ANAPHORA RESOLUTION: SHORT-TERM MEMORY AND FOCUSING 
RAYMONDE GUINDON 
Microeleotronlcs and Computer Technology Corporation 
(MCC) 
9430 Research Blvd. 
Austin, Texas ?8759. 
ABSTRACT INTRODUCTION 
Anaphora resolution is the process of 
determining the referent of ~uaphors. 
such as definite noun phrases and 
pronouns, in a discourse. Computational 
linguists, in modeling the process of 
anaphora resolution, have proposed the 
notion of focusing. Focusing is the 
process, engaged in by a reader, of 
selecting a subset of the discourse 
items and maJ£ing them highly available 
for further computations. This paper 
provides a cognitive basis for anaphora 
resolution and focusing. Human memory 
is divided into a short-term, an 
operating, and a long-term memory. 
Short-term memory can only contain a 
small number of meaning units and its 
retrieval time is fast. Short-term 
memory is divided into a cache and a 
buffer. The cache contains a subset of 
meaning units expressed in the previous 
sentences and the buffer holds a 
representation of ~he incoming sentence. 
Focusing is realized in ~he cache that 
contains a subset of the most topical 
units and a subset of the mos~ recent 
units in the text. The information 
stored in the cache is used to integrate 
~he incoming sentence with the preceding 
discourse. Pronouns should be used to 
refer to units in focus. Operating 
memory contains a very large number of 
units but its re~rleval time is slow. 
It contains the previous tex~ units that 
are not in the cache. It comprises the 
tex~ units not in focus. Definite noun 
phrases should be used to refer to unite 
not in focus. Two empirical studies are 
described that demonstrate the cognitive 
basis for focusing, the use of definite 
noun phrases to refer to antecedents not 
in focus, and the use of pronouns to 
refer to antecedents in focus. 
The goal of thls research is to 
show the relation between the 
psychological work on anaphora 
resolution based on the notion of a 
limited short-term or working memory and 
the computational linguistics work based 
on the notion of focusing. 
This rapprochement is important for 
the following reasons: 
I) From a theoretical viewpoint. 
cognitive evidence increases the 
validity of the computational notion of 
focus. 
2) Focusing corresponds to one of the 
reader's comprehension processes and it 
needs to be incorporated in the model of 
the user in language understanding 
systems to adequately resolve 
am~iguitles in the user's utterances and 
to handle language generation. 
FOCUSING IN COMPUTATIONAL LINGUISTICS 
According to Grosz (1977). who was 
interested in ~he resolution of definite 
noun phrases, focusing is the process. 
engaged in by participants in a 
discourse, of highlighting a subset of 
their shared reality. Grosz. Joshi. and 
weinstein (1983) distinguish between two 
levels of focus, global focus and 
centerimg. Global focusing is a major 
factor in maintaining global coherence 
and in the interpretation of definite 
noun phrases. Centering is a major 
factor in maintaining local coherence 
and in the interpretation of pronouns. 
Grosz. Joshi. and Weinstein further 
define the notion of centering. Each 
sentence has two types of centers whose 
purpose is to integrate the sentence to 
the discourse. The backward-looking 
center links the current sentence to the 
preceding discourse. The set of 
forward-looklng centers provides th~ set 
of entities to which further anaphors 
m~y refer. The b6okw~rd-looklng center 
corresponds, roughly.- to Sidner's focus 
and the forward-looklng centers to 
Sidner's potentla~l fool. 
~8 
• L 
One principle derived by Grosz, 
Joshl, and Weins~ein is the following: 
if the b~okward-looking center of the 
ourren~ utterance is the same as the 
baokward-looklng cen~er of the previous 
utterance, a pronoun should be used. In 
other words, if there are no ~oplc 
shifts, continue to refer to the same 
entity by using a pronoun. 
However, violations of- this 
principle have been presented in Grosz 
(1977) and noted in Grosz, Joshl, and 
Welns~eln (198~). They have shown that 
pronouns are sometimes used to refer to 
entities mentioned many sentences back, 
even though the backward-looklng center 
of intervening sentences has been 
changed by topic shifts. 
Sidner (19V9. 1983) has proposed 
the notion of focus in the context of 
interpreting anaphors, especially 
pronouns. In Sidner's theory, an 
anaphor neither refers ~o another word 
nor co-refers to another word. but 
rather co-specifies a cognitive elemen~ 
in the reader's mind. Moreover. a 
theory of an&phora resolution must 
predict the pattern of reader's correct 
and incorrect choices of co-specifiers 
and ~he failures ~o understand. This 
view makes explicit the consideration of 
the reader's mental model and 
inferential capa~bili~ies 
A sEetch of Sidner's focusing 
process follows. First. an initial 
focus is selected on the basis of 
syntactic features and thematic roles 
indicating toplc~lity in the flrs~ 
sentence. Other elements introduced in 
the sentence are stored as potential 
loci for later sentences. When an 
anaphorlc expression is encountered. 
this focus is tested as a co-speclfler 
for ~he anaphor. It has to satisfy 
syntaotlo res~rlo~ions on co-references 
(L~snlk, 1976), semantic seleo~ional 
restrlo~ions (Katz and Fodor, 1963), and 
pragmatic plausibility oons~raln~s 
expressed in the remainder of the 
sentence. If the focus fails ~s a 
co-speclfier for the ~n~phor, the 
potential fool are tried in turn. At 
the same time, the new elements 
introduced in the sentence are stored as 
potential loci for later sentences. 
Third, the focus is updated to the 
selected co-speclfler for the anaphor. 
If the focus has changed, a topic s~ift 
has occurred. The second and third 
s~eps are cyclically applied after each 
sentence. 
The advantage of using a focus 
mechanism is tha~ it priorltlzes and 
restrlc~s the search for a co-speclfier, 
and as a consequence, reduces the 
oomputatlon~l costs assoolated with 
inferential processing when testln~ the 
applicability of the oo-speclfler to the 
anaphor. 
COGNITIVE STUDIES OF ANAPHORA RESOLUTION 
A few representative empirical 
studies of anaphora resolution are 
described below. All the experimental 
par~dlgms used share the following 
assumptions: 
1) human memory is func~ionally or 
s~ruc~urally divided into at least two 
types of memories, a short-term memory 
with small storage capacity but very 
fast retrieval time and a long-term 
memory with very large s~orage capacity 
but slow retrieval time: 
2) a topic shift transfers the units 
currently in short-term memory to 
lon~-term memory: 
3) ~n anaphor transfers its referent 
from long-term memory to short-term 
memory (i.e. reinstates its referent), 
if it was not already in short-term 
memory. 
The first assumption is crucial. 
Other things being equal, computations 
involving retrieval from short-term 
memory will be faster than those 
involving retrieval from long-term 
memory. Turning to the second 
assumption, topic shifts have been found 
to be induced wlth a varify of 
linguls%ic devices. One of the devices 
is the introduction of intervening 
sentences between the referent and its 
anaphor. The intervening sentences are 
unrelated zo the referent but related to 
the overall text. Another device is the 
specification of a temporal or Spatial 
parameter that is outside the normal 
range of a situation. When describing a 
dinner, the phrase "Five hours later," 
signals ~h~t the topic of conversation 
is no longer the dinner. Another device 
is the use of an anaphor, frequently a 
deflnlte noun phrase, to refer to an 
antecedent tha~ is not currently the 
topic of conversation bu~ is in the 
"background". Finally, there is the use 
of key phrases to signal a diversion in 
the flow of discourse, such as "Let's 
turn to.". as documented in Relchman 
(1978, 1984). 
The general pattern for the 
material used in these experiments is 
the following. A~ the beginning of the 
tex~ appears a sentence containing a 
referent (e.g. biologist). For 
example, "The mission included a 
biologist". Then, if ~he referent 
should not be in focus, the nex~ 
sentence or sentences indloate a topic 
shift as described aJ3ovs (e.g. 
~9 
unrelated intervening sentences). If 
the referent should be in focus, no 
devices for topic shifts are used. The 
following sentence then contains an 
an&phor (e.g. scientist, he) to the 
focused or non-focused referent (e.g. 
biologist). For example, "The scientlst 
collected samples from the cultures". 
Another example is shown in Table 1 of 
this paper. 
Carpenter and Just (1977) used eye 
traoklng with other converging 
techniques to study anaphora resolution. 
Wlth eye tracking, one can monitor very 
precisely the trajectory of the eyes, 
with their forward and regressive 
movements, and the duration of eye 
fixations on small segments of the te~. 
The assumption behind using this 
technique is that eye movements are 
closely related to higher level 
cognitive activities such as 
comprehension. Therefore. one can 
expect longer fixation durations on text 
segments requiring additional processing 
to be comprehended and one can expect 
the eye movement pattern to mirror the 
selective pickup of important 
information in the text. 
They performed a series of 
experiments testln~ the effect of 
recency of a referent on the time course 
of anaphora resolution. Indirectly. 
they tested the effect of recency on the 
availability of an item in short-term 
memory. They presented texts where the 
number of sentences between the referent 
and the anaphor was varied from zero to 
three. The subjects read each sentence 
and. after the sentence, had to decide 
whether it was consistent or 
inconsistent with the previous 
sentences. The consistency Judgment 
times and the eye fixations were 
recorded. The consistency Judgment 
task, used as converging evidence with 
the eye movement technique, is believed 
to induce the subjects to integrate each 
new sentence and should pars,llel the 
difficulty of ~phora resolution. The 
overall reading time of the ~n&phorlo 
sentence was measured using the eye 
tracking technique. Each of these tasks 
should be faster if the referent was in 
short-term memory than if the referent 
was in long-term memory. 
Response times for the consistency 
Judgments and reading times of the 
anaphorlc sentences increased as the 
n-mher of intervening sentences 
increased. The sharpest difference 
appeared between zero and one 
intervening sentence. Gaze durations 
within the anaphorlo sentence were 
shorter when there were no intervenlng 
sentences th~n in the other conditions. 
These results show not only that 
&naphora resolution is easier when the 
referent is nearer the ~naphor but also 
that one intervenln E sentence may be 
sufflolent to produce a topic shift. 
Clare and Sengul (1979) used the 
sentence reading time technique to study 
anaphora resolution. In this technique. 
subjects control the onset and offset of 
the presentation of a sentence by 
pressing a button. The subjects are 
instructed to press the button to see a 
new sentence as soon as they have 
understood the current sentence. The 
assumption behind this technique is that 
additional processing required for 
comprehension will increase sentence 
reading time. 
Clare and Sengul (1979) measured 
the reading time of a sentence 
containing an anaphor. They 
distinguished between two models of the 
effect of recency of a referent on the 
speed of ~naphora resolution. In the 
first model, called the "continuity 
model", entities mentioned in the 
discourse are searched backward from the 
last one. One should expect 
monotonically increasing re~din~ time as 
the searched entity is farther back. In 
the second model, called the 
"discontinuity model", entities 
mentioned in the current or last 
sentence are kept in short-term memory 
and accessed first. All the entities 
that are further back are more likely to 
be in long-term memory (and not in 
shor~-term memory) and accessed second. 
Subjects rea~ short paragraphs 
where a referent could be separated from 
the anaphor by zero ~o two intervenin~ 
sentences. The readln~ time of ~he 
sentence containing the anaphor was fast 
when the referent was in the immediately 
preceding sentence but ~allx ~ when 
it was two or three sentences before. 
This finding supports the discontinuity 
model. Entities in the last processing 
cycle are more likely to be kept in 
short-term memory than entities in 
previously processed cycles. Once a 
tex~ entity is not in short-term, the 
number of intervening sentences does not 
affect the speed of an~phora resolution. 
Lesgold, Roth, and Curtis (1979), 
who related the linguistic notion of 
foregrounding (Chafe, 1972) to ~he 
psychological notion of short-term 
memory, performed a series of 
experiments similar ~o those of Clark 
~nd Sengul (1979), using more varied 
ways to produce topic shifts, and 
replicated the above findings. 
220 
McKoon and gatoliff (1980) used an 
activation procedure based on Chang 
(1980). A desoriptlon of the baslo 
paradigm and its underlying loglo 
follows. When one reads a text, only a 
small part of the text information is 
stored in short-term memory and most of 
the information is stored in long-term 
memory. This is due to the very small 
storage capacity of short-term memory (7 
t2 chunEs; Miller, 1956). Given that 
retrieval time in short-term memory is 
much faster than retrieval time in 
long-term memory, it will tame longer to 
remember something from the text if the 
memory is stored in long-term memory 
than in short-term memory. 
In their study, subjects read a 
paragraph sentence by sentence. 
Immediately after the last sentence, the 
subjects were presented with a single 
word and the subjects had to remember 
whether the word had appeared previously 
in the text or not (an old-new 
recognition). If the tested word was 
still in short-term memory, the old-new 
recognition time should be faster than 
if it was in long-term memory. 
To test this hypothesis, the 
paragraphs were constructed in the 
following manner. The referent (e.g. 
burglar) was separated from the anaphor 
by either zero or ~wo in~ervenlng 
sentences. The anaphor appeared in the 
last sentence of the paragraph. The 
last sentence was presented in one of 
three versions: i) the subject of the 
sentence was a repetition (i.e. 
burglar) of the referent in the first 
sentence (anaphorio-identioal); 2) the 
subject was the name of the category- 
(e.g. criminal) in which the referent 
belonged (anaphorlc- category); 3) the 
subject was a noun (e.g. ca~) unrelated 
~o the referent (non-anaphoric). During 
the experimental trials, the "referent" 
(i.e. burglar) was presented 
immediately after the last sentence for 
an old-new recognition. 
Assuming that an anaphor activates 
its referent by making it available in 
short-term memory, one can expect 
slgnifloantly faster old-new recognition 
times for "burglar" in the 
anaphorlc-ca~egory oondi~lon than in the 
non-anaphorlo condition. This 
prediction was observed. 
Surprisingly, the number of 
intervening sentences did not have an 
effect. This suggests that the two 
intervening sentences did not remove the 
referent from short-term memory (i.e. 
"backgrounds" the referent). It is 
probably not the case. Rather. i~ is 
llkely that by testing the referent at 
the end of the clause, as opposed to 
when the anaphor is encountered, the 
referent had time to be reinstated in 
shor~-term memory and be highly 
available. This is an important point. 
The activation procedure was not on-llne 
since the old-new recognition ocoured at 
the ~n~ of the sentence as opposed to 
M~ll~ the sentence was read and the 
anaphor encountered. 
Another initially surprising effect 
was that ~he old-new recognition times 
for the referents were slower in the 
zero intervening sentences when the 
anaphor was a repetition of the referent 
itself than when the anaphor was the 
category name. This last result 
suggests that it is not appropriate to 
use a definite noun phrase, especially a 
repetition of the referent, to refer to 
a antecedent in short-term memory. 
As explained previously, 
intervening sentences are not the only 
devices that transfer text units from 
short-term to long-term memory. 
Stereotypical situations have spatial 
and temporal parameters with legal 
ranges of values. If one specifies a 
spatial or ~emporal value outside these 
ranges, a scenario-shift occurs. For 
example. Anderson (in Sanford and 
Garrodo 1981) constructed texts about 
stereotypical situations such as going 
to a restaurant. In one sentence of the 
text, there was a reference to a 
character related to the script, say a 
waiter. AZ the beginning of the next 
sentence, there was a mention of a 
temporal or spatial parameter, such as 
"One hour later" or "Five hours la~er". 
In the flrs~ case the parameter is 
within the range defining the scrip~, in 
the second case it is not. The rest of 
~he sentence contained an anaphor to the 
previously mentioned character, the 
walter. Measumlng ~he reading time of 
the anaphorlo sentence. Anderson showed 
longer reading time when the spatial or 
temporal parameter w~s outside the range 
of the script th~n inside. This 
suggests that the referent was 
transfered from short-term to long-term 
memory by the scenarlo-shlft and it took 
longer ~o retrieve the referent during 
anaphora resolution. 
The results from all these 
experiments support the notion tha~ an 
anaphor activates its referent by malting 
it highly available in short-term memory 
and ~hat topic shifts transfer units 
from short-term memory to long-term 
memoz'y. However. none of these studles~ 
except some eye movement siudles. 
provide data on ~ anaphora resolution 
occurs during the reading of a sentence 
~nd when i~ ooou2s in relation to the 
2~ 
lexioal, syntactic. 
pragmatic analyses. 
semantic, and 
COGNITIVE BASIS FOR FOCUSING 
A sketch of a cognitive model of 
anaphora resolution is offered here. It 
has been heavily influenced by the 
short-term~long-term memory model of 
Kintsch and van DiJk (19~8) and 
especially its leading edge strategy. 
~tructure ~f ~ memg/~ 
Analogically, human memory can be 
conceptualized as a three level 
structure similar to the memory of most 
mini and main frame computers. It 
consists of a small, very fast memory 
called short-term memory (STM); a 
relatively larger main or operating 
memory (OM): and a vast store of 
general world knowledge called long-term 
memory (LTM). 
The total STM is only large enough 
to contain 7t2 chunks of information at 
any one time (Simon, 1974; Miller. 
1956). The resources for STM are 
dynamically allocated to one of two 
uses. First, par~ of the STM is used to 
store the incoming sentence or clause. 
This is a temporary storage of the 
sentence or clause before further 
processing and is called the STM buffer. 
The second part of STM is called the STM 
cache. It is used to hold over. from 
one sentence or clause to the next. the 
information necessary to provide local 
and global coherence. It contains a 
subset of the previous text items that 
are topical and a subset of those that 
are recent. Retrieval times from 
short-term memory are very fast. 
Conceptually. operating memory is 
the subset of the world knowledge in 
long-term memory which is deemed 
relev~n~ to the prooesslng of the 
current par~ of the text. It also 
contains the growing memory structure 
oorrsspondin~ to the tex~ read so f~r. 
I~ contains the less topical and less 
recent information from the text. 
Retrieval times are much longer than for 
short-term memory. 
The time course of anaphora 
resolution is greatly determined by the 
current content of shor~-term memory and 
of operating memory. Moroever, pronouns 
and definite noun phrases are resolved 
using different s~rategies. 
Cache ~. During the input 
of a sentence into the buffer ~nd the 
concurrent integration of the sentence 
into the cache, a subset of the semantic 
units held in the STM is selected to be 
held over in the cache for the next 
cycle. Following Elntsch and van Dijk 
(1978), the cache management strategy 
selects a subset T of the most topical 
items and a subset R of the most recent 
items to be held over in the cache. The 
selection strategy aims at m~xlmizin~ 
the probability that an anaphor in the 
nex~ sentence will refer to a semantic 
unit held in the cache. Cache 
management is applied after each 
sentence or clause. 
Pronouns and definite noun phrases are 
resolved using different strategies, we 
will describe four cases: 
i. The anaphor is a definite noun 
phrase and the referent is not 
in focus, that is, i~ is in 
operating memory, 
2. The anaphor is a definite noun 
phrase and the referent is in 
focus, that is. it is in the 
cache. 
3. The anaphor is a pronoun and 
the referent is in the cache 
(in fOCUS). 
4. The anaphor is a pronoun and 
the referent is in operating 
memory (not in focus). 
It is hypothesized that the 
explicitness of sm anaphor is a signal. 
used by the readier, which denotes 
whether the referent is in the cache or 
in operating memory. 
If the ~naphor is a definite noun 
phrase, operating memory is searched 
immediately. If the referent is in 
operating memory it is then reinstated 
into the cache. A topic shift has 
occured. 
If the anaphor is a definite noun 
phrase and the referent is in focus 
(i.e. in the cache), anaphora 
resolution will be hindered. The reader 
searches operating memory while the 
referent is in short-term memory. 
Correspondingly. this violates a rule of 
cooperative communication: use a 
definite noun phrase to refer to an 
~ntecedent not in focus. The definite 
noun phrase signals a topic shift, while 
in fact. the same entity is being talked 
about. 
999 
If the anaphor is a pronoun, the 
cache is searched for a plausible 
referent. If found, mnaphora resolution 
is completed. Because cache management 
is based on topioallty and recency, 
pronouns can refer to ~he main ~opio of 
~he text even when the main ~opio has 
no~ been mentioned directly for mamy 
sentences. Unless there is a global 
~opic shift, the main topic in the cache 
remains unchanged throughout ~he text. 
If the anaphor is a pronoun but no 
referent is found in the cache, it is 
then necessary to search operating 
memory. If a referen~ is found in 
operating memory, it is reinstated into 
the c~che. A ~opic shift has occured. 
Using a pronoun ~o refer ~o information 
in operating memory is de~rlmental ~o 
amaphora resolution. The reader first 
searches the cache. ~hen ~he operating 
memory, and ~hen has ~o relnst~te ~he 
referent into the cache. 
COMPARISONS 
A clear relation exists between ~he 
notion of focusing proposed in 
computational linguistics and the model 
of human memory and discourse processing 
proposed in cognitive psychology. 
The Q~h~ is used to store the 
items in f.~Q~. Given the small number 
of items stored in the cache, a sketchy 
anaphor such as ~ ~ is sufflclen~ 
to retrieve the referent. The cache 
management strategy in human .memory is 
aimed at maximizing ~he probability that 
the cache contains the information 
relevant to the next cycle of 
computation. The cache, by containing 
topical and recen~ i~ems, allows to 
maintain global and local coherence. 
Q~ m~y~ is used ~o store 
items that are not in f~A~. Because 
the set of items is large, an 
informative descrlp~ion of the Item ~o 
be searched for is needed. D~fi~i~ 
~ou~ ~h/~es a/e used ~o indlc~te to the 
reader ~ha~ the i~em is no~ in focus. 
thus In operating memory. Other things 
being equal, it will tame more time to 
retrieve an item from operating memory 
than from the cache. The referent will 
need to be reinstated into the cache. 
This will produce a topic shift. The 
reinstated referent is then highly 
available and can be referred to by 
using a pronoun. 
TWO ON-LINE STUDIES OF ANAPHORA 
RESOLUTION 
The presented studies test the 
notion tha~ focus is cognltively 
realized in the reader's limited 
short-term memory. They also test 
Grosz. Joshl. and Welnsteln's claim that 
definite noun phrases, and not pronouns, 
should be used to refer ~o items no 
longer in focus and ~hat pronouns, ~nd 
not definite noun phrases, should be 
used to refer to items in focus. 
Moreover, if one assumes that the 
content of short-term memory is 
dynamically updated on ~he basis of 
recency ~nd topicality, one can explain 
why pronouns can be used to refer Zo 
recent items ~nd also to topical 
non-recen~ items. 
A new technique, called Q~zli~ 
~iQn, was developed specifically 
to provide the empirical da~a for these 
studies. The on-line activation 
technique can be compared to "closely" 
tracing the execution of ~ program. 
In the on-line activation 
technique, passages are presented using 
rapid serial visual presentation (RSVP), 
one word a~ a time. In ~dditlon to 
reading each text. the participants were 
also given the ~ask to recognize whether 
some specially marked words, presented 
surreptitiously wi~hln ~he ~ext, had 
appemred before in the tex~ or not. 
Some of ~hese special words were 
presented before in the text and others 
were not.. We will call ~hese specially 
marked words zest words. This task is 
called am old-new recognition task. 
The passages contained anaphors 
referring ~o antecedents which were 
either in focus or not in focus. An 
antecedent was removed from focus by 
introducing a topic shift, with ~he 
restrlc~ion that the antecedent was not 
the main topic of the discourse. An 
example ter~ is presented in table I. 
Note that only one of the alternative 
sentences 5a, 5b. or 50 was presented 
for each text to the participants of the 
study. 
In each text. one of the test words 
was the referent of the anaphor. At 
some point before or after the anaphor 
was presented on the CRT, its referent 
was presented for old-new recognition 
and recognition times and errors were 
collected. The delay between the onse~ 
of the anaphor and the onset of the test 
word is called the stimulus onset 
asynchrony (SOA). The ~naphor is acting 
as a prime, which should activate the 
referent. The old-new recognition time 
for the referent test word indicates 
223 
whether the referent is in the cache or 
in operating memory. 
TABLE 1 
EXAMPLE OF TEXTS WITH ANTECEDENTS 
IN FOCUS AND NOT IN FOCUS 
Antecedent: thermometer 
Anaphor: instrument 
Antecedent in Focus 
1- The assistant was preparing 
solutions for a chemistry experiment. 
2- The experiment would take at least 
four hours. 
3- There would then be a ten hour wait 
for the reaction to complete. 
4- He measured the temperature of a 
solution using a thermometer. 
5a- The thin instrument was not giving 
the expected re~ding. 
5b- A broken instrument was not giving 
the expected reading. 
5c- The compuzer terminal was not giving 
the expected reading. 
Antecedent not in Focus 
I- The assistant was preparing 
solutions for a chemistry experiment. 
2- He measured the temperature of a 
solution using a thermometer. 
3- The experiment would take at least 
four hours. 
4- There would then be a ten hour w~it 
for the reaction to complete. 
5a- The thin instrument was not givlng 
the expected reading. 
5b- A broken instrument was not giving 
the expected reading. 
50- The computer terminal was not giving 
the expected reading. 
In addition, there were three types 
of primes, as shown in sentences 5a, 5b, 
8~d 5o in Table i. The prime could be 
either semantically related and 
referential (S+R÷) ~ in 5a, 
semantically related and not referential 
(S+R-) as in 5b, or semantically 
unrelated and not referential (S-R-) as 
in 5c. In the S÷R÷ condition, the prime 
is the an~phor. The two conditions S÷R- 
and S-R- were control conditions to 
separate the effect of semantic priming, 
due ~o semantic ~ssociation between the 
anaphor and the referent, on the old-new 
reccgnltlon for referents. 
A schema of the procedure is shown 
in Table 2. The words surrounded by 
stars a~e the test words. 
TABLE 2 
SCHEMA OF THE PROCEDURE 
SOAs Before ~50 msec 1250 msec 
Time 
T1 The The The 
T2 thin thin thin 
T~ "thermometer* instrument instrument 
T4 instrument *thermometer" was 
T5 was was not 
T8 not not giving 
T7 giving giving *thermometer" 
The predictions were: 
I. If a referent is not in focus, 
due to a topic shift, the 
ooourenoe of the anaphor should 
reinstate the referent into the 
cache, leading to faster 
old-new recognition times. In 
terms of the experimental 
conditions, there should be a 
decrease in old-new recognition 
time at the 350 and 1250 msec 
conditions in the S+R÷ 
condition (i.e. after the 
anaphor), but not in the S+R- 
and S-R- conditions, which are 
not anaphorio. 
2. The use of a definite noun 
phrase to refer to an 
antecedent in the cache (i.e. 
in focus) should be detrimental 
to anaphora resolution. IZ 
should slow down the 
recognition of the referent as 
old or new. In terms of the 
ex~erlmental conditions, if the 
referent is in focus, the 
old-new recognition times in 
the 350 and 1250 msec SOA 
conditions should be slower 
than in the before SOA 
coD~Litlon. 
Method 
ELT.TJ,~,pA~ There 
p~rtioipants in this study. 
were 36 
~/~I~ There were 36 
experimental texts. They contained as a 
referent an instance of a cl~ss (e.g. 
thermometer) to be used later as a test 
word, and a~ an an~phor the class name 
(e.g. instrument). In this study, the 
an~phor w~s a definite noun phrase. An 
example of the material was presented in 
Table i. There were three p~imlng 
oondltlons, S+R+. S+R-, and S-R-, 
224 
exemplified respectively by sentences 
5a, 5b, and 50. 
During the presentation of each 
text. two or three test words were 
presented, one experimental and one or 
two fillers. The filler words were 
presented at semi-random locations in 
the text. In the entire experiment 
there was an equal number of old and new 
test words. 
~r~re The experiment was 
computer-controlled using real-tlme 
routines on the VAX/VMS 11/780 of the 
Computer Laboratory for Instruction in 
Psychological Research at the University 
of Colorado. Each participant sat in 
front of a CRT screen with a keyboard 
which had a "yes" button on the right. 
for old test words, and a "no" button on 
the left. for new test words. The tex~s 
were presented using RSVP. with each 
word presented in the center of the 
screen for 300 msec. The participants 
were asked to recognize whether the test 
words were old or new. as fast as 
possible but without making mistakes. 
D~i~ There were 36 experimental 
texts and 18 experimental conditions. 
The first manipulation was the focusing 
of the referent: in focus or not in 
focus. The second manipulation was the 
SOA: immediately before ~he prime. 350 
msec after. 1250 msec after. The third 
manipulation was priming: S+R+. S+R-. 
S-R-. The design was completely 
within-subject, with two texts randomly 
assigned to each experimental condition 
usin~ two randomly sampled 18 by 18 
Latin Squares. Each participant was 
randomly assigned to a row of the Latin 
Squares. 
~sul~a and D~.scusl~ 
The predicted interaction of 
focusing and priming is shown in Figure 
I: the prime in the S+R+ condition 
(i.e. the anaphor) reinstates the 
referent into the cache, focusing it. 
while ~he referent is not relnstazed in 
the non-referentlal conditions. 
E(2.70) = 3.6. ~ , 0.04. MSe = 213~21 by 
subjects and E(2.70) = 2.5, ~ , O.Og, 
MSe = 277568 by items. A priori 
comparisons show that the difference 
between the recogniticn times in the two 
focus conditions in ~he S¢R+ condition 
is much smaller than in the other two 
priming conditions, S-R- and S-R-. which 
do mot differ between themselves, 
~(35) ° 2.6. ~ , 0.01. MSe - 87 by 
subjects, and ~(35) = 2.14. ; , 0.02, 
MSe = 114 by items. These resul~s 
support the notions that i~ems in focus 
are more accessible than items not in 
focus and that focus is realized into 
the cache. They also support the notion 
that an anaphor reinstates a referent 
not in focus and does so by transferring 
the r@ferent to the cache. 
L 
A 
T 
E 
N 
C 
I 
E 
S (msec) 
FIGURE I. 
1345. 
1305. 
1265 m Not in Focus 
1225 ~ In Focus 
1185 
1145 
1105 
1065 
1025 
S+R+S*R-S-R- 
PRIMING 
Recognition latencies az each 
focus and priming condition. 
An a priori comparison demonstrates 
that using a definite noun phrase ~o 
refer to an item in focus hinders 
anaphora resolution. What seems ~o 
happen is a surprize effect caused by 
the violation of a linguistic usage 
relating the form of the anaphor to the 
fOCUS S~atus of its referent. The 
recognition time for the referent, in 
the focus condition, was longer at the 
350 msec and 1250 msec SOAs than in the 
before SOA. ~(35) - -4.1. R ~ 0.001. 
MSe - 24 by subjects, and ~(35) - -2.9, 
, 0.008. MSe - 31 by items. This is 
shown in Figure 2. 
L 1345. 
A 1305- T 
E 1265- 
N C 1225- 
I 1185- E 
(msec) 1105- 
1065- 
1025 • before 350 1250 
SOA 
FIGURE 2. 
(~sec) 
Recognition la~encies a~ each 
SOA for a referent in focus. 
225 
In another study (Gulndon, 1982), 
using ~he same on-llne ~c~iva~ion 
technique, the ~c~ivation of an 
antecedent by a pronoun was ~raced. In 
this study, it was fo%L~d tha~ referring 
~o an anteceden~ not in focus by using a 
pronoun was detrimental to anaphora 
resolution. The delay between reading 
the anaphor and reins~atlng the 
an~eceden~ was as long as 2400 msec. 
The actlva~ion of an anteceden~ no~ in 
focus by a pronoun takes a long ~ime 
because ~he reader is induced: I) to 
search the cache unsuocesfully; 2) to 
search operating memory with a "sketchy" 
pronoun: 3) to relnstaZe the referent 
into the cache. Activation was 
immediate for ~he antecedents in focus. 
As opposed ~o the previous s~udy where 
referring to a focused referen~ using a 
definite noun phrase hindered anaphora 
resolution, no such effect was observed 
when using a pronoun. This is expected 
since pronouns signal tha~ ~he referent 
is in the cache. 
SUMMARY 
The notion of focusing and the 
notion that the form of the anaphor 
signals whether ~he referen~ is in focus 
or no~ have cognitive support. Items in 
focus are items in the cache which is 
dynamically updated ~o contain ~he T 
most ~opical and the R most recen~ items 
in the ~ex~. Because the cache con~alns 
few items, pronouns should be used ~o 
refer to items in focus. O~her things 
being equal, anaphora resolution will be 
easier if the antecedent is in focus, 
because ~he retrieval ~imes from the 
cache are much faster ~han those from 
the operating memory. Antecedents not 
in focus are in operating memory. I~ems 
no~ in focus are in operating memory. A 
definite noun phrase, because it is more 
descriptive ~han a pronoun, should be 
used to re~rieve the ~nteceden~ from ~he 
large set of i~ems in operating memory. 
However, because ~he reErleval ~ime is 
slow in opera~in~ memory, anaphora 
resolution is more dlfflcul~ for i~ems 
~ha~ are no~ in focus. The 
relns~a~emen~ of am an~eceden~ into ~he 
cache effects a ~oplc shift. 
The on-llne activation ~echnique 
was developed specifically to provide 
empirical data on the no~ion of focus. 
The ~dvan~age of this technique over 
conventional memory experiments is that 
one can ~est precisely the ~emporal 
properties of various analyses and 
processes occurring durln~ sentence and 
ter~ comprehension. This technique can 
be used to distinguish between different 
models of anaphora resolution when ~hese 
models are no~ easily distinguished on 
the basis of discourse or dialogue 
an~iysls. 
REFERENCES 
CarpenZer, P.A. ~ Just. M.A. 
lnZegraZlve processes in 
comprehension. In D. LaBer~e 
~.j. Samuels (Eds.), ~i~ 
P/.OD~ses i~ E.~,~&L'LD~. Hillsdale, 
N.g.: Erlbaum, 1977. 
Chafe, w. Discourse structure and human 
knowledge. In J.B. Carroll ~ R.O. 
Freedle "(Eds.), L~n~ 
co~mmhmna~mn ~n~ ~hm amg~l~imn of 
~i~. Washington: Winston. 
1972. 
Chang, F. AcZive memory processes in 
sentence comprehension: Clause 
effects and pronominal reference. 
~m~ ~n~ G~ni~n, 1980, 8, 58 - 
64. 
Clark, H.H., ~ Sengul. C.J. In search 
of referents for nouns and pronouns. 
~m~=~ ~n~ C_Q~nl~i~n. 1979, Z, 35 - 
~I. 
van DiJk, T.A. ~ Kintsch. W. ~X~gi~S 
~f ~l~cou=g2 G~m~x~h~si~a. New 
YorE: Academic Press, 1963. 
af focus in ~i~la~um ~n~nGin~. 
Technical No~e 151. Artificial 
InZeiligence Center, SRI, 1977. 
Grosz, B.J.. Joshi, A.K., ~ WeinsZein. 
S. Providing a unified account of 
~~ nmm ~ in ~lggm~na~. 
Technical No~e ~92, Artificial 
In~elligence Center, SRI, 1983. 
Gulndon, R. Q~=Ii~ ~oc~ing ~f 
~i~s~Sm~3 searcheS. Unpublished 
manuscript. Universl~y of Colorado. 
Boulder, 1962. 
Guindon, R. ~hz ~ff~ct of re~en~ ~n~ 
Doctoral Dissertation. University 
of Colorado, Boulder. 198~. 
Just, M.A. ~ Carpenter. P.A. A theory 
of rea~ing: From eye fixations to 
comprehension. ~chologi~l 
Ke.J.l~, IgBO. ~Z, 329 - 3S4. 
E~z, J.J. ~ Fodor, J.A. The 
of a sem~nZlc ~heory. 
1963, ~, 170 - 210. 
structure L~uEu~g~. 
226 
Ein%scho W. ~ van DiJk, T.A. Toward a 
model of %ex~ comprehension and 
production. ~ Review, 
1978. 85, 363 - 394. 
LasniE. H. Remarks on co-reference. 
LinglL~ An~l~.~is, 1976, ~, 1-22. 
Lesgold. A.M.. Ro~h, S.F.. ~ Curtis, 
M.E. Foregrounding effects in 
discourse comprehension. ~rnal of 
Ver~a~ Le~Luin~ ~ Ver~l 
~nslon, 1979, i~, 281- 308. 
McEoon. G. ~ Ra%Ollff. R. The 
comprehension processes and memory 
s%ruc~ures involved in anaphorlc 
references. Journ~l of Y~I 
L~mnlng ~n~ Y~=L~I ~;~,.V.i.~, 1980. 
19, 668 - 682. 
Miller. G.A. The magical n,~mher seven. 
plus or minus ~wo: Some llmi~s on 
our capacity for processing 
informaZion. ~l~gl~l E~Xi~. 
1956, ~, 81 - 97. 
Reichman. R. Conversational coherency, 
C~g~i~ix~ ~i.~, 19?8, ~, 283-327. 
Reichman, R. Ex~ended person-machlne 
in%erface. &~l Zn~elllEenoe. 
1884. ~, 157 - 218. 
Sanford, A.J. ~ Garrod. S.C. 
~n~fi~n~in~ ~i~J~n I.~g,~&g~. New 
York: Wiley, 1961. 
~heory of definite anaphor& 
~fih~nsion i= English ~L~g~urse. 
Technical repor~ 537. MIT 
Ar%ificlal In~elllgenoe Laboratory, 
C~mhrldge MA, 1979. 
Sidner. C. Focusing in %he 
comprehension of definite anaphora. 
In M. Brady and R. C. Berwlck 
(Eds.). com~tQn~l ~ of 
~iH~g~. Cambridge: MIT Press. 
1983. 
Simon, E.A. Eow big is a chunk? 
~Ql~fi, 1974. IE~, 482 - 488. 
ACKNOWLEDGMENT 
Thls research was performed as par% of 
the auZhor's doctoral dissertation while 
a~ ~he University of Colorado. She is 
ex%remely grateful for ~he help of her 
dissertation oommlZ~ee. Wal~er EinZsch. 
Peter Polson, Alice Healy. Richard 
Olson. AndrzeJ Ehrenfeuch~. Bur%on 
Wagner has provided many insightful 
comments on this paper. MCC is kindly 
~hanked for ~he technlcal suppor% 
provided while oomposlng ~hls paper. 
227 
