinate, but they do not have as accessible an instance. There are so few of these cases (and in all 6, there is less than .8-sec. difference in the RT to produce a subordinate vs. a superordinate), that we find it difficult to agree with any overall statement that "the instances of a concept are not easily accessible [Collins & Quillian, 1972, p. 320]." In fact, the results of both experiments point out the need for recognizing that statements such as "the subordinate-superordinate direction of association is stronger" (cf. Miller, 1969) are, at best, only sometimes true. REFERENCES COLLINS, A. M., & QUILLIAN, M. R. How to make a language user. In E. Tulving & W. Donaldson (Eds.), Organization of memory. New York: Academic Press, 1972. KENT, G. H., & ROSANOFF, A. J. A study of association in insanity. American Journal of Insanity, 1910, 67, 37-96, 317-390. LOFTUS, E. F., FREEDMAN, J. L., & LOFTUS, G. R. Retrieval of words from subordinate and superordinate categories in semantic hierarchies. Psychonomic Science, 1970, 21, 235-236. MILLER, G. A. The organization of lexical memory: Are word associations sufficient. In G. A. Talland & N. C. Waugh (Eds.), The pathology of memory. New York: Academic Press, 1969. PETERS, H. N. Supraordinality of associations and maladjustment. Journal of Psychology, 1952,33, 217-225. RUMELHART, D. E., LlNDSAV, P. H., & NoSMAN,
D. A. A process model of long-term memory. In E. Tulving & W. Donaldson (Eds.), Organization of memory. New York: Academic Press, 1972. WOODROW, H., & LOWELL, F. Children's association frequency tables. Psychological Monographs, 1916, 22(5, Whole No. 97). WOODWORTH, R. S., & WELLS, F. L. Association tests. Psychological Monographs, 1911, 13(5, Whole No. 57). (Received April 13, 1973)
