Content uploaded by Lisa Tabor Connor
Author content
All content in this area was uploaded by Lisa Tabor Connor
Content may be subject to copyright.
Inhibition and auditory comprehension in
Wernicke's aphasia
Debra A. Wiener
Boston University School of Medicine, Boston, MA, USA
Lisa Tabor Connor
Washington University School of Medicine, St. Louis, MO, USA
Loraine K. Obler
Boston University School of Medicine, Boston, and City University of New York Graduate
School and University Center, NY, USA
Background: While research findings support the presence of inefficiencies in allocation of
attention in individuals with aphasia, the cognitive mechanisms behind these inefficiencies
remain unclear. One mechanism that would affect resource allocation for selective pro-
cessing is an impaired inhibitory mechanism which, when normally functioning, would
actively suppress distracting information.
Aims: The purpose of this study was to investigate the cognitive process of inhibition, at the
lexical-semantic level of language processing, and its relation to auditory comprehension in
Wernicke's aphasia.
Methods & Procedures: The classic Stroop Colour-Word Test was adapted to be applicable
for use with an aphasic population. We administered this computerised manual-response,
numerical version of the Stroop test to five individuals with Wernicke's aphasia and twelve
age- and education-matched non-brain-injured controls. Correlations with Stroop inter-
ference examined associations with auditory comprehension as measured by the Token Test
and the Complex Ideational Material subtest of the Boston Diagnostic Aphasia Examination.
Outcomes & Results: Analysis of the Stroop reaction time and error percentage data indi-
cated that the interference effect was significantly larger for the participants with Wernicke's
aphasia than for the controls, without an accompanying increase in facilitation, reflecting an
impairment of inhibition in Wernicke's aphasia. In addition, the magnitude of Stroop
interference was significantly positively correlated with the clinical-behavioural symptom of
severity of auditory comprehension deficits as measured by the Token Test.
Conclusions: Findings support an impairment in inhibition at the lexical-semantic level of
language processing in Wernicke's aphasia, reflecting the inability to effectively ignore
the automatically evoked, distracting stimulus. The significant correlation between the
Stroop interference effect and the severity of auditory comprehension deficits suggests
that at least part of the attentional difficulties contributing to the striking reductions in
auditory comprehension in this population can be attributed to impaired inhibition. Our
#2004 Psychology Press Ltd
http://www.tandf.co.uk/journals/pp/02687038.html DOI: 10.1080/02687030444000228
Address correspondence to: Dr Debra Wiener, Harold Goodglass Aphasia Research Center, VA Medical
Center (12A), 150 S. Huntington Avenue, Boston, MA 02130, USA. Email: WienerDobn@aol.com
This study was performed as part of a dissertation by the first author in partial fulfilment of the requirements
for a PhD in Speech and Hearing Sciences at the City University of New York Graduate School and University
Center. We thank Dr Errol Baker and Dr Avron Spiro III for their statistical guidance. This project was
supported in part by the National Institutes of Health (NIDCD) and by the Medical Research Service of the
Department of Veterans Affairs.
APHASIOLOGY, 2004, 18 (5/6/7), 599±609
findings expand upon our understanding of resource allocation in aphasia and reinforce
our need to clinically assess and treat reductions in attention for maximised rehabilitation
outcome.
Increasingly, aphasiologists have been focusing on the role that attention plays in diffi-
culties with auditory processing. While research findings support the presence of inef-
ficient attention allocation in individuals with aphasia (e.g., McNeil, Odell, & Tseng,
1991; Murray, Holland, & Beeson, 1997; Tseng, McNeil, & Milenkovic, 1993), the
cognitive mechanisms underlying these inefficiencies remain unclear. In theorising on the
role of attentional control of language functions, McNeil et al. considered the interplay of
controlled and automatic processing. One mechanism that would reduce the allocation of
resources necessary for selective processing is an impaired inhibitory mechanism which,
when normally functioning, would serve to limit the generation and maintenance of
irrelevant information. The purpose of the present study was to investigate the cognitive
process of inhibition at the lexical-semantic level of language processing and its impact
on auditory comprehension in Wernicke's aphasia.
NEUROPSYCHOLOGICAL EVIDENCE
Theories of selective attention emphasise the role that the process of inhibition plays in
suppressing irrelevant information for improved focus in such higher-level cognitive
tasks as verbal working memory and language performance (e.g., Hasher & Zacks, 1988;
Tipper, 1985). Traditionally, attention theories placed the emphasis on the target of
selection. Unselected information was thought to passively decay (Broadbent, 1970).
However, more recent theories of selective attention (e.g., Tipper, 1985) propose an
active suppression or inhibition of distracting information during selection for increased
efficiency of processing.
Support for inhibition theory comes from the negative priming paradigm (Tipper,
1985). A participant is asked to respond to a target item presented simultaneously with a
similar distractor item. The critical manipulation occurs between consecutive trials. The
participant responds to a target on the test trial that had been ignored on the previous trial.
The negative priming effect is lengthened response time on experimental trials as
compared with control trials, where the distractor is an item not seen before. The source
of the slower response time to the repeated item is theorised to be the inhibition that has
accrued to the current target during its role as an ignored item in the previous trial.
INHIBITORY FUNCTION IN WERNICKE'S APHASIA
Inhibitory function has been investigated in a variety of populations evidencing selection
difficulties, including the elderly (e.g., Earles, Connor, Frieske, Park, Smith, & Zwahr,
1997; Hasher & Zacks, 1988), individuals with schizophrenia (e.g., Maher, 1983), and
those with dementia of the Alzheimer type (e.g., Sullivan, Faust, & Balota, 1995). In
addition, Milberg, Blumstein, Katz, Gershberg, and Brown (1995) investigated inhibitory
function in the presence of aphasia.
Milberg et al. (1995) conducted experiments to examine the extent to which deficits in
controlled or automatic processing could characterise lexical access deficits in Wer-
nicke's and Broca's aphasia. They administered two auditory lexical decision priming
experiments to seven participants with Wernicke's aphasia and ten with Broca's aphasia
(mean age 68.3 and 59.6 years, respectively) and to young (college-aged) and older
600 WIENER, CONNOR, OBLER
(mean age 63.8) non-brain-injured controls. In one experiment, they varied prime±target
predictability. The expectation was that those with normal controlled processing would
show slowed response times for unrelated prime±target pairs as compared with neutral
pairs when the unrelated pairs had been preceded by an induction set consisting of a
series of word pairs all semantically related. In the second experiment, they manipulated
the prime±target interstimulus interval (ISI). At the 2000 ms ISI, both facilitation for
related pairs and inhibition for unrelated pairs should be obtained. Of the four subject
groups, neither the older control group nor the Wernicke's aphasics were affected by
manipulations that were to have invoked controlled processes. That is, they did not
demonstrate inhibition in the high-probability condition, nor did these two groups
demonstrate inhibition at the 2000 ms ISI. Thus, while inhibitory function appears
reduced in Wernicke's aphasia, it is unclear whether this reduction is due to the aphasia
type or the impact of age. This distinction is an important one, as inhibitory control is
thought to decrease with age (e.g., Balota, Black, & Cheney, 1992; Earles et al., 1997;
Hasher & Zacks, 1988), and patients with Wernicke's aphasia are, on average, sig-
nificantly older than individuals with Broca's aphasia (Obler, Albert, Goodglass, &
Benson, 1978).
In the neuropsychological literature, a common tool used to measure inhibition in non-
aphasic populations is the Stroop Colour-Word Test (Stroop, 1935). Although there are
now many variations on this task, the basic design is such that a participant is asked to
name the ink colour of a printed word and ignore the meaning of the word. Ink colour
naming is slower when the ink colour and the word meaning are incompatible (e.g., blue
written in red ink) than when they are compatible (e.g., red written in red ink) or when
they are neutral (e.g., XXX written in red ink). The prevailing interpretation of this effect
is that the word information is activated automatically, and the participant needs to inhibit
this information during the slower process of colour naming (MacLeod, 1991). Greater
interference on this task, as measured by the difference between reaction times to the
incompatible versus neutral conditions, without an accompanying increase in facilitation
(the difference between reaction times in the neutral and compatible conditions), has been
interpreted as reflecting reduced inhibitory abilities.
This pattern of findings, a larger-than-normal interference effect accompanied by no-
greater-than-normal facilitation effect, is an important way to distinguish the effects of
reduced inhibitory control from generalised cognitive slowing. An example from the
ageing literature demonstrates this issue quite effectively. Prior to 1998, 20 studies had
been conducted comparing older adults to younger adults on variations of the Stroop task
(see review by Verhaeghen & De Meersman, 1998). Nearly all had obtained findings of a
larger interference effect in older adults than in younger adults. Nearly all of the authors
of these studies concluded, on the basis of these findings, that older adults show poorer
inhibitory control than younger adults. In every one of these studies, response latencies
were much longer for older than for younger adults. Slowing across all conditions in the
study not only produced larger interference effects for the old, but larger facilitation
effects as well. Verhaeghen and De Meersman demonstrated through meta-analysis of
these studies that generalised slowing of all cognitive processes was likely the cause
of these larger than normal interference effects, rather than a deficit in inhibitory control
per se.
The aphasia literature contains very few studies of the Stroop effect, probably due to
the high verbal demands of the original task. The validity of measuring a cognitive
function via a variably impaired verbal response is, obviously, questionable. In order to
adapt the Stroop test for use with a Wernicke's aphasic population, a manual-response
INHIBITION IN WERNICKE'S APHASIA 601
version appears necessary given the high frequency of verbal paraphasia associated with
Wernicke's aphasia. MacLeod (1991) compiled an extensive review of studies investi-
gating the Stroop effect since J. R. Stroop's classic 1935 article, concluding that although
the interference effect may be reduced when response modality is switched from oral to
manual, it remains robust. A number of researchers (e.g., Fox, Shor, & Steinman, 1971;
Shor, 1971; Windes, 1968) have found that numbers also can produce significant inter-
ference effects. For example, the naming of an Arabic numeral is interfered with when it
appears in incongruent quantities. Use of numerical stimuli appears warranted in an
adaptation of the Stroop test for Wernicke's aphasia, as it allows for a manual, computer
keyboard response. While such stimuli tap into the lexical-semantic level of language,
they avoid the need for the participant's verbal response.
The present study involved administration of a computerised manual-response,
numerical version of the Stroop test to individuals with Wernicke's aphasia and age- and
education-matched non-brain-injured controls. In order to determine whether individuals
with Wernicke's aphasia evidence impaired inhibition in processing lexical-semantic
information, we compared them to age-matched controls to help disentangle effects of
ageing from effects due to stroke. Moreover, to accept the hypothesis that individuals
with Wernicke's aphasia have a specific deficit of inhibition and not generalised slowing
due to stroke, our design required both that the size of the facilitation effect was
equivalent in participants with aphasia and age-matched controls and that the size of the
interference effect was significantly greater.
We suggest, further, that one possible behavioural manifestation of impaired inhibition
may be reduced auditory comprehension. Correlating the severity of auditory compre-
hension deficits with the interference score obtained on the Stroop test permitted
exploration of the relationship between inhibition and auditory comprehension.
METHOD
Participants
Five adult participants with chronic Wernicke's aphasia and twelve non-brain-injured
controls were tested. Participants were recruited from the subject pool of the Harold
Goodglass Aphasia Research Center, which consists of both individuals who have sus-
tained aphasia and normal adults.
The five participants with Wernicke's aphasia were selected based on the following
criteria: a single onset of a left posterior infarct post cerebral vascular accident; no history
of dementia, prior neurological trauma, drug or alcohol abuse, or chronic psychiatric
disorder; English as native and primary language; right-hand dominance; normal visual
acuity, with or without correction; and normal hearing thresholds across the speech
frequencies, with or without correction. The diagnosis of Wernicke's aphasia was based
on clinical observation and language examination. Six subtests of the Neurosensory
Center Comprehensive Examination for Aphasia (NCCEA: Spreen & Benton, 1969) were
administered to each participant with aphasia: Visual Naming, Description of Use,
Sentence Repetition, Word Fluency, Identification by Sentence (the Token Test), and
Reading Names for Meaning (Pointing). In addition, the Complex Ideational Material
subtest of the Boston Diagnostic Aphasia Examination (Goodglass & Kaplan, 1983) was
administered. The ``Speech'' and ``Understanding'' subsets of the Functional Commu-
nication Profile (Sarno, 1969) also were rated for each participant with aphasia for
purposes of a comprehensive participant profile. Table 1 summarises the relevant
demographic and clinical characteristics of the aphasic participants. All of these parti-
602 WIENER, CONNOR, OBLER
cipants were male. Their mean age was 72 years, with a range of 63±76 years. Their mean
level of formal education was 11.4 years, with a range of 10±12 years.
The twelve non-clinical controls were selected using the same criteria as the partici-
pants with aphasia, with two additional requirements: no history of neurological trauma
or disease and a score of 28 or greater on the Mini-Mental State Examination (Folstein,
Folstein, & McHugh, 1975). They were matched to the aphasic participants by age (mean
age of 71.5 years, range 62±77 years) and level of formal education (mean of 12.6 years,
range 12±16 years). Six of the control participants were male (Participants 6±11) and six
were female (Participants 12±17). All research participants were treated in accordance
with the Human Studies Committees of Boston University School of Medicine, the VA
Boston Healthcare System, and the City University of New York Graduate Center.
Participants received a modest payment for their participation at the conclusion of the
study.
In order to measure auditory comprehension, the Token Test and the Complex
Ideational Material subtest of the BDAE were administered to all participants. The
participants with Wernicke's aphasia obtained raw scores on the Token Test ranging from
73 to 104 out of a possible 163 correct, reflecting severe to moderate-severe deficits when
plotted on the NCCEA aphasia profile. Their raw scores on the Complex Ideational
Material subtest ranged from 5 to 9 of a possible 12 correct, reflecting moderate-severe to
mild deficits when plotted on the BDAE aphasia summary profile. As expected, the non-
brain-injured controls demonstrated only minimal reductions on these two tests, reflected
by a mean score of 161 on the Token Test and 11.2 on the Complex Ideational Material
subtest.
Materials
The variation of the Stroop test used was modelled after Salthouse and Meinz's (1995)
version which lent itself to modifications for increased validity in a language-impaired
population. In order to create a measure of facilitation and interference, three conditions
were established. The compatible condition was represented by the Arabic numerals 1 to
4 presented in congruent quantities (e.g., 333), consisting of four stimuli. The neutral
condition was represented by an ``X'' in its four possible quantities. The incompatible
TABLE 1
Demographic and clinical characteristics of the participants with Wernicke's aphasia
Subject Age Educ
Time
post-onset
Aphasia
severity
NCCEA
range*
FCP
speech**
FCP
comp**
172yrs 12 yrs 177 mos moderate 20±88% 56% 57%
276yrs 10 yrs 56 mos mod-severe 20±61% 49% 55%
363yrs 12 yrs 163 mos moderate 13±88% 55% 58%
474yrs 12 yrs 114 mos severe 6±61% 50% 50%
575yrs 11 yrs 102 mos mod-severe 8±61% 49% 47%
Including: chronological age; level of formal education; time post-onset of CVA in months;
overall aphasia severity rating; range of percentiles of subtests of the NCCEA (Spreen & Benton,
1969) administered; and percentiles of estimated function in ``Speech'' and ``Understanding''
subsets of the FCP (Sarno, 1969).
* Percentiles are based on an aphasic population.
** Percentile represents functional communicative effectiveness in this modality based on
estimated premorbid language proficiency.
INHIBITION IN WERNICKE'S APHASIA 603
condition was represented by the Arabic numerals 1 to 4 presented in incongruent
quantities (e.g., 33), consisting of 12 stimulus items. The three experimental conditions
provide a measure of facilitation (compatible vs neutral condition) and interference
(incompatible vs neutral condition).
The experimental task consisted of 216 itemsÐ72 items in each condition. For each
condition to be equally represented, the stimuli in both the compatible and neutral
conditions were tripled in quantity. Stimuli were presented in random order for each
participant. Three filler items were presented at the beginning of the experiment but were
not included in the analysis.
The experimental trials were preceded by 10 practice items presented in random
orderÐ3 compatible, 3 neutral, and 4 incompatible trials. The same set of practice items
was administered to each participant in random order.
Procedure
Participants were seated at a comfortable distance in front of a Macintosh PowerBook
180 computer with a 10-inch black and white screen. On the attached keyboard, four keys
were exposed labelled ``1'', ``2'', ``3'', and ``4''. Participants were instructed to press
the key that corresponded to the quantity of items on the screen. They were told to
respond as quickly as possible and directed to use their left hand only.
The stimuli were presented in black on a white background via the software package
PsyScope (Cohen, MacWhinney, Flatt, & Provost, 1993). Practice items were given and
repeated, when necessary, until comprehension of the task was demonstrated by three
consecutive correct responses. The 216 experimental trials followed. A PsyScope button
box was used to increase timing accuracy to 1 Ô 4 ms. Responses and latencies were
recorded. The stimulus remained on the screen until the participant depressed one of the
four response keys. The inter-trial interval was 500 ms.
RESULTS
The data for each participant were screened for mistrials (response latencies greater than
5 seconds) and outliers. Outliers were defined as responses greater than three standard
deviations from the mean of all remaining responses for that participant. The mean
number of mistrials for participants with Wernicke's aphasia was 0.6%, and the mean
number of outliers was 2%. For the non-brain-injured controls, the mean number of
mistrials was 0.3%, and the average number of outliers was 1.4%.
Reaction time data
The mean reaction times of the Wernicke's aphasic group and the control group are
displayed in Figure 1. A 2 (group) 63 (condition) mixed factor ANOVA was conducted
on reaction time. RTs were longer for the participants with aphasia, F(1, 15) = 5.66, MSE
= 67,710.77, p< .05, there was a significant difference among the conditions, F(2, 30) =
88.85, MSE = 582.83, p<.001, and the condition by group interaction was significant,
F(2, 30) = 28.12, MSE = 582.83, p< .001, indicating that the increase in response time
across conditions was larger for the participants with Wernicke's aphasia than for the
controls.
Each group was examined separately. Each group showed a significant difference
among the conditions: Wernicke's aphasics, F(2, 8) = 29.97, MSE = 1,492, p< .001;
controls, F(2, 22) = 34.06, MSE = 252.22, p< .001. Post-hoc Newman-Keuls t-tests were
604 WIENER, CONNOR, OBLER
then performed. For each group, three paired comparisons were made: (1) the difference
between the neutral and compatible conditions (the facilitation effect); (2) the difference
between the incompatible and the neutral conditions (the interference effect); and (3) the
difference between the facilitation effect and the interference effect. For the participants
with Wernicke's aphasia, the facilitation effect was not significant, t(8) = 2.50, p> .05,
although the interference effect, t(8) = 7.99, p< .001, and the difference between the
facilitation and the interference effects, were significant, t(8) = 10.48, p< .001. For the
controls, the facilitation effect, t(22) = 4.18, p< .01, the interference effect, t(22) = 7.36,
p< .001, and the difference between the facilitation effect and the interference effect,
t(22) = 11.54, p<.001, were all statistically significant.
The final step in the analysis of the reaction time data involved a comparison across
groups, between the non-brain-injured controls and the participants with Wernicke's
aphasia: the difference between the facilitation effect and the difference between the
interference effect. The facilitation effect was no larger for the aphasic group (M=43ms)
than for the controls (M=19ms), t(15) = 1.91, p= .075. However, the interference effect
was significantly larger for the participants with Wernicke's aphasia (M= 138 ms) than
for the controls (M=34ms), t(15) = 4.35, p< .001.
Error percentage data
The mean error percentages of the Wernicke's aphasic group and the control group, by
condition, are displayed in Figure 2. Most participants made no errors in the compatible
and neutral conditions, and error rate was very low in these conditions; however, for both
Figure 1. Stroop mean reaction times for the Wernicke's aphasic group and the non-brain-injured control
group, by condition.
INHIBITION IN WERNICKE'S APHASIA 605
the aphasic group and the control group in the incompatible condition, the mean per-
centage of errors was significantly greater than zero, t(4) = 2.77, p= .05 and t(11) = 4.30,
p< .01, respectively. The facilitation effect for errors (Wernicke's aphasics M= ±0.05;
controls M= 0.35) was not different between the groups, t(15) = 0.637, p> .50, whereas
the interference effect for the aphasic group (M=3.45) was significantly larger than for
the controls (M=1.5), t(15) = 2.19, p< .05.
Cross-measures comparisons
APearson correlation was performed to examine factors that may help to predict Stroop
interference performance in Wernicke's aphasia, including the clinical-behavioural
measures of auditory comprehension and the demographic factors of age, education, and
time post-onset. Neither the Complex Ideational Material score nor the demographic
factors examined were significantly correlated with Stroop performance, with all at r<
.77, ns. However, a significant negative correlation was found between the Stroop error
percentage interference effect and the Token Test score, r(5) = ±.91, p< .05; that is, the
greater the Stroop interference effect, the lower the Token Test score.
DISCUSSION
The goal of this study was to investigate inhibition at the lexical-semantic level of
language processing in Wernicke's aphasia utilising the classic Stroop test, which we
adapted to be applicable for an aphasic population. We expected that the participants with
Wernicke's aphasia would show greater difficulty than the non-clinical controls in
Figure 2. Stroop mean error percentages for the Wernicke's aphasic group and the non-brain-injured control
group, by condition.
606 WIENER, CONNOR, OBLER
inhibiting the automatically activated word information, represented by the Arabic
numeral, when attempting to respond to the quantity of items. We also examined whether
there would be a significant association between the extent of inhibitory impairment and
auditory comprehension deficit in Wernicke's aphasia.
Reaction time analyses indicated that the interference effect was significantly larger
for the participants with Wernicke's aphasia than for the controls, without an accom-
panying increase in facilitation. Although the difference between the facilitation effect
for these two groups might be considered as marginally significant, a post-hoc power
analysis indicated that, with a difference of approximately 1 standard deviation between
the mean reaction times of the Wernicke's aphasic group and the control group, we had
nearly 90% power to detect it as significant (Cohen, 1988). Thus, the relatively small
sample size (n= 17) was not an issue, and the facilitation effect was no larger for the
aphasic group than for the controls. Likewise, not only were the error rates low, con-
firming that the reaction time data were not the result of a speed±accuracy trade-off, but
these data, too, revealed significantly greater interference in the aphasic group than in the
control group. Although the participants with Wernicke's aphasia were nearly 200 ms
slower overall than their age-matched controlsÐa situation similar to that found in
studies that compared Stroop performance between younger and older adultsÐthere is no
indication that generalised slowing could account for the results. That is, while the
interference effect for the Wernicke's aphasic group was much larger than for the con-
trols, the facilitation effects were equivalent for the two groups. Based on these findings,
it appears that the individual with Wernicke's aphasia has a selective deficit of inhibitory
control.
One might argue that our findings in this study reflect brain damage more generally,
rather than damage resulting exclusively in Wernicke's aphasia. Recall, however, that
Milberg et al. (1995) demonstrated relatively preserved inhibitory function in their 10
participants with Broca's aphasia. In the future, comparing the performance of indivi-
duals with Broca's aphasia on our version of the Stroop test with our data from Wer-
nicke's participants will be useful to confirm these differences in inhibitory function
between the aphasia types. Furthermore, examination of a group of individuals with
Broca's aphasia with pure frontal lesions will increase our understanding of the inter-
actions between frontal and posterior brain regions in the modulation of attention (e.g.
Mesulam, 1981).
Additionally, the exploratory correlational analyses between inhibitory control deficits
and impairment in auditory comprehension revealed a statistically significant association
between the magnitude of Stroop interference and auditory comprehension as measured
by the Token Test. Although the participants with Wernicke's aphasia were also impaired
on auditory comprehension as measured by the Complex Ideational Material subtest of
the BDAE, there was no correlation with the magnitude of Stroop interference. Of course
it is difficult to support any particular argument for this pattern of results given the low
statistical power. However, one may speculate that this pattern may be due to inhibitory
control at different levels of the cognitive system for two measures of auditory com-
prehension. The large Stroop interference effect in the participants with Wernicke's
aphasia corresponds to deficits at the lexical-semantic level of the language system, and
the Token Test appears to be more heavily weighted towards proper inhibitory control at
that lexical-semantic level (e.g., touch the large white circle and the small green square)
than does Complex Ideational Material. If a participant has difficulty in inhibiting
competing lexical information that has become activated (in the example above, both
white and green, large and small, and circle and square are active), then comprehension
INHIBITION IN WERNICKE'S APHASIA 607
performance will suffer. To perform successfully on Complex Ideational Material, lexical
semantic inhibitory control does not seem as important as the ability to build a coherent
structure for the narratives.
These findings expand on our understanding of resource allocation in aphasia. First,
the relative dissociation between automatic and controlled processing in Wernicke's
aphasia is further reinforced. Not only does automatic processing, regarding both lexical-
semantic activation (e.g., Blumstein, Milberg, & Shrier, 1982) and deactivation (Wiener,
2000), appear to be preserved in Wernicke's aphasia, but our finding of a smaller
facilitation effect than would be predicted based on the overall performance speed of the
Wernicke's participants assures us that the greater interference evidenced was not a result
of more potent automatic activation. Second, the results not only reinforce semantic
impairments in this population when attentional resources are demanded at the level of
controlled processing, but also direct us towards a faulty mechanism. The individual with
Wernicke's aphasia cannot effectively ignore the automatically evoked, distracting
stimulus. This deficit is not due to more potent automatic activation, but rather due to
decreased inhibition. This faulty mechanism may result in a reduction in the ability to
allocate attention, although it is premature to conclude that the inhibition effect is
primary and causal, as the impaired inhibitory mechanism may itself be the result of
inefficient resource allocation. Nonetheless, as the necessary interaction between the
inhibitory mechanism and attention allocation is impaired, reduced effectiveness of
auditory processing may result. Further research is clearly warranted to delineate the role
of inhibitory function in auditory comprehension in aphasia.
REFERENCES
Balota, D. A., Black, S. R., & Cheney, M. (1992). Automatic and attentional priming in young and older adults:
Reevaluation of the two-process model. Journal of Experimental Psychology: Human Perception and
Performance,18, 485±502.
Blumstein, S. E., Milberg, W., & Shrier, R. (1982). Semantic processing in aphasia: Evidence from an auditory
lexical decision task. Brain and Language,17, 301±315.
Broadbent, D. E. (1970). Stimulus set and response set. In D. I. Mortofsky (Ed.), Attention: Contemporary
theories and analysis. New York: Appleton-Century-Crofts.
Cohen, J. (1988). Statistical power analysis for the behavioral sciences, Second edition. New York: Academic
Press.
Cohen, J. D., MacWhinney, B., Flatt, M., & Provost, J. (1993). PsyScope: An interactive graphic system for
designing and controlling experiments in the psychology laboratory using Macintosh computers. Behavior
Research Methods, Instruments and Computers,25, 257±271.
Earles, J. L., Connor, L. T., Frieske, D., Park, D. C., Smith, A. D., & Zwahr, M.(1997). Age differences in
inhibition: Possible causes and consequences. Aging, Neuropsychology, and Cognition,4, 45±57.
Folstein, M. F., Folstein, S. E., & McHugh, P. R. (1975). ``Mini-Mental State'': A practical method for grading
the cognitive state of patients for the clinician. Journal of Psychiatric Research,12, 189±198.
Fox, L. A., Shor, R. E., & Steinman, R. J. (1971). Semantic gradients and interference in naming color, spatial
direction, and numerosity. Journal of Experimental Psychology,91, 59±65.
Goodglass, H., & Kaplan, E. (1983). The assessment of aphasia and related disorders, Second edition. Phila-
delphia: Lea & Febiger.
Hasher, L., & Zacks, R. T. (1988). Working memory, comprehension, and aging: A review and a new view. In
G. H. Bower (Ed.), The psychology of learning and motivation, Vol. 22. San Diego, CA: Academic Press.
MacLeod, C. M. (1991). Half a century of research on the Stroop effect: An integrative review. Psychological
Bulletin,109, 163±203.
Maher, B. A. (1983). A tentative theory of schizophrenic utterance. In B. A. Maher & W. B. Maher (Eds.),
Progress in experimental personality research, Vol. 12. New York: Academic Press.
McNeil, M. R., Odell, K. & Tseng, C-H. (1991). Toward the integration of resource allocation into a general
theory of aphasia. Clinical Aphasiology,20, 21±39.
608 WIENER, CONNOR, OBLER
Mesulam, M. M. (1981). A cortical network for directed attention and unilateral neglect. Annals of Neurology,
10, 309±325.
Milberg, W., Blumstein, S. E., Katz, D., Gershberg, F., & Brown, T. (1995). Semantic facilitation in aphasia:
Effects of time and expectancy. Journal of Cognitive Neuroscience,7, 33±50.
Murray, L. L., Holland, A. L., & Beeson, P. M. (1997). Auditory processing in individuals with mild aphasia: A
study of resource allocation. Journal of Speech, Language, and Hearing Research,40, 792±808.
Obler, L. K., Albert, M. L., Goodglass, H., & Benson, D. F. (1978). Aphasia type and aging. Brain and
Language,6, 318±322.
Salthouse, T. A., & Meinz, E. J. (1995). Aging, inhibition, working memory, and speed. Journal of Gerontology:
Psychological Sciences,50B, P297±P306.
Sarno, M. T. (1969). The Functional Communication Profile. New York: New York University Medical Center,
Rusk Institute of Rehabilitation Medicine.
Shor, R. E. (1971). Symbol processing speed differences and symbol interference effects in a variety of concept
domains. The Journal of General Psychology,85, 187±205.
Spreen, O., & Benton, A. L. (1969). Neurosensory center comprehensive examination for aphasia. Victoria,
Canada: University of Victoria, Department of Psychology, Neuropsychology Laboratory.
Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology,18,
643±662.
Sullivan, M. P., Faust, M. E., & Balota, D. A. (1995). Identity negative priming in older adults and individuals
with dementia of the Alzheimer type. Neuropsychology,9, 537±555.
Tipper, S. P. (1985). The negative priming effect: Inhibitory priming by ignored objects. Quarterly Journal of
Experimental Psychology,37A, 571±590.
Tseng, C-H., McNeil, M. R., & Milenkovic, P. (1993). An investigation of attention allocation deficits in
aphasia. Brain and Language,45, 276±296.
Verhaeghen, P., & De Meersman, L. (1998). Aging and the Stroop effect: A meta-analysis. Psychology and
Aging,13, 120±126.
Wiener, D. A. (2000). Mechanisms of inhibition in Wernicke's aphasia. Unpublished doctoral dissertation, City
University of New York, USA.
Windes, J. D. (1968). Reaction time for numerical coding and naming of numerals. Journal of Experimental
Psychology,78, 318±322.
INHIBITION IN WERNICKE'S APHASIA 609
