Interpreting Intended Meanings after Right Hemisphere Brain Damage 29
Interpreting Intended Meanings after
Right Hemisphere Brain Damage:
An Analysis of Evidence, Potential
Accounts, and Clinical Implications
This paper considers the nature and generality of right brain-damaged patients difficulties with interpreting
intended meanings. Evidence is summarized from the authors research program, which highlights
(1) cognitive processing influences on the comprehension of nonliteral forms and inferences, and
(2) deficiencies in a specific comprehension process, the suppression mechanism (Gernsbacher, 1990). A
suppression deficit hypothesis is proposed as one predictor of patients characteristic discourse comprehen-
sion difficulties. Other current accounts are reviewed briefly, and their intersection with the suppression
deficit hypothesis is explored. The paper also discusses methodologic factors that help to explain why the
authors findings at times diverge from the conventional wisdom about patients deficits. Finally, clinical
implications of the authors research are considered. Key words: comprehension, right brain damage,
suppression
Connie A. Tompkins, PhD ESPITE THE FACT that left hemi-
Department of Communication Science Dsphere functions have been the overrid-
and Disorders ing focus of language processing research for
University of Pittsburgh more than a century, it is now well-estab-
University Center for Social and Urban lished that unilateral right hemisphere dam-
Research age (RHD) interferes with interpreting the
Pittsburgh, Pennsylvania intent of a variety of language forms and
communicative interactions. For example,
Margaret T. Lehman, MS adults with RHD have been demonstrated to
Department of Communication Science have problems extracting meanings from
and Disorders figurative expressions, indirect speech acts,
University of Pittsburgh facial or vocal cues, and stimuli requiring
University Center for Social and Urban
Research
Preparation of this manuscript was supported in part by Grant
Pittsburgh, Pennsylvania # DC01820 from the National Institute on Deafness and Other
Communication Disorders. The authors thank Amy D. Wyatt
for her capable editorial assistance and the coauthors of the
original articles that were summarized here (Annette
Baumgaertner, Cynthia Bloise, Richard Boada, Tepanta
Fossett, Kathrine McGarry, Maura Timko, and Janice Vance).
The authors also appreciate the cooperation of the various
hospitals and rehabilitation centers that have helped them to
identify and recruit patients (HealthSouth Harmarville Reha-
bilitation Center, HealthSouth Rehabilitation Hospital of
Greater Pittsburgh, Mercy Hospital of Pittsburgh, University
of Pittsburgh Medical Center). Finally, the authors remain
indebted to their patients for their continuing interest and
participation in their projects.
Top Stroke Rehabil 1998;5(1):29 47
© 1998 Aspen Publishers, Inc.
29
30 TOPICS IN STROKE REHABILITATION/SPRING 1998
linguistic inferencing for comprehension sessed the influence of task-processing de-
(see, e.g., Joanette, Goulet, & Hannequin, mands and individual subjects cognitive re-
1990; Molloy, Brownell, & Gardner, 1990; sources on the interpretation of intended
Tompkins, 1995). In large part, such prob- meanings. More recently, guided by a theo-
lems are manifest with materials that support retical framework on normal language com-
or induce multiple interpretations (Joanette prehension, they have begun to evaluate
et al., 1990; Tompkins, 1995). Typical dis- whether deficits in specific comprehension
course comprehension deficits for RHD pa- mechanisms may contribute to RHD adults
tients also are particularly apparent when characteristic problems with ambiguity resolu-
there is some conflict between or ambiguity tion and, more generally, to their overall com-
in available clues to meaning (see, e.g., prehension ability. Before their efforts are
Brownell & Martino, 1998; Joanette et al., summarized in these areas and their interpreta-
1990; Stemmer & Joanette, 1998; Tompkins, tions related to other accounts, the authors raise
1995; Tompkins, Bloise, Timko, & some methodologic considerations that are
Baumgaertner, 1994). For example, dis- central to understanding some of the differ-
course comprehension problems occur when ences between this work and much of that
understanding hinges on integrating multiple conducted by other investigators.
or disparate aspects of the discourse context,
such as cues to speaker mood or motives and METHODOLOGIC FACTORS IN
plausibility (e.g., Brownell, Carroll, Rehak, & RHD COMPREHENSION RESEARCH
Wingfield, 1992; Weylman, Brownell, Ro-
man, & Gardner, 1989); when initial assump- The familiar list of comprehension diffi-
tions must be revised to make sense of dis- culties, presented in the opening of this ar-
course units (Brownell, Potter, Birhle, & ticle, has been compiled primarily on the
Gardner, 1986; Frederiksen & Stemmer, 1993; basis of research that has two key method-
Tompkins & Mateer, 1985); and with literally ologic characteristics. First, it employs
false material like jokes and indirect requests, metalinguistic comprehension measures,
where alternative meanings must be reconciled which require respondents to reflect on or
with other contextual cues (Hirst, LeDoux, & make judgments about how they interpret the
Stein, 1984; Molloy et al., 1990). stimuli in question. Performance on such
Various hypotheses have been advanced tasks may not capture a patient s ability in
to account for such problems, and some of naturalistic contexts, when he or she actually
these accounts will be considered later in this encounters the same stimuli in naturalistic
article. For a number of years, however, the situations. For example, Lemieux, Goulet,
authors have conducted a research program and Joanette (1993) reported that RHD
that has raised questions about the nature and adults had no difficulty interpreting indirect
generality of RHD patients deficiencies speech acts in a natural therapy setting. Simi-
with interpreting communicative intents. larly, Tompkins (1995) describes a group of
This article describes two hypotheses that RHD patients who initiated various ques-
have guided the authors work and presents tions and conversational topics to greet a
results and implications of the research to newcomer but faltered in the same session
date. In early investigations, the authors as- when asked to describe how they would
Interpreting Intended Meanings after Right Hemisphere Brain Damage 31
strike up a conversation with someone they numerous cognitive operations that occur on
did not know. The second feature of most the way to a final interpretation or response,
assessments is that they are applied off- thus obscuring areas of strength and weak-
line, or after stimulus processing has taken ness during language processing. As a result,
place. Off-line measures also require varying information gained from off-line measures
degrees of stimulus awareness and associa- may misrepresent respondents underlying
tion. Tasks that reflect these two characteris- capacities and deficits (see Tompkins &
tics include the activities that make up pub- Baumgaertner, 1998). By contrast, on-line
lished tests and informal evaluations for techniques are implemented close in time to
RHD adults, such as matching metaphors the cognitive operations under study and thus
and pictures, explaining idioms and other can be used to track dynamic aspects of
figurative language forms, or answering in- language comprehension as it occurs. On-
ferential questions about narrative passages. line assessment methods also are intended to
Despite their widespread application, tap language functioning fairly implicitly,
these methodologic characteristics limit un- reducing demands for metalinguistic analy-
derstanding of RHD patients communica- sis and decision. Such measures include vari-
tive strengths and weaknesses. To add to the ous kinds of word monitoring and priming
caveats above, the mental effort and con- tasks (described below; see Kempler, Almor,
scious awareness of stimulus properties that & McDonald, 1998; Shapiro, Swinney, &
are required by these kinds of tasks render Borsky, 1998; Tompkins & Baumgaertner,
them inappropriate for assessing the rela- 1998, for further discussion of these tasks
tively automatic operations that are integral and of the clinical value of on-line measures
to language processing and other aspects of of language comprehension).
cognitive functioning. Automatic processes On-line measures have revealed facets of
call up or activate stored knowledge that normal language processing that are unex-
helps to direct routine actions and to access pected and sometimes counterintuitive. For
habitual interpretations, without intention example, on-line studies have demonstrated
and without a significant demand on the that multiple senses of balanced lexical am-
mental capacity available to devote to other biguities, or words with two relatively
processing. Accessing familiar words is a equiprobable meanings (e.g., bat), are auto-
good example of an automatic process. matically activated and available for a brief
Comprehenders do not have to decide to period of time to normal comprehenders.
activate or search for the meaning of a famil- This is true regardless of how strongly the
iar word like girl, nor can they stop its mean- surrounding context points to a single inter-
ing from becoming activated and available pretation (Swinney, 1979; see Simpson &
for further processing and interpretation. Burgess, 1988, for review). The results of
Tyler (1992) suggests that unconscious men- this automatic activation are opaque to con-
tal representations and operations form the scious reflection. That is, if questioned about
core of the language comprehension system; their interpretation of an ambiguous word
automatic processing is a subset of this core. like bat, comprehenders are not aware that
Another restriction of off-line measures is they have activated momentarily a meaning
that they capture only the end products of the that is inappropriate or irrelevant to the given
32 TOPICS IN STROKE REHABILITATION/SPRING 1998
context. Again, this makes metalinguistic Drawing on theories and methods from cog-
tasks a poor choice for assessing the nature of nitive psychology, the authors have investi-
stored knowledge and unconscious process- gated some attentional and memory mecha-
ing operations. nisms that they reasoned might be associated
Given these caveats about the assessment with various communicative symptoms, in
methods that typically are used with RHD conditions designed to vary processing de-
adults, the authors have tried to evaluate mands. In particular, these methods have
these patients comprehension performance allowed them to draw inferences about the
under conditions of reduced cognitive effort integrity of stored knowledge and initial ac-
and conscious reflection. They have applied tivation of intended meanings, either of
methods from cognitive psychology and which may be implicated erroneously when
psycholinguistics to assess distinctions be- RHD patients have difficulties with
tween relatively automatic meaning activa- metacognitive tasks. In general, this line of
tion and more effortful mental processing. In research has identified preserved abilities in
addition, in some cases, they have adminis- metaphoric, emotional, prosodic, and infer-
tered these tasks on-line, or close in time to ential domains that typically are considered
the mental representations or processes of in- problematic for RHD adults and has uncov-
terest. Using such methods with stimulus ma- ered conditions under which these patients
terials from many of the domains commonly represent alternative meanings, make pre-
reported to cause comprehension difficulty for dictions from context, integrate information,
RHD adults, the research has both extended and revise interpretations successfully in
and modified the conventional wisdom sum- these domains.
marized above regarding interpretation of An early study (Tompkins, 1990) evalu-
communicative intents. The next section of this ated RHD adults knowledge and processing
article will tell more precisely how. of ambiguous adjectives that can convey
either metaphoric or literal meanings. In
COGNITIVE PROCESSING prior work by another research group, using
INFLUENCES ON a semantic similarity judgment task, RHD
COMPREHENSION OF INTENDED adults primarily grouped such words (e.g.,
MEANINGS deep) with literal associates (shallow) rather
than figurative associates (wise), while nor-
The authors approach to understanding mal control subjects grouped flexibly
the nature and generality of RHD patients (Brownell, Potter, Michelow, & Gardner,
deficits with intended meanings has involved 1984). Synthesizing their results with other
evaluating cognitive mechanisms that may findings, these authors speculated that
underlie, predict, and relate some of the com- knowledge of connotative aspects of lan-
municative symptoms observed in RHD guage might be lost to RHD adults but cau-
adults. As noted above, much of the work tioned, appropriately, that their task was not
done by other researchers has used designed to address that issue. The present
metacognitive, off-line tasks and methods authors addressed the issue using a within-
that entail relatively high processing require- subject, auditory priming study. In a standard
ments and generate end-product responses. priming paradigm, related or unrelated mate-
Interpreting Intended Meanings after Right Hemisphere Brain Damage 33
rial is presented before a target stimulus to Prime-target pairs were presented under
influence the response to that target. As an several conditions. One was designed to tap
example, for the target word nurse, a related relatively automatic meaning activation.
prime might be doctor, and an unrelated Two other conditions were developed to as-
prime might be bread. Primes activate their sess more effortful mental processing, either
own lexical-semantic representations, and when guided and constrained by the exam-
that activation spreads rapidly to conceptual iner or when the expectations provided by the
entries of closely associated items. Thus, examiner were violated without warning,
related primes activate and make mentally necessitating some adaptation to maintain
available the target concept, speeding re- success. RHD patients performed similarly
sponse times for that target. The present to those that had left hemisphere damage
authors reasoned that, if patients with RHD (LHD) and normal control subjects in the
have lost their knowledge of figurative ele- automatic condition; for all groups, response
ments of word meaning, then words related times to critical target words were faster in
to the metaphoric interpretations of ambigu- both types of related prime trials than in
ous adjectives should not generate this neutral or unrelated prime trials. All groups
priming effect. again performed similarly when the exam-
Critical target stimuli in the authors study iner provided pretask orientation, specific
were ambiguous adjectives (e.g., sharp) that instructions, and practice to guide their
were preceded by one of several kinds of effortful processing of metaphoric words.
primes. Two were related words, one a literal However, when it was left for subjects to
associate (dull), and one a metaphoric asso- notice the violation of expectations, and/or to
ciate (smart). The word next was used as a glean a strategy to cope with it, both groups
neutral prime, as it did not provide any basis of brain-damaged patients were impaired
for predicting the target word. One unrelated relative to control subjects.
prime was included as well, represented by a This study documented that RHD pa-
word that pointed away from the meaning of tients deficits in this nonliteral domain may
the ambiguous adjective in question (e.g., have more to do with strategic processing
warm). The subject s task was to listen to the abilities than with knowledge loss. Based on
prime-target pairs and make lexical deci- the distinction between the results in the first
sions about the second item, indicating as two, relatively less effortful conditions and
quickly as possible whether the target pho- those obtained with more effortful tasks, the
neme string was a real word. The lexical authors interpreted these findings in a cogni-
decision task allows an implicit measure of tive processing framework. That is, RHD
the subject s stored knowledge and initial adults typical deficits emerge as demands
activation of metaphoric word meanings. for mental resources (e.g., attention, working
That is, if target lexical decisions are speeded
by metaphoric associates, it can be inferred
that subjects had access to metaphoric inter- RHD adults typical deficits emerge
pretations and activated the figurative sense as demands for mental resources (e.g.,
of an ambiguous adjective when presented attention, working memory) increase.
with the metaphorically related prime.
34 TOPICS IN STROKE REHABILITATION/SPRING 1998
memory) increase. To account for the differ- revision also was required for the neutral
ence in performance between the two aspects prime-emotional target combinations, and
of the effortful processing task, the authors performance in this condition did not distin-
postulated that examiner-provided guidance guish RHD from control subjects. The au-
and constraint reduced one source of demand thors melded two lines of evidence from the
on the brain-damaged subjects attentional res- emotion literature to suggest that a greater
ervoirs, allowing them to perform successfully processing load might be involved in revis-
when appropriately guided, but that they did ing expectations based on incongruent
not have sufficient cognitive resources left over primes than when amending predictions
for incidental aspects of the task, such as notic- based on neutral primes. This analysis led
ing a violation of expectations or forming a them to propose that deficient capacity or
strategy to maintain success. allocation of mental resources could account
A subsequent investigation extended the for RHD subjects disproportionate slowing
theoretical predictions and priming methods in the incongruent prime condition.
of the first to examine the processing of In an extension of the emotional intona-
semantically neutral phrases (e.g., What are tion study (Tompkins, 1991b), the authors
you doing here? ) that communicated in- varied the semantic redundancy of the emo-
tended emotional meanings through vocal tional story primes in the effortful processing
intonation (Tompkins, 1991a). Subjects condition by providing differing numbers of
judged the moods of target phrases from four lexical and phrasal clues to the main
choices. Targets were preceded by story character s mood. Results indicated that in-
primes describing events that were congru- creased semantic redundancy of story primes
ent with the mood conveyed by the intona- enhanced RHD adults mood judgments of
tion of a target phrase, incongruent with both the stories and subsequent target
target mood, or emotionally neutral. Again, phrases. One possible mechanism for this
prime-target pairs were presented in several effect is that redundant messages decrease
conditions, one each designed to induce ei- some pertinent processing demand for the
ther relatively automatic or effortful mental listeners. In another offshoot of the emo-
processing. In the automatic condition, tional intonation study, the authors used the
there were no qualitative differences be- original, nonredundant story primes with
tween RHD, LHD, or control subjects. Con- emotionally ambiguous target stimuli
gruent primes speeded response times for (Tompkins, Spencer, & Boada, 1994). Each
judging target mood relative to either neutral target phrase, presented in isolation, was
or incongruent primes. In the effortful condi- judged to communicate more than one mood,
tion, target response times for each group both across normal older adult subjects and
again were similarly improved by congruent in repeated presentations to the same sub-
primes (relative to neutral primes), but RHD jects. For this study, each ambiguous target
subjects were disproportionately slower than was paired with emotional story primes that
other subjects when making target judg- conveyed any of the possible judgments of
ments for incongruent prime-target pairs. the target stimulus mood. Experimental con-
This performance difference was not due to a ditions were designed to favor relatively au-
revision deficit per se, because inference tomatic processing of these prime-target
Interpreting Intended Meanings after Right Hemisphere Brain Damage 35
pairs. Under these conditions, RHD subjects phrase. In addition, subjects made no errors
again exploited contextual information suc- on the word monitoring task, and there were
cessfully. That is, as often as normal control no group differences in response times, after
subjects did, the RHD patients chose a mood adjusting for simple manual response speed.
for the ambiguous stimulus that matched the By contrast, on the more effortful, off-line
one conveyed by the preceding story prime. task that required subjects to explain the
An investigation of the processing of fa- same idiomatic phrases, clinical subjects
miliar idioms generated similar conclusions performed significantly worse than control
about the influence of processing load and subjects. Interestingly, there were no mean-
the initial activation of stored knowledge of ingful correlations between performances on
nonliteral interpretations (Tompkins, Boada, the on-line and off-line tasks, underscoring
& McGarry, 1992). An off-line task, requir- the earlier observation that performance on
ing explanation of familiar idiomatic one type of measure may not accurately rep-
phrases, was modeled after standard clinical resent, or predict, performance on the other
procedure with brain-damaged adults. An kind of measure.
on-line task required auditory word monitor- Results from these within-subject studies
ing to assess the early, relatively automatic can be interpreted to indicate that RHD
stages of access and processing for these adults retain knowledge of (at least some)
same idioms. Subjects listened to two-sen- intended figurative and emotional meanings.
tence stimuli and pushed a button as quickly In addition, they activate and use that knowl-
as possible when they heard a specified target edge to facilitate performance in conditions
noun. The target nouns of interest were the designed to favor relatively automatic proc-
final words of familiar, dual-meaning idiom- essing or to constrain or limit effortful proc-
atic phrases (e.g., rat in smell a rat ). The essing demands in ways that may reduce the
idiomatic phrases were embedded in two load on cognitive resources (e.g., through
types of sentence contexts. One supported instruction and practice, internally congru-
the usual figurative interpretation of the idi- ent material, semantic redundancy). Another
omatic phrase and the other biased interpre- investigation examined the link between
tation of the phrase to its familiar literal processing demands and performance in a
meaning. In a third condition, the same target between-subjects context. In this study,
noun appeared in a nonidiomatic phrase Tompkins and colleagues (1994) pursued
(e.g., see a rat ), which was embedded in a predictors of RHD patients often-reported
control context that was structurally similar difficulty with revising initial inferences
to the other contexts. Consistent with a num- when faced with ostensibly discrepant infor-
ber of idiom processing models (e.g., mation (e.g., Brownell et al., 1986). It was
Ortony, Schallert, Reynolds, & Antos, 1978; reasoned that, during spoken discourse
Swinney & Cutler, 1979), the initial portion comprehension, working memory (WM)
of the familiar idiomatic phrase was suffi- limitations might impede the updating that is
cient to contact the representation for the necessary to resolve such conflicts. The ex-
entire expression, making the target word in pectation was that patients with lesser WM
that phrase available to all groups more rap- capacity (operationalized as the ability to
idly than the same word in the nonidiomatic process and store information concurrently)
36 TOPICS IN STROKE REHABILITATION/SPRING 1998
would have more difficulty with inference hension in RHD patients have uncovered im-
revisions in demanding conditions that taxed portant influences of cognitive effort or proc-
their processing capacity than would patients essing load, both within and between subjects.
whose WM performance was closer to that of The following observations were made:
normal control subjects. At the same time, 1. RHD adults can use contextual cues to
WM status should not bear any relationship predict, infer, integrate, revise, and
to performance in conditions that did not activate aspects of intended meaning
approach the limits of resource capacity or when processing demands are limited.
availability. 2. RHD patients difficulties with deriv-
To evaluate these hypotheses, the authors ing communicative intent in typical
administered an auditory WM measure de- problem domains (e.g., nonliteral,
signed to tap simultaneous language process- emotional, prosodic, inferential) vary
ing and storage (adapted from Daneman & with the processing demands placed
Carpenter, 1983), and several narrative pas- on their cognitive resources.
sages to assess comprehension. The passages 3. RHD adults inferencing performance
varied in the consistency with which they in conditions of higher processing load
supported a single inference: some incorpo- covaries with the capacity or alloca-
rated an apparent conflict that required an tion of WM for language.
inference revision for its resolution, while Also in line with these observations, prob-
others contained no conflicting information. lems identified by other researchers, such as
Passages also differed in length, and some of those with interpreting discourse units that
the longer passages included redundant clues contain ambiguous or conflicting elements,
to a single inference that later became unten- often are noted in the context of tasks that can
able and had to be revised. Results for the off- be argued to place relatively high demands
line measure, which required patients to an- on patients mental resources. Indeed, the
swer factual and inferential yes/no questions influence of cognitive processing demands is
after hearing each narrative stimulus, con- now frequently acknowledged in writings on
formed to expectations. RHD patients accu- RHD comprehension. For example, much
racy in answering questions about inference recent work notes that RHD patients com-
revisions was substantially related to perfor- prehension performance varies with the
mance on the WM measure but only for the mental effort involved to construct and/or
condition hypothesized to be most repair interpretations (e.g., Brownell &
cognitively demanding (the longer passages Martino, 1998; Leonard, Waters & Caplan,
that contained multiple cues to an original 1997a, 1997b; Stemmer & Joanette, 1998).
inference but ultimately required an inference
revision). Specifically, under circumstances of DEVELOPING AND TESTING A
relatively high processing demand, poor per- SUPPRESSION DEFICIT
formance on the working memory task pre- HYPOTHESIS
dicted poor performance on an off-line index of
inference revision. The authors early work identified circum-
In summary, then, the results of the authors stances in which RHD patients perform well
studies of cognitive processing and compre- in domains that typically are considered to be
Interpreting Intended Meanings after Right Hemisphere Brain Damage 37
problematic for them. More recently, they Although not their original intent, some of
have turned their focus to exploring mecha- the authors early studies suggested that
nisms that could account for the decrements RHD adults activate multiple meanings
that patients exhibit in the same domains, when processing materials that support or
under more effortful processing conditions. induce competing interpretations. This is the
Although prior results suggest a general link case for lexical ambiguities that convey both
between processing resource demands and literal and metaphoric meanings (Tompkins,
discourse comprehension deficits for RHD 1990), familiar dual-meaning idiomatic ex-
adults, this observation lacks precision. Ac- pressions (Tompkins et al., 1992), and emo-
cordingly, the authors set out to evaluate tionally and prosodically ambiguous phrases
several specific, theoretically motivated and passages (Tompkins, 1991a, 1991b;
comprehension mechanisms that they hy- Tompkins et al., 1994). Since multiple mean-
pothesized would predict discourse compre- ing activation makes several readings of a
hension performance after RHD. stimulus available for further processing, the
In particular, given the robust evidence that authors reasoned that RHD patients com-
RHD patients discourse comprehension prob- prehension difficulties for such materials
lems are especially apparent when alternative may be due in part to problems with sup-
or competing meanings must be considered pressing interpretations that are initially acti-
and resolved, the authors chose to examine the vated and represented but eventually are ir-
suppression mechanism that is a central feature relevant or incompatible. Thus, they
of Gernsbacher s (1990) Structure Building formulated a suppression deficit hypoth-
Framework of comprehension. The suppres- esis, predicting that the suppression mecha-
sion mechanism serves to inhibit activated nism (Gernsbacher, 1990) would operate
information that becomes inappropriate or ir- less effectively in adults with RHD than in
relevant to a final interpretation. For example, normally aging persons and that suppression
in a sentence that contains a balanced lexical function after RHD would correlate with
ambiguity, like He dug with a spade, the discourse comprehension.
playing card interpretation of the ambiguity, Currently, the authors are completing two
which is activated momentarily by normal investigations of the relationship between
comprehenders despite the given context (e.g., suppression and discourse comprehension in
Swinney, 1979; Onifer & Swinney, 1981), is RHD adults. In these studies, subjects listen
quickly dampened by the suppression mecha- to single sentences or short narratives built
nism. In a series of experiments with young around lexical or inferential ambiguities.
normal adults, Gernsbacher and colleagues Their task is to judge whether a subsequent,
(Gernsbacher & Faust, 1991; Gernsbacher, auditorily presented probe word fits with the
Varner, & Faust, 1990) have tied suppression contextually appropriate meaning of the ex-
function to comprehension skill: poorer perimental stimulus. To assess suppression
comprehenders do not suppress inappropri- function, probes are presented that reflect a
ate information as quickly as more skilled plausible interpretation of the ambiguity but
comprehenders across tasks, modalities, or that are incompatible with the meaning con-
domains (auditory and visual, linguistic and veyed by the entire context. Thus, an accu-
nonlinguistic). rate response requires rejecting that probe
38 TOPICS IN STROKE REHABILITATION/SPRING 1998
word, since it does not reflect the intended a dominant or preferred meaning (e.g., Sally
overall interpretation of the stimulus. Imme- was a tourist) and a less likely alternative
diate and delayed probes allow assessment of (e.g., she was a realtor). The second sentence
what elements of meaning are activated and reinforces the alternate interpretation, lead-
maintained as stimuli are processed. ing to inference revision (e.g., If she sold it,
Results to date, gleaned from tasks assess- her bonus would be especially large ). A
ing lexical and inferential ambiguity proc- preexperimental task, in which subjects
essing, are consistent with the suppression judge probe words that are related to both
deficit hypothesis. For experimental sen- meanings of the isolated, inferentially am-
tences containing lexical ambiguities, such biguous sentences, has verified the infer-
as, He dug with the spade, RHD patients ential ambiguity and preferred meanings of
suppress contextually inappropriate inter- the first sentences and indicates that both
pretations less well than normally aging con- interpretations are rapidly available to RHD
trol subjects (Tompkins, Baumgaertner, and normal older adult control subjects. Pre-
Lehman, & Fossett, 1997). Both groups evi- liminary results for the suppression task
dence activation of both meanings at the show that neither RHD nor normally aging
immediate probe. However, 1,000 ms after adults show much evidence of suppressing
the ambiguous word, RHD subjects are dis- the eventually inappropriate interpretations
proportionately slow to reject probe words (e.g., probe word tourist) in the probe inter-
that are related to the inappropriate meanings vals used in this study. Thus, both groups
of the lexical ambiguities (e.g., cards), rela- experience interference from initially domi-
tive to the speed with which they reject the nant interpretations of the ambiguous sen-
same probe words after hearing sentences that tences. In retrospect, this outcome is not
contain an unambiguous word in the final entirely surprising, given recent evidence
position (e.g., He dug with the shovel ). RHD that normal older adults have difficulty in-
patients suppression function also correlates hibiting meaning-bearing information
with a standardized measure of general dis- (Connelly & Hasher, 1993; Kane, Hasher,
course comprehension skill (the Discourse Stoltzfus, Zacks, & Connelly, 1994; Shaw,
Comprehension Test, Brookshire & Nicholas, 1991). However, suppression effectiveness
1993), but in the present authors preliminary is correlated with discourse comprehension
analyses, suppression effectiveness is not only for the RHD group (r = .60) and only
associated with measures of neglect, vocabu- for comprehension questions that require re-
lary knowledge, or estimated premorbid in- jecting initially dominant inferences
telligence quotient. (Tompkins et al., 1996). As in the authors
The methods and predictions of the lexical prior work (Tompkins et al., 1994), they
ambiguity study were extended to an investi- hypothesized that this result reflects the de-
gation of inferential ambiguity processing. mands of the inference revisions on RHD
In this study (Tompkins, Lehman, Baum- subjects WM capacity.
gaertner, Fossett, & Vance, 1996), subjects At first glance, results showing that RHD
hear two-sentence stimuli modeled after patients activate multiple interpretations and
those of Brownell and colleagues (1986). An retain them too long may appear to be incon-
ambiguous first sentence (e.g., Sally ad- sistent with other proposals about hemi-
mired the historic farmhouse ) imparts both spheric processing of ambiguous language
Interpreting Intended Meanings after Right Hemisphere Brain Damage 39
stimuli (e.g., Beeman, 1993; Burgess & vation (Beeman, 1993, is the exception; see
Simpson, 1988; Chiarello, 1988). Based on next section).
data suggesting that the normal right hemi- A focus on suppression is intriguing given
sphere takes a dominant role in maintaining evidence that neurotransmitter systems im-
subordinate meaning activation over time portant for filtering irrelevant stimuli are
while the normal left hemisphere quickly more concentrated in the right hemisphere
selects a context-appropriate meaning (Bur- and more disrupted by RHD than by LHD
gess & Simpson, 1988), several authors sug- (Tucker & Williamson, 1984). Although the
gest that adults with RHD should be unable to authors have in the past invoked a processing
activate and/or maintain alternative mean- resource perspective to interpret extant data
ings (e.g., Beeman, 1993, 1998; Chiarello, and test new hypotheses, some of their find-
1988, 1998; Molloy et al., 1990). In reconcil- ings also are compatible with a suppression
ing their findings with those generated from perspective. For example, in the emotional
studies with normal subjects, the authors intonation study (Tompkins, 1991a), incon-
have presented a variety of evidence and gruent primes strongly invited a single inter-
arguments against this apparently logical, pretation that had to be inhibited to make
but not necessarily valid, conclusion target judgments; ineffective suppression
(Tompkins et al., 1997). For example, it may could account for RHD subjects dispropor-
be more complicated to generalize results tionately longer RTs in the incongruent
from normal brains to damaged brains than prime condition. Also, in the idiom study
such a conclusion suggests. Further, it is (Tompkins et al., 1992), 80% of RHD sub-
unlikely that a single lesion in one hemi- jects idiom explanation errors were related
sphere totally eradicates its processing sub- to the phrases figurative meanings. This
strates. Also, brain damage can bring about result could indicate that RHD subjects had
an exaggeration of function through impair- difficulty dampening activation of associ-
ment of inhibitory circuitry, rather than a loss ated but irrelevant aspects of meaning. Fur-
of function. Damage to one hemisphere also ther, the suppression deficit hypothesis has
might interfere with utilizing input from the broad appeal because ineffective suppres-
other hemisphere that is crucial to an inte- sion could underlie a variety of other obser-
grated interpretation or response. Thus, the vations about RHD adults performance in
authors results are not inconsistent with the expressive, receptive, and metalinguistic
position, and some direct evidence (Faust & tasks (see the box for examples, and see
Gernsbacher, 1996), that left hemisphere further analysis in the next section).
functions might take precedence in suppress-
ing unintended interpretations. However, CONSIDERING THE SUPPRESSION
rather than alternative interpretations not DEFICIT HYPOTHESIS IN LIGHT OF
being activated after RHD, they may in fact OTHER POSITIONS ON RHD
be activated and take more time or greater COMPREHENSION PROBLEMS
mental effort to suppress. Finally, as noted
earlier, most of the evidence documenting The following summarizes what the au-
RHD adults difficulties with multiple mean- thors deem at present to be the primary pro-
ings comes from off-line studies and, as such, posals offered by others to account for RHD
cannot address the question of meaning acti- patients typical comprehension difficulties
40 TOPICS IN STROKE REHABILITATION/SPRING 1998
Some Data and Observations Consistent with a Suppression Deficit Hypothesis
" RHD patients tend to pursue incorrect asso- " They have difficulty appreciating connota-
ciations in continuations of structured conver- tive meanings of ambiguous words in
sations (Rehak et al., 1992) as well as in metalinguistic tasks (Schmitzer, Strauss &
comprehension tasks (Brownell et al., 1986). DeMarco, 1997), which could be due to
" They have difficulty rejecting plausible but difficulty overcoming the stronger activa-
false statements or inferences that are not tion of the denotative interpretations
part of presented narrative stimuli (Joanette (Tompkins, 1990).
& Goulet, 1987; Schneiderman, Murasugi, " On an unconstrained word fluency task,
& Saddy, 1992). RHD adults generate items that are less
" When describing scenes, RHD adults pro- prototypical than control subjects produc-
duce more inaccurate inferences than tions (Leblanc & Joanette, 1996), possibly
non brain-damaged subjects, especially for reflecting a difficulty suppressing the acti-
inferentially complex scenes (Myers & vation of distantly related items.
Brookshire, 1994), consistent with the pos- " Some RHD patients connected speech is
sibility that inaccurate inferences are not embellished, tangential, and excessively
suppressed effectively. detailed (Joanette et al., 1990; Myers, 1991;
" They evidence problems in linking dispar- Wapner, Hamby, & Gardner, 1981), sug-
ate mental models or representations at the gesting that related but irrelevant informa-
discourse level (Frederiksen & Stemmer, tion is not being dampened.
1993; Stemmer et al., 1994; Stemmer & " Even in the linguistic domain, an area of
Joanette, 1998). relative strength, RHD adults have prob-
" They make intrusion errors in descriptions lems with tasks that require reassigning the
based on common scripts (Roman, Brownell, syntactic status of elements contained in a
Potter & Seibold, 1987) and require more single stimulus (Schneiderman & Saddy,
prompting to complete script continuations, 1988), highlighting what may be a general
in some cases being diverted from the topic or difficulty with shifting from one interpreta-
task by their own intrusions. tion to another.
(see Tompkins, 1995, for several additional will have to be developed. But in the mean-
possibilities). They also consider how their time, the proposals can provide some guid-
data and hypotheses intersect with these ac- ance to clinicians as they attempt to docu-
counts. Most likely because the study of ment patients strengths and weaknesses and
RHD communication problems is still in its to generate treatments that capitalize on this
infancy, none of these proposals in their analysis.
current forms provides adequate accounts of
RHD comprehension difficulties. All must
be more rigorously specified to make predic- Inference failure refers to faulty
inferencing rather than absence of
tions that can be tested and falsified. Further,
it would be surprising if any single explana- inferencing.
tion would suffice; an integrated framework
Interpreting Intended Meanings after Right Hemisphere Brain Damage 41
Inference Failure become inappropriate to a final, integrated
interpretation.
Myers (1991) coined the term inference
failure as a general hypothesis about the Integration Deficits
nature of deficits in RHD patients. Inference
failure refers to faulty inferencing rather than The term integration deficits refers to dif-
absence of inferencing. Myers proposes that ficulties with incorporating distinct elements
it can occur at all levels of cognitive and into a larger, meaningful unit. Integration
perceptual processing and recounts numer- deficits have been invoked by many to de-
ous symptoms that could be manifestations scribe RHD patients impaired performances
of inference failure. To Myers, inference at both perceptual and discourse levels.
appears dependent upon an ability to iden- However, the term often has been used rather
tify available cues, integrate them with one globally and applied in a post hoc fashion
another and with other sensory input, and (Tompkins, 1995). As with the inference
form relationships that specify meaning be- failure hypothesis, ascribing a symptom to an
yond the sensory data (p. 178). However, as integration deficit may not be very helpful in
Tompkins (1995) notes, there are many ways determining how and why performance
in which this chain of events and operations breaks down. However, some investigators
could break down, and other impairments (e.g., Brownell et al., 1992, 1997; Stemmer et
could masquerade as inference failures. In al., 1994) have tried to specify and evaluate
addition, the inference failure position is more precisely various factors that contrib-
hard to reconcile with research showing that ute to integration deficits. Suppression defi-
adults with RHD can generate a variety of cits might be one such factor. Evidence from
inferences, particularly in conditions that in the aforementioned studies and others (e.g.,
some ways restrict cognitive demands (see Frederiksen & Stemmer, 1993; Rehak et al.,
above; also Brownell & Martino, 1998; 1992) indicates that, like inference problems,
Stemmer & Joanette, 1998; Tompkins, RHD patients integration deficits are espe-
1995). Myers alludes to the role of mental cially apparent when the stimulus context
effort in inferencing, suggesting that a provides multiple, sometimes disparate cues
patient s effort to perceive may use up re- to meaning or induces conflicting interpreta-
sources that would be needed for ascertain- tions. For example, Frederiksen and
ing relationships, but she does not pursue this Stemmer (1993) note that their RHD patient
possibility further. If cognitively demanding had particular difficulty reconceptualizing
conditions lead to inference failures, the an original interpretation to reconcile seem-
original hypothesis may need to be modified. ing discrepancies (see also Stemmer &
It also is not clear how the original hypothesis Joanette, 1998). Brownell and Martino
would accommodate results of studies on (1998) also highlight difficulties with revis-
inference revision (e.g., Brownell et al., ing mental models as one key component of
1986). For example, the preliminary data RHD patients difficulties with generating
from a suppression study (Tompkins et al., integrated interpretations from discourse.
1996) suggest that RHD patients do generate Hence, it seems likely that a suppression
inferences and hold on too long to those that deficit, reflecting a problem with dampening
42 TOPICS IN STROKE REHABILITATION/SPRING 1998
the activation of an eventually inappropriate line, cross-modal lexical decision data. Sub-
interpretation, could contribute to this kind jects made lexical decisions to visual stimuli
of integration problem. while listening to passages that were de-
signed to induce coherence inferences. In
Two Proposals That Highlight this task, RHD adults did not show a priming
Particular Inference Deficits effect for lexical decisions to inference-re-
lated target words compared to unrelated
Brownell and Martino (1998) note that target words. Although Beeman used an on-
inferences are necessary to integrate indi- line measure to tap inference-related proc-
vidual parts of a discourse unit and to gener- esses, it is possible that the task demands in
ate a coherent interpretation. Summarizing his study diminished or obscured evidence of
evidence from their research program (e.g., the semantic activation that is associated
studies of inferences supporting comprehen- with inferencing. Suggestive in this regard
sion of gist, especially when subsequent text was the control group s performance in an
entails a reinterpretation, and investigations episode shift condition. In that condition,
of inferences involving affective state, two sentences critical to inducing the target
knowledge state, and causal attribution), inference were separated by a new episode
these authors propose two main sources of cue that elicited a shift to a new comprehen-
RHD discourse comprehension deficits. The sion substructure. This condition was quite
first involves difficulties with self-di- anomalous in that the new substructures
rected inferencing (p. 325). Self-directed were not fulfilled; subsequent portions of the
inferences are invoked in the absence of stimuli returned to the original structure or
overlearned syntactic and discourse rules, theme. Inspection of the data for this episode
when the text alone does not provide suffi- shift condition suggests that Beeman s older
cient guidance as to how all of its elements fit adult control subjects did not show the infer-
together. In such cases, comprehenders cre- ence-related priming effect that one would
ate and elaborate their own mental structures. expect if the test paradigm captured auto-
However, the stimulus materials that elicit matic semantic activation. Tompkins and
such difficulties contain competing frames colleagues (1994) also note that RHD pa-
of reference or multiple cues to alternate or tients performance may have been influ-
competing possible interpretations. Thus, enced by requirements to coordinate concur-
again, suppression deficits could be a com- rent, cognitively demanding activities
ponent of such problems. Decreased social during this on-line task. It is possible as well
cognition and empathy, Brownell and that ineffective suppression could influence
Martino s second proposed origin of RHD RHD subjects performance on a task like
discourse comprehension problems, is con- Beeman s. The stimuli may have generated
sidered below. semantic activation germane to several infer-
In a study of coherence inferencing in ences: (1) each vignette targeted two infer-
discourse, Beeman (1993) concluded that ences that did not cohere too well into a single
RHD adults fail to activate the semantic story; (2) premise sentences preceding each
information that supports such inferences. inference-inducing sentence were at times
The most pertinent evidence comes from on- ambiguous; and (3) pilot testing showed the
Interpreting Intended Meanings after Right Hemisphere Brain Damage 43
inference-inducing sentences, in isolation, to deficits appear in addition to have a more
set up unintended inferences. purely social basis; that is, RHD patients
seem to lack empathy and to find other
Deficits in Social Cognition
people less salient or interesting. This in-
The second key component of RHD pa- triguing possibility awaits more evidence.
tients discourse problems, according to Because much of Brownell and Martino s
Brownell and Martino (1998), is related to evidence comes from metacognitive expla-
deficits in reasoning from a theory of mind. nation tasks, it is not clear how well their
Theory of mind involves the ability to con- results would reflect patients performance
ceptualize other people s feelings, knowl- in more natural situations. In addition, it is
edge, beliefs, and the like, and to use that possible that at least part of the difference
conceptualization to interpret, predict, and between RHD patients and control subjects
evaluate the behavior of others. By defini- stems from the latter group s superiority at
tion, then, comprehending based on a theory guessing, or greater concern about, what the
of mind requires simultaneous consideration expected response would be, even if it was
of different sources of information, some of not consistent with what they would do. This
which may be conflicting. Brownell and possibility is similar to one raised by Joanette
Martino describe evidence suggesting that and colleagues (1990) in their discussion of
RHD patients have difficulty assuming an- the pragmatic attitude that is required of a
other person s point of view in terms of good subject.
beliefs about the world, or about a third
Predictions from Studies of Normal
person s knowledge. They emphasize both
Hemispheric Specialization or
processing factors and constructs related to
Processing Preferences
suppression in their statement that reason-
ing on the basis of a theory of mind tends to An earlier section of this article alluded to
be less constrained than other forms of rea- some apparent conflicts between data from
soning and requires shifting, or revising, per- the authors suppression studies and prob-
spective from one s own point of view to that lems that are hypothesized on the basis of
of someone else (p. 324). Stemmer and normal hemisphere functioning. The litera-
Joanette (1998) similarly note that difficulty ture is replete with both explicit and implicit
with theory of mind inferences could reflect statements that once adults sustain RHD,
an impairment of reconciling one s own con- unopposed left hemisphere processing
ceptual model of the world with that of an- (Chiarello, 1998) dictates their performance.
other person. As a logical extension, one As indicated earlier, this notion is not entirely
might propose that a suppression deficit consistent with extant data. As another ex-
could contribute to broad difficulties in dis- ample, consider several other findings from
carding one s own point of view or to more visual hemifield priming studies with normal
specific problems with inhibiting competing adults (see, e.g., Chiarello, 1998). In addition
activation from multiple sources of informa- to the data cited earlier, suggesting that sub-
tion. Brownell and Martino anticipate some ordinate meanings are activated only in the
of these kinds of interpretations for their data right hemisphere and that this activation is
and argue that RHD patients interpersonal maintained over a relatively long period of
44 TOPICS IN STROKE REHABILITATION/SPRING 1998
time, there is consistent evidence that weakly the authors think a suppression deficit tells
related words also are activated only in the the whole story; far from it. At present, all
right hemisphere (Chiarello, Burgess, that can be suggested is that it may be an
Richards & Pollock, 1990), and dominant important piece of the puzzle. As well, there
meanings or strongly associated words are are several major issues regarding the sup-
primed in both the left and right hemispheres pression construct that are currently unre-
(Burgess & Simpson, 1988; Chiarello, 1985; solved. First, it is not evident how distinct
Chiarello et al., 1990; Richards & Chiarello, this suppression mechanism is from broader
1995). Further, equal priming of high- and constructs, such as selective attention.
low-typicality category exemplars is found Second, it is not clear whether a suppression
in the right hemisphere, but asymmetric deficit of the sort described here, and docu-
priming, favoring highly typical items, is the mented thus far at only a few fairly restricted
rule in the left hemisphere (Chiarello & linguistic levels, would act generally across
Richards, 1992). Applying the assumption the broader conceptual domains that encom-
that the left hemisphere directs performance pass, for example, operations invoked to re-
after RHD, one would expect RHD subjects vise mental models or to reason from a theory
to generate only typical or highly frequent of mind. In the original theoretical formula-
items in a word fluency task. However, this tion, Gernsbacher (1990; Gernsbacher et al.,
prediction does not fit with data demonstrat- 1990; Gernsbacher & Faust, 1991) charac-
ing that, while producing fewer words over- terizes suppression as a general mechanism:
all in an unconstrained oral naming task, one that is central to both nonlinguistic and
RHD subjects generated a lower proportion linguistic processing and that functions
of prototypical items and a higher proportion across language levels and modalities. How-
of atypical items than non brain-damaged ever, the generality of the construct, the gen-
controls (Leblanc & Joanette, 1996). On a erality of suppression deficits after RHD, and
semantic fluency task, RHD adults clusters their predictive power for RHD comprehen-
of related items consisted of a greater number sion function remain to be determined.
of less-prototypical items than did the clus-
ters of left brain-damaged subjects CLINICAL IMPLICATIONS
(Grossman, 1981). It appears that caution is
warranted in generating predictions about There are several broad clinical implica-
patients performance from studies of nor- tions of the research summarized above. The
mal hemispheric function. performance variations that can be achieved
by manipulating task processing demands,
Some Caveats Related to the
particularly in light of patients individual
Suppression Deficit Hypothesis
processing capacities, have immediate rel-
The preceding analysis noted a number of evance for clinical management. Tompkins
possible points of intersection between the (1995) discusses a variety of processing fac-
suppression deficit hypothesis and other in- tors that one might modify in treatment,
vestigators proposals about the nature of whether the overall rehabilitation approach
RHD discourse comprehension impair- centers on facilitation or compensation. The
ments. This does not imply in any way that suppression deficit hypothesis also has gen-
Interpreting Intended Meanings after Right Hemisphere Brain Damage 45
eral clinical relevance. Findings like those meaning stimuli and that they can activate
summarized above, when replicated and ex- this knowledge base. Indeed, rather than fail-
tended, should contribute to formulating ing to generate multiple meanings or infer-
plausible accounts of the nature of RHD ences, their recent work suggests that contex-
adults communicative strengths and weak- tually inappropriate meanings may stay
nesses. Thus, they should assist in determin- active too long for RHD patients. This un-
ing what to assess, how to assess it, and what wanted activation may interfere with their
to treat. Also, the results provide a principled ability to select an interpretation that is ap-
foundation for the development and applica- propriate to a given context. Thus, perhaps
tion of treatment techniques. For example, it professionals should not have these patients
is common to work with RHD adults on work on generating or providing alternate
identifying relevant and irrelevant informa- meanings for stimuli. Perhaps, instead, pro-
tion and discounting that which is less appro- fessionals should assess and treat their ability
priate. If professionals can identify suppres- to determine the contextual relevance or ap-
sion deficits in individual patients, and these propriateness of alternative meanings that
deficits limit comprehension, it should be professionals furnish to them. Tompkins and
possible in the future to predict and test who Baumgaertner (1998) provide some concrete
might be appropriate candidates for such a suggestions for targeting this goal.
treatment approach. More specific clinical
implications also emerge from these data and
hypotheses. Consider the frequent difficul- In sum, this theoretically oriented research
ties of patients with RHD in interpreting program has generated findings that have
material that can convey multiple or alternate broad clinical relevance. Task processing
meanings. These difficulties often are as- considerations generally play a central role
sessed and treated with tasks like generating in communication assessment and treatment
or explaining more than one meaning for for adults with RHD, while the suppression
stimuli that, in the absence of context, could framework provides a perspective for ana-
be interpreted in more than one way. How- lyzing discourse comprehension impair-
ever, the authors studies suggest that RHD ments in these patients and for organizing the
patients have not lost their knowledge of clinical decision-making process related to
figurative language and other multiple- such problems.
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