Prototypicality in a linguistic context: Effects on sentence structure

JOURNAL

OF MEMORY

Prototypicality

AND LANGUAGE

25, 59-74 (1986)

in a Linguistic

Context:

Effects

on Sentence

Structure

MICHAEL H. KELLY Cornell

University

J. KATHRYN BOCK Michigan

State

University

AND

FRANK C. KEIL Cornell

University

Three studiesexploredrelationships between prototypicahty and the structure of sentences in recall, preference ratings, and natural dictionary definitions. The first experiment showed that sentences were systematically changed in retail to allow prototypical instances of categories to be mentioned before nonprototypical instances. In the second experiment, sentences in which the prototype preceded the nonprototype were judged more natural than sentences with the opposite order. Finally, an examination of dictionary definitions of categories found that prototypes tended to occur before nonprototypes. These results can be explained in terms of the sensitivity of sentence production processes to the lexical or conceptual accessibility of prototypes. Such processes appear to adjust serial positions and, to a lesser extent, grammatical roles in order to allow lexical items to be produced soon after they are retrieved. 0 1986 Academic PRSS. IIK.

This paper examines the impact of prototypicality on sentence structure within a framework concerned with possible mechanisms underlying sentence production. Considerable research has indicated that conceptual categories are organized around “prototypes,” or central category members (Rosch & Mervis, 1975; Smith, Shoben, & Rips, 1974). Much of this research has been concerned with such problems as the structure of category representations, the determination of class member-

ships, and the composition of word meanings (see Smith & Medin, 1981, for review). Relatively little work has explored the role of prototypicality in normal language use. Most investigations have dealt instead with category instances presented in isolation, or in such simple equative constructions as A robin is a bird. Since past the age of two-if then-little of our speaking and understanding is devoted to the production and comprehension of discrete labels, it is important to study the relationships between prototypicality and the use of words in sentential contexts. In addition, the pervasiveness of the finding that conceptual categories are organized around prototypes makes this a promising domain in which to explore interactions between lexical/conceptual representations and language performance. The particular aspect of this interaction

This research was supported in part by an NSF predoctoral fellowship to the first author, and by NSF Grant BNS-81-02665. We thank Sharon August, Judy Loitherstein, Rachel Sheffet, and Jacqueline Toribio for assistance in running subjects, and Thomas H. Carr, Howard Kurtzman, and Rose T. Zacks for comments on the manuscript. Requests for reprints should be sent to Kathryn Bock, Department of Psychology, Psychology Research Building, Michigan State University, East Lansing, Ml 48824. 59

0749-596X/86 $3.00 Copyright 0 1986 by Academic Press. Inc. All rights of reoroduciion in anv form recerved

60

KELLY,BOCK,AND

that we investigated concerns the placement in sentences of constituents that denoted concepts varying in prototypicality. Our basic hypothesis was that words denoting “primary” concepts, such as prototypes, should be accorded primary positions in sentences, in terms of either grammatical role assignments or serial position. For example, the subject “of a sentence plays an important role as an anchor or focus (MacWhinney, 1977; Olson & Filby, 1972). In selecting constituents to serve this anchoring role, sentence production processes may favor elements that represent cognitive reference points, such as prototypes (Rosch, 1975). However, sentence production processes may not be directly sensitive to the conceptual importance of prototypes, but rather to factors correlated with that importance. We will develop these possibilities within a model of sentence production formulated by Garrett (1975, 1980, 1982). Based on analyses of speech errors, Garrett has proposed that two levels of linguistic processing are required for sentence construction, the functional level and the positional level. The functional level creates an abstract relational representation of the sentence, in which semantically specified words are assigned to phrases. Neither the order of elements in the eventual string nor their sounds are relevant at this level. Positional level processing, on the other hand, creates a serially ordered representation of the components of the sentence in terms of their phonological characteristics. Given their different roles in constructing a sentence, it is argued that the functional and positional levels draw upon different types of information. The functional level is the product of a mapping from the conceptual representation of the message onto a linguistic representation that specifies grammatical role assignments, such as the subject and object. The representation of the sentence after positional-level processing, on the other hand, consists of an ordered string of phonologi-

KEIL

cally specified words. Thus, whereas the functional level draws on conceptual/semantic information, the positional level draws on lexical/phonological information. In order to produce sentences fluently, it may be important for these processes to be sensitive to differences in the accessibility of conceptual and lexical information. “Accessibility” in this case means the relative ease with which a concept and its lexical representation can be retrieved and integrated with sentence production mechanisms. Conceptual accessibility may have an impact on assignments to grammatical roles such as those of the subject, direct object, and indirect object. Grammatical roles seem to be organized into a hierarchy (Keenan & Comrie, 1977) in which the subject dominates the direct object, the direct object dominates the indirect object, and so on. Bock and Warren (1985) found that more accessible concepts (as indexed by concreteness or imageability; Paivio, 1971) tended to appear in higher-level grammatical roles: Sentences were changed in recall in such a way that the subjects of the sentences were more concrete than the direct objects, and the direct objects more concrete than the indirect objects. Variations in imageability did not affect simple word order in conjoined phrases, suggesting that the effect was specific to the determination of grammatical relations. Because of its link to conceptual information and the assignment of grammatical roles, this type of accessibility appears to be related to functional level processing in Garrett’s framework. Lexical accessibility may also be important in sentence formulation. Variations in the accessibility of particular words during production may influence the integration of abstract syntactic frames with lexical information, causing the formulation system to alter the syntax or the word order of sentences to allow words to be produced soon after they are retrieved (Bock, 1982). To the extent that the effects of lexical accessibility are connected with the retrieval of

PROTOTYPICALITY

AND

words forms and the determination of serial order, they are most closely related to positional level processing. Prototypical members of categories appear to be both conceptually and lexically more accessible than less prototypical category members. Their conceptual accessibility is reflected in the ease of learning and of verifying their category membership (Heider & Olivier, 1972; Rosch, 1973). Their greater lexical accessibility is reflected in the speed and reliability of naming within and across languages (Berlin & Kay, 1969; Brown & Lenneberg, 1954). Because objects that are prototypical of their categories elicit few alternative labels, they are likely to be named faster than objects with many alternative labels (Lachman, Shaffer, & Hennrikus, 1974). High category dominance (which is strongly correlated with prototypicality, cf. Mervis, Catlin, & Rosch, 1976) is also associated with faster naming times (Freedman & Loftus, 1971). Finally, words denoting prototypes tend to be monosyllabic or monomorphemic (Brown & Lenneberg, 1954), and words with these characteristics may also be more accessible than polysyllabic or polymorphemic words (see Bock, 1982, for discussion). Because of differences in their conceptual accessibility, concepts that vary in prototypicality should be assigned to different grammatical roles at the functional level, with more prototypical concepts tending to appear as the subjects of sentences, and less prototypical concepts as direct objects. Because of their greater lexical accessibility, prototypes should be placed earlier than nonprototypes in the representation of the sentence at the positional level, especially when they both serve the same grammatical function. For example, when a prototype and nonprototype occur in a phrasal conjunct that serves as the direct object of a sentence (e.g., The student studied biology and geography to fulfill his science requirement), the prototype should tend to occur in the initial slot of the conjunct.

SENTENCE

STRUCTURE

61

In the experiments and observations that follow, we investigated these hypotheses about prototypicality and sentence structure in a memory task, in judgments of sentence naturalness, and in actual dictionary definitions of categories. In the tirst experiment, a sentence recall paradigm was used to assess the effects of prototypicality on sentence production. The sentences that were employed varied the order of mention of two expressions that denoted concepts differing in prototypicality. In half the sentences, the expression containing the more prototypical category member occurred before the expression containing the less prototypical member. The remaining sentences had the reversed order. In the initial phase of the experiment, these sentences were presented to subjects as the answers to a set of questions. In the second phase, the questions served as cues for recall (cf. Bock, 1977). The basic measure examined in the recalled sentences was the probability of inverting the order of the prototype and the nonprototype. If prototypical concepts and the words that denote them are more accessible than less prototypical concepts and the words that denote them, they should be placed earlier in reconstructed sentences. Thus, an expression that occurs Iater in a presented sentence, and mentions a prototypical concept, should tend to be shifted toward the front of the sentence in recall, ahead of an expression denoting a less prototypical concept. The opposite pattern, moving an expression mentioning a nonprototypical concept to a point earlier in the sentence, should be less common. Two types of sentences were used, simple declaratives (e.g.. The ring scratched the brooch in the jewelry box) and sentences with phrasal conjuncts (e.g., The flag’s colors were red and gold). In declarative sentences, the prototypical and the less prototypical category members occurred as the subjects and objects of active and passive sentences. A meaning-preserving shift in the order of expressions thus required a

62

KELLY.BOCK.AND

change in sentence structure and grammatical role assignments: An active sentence recalled in place of a semantically comparable passive has the original sentence’s subject as the object, and vice versa. In phrasal conjuncts, the words denoting more and less prototypical concepts occurred within conjunctive noun phrases. A change in their order does not affect syntactic structure or grammatical role assignments. Contrasting declaratives and phrasal conjuncts makes it possible to determine whether grammatical form is influenced to the same degree as serial order by the differential accessibility of concepts that vary in prototypicality. Words denoting prototypical versus less prototypical concepts may differ in other ways that could influence the order of words in and the structure of sentences. For example, the relative frequency of the former may be higher than that of the latter, and the former may commonly have fewer syllables than the latter. There appears to be some tendency for words used or heard recently to occur earlier in produced sentences (Bock & Irwin, 1980; see Scarborough, Cortese, & Scarborough, 1977, for evidence linking frequency effects to recency), and for words with fewer syllables to occur earlier, at least in phrasal conjuncts (Cooper & Ross, 1975; Pinker & Birdsong, 1979). These factors were controlled in the first experiment in order to ensure that they did not contribute to subjects’ performance. Because distortions in recall will be used to infer characteristics of the sentence production system, it is necessary to justify this linkage. There are a number of arguments in its favor. The dissociation between memory for the meaning and for the syntactic form of sentences, with the latter decaying relatively quickly (Anderson, 1974; Anderson & Paulson, 1977; Sachs, 1967), argues against the assumption that syntactic information is stored or, if stored, readily retrieved. In recalling sentences, then, subjects are likely to draw upon

KEIL

normal sentence production mechanisms to reconstruct the answers. The types of syntactic changes that typically occur in recall in fact tend to reflect the syntactic biases of normal speech (Binet & Henri, 1894; Bock & Brewer, 1974; Doob, 1962; James, Thompson, & Baldwin, 1973; Levelt & Kempen, 1975). With respect to syntactic formulation processes, then, the reconstructive recall paradigm may differ in relatively insignificant ways from normal conditions requiring descriptive or narrative speech, warranting certain generalizations from one situation to the other.

STUDY

1

Subjects. Eighty members of the Cornell

University participate teers.

community were paid $2.50 to or took part as unpaid volun-

Materials. Forty-four question-answer pairs were constructed, including 20 phrasal conjuncts and 24 simple declaratives. Half of the declaratives were in the active and half in the passive voice. Each answer consisted of a sentence containing two nouns from the same category. One noun was high and the other low in prototypicality as determined from their rankings in the Battig and Montague (1969) or McEvoy and Nelson (1982) category norms (see Mervis et al., 1976, for evidence that rankings of items in category norms are highly correlated with prototypicality ratings). We will designate these the prototypes and nonprototypes, respectively, as shorthand for “words in expressions denoting prototypical concepts” and “words in expressions denoting less prototypical concepts. ” For the phrasal conjuncts, the mean rank of the prototypes was 1.5 and that of the nonprototypes was 19.7. For the simple declaratives, the mean ranks were 1.1 and 15.0 for prototypes and nonprototypes, respectively. The prototypes appeared earlier than the nonprototypes in half the sentences of each type (phrasal

PROTOTYPICALITY

AND SENTENCE

conjunct, active, and passive). Word frequency (Kucera & Francis, 1967) was varied orthogonally to the prototypicality variable, so that in half of the sentences in which the prototype appeared first, the prototype was more frequent than the nonprototype, and similarly for that half of the sentences in which the prototype appeared second. The number of syllables in the prototype and nonprototype was equated within each sentence. Each sentence also included the name of the category to which the items belonged. The questions that were paired with the sentences were constructed to relate sensibly to the answers that the sentences provided. They did not contain the prototypical or nonprototypical expressions, synonyms, or definite descriptions that had the same referents as these expressions, nor the name of the category to which the items belonged. Examples of the questions and sentences are shown in Table 1. The Appendix contains a list of all the noun pairs used in the experiment. A second set of question-sentence pairs was created by altering each sentence while keeping the question the same. Declarative sentences changed in voice while pre-

OF SENTENCES

Sentence type

1 USED IN

STUDY

I

Question-sentence

pair

Phrasal conjunct Prototype first Prototype second Declarative Prototype first (active) Prototype second (passive)

Prototype first (passive) Prototype second (active)

63

serving the meaning of the sentence, so that a sentence that was passive in the first set was active in the second, and vice versa. Phrasal conjuncts were altered by interchanging the conjoined nouns. The question-sentence pairs from the two sets were assigned to two different lists. In each list, the pairs were arranged in four blocks of eleven sentences each. Each block contained a random arrangement of five phrasal conjuncts, three actives, and three passives, constrained to allow no more than three phrasal conjunct or three declarative sentences to appear consecutively. The order of the items within each block was identical across lists. Thus sentences with the same meaning occurred in the same serial position within the blocks of the two lists. One sentence at the beginning of each block and two at the end were added as fillers. Four different orders of the blocks within the lists were constructed according to a Latin square. There were thus eight separate conditions, four for each list. Ten subjects were assigned to each of the eight conditions. Procedure. Subjects were run in small groups, with 2 to 10 subjects in each 45 to 60-min session. For each of the four blocks

TABLE EXAMPLES

STRUCTURE

Q: What was the child’s errand? A: The child’s errand was to buy an APPLE and lemon at the fruit stand. A: The child’s errand was to buy a lemon and APPLE at the fruit stand. Q: What did Sears Roebuck report about sales? A: Sears Roebuck reported that SHIRTS outsold louts in their clothing department. A: Sears Roebuck reported that ha/s were outsold by SHIRTS in their clothing department. Q: What did the analysis of the meteorite reveal? A: The analysis of the metals in the meteorite revealed that IRON was surrounded by nickel. A: The analysis of the metals in the meteorite revealed that nickel surrounded IRON.

Note. Prototypical items are capitalized; nonprototypical

are italicized.

64

KELLY.

BOCK. AND KEIL

in a list, the experimenter first read aloud all 14 question-answer pairs. After reading the pairs, the experimenter read the questions alone. in the order in which they were originally presented. The subjects attempted to write the answer to each question in booklets. They were told at the beginning of the experiment that they would be asked to recall the answer to each question, and that the recalled answers should be complete sentences. Scoring. Two scorers examined all of the subjects’ answers and classified each into one of the following categories: (a) convct rccczll-recalled sentences were considered correct when they preserved the syntax and were consistent with the general meaning of the presented sentences, and maintained the original order of the prototype and nonprototype; (b) inrr~sion-an inversion was scored when the recalled sentence preserved the general meaning and syntax of the presented sentence while changing the order of the prototype and nonprototype, so that the prototype and nonprototype were reversed in phrasal conjuncts and were both reversed and in a different voice for simple declaratives: (c) con’ect appro.uimr~tion-correct approximations maintained the general meaning of the original sentence and the order of the prototype and nonprototype, but with a syntactic change; (d) inversion nppro.uOnation-an inversion approximation occurred under the same conditions as inversions except that the syntax of the recalled sentence did not fall into one of the appropriate syntactic categories (phrasal conjunct: active, or passive): (e) substitrltion-a substitution resulted from an incorrect recall in which another member of the same semantic category was substituted for the prototype or nonprototype; and (f) deletion-a deletion occurred when the prototype was recalled, but the nonprototype was not, or vice versa. Examples of sentences classified into each of these categories are provided in Table 2. All other recalled sentences were treated as errors.

Results The main analysis examined whether more inversions occurred for prototypesecond sentences (sentences in which the prototype followed the nonprototype in the presented version) than for prototype-first sentences (sentences in which the prototype preceded the nonprototype in the presented version) in subjects’ recall. Each subject received two recall scores for the phrasal conjunct sentences and two for the simple declaratives. The first represented the number of inversions for prototype-first sentences as a proportion of the number of such sentences whose meanings were correctly recalled. The second was the number of inversions for prototype-second sentences, again as a proportion of the number of such sentences whose meanings were correctly recalled. The use of these proportions neutralizes effects due to differences in the frequency with which the meanings of the sentences in the various conditions were recalled. The arc-sine transformation of these proportions were submitted to a 2 x 2 x 2 within-subjects analysis of variance. The factors were inversion type (prototype shifted ahead of the nonprototype or the reverse), sentence type (phrasal conjunct or simple declarative), and word frequency (prototype more frequent or nonprototype more frequent). No significant influences of word frequency were found, either as a main effect or in the interactions, so it will not be considered further. In all of the analyses to be reported, effects were considered significant when their associated probabilities were s.05. As Figure 1 shows, the proportion of inversions was greater when the inversion placed the prototype before the nonprototype (.19) than when the inversion placed the prototype after the nonprototype (. 1 I ). F( 1,79) = 16.89. However, this result was qualified by a significant interaction between inversion type and sentence type. F( 1.79) = 6.16. Planned comparisons re-

PROTOTYPICALITY

AND SENTENCE

65

STRUCTURE

TABLE 2 EXAMPLES

OF THE SCORING

Original sentence: The flag’s

colors

SYSTEM FOR STUDY 1 were gold and red.

Scoring category Correct recall Inversion Correct approximation lnversion approximation Substitution Deletion

vealed that the difference between these two types of inversions was significantly larger for phrasal conjuncts (.14) than for simple declaratives (.04), t(79) = 2.26. Overall, a higher proportion of inversions occurred for phrasal conjuncts (.20) than for simple declaratives (. 1 I), F(1,79) = 15.23. This difference suggests that subjects were better able to recall the original forms of the active and passive sentences. Because actives and passives differ not only in word order, but also in the closedclass words (was, is, by, and so on) used to mark syntactic differences, the probability of remembering information relevant to the presented forms of the sentences may be higher for declaratives than for conjuncts, where only the order differs. In item analyses, the proportion of items in which the initial constituent order was inverted to place the prototype before the

Example The The The The The The

flag’s flag’s flag’s flag’s flag’s flag’s

colors were gold and red. colors were red and gold. colors had gold next to red. colors had red next to gold. colors were blue and red. color was red.

nonprototype (.16) was greater than the proportion in which the nonprototype was placed earlier (. 10). This effect was significant in a matched-pairs t test, t(43) = 2.24. Because of the relatively small numbers of items for the individual sentence types, separate item analyses for phrasal conjuncts [t(19> = 1.62, p < .I.51 and declaratives [t(23) = 1.48, p < .20] were not significant . These findings point to the greater accessibility of prototypes in the production process, reflecting the ease of retrieving them from memory. Two additional effects support this conclusion. First, subjects tended to omit nonprototypes from their recalled sentences more often than prototypes (see Table 3). This was significant for declarative sentences [t(79) = 2.30 for subjects and t(23) = 2.10 for items], but not for phrasal conjuncts, although the trend was similar. Second, substitutions occurred more often for the nonprototypes than the prototypes.

Shift toward prototype before non-prototype Shift toword non-prototype

TABLE

3

MEAN NUMBER OF SUBSTITUTIONS AND DELETIONS OF PROTOTYPICAL AND NONPROTOTYPICAL ITEMS IN STUDY 1

Type of error PHRASAL CONJUNCTS

DECLARATIVES

FIG. 1. Mean proportions of phrasal conjunct and declarative sentences that inverted the order of the prototype and nonprototype in recall. Error bars represent the standard errors.

New word substituted for prototype New word substituted for nonprototype Prototype deleted Nonprototype deleted

Phrasal conjuncts

Declaratives

1.2

0.7

1.9 0.5 0.6

1.4 0.5 0.8

66

KELLY,

BOCK, AND KEIL

For declarative sentences, this effect was significant over both subjects and items [t(79) = 4.73 and r(23) = 2.24, respectively]. For phrasal conjuncts, the effect was significant over subjects [t(79) = 3.871 but not over items [t( 19) = 1.59, p < .20]. One final analysis examined whether there were any differences in recall of the meanings of the sentences across different conditions. For each subject, the number of sentences whose meaning was recalled correctly was tallied separately for prototypefirst and prototype-second sentences within the phrasal conjunct and declarative sentence types. This number included correct sentences, inversions, correct approximations, and inversion approximations (see the Scoring section). These data were analyzed using a 2 x 2 x 2 within-subjects analysis of variance. The factors were order in the original sentence (prototype first or second), syntactic type of the original sentence (phrasal conjunct or declarative), and word frequency (prototype more or less frequent than the nonprototype). A higher degree of meaning-preserving recall was found when the prototype preceded the nonprototype in the original sentence, F(1,79) = 14.19. Subjects recalled the meaning of an average of 12.7 sentences when the prototype was first in the original sentence compared with I I.5 sentences when the nonprototype was first. However, as Figure 2 shows, this effect was confined to declarative sentences, producing a significant interaction between item order and sentence type, F(1,79) = 11.44. Recall was higher for prototype-first than prototype-second sentences among declaratives, t(79) = 4.72, but not among phrasal conjuncts, t(79) = 0.36, p >.50. These patterns were replicated in the items analysis: More declarative items were recalled when the prototype preceded rather than followed the nonprototype, r(23) = 2.22. This difference was not significant for phrasal conjuncts @ > .50). The only other significant effect obtained in this analysis was for word frequency.

7.2 7.0 -

z

6.8-

6.6 y D 6.4 Fy 62=13 A 6.0 w 5.6 5 @Z 5.6ti 5.4 5.2 50iOECLARATIVES

PHRASAL CONJUNCTS

FIG. 2. Mean number of phrasal conjunct and declarative sentences in which the meanings were correctly recalled, as a function of whether the prototype or nonprototype appeared earlier in the presented sentence. Error bars represent the standard errors.

Mean levels of meaning-preserving recall were higher (12.7 to 11.4) for sentences in which the prototype was more frequent than the nonprototype, F(1,79) = 16.75. This frequency effect did not interact with the effects found for the order of the items in the original sentences. Declarative sentences with the prototype first were recalled more accurately than declaratives with the prototype second both when the prototype was more frequent [t(79) = 3.321 and when it was less frequent [t(79) = 3.331 than the nonprototype. Discussiorz The greater accessibility of prototypical concepts and the words that denote them affects the structure of recalled sentences in which they are instantiated. Assuming a connection between the reconstruction of sentences in recall and normal sentence formulation, the results indicate a preference for producing sentence forms that place expressions mentioning prototypical concepts before expressions mentioning nonprototypical concepts. The effect of variations in prototypicality suggests that sentence structure may be tailored to accommodate differences in the accessibility of the elements in a sentence (Bock, 1982). However, the results also showed that sentence production reflects the relative accessibility of category members

PROTOTYPICALITY

AND

more strongly in some cases than in others. Phrasal conjuncts were very sensitive to variations in prototypicality, whereas the trend toward placing prototypes in subject rather than object position was significantly weaker among declaratives. This difference is consistent with a distinction between different types of accessibility, conceptual versus lexical accessibility, operating at different levels of the production process, the functional versus the positional level (Garrett, 1975, 1980). We will consider other explanations for this difference under General Discussion. Placing the more prototypical member of a category in subject rather than object position also appeared to facilitate memory for the meanings of declarative sentences. If the ease of recall is correlated with initial comprehension, this result suggests that the most typical sentence structures formed in production correspond to those most readily understood. Along related lines, Clark and Chase (1974) found that people tended to describe an array such as * as “The star is above the line” rather than “The line is below the star,” and the former description was also more rapidly verified. MacWhinney (1977) has explained this pattern in terms of a figure-ground relation between the star and line. The former stands out as the figure, and so becomes the focus or starting point for comprehending descriptions of the array. Analogously, perhaps prototypes are a focus or reference point within their categories and so may serve as anchors in comprehension (Rosch, 1975). However, the order of the prototype and nonprototype influenced meaning-preserving recall only for declaratives. This result is consistent with the assumption that parsing operations treat phrases as minimal units (Kimball, 1973). If the parser delivers an analysis of the phrase as a whole to higher level comprehension processes, the

SENTENCE

STRUCTURE

67

original order of the nouns within the phrase will be irrelevant to those higher level processes. Placing a prototype before a nonprototype in conjunctive noun phrases may thus have little impact on sentence comprehension. This interpretation, of course, is tentative and needs to be explored in future investigations. In summary, the results of Study 1 suggest that some arrangements of the information in sentences are cognitively simpler than others. Our second experiment explored the extent to which subjects’ intuitions about the relative naturalness of sentences with different word orders support this conclusion. 2 There is considerable uniformity in judgments of the acceptability or naturalness of sentences, even when informants are not aware of the variables that influence their decisions. Thus, subjects are sensitive to the placement of definite and indefinite noun phrases (Hupet & Le Bouedec, 1975), to the animacy of sentence subjects (Clark & Begun, 1971), to variations in the syntax of semantically similar sentences (Bock & Brewer, 1974), and to subtle phonological differences (Oden & Lopes, 1981; Pinker & Birdsong, 1979). These preferences often appear to reflect normal production biases. For example, the properties of sentences created by subjects who filled in schematic sentence frames in an experiment by Clark (1965) were comparable to the properties of the sentences preferred in later studies by Clark and Begun (1971). In this experiment, we examined whether subjects would prefer sentences in which a prototype preceded a nonprototype more than sentences with the opposite order. Subjects. Twenty-four members of the Cornell community volunteered to participate. Materials. The same sentences used in Study 1 were employed here. The 44 pairs of phrasal conjunct and declarative sentences were randomly arranged in a twoSTUDY

68

KELLY,

BOCK,

page booklet. In half the pairs of each type, the sentence with the prototype first was placed above its meaning-preserving alternative with the prototype second. This arrangement was reversed for the remaining sentences. In a corresponding second list of sentence pairs, the order of the sentences in the pairs was reversed. Procedure. Twelve subjects were assigned to each of the two sentence lists, and run in groups of two to five. They were instructed to read the sentences in each pair and place a check next to the one that seemed most natural. The sessions required 10 to 15 min to complete. Results and Discussion If there were no systematic preference for one of the two sentences in a pair, the sentence with the prototype first would be chosen as more natural half of the time. For both the phrasal conjunct and declarative sentence types, this expected value was subtracted from the actual number of sentences with a prototype-first order that a particular subject selected. These difference scores should, on average, be positive if there is a bias toward the prototype-first sentences. Across subjects, the prototype-first sentences were judged to be more natural than the corresponding prototype-second sentences. For phrasal conjuncts, the subjects selected a mean of 62% of the prototypefirst sentences as more natural, t(23) = 3.82, p < .OOl. For declaratives, a mean of 54% of the prototype-first sentences were considered more natural, t(23) = 2.63, p < .025. The strong preference for active over passive sentences is likely to have attenuated the effect of prototypicality for declaratives. The item analysis for the phrasal conjuncts revealed that subjects consistently chose the prototype-first member of a given pair, t(19) = 2.95, p < .Ol. To determine whether the order of the prototype and nonprototype affected the declarative items, we analyzed the extent to which the differ-

AND

KEIL

ence between the active and passive sentences was reduced when the prototype was placed in the surface subject position of the passives. With prototypes as subjects of passive sentences, the preference for the active construction diminished from 72 to 67%, although the effect was only marginally significant, t(22) = 1.74, p < .lO. Subjects thus appear to be sensitive to the relations between prototypicality and sentence form. Of course, the ratings of sentence naturalness obtained here cannot indicate conclusively whether the subjects’ sensitivity is based on sentence production or comprehension mechanisms, neither, or both. Bock and Brewer (1974) found that the less natural a sentence was rated, the greater the likelihood that it would be transformed to a more natural structure in recall. However, naturalness ratings did not predict the ease of recalling the meaning of a sentence. If reconstructions in recall predominantly reflect sentence production mechanisms while levels of meaning-preserving recall reflect comprehension success, then Bock and Brewer’s study implies that the rated naturalness of a sentence is based at least partially on sensitivity to the way one constructs sentences. A somewhat similar pattern was obtained in a comparison of the results of this study with those of the previous experiment. For the phrasal conjunct and declarative sentences, the items were ranked in terms of (1) the degree of asymmetry in shifting the prototype ahead of the nonprototype rather than the reverse, and (2) the degree of asymmetry in meaning-preserving recall when the prototype appeared first in the original sentence as opposed to second. The same items from Study 2 were ranked in terms of the strength with which a sentence with the prototype first was judged as more natural than its meaning-preserving counterpart with the prototype second. The two ranks from Study 1 were each correlated with the rank from Study 2. Among phrasal conjuncts, a significant correlation was obtained between the distortions and

PROTOTYPICALITY

AND SENTENCE

naturalness ratings (rrhO = S25, p < .05), but not between meaning-preserving recall and naturalness ratings (rrho = ,020, p > .lO). This pattern is consistent with the hypothesis that the naturalness ratings for phrasal conjuncts reflect sensitivity to the way such structures are produced. For the declaratives, significant correlations were obtained for both the relation between distortions and naturalness ratings (r,,,O = .603, p < .OOS) and the relation between meaning-preserving recall and naturalness ratings (rrhO = .643, p < .005). Thus we cannot differentiate the sources of information subjects used to make their naturalness judgments for declaratives. The interpretations of Studies 1 and 2 rely on the degree to which sentence production mechanisms are reflected in sentence recall and preference ratings. Though many experiments point to the validity of this relationship, it is clearly worthwhile to explore whether prototypicality is correlated with sentence structure in a more naturalistic setting. Study 3 addressed this issue. STUDY

3

Definitions of category terms in a dictionary of English were analyzed to determine whether prototypical category members tended to be mentioned before less prototypical members. Four considerations led to the selection of a dictionary as a suitable source for analysis. First, a text was needed in which a large number of categories would be mentioned. Second, sentence structures similar to those used in Studies 1 and 2 were desired. In describing categories, dictionaries often mention instances of the category in phrasal conjunct constructions, so this second consideration was met. Third, we needed to be reasonably sure what category the writer had in mind when placing particular items in sentences, since Roth and Shoben (1983) have shown that prototypicality relations change with sentence context. A final advantage of a dictionary is the fact that the age of

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Samuel Johnson is gone: dictionaries are no longer written by a single person. Instead, a dictionary offers samples of writing from a large number of individuals. Any patterns of sentence structure gleaned from our analysis, then, cannot be attributed to the idiosyncrasies of a single writer. Of course, we must assume that in writing the text. normal language formulation processes were operative. Though many dictionary definitions are not couched in complete sentences, they certainly follow standard grammatical rules at a phrase level. It thus seems reasonable to assume that the writers of dictionaries rely on normal sentence production mechanisms in formulating definitions. Method The Random House Dictionary of the English Language (1969) served in the anal-

ysis. Definitions of categories used in the Battig and Montague (1969) and McEvoy and Nelson (1982) category norms were examined. It was often the case that the exact category titles from the norms did not appear in the dictionary, so reasonable approximations were used. Thus, for “part of an atom” in McEvoy and Nelson (1982), the definition of “atom” was examined in the dictionary. Fifty-eight cases were found in which at least two members of a category were mentioned. In each definition, it was noted whether examples of category instances were mentioned in a phrasal conjunct. If instances were mentioned, their order of appearance was recorded. For each definition, the order of appearance was correlated with the number of subjects who gave the item in the published category norm. When an item in the definition was unlisted in the norms, it received a score of 0. The norms were our measure of relative prototypicality. The orders of mention in definitions were also correlated with (a) word frequency (Kucera & Francis, 1967) and (b) length in syllables. Intercorrelations among prototypicality, word frequency, and syl-

70

KELLY,

BOCK, AND

lable length were also calculated for each definition. In 19 cases, the conjunctions of category members cited in a definition consisted of only two items, so that correlations in these cases could only be + 1 or - 1. Nonetheless, if associations between word order and the variables in question exist, most of the observed correlations should be positive. Results and Discussion The correlations for each item were treated as a type of score or index number (Darlington, 1975), and the means for these scores were evaluated using t tests to determine if they were significantly different from 0. Table 4 shows the mean correlations for the six comparisons. All of the correlations were significant except the one between word frequency and length in syllables. Thus, greater prototypicality, higher word frequency, and fewer syllables were all associated with earlier placement of a word in a definition. In addition, words denoting prototypical concepts tended to be more frequent and to have fewer syllables than words denoting less prototypical concepts. Because of the strong associations among prototypicality, word frequency, and syllable length, it is impossible to determine which of the variables is most closely related to the orders of the items in definitions. (Partial correlations cannot be calculated for three predictor variables when there are fewer than four values that

KEIL

the dependent variable can take. Of the 58 cases, there were 43 for which the definitions listed fewer than four examples of the category.) However, by controlling syllable length and word frequency, Study 1 demonstrated that prototypicality by itself could affect the placement of items in sentences: Distortions in recall produced sentences in which prototypical words were placed early in sentences. In the dictionary definitions generated by normal sentence production processes, the same pattern was found. The dictionary analysis is thus consistent with the inference from characteristics of sentence recall to those of sentence production. GENERAL Drscussro~

The structure of sentences is influenced by differences in the prototypicality of category members mentioned in them. In Study 1. sentences were changed in recall in a way that permitted more prototypical category members to be placed before less prototypical members of the same category. To the extent that these recall patterns reflect sentence production processes. it can be concluded that the relative prototypicality of concepts instantiated in different constituents of a sentence affects the order in which those constituents appear. Studies 2 and 3 provided converging evidence for the importance of category structure in sentence processing. In Study 2. sentences with a prototypical item preceding a nonprototypical item were con-

TABLE 4 AVERAGE

INTERCORRELATIONS

Word Order Prototypicality Syllables Frequency

* p < .05. ** p < .Ol. *** I, < ,001

AMONG

WORD ORDER, FREQUENCY

PROTOTYPICALITY, IN STUDY 3

Word order

Prototypicality

-

- .357*** -

SYLLABLE

Syllables

.250** -.197+ -

LENGTH,

AND

WORD

Frequency - .252** .385*** - .099 -

PROTOTYPICALITY

APPENDIX:

ANDSENTENCE

NOUN PAIRS USED IN STUDIES 1 AND 2

Category

Prototype

Phrasal conjuncts Color Vegetable Fruit Alcoholic beverage Religious article Flavoring Part of the body Kitchen utensil Science Weapon Furniture

Red Carrot Apple Beer Bible Salt Arms Knife Biology Guns Chair sport Football Gardening tool Rake Occupation Doctors Farm animal cow Insect Ants Bread Wheat Weather phenomena In Rain Surgical instrument Saclpel Camping equipment Tent

Declaratives Jewelry Singing voice Bird Metal Vehicle Relative Fuel Bird of prey City Circus act Tool Wood Precious stone Snake Cosmetic Building Musical instrument Geometric shape Natural earth formation TOY Part of speech Clothing Clergy Train car

Nonprototype Gold Onion Lemon Rye Candle Milk Face Glass Geography Stone Shelf Sailing Plow Writers Duck Worms Corn Ice Needle Stove

Ring Soprano Robin Iron Car Aunt Oil Hawk New York Clown Hammer Oak Diamond Rattlesnake Lipstick Skyscraper Piano Triangle

Brooch Falsetto Chicken Nickel Boat Wife Peat Owl Detroit Dog Crowbar Beech Silver Constrictor Perfume Apartment Tambourine Pentagon

Mountain Dolls Verb Shirts Priest Caboose

River Kites Vowel Hats Monk Sleeper

sidered more natural than sentences with the opposite ordering. In addition, the probability of selecting as more natural a particular sentence with the prototype first, determined in Study 2, was highly corre-

STRUCTURE

71

lated with the strength of the tendency to shift the prototype in front of the nonprototype in recalling that sentence in Study I. The results of Study 3 were consistent with the assumptions about relationships between recall and characteristics of sentence production that were made in the first experiment. An analysis of written samples of English taken from a dictionary found that prototypical members of a category were indeed placed before nonprototypical members in sentences with phrasal conjunct constructions. Sensitivity to the effects of prototypicality nonetheless differed as a function of the syntactic structure of the recalled sentences. In the production of sentences in Experiment 1, prototypicality had a stronger effect on constituent order in phrasal conjuncts than in declaratives. Thus, prototypicality influenced the order of words whose grammatical roles were the same significantly more than it influenced the determination of the subjects and objects of declarative sentences. In terms of the sentence production model outlined in the introduction, these results suggest that production processes are more sensitive to the relative accessibility of prototypes at the positional than at the functional level, so that prototypicality interacts more with serial positioning in sentences than with grammatical role assignments. Thus, the conceptual accessibility of prototypical concepts may be less important in sentence formulation than the accessibility of the words that denote them. The relationship between conceptual and lexical accessibility has received relatively little attention in investigations of prototypicality, despite a radical shift in the attribution of prototypicality phenomena from the linguistic to the conceptual domain (Brown, 1976). In Brown and Lenneberg’s (1954) classic paper, the finding that the most easily remembered colors were also those that were named with the greatest univocality was attributed to weak linguistic determinism: What makes certain categories of experience more salient than

72

KELLY.

BOCK,

others is the ease of talking about them. The finding that particular regions of the spectrum are prominent regardless of how or even whether a language or its users name them (Heider, I97 1: Heider & Olivier, 1972) forced a reevaluation of this conclusion. Prototypicality effects have since been widely regarded as reflections of basic features of perceptual or conceptual organization. Questions nonetheless remain about the nature of prototypicality. Recent findings suggest that decidedly nonnatural, ad hoc categories (e.g., “things not to eat on a diet”) exhibit strong typicality gradients (Barsalou, 1983), that categories with clear defining features (e.g.. even numbers) also show typicality effects (Armstrong, Gleitman, & Gleitman, 1983), and that typicality ratings for category members obtained out of context do not predict the typicality of instances mentioned in particular contexts (Roth & Shoben, 1983). The difficulties posed by findings such as these for a conceptual-representation account of prototypicality might be resolved if the role of lexical factors were considered. In light of the emphasis on linguistic responses in some studies of prototypicality. perhaps the ease of retrieving a word with the right denotative properties (from a much larger preliminary candidate set) plays an important part in many of the typicality effects that have been observed. This is particularly applicable to the category dominance norms that provide the materials for many investigations of prototypicality, including the present ones. The possibility that lexical accessibility may sometimes account for more of the variance than conceptual accessibility in the production of words is suggested in research reported by Wingfield (1968). Oldfield and Wingfield (1965) had found that the time required to name an object was inversely proportional to the frequency of the name. Wingfield (1968) then explored whether this effect was due to lexical retrieval or the speed with which objects are identified. Wingfield found that the time

AND

KEIL

needed to match a name to a picture did not depend on the relative rarity or commonness of the object portrayed, and concluded that naming difficulty reflected lexical access rather than identification problems. Wingfield’s findings are consistent with the assumption that prototypical objects are not recognized any faster than nonprototypical objects. If recognizing an object requires linking it to its conceptual representation, and the conceptual representations of prototypical objects are more accessible than those of nonprototypical objects, instances of prototypical concepts (which Wingfield’s common objects seem to have been) should have been identified more rapidly than instances of nonprototypical concepts. This did not happen. It is thus possible that in the production of sentences, prototypicality primarily influences the retrieval of words. If so, a simpler account of the prototype ordering effects can be developed. This account attributes all of the effects of prototypicality found in the present experiments to the positional level. One of the positional level processes hypothesized by Garrett t 1975, 1980, 1982) involves the construction of an abstract planning frame consisting of closed class words and bound morphemes. The frame seems to be developed before content words are inserted, since the usual error pattern involves misplacement of content words, with the frame elements appearing in their intended positions (as in She’s already tr-ttnked tuv paclis, Garrett, 1975). There is some evidence that planning frames may be altered during production to accommodate differences in the retrievability of lexical items (Levelt & Maassen. 1981, Experiment 3). The results of Study 1 can be explained if the sentence production system adapts to the relative accessibility of words more readily when alterations of a previously constructed sentence frame are not required. Thus. reversing the order of nouns in a phrasal conjunct requires little or no revision of the planning frame. But for the subject and object nouns

PROTOTYPICALITY

AND SENTENCE

in a declarative sentence to interchange, without changing the meaning, a different frame must be used. This accords with the pattern found in the first experiment: Phrasal conjunct sentences were more sensitive than simple declaratives to variations in the prototypicality of words in different sentence locations, with prototypical items being shifted toward the front of sentences more often. The fact that more changes occurred overall in phrasal conjuncts than in declaratives is also consistent with this account. In summary, these studies have shown that sentence production processes are sensitive to the accessibility of prototypical concepts or the words that denote them. This sensitivity is reflected in the preferential placement of words denoting prototypes in the initial slot of a conjunctive phrase and, to a lesser extent, in the position of surface subject. We have suggested two alternative explanations for the effects of prototypicality on production processes. One of these assumes that both conceptual and lexical characteristics of prototypicality influence production, but at different levels of processing. The second suggests that only the lexical correlates of prototypicality play a role in the determination of sentence form, with different consequences for the assignment of grammatical roles versus the ordering of words. These differences result from the way in which lexical information is integrated with the syntactic configurations of incipient sentences. Too little is known at present, about either prototypicality or production, to decide between these alternatives. However, further development of the links between theories of sentence processing and theories of conceptual representation should yield a richer and more constrained understanding of human language ability. REFERENCES ANDERSON, J. R. (1974). Verbatim and propositional representation of sentences in immediate and long-term memory. Journal of Verbal Learning and Verbal

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