Lexical retrieval and error recovery in reading: A model based on eye fixations

JOURNAL OF VERBAL LEARNING AND VERBAL BEHAVIOR 20, 137--160 (1981)

Lexical Retrieval and Error Recovery in Reading: A Model Based on Eye Fixations PATRICIA A.

CARPENTER AND MEREDYTH DANEMAN Carnegie-Mellon University

This paper p r e s e n t s a model of reading that accounts for the oral interpretation of an a m b i g u o u s word, the time it takes to derive and integrate the interpretation, and the time it takes to detect a s u b s e q u e n t inconsistency. The m o d e l ' s predictions are compared to the s e q u e n c e and duration o f the readers' eye fixations on " g a r d e n p a t h " passages such as: Cinderella was sad because she couldn't go to the dance that night. There were big tears in her brown dress. The model predicts that the interpretation of an a m b i g u o u s word (such as tears) d e p e n d s on the contextual priming and the interpretation's relative frequency. The duration of the eye fixations on a disambiguating word (such as dress) d e p e n d s on how consistent it is with the r e a d e r ' s prior interpretation of the text. The eye fixations and q u e s t i o n - a n s w e r i n g data also indicate different w a y s of recovering from the initial misinterpretation.

This paper presents a model of how readers initially interpret words and how they detect and revise incorrect interpretations. The research methodology examines eye fixations and the oral reading of "garden path" passages that prime one meaning of an ambiguous word and subsequently presuppose the other meaning. These passages contained homographs, such as the following: T h e y o u n g m a n turned his back on the rock concert stage and looked across the resort lake. T o m o r r o w was the annual one-day fishing c o n t e s t and f i s h e r m e n would invade the place. Some o f the best bass guitarists in the c o u n t r y would c o m e to this spot. T h e usual routine o f the fishing resort would be disrupted by the festivities.

Most readers initially interpret the word bass in line 5 to mean " a kind of fish" because this interpretation is primed by the prior sentence. However, " a kind of fish" is incompatible with the subsequent disambiguating word guitarists and the resolution R e q u e s t s for reprints should be sent to Patricia A. Carpenter, Department of Psychology, CarnegieMellon University. Pittsburgh, Pa 15213. This research was partially supported by the National Institute o f Education Grant-G-79-0119 to P. Carpenter. We especially would like to t h a n k Marcel Just for his help in all p h a s e s of the research.

requires a reinterpretation of bass to mean " a low music note." This paper presents a model of reading that accounts for the initial interpretation given an ambiguous word, the time it takes to retrieve and integrate the interpretation, and the time it takes to detect and correct a subsequent inconsistency. These processes were studied by recording readers' eye fixations to obtain a trace of their left-to-right computational processes in reading. Previous research has shown that readers pause longer on words that require more semantic processing (Carpenter & Just, 1977, in press; Just & Carpenter, 1978, 1980). The present data will show that the time on a word reflects the duration of reading processes such as encoding, retrieving a word's representation, and integrating it with prior information. Moreover, the sequence of regressive fixations reflects the process of detecting and correcting a prior misinterpretation. An example of one reader's protocol will indicate how eye fixations reflect the duration and sequence of comprehension processes. Figure 1 shows a reader's eye fixations and verbal protocol while reading the bass sentence in the passage above. The sequence of fixations is denoted by the suc-

137 0022-5371/81/020137-24502.00/0 Copyright(~) 1981by AcademicPress, Inc. All rights of reproduction in any form reserved.

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cessive numbers a b o v e and below the word being fixated. The r e a d e r made a series of forward fixations f r o m left to right until the disambiguating word guitarists, at which point he regressed b a c k to bass to reread the phrase (fixations 6 - 7 ) and then finished the sentence (fixations 8 - 1 2 ) . The duration of each fixation (in milliseconds) is shown below the associated fixation. The model assumes that the gaze duration on a word reflects the duration of the reading processes initiated by that word. The duration o f the initial fixation on the a m b i g u o u s word bass (fixation 4) reflects the time it takes to encode the visual stimulus, retrieve its interpretation f r o m semantic m e m o r y , and integrate it with the representation of the text that has been read up to that point. This duration will be shown to depend upon both the prior context and the base activation level o f the h o m o g r a p h . The long duration on the disambiguating word (fixation 5) reflects the a t t e m p t to integrate the word guitarists and the detection of an inconsistency with the preceding text. The long regressive fixation on bass reflects the errorr e c o v e r y p r o c e s s that r e i n t e r p r e t s bass. The oral reading protocol is in small type and c o n n e c t e d to the associated fixations

by dots. It indicates that this reader successfully r e c o v e r e d from the inconsistency by reinterpreting bass as "beYs ' ' (a low music note). This protocol also d e m o n s t r a t e s an important point about the relation between the eye fixations and the voice in oral reading. The voice lags behind the eye, giving rise to the e y e - v o i c e span m e a s u r e (cf. Buswell, 1922; Danks & Fears, 1979). H o w e v e r , the locus o f the eye fixation is a better index of what is currently being c o m p r e h e n d e d than is the voice. As s h o w n in Figure 1, the reader typically detects the inconsistency when he fixates the disambiguating word; he does not have to verbalize the inconsistency and then process his verbalization. A more detailed discussion of the relationship b e t w e e n oral reading and c o m p r e h e n s i o n processes will be presented in the last section of the paper. The p a p e r is divided into three parts. The first p r e s e n t s a m o d e l o f the m a j o r proc e s s e s o f interest: retrieval, integration, and e r r o r detection and r e c o v e r y . T h e s e processes are more detailed specifications o f the c o m p o n e n t s o f a g e n e r a l reading theory described elsewhere (Just & Carpenter, 1980). The second part presents an b eYs] guttar

(650) -.

s o m e

of t h e b e s t

bass

1

2

3

4

1650)

(2t7)

(366)

(284)

some

cf

fhe

isis

(400)

guitarists in the country would come to this

spot.

5

8

9

iO

11

~2

(433)

(250}

(467)

(450)

(4~7)

(567)

try

would come

best [bS~s]

in

the

ceun

to

this

FIG. 1. The bass target sentence with a reader's eye fixations and read-aloud protocol in small print. The numbers 1-12 indicate the sequence of fixations; the forward fixations are indicated by the numbers below the fixated word and the regressive fixations are indicated by the numbers above the fixated word. The numbers in parentheses indicate the fixation duration (in milliseconds). The readaloud protocol shows that bass was initially interpreted as [bzes], meaning (fish), and then revised to [be~s], meaning (music note).

LEXICAL RETRIEVAL AND ERROR RECOVERY

experiment that provides empirical support for the major aspects of the model. The third section discusses the general implications of the model for reading.

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fixated and encoded, Whether a concept is retrieved depends on the activation it receives from the prior context and the encoded word. When at least one concept reaches threshold, there is an attempt to THE MODEL integrate it with the representation of the The model assumes that semantic infor- text. Integration consists of computing the mation is stored in a n o d e - l i n k network in syntactic and semantic relations between which the concepts are nodes that are the current word and the previous text, and linked by labeled relations. Each concept incrementally constructing a representation has a base level of activation. Concepts can of the text as it is being read. If the concept accumulate activation and when a con- is selected as compatible with the context, cept's level of activation reaches some it will be used in further processing. The threshold, the c o n c e p t is retrieved to activation levels of retrieved concepts that short-term m e m o r y (Collins & Loftus, are not selected for further processing will 1975; Morton, 1969). Short-term memory is decay to base level (Swinney, 1979) or they conceived of as an active part of the pro- may be actively dampened. If an inconsiscessing system that serves as the site for tency is detected during the integration executing processes, as well as for storing process, the r e a d e r will evoke errorthe products of these processes. Indeed, recovery heuristics to repair the inconsisthe functional capacity of short-term mem- tency. ory may be a significant source of individual differences in reading (Daneman & Retrieval and Integration Carpenter, 1980). Figure 2 indicates the reThe retrieval process must produce at trieval process along with the other major least one interpretation that can be operprocesses beginning from when a word is ated upon by the integrative processes. The probability that a concept reaches threshold partially depends on the prior context, Fixate and encede next word which can prime a particular interpretation by temporarily increasing its level of activation. Context includes structures that are Retrieve concept er concepts that constructed in short-term memory by comare sufficiently activated by fixated word and prior context bining the preceding information represented from the text with information retrieved from semantic memory. Context t Try to assign case role (s) and effects have been found in many language =ntegrate retrieved concept(s) tasks that involve isolated words, rather than text. In lexical decision tasks, a decision about one word (like bread) facilitates a subsequent decision about a related word (like butter) (Meyer & Schvaneveldt, 1971; Neely, 1977; Tweedy, Lapinski, & Schvane~Ne Yes veldt, 1977). This priming effect has been attributed to automatic activation among associated concepts in semantic memory ] Go to error recovery heuristics J (Posner & Snyder, 1975). The model assumes a similar mechanism operates in FIG. 2. A flow chart o f the p r o c e s s e s o f encoding, reading where the context includes prior activation and lexical retrieval, integration, and error recovery. syntactic information, the specific scenario,

1__

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the general topic, and information related to the reader's goals, as well as semantic associates. The model proposes that the speed and amount of activation partially depend on the strength of the relation between the context and the related concept. For instance, in the example passage about bass, the model postulates that the topic of a fishing contest and references to a resort lake and fishermen increased the level of activation of the concept bass (fish) before the word bass was encoded and this activation facilitated its subsequent encoding and retrieval. The probability of retrieval also depends on the activation a concept receives from the encoded word. When a word is encoded, a p e r c e p t u a l r e p r e s e n t a t i o n is transferred to short-term memory and activation spreads from it to the associated interpretations. If the word has only one interpretation, it receives all of the activation. If the word has more than one interpretation, the activation is divided among them in proportion to their relative frequencies of usage. The role of relative frequency in lexical retrieval is especially striking when a word has one meaning that is relatively frequent and one that is relatively infrequent. As an example, consider the words does and shower; the infrequent meanings are hard to retrieve, even when consciously searching for them. If a word has several meanings, they essentially compete to be selected as the final interpretation of the word. To be selected, a concept must be both retrieved and integrated. The meaning with a very high relative frequency may be retrieved and integrated before the o t h e r m e a n i n g - e v e r reaches threshold. If the two meanings have similar relative frequencies, they may both reach threshold and the integration process must select one of them. In the absence of a prior context, relative frequency has a determining role in the activation and retrieval process. The duration of the retrieval process for a particular interpretation depends on its

base level of activation, which reflects its frequency of usage~ When a word has only one interpretation, this formulation corresponds directly to the well-known proposal that encoding and retrieval time varies with word frequency (Morton, 1969). In fact, retrieval time has been found to be a logarithmic function of word frequency (Just & Carpenter, 1980; Mitchell & Green, 1978). The log function reflects the fact that a small difference in frequency among infrequent words has the same effect as a large difference among frequent words. When a word has more than one meaning, the word frequency measure must be divided up among them according to their relative frequencies of usage. The model predicts that interpretations with higher base levels of activation should take less time to retrieve. For example, relative frequency predicts that the (auxiliary verb) interpretation of does will be retrieved before the (female deer) interpretation. Similarly, the (water) interpretation of shower will be retrieved before the (demonstrator) interpretation. In addition, the retrieval time for does (auxiliary verb) will be shorter than the retrieval time for shower (water) because does (auxiliary verb) has a higher base level of activation and requires less additional activation to reach threshold. Once a concept is retrieved, it is assigned a case role that depends upon its syntactic and semantic properties and on the constraints of the prior context and it is integrated with the representation of the preceding discourse. The speed of these processes depends upon how well the retrieved meaning matches the requirements of the context. Hence, the model proposes that context influences the comprehension process at two points. First, activation from the prior context increases the probability and speed of retrieving a related concept. Second, the relation between the context and the retrieved meaning determines the speed of the integration process. If more than one meaning of a word is retrieved to short-term memory, the integration pro-

LEXICAL RETRIEVAL AND ERROR RECOVERY

cesses begin computation with the most activated concept. This will tend to be the one that has a higher relative frequency; if the relative frequencies are equal, it will be one that was more strongly primed by the context. The processes terminate when one interpretation is successfully assigned a case role and integrated.

Error Detection and Recovery It is common in reading to misinterpret a word or phrase and consequently encounter an inconsistency. The inconsistency could be detected if the features of the retrieved concept explicitly contradict some semantic or syntactic constraint of the context or if the integration process does not compute an acceptable relation before some cutoff time. For example, in the bass passage, a reader who had interpreted bass as (fish) would find that guitarists is semantically unacceptable. In the sentence There were big tears in her brown dress, a reader who had interpreted tears as (droplets) would find dress unacceptable. When a reader encounters an inconsist e n c y , the model proposes that errorrecovery heuristics are evoked to uncover the source of the difficulty and correct it. For instance, one heuristic is to simply check that the inconsistent word was encoded correctly and also to check for alternative interpretations of the word that would fit the context better. If these procedures d o n ' t resolve the problem (they w o u l d n ' t for guitarists and dress), the reader could try other heuristics, such as checking the previous words in the sentence. This checking was overtly manifested in the protocol in Figure 1, where the reader regressed from guitarists to bass. This protocol suggests that readers search selectively, they do not simply reread the entire sentence. Another heuristic is to resolve an inconsistency by making an inference larger than normal to integrate the inconsistent concept with the preceding information. Data to be presented below suggest that this occurs if the inconsistency

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does not involve a syntactic violation and if it is only mildly semantically inconsistent. Finally, the reader might continue reading and hope that later information in the text will provide some resolution. The conditions that determine which heuristic is utilized will be discussed later. Irrespective of which heuristic is employed, detecting and recovering from an i n c o n s i s t e n c y should increase processing time.

Predictions In summary, the model makes three major predictions. First, the model postulates that the outcome of the interpretive process depends upon both the strength of the prior context and the relative frequencies of the meanings associated with a word. This prediction can be tested by having subjects read aloud ambiguous words whose meanings have different pronunciations (homographs). Readers should be more likely to interpret the ambiguous word as the homograph that has the higher relative frequency, particularly when the context primes that homograph. Second, the model postulates that it should take less time to encode, retrieve, and integrate a homograph that is more strongly primed by the prior context. It should also take less time if the homograph has a higher base level of activation, as reflected in its base frequency of usage. If the encoding, retrieval, and integrative processes occur while the reader fixates the ambiguous word, the duration of these processes will be reflected in the reader's gaze duration on the word. Consequently, the forward and regressive fixations on the ambiguous word should be shorter when the retrieved homograph is more strongly primed by the context and when it has a higher base frequency. Third, the model predicts that processing time should increase if the reader evokes error-recovery heuristics when a word that is inconsistent with some prior interpretation is encountered. This implies that the fixation duration on a disambiguating word

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should be longer if it is inconsistent with respect to the reader's interpretation of a prior ambiguous word. This model will be tested with passages that contain ambiguities and subsequent disambiguations, like the bass paragraph. The ambiguities highlight the retrieval and integration processes. The disambiguations highlight the error detection and recovery process. However, the model is not specific to the comprehension of ambiguous words or garden path sentences and its general implications for reading will be presented in the final discussion. METHOD

Materials The experimental passages involved 14 ambiguous words that could be interpreted as either of two homographs. The two homographs are denoted by synonyms or explanations in parentheses: bass (music

note) (fish), wound (to hurt) (wrapped), bow (a bend) (violin part), lead (metal) (clue), read (present tense) (past tense), close (shut) (near), winds (excites) (exhausts), tears (droplets) (rips), buffet (meal) (knock), sewer (drain) (tailor), shower (water) (demonstrator), row (seat) (fight), minute (60 sec) (detailed), and bases (reasons) (baseball bases), The results for bases were not analyzed since the two homographs were pronounced identically by our readers, leaving 13 ambiguous words for analysis. In the rest of the paper, specific homographs will be denoted by these synonyms. Passages were constructed so that the initial context more strongly primed one homograph. Then, in half of the passages, information that was inconsistent with the primed homograph was later presented. In the other half, information that was consistent was presented. The passage construction can be illustrated with the bass passage: The young man turned his back on the rock concert stage and looked across the resort lake. Tomorrow was the annual one-day fishing con-

test and fishermen would invade the place. Some of the best bass guitarists in the country would come to this spot. The usual routine of the fishing resort would be disrupted by the festivities.

The opening sentences in each paragraph were consistent with either interpretation of the ambiguous word. In the example passage, the phrase rock concert stage in the first sentence is mildly related to the (music note) interpretation of bass and the phrase resort lake is mildly related to the (fish) interpretation. Then one sentence, the context sentence, was constructed to more strongly prime one homograph, in this example, the (fish) interpretation. This sentence was the second one in half of the passages and the third in the remaining passages. The next sentence, the target sentence, contained the ambiguous word itself and a subsequent disambiguating word or phrase that was either consistent or inconsistent with the homograph that was more strongly primed by the context sentence. The target sentence for each homograph is given in Appendix A. The two different target sentences for an ambiguous, word were identical in wording and physical positioning up to and including the ambiguous word itself, but they differed in the subsequent disambiguating phrase. The last sentence was constructed to be reasonable given either interpretation of the homograph. The opening and final sentences were purposely constructed to be equally biased toward either interpretation so that even the inconsistent passages would be fairly coherent. The content and style of the 14 passages varied, although they were primarily narratives. Four passages were constructed for each ambiguous word. In two passages, the context sentence more strongly primed one homograph and in two passages, it more strongly primed the other homograph. Within each context condition, a disambiguating phrase after the homograph either was consistent or inconsistent with the more strongly primed homograph. These manipulations were accomplished by cross-

L E X I C A L R E T R I E V A L A N D ERR O R R E C O V E R Y

ing the context and target sentences in the four passages, but maintaining the same opening sentences and the same final sentence. Two different context sentences were paired with two different target sentences to make the four versions: (1) context primes (music note); target is

(music note) • . . T o m o r r o w was the annual one-day rock c o n c e r t and m u s i c i a n s would invade the place. Some of the best bass guitarists in the c o u n t r y would c o m e to this spot.

(2) context primes (fish); target is (music

note) • . . T o m o r r o w was the annual one-day fishing c o n t e s t and fishermen would invade the place. Some of the best bass guitarists in the c o u n t r y would come to this spot.

(3) context primes (fish); target is (fish) • . . T o m o r r o w was the annual one- day fishing c o n t e s t and fishermen would invade the place• Some of the best bass c a t c h e r s in the c o u n t r y would come to this spot.

(4) context primes (music note); target is

(fish) • . . T o m o r r o w was the annual one-day rock c o n c e r t and m u s i c i a n s would invade the place. Some of the best bass c a t c h e r s in the c o u n t r y would come to this spot.

The passages with the sentences in (1) and (3) were considered consistent because the more strongly primed homograph agreed with the disambiguating phrase. The passages with the sentences in (2) and (4) were considered inconsistent because the more strongly primed homograph disagreed with the disambiguating phrase. E a c h of the four passages for an ambiguous word were assigned to one o f four groups with the constraint that there be seven consistent and seven inconsistent passages in each group.

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Subjects The experiment involved 20 C a r n e g i e Mellon undergraduates who were randomly assigned to one of four groups. Each of five readers in a group read the same set of seven consistent and seven inconsistent passages e m b e d d e d among practice and filler passages.

Rating of Contexts To measure the strength of the context, two judges independently rated how much the sentences preceding the target primed each homograph on a scale from 1 to 5 : 1 meant the context was close to neutral; 2 meant that the context contained at least one semantic associate of the homograph; 3 m e a n t that it c o n t a i n e d m o r e t h a n one semantic associate or a s y n o n y m of the homograph; 4 meant the homograph was strongly implied by the scene and there were semantic associates; and 5 meant it was r e l a t e d to the s c e n e , t h e r e w e r e semantic associates, and there was a cliche or stereotypic phrase involving the homograph. The interjudge reliability of the ratings for the 52 judgments (2 contexts for e a c h o f the 2 i n t e r p r e t a t i o n s o f the 13 h o m o g r a p h s ) was .80. T h e r e w e r e disagreements of 1 point on 26 passages and these were r e s o l v e d through discussion. Two judges also rated the single major disambiguating word in each sentence (such as the word guitarists in the bass passage) and the entire disambiguating phrase. The inconsistencies were rated from - 1 (mildly inconsistent) to - 5 (very inconsistent). Ratings from 1 to 5 also were given for how consistent these phrases were with the correct homograph. The interjudge reliability for these judgments was .96.

Frequency To predict the effects o f relative frequency on interpretation, it is necessary to estimate the frequency with which an ambiguous word is interpreted as a particular homograph in the absence of context. To do this, a pronunciation task was patterned

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after the procedure of Warren, Bresnick, and Green (1977). A new group of 24 subjects was shown a series of isolated words and asked to pronounce each one as quickly as possible and then give a sentence using that word. The 13 ambiguous words were embedded among 13 unrelated, unambiguous words. The frequencies were collapsed over similar noun and verb concepts, such as a bow (a bend) and to bow, and a wound and to wound (to hurt). In some cases, subjects gave interpretations that were neither of the homographs being studied, such as (a ribbon) for bow, so the frequencies for the two homographs do not necessarily add to 100%. One limitation of this procedure was that the lack of sentential context operated like a sentence initial context. This meant that the words read and close usually were interpreted as imperatives and this task may distort the relative frequencies of the interpretations for these words. The frequency with which a particular homograph was elicited in the pronunciation task is given in Appendix B. To compute the base frequency of a homograph, its relative frequency was multiplied by the word frequency listed in Kurera and Francis (1967). The logarithm (base 10) of the frequencies will be used in the statistical analyses reported below. For convenience, the relative frequencies were increased by 1%, to eliminate the problem of taking the log of zero.

Procedure The subjects read aloud a series of paragraphs containing homographs in "garden path" contexts while their eye fixations and verbal protocols were recorded. Subjects were instructed to aim for comprehension and to read "as for an audienco:'; this instruction was an a t t e m p t to minimize superfluous disfluencies. After reading a paragraph, the subject answered two questions about it. The first question attempted to elicit the reader's final interpretation of the homograph. The second question interrogated some other fact mentioned in the

passage. The subjects first read two practice passages followed by 14 experimental passages randomly intermixed with four filler passages. After the 20 passages, the subjects were questioned about their reading strategies. No reader guessed that the passages contained systematic inconsistencies, probably because he would have encountered inconsistencies in less than half of the 20 passages that he had read. At the end of the session, the reader was given a vocabulary test to determine if he knew the meanings of the homographs. The test indicated that the readers knew the homographs. In only eight of the 240 cases was a reader unaware of a homograph; these cases all involved buffet (knock) and row (fight). The reader initiated the presentation by pressing a start button while fixating an asterisk presented where the first letter of the paragraph would appear. The x and y coordinates of the reader's point of regard were calculated every 16.7 milliseconds by a Gulf and Western corneal-reflection and pupilcenter eye tracker. The coordinates were recorded and monitored by a PDP-11/04 computer. If the reader was fixating the asterisk when he pressed the button, the asterisk disappeared and the passage was presented 500 milliseconds later. This procedure as well as the formal calibration, assured that the tracker was within 1 degree accuracy, an area subtended by approximately three character spaces. This is comparable to the visual angle subtended by elite type at normal reading distance. When the reader finished the passage he terminated the presentation by pressing a second button on a two-button response box. The passages were typed in conventional format in upper and lower case and displayed on a television monitor in front of the reader. During the experiment, a videotape record was made of the eye fixations. A pair of crosshairs, corresponding to the locus of gaze, was electronically superimposed on an image of the text. The subject's oral reading protocol was recorded on the same

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videotape so that it could be coordinated with the locus of fixation. The oral protocols were scored by playing the tape repeatedly in slow motion until the pronunciation of a syllable was reliably associated with a particular fixation. The eye fixation behavior was quantified by computing the gaze duration on each word in a sentence for each reader. The gaze duration is the sum of the durations of consecutive fixations on a word. Gazes on words to the right of any previously fixated word were classified as forward. Gazes on words to the left of the most advanced word that was read were classified as regressions. In Figure 1, fixations 6 - 7 were classified as regressions and fixations 1 - 5 and 8 - 1 2 were classified as forward fixations. RESULTS AND DISCUSSION

Oral Reading Interpretation The model predicted that the probability of a particular interpretation depends on the strength of the context and the relative frequency of that interpretation. This was tested by analyzing the percentage of oral i n t e r p r e t a t i o n s that m a t c h e d the more strongly primed homograph in the 26 passages? As shown in Table 1, the oral interpretations agreed with the context 87% of the time when the context sentence had more strongly primed the higher-frequency homograph, and 38% of the time when the c o n t e x t had mo r e strongly primed the lower-frequency homograph. The percentage of interpretations that matched the m o re strongly p r im e d h o m o g r a p h was analyzed by a regression analysis that had two independent variables--the strength of

This analysis and others to be reported are based on 247 d a t a points; 13 data points were not included. For two p assages, the eye fixations were unscorable. For 11 cases, the original interpretation given the ambiguous word was unclear. These were all cases where the r e a d e r fixated the d i s a m b i g u a t i n g word before pronouncing the a m b i g u o u s word, made a m a r k e d hesitation, and then p r o n o u n c e d the a m b i g u o u s word in a way that was c o n s i s t e n t with the disarnbiguatmg word.

the context for that homograph (the rating from 1 to 5) and the log of the homograph's relative frequency (as estimated in the pronunciation task). The regression coefficient for the context indicated roughly an 11.5% increase in the interpretations that matched the context for every unit of increase in the strength of the context, t(23) = 2.62, p < .01. The regression coefficient for relative frequency indicated roughly a 34% increase for one log unit in relative frequency, t(23) = 6.28, p < .01. Thus, a homograph like tears (water droplets) with a log relative frequency of 2 was much more likely to be pronounced than a homograph like winds (excites) with a log relative frequency of 1.15. The standardized regression coefficients indicated that for these stimuli, relative frequency was more important than context in determining the oral interpretation; the standard regression coefficient was .71 for relative frequency and .30 for context. The two variables accounted for 73% of the variance in percentage of oral interpretations among the 26 passages, F(2,23) = 19.91, p < .01. Relative frequency played an important role in d e t e r m i n i n g w h e t h e r the m ore strongly primed homograph was produced. The seven ambiguous words whose two homographs have fairly symmetrical relaTABLE1 PERCENTAGE OFINTERPRETATIONSTHAT WITH THE CONTEXT

AGREED

Context primed Ambiguous word

Higher-frequency homograph

Lower-frequency homograph

bass wound bow lead read close winds tears buffet sewer shower row minute Mean

100 67 80 86 70 57 70 100 100 100 100 I00 100 87

90 90 70 56 60 67 33 20 10 0 0 0 0 38

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tive frequencies (bass, wound, bow, winds, lead, close, and read) were generally but not always interpreted as the more strongly primed homograph. However, the six ambiguous wo r d s th at have one v e r y inf r e q u e n t i n t e r p r e t a t i o n (tears, buffet, sewer, shower, row, and minute) were almost never interpreted as the homograph with the lower relative frequency, even when they were more strongly primed by the context. There are at least three possible explanations for this result. One is that the homograph with the very low relative frequency did not receive sufficient activation to be retrieved; only the interpretation with the higher relative frequency was retrieved and it was integrated even though it was only weakly related to the prior content. An alternative hypothesis is that context is ineffectual if the relative frequency is below some threshold. This would occur if relative frequency alone were the determinant of retrieval and context only selected among the retrieved concepts. Finally, both homographs may have been retrieved, but this account has difficulty explaining why context did not select the more strongly primed interpretation. These hypotheses were tested in a second experiment that provided extremely strong contexts for the six homographs with low relative frequencies. For example, in the main experiment the sewer (tailor) passage was: After months of fruitless searching, we finally found what we thought was our dream home. We have since discovered, however, that the new TABLE 2 PERCENTAGE OF INTERPRETATIONS THAT AGREED WITH THE CONTEXT WHEN THE INFREQUENT HOMOGRAPH WAS MORE STRONGLY PRIMED Interpretations that matched the context Ambiguous word

Infrequent homograph

Main expt.

Expt. 2

tears buffet sewer shower row minute

(rips) (knock) (tailor) (demonstrator) (fight) (detailed)

20 10 0 0 0 0

40 30 30 20 50 0

neighborhood has both advantages and disadvantages. The main advantage is that there are several small stores nearby that sell hand-made clothes. There is also one sewer near our home who makes terrific suits. We will have to weigh the pros and cons before we decide to buy it.

In the second experiment, the context sentence preceding the target primed (tailor) more strongly: We are thrilled that there are several tailors; one even makes and mends coats. Whereas the six original contexts had a mean rating of 2.7, the new contexts had a mean rating of 4.6, close to the maximum possible rating of 5. The six new homograph passages and five filler passages were presented to a new set of 10 readers who had not participated in the main experiment or in the pronunciation task. The procedure was identical to that of the main experiment except that eye fixations were not recorded. The major dependent measure was the oral interpretation of the ambiguous word. Table 2 shows that the stronger contexts did increase the percentage of low-frequency interpretations that were produced from 5% to 28% for these six passages, t(5) = 3.50, p < .01. 2 This result argues against the hypothesis that relative frequency alone determines lexical retrieval and context only selects among retrieved concepts. If this hypothesis had been correct, the essentially zero-frequency homographs would almost never be retrieved (and hence, almost never selected), even when the context was strong. The fact that the l o w - f r e q u e n c y h o m o g r a p h s w e r e pronounced more often suggests that context influenced their initial activation and re-

The stronger context did not increase the percentage of low frequency homographs for one of the six passages, the passage that primed minute (detailed). One explanation for why the context sentence was ineffective has to do with the minute (detailed) target sentence itself: After a minute but rapid examination o f the victim, the doctor detected signs o f life. The cliche after a minute is strongly associated with the (60 sec) interpretation, and so this homograph had a very strong local context that may have overshadowed the preceding context sentence.

L E X I C A L R E T R I E V A L A N D ERR O R R E C O V E R Y

trieval, as well as the subsequent selection process. The stronger contexts in Experiment 2 not only helped the reader orally produce the correct interpretation, they also helped in recovering from incorrect initial interpretations. This was indicated by the number of times readers overtly corrected their oral reading pronunciation. Consider those cases in which the reader incorrectly interpreted the ambiguous word as the higher-frequency homograph. Oral corrections occurred 50% of the time in Experiment 2, but only 24% of the time in the main experiment for the corresponding six passages, t(5) = 2.40, p < .05. The processes and factors discussed here with regard to homographs probably also operate in the retrieval and interpretation of ambiguous words whose alternative meanings have the same pronunciation (homonyms). Consider the sentence: The dentist used the drill to learn the Latin words. The "garden p a t h " phenomenon occurs here because both the prior context and relative frequency favor the (tool) interpretation of drill over the (language exercise) interpretation. Homonyms were not studied in this experiment because the oral pronunciation of a homonym does not indicate its interpretation. However, it seems probable that similar mechanisms are used to interpret homonyms like drill and homographs like tears. Because ambiguity is a pervasive feature of language, considerable research has addressed the issue of whether more than one meaning is retrieved for an ambiguous word. There have been at least three major positions on this issue. One theory, the Multiple Meanings Theory, holds that multiple meanings are always retrieved and one is immediately selected (MacKay, 1970: Swinney, 1979) or at least selected by the end of the clause (Conrad, 1974; Foss & Jenkins, 1973; Garrett, 1970; M a c K a y , 1973; Warren & Warren, 1976). An opposing theory, called the Garden Path Theory, proposes that only one meaning is retrieved and that the retrieved meaning is deter-

147

mined entirely by the prior c o n t e x t (Schvaneveldt, Meyer, & Becker, 1976). Finally, the Ordered Activation Model proposes that meanings are retrieved in order of their relative frequencies of usage until a meaning is located that matches the context (Hogaboam & Perfetti, 1975) so that multiple meanings would only be retrieved if the less frequent meaning were primed. The current results and recent other resuits in a lexical decision task indicate that no one of these previous models is correct. The Garden Path and Ordered Activation Models are contradicted by recent results from a lexical decision task (Swinney, 1979). In that task, subjects listened to a sentence like The man found several spiders, roaches, and bugs in the corner of his room and made a lexical decision about a concurrent visual stimulus. When the visual probe was presented simultaneously with the offset of the ambiguous word (bug), a lexical decision related to either meaning (insect or spy) was faster than a control. If the probe was delayed by 200 milliseconds or more, the decision related to the unselected meaning took as long as the control probe (Tanenhaus, Leiman, & Seidenberg, 1979). This lexical decision research (and most ambiguity research) used ambiguous words whose two interpretations have fairly symmetrical relative frequencies. The results suggest that both meanings were initially retrieved, but one meaning was selected and the other meaning's activation went back to base level very rapidly. However, the Multiple Meanings Theory has difficulty with the current results that homographs with extremely low relative frequencies tended not to be pronounced, even when strongly primed. If the lowfrequency meaning had been retrieved it should have been selected by the context. The suggestion is that very low-frequency meanings were often not sufficiently activated to be retrieved. The current model offers a resolution to the problems facing all three of the previous models. It postulates that whether one or more meanings are retrieved depends upon

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the strength of the context and the relative frequencies of the interpretations. If the context is weak and the relative frequencies are very asymmetrical, only one interpretation (the one with the high relative frequency) is retrieved. If the context strongly primes the relatively infrequent interpretation or if the two interpretations have symmetrical relative frequencies, then both interpretations are more likely to be retrieved.

the regressions in this category primarily reflect error-detection and error-recovery processes. One example in Figure 1 is the regression from guitarists back to bass. When the disambiguation was a phrase, the third category included any regressions after the first disambiguating word was fixated. These three categories were used to generate six dependent measures for each s e n t e n c e read by a subject: (1) the forward-gaze duration on the ambiguous Eye Fixation Durations word, (2) the forward-gaze duration plus This section presents the results from the regressions on the ambiguous word before analysis of the gaze durations. The analyses the disambiguating word. was fixated, (3) address the model's remaining two predic- the forward-gaze duration on the disamtions concerning the duration of the en- biguating word, (4) the forward-gaze duracoding, retrieval, and integration processes tion on the disambiguating phrase, (5) the and the duration of the error detection and regressive gaze duration on the ambiguous recovery processes. word after the disambiguating word was Six dependent measures were derived by fixated, and (6) the regressive gaze duration classifying the gazes on a target sentence on the disambiguating word. When a subinto three categories. The first category, the ject did not fixate (or regress to) a word, the forward gaze on each word, was assumed entry for that cell was zero. These six meato reflect the initial encoding, retrieval, and sures were used to test the two remaining integration processes. The second category predictions of the model. included any regressions leftward, before the disambiguating word was initially fix- Retrieval and Integration The predictions were tested with a reated. When these regressions land on the homograph, they primarily reflect integra- gression analysis where the dependent tion problems with the homograph. To see variable was the 247 individual forward'how this classification worked, consider the gaze durations for each homograph proopening of the bass target sentence: Some duced by each reader. The independent of the best b a s s . . , and a hypothetical se- variables were the rating of the context for quence of five fixations on the words (1) the homograph that was orally produced on Some, (2) best, (3) bass, (4) best, (5) bass. that trial, the logarithm of its base freThe fixations (4) best and (5) bass would be quency, and the length of the word (the classified as regressions to those two number of character spaces). This analysis words. These regressions were initiated examined the effects of context and frebefore the disambiguating word (in this quency while statistically controlling length case, guitarists) was fixated. Hence they differences among the words. As predicted, stronger priming contexts could not be attributed to the detection of an inconsistency between the initial in- did shorten the forward-gaze duration, terpretation of the ambiguous word and the t(243) = 2.84, p < .01; the regression coefdisambiguating word. The regressions in ficient indicated a 39 millisecond advantage this category can be contrasted with those for each increase in the context rating scale, in the third category that included only the or roughly a 156 millisecond advantage for a regressions after the disambiguating word homograph in the strongest context over a was fixated. In the inconsistent sentences, homograph of the same length and fre-

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LEXICAL RETRIEVAL AND ERROR RECOVERY

quency in a neutral context. Also as predicted, the forward-gaze duration was shorter when the pronounced homograph had a higher base f r e q u e n c y , 40 milliseconds less per log unit, t(243) = 1.70, p < .05, supporting the prediction that base activation level influences retrieval time. Finally, the forward-gaze duration on the ambiguous word was longer by 40 milliseconds for each additional character, t(243) = 2.54, p < .01. The three variables accounted for a significant portion of the variance among the forward-gaze durations, F(3,243) = 5.62, p < .01. A subsequent regression analysis indicated that the interaction of frequency and context did not contribute beyond what was accounted for by the main effects, t < 1. The results were very similar for the total gaze duration on the ambiguous word (forward gazes plus any regressions before the disambiguating word was fixated). Table 3 illustrates the major effects of contextual priming and the base activation level on the gaze durations. It shows the adjusted mean gaze duration on the ambiguous word depending on the properties of the homograph that was pronounced. The Table separates those homographs that were more strongly primed by the context from those that weren't. It also separates the homographs according to their frequencies; the division point was the mean of the logarithm of their base frequencies (.71). These comparisons involve words of different lengths, a factor that is statistically controlled in the regression analysis. To

convey the effects of context and frequency in Table 3 without the effects of length, the reading time per character was computed for each word and then multiplied by the average number of characters in an ambiguous word (5.7). The means illustrate the results of the regression analysis that both context and frequency influence the gaze duration on the ambiguous word. This supports the assumption that the reader encodes, retrieves, and integrates an interpretation while fixating the ambiguous word.

Inconsistency Detection and Recovery As predicted, the forward-gaze duration on the disambiguating word was longer when it was inconsistent with the reader's initial oral interpretation of the prior ambiguous word. This result also supports the assumption that readers attempt to integrate a concept with the previous context as soon as the word is fixated. A regression analysis was p e r f o r m e d on the 247 forward-gaze durations as a function of the reader's initial oral interpretation of the ambiguous word. The regression analysis had two factors as independent variables, the consistency rating given to the disambiguating word (from - 5 to +5) and the length of the disambiguating word (in number of character spaces). Forward gazes were longer for more inconsistent disambiguating words, approximately 10 milliseconds longer for each unit of the rating scale, t(244) = 2.35, p < .01. This means that a disambiguating word that was rated

TABLE 3 THE ADJUSTED FORWARD-GAzE DURATION (msec) ON AMBIGUOUSWORD Oral interpretation High frequency homograph (Log of base frequency above .71) Low-frequency homograph (Log of base frequency below .71)

Context matched interpretation

Context mismatched interpretation

(N = 126) 331

(N = 79) 361

( N = 28)

(N =

378

407

14)

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CARPENTER AND DANEMAN

as very inconsistent ( - 5 ) would be fixated approximately 100 milliseconds longer than a word of the same length that was rated as very consistent (+5). Also, the forwardgaze duration on the disambiguating word was longer by 64 milliseconds for each additional character, t(244) = 9.97, p < .01. These two variables accounted for a significant portion of the variance among the mean gaze durations, F(2,244) = 57.60, p < .01. Table 4 illustrates the effects of error detection and recovery. It presents the average forward and regressive gaze durations on various words when the disambiguating word was consistent (rated as 1 to 5) and when it was inconsistent (rated as - 1 to -5 ). These comparisons involve words of different lengths. To convey the consistency effects in Table 4 without the effect of word length, the average gaze duration per character was computed for each word and then multiplied by the average number of characters across all the words being compared. Table 4 illustrates how the forwardgaze duration on the disambiguating word increased when the word was inconsistent with the reader' s prior interpretation of the ambiguous word. A parallel analysis was done on the entire disambiguating phrase; in some cases this was a single word but in most sentences it contained several words. The regression analysis examined the mean forward-gaze duration on each disambiguating phrase,

collapsing over readers who had given the same oral interpretations to the ambiguous word. The independent variables were the consistency rating for the entire phrase and the length of the phrase. As predicted, the forward gaze durations on such phrases were longer when the phrases were inconsistent with the interpretation given to the prior ambiguous word, t(40) = 2.89, p < .01. The functional relation between the inconsistency and gaze duration indicated a large effect, approximately 27 milliseconds per rating unit; consequently, a very inconsistent phrase would be fixated roughly 270 milliseconds longer than a very consistent phrase of the same length. Also as expected, longer phrases had longer gaze durations, t(49) = 12.50, p < .01, approximately 44 milliseconds per character. The analysis accounted for a significant portion of the variance among the 43 means, F(2,40) = 88.56, p < .01. The results support the model's prediction that error detection and recovery processes would take additional time and that the processes are evoked while the r e a d e r is fixating the disambiguating word and phrase. One error-recovery process, which was obvious in the b a s s prot ocol , includes checking previous words that were difficult to integrate. The use of this heuristic predicts that readers should tend to regress to the ambiguous word. Hence, the duration of regressions on the ambiguous word after the disambiguating word was fixated should

TABLE 4 ADJUSTED GAZE DURATION (MSEC) FOR CONSISTENT AND INCONSISTENT INTERPRETATIONS Relation o f initial interpretation and disambiguating word

Forward-gaze duration on disambiguating word Regressive gaze duration on disambiguating word Regressive gaze duration on a m b i g u o u s word

Consistent (n = 126)

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317

423

33

229

16

269

L E X I C A L R E T R I E V A L A N D ERR O R R E C O V E R Y

be greater in the inconsistent condition. As shown in Table 4, the duration of regressions on the ambiguous word averaged over subjects was roughly 269 milliseconds when the initial interpretation was inconsistent and only 16 milliseconds when it was consistent. The more inconsistent the disambiguating phrase was, the more time was spent in regressions on the ambiguous word. Readers spent approximately 31 milliseconds extra for each unit on the rating scale. The consistency rating alone accounted for a significant portion of the variance among the 43 means, F(1,41) = 63.74, p < .01. The length of the ambiguous word accounted for no variance in the duration of regressions. Readers also often refixated the disambiguating word itself during the errorrecovery process. As shown in Table 4, the average time in regressions to the disambiguating word was much larger when it initially had been inconsistent with the prior homograph, roughly 229 milliseconds compared to 33 milliseconds when it had been consistent. The regression analysis indicated that readers spent approximately 38 milliseconds extra for each unit on the rating scale. The consistency rating of the disambiguating word accounted for a significant portion of the variance in the duration of regressions on the disambiguating word, F(1,41) = 17.24, p < .01; the length of the disambiguating word accounted for no variance in the duration of regressions. Thus, the regressions strongly reflect the postulated error detection and recovery processes. Other error-recovery heuristics will be discussed in the following sections.

Eye Fixation Protocols The next section gives a detailed exlaosition of the eye fixations on three target sentences, bass (note), sewer (tailor), and tears (rips), that serve as prototypical examples of the results presented in the preceding section. The individual protocols are useful to explicate the nature of eye fixations and to show how their sequence and

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duration reflect the moment-by-moment computations in reading. Moreover, the protocols reflect specific error-recovery heuristics that will be supported by converging evidence from the oral reading protocols and the question-answering data. The same three dependent measures described in the results section are presented in three panels of each group. The top panel shows the average forward-gaze duration on each word in the sentence. The middle panel shows the average duration of regressions initiated after the disambiguating word was fixated. The bottom panel shows average duration of regressions initiated before the major disambiguating word was fixated. Each curve is averaged over readers who gave the same oral interpretation of the ambiguous word and who had the same context.

Bass This protocol is typical of the cases where the two interpretations were equally frequent and the context determined which interpretation was selected. Figure 3 shows the gaze durations for the bass (note) target sentence: Some of the best bass guitarists in the country would come to this spot. The two curves represent the two contexts; one more strongly primed the (note) homograph and the other more strongly primed the (fish) homograph. All of the readers gave the oral interpretations that were more strongly primed by their respective contexts. The most interesting aspect of this protocol is the evidence for the detection of an inconsistency. Inconsistency detection and recovery. Readers who had interpreted bass as (fish) had longer forward gazes on the disambiguating word, guitarists (shown in the top panel). Moreover, these readers spent slightly more time in regressions after guitarists was fixated (shown in the middle panel). Readers in both groups spent longer on guitarists than on other words because of its length. But the effect of the inconsistency is evident in the difference in the time

152

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the two groups spent on the disambiguating word. The longer gazes for the inconsistent group d e m o n s t r a t e s that one meaning o f bass already had b e e n selected and readers had to r e c o m p u t e an alternative interpretation. All five readers orally corrected themselves. The r e c o m p u t a t i o n might have been facilitated b e c a u s e bass was the word that immediately preceded guitarists. Consequently, a b a c k w a r d search or a search for the m o s t syntactically related w o r d (the modifier of guitarists), would have revealed the source of the inconsistency. Another possibility is that b o t h interpretations o f bass were originally retrieved and a trace of a previous choice point directed the search. I f the alternative interpretation had not yet decayed, there would have been no need for a n o t h e r lexical retrieval p r o c e s s and only the selection process would have been reexecuted.

Sewer The sewer protocol is typical of the sentences that have one relatively infrequent

h o m o g r a p h that is not retrieved, e v e n when it is more strongly primed. I r r e s p e c t i v e of w h e t h e r the c o n t e x t p r i m e d (tailor) or (drain), all o f the readers interpreted sewer as (drain). Figure 4 shows the average gaze durations for the groups who had the (tailor) a n d the (drain) c o n t e x t s on the (tailor) target sentence, There is also one sewer near our home who makes terrific suits. R e t r i e v a l and integration. T h e m o d e l predicted that the time to encode, retrieve, and i n t e g r a t e the (drain) i n t e r p r e t a t i o n would be shorter w h e n the context primed the (drain) interpretation. As shown in the top panel, the duration of the forward gaze on s e w e r w a s 290 m i l l i s e c o n d s f o r the (drain) context and 437 milliseconds for the (tailor) context. The (drain) context also resuited in f e w e r regressions to sewer when readers were processing the initial part of the sentence; the b o t t o m panel shows an a v e r a g e o f 77 milliseconds in r e g r e s s i v e fixations on sewer c o m p a r e d to 187 milliseconds for the (tailor) context.

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LEXICAL RETRIEVAL AND ERROR RECOVERY

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FIG. 4. The average gaze duration on each word of the s e w e r (tailor) sentence for readers in the two priming conditions. All ten subjects read s e w e r as (drain). The top panel shows the forward gazes: the middle panel shows regressions after readers fixated w h o ; the bottom panel shows regressions before readers fixated w h o .

Inconsistency detection and recovery. The (drain) interpretation was inconsistent with the disambiguating phrase who makes terrific suits. The difficulties this phrase caused are reflected in the relatively long forward gazes on the phrase (shown in the top panel) and in the extremely long regressions after the w o r d w h o was f i x a t e d (shown in the middle panel). The effect of the inconsistency is particularly apparent when compared to the eye fixations on the (drain) target sentence: There is also one sewer near our home that gives off strong odors. All 10 readers who had this sentence also initially interpreted sewer as (drain). However, the (drain) interpretation was consistent with the disambiguating phrase, that gives o f f strong odors and there were only an average of 53 milliseconds in regressions after the word that compared to 2145 milliseconds after who in the middle panel of Figure 4. A more detailed examination of the eye fixation behavior suggests an interesting heuristic process that was used to resolve

the inconsistency. The middle panel of Figure 4 indicates that the readers who had the most difficulty retrieving and integrating sewer, those with the (tailor) context, spent more time in regressions on sewer. The initial difficulty may have left some trace so that they were able to emplo), a heuristic search that rechecked any recent words that were difficult to retrieve or integrate. In rechecking sewer, the reader would attempt to retrieve an alternative interpretation that was consistent with the phrase who makes terrific suits and thereby derive the (tailor) interpretation. In fact, three of the five readers overtly corrected themselves while reading the sentence. One more reader at least recovered the correct interpretation by the end of the passage; he correctly answered the probe "w ho makes terrific suits?" Only one reader didn't rec o v e r the (tailor) i n t e r p r e t a t i o n ; when asked the probe question he responded that he didn't know. The pattern of regressions for the other groups of readers reveals the other side of

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CARPENTER AND DANEMAN

the heuristic. Readers who had the (drain) context spent less time in regressions on sewer and more time on the disambiguating phrase, who makes terrific suits. The fixation pattern suggests that they tried to reinterpret the disambiguating phrase itself. Without any problem initially retrieving or integrating (drain), they were less likely to discover the misinterpretation. Only two of the five readers overtly c o r r e c t e d their misinterpretations. One recovered by the end of the passage and answered the probe correctly. The remaining two gave evidence of not having resolved the inconsistency; one answered the question " w h o made terrific suits?" with sewer (drain) and one said he didn't know. This difference in error-recovery processes was consistent across the six target sentences where the correct interpretation had a very low relative frequency. There were longer regressions on the ambiguous w o r d when the c o n t e x t more s t r ongl y primed the interpretation with a low relative frequency than when the context primed the interpretation with a higher relative frequency, t(5) = 2.77, p < .05. Moreover, readers were more likely to recover the low-frequency interpretation if it had been more strongly primed by the prior context, as indexed by the percentage of overt corrections during oral reading, t(5) = 2.18, p < .05. The general heuristic to check previous points of processing difficulty may also explain why the readers in Experiment 2 were more successful in recovering from inconsistencies than readers in the main experiment. Experiment 2 passages provided extremely strong contexts for the low-frequency homographs. Although readers still tended to retrieve the higher frequency homograph, the stronger contexts should have made the initial integration process more difficult. This would have left a trace that could be used to identify the ambiguous word as a potential source of the inconsistency. In addition, the stronger contexts included more explicit clues that could aid in retrieving the homograph with the low relative frequency.

Tears This example allows a contrast between readers who gave the high-frequency interpretation (droplets) and a few who produced the low-frequency interpretation, (rips). Figure 5 shows the eye fixations for nine of the ten readers who initially read tears as (droplets) for the sentence There were big tears in her brown dress. The tenth reader will be discussed below; he was one of the two readers who produced (rips). Retrieval and integration. Consistent with the model, the top panel shows that the forward-gaze duration on tears was 128 milliseconds s h o r t e r w hen the c o n t e x t primed (droplets) and the readers retrieved (droplets) than when the context primed (rips) and the reader retrieved (droplets). The very longest time on tears was shown by the two readers who produced the (rips) interpretation after reading the (rips) context. While their data are not shown here, these two readers had a mean forward-gaze duration of 392 milliseconds on tears. Inconsistency detection and recovery. The word dress was inconsistent for all nine readers and there was a long forward-gaze duration on this word, 430 milliseconds, and as the middle panel shows, an average of 1080 milliseconds in regressions overall. The effect of the inconsistency is particularly apparent when the regressions in Figure 5 are compared to the eye fixations on the (droplets) target sentence There were big tears in her brown eyes. The nine readers who i n t e r p r e t e d tears as (droplets) found eyes to be consistent and they spent less than 25 milliseconds in regressions overall. The patterns of regressions in the second panel in Figure 5 resemble the patterns found in the sewer passage. The readers with the low-frequency prime (rips) were more likely to refixate tears and recover the correct interpretation. Two of these readers orally revised their reading interpretation. A third reader resolved the inconsistency by the end of the passage. She answered the probe "describe her dress" with (rips). A fourth did not resolve the

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FIG. 5. The average gaze duration on each word of the tears (rips) sentence for readers in the two priming conditions. All nine subjects read tears as (droplets). The top panel shows the forward gazes; the middle panel shows regressions after readers fixated dress; the bottom panel shows regressions before readers fixated dress. problem; he responded to the probe question with (droplets). By contrast, readers who had the (droplets) context spent less time in regressions on tears and more time on brown dress. N o n e of these five readers orally revised their m i s i n t e r p r e t a t i o n o f tears. Two readers incorrectly resolved the inconsistency by reinterpreting the prepositional phrase in her brown dress as on her brown dress, so that it fit the (droplets) interpretation o f tears. The two readers who retrieved (rips) also show the predicted pattern of eye fixations. For one reader, the (rips) interpretation was consistent because he was reading a (rips) target sentence and he made no regressions. For the other reader, the (rips) interpretation was inconsistent because he was reading a (droplets) target sentence, There were big tears in her brown eyes. This reader spent 2083 milliseconds in regressions after fixating eyes, with the longest times on tears (383 milliseconds) and eyes (883 milliseconds). The long regressions suggest

that the (droplets) concept was no longer available by the time the reader encoded eyes and he had to reencode tears to retrieve the originally rejected interpretation. H o w e v e r , he did r e c o v e r from the incons i s t e n c y and o v e r t l y c o r r e c t e d his oral reading of tears from (rips) to (droplets). In summary, these protocols illustrate the two major temporal predictions of the model. First, the durations of forward gazes and regressions on the ambiguous w o r d were shorter when the readers' interpretation matched the homograph that was more strongly primed by the context. Second, the duration on the disambiguating word was longer when it was inconsistent. Finally, the eye fixation protocols reflected specific r e c o v e r y heuristics. Error Recovery R e c o v e r y from the initial misinterpretation was indexed by two measures, overt c o r r e c t i o n s while reading aloud and answers to the probe question at the end o f

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the passage. In the main experiment, 43 of the 120 misinterpretations were overtly corrected. This is evidence that these readers located the source of the problem and retrieved the correct interpretation in time to say it while reading. Of course, whether a reader corrects a mispronunciation is partially a matter of reading style, since some readers believe that corrections are more disruptive to the audience than the original error. The answers to probe questions showed that another 26 misinterpretations were resolved at least by the end of the passage and 23 answers were ambiguous. Finally, there were 28 cases where the misinterpretations clearly were not resolved. One index of when the error-recovery p r o c e ss occurs is the point at which a reader regresses. There were 150 regression episodes after the disambiguating word was e n c o u n t e r e d when it was inconsistent, compared to 38 when it was consistent. For purposes of this count, a person who regressed and th en r e r e a d a phr a s e was counted as having one regression episode. The majority of these episodes were initiated when the reader fixated the disambiguating word or phrase. Three were initiated after the reader fixated the first word o f the next sentence; these all occurred in the tears p a s s a g e s . F o r t y - o n e o f the episodes were initiated by the sentencefinal word; these were all cases in which the sentence-final word was also part of the disambiguating phrase. Hence, these regressions may have been initiated because of the disambiguating phrase or because the reader encountered the end of the sentence. Finally, five episodes were initiated at the end o f the entire passage. These were all cases in which the reader had not made overt oral revisions and indicate that the reader was still troubled by the lack of resolution. Thus, the error-recovery heuristics that involve overt search are often evoked soon after the inconsistency is encountered. But sometimes the reader continues to read, perhaps hoping that the rest of the passage will clarify the problem. Moreover, readers tend to use the ends of sentences

and passages as places to again attempt to resolve the inconsistency. Another error-recovery heuristic manifested itself in the question-answering data; readers sometimes resolved a discrepancy by maintaining their initial interpretation of the ambiguous word and elaborating the disambiguating word or phrase to make it consistent with their prior interpretation. This heuristic illustrates how inconsistency detection and recovery are part of the integration process. One example occurred in a passage about a violin concert, where the disambiguation was only mildly inconsistent. Four readers were misled by the context so that they initially interpreted bow as meaning (a violin part). In fact, bow meant (a bend at the waist) in the target sentence, He took a bow that was stately and yet humble. Although these readers spent longer on the phrase stately and yet humble, they did not revise their misinterpretation of bow. When answering the question " W h a t did he do that was stately and yet humble?", all four talked about "putting the stately bow (violin part) under his chin." An analogous case occurred with another passage about a detective who was looking around a toolshed for a possible murder weapon when he saw a metal hammer. The target sentence was: It

was the lead in the inquiry that enabled him to solve the mystery. The inferential leap occurred with one reader who initially interpreted lead as (metal) and elaborated the disambiguation rather than reinterpret lead as (clue). When asked, " W h a t enabled the detective to solve the m y s t e r y ? " he res p o n d e d by saying, " T h e lead (metal) poisoning that came up in the inquiry." When a phrase is not too inconsistent, readers may resolve the "inconsistency" by making a larger inferential leap that maintains the original misinterpretation. Oral Reading The oral reading task may have influenced two aspects of the eye fixations. First, the durations of eye fixations tend to be longer in oral than in silent reading

LEXICAL RETRIEVAL AND ERROR RECOVERY

(Buswell, 1937). Second, readers tend to make more fixations in oral reading tasks (Buswell, 1937). Since the majority of content words are fixated in careful silent reading as well (Just & Carpenter, 1980), the increase in forward gazes may be only slight. As mentioned in the introduction, the eye fixations seem to be more closely attuned to the comprehension process than does the voice. The voice was often several words behind the locus of gaze, but the precise span varied among readers and points in the sentence. The execution and timing of the articulation process seem partially autonomous of the comprehension process. For instance, it was relatively difficult for a reader to interrupt articulation when he wished to revise his earlier interpretation. If a reader started saying the inconsistent homograph just as he fixated the disambiguating word, he would inevitably complete the incorrect pronunciation; the incorrect pronunciation could be aborted only if the reader's voice lagged by at least two syllables. Also, there was no obvious synchrony between individual eye fixations and the pronunciation of words or syllables. The initial syllable of a word might be initiated during a fixation on one word and completed during a fixation on the next word. These observations are consistent with the idea of a buffer that stores the output of the comprehension process in a format that is suitable for articulation. After a concept is retrieved and integrated, its retrieved articulatory plan might be sent to a buffer that has the capacity for several words. A fluent speaker may not initiate oral reading at the beginning of a sentence until the buffer has several words; such a backup will prevent hesitations if the comprehension process encounters minor difficulties. Hesitations should occur if the reader encounters a complex clause and finishes articulating the information in the buffer before the next word or phrase is encoded and integrated. In fact, such pauses did occur when the reader had difficulty resolving the inconsistency.

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Some mistakes and anticipations in oral reading provide further evidence for the top-down influence of context on lexical retrieval. In the present experiments there were a few cases where a reader incorrectly anticipated a strongly primed word. For example, one reader of the tears passage evidently activated and retrieved the word eyes based on the context big tears in her brown . . . . He said eyes even though the sentence actually ended with the word dress and his eye fixations indicated that he detected the inconsistent disambiguation before he pronounced eyes. Very strong contexts may activate and retrieve a concept to s h o r t - t e r m m e m o r y before the " b o t t o m - u p " encodi ng process is executed; this is one way to explain why oral readers sometimes articulate a contextually appropriate word that does not appear in the text. However, explicit expectations are an extreme form of contextual activation. The context alone usually is not strong enough to retrieve a single candidate for the next word. Generating a prediction would be more of a hinderance than a help since the guess would likely be incorrect. In this respect, it is misleading to make a strong analogy between the reading process and the cloze procedure in which subjects are forced to generate explicit guesses about a missing word. In reading, the subject usually relies on information from both the prior context and the encoded word itself. GENERAL DISCUSSION

The model has been tested with ambiguous words and garden path sentences. However, the passages were used to highlight processes that are common to most reading tasks, including words that are unambiguous and sentences that do not purposely mislead the reader. This section of the paper will present the implications of the model and the results for a general theory of reading. Retrieval and Integration

The model suggests that readers attempt to integrate a retrieved concept as soon as

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possible, usually while fixating the word they are processing (Just & Carpenter, 1980). This immediacy assumption can be contrasted with the assumption of other models of c o m p r e h e n s i o n that readers delay integration and selection until the end of a clause or sentence. Three sources of evidence favor the immediacy assumption. The current results suggest that readers selected an interpretation of the ambiguous word while fixating it. If the next word was inconsistent, they needed time to recover. One example of this is the bass sentence where the reader's interpretation of the ambiguous word determined the ease or difficulty of processing the very next word. A related result has been found in a silent reading task where the passages required inferences of varying difficulty (Just & Carpenter, 1978). For example, one passage described a millionaire as murdered, another described him as dead. A later sentence introduced the word killer. The additional time to make the dead-killer inference could be detected in the gaze duration on the word killer. This indicates that the inference occurred when the word was initially fixated. A third source of evidence comes from lexical decision tasks described earlier (Swinney, 1979). Those studies indicate that both meanings of an ambiguous word may be retrieved initially, but the level of activation of the unselected meaning decays within a short time, suggesting that the selection process was completed fairly rapidly. The immediate processing strategy has two important advantages in reading. First, it allows the comprehension process to remain focused on the appropriate topic. This is particularly apparent in the case of ambiguous words, where the two retrieved meanings are semantically dissimilar. The model postulates that after the concepts are retrieved, the integration process selects the one that fits the prior context. The selected concept becomes part of the text representation that activates other associated concepts. By contrast, the unselected concept' s level of activation can be

allowed to d e c a y to base line. Consequently, the unselected concept will not activate irrelevant semantic associates and interfere with subsequent processing. Second, the immediate processing strategy reduces the memory load that ambiguity could impose on the comprehension process. Since the selection tends to occur immediately, only one concept needs to be maintained in short-term memory rather than two or more.

Error Recovery The error-recovery heuristics minimize the cost associated with attempting to assign a case role and integrate a concept immediately. The current "garden path" passages accentuated comprehension errors, but misinterpretations do occur in reading normal text. Such errors are a natural consequence of the immediate processing strategy because it operates by making choices on the basis of incomplete information. To compensate for errors, there must be some efficient way to recover correct interpretations. This study documented a number of strategies that allow for relatively efficient recovery from misinterpretations. They include attempting to reinterpret the word that initially seemed inconsistent, checking previous words that caused processing difficulty, reading on for further information, and elaborating the apparent inconsistency to make it consistent. In summary, several convergent measures were used to trace the reading process, including the reader's initial oral interpretations of a word and corrections, the duration of forward and regressive eye fixations on several parts of the sentence, the sequence of eye fixations, and the reader's question-answering performance. These results supported the model of comprehension that focuses on the processes of encoding, retrieval, integration, error detection, and recovery. This model shows how the comprehension of ambiguous words and garden path sentences can be understood in terms of a more general model of reading comprehension.

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LEXICAL RETRIEVAL AND ERROR RECOVERY A P P E N D I X A : TARGET SENTENCE FOR E A C H HOMOGRAPH

1. Bass (note): Some o f the best bass/ guitarists in the country would come to this spot.1 (fish): Some of the best b a s s / c a t c h e r s in the country would come to this spot. 2. Wound (hurt): " I f I wound t h e / s n a k e with this stick you may be able to e s c a p e . " (wrapped): " I f I wound t h e / t o u r n i q u e t around her arm, that might stop the venom." 3. B o w (a bend): He took a bow that was stately and yet humble . . . . / (violin part): He took a bow that was propped on the music stand . . . . / 4. L e a d (metal): It was the lead in the h a n d l e / t h a t made it very heavy. (clue): It was the lead in the inquiry/ that enabled him to solve the mystery. 5. R e a d (present tense): I read the Wall S t r e e t J o u r n a l and m a k e m y d e c i s i o n s / based on their financial reports. (past tense): I read the Wall Street Journal the first thing this/morning. 6. Close (shut): His v o i c e d r o n e d on " . . . and close the basement door before I c a t c h / c o l d from the draft. (near): His voice droned on " a n d close to the kitchen was the wine cellar."/ 7. Winds (excites): The strenuous exercise sometimes w i n d s / m e up for the day's work. (exhausts): T h e s t r e n u o u s e x e r c i s e sometimes completely winds/ me for the rest o f the day. 8. Tears (droplets): There were big tears in her b r o w n / e y e s . (rips): T h e r e w e r e big tears in her brown/dress. 9. Buffet (meal): You should have seen the buffet/ our ship provided for the captain's banquet. (knock): You should have seen the buffet/ our ship received from the choppy seas. 10. Sewer (drain): There is also one sewer near our h o m e / t h a t gives off strong odors.

(tailor): There is also one sewer near our h o m e / w h o makes terrific suits. 11. Shower (water): The shower o f / w a t e r from the water-pik was the technological masterpiece of the American display. ( d e m o n s t r a t o r ) : The s h o w e r of/ the baskets was a w e a v e r from India. 12. Row (seat): Jay had a second row seat in the t h e a t e r / b u t she wanted one further back. (fight): Jay had a second row with his wife on the/ way home because she was unhappy with the play. 13. Minute (60 seconds): After a minute the doctor detected signs of life . . . . / (detailed): After a minute but rapid examination of the v i c t i m , / t h e doctor detected signs of life. A P P E N D I X B : FREQUENCY R A T I N G FROM THE PRONUNCIATION TASK Ambiguous word bass wound bow lead read close winds tears buffet sewer shower row minute

Interpretation

Percentage

(note) (fish) (hurt) (wrapped) (a bend) (violin part) (metal) (clue) (present tense) (past tense) (shut) (near) (excites) (exhausts) (droplets) (rips) (meal) (knock) (drain) (tailor) (water) (demonstrator) (seat) (fight) (60 sec) (detailed)

54 46 79 21 17 0 54 46 75 25 75 25 13 0 96 4 100 0 92 8 100 0 25 0 100 0

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