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Not so fast: Domain-general factors can account for selective deficits in grammatical processing

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Abstract

Abstract Normals display selective deficits in morphology,and syntax under adverse processing conditions. Digit loads do not,impair processing of passives and object relatives, but do impair processing of grammatical morphemes. Perceptual degradation and temporal compression selectively impair several aspects of grammar, including passives and object relatives. Hence we replicate CW’s specific findings but reach opposite conclusions, based on wider evidence. Passives and object relatives are more difficult for agrammatic,aphasics to process ,and interpret than actives and object relatives. CW (Caplan & Waters, in press) ascribe this well-known ,fact to deficits in a domain-specific grammatical processor, with a syntax- specific pool of working-memory resources. They base this conclusion on evidence ,involving comprehension
NOT SO FAST: DOMAIN-GENERAL FACTORS CAN ACCOUNT FOR SELECTIVE
DEFICITS IN GRAMMATICAL PROCESSING
Elizabeth Bates
Center for Research in Language, 0526
University of California, San Diego
La Jolla, CA 92093-0526
bates@crl.ucsd.edu
Frederick Dick
Center for Research in Language, 0526
University of California, San Diego
La Jolla, CA 92093-0526
fdick@crl.ucsd.edu
Beverly Wulfeck
Dept. of Communicative Disorders
San Diego State University
San Diego, CA 92182-1518
wulfeck@crl.ucsd.edu
Supported by NIDCD 2-R01-DC00216 and NINDS NS22343. Please address correspondence to Frederic Dick,
University of California, San Diego, La Jolla, Ca. 92093-0526.
Behavioral and Brain Sciences, 1999, 22(1), 96-97.
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NOT SO FAST: DOMAIN-GENERAL FACTORS CAN ACCOUNT FOR SELECTIVE DEFICITS
IN GRAMMATICAL PROCESSING
Elizabeth Bates, Frederick Dick and Beverly Wulfeck
Abstract
Normals display selective deficits in morphology and syntax under adverse processing conditions. Digit loads do not impair
processing of passives and object relatives, but do impair processing of grammatical morphemes. Perceptual degradation and
temporal compression selectively impair several aspects of grammar, including passives and object relatives. Hence we replicate
CW’s specific findings but reach opposite conclusions, based on wider evidence.
Passives and object relatives are more difficult for
agrammatic aphasics to process and interpret than
actives and object relatives. CW (Caplan & Waters, in
press) ascribe this well-known fact to deficits in a
domain-specific grammatical processor, with a syntax-
specific pool of working-memory resources. They base
this conclusion on evidence involving comprehension
of a small subset of English syntactic structures, in
patients with agrammatic aphasia, patients without re-
ceptive agammatism despite working-memory deficits,
and young adults stratified by memory span and/or
tested under a digit load to simulate deficits in domain-
general working memory. Against MCJ (Miyake,
Carpenter, & Just, 1994), who simulated receptive
agrammatism in normals with speeded visual stimuli,
CW do not find specific effects on “hard” sentence
types as a function of digit load or memory span. We
have replicated CW’s results, but we have also
replicated those of MCJ, and we believe that CW have
moved too fast in their broad conclusions about the
autonomy of grammatical processing. Using a broader
range of structures, languages, and patient groups, with
controls tested under a broader range of adverse
processing conditions, we conclude that specific deficits
in grammar can be explained without recourse to a
domain-specific resource or processing device. Our
interpretation differs from that of MCJ, but it is similar
in spirit.
First, the same hierarchy of difficulty (actives,
subject relatives > passives, object relatives) has been
observed in several languages, in many different
populations, including Broca’s aphasics, Wernicke’s
aphasics, anomics without expressive agrammatism,
and individuals in the early stages of first- or second-
language acquisition. The pattern is not unique to any
form of aphasia or to any lesion site.
Second, other facets of receptive agrammatism
(deficits in the use of function words and grammatical
inflections) have been observed in a broad range of
patient populations, and in normals subjected to a broad
range of stressors. Published and unpublished studies
from our laboratory have simulated selective deficits in
morphology (with relative sparing of word order) in
college students processing under a digit load, a partial
noise mask, low-pass filtering and/or auditory compres-
sion. These results hold, in varying degrees (depending
on the strength of each information type under normal
conditions) in English, Italian and German.
Third (and most relevant to CW’s claim), selective
deficits in the processing of passives and object clefts
have been demonstrated in English college students, but
under conditions different from those adopted by CW.
Because they failed to demonstrate effects of digit load
or working-memory capacity on the above sentence
hierarchy, CW conclude that syntactic processing is
affected only by deficits within a syntax-specific pool
of processing resources, and not by reductions in
working memory outside this domain (as claimed by
MCJ, based on results with speeded presentation). We
have shown that CW and MCJ are both right: College
students tested under a digit load (a task that disrupts
computation of subject-verb agreement and other
inflectional phenomena in our laboratory) are unim-
paired in their ability to process passives and object
clefts (replicating CW), but (2) students tested under
perceptual degradation and/or temporal compression
are selectively impaired on precisely those sentence
types (replicating MCJ, in the auditory modality).
Further-more, students tested with both compression
and noise produced super-additive results, greater than
we would expect by adding separate effects of
compression and degradation alone, and strikingly
similar to results for aphasic patients in the same
paradigm (similar error rates, and similar patterns of
individual variation in a cluster analysis).
We conclude that the specific challenges posed by
passive and object relatives are not unique to a single
aphasia type, and can be explained without recourse to
syntax-specific mechanisms or to damage involving
specific lesion sites. We propose a domain-general
account of the specific difficulties posed by low-
frequency syntactic structures that differs from the
working-memory proposal of MCJ, reflecting the
effects of structural frequency on encoding (activation
of stimuli) rather than memory (maintenance of stimuli
in working memory). Grammatical morphemes are
vulnerable to stressors of either type (including digits);
low-frequency word orders are vulnerable at encoding,
but form solid memory traces that are mnemonically
robust if they make it over the encoding threshold. This
3
would explain why patients with working-memory
deficits do not show the predicted pattern, but it does
not permit CW to leap to a much stronger conclusion,
i.e., that syntactic deficits reflect damage to an auto-
nomous processor, independent from the processing
resources used by other cognitive systems. Our account
makes differential predictions for the fate of complex
sentence types under stress in cross-linguistic compari-
sons, results that are supported by preliminary findings
for German and Italian.
REFERENCES
Bates, E., Devescovi, A., Dronkers, N., Pizzamiglio, L.,
Wulfeck, B., Hernandez, A., Juarez, L., &
Marangolo, P. (1994). Grammatical deficits in
patients without agrammatism. Brain and
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Blackwell, A., & Bates, E. (1995). Inducing
agrammatic profiles in normals. Journal of
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Caplan, D. & Waters, G. (in press). Verbal working
memory and sentence comprehension. The
Behavioral and Brain Sciences.
Dick, F., Bates, E., Wulfeck, B. & Dronkers, N. (1998).
Deficits in the interpretation of complex sentences
in aphasic patients in normals under adverse
processing conditions. University of California,
San Diego, Center for Research in Language.
Kilborn, K. (1991) Selective impairment of
grammatical morphology due to induced stress in
normal listeners: Implications for aphasia. Brain
and Language, 41, 275-288.
Miyake, A., Carpenter, P., & Just, M. (1994). A
capacity approach to syntactic comprehension
disorders: Making normal adults perform like
aphasic patients. Cognitive Neuropsychology, 11,
671-717.
Naucler, N., Wulfeck, B., & Bates, E. (1998). A
developmental study of complex sentence
interpretation abilities (Tech. Rep. CND-9803).
University of California, San Diego, Center for
Research in Language, Project in Cognitive and
Neural Development.
Article
Background: Theoretical studies have shown that some deficits in verbal short-term/working memory can impact comprehension abilities. Clinicians often suspect that their clients are failing to understand speech because they cannot remember what has been said. Yet there are no reports of how to treat such a problem. Aims: To see if improving the short-term/working memory abilities of a person with aphasia would improve her comprehension at the sentence level. In addition, we sought to explore the issues involved in carrying out research-based therapy in a clinical environment. Methods & Procedures: The memory and language impairments of a person with aphasia were assessed. The memory impairments were then targeted in therapy by requiring the repetition of gradually more demanding sentences. Comprehension itself was not practised at all during therapy. Outcome and Results: Certain aspects of short-term and working memory improved post-therapy, notably an increase in digit span and an ability to repeat more words in sentences. There was a limited generalisation of improvement to comprehension tasks, meaning that the client could understand longer sentences and required fewer repetitions. The existence of possible additional impairments was revealed post-therapy. Conclusions: If memory limitations are causing comprehension difficulty, therapy may need to take the focus away from language and on to short-term/working memory. However, improvement may be limited. In addition, we suggest that within the context of a clinical setting, a reasonable balance between research and therapy can be struck (albeit with some difficulty) if compromises are made.
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This target article discusses the verbal working memory system used in sentence comprehension. We review the idea of working memory as a short duration system in which small amounts of information are simultaneously stored and manipulated in the service of a task and that syntactic processing in sentence comprehension requires such a storage and computational system. We inquire whether the working memory system used in syntactic processing is the same as that used in verbally mediated tasks involving conscious, controlled processing. Various forms of evidence are considered: the relationship between individual differences in working memory and individual differences in the efficiency of syntactic processing; the effect of concurrent verbal memory load on syntactic processing; and syntactic processing in patients with poor short term memory, poor working memory, or aphasia. The experimental results suggest that the verbal working memory system specialized for assigning the syntactic structure of a sentence and for using that structure in determining sentence meaning is distinct from the working memory system that underlies the use of sentence meaning to accomplish further functions. We present a theory of the components of the verbal working memory system and suggestions as to its neural basis.
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The selective vulnerability of morphology in agrammatic aphasia is often interpreted as evidence that closedclass items reside in a particular part of the brain (i.e., Broca's area); thus, damage to a part of the language processor maps onto behavior in a transparent fashion. We propose that the selective vulnerability of grammatical morphemes in receptive processing may be the result of decrements in overall processing capacity, and not the result of a selective lesion. We demonstrate agrammatic profiles in healthy adults who have their processing capacity diminished by engaging in a secondary task during testing. Our results suggest that this selective profile does not necessarily indicate the existence of a distinct subsystem specialized for the implicated aspects of syntax, but rather may be due to the vulnerability of these forms in the face of global resource diminution, at least in grammaticality judgment.
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This paper presents a theory of syntactic comprehension disorders in aphasic patients. In line with some recent proposals, the current theory assumes that aphasic patients still possess the structural (syntactic) and procedural knowledge necessary to perform syntactic analysis. This paper, however, postulates that patients' comprehension deficits originate, at least in part, from reductions in working memory capacity for language. Based on a recently developed theory of capacity constraints in normal language comprehension (Just&Carpenter, 1992), the theory explains how reductions in working memory capacity can lead to the pattern of comprehension breakdown in aphasics, which can be characterised as a conjoint function of the patient's severity level and the structural complexity of the sentence. As supporting evidence for the theory, we report two “simulation” experiments in which we increased the computational demands on normal adults of varying working memory capacities and thereby induced in them the interaction of “severity” by complexity usually observed among aphasic patients.
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The traditional clinical picture for English nonfluent aphasics has generally presented the deficit as one of total loss of control over grammatical morphology, with some sparing of word order. This is at odds with recent research involving nonfluent aphasic speakers of highly inflected languages, which has shown that agrammatic performance is characterized by morphological substitution rather than omission errors. If the deficit associated with focal brain damage cannot be adequately accounted for in syndrome-specific ways, we may need to look for language-specific processing explanations. One such explanation has to do with language-specific response to global processing difficulty. The current experiment is designed to study the effects of a stress-related limitation on morphological processing. Normal speakers of a language with a relatively rich morphological system (German) are compared with those of a comparatively impoverished system (English) on different forms of a sentence comprehension task. In one form, "clean" stimuli permit full reliance on all available cues to meaning in each language. In another test, a low-level noise mask partially obscured the stimulus sentences. English speakers, who rely almost exclusively on word order cues, were not affected by the noise manipulation. German speakers relied heavily on morphological and semantic information rather than on word order under "clean" conditions. However, under noise Germans made significantly less use of grammatical morphology, with a trend toward compensatory reliance on word order. The results indicate that a global reduction in processing capacity can affect some aspects of language more than others and suggest that such factors must be taken into account in trying to understand specific impairment of morphology in aphasia.
Deficits in the interpretation of complex sentences in aphasic patients in normals under adverse processing conditions. University of California Selective impairment of grammatical morphology due to induced stress in normal listeners: Implications for aphasia
  • F Dick
  • E Bates
  • B Wulfeck
  • N Dronkers
Dick, F., Bates, E., Wulfeck, B. & Dronkers, N. (1998). Deficits in the interpretation of complex sentences in aphasic patients in normals under adverse processing conditions. University of California, San Diego, Center for Research in Language. Kilborn, K. (1991) Selective impairment of grammatical morphology due to induced stress in normal listeners: Implications for aphasia. Brain and Language, 41, 275-288.
A developmental study of complex sentence interpretation abilities (Tech. Rep. CND-9803) University of California
  • N Naucler
  • B Wulfeck
  • E Bates
Naucler, N., Wulfeck, B., & Bates, E. (1998). A developmental study of complex sentence interpretation abilities (Tech. Rep. CND-9803). University of California, San Diego, Center for Research in Language, Project in Cognitive and Neural Development.