Filling in the Missing Links - Science Direct

JOURNAL OF VERBAL LEARNING AND VERBAL BEHAVIOR 21, 99--107 (1982)

Filling in the Missing Links SUSAN KEMPER

University of Kansas In two e x p e r i m e n t s , readers were asked to restore missing actions and physical and mental states to short narratives. T h e narratives were written using a t a x o n o m y of the possible causal connections b e t w e e n actions and states. Gaps were created in the e v e n t chains underlying the narratives by deleting actions and physical and mental states. Some deletions resulted in violations of the e v e n t chain t a x o n o m y while others did not. The results of both e x p e r i m e n t s indicate that readers use knowledge of possible causal s e q u e n c e s to detect and repair gaps in stories. Violations were detected and repaired more often than nonviolations and few u n n e c e s s a r y additions were made to the stories. However, familiarity with the plots a n d characters did facilitate detecting and repairing gaps. In E x p e r i m e n t I, actions were more likely to be restored than physical or mental states. H o w e v e r , the incidence of restored physical and mental states increased from the first to the last third of each story. In E x p e r i m e n t II, readers restored superordinate actions m o r e often than subordinate ones. Further, subordinate actions missing from the last third of the stories were restored more often than those missing from the first third. K n o w l e d g e of the hierarchical structure of plans and actions as well as knowledge of the e v e n t chain t a x o n o m y is used by readers to detect and repair gaps in stories.

tions. Rather, a sentence is decomposed into one or more underlying states or actions. This decomposition is based on both linguistic knowledge about word meanings and usage and world knowledge about the causes and c o n s e q u e n c e s of physical events and human actions (de Beaugrande, 1980; Trabasso, 1980). Inferences, guided by both linguistic knowledge and world knowledge, establish the causal and temporal connections between the actions and states described by the text. The reader must understand each of the links in the event chain underlying the text. The links, like the connections between them, can be directly stated in the text or inferred by the reader. As Schank and Abelson (1977), Omanson et al. (1978), and Warren et al. (1979) have argued, inferring the causal connections and links in event chains is an orderly, rule-governed activity. These researchers have proposed a taxonomy of possible connections between the actions and state described in stories. This taxonomy identifies four types of causality: (1) new physical states result from actions, (2) new mental

Stories describe chains of events unfolding in time (Schank, 1975; Schank & Abelson, 1977; Trabasso, 1980). The links of these event chains are the actions and mental states of the story characters and the physical states of the story worlds. Causal and temporal connections between the states and actions described in the stories tie them together as chains of events (Graesser, Robertson, Lovelace, & Swinehart, 1980; Graesser, Robertson, & Anderson, 1981; Graesser, Woll, Kowalski, & Smith, 1980; Omanson, Warren, & Trabasso, 1978; Warren, Nicholas, & Trabasso, 1979). In order to understand a story, a reader must understand the causal connections between the story's actions and states. In conceptual dependency theory (Riesbeck & Schank, .1978; Schank & Abelson, 1977) there is no direct correspondence between linguistic entities (e.g., verbs, clauses, or sentences) and underlying states and acThis research was supported by University of Kansas General R e s e a r c h Allocation 3430-x0-0038. Req u e s t s for reprints m a y be a d d r e s s e d to the author at: D e p a r t m e n t of Psychology, 426 F r a s e r Hall, University o f K a n s a s , L a w r e n c e , K a n s . 66045. 99

0022-5371/82/010099-09502.00/0 Copyright © 1982by AcademicPress, Inc. All rights of reproduction in any form reserved.

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SUSAN KEMPER

states are initiated by actions or physical states, (3) actions are enabled or disenabled by physical states, and (4) mental states are the r e a s o n s f o r a c t i o n s . T h i s c a u s a l t a x o n o m y in turn characterizes a t a x o n o m y of possible chains of events. Five types of causal s e q u e n c e s are p e r m i t t e d by the taxonomy: (1) A C T I O N S - result i n - - P H Y S I C A L STATES, (2) A C T I O N S - initiate--~MENTAL STATES, (3) P H Y S I C A L S T A T E S - ( d i s ) e n able---~ACTIONS, (4) P H Y S I C A L STATES-initiate---~ MENTAL STATES, (5) M E N T A L S T A T E S - r e a s o n for--+ ACTIONS. The t a x o n o m y categorizes those types of action and state sequences that are logically possible. It also identifies four sequences that violate the causal rules: (1) a c t i o n - a c tion, (2) physical s t a t e - p h y s i c a l state, (3) mental s t a t e - p h y s i c a l state, and (4) mental s t a t e - m e n t a l state sequences violate the taxonomy. Thus one action can neither initiate nor result in a second action, a mental state can never be the reason for another mental state or for a physical state, and one physical state cannot enable or initiate another. To the extent that the casual event chain taxonomy is used by readers to interpret the events unfolding in a story, readers should detect violations o f the taxonomy. Further, if readers do use the event chain t a x o n o m y in o r d e r to infer the actions, physical states, and mental states implicitly required by the story, they should be able to repair violations o f the t a x o n o m y by restoring missing actions and states. EXPERIMENT I

E x p e r i m e n t I was designed to explore whether readers can detect and repair gaps in event chains. Eight types of three-link event chains were considered:

1. A C T I O N - r e s u l t s i n - - ~ P H Y S I C A L S T A T E - e n a b l e s--~ M E N T A L STATE, 2. A C T I O N - initiate s--~MENTAL STATE-reason for~ACTION, 3. A C T I O N - r e s u l t s i n - - P H Y S I C A L S T A T E - enables---~ACTION, 4. P H Y S I C A L S T A T E - i n i t i a t e s ~ MENTAL STATE-reason for---~ACTION, 5. P H Y S I C A L STATE-enables---~ACT I O N - r e s u l t s in--~PHYSICAL STATE, 6. P H Y S I C A L STATE-enables---~ACT I O N - initiate s---~M E N T A L S T A T E , 7. M E N T A L S T A T E - r e a s o n for---~ A C T I O N - initiates---~MENTAL STATE, 8. M E N T A L S T A T E - r e a s o n f o r ~ ACTION-results in--PHYSICAL STATE. These eight types of three-link event chains conform to the rules of the e v e n t chain taxonomy. Three-link event chains may be transformed into two-link chains by deleting the medial link. When the medial link of chains (1), (4), and (6) is deleted, the resulting c h a i n is n o t a v i o l a t i o n o f the e v e n t taxonomy. An action can directly initiate a mental state so that the deletion of a physical s t a t e in (1) d o e s n o t v i o l a t e the taxonomy. So too, a physical state can initiate a mental state or enable an action so that deleting the medial link of chains (4) and (6) does not violate the taxonomy. The taxonomy proscribes a c t i o n - a c t i o n , physical s t a t e - p h y s i c a l state, and mental s t a t e - m e n t a l state causal s e q u e n c e s as well as mental s t a t e - p h y s i c a l state causality. Thus when the medial link in chains (2), (3), (5), (7), and (8) is deleted, the t a x o n o m y is violated. If readers apply the rules of the event chain t a x o n o m y in order to establish connections between story elements, they should detect violations of the taxonomy. Further, when given the opportunity to repair or extend stories, readers should be

MISSING LINKS

able to repair gaps in story e v e n t chains by restoring missing actions, physical states, and mental states. E x p e r i m e n t I thus c o m p a r e s how likely readers are to detect and repair gaps that violate the t a x o n o m y and gaps that do not violate the t a x o n o m y . Readers were asked to modify stories by inserting additional material to fill in any gaps they detected. Their a c c u r a c y in detecting and restoring missing actions, physical states, and mental states was examined for gaps occurring in each third of the stories' event chains.

Method Subjects. Thirty-six naive, native speakers of English were recruited from introductory p s y c h o l o g y classes. All received course credit for their participation. Materials. Six basic stories were created. Each consisted of a chain of 30 actions, p h y s i c a l states, and m e n t a l states connected according to the rules of the event chain t a x o n o m y . Six different versions of each story were then constructed by creating gaps in the event chain. In each version three links in the event chain were deleted. One gap occurred in the first, middle, and last third of the story chain. One action, one physical state, and one mental state were deleted per story version. H a l f of the deletions resulted in violations of the e v e n t chain t a x o n o m y ; half did not violate the t a x o n o m y . Across the entire set of materials, each type of gap o c c u r r e d equally often in each position. An e x a m p l e story chain is presented in Table 1; the gaps made in the chain to produce the different versions are indicated. Task. Each subject read six stories. F o r each story, the subjects received an ord e r e d d e c k of 27 cards. E a c h card contained a sentence describing one link in the underlying event chain. The subjects were instructed to read through the story deck. When finished, they were to fill out and insert additional cards into the deck to repair any gaps in the story event chain. That is, t h e y w e r e told " S o m e e v e n t s f r o m the

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stories m a y be missing. If the story seems incomplete to you, please supply the missing information. As you read the stories, you m a y detect " g a p s " in them. Please fill in the gaps by writing one or more sentences on a card and inserting the card into the gap in the s t o r y . " No restrictions were placed on the n u m b e r or type of additions subjects could m a k e to the stories. Across the six stories read b y each subject, each combination of gap type (violation vs nonviolation), type of missing link (action vs physical state vs mental state), and position within the story occurred once.

Results T w o separate analyses were perfomed: the first examined the locations of all the additions to the stories the subjects made; the second examined how the subjects filled in the actual gaps in the story chains. The subjects' insertions were classified as either actions, physical states, or mental states according to the rules stated above. T w o coders independently classified the insertions. T h e y agreed on 95% of the insertions; 93% of the insertions fell into one or another of the three categories. In the first analysis, the n u m b e r of additions each subject made to the stories was tabulated by summing together the n u m b e r o f a c t i o n s , m e n t a l s t a t e s , and p h y s i c a l states inserted into each third of the stories. E a c h i n s e r t i o n w a s c l a s s i f i e d as e i t h e r n e c e s s a r y to the e v e n t chain b e c a u s e it filled an actual gap in the chain or unnecessary because no gap occurred at that point in the e v e n t chain. A s u m m a r y o f these results is presented in Table 2. F e w u n n e c e s s a r y links were added to the event chains; more links were added to the last third of the stories than to the first two-thirds. These observations were confirmed by a 2 x 3 A N O V A of the incidence of additions to the stories. N e c e s s a r y versus u n n e c e s s a r y additions and position of the addition (early vs middle vs late) were within-subject factors. Both main effects were significant (type of addition: F(1,35) =

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SUSAN KEMPER TABLE 1

THE EVENT CHAIN UNDERLYING ONE STORY AND THE DELETIONS MADE IN ORDER TO PRODUCE THE SIX DIFFERENT VERSIONS. EACH LINK IN THE CHAIN IS NUMBERED SO THAT PARTICULAR DELETIONS CAN BE IDENTIFIED

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Physical state Mental State Action Physical state Action Mental state Action Physical state Mental state Action Physical state Action Physical state Mental state Action Physical state Action Mental state Action Mental state Action Mental state Action Physical state Action Mental state Action Physical state Mental state Action

The sun was shining and a brisk breeze was blowing Johnny wanted to fly his new kite He ran down the street Johnny arrived at home He walked into the garage He saw his kite and string Johnny grabbed the kite and string Johnny held the kite and string Johnny decided to take it to the meadow Johnny rode his bike Johnny arrived at the meadow Johnny tied the string to the kite The string was attached to the kite Johnny knew the kite could safely fly high Johnny ran, pulling the kite behind him The kite caught the wind and rose Johnny let out lots of string Johnny was happy to see the kite so high Johnny let out even more string Johnny was sad because the kite pulled at the string Johnny let out the rest of the string Johnny was upset because the kite strained so at the string Johnny broke the string The kite flew up and up Johnny gazed for a long time at the kite Johnny realized it was time for dinner Johnny rode his bike Johnny arrived at home Johnny realized he could never fly his kite again Johnny cried

TABLE l--Continued Code number of the links deleted Position

Actions Violations Nonviolations Physical states Violations Nonviolations Mental states Violations Nonviolations

Early

Middi~

Late

7 5

19 17

27 25

4 8

16 13

24 28

6 9

18 14

26 29

69.30; position: F(2,70) = 3.88; both p < O.O5). In the s e c o n d a n a l y s i s , only a c t i o n s , physical states, and mental states inserted into actual gaps in the event chains were

c o n s i d e r e d . All o t h e r a d d i t i o n s to the stories were ignored. F o r each subject, correctly restored actions, physical states, and mental states were identified. T h e y were classified by location of the original gap and whether or not the gap resulted in a violation of the event chain t a x o n o m y . A summ a r y of these results is presented in Table 3. A 3 x 2 × 3 A N O V A on position of the gap TABLE 2 NUMBER OF ADDITIONS TO THE STORIES MADE BY THE 36 SUBJECTS Position

Necessary addition Unnecessary addition

Early

Middle

Late

60 12

67 19

80 28

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TABLE 3 NUMBER OF ACTIONS, PHYSICAL STATES, AND MENTAL STATES RESTORED TO THE STORIES BY THE 36 SUBJECTS

Position Type of gap and addition Early

Middle Late

Violation Actions Physical states Mental states

27 7 5

28 13 8

27 16 13

Nonviolation Actions Physical states Mental states

10 6 4

10 6 3

9 9 5

(early vs middle vs late in the story), type of gap (violation vs nonviolation), and type of r e s t o r a t i o n (action vs p h y s i c a l s t a t e vs mental state) was performed. The main effects of type of gap, F(1,35) = 55.43, p < 0.001, and type of restoration, F(2,70) = 57.03, p < 0.001, were highly significant. Further, their interaction was significant, F(2,70 = 12.22, p < 0.001. The main effect of position, F = 1.76, p > 0.05, was not significant although the t h r e e - w a y interaction was, F(4,140) = 2.79, p < 0.05. Gaps that violated the event chain t a x o n o m y were repaired more often than gaps that did not. Missing actions were correctly restored more often than were either missing p h y s i c a l states, t(35) = 3.00, p < 0.05, or mental states, t(35) = 4.13, p < 0.05. Physical states and mental states were correctly restored equally often, t(35) = 1.13, p > .05. F o r gaps that violated the t a x o n o m y , the incidence of missing actions supplied correctly was not affected by the position of the gap within the story. H o w ever, physical states, t(35) = 3.50, and mental states, t(35) = 2.75, missing from the last third of the stories w e r e r e s t o r e d m o r e often than those missing f r o m the first third (both p < 0.05). Discussion

E x p e r i m e n t I was designed to demonstrate that readers use the rules of the event chain t a x o n o m y in order to detect and re-

pair gaps in stories. The results support the prediction that violations of the event chain t a x o n o m y would be detected and that readers would be able to restore missing actions, physical states, and mental states. When given the opportunity to improve the stories by supplying missing links, readers insert new information into the gaps, rep a i r i n g v i o l a t i o n s o f the e v e n t c h a i n t a x o n o m y . Readers recognize the integrity of the intact story event chains since few spurious, unnecessary insertions were made into these stories. R e a d e r s a c c u r a t e l y d e t e c t and r e c o n s t r u c t m i s s i n g a c t i o n s t h r o u g h o u t the stories. Such gaps can be filled on the basis of knowledge of the rules of the event chain t a x o n o m y alone. H o w e v e r , knowledge of the actual events unfolding in the story is n e c e s s a r y in order to detect and restore missing m e n t a l and p h y s i c a l states. As readers progress further into the stories, they are better able to reconstruct missing mental and physical states. The event chain t a x o n o m y describes the possible causal connections among actions, physical states, and mental states. It does not directly account for r e a d e r s ' bias in favor of restoring missing actions. Throughout the stories, readers restored more missing actions than either missing p h y s i c a l states or mental states. This finding as well as those of Black and B o w e r (1979) and G r a e s s e r et al. (1981) suggests that readers' i n t e r p r e t a t i o n s o f stories are o r g a n i z e d around the sequence of actions executed by the protagonist. While physical states and mental states m a y be essential to a c o m p l e t e c h a r a c t e r i z a t i o n of the causal c o n n e c t i o n s b e t w e e n story constituents, readers detect and restore only 22% of the missing states. In contrast, readers restore 51% of the missing actions. Missing actions are more salient and the resulting gaps more easily filled than missing physical or mental states. EXPERIMENT II The event chain t a x o n o m y describes only the linear, c a u s a l s t r u c t u r e o f s t o r i e s .

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S t o r i e s , h o w e v e r , have a h i e r a r c h i c a l structure as well as a linear structure. As the story grammar approach to narrative analysis suggests (for example, Mandler & Johnson, 1977; Stein & Glenn, 1979) stories may be characterized by a sequence of episodes; further episodes may be composed of s u b o r d i n a t e constituents. As Black and Bower (1980) and Graesser, Robertson, Lovelace, & Swinehart (1980) have argued, the actions that story characters execute may themselves be decomposed into a hierarchy. When confronted with a problem or task, a character executes both general, low-level instrumental actions and more task-specific, high-level actions. Low-level or subordinate actions are the basic components of many different problem solutions and are the temporal and causal prerequisites for the superordinate actions. High-level, superordinate actions resolve the problem by resulting in the desired physical state. Experiment II was designed to explore w h e t h e r r e a d e r s distinguish b e t w e e n superordinate and subordinate constituents of stories. In particular, the depth of an action within an action hierarchy may determine whether or not a reader will spontaneously fill in a gap created by deleting the action. The event chain t a x o n o m y may interact with the hierarchical structure of stories such that missing subordinate actions are not detected and restored.

Method Subjects~ Forty native speakers of English participated. All were recruited from introductory psychology courses. Materials. F o u r basic stories w e r e created. In each, the character was confronted with a general problem such as obtaining a present or renting an apartment. Each story included three temporally and c a u s a l l y o r d e r e d e p i s o d e s that c o r r e sponded to different subproblems. For example, in order to obtain a present, the character was required to first get some money, then to go downtown, and finally,

to select the present. Each episode, in turn, involved a sequence of six actions. The actions were temporally and causally ordered from subordinate, instrumental actions to superordinate actions. Different versions of each story were then created by deleting actions to create gaps in the stories. Half of the resulting gaps violated the event chain taxonomy; half were consistent with the taxonomy. One action was deleted from each episode of the stories. Further, half the deleted actions were from the first, second, or third levels of the underlying action hierarchy (subordinate actions) and half were from the fourth, fifth, or sixth levels of the underlying action hierarchy (superordinate actions). Across the set of stories, each type of gap (violation vs nonviolation) and each type of action deleted (superordinate vs subordinate) occurred equally often in each of the three episodes. Table 4 presents the event chain underlying the first episode of one story and indicates the deletions made for the different versions? Task. Each subject read four stories. As in Experiment I, they were instructed to look for and repair gaps in the stories. Across the four stories read by each subject, each combination of gap and action deletion occurred once in each episode location.

Results Two judges i n d e p e n d e n t l y identified those actions the subjects correctly restored to the stories. They agreed on 97% of their decisions. Only actions correctly located within the gaps in the story event chains were considered; all other additions were ignored by the judges. For each subj e c t , c o r r e c t l y r e s t o r e d actions were categorized by location (first vs second vs third episode), gap (violation vs nonviolation), and action type (superordinate vs 1 The four stories used in Experiement II varied in length. The shortest had 42 links while the longest included 63. The three episodes composing each story also varied in length between 15 and 24 links.

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TABLE 4 THE EVENT CHAIN UNDERLYING THE FIRST EPISODE OF ONE STORY. ACTIONS DELETED IN THE DIFFERENT VERSIONS ARE INDICATED BELOW. THE ACTIONS ARE NUMBERED So THAT THE DELETED ACTIONS CAN BE IDENTIFIED

1 2 3 4 5 6

Sunday was Mother's Day John wanted to give his mother some flowers John had no money John searched through all his pockets John decided to open his piggy bank John took the bank down from the shelf John held the bank John tried to open the lid with his fingers The latch snapped off John tried to pry open the lid with a screwdriver John realized he couldn't pry open the lid John dropped the bank It broke John counted the coins John learned he had $4.79

Physical state Mental state Physical state Action Mental state Action Physical state Action Physical state Action Mental state Action Physical state Action Mental state TABLE 4~[7ontinued Code number of the actions deleted

Violations Nonviolations

Subordinate action 2 I

Superordinate action 5 4

s u b o r d i n a t e ) . T h e s e r e s u l t s a r e p r e s e n t e d in T a b l e 5. A 3 × 2 x 3 A N O V A w a s p e r f o r m e d ; location, t y p e o f g a p , a n d t y p e o f a c t i o n w e r e within-subject factors. In this analysis, superordinate actions were restored more often than were subordinate actions, F(1,39) = 17.19, p < 0.001. G a p s t h a t viol a t e d t h e e v e n t c h a i n t a x o n o m y w e r e corTABLE 5 NUMBER OF MISSING SUPERORDINATE AND SUBORDINATE ACTIONS RESTORED TO EACH EPISODE BY THE 40 SUBJECTS Episode Type of gap and action Violation Superordinate Subordinate Nonviolation Superordinate Subordinate

First

Second

Third

29 7

27 10

29 14

14 7

20 8

22 7

r e c t e d m o r e o f t e n t h a n g a p s t h a t d i d not, F(1,39) = 75.20, p < 0.001. F u r t h e r , the i n t e r a c t i o n o f a c t i o n t y p e a n d gap t y p e w a s significant, F (1,39) = 5.13, p < 0.05, as was the three-way interaction among location o f t h e g a p , the t y p e o f g a p , a n d t h e t y p e o f a c t i o n d e l e t e d , F(2,78) = 3.56, p < 0.05. A s e r i e s o f t t e s t s w e r e p e r f o r m e d using a B o n f e r r o n i p r o c e d u r e w i t h o~ = .05 to examine the three-way interaction. As Table 5 s h o w s , s u b j e c t s r e s t o r e d s u p e r o r d i n a t e act i o n s to g a p s t h a t v i o l a t e d t h e t a x o n o m y e q u a l l y o f t e n in e a c h e p i s o d e o f the s t o r i e s ( b o t h t(39) < 1.0, p > .05). T h e p o s i t i o n o f t h e g a p d i d n o t affect t h e i n c i d e n c e o f res t o r e d s u b o r d i n a t e a c t i o n s as long as the g a p d i d n o t v i o l a t e the t a x o n o m y ( b o t h t (39) < 1.0, p > .05). In c o n t r a s t , t h e r e w e r e s i g n i f i c a n t i n c r e a s e s f r o m t h e first to t h e t h i r d e p i s o d e in the i n c i d e n c e o f r e s t o r e d a c t i o n s to g a p s t h a t v i o l a t e d the t a x o n o m y ( b o t h t(39) < 2.80, p < .05) a n d in t h e incid e n c e o f r e s t o r e d s u p e r o r d i n a t e a c t i o n s to gaps that did not violate the taxonomy ( b o t h t(39) > 2.50, p < .05). Overall, violations created by deleting superordinate actions were restored more o f t e n t h a n w e r e n o n v i o l a t i o n s d u e to m i s s ing s u p e r o r d i n a t e a c t i o n s , t(39) = 4.00, p < 0.05. V i o l a t i o n s a n d n o n v i o l a t i o n s d u e to deleting subordinate actions were restored

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equally often, t(39) = 1.67, p > 0.05. However, both were restored less often than were nonviolations due to missing superordinate actions (both t(39) ~> 3.50, p < 0.05). Discussion Experiment II demonstrates that the hierarchical structure of narratives interacts with their causal structure to determine which missing actions readers will restore. In this task, as in question-answering and recall tasks (Black & Bower, 1979, 1980; Graesser, Robertson, Lovelace, & Swinehart, 1980), readers distinguish between superordinate and subordinate actions. They detected and restored more missing superordinate than subordinate actions. As in Experiment I, readers detect and repair gaps that violate the taxonomy more often than those that do not. However, the location of missing actions affects whether or not readers will restore them. Superordinate actions missing from the third episodes are more likely to be restored than those missing from the first episodes only if the gaps violate the taxonomy. Nonviolations due to missing superordinate actions also are more likely to be repaired in the third episodes than in the first, whereas nonviolations due to missing subordinate actions are not affected by position of the gap. The event chain taxonomy itself does not account for the effects of hierarchical and e p i s o d e s t r u c t u r e . R a t h e r the results suggest that readers become increasingly sensitive to missing actions as they read through the stories. KnowJedge of the pl0t and familiarity with the behavior of the protagonist enable the reader to more accurately detect and restore missing superordinate nonviolations and subordinate violations of the taxonomy in the later episodes. CONCLUSIONS

Causal connections among the actions, physical states, and mental states described in a story can be directly conveyed by linguistic markers or inferred by readers. Four types of causal connections need to be es-

tablished: (1) physical states result from actions, (2) mental states are initiated by actions or physical states, (3) actions are enabled by physical states, and (4) mental states are the reasons for actions. These possible causal connections constitute a taxonomy of the sequences of events that can logically occur in stories. One consequence of this taxonomy is that four types of action, physical state, and mental state sequences cannot logically occur: (1) actions cannot immediately cause new actions, (2) physical states cannot bring about new physical states, (3) mental states cannot directly cause new mental states, and (4) mental states cannot change physical states. Whenever such sequences do occur, inferences are required in order to fill in the missing links. Experiments I and II demonstrate that the event chain taxomony is used by readers in order to understand narratives. Violations of the taxonomy are spontaneously detected and the missing actions, physical states, and mental states are accurately restored. However, these studies also suggest that the event chain taxonomy interacts with specific information about the plot and characters of a story. As readers acquire more knowledge of the events described by a story, their accuracy in detecting and repairing violations of the t a x o n o m y increases. Although the event chain taxonomy can account for how readers infer some of the missing connections among the actions, physical states, and mental states of stories, it is not sufficient. Knowledge of possible causal connections may be necessary in order to infer the results of or reasons for an action. N o n e t h e l e s s , o t h e r k n o w l e d g e structures such as scripts (Bower, Black, & Turner, 1979; Graesser, Woll, Kowalski, & Smith, 1980), and plans (Black & Bower, 1979) are also necessary. These knowledge structures, like the event chain taxonomy, can enable readers to infer missing links in story event chains from information about the specific plot and story characters.

MISSING LINKS REFERENCES DE BEAUGRANDE, R. Text, discourse, and process. Vol. IV. Advances in discourse processes. Norwood, N. J.: Ablex, 1980. BLACK, J. B., & BOWER, G. H. Story understanding as problem-solving. Poetics, 1980, 9, 223-250. BLACK, J. B., & BOWER, G. H. Episodes as chunks in story memory. Journal of Verbal Learning and Verbal Behavior, 1979, 18, 309-318. BOWER, G. H., BLACK, J. B., & TURNER, T . T . Scripts in text comprehension and memory. Cognitive Psychology, 1979, 11, 177-220. GRAESSER, A. C. How to catch a fish: The representation and memory of common procedures. Discourse Processes, 1978, 1, 72-89. GRAESSER, A . C . , ROBERTSON, S . P . , LOVELACE, E . R . , & SWINEHART, D . M . Answers to whyquestions expose the organization of story plots and predict recall of actions. Journal of Verbal Learning and Verbal Behavior, 1980, 19, 110-119. GRAESSER, A. C., ROBERTSON, S. P., & ANDERSON, P. A. Incorporating inferences in narrative representation: A study of how and why. Cognitive Psychology, 1981, 13, 1-26. GRAESSER, A. C., WOLL, S. E., KOWALSKI, D. J., & SMITH, D . A . Memory for typical and atypical actions in scripted activities. Journal of Experimental Psychology: Human Learning and Memory, 1980, 6, 503-515. MANDLER, J. M., & JOHNSON, N. S. Remembrance of

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things parsed: Story structure and recall. Cognitive Psychology, 1977, 9, 111 - 151. OMANSON, R. C., WARREN, W. H., & TRABASSO, T. Goals, inferential comprehension, and recall of stories by children. Discourse Processes, 1978, 1, 355-372. RIESBECK, C., & SCHANK, R. Comprehension by computer: Expectation-based analysis of sentences in context. In W. Levelt & G. Flores d'Arcais (Eds.), Studies in the perception of language. New York: Wiley, 1978. SCHANK, R. The structure of episodes in memory. In D. G. Bobrow & A. Collins (Eds.), Representation and understanding. Hillsdale, N. J.: Eflbaum, 1977. SCHANK, R., & ABELSON, R. Scripts, plans, goals, and understanding: An inquily into human knowledge structures. Hillsdale, N. J.: Erlbaum, 1977. STEIN, N. L., & GLENN, C. C. An analysis of story comprehension in elementary school children. In R. O. Freedle (Ed.), New directions in discourse processing. Norwood, N. J.: Ablex, 1979. Vol. 2. TRABASSO, T. On the making of inferences during reading and their assessment., Tech. Rep. No. 157. Champaign II.: University of Illinois, 1980. WARREN, W. H., NICHOLAS, D. W., & TRABASSO, T. Event chains and inferences in understanding narratives. In R. O. Freedle (Ed.), New directions in discourse processing. Norwood, N. J.: Ablex, 1979. Vol. 2. (Received April 29, 1981)