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| Proc Natl Acad Sci U S A. 1998 February 3; 95(3): 899–905. | PMCID: PMC33814 |
Copyright © 1998, The National Academy of Sciences Anatomy of word and sentence meaning Michael I. Posner * and Antonella Pavese Department of Psychology, University of Oregon, Eugene, OR
97403-1227 |
Abstract Reading and listening involve complex psychological processes that
recruit many brain areas. The anatomy of processing English words has
been studied by a variety of imaging methods. Although there is
widespread agreement on the general anatomical areas involved in
comprehending words, there are still disputes about the computations
that go on in these areas. Examination of the time relations
(circuitry) among these anatomical areas can aid in understanding their
computations. In this paper, we concentrate on tasks that involve
obtaining the meaning of a word in isolation or in relation to a
sentence. Our current data support a finding in the literature that
frontal semantic areas are active well before posterior areas. We use
the subject’s attention to amplify relevant brain areas involved
either in semantic classification or in judging the relation of the
word to a sentence to test the hypothesis that frontal areas are
concerned with lexical semantics and posterior areas are more involved
in comprehension of propositions that involve several words. |
The language section of this colloquium presents papers with
images of brain areas active during the processing of visual and
auditory words and sentences. Although there is a heavy emphasis on
visual words, it is also important to be able to connect the findings
on individual word processing with studies of written and spoken
sentences and longer passages. To do this, it is necessary to explore
the mechanisms that relate individual words to the context of which
they are a part. The findings of imaging studies of language reflect the complex
networks that can be activated by tasks involving words. When the words
are combined into phrases and sentences, the networks become even more
complex. One of the goals of our paper is to suggest productive ways of
linking findings at the single word level with those that involve
comprehension of continuous passages. Imaging studies have shown that language tasks can activate many brain
areas ( 1), predominately but not exclusively in the left cerebral
hemisphere. However, much greater anatomical specificity can be
obtained when specific mental operations are isolated ( 2, 3). The
mental operations related to activation and chunking of visual letters
or phonemes into visual or auditory units, often called “word
forms,” tend to occur near to the sensory systems involved in
language. These same sensory systems are also active during
translations of auditory stimuli into visual letters or the reverse
( 4). Additional mental operations are involved in relating the sound of two
words whether presented aurally or visually, as in rhyming tasks or
storing the words in working memory. These operations involve
phonological processing that appears to be common to auditory and
visual input. Understanding the meaning of words also invokes common
systems whether they had been presented visually or aurally. Of course,
understanding the meaning of a word can involve sensory specific and
phonological processes in addition to those strictly related to word
meaning. In this paper, we are concerned primarily with reading to comprehend
the meaning of the word or sentence. We label the mental operations
specific to comprehension as “semantic.” Tasks requiring
comprehension usually give specific activation of both left frontal and
posterior brain areas when the semantic operations are isolated by
subtracting away sensory, motor, and other processes. Semantic tasks
that have been studied include generating the uses for visual and
auditory input ( 4, 5), detecting targets in one class (e.g., animals)
or classifying each word into categories (e.g., manufactured vs.
natural) ( 4). There has been considerable dispute about the role of the left frontal
area in processing of visual words. One view ( 6) is illustrated in Fig.
1, which suggests that, within
the left frontal area, more anterior activations (e.g., area 47) seem
to be related to tasks that involve semantic classification or
generation of a semantic association whereas frontal areas slightly
more posterior (e.g., areas 44 and 45) are engaged by phonological
tasks such as rhyming ( 2, 3) or use of verbal working memory. This more
posterior frontal area includes the third frontal convolution on the
left side (Broca’s area). Although the bulk of studies that try to
separate meaning from phonology supports separation of the two within
the frontal brain areas, as indicated in Fig. 1, there are also some
studies that fail to show such separation (see refs. 7 and 8 for
detailed reviews of semantic and phonological anatomy). Fig. 1 also
shows that posterior brain areas (Wernicke’s area) are activated
during semantic and phonological operations on visual and auditory
words.
| Figure 1Summary of frontal and posterior cortical
activations found in various positron emission tomography, functional
MRI, and cellular studies of semantic (filled squares) and phonological
(open squares) processing of visual and auditory words. The more
(more ...) |
Recently, studies have been designed to give the time course of
these activations by use of scalp recordings from high density
electrodes ( 9, 10). For example, when reading aloud is subtracted from
generating the use of a visual word, the resulting difference waves
show increased positivity over frontal sites starting at ≈160 ms.
Efforts to estimate best fitting dipoles by use of brain electrical
source analysis ( 11) suggest an area of left frontal activation at 200
ms, corresponding roughly to that shown in Fig. 1. Depth recording from
area 47 in patients with indwelling electrodes, during the task of
distinguishing animate from inanimate words, confirms this time course
( 12). The difference waves in the generate minus repeat subtraction
also show greater positivity for the generate task over left posterior
electrodes (Wernicke’s area) starting at ≈600 ms. When a novel
association is required after long practice on more usual associations,
this left posterior area is joined by a right posterior homologue of
Wernicke’s area ( 9). It is not yet known how the frontal and posterior areas share semantic
processing during reading and listening. However, one clue comes from
the study of eye movements during skilled reading ( 13). Skilled readers
fixate on a word for only ≈300 ms, and the length and even the
direction of the saccade after this fixation are influenced by the
meaning of the word currently fixated ( 14). The time course of
fixations during skilled reading suggests that frontal areas are
activated in time to influence saccades to the next word but that the
posterior activity is too late to play this role. Previous analysis of
semantic processing, such as the N400 ( 15), has involved components
that are also too late to influence the saccade during normal skilled
reading. Because the distance of the saccade during skilled reading reflects the
meaning of the lexical item currently fixated, it is necessary that at
least some of the brain areas reflecting semantic processing occur in
time to influence the saccade. Areas involved in chunking visual
letters into a unit (visual word form) and those related to attention
as well as the anterior semantic areas are active early enough to
influence saccades ( 3). Partly for this reason, we have suggested that
the left anterior area that is active during the processing of single
words reflects the meaning of the single word (lexical semantics), and
the posterior area is involved in relating the current word to other
words within the same phrase or sentence (sentential or propositional
semantics). The distinction between lexical and propositional semantics is a common
one in linguistics ( 16). Many psycholinguistic studies ( 17, 18) also
draw on this or similar distinctions. It is clear that the meaning of
each individual lexical item taken in isolation gives little that would
serve as a reliable cue to the overall meaning of a passage. If even
giving a highly familiar use of a word requires activation of left
posterior areas, as the positron-emission tomography studies argue ( 5),
this left posterior area also must be important to obtaining the
overall meaning of passages that rely on integrating many words. Most
psycholinguistic studies draw heavily on working memory to perform this
role ( 19). Thus, it may be of importance that the portion of working
memory involved in the storage of verbal items lies in a brain area
near Wernicke’s area (ref. 6; see also ref. 25). For all of these reasons, we tried to test the specific hypothesis that
frontal areas will be more important in obtaining information about the
meaning of a lexical item and posterior areas will be more important in
determining whether the item fits a sentence frame. Our basic approach
was to have each subject perform these two tasks on the same lexical
items in separate sessions. We then compared the electrical activity
generated during the two tasks to determine whether the lexical task
produces increased activity in the front of the head while the sentence
task does so in posterior regions. A secondary hypothesis refers to the ability of subjects to give
priority voluntarily to the lexical or sentence level computation. Our
basic idea ( 4) is that the subject can increase the activation in any
brain area by giving attention to that area. Accordingly, in one
session, we trained subjects to press a key if “the word is
manufactured and fits the sentence,” and in another session, we
asked them to press a key if the word “fits the sentence and is
manufactured.” These two conjunctions are identical in terms of
their elements, but they are to be performed with opposite priorities.
Our general view is that attention reenters the same anatomical areas
at which the computation is made originally and serves to increase
neuronal activity within that area. In accord with this view, we expect that, in the front of the head, we
will see more activity early in process under the instruction to give
priority to the lexical computation, and late in processing, there will
be more frontal activity when the sentence elements has been given
priority. At posterior sites, the effect of instruction will be
reversed. |
Twelve right-handed native English speakers (six women)
participated in the main experiment. Handedness of participants was
assessed by the Edinburgh Handedness Questionnaire ( 20, 21). Their ages
ranged between 19 and 30 years and averaged 21.9 years. EEG was recorded from the scalp by using the 128-channel Geodesic
Sensor Net (Electrical Geodesics, Eugene, OH) ( 22). The recorded EEG
was amplified with a 0.1- to 50-Hz bandpass, 3-dB attenuation, and
60-Hz notch filter, digitized at 250 Hz with a 12-bit A/D converter,
and stored on a magnetic disk. Each EEG epoch lasted 2 s and began
with a 195-ms prestimulus baseline before the onset of the word
stimulus. All recordings were referenced to Cz. ERPs were re-referenced
against an average reference and averaged for each condition and for
each subject after automatic exclusion of trials containing eye blinks
and movements. A grand average across subjects was computed; difference
waves as well as statistical ( t test) values comparing
different tasks were interpolated onto the head surface for each 4-ms
sample (these methods are described further in refs. 9 and 10). The experimental trials began with the presentation of a sentence with
a missing word (e.g., “He ate his food with his ”).
The sentence was displayed until the subject pressed a key, and then a
fixation cross appeared in the center of the screen for a variable
interval of 1,800–2,800 ms. After the fixation cross, a word (e.g.,
“fork”) was presented for 150 ms and then replaced again by the
fixation stimulus. After a 1200-ms interval, a question mark, which
served as a response cue, was displayed for 150 ms. To exclude motor
artifacts, participants were instructed to respond only after the
question mark was presented, and anticipation trials were excluded from
the analysis. Participants responded by pressing one of two keys. The
correspondence between keys and responses (“yes” and “no”)
was counterbalanced across subjects. The same sequence of events was used to perform three different tasks.
In the single lexical task, subjects were asked to ignore the sentence
and to decide whether the word represented a natural or a manufactured
object; for half of the participants, the “yes” category was
“natural objects,” and for the other half, the “yes”
category was “manufactured objects.” In the single sentence
task, participants were instructed to press the “yes”
key if the word fit the previously presented sentence and the
“no” key if the word did not fit the sentence. In the conjunction
task, participants were asked to respond “yes” only if the word
was a member of the “yes” category AND it fit the sentence. Subjects participated in two sessions. In session A, they performed the
single lexical task, followed by the conjunction task in which the
lexical element was given priority. In session B, subjects performed
the single sentence task, followed by the conjunction task in which the
sentence element was given priority. The order of the two sessions was
counterbalanced between subjects. The conjunction tasks performed in
the two sessions differed in two respects: (i) In session A,
the conjunction task followed extended practice with the single lexical
task whereas in session B it followed extended practice with the single
sentence task; (ii) in session A, the instructions asked the
subjects to first perform the lexical decision and then the sentence
decision whereas the opposite was required in session B. It was hoped
that these manipulations would modify the priority of the two
decisions: In session A, the lexical decision had priority over the
sentence decision (conjunction task–lexical first) whereas in session
B the sentence decision had priority (conjunction task–sentence
first). An additional eight subjects (four women; age between 19 and 29 years,
average 21 years) were run in a purely behavioral study of reaction
time in the same experiment. The only difference in this study was that
subjects responded as quickly as possible after the word rather than
waiting for a response cue to appear. No EEG was recorded in these
sessions, and the reaction time to respond to the probe word was the
dependent measure. |
Behavioral Study. Medians of the response times (RTs) were
computed for each subject and each condition of the behavioral study.
The single lexical task was slightly faster than the single sentence
task (727 and 739 ms, respectively), but this difference was not
significant {t test [t(7) = −0.216],
P > 0.4}. Mean RTs across subjects were 733 ms for
the single tasks and 794 ms for the conjunction tasks. These two
conditions did not significantly differ from each other
[t(7) = −1.529, P > 0.15]. Although the
lack of significance of this effect may have been because of the small
sample size, it is worth noting that the conjunction task was always
the second task of the session and was performed after extensive
practice with the single task on the same stimulus material. It is
therefore likely that a practice effect was responsible for the
relatively small increase in RTs in the conjunction tasks when compared
with the much simpler single tasks. An important prediction is that RTs should reflect the priority of the
two decisions in the conjunction task. If our manipulation was
successful in determining the order of the lexical and of the sentence
decision, we should find a particular pattern of RTs in the “no”
responses. When the word is not a member of the appropriate category
(e.g., manufactured) and it does fit the sentence, subjects can
correctly respond “no” after they make the semantic
classification on the lexical item. On the other hand, when the word is
a member of the appropriate category and it does not fit the sentence,
they can respond “no” after they make the sentence decision. In
these two conditions, RTs should therefore reflect the priority of the
two tasks. When subjects respond “no” because the word does not
belong to the specified lexical category, they should be faster when
priority is given to the lexical task than when priority is given to
the sentence task. However, when subjects respond “no” because
the word does not fit the sentence, they should be faster when priority
is given to the sentence task than when priority is given to the
lexical task. To verify this prediction, we carried out a repeated measures ANOVA
with two factors: type of conjunction task (lexical first vs. sentence
first) and response (“no” because of the word vs. “no”
because of the sentence). The main effects of task and response were
not significant (Fs < 1). However, the interaction task by
response was significant [F(1, 7) = 6.148, P < .05]
(see Fig. 2).
| Figure 2RT to reject a word in the conjunction task as a
function priority give to lexical or sentence semantics. Only data from
“no” responses are presented. The cross-over interaction
indicates that the instruction, and training, to give (more ...) |
As predicted, when the lexical decision had the priority in the
conjunction task, subjects were faster to respond “no” when the
word was not a member of the targeted lexical category than when the
word did not fit the sentence. The opposite was true when the sentence
decision had the priority. This result suggests that the priority of
the two decisions was manipulated effectively in the two conjunction
tasks. Event-Related Potentials (ERP) Study. The ERP analysis focuses
on the anatomical regions that have been associated previously with
written word processing during semantic tasks. As outlined in Fig. 1,
left frontal regions and left parieto–temporal regions have been found
active in positron emission tomography and functional MRI studies of
use generation and semantic classification. As discussed in the
introduction, ERP and depth recording studies suggest that the frontal
activation occurs at ≈200 ms and that the posterior regions are
activated much later. Fig. 3 shows the grand-averaged
ERPs of the 128 channels in the semantic classification compared with
the sentence task. Important differences occur in left frontal channels
during the first positive component starting ≈160 ms after input. In
these frontal channels, the lexical task is more positive and thus
further from the baseline than the sentence task. We interpreted this
larger amplitude as reflecting greater activation of the frontal area
in the lexical task. This difference can be seen as early as 200 ms
after presentation. A much larger difference is found in posterior
channels at ≈400 ms after input.
| Figure 3Grand-average data from the 128 electrodes of the
event-related potentials for a lexical task (classifying words into one
of two categories) and a sentence task (deciding whether the word fits
the sentence frame). The time of presentation of the stimulus (more ...) |
To examine these differences in more detail, each of the four tasks was
shown for channels 29 (between F7 and F3) and 59 (between T5 and P3),
which are representative channels for the frontal and posterior areas
as illustrated in Fig. 4.
| Figure 4Representative frontal (ch 29) and posterior (ch
59) channels selected to indicate differences between ERPs to lexical
and sentence component tasks and lexical and sentence conjunctions.
Black areas indicate significant differences between conditions
(more ...) |
The single lexical task was more positive than the single sentence task
in the frontal channel, starting at ≈120 ms and continuing until
≈500 ms. Because this difference was during a positive excursion of
the waveform, the greater positivity in it indicates that there was
more electrical activity during the lexical task. In the posterior
channel, however, the sentence task was more positive than the lexical
task, starting at 350 ms, significant by 550 ms, and continuing to the
end of the 800-ms epoch. Because both tasks produced a positive wave
during this time, the sentence task showed more activity than the
lexical task. This pattern would fit with the early involvement of the
left frontal area in the lexical task and the later involvement of the
left posterior area in the sentential task. In the conjunction task, the frontal channel showed a larger activation
in the lexical first condition from ≈100 ms, which suggested a
stronger activation of the frontal region in which the lexical category
was computed when the conjunction was done with priority given to the
lexical category element. We also would have expected that the sentence
priority condition would have shown a late enhancement in this channel
reflecting the delayed processing of the lexical component. There is no
evidence favoring this idea. Because this effect was expected to be
quite late, variability in exactly when the second element of the
conjunction is processed may make it hard to see in time-locked
averages. In the posterior channel, the sentence first condition showed enhanced
negativity at ≈200 ms. However, the lexical priority condition was
generally much more positive than the sentence priority condition after
≈400 ms. Indeed, the lexical priority condition looked much like the
single sentence task during this portion of the epoch. Both of these
findings in the posterior channels fit with the idea that this area is
involved in computing information related to the sentence. The sentence
priority condition activated this sentence computation relatively early
whereas the lexical priority condition activated it relatively late. The overall pattern of results generally supports the hypothesis that
left anterior regions reflect decisions based on the word
categorization and the posterior area reflects decisions related to the
sentence. A map of the significant t tests was computed on the
difference waves of the average ERP of the four tasks. The results of
this computation are plotted in a spherical interpolation in Fig.
5. The significance of the
t values are plotted as increasing with the darkness of the
area.
| Figure 5 T-maps of significant differences between lexical
and sentence components and the two forms of conjunctions at one early
and one late time interval after the probe word. |
The comparison between the single lexical task and the single sentence
task revealed a significant difference in a left anterior area ≈160
ms. In this interval, the single lexical task’s waveform had a larger
amplitude than the single sentence task. At 460 ms, both left anterior
and left posterior areas showed a significant difference. In the left
anterior regions, the single lexical task was more positive than the
sentence task whereas in the posterior regions the single sentential
task was more positive than the lexical task. These differences
correspond to the results suggested before from the waveform analysis. In the conjunction task, a left anterior difference between the lexical
first and the sentential first tasks reached significance slightly
earlier (140 ms) than in the single task. This difference indicates a
larger amplitude in the waveform associated with the lexical first
condition, which reflects greater positivity of the lexical computation
in frontal electrodes when this element of the conjunction is given
priority. Another significant difference was present in a posterior
region ≈430 ms. This difference occurred when the lexical element was
given priority and indicates a greater late positivity than when the
sentence element was given priority. In the conjunction tasks, both
groups of differences appeared earlier than in the single tasks. A
possible explanation is the practice effect already mentioned in the
discussion of the RT data. A number of other findings are present in these data that are less
related to the main theme of this paper. A large late negativity
appeared when words that fit the sentence frame were subtracted from
those that did not. This is clearly related to the so-called N 400 and
represents a semantic incongruity effect. Although this effect was
broadly distributed, it appears to have been strong over right frontal
electrodes as has been reported often in the literature ( 15). |
The study of almost all cognitive tasks by positron emission
tomography and functional MRI have produced complex networks of active
brain areas. This is true even when subtraction is used to eliminate as
many of the mental operations involved in the task as possible. One
example of this complexity is the brain areas involved in comprehending
the meanings of words and sentences. Two of the most prominent areas
that have been related by many studies of comprehension are left
frontal and left temporo–parietal areas (see refs. 2 and 6; Fig. 1). Studies of the time course of these mental operations reveal some
important constraints on the computations they perform. The frontal
area is active at ≈200 ms whereas the posterior becomes active later.
Because saccades have been shown to reflect access to lexical semantics
and take place by 300 ms, only the frontal area is active in time to
influence saccades in skilled reading. During skilled reading, only one
or two words are comprehended in any fixation. Thus, the time course of
comprehension of a word when it appears by itself must be well within
300 ms if the data from word reading are to be appropriate to the study
of skilled reading of continuous text. This constraint led us to the
hypothesis that the frontal area represent the meaning of the current
word. Our study represents a test of the hypothesis that the frontal area is
involved in lexical semantics and the posterior area is involved in
integration of words into propositions. The data from the single task
condition fit well with the temporal and spatial locations defined by
this hypothesis. Despite this support from the data, it may be
surprising that frontal areas are involved in semantic processing
because the classical lesion literature argues that semantic functions
involve Wernicke’s area. Lesions in Wernicke’s area do produce a
semantic aphasia in which sentences are uttered with fluent form but do
not make sense. However, studies of single word processing, which prime
a meaning and then have subjects respond to a target, have shown
greater impairment or priming from frontal than from posterior lesions
( 23). Thus, the lesion data also provide some support for the
involvement of frontal structures in lexical meaning and posterior
structures in sentence processing. Our data also suggest that the meaning of the lexical item is active by
≈200 ms after input. Psycholinguistic studies of the enhancement and
suppression of appropriate and inappropriate meanings of ambiguous
words suggest that the appropriate and inappropriate meanings are both
active at ≈200 ms but that at 700 ms only the appropriate meaning
remains active, suggesting a suppression of the inappropriate meaning
by the context of the sentence ( 24). The time course of these
behavioral studies fits quite well with what has been suggested by our
ERP studies. Another source of support for the relation of the frontal area to
processing individual words and the posterior area for combining words
is found in studies of verbal working memory ( 25). These studies
suggest that frontal areas (e.g., areas 44 and 45) are involved in the
rehearsal of items in working memory and that posterior areas close to
Wernicke’s area are involved in the storage of verbal items. Such a
specialization suggests that the sound and meaning of individual words
are looked up and that the individual words are subject to rehearsal
within the frontal systems. The posterior system has the capability of
holding several of these words in an active state while their overall
meaning is integrated. Also in support of this view is the finding that
Wernicke’s area shows systematic increases in blood flow enhanced with
the difficulty of processing a sentence ( 26). The conjunction of a lexical category and a fit to a sentence frame is
a very unusual task to perform. Subjects have to organize the two
components, and it is quite effortful to carry out the instruction.
Yet, as far as we can tell from our data, the anatomical areas that
carry out the component computations remain the same as in the
individual tasks. Thus, when subjects have to rely on an arbitrary
ordering of the task components, they use the same anatomical areas as
would normally be required by these components. However, the ERP data
from the two conjunction conditions are quite different. This is rather
remarkable because the two conditions involve exactly the same
component computations. The results we have obtained are best explained
by the view that the subjects use attention to amplify signals carrying
out the selected computation and in this way establish a priority that
allows one of the component computations to be started first. Such a
mechanism would be consistent with the many studies showing that
attention serves to increase blood flow and scalp electrical activity
( 4). Defining a target in terms of a conjunction of anatomical areas is
a powerful method to use the subjects’ attention to test hypotheses
about the function of brain areas. Our results fit well with the idea
that frontal areas are most important for the classification of the
input item and posterior areas serve mainly to integrate that word with
the context arising from the sentence. |
Acknowledgments We are grateful to Y. G. Abdullaev for help in preparing Fig.
1. This paper was supported by a grant from the Office of Naval
Research N00014-96-0273 and by the James S. McDonnell and Pew Memorial
Trusts through a grant to the Center for the Cognitive Neuroscience of
Attention. |
ABBREVIATIONS RT | reaction time | ERP | event-related
potentials |
|
References 1. Cabeza, R; Nyberg, L. J Cognit Neurosci. 1997;9:1–26. 2. Demb, J. B. & Gabrieli, G. D. (in press) in
Converging Methods for Understanding Reading and Dyslexia,
eds. Klein, R. & McMullen, P. (MIT Press, Cambridge, MA). 3. Posner, M. I., McCandliss, B. D., Abdullaev,
Y. G. & Sereno, S. in Normal Reading and Dyslexia, ed.
Everatt, J. (Routledge, London), in press. 4. Posner, M I; Raichle, M E. Images of Mind. New York: Scientific American Library; 1994. 5. Raichle, M E; Fiez, J A; Videen, T O; MacLeod, A M K; Pardo, J V; Petersen, S E. Cereb Cortex. 1994;4:8–26. [PubMed]6. Fiez, J A. Hum Brain Mapp. 1997;5:79–83. [PubMed]7. Gabrieli, J D E; Poldrack, R A; Desmond, J E. Proc Natl Acad Sci USA. 1998;95(3):906–913. [PubMed]8. Fiez, J A; Petersen, S E. Proc Natl Acad Sci USA. 1998;95(3):914–921. [PubMed]9. Abdullaev, Y G; Posner, M I. Psychol Sci. 1997;8:56–59. 10. Snyder, A Z; Abdullaev, Y G; Posner, M I; Raichle, M E. Proc Natl Acad Sci USA. 1995;92:1689–1693. [PubMed]11. Scherg, M; Berg, P. Brain Electrical Source Analysis. Herndon, VA: NeuroScan; 1993. , Ver. 2.0. 12. Abdullaev, Y G; Bechtereva, N P. Int J Psychophysiol. 1993;14:167–177. [PubMed]13. Rayner, K; Pollatsek, A. The Psychology of Reading. Englewood Cliffs, NJ: Prentice–Hall; 1989. 14. Sereno, S C; Pacht, J M; Rayner, K. Psychol Sci. 1992;3:296–300. 15. Kutas, M; Van Petten, C K. Handbook of Psycholinguistics. Gernsbacher M A. , editor. San Diego: Academic; 1994. pp. 83–143. 16. Givón, T. Functionalism and Grammar. Amsterdam: Benjamins; 1995. 17. Kellas, G; Paul, S T; Martin, M; Simpson, G B. Understanding Word and Sentence. Simpson G B. , editor. Amsterdam: North–Holland; 1991. pp. 47–71. 18. Van Petten, C. Lang Cognit Processes. 1993;8:485–531. 19. Carpenter, P A; Miyake, A; Just, M A. Annu Rev Psychol. 1995;46:91–100. [PubMed]20. Oldfield, R C. Neuropsychologia. 1971;9:97–113. [PubMed]21. Raczkowski, D; Kalat, J W; Nebes, R. Neuropsychologia. 1974;12:43–47. [PubMed]22. Tucker, D M. Electroencephalograph Clin Neurophysiol. 1993;87:154–163. [PubMed]23. Milberg, W; Blumstein, S E; Katz, D; Gershber, F; Brown, T. J Cognit Neurosci. 1995;7:33–50. 24. Gernsbacher, M A; Faust, M. Understanding Word and Sentence. Simpson G B. , editor. Amsterdam: North–Holland; 1991. pp. 97–128. 25. Awh, E; Jonides, J; Smith, E E; Schumacher, E H; Koeppe, R A; Katz, S. Psychol Sci. 1996;7:25–31. 26. Just, M A; Carpenter, P A; Keller, T A; Eddy, W F; Thulborn, K R. Science. 1996;274:114–116. [PubMed] |
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