Chronometric Studies of Lexical Ambiguity Resolution 
Mark S. Seidenberg 
University of Illinois at Urbana-Champaign 
Bolt, Beranek and Newman, Inc. 
Michael g. Tanenhaus 
Wayne State University 
Languages such as English contain a large number of words 
with multiple meanings. These words are commonly termed 
"lexlcal ambiguities", although it is probably more 
accurate to speak of them as potentially ambiguous. 
Determining how the contextually appropriate reading of a 
word is identified presents an important and unavoidable 
problem for persons developing theories of natural 
language processing. A large body of psycholingulstlc 
research on ambiguity resolution has failed to yield a 
consistent set of findings or a general, 
non-controverslal theory. In this paper, we review the 
results of six experiments which form the basis of a 
model of ambiguity resolution in context, and at the same 
account for some of the contradictions in the existing 
literature. 
This work has three foci. The first is that we consider 
the lexlcal structure of words with multiple meanings, 
that is, relations among the meanings which presumably 
govern their representation in memory, and their access 
in context. Second, we attempt to characterize the 
structure and content of the llngulstlc context in which 
an ambiguous word occurs. It is clear that the 
llstener/reader uses context to compute the correct 
reading of a word; however, contexts provide different 
types of information which may be utillzed in different 
ways. Third, we consider real-time aspects of ambiguity 
resolution as it occurs in people, using a methodology 
that permits us to evaluate successive stages in 
processing. 
Relations among the meanings of ambiguous words vary 
along several dimensions. The component readings may be 
semantlcally related (the senses of GRASP in "to grasp a 
baseball" and "to grasp an idea") or semantically 
unrelated (e.g., the meanings of TIRE related to 
"sleeplng" and "wheel"). This dimension underlies the 
traditional distinction between polysemy and homonymy 
\[Lyons, 1978\].(I) The number of component readings also 
varies. The readings of a word can fall into different 
grammatical classes (e.g., the "sleep" reading of TIRE is 
a verb, the "wheel" reading a noun) or the same class 
(the meanings of STRAW related to "sipping" and "hay" are 
both nouns). The readings may be used approximately 
equally often in the language (e.g., WATCH) or they may 
be of unequal frequency (e.g., PEN, COUNT). Our research 
is concerned with homonymous words with two common 
readings of approximately equal frequency. 
Contexts provide several different types of information 
which are utilized in resolving amblgulty.(2) In example 
\[I\], the context provides syntactic information that 
i. John began to tire. 
favors the verb reading of the ambiguous word TIRE, and 
blocks the alternate noun reading. Syntax can function 
in this way only for ambiguous words with readings that 
fall into different gr-m.mtical classes. In \[2\], syntax 
2. A doctor removed Henry*s 
damaged organ. 
is neutral with respect to the alternate readings of 
ORGAN (because both are nouns), but a word in the context 
("doctor") is highly semantically related to one reading, 
and thus favors it; the alternate reading is not blocked, 
but merely implausible in the absence of any further 
information. The appropriate reading of DECK in \[3\] is 
3. John walked on the deck. 
indicated by a different means, which eLight be termed 
pragmatic. The perceiver knows that a person is much 
more likely to walk on the surface of a ship than on the 
surface of a pack of playing cards. 
Other types of contextual information can be brought to 
bear on ambiguity resolution as well. For example, \[4\] is 
disamblguated by exploiting ~ass noun/count noun 
information; \[5\] might be disamblguated by applying 
knowledge of a stereotyplc situation (a script or frame; 
Schank & Abelson, 1977; Minsky, 1975). 
4. Henry wanted a straw. 
5. John avoided the check. 
Extended contexts frequently contain multiple sources of 
dlsamblguatlng information. 
Leaving aside vague or misleading cases, it is clear 
that all of these types of information yield the same 
outcome, assignment of the contextually-approprlate 
reading of a word. We sought to determine whether they 
produced this effect by the same means. Broadly 
speaking, there are two alternative mechanisms by which 
the correct reading could be assigned. The perceiver 
could access all of the common readings of the word in 
parallel, and use contextual information to perform a 
subsequent selection. This alternative --traditionally 
termed "multiple access'--holds that while the perceiver 
usually is aware of only a single reading, there is 
transient subconscious activation of others as well. The 
other posslbillty--"selectlve access"--is that contexts 
restrict lexlcal access to the single appropriate 
reading. Both of these alternatives have been supported 
by experimental evidence. 
The time course of processing events is evaluated by 
using a variable stlmulus onset asynchrony (SOA) priming 
methodology \[Warren, 1977\]. The subject bears a sentence 
that is followed by the presentation of a single word on 
a screen. Latency to read the word aloud is used to 
diagnose the availability of alternate word senses. For 
example, sentence \[1\] above favors the verb reading of 
TIRE. If subjects access that meaning, they should be 
faster to read the semantically-related target word SLEEP 
than when it follows an unambiguous, unrelated control 
sentence (e.g., "John began to leave"). However, if 
subjects also access the contextually inappropriate 
reading of TIRE, faster naming latencles will be 
observed for a word related to it (e.g. WHEEL) as well. 
Similar considerations hold for \[6\], in which the context 
favors the noun reading of TIRE. 
6. John bought the tire. 
Changes in the availability of alternate readings over 
time can be tracked by presenting targets at a variable 
time interval following the ambiguous word or its 
control. In our experiments, targets appeared at a delay 
of either 0 or 200 msec. 
The first experiment (Tanenhaus, Leiman and Seldenberg, 
1979) examlned the resolution of noun-verb (N-V) 
ambiguities such as TIRE in syntactic frames such as 
those in \[i\] and \[6\]. The results were clear: ar 0 msec 
SOA, targets related to both the appropriate and 
inappropriate readings showed faster naming latencles 
than controls. With a 200 msec delay interposed between 
ambiguous word and target, however, only targets related 
to the contextually appropriate reading showed 
facilitation. The results indicated that syntactic 
information in the context did not restrict lexlcal 
155 
access to a single reading, but instead permitted a rapid 
selection between alternatives. Thls occurred despite 
the fact that the context made it impossible to derive a 
coherent interpretation of the utterance using the 
alternate readlng.(3) 
Seidenber8, Tanenhaus and Leiman \[1980\] found largely the 
same pattern of results wlth noun-noun (N-~) ambiguities 
such as ORGAN or STRAw and contexts such as \[7\], which 
were neutral 
7. John removed the organ. 
with respect to alternate readings of the ambiguous 
word. At 0 msec $OA, targets related to both readings 
showed facilitation, as might be expected since the 
context did not favor either one. At 200 nsec $OA, 
however, facilitation occurred on approximately half the 
trials, which would result if listeners had retained only 
one reading of the ambiguous word on each trial.(&) 
The pattern of results was similar to that in the 
Tanenhaus et al. (1979) study of syntactic contexts: 
multiple access, followed by avilabillty of only one 
reading 200 msec later. However, the underlying 
processes were quits different. In the syntactic frames 
study, listeners accessed multiple readings and used the 
context to select the appropriate one. In the Seldenberg 
e~ al. (1980) study, listeners accessed multiple readings 
but the context could not be used to perform a selection. 
They nonetheless assigned a default value within 200 
msec. The results suggest that ambiguity resolution is 
subject not only to constraints imposed by the nature of 
the context, but also to llmitatlons of time. Subjects 
avoid carrying multiple readings longer than 200 msec 
even when contexts do not unambiguously isolate one. The 
experiment was designed so that at the moment the 
ambiguous word occurred, they had no reason to believe 
that disambtguating information would not be forthcoming. 
Under this circumstance, they might have been expected to 
retain multiple meanings. Instead, subjects assigned 
their best guess, risking the possibility that subsequent 
re-processlng would be necessary. It appears that 
reprocessing imposes less of a burden on the processing 
system than that associated with retaining multiple 
readings over time. 
In another experiment, Seidenberg etal. (1980) examined 
the effects of biasing semantic information on N-N 
ambiguities in contexts such as \[8\]. 
8. The farmer removed the straw. 
As in \[2\], the context contains a word 
semantically-related to one meaning of the ambiguous 
word; syntactic information is neutral. These contexts 
produced selective access: for each item, only the target 
related to the contextually-appropriate reading of the 
ambiguous word showed facilitation; the target related 
to the inappropriate reading showed naming latencles 
comparable to those in the unrelated control. These 
outcomes held at both SOAs. Although N-N amblgu/tles 
produced multiple access in the previous experiment with 
neutral contexts, the biasing contextual information in 
thls experiment affected the initial access of meaning. 
Ne suggested such contexts Rrlme one reading of the 
ambiguous word, in the sense of Collins and Loftus 
(1975), Meyer and Schvaneveldt (1975), Warren (1977) and 
others. The readings of an ambiguous word are assumed to 
be coded in memory in terms of relative activation levels 
which reflect frequency and recency of use. A word or 
phrase semantically-related to one reading produces a 
transient increase in its activation level, possibly 
through a spreading activation process (Collins & Loftus, 
1975). The readings are accessed in order of relative 
actlvatlon; the primed reading is accessed first, and 
assigned on-llne.(5) 
As noted above, N-N ambiguities can be resolved by using 
other types of information, e.g. pragmatic, mass 
noun/count noun, etc. These differ from the priming 
contexts used in the previous experiment because they do 
not contain any words or phrases semantically or 
assoctattvely related to a reading of the ambiguous word. 
In this way they are comparable co the syntactic contexts 
of the first experiment. The fourth experiment compared 
the use of non-priming contextual information in the 
resolution of N-N and N--V ambiguities. Again the 
variable S0A methodology was used, with targets appearing 
at 0 and 200 msec delays. The results in both the N-N 
and N-V conditions replicated those of our first 
experiment, showlng multiple access at 0 msec, followed 
by availability of only a single readlng 200 msec later. 
The experiments to this point can be summarized as 
follows. There appear to be two classes of contexts that 
have very different effects on ambiguity resolution. 
Priming contexts contain words or phrases semantically or 
assoclatively related to one reading of an ambiguous 
word. They increase the activation level of the reading 
before It is encountered through a non-directed, 
automatic process. In this way, they can alter the order 
in which readings are evaluated. These effects are 
lntra-lexical (Forster, 1979), solely due to 
tnterconnecttons among nodes in semantic memory. 
Non-priming contexts include various types of 
information--syntactic, pragmatic, and others--which 
require access of gr-m-mttcal knowledge and knowledge of 
the world. The word recognition process yields one or 
more readings of the ambiguous word to be evaluated 
against the demands imposed by these contexts. The 
number of readings accessed and the order in which they 
are evaluated depends upon their relative activation 
levels, which any be altered by priming. 
In experiment five, we tested an implication of the 
priming hypothesis. Recall that N-V ambiguities yleld 
multiple access, as do N-N ambiguities, except when the 
latter occur in priming contexts. Clearly, thls suggests 
that N-V ambiguities might also produce selective access 
If the context contained a priming word or phrase, as in 
\[9\]. 
9. The nearsighted timekeeper 
dropped his watch. 
Thus, we compared the processing of ~-N and N-V 
ambiguities in priming contexts. The N-N results 
replicated those of the Seldenberg et al. (1980) 
experiment, selective access. The noun-verb conditions, 
however, continued to show ~ulglple access. Because 
the result was unexpected, we undertook a replication; it 
too showed thls pattern. 
The results of this series of experiments are summarized 
in Table I. We found no evidence that listeuers could 
use their knowledge of a language and knowledge of the 
world to restrict access to a single reading, at least 
for the class of ambiguous words with two common 
readings. Although these types of Information can 
facilitate the immediate pronesslng of a word (as 
demonstrated by Marslen-Wilson and Tyler, 1980), they do 
not influence the activation of word senses. It w~s 
suggested that the latter could be affected only by 
p~lming; however, the status of thls hypothesis is In 
doubt. Twice we observed selective access for N'N 
ambiguities in priming contexts; twice w- falle~ to 
obtain selective access with N-V ambiguities in similar 
contexts. Thls forces us to conclude that priming 
affects nouns differently than verbs, and strongly 
suggests that theories of lexlcal memory and recognition 
must begin to take into account the syntacElc functions 
of worr . 
156 
Table I 
Type of Context Type of Ambiguous Word 
1,3. syntactic N-V 
2. neutral N-N 
3,5. priming N-N 
4. norr-primlng bias N-N 
5,6. prlmlng N-V 
Outcome 
multlple--->selectlon 
multlple--->selectlon 
selective access 
multlple--->selectlon 
multlple-=->selectlon 
References 
Collins, A.M. and Loftus, E.F. A spreadlng-actlvatlon 
theory of semantic processing. Psychological 
Review, 1975, 82, 407-428. 
Forster, g.I. Levels of processing and the structure 
of the language processor. In W.E. Cooper and 
E.C.T. Walker (eds.), Se..__nntence pr_oc__.eeessln~:Studles 
presented to Merrill Garrett. LEA, 1979. 
Lyons, J. Semantics. Cambridge University Press, 
1978. 
Marslen-Wilson, W.D. and Tyler, L.K. The temporal 
structure of spoken language understanding. 
Co~nltion, 1980, 8, 1-71. 
Meyer, D. and Schvaneveldt, R. Meaning, memory, 
structure, and mental processes. In C.N. Cofer 
(ed.), The structure of human memory. Freeman, 
1975. 
M/risky, M. A framework for representing knowledge. 
In P. Winston (ed.), The psychology of computer 
vision. McGraw-Hill, 1975. 
Schank, R. and Abelson, R. Scripts, plans, goals 
and understanding. LEA, 1977. 
Seldenberg, H., Tanenhaus, M. and Leiman, J. The 
time course of lexlcal ambiguity resolution in 
context. Center for the Study of Reading Tech 
Report #164, 1980. 
Tanenhaus~ M., Lelman, J. and Seldenberg, M. Evi- 
dence for multiple stages in the processing of 
ambiguous words in syntactic contexts. J.Verbal 
Learning and Verbal Behavior, 1979, 18, "~. 
Warren, R. Time and the spread of activation in 
memory. J. Experimental Psychology: Human 
Learnln~ and Memory, 1977, ~, 458-466. 
Footnotes 
This research was supported by the National 
Institute of Education under Contract No. 
US-NIE-C-400-76-OII6 to the Center for the 
Study of Reading, and by a Wayne State U. 
research development award. 
i. Of course,a word can have semantlcally-dlstlnct 
readings that are themselves polysemous. 
2. These distinctions among types of context are not 
intended to prejudge any theoretical issues, only to 
facilitate exploratory research. 
3. It should be noted Chat a large number of sentences 
were utilized, and that precautions were taken to ensure 
that the experimental procedure itself would not induce 
subjects to access meanings they would otherwise ignore. 
4. For details, see the cited reference. Essentially, 
the experiment included control conditions which provided 
estimates of the amount of facilitation that would occur 
if either both readings or no readings were accessed on 
every trial. At 200 msec SOA, the amount of facilitation 
was almost exactly halfway between these two figures, 
suggesting that only one reading was available. 
5. The data are unclear as to whether activation of the 
alternate reading is entirely suppressed, or merely 
delayed. 
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