Effects of Semantic Impairment on Language Processing in Semantic Dementia

Jamie Reilly, Ph.D.,1,2 and Jonathan E. Peelle, Ph.D.3

ABSTRACT

Semantic dementia is a neurodegenerative disease character- ized by progressive loss of conceptual and lexical knowledge. Cortical atrophy remains relatively isolated to anterior and inferior portions of the temporal lobe early in semantic dementia, later affecting more extensive regions of temporal cortex. Throughout much of the disease course, frontal and parietal lobe structures remain relatively intact. This distribution of cortical damage produces a unique language profile. Patients with semantic dementia typically experience profound deficits in language comprehension and production in the context of relatively well-preserved functioning in domains such as phonology, executive function, visuospatial processing, and speech perception. We discuss the effects of semantic impairment on language processing in semantic dementia within the context of an interactive theory of semantic cognition that assumes the active coordination of modality-neutral and modality-specific components. Finally, we argue the need for an etiology-specific language intervention for this population.

KEYWORDS: Dementia, language, semantic memory, semantic dementia

Learning Outcomes: As a result of this activity, the reader will be able to describe the speech and language Downloaded by: University of Pennsylvania Library. Copyrighted material. profile of semantic dementia.

Dementia is a nonspecific term that of causes, including the accumulation of denotes a constellation of deficits in memory, neuritic plaques, hypoxia/anoxia, metabolic attention, and behavior that are associated with insufficiencies, or vascular damage. Despite neurologic impairment. Dementia has a variety such varied causes, our strongest association

1Departments of Neurology and Communicative Disorders, tive Disorders, University of Florida, P.O. Box 100174, University of Florida, Gainesville, Florida; 2Brain Rehabil- Gainesville, FL 32610 (e-mail: [email protected]fl.edu). itation Research Center, Malcom Randall Veterans Affairs Semantic Memory and Language Processing in Aphasia Hospital, Gainesville, Florida; 3Department of Neurology, and Dementia; Guest Editor, Jamie Reilly, Ph.D. University of Pennsylvania School of Medicine, Philadel- Semin Speech Lang 2008;29:32–43. Copyright # 2008 phia, Pennsylvania. by Thieme Medical Publishers, Inc., 333 Seventh Avenue, Address for correspondence and reprint requests: Jamie New York, NY 10001, USA. Tel: +1(212) 584-4662. Reilly, Ph.D., Departments of Neurology & Communica- DOI 10.1055/s-2008-1061623. ISSN 0734-0478. 32 EFFECTS OF SEMANTIC IMPAIRMENT IN SD/REILLY, PEELLE 33 with dementia is Alzheimer’s disease (AD), work, broad consensus has swung to the con- and indeed AD is the most common form clusion that semantic impairment underlies of dementia worldwide.1 Nevertheless, many much of the associated language difficulties in other dementia subpopulations exist, each this population. Accordingly, Snowden and with differing etiologies and cognitive pro- colleagues labeled this variant of FTD semantic files. Frontotemporal dementia (FTD) is one dementia (SD), a term commonly used today.11 such family of dementias that has recently received considerable attention. Semantic de- mentia is among the most striking behavioral ANATOMIC LOCALIZATION OF and anatomic variants of FTD.2–7 ATROPHY IN SD SD is a neurodegenerative disease associated with a progressive reduction of gray matter WHAT IS SEMANTIC DEMENTIA? volume (i.e., cortical atrophy) in specific re- Warrington reported a series of patients who gions of the temporal lobe. Figure 1 illustrates showed severe deficits in object recognition and typical loci of damage in SD in both early and naming.8 After ruling out specific perceptual later stages of the disease. Shaded areas indicate disorders such as visual agnosia, Warrington regions commonly identified as atrophied in concluded that these patients experienced a anatomic studies of SD. selective loss of conceptual knowledge. This The early course of SD is characterized by landmark study demonstrated the effects of a cortical atrophy that remains relatively con- selective impairment of semantic memory on fined to anterior, lateral, and ventral portions language processing. In ensuing years, several of the temporal lobe, including the left tempo- similar cases were reported under characteristic ral pole and the inferior and middle temporal descriptions of progressive fluent aphasia and/ gyri.6,11–13 For unclear reasons, there is often or primary progressive aphasia (PPA), a con- an asymmetric hemispheric presentation of the dition described by Mesulum as ‘‘progressive disease. SD often compromises the left cerebral aphasia without generalized dementia.’’9,10 hemisphere first, later spreading to homolo- Since the publication of Mesulum’s original gous regions of the right.2,14 Downloaded by: University of Pennsylvania Library. Copyrighted material.

Figure 1 Illustration of stereotypical atrophy in patients with evolving SD. SD typically affects the left hemisphere first and most strongly, but eventually damage is apparent bilaterally. The ventral and inferior temporal lobes, particularly the temporal poles, are most strongly affected, although damage extends to include the lateral temporal lobes. Damage to medial temporal lobe areas is generally found to be less extensive than is observed in AD. 34 SEMINARS IN SPEECH AND LANGUAGE/VOLUME 29, NUMBER 1 2008

One common impression of SD is that Disturbed Cognitive and Linguistic medial temporal lobe (MTL) structures remain Functions intact. Behaviorally, SD patients have been Patients with SD experience an insidious onset reported to show fair recent episodic memory and gradual worsening of symptoms in the relative to a temporally graded impairment for absence of a focal neurologic insult (e.g., stroke remote events.15 For example, an SD patient or closed head injury). One of the earliest might better recall details from today’s lunch markers is a language disturbance that is char- than from his wedding day 40 years ago. In acterized by loss of word meaning that affects contrast, patients with AD may show the both production and comprehension. Patients reverse trend, characterized by an advantage commonly produce semantic paraphasias such in recall for remote over recent events. In as the word ‘‘ball’’ when the target word is AD, this characteristic pattern of forgetting ‘‘apple.’’ Patients also commonly show proso- known as anterograde amnesia has been linked pagnosia (impaired familiar face recognition) to atrophy in MTL regions such as the hippo- and associative visual agnosia (impaired visual campus and entorhinal cortex.12,16 The double object recognition). As the disease progresses, dissociation observed between AD and SD in patients commonly show reading and writing regard to episodic memory suggests greater impairments that manifest as surface dyslexia preservation of MTL structures that support and dysgraphia. the formation of new episodic memories in SD. Behavioral inference of preserved MTL was further corroborated by Mummery and Preserved Cognitive and Linguistic colleagues in a structural imaging study, Functions wherein the authors examined regional gray Regions of frontal, parietal, and occipital cortex matter atrophy in a cohort of SD patients using are often spared in SD (Fig. 1). Patients cor- voxel-based morphometry.13 The authors found respondingly present with preserved function that significant atrophy did not extend to re- in several cognitive domains, including execu- gions of the MTL such as hippocampal, ento- tive processing, personality, calculation, recent rhinal, or perirhinal cortex.13 It should be noted, episodic memory, visuospatial processing, audi- however, that other imaging studies have re- tory perception, and speech praxis.6,18–20 De- ported conflicting results. For example, Galton spite this range of preserved abilities, patients et al12 and van de Pol et al17 report volumetric develop profound difficulties negotiating their loss of the hippocampi of SD patients (left interactions with the world, and in few do- > right; AD > SD). Nevertheless, despite di- mains is this impairment more evident than in vergence in the published anatomic studies of language. SD, there is general consensus that the disease

compromises lateral temporal cortex to a greater Downloaded by: University of Pennsylvania Library. Copyrighted material. extent than MTL structures that support the THE RELATIONSHIP BETWEEN formation of new declarative memories. VISUAL AGNOSIA, APHASIA, AND SEMANTIC DEGRADATION Among healthy adults, inferior and ventral CLINICAL DIAGNOSIS OF SD portions of the temporal lobe comprise a crit- The differential diagnosis of SD can be difficult ical pathway dedicated to visual object recog- because of its overlap in presenting symptoms nition. Damage to these structures is associated with AD. However, the distinction is impor- with visual agnosia, a perceptual disorder tant because these populations require different wherein patients have difficulties accessing pharmacologic and behavioral management. In the semantic system for objects presented in a 1998, a clinical consensus meeting delineated a visual modality.21–23 Optic aphasia, a manifes- set of core and supporting features for SD.6 We tation of visual agnosia, results in confrontation paraphrase in the following these core criteria naming impairment for objects presented vis- with respect to relevant speech and language ually.21,24 In both conditions, patients are typ- processing deficits. ically able to access meaning from unimpaired EFFECTS OF SEMANTIC IMPAIRMENT IN SD/REILLY, PEELLE 35 perceptual modalities (e.g., tactile manipula- use of tools31 and gesturing the functions of tion or odor). Accordingly, it has been pro- common objects32 (but see Buxbaum et al33). posed that agnosia and aphasia represent Such cross-modality consistency is difficult to disconnection syndromes that affect modality- reconcile within a theory of impaired modality- specific access from a particular modality (e.g., specific access to an intact semantic system. visual or verbal) to the central semantic sys- Tyler, Moss, and colleagues offer a ‘‘softer’’ tem.25 visual degradation theory of SD, citing exten- SD atrophy affects anterior portions of the sive research in cortical visual processing of temporal lobe that form the terminus of the nonhuman primates.34,35 Ablation of the ven- ventral visual processing pathway as well as tromedial temporal cortex of the Macaque more ventral structures such as the fusiform impairs the animal’s ability to make fine- gyrus that are also affected in visual agnosia.26–28 grained visual distinctions.34 Tyler et al dem- The locus of this damage, therefore, suggests onstrated in functional imaging of healthy the possibility of a visual-perceptual basis for adults that an analogous area of cortex to that language difficulties in SD. However, it is also ablated in the Macaque (i.e., perirhinal cortex) apparent that SD affects left hemisphere tem- is active when naming common objects at the poral lobe structures critical for lexical process- basic category level (e.g., dog vs. cat) but not ing.9,10 This distribution of damage to both active when making domain-level judgments visual association cortex and left hemisphere (e.g., living thing or man-made object).35 Tyler language regions informed Mesulum’s influen- et al suggested that perirhinal cortex may be tial theory of PPA.9,29 Mesulum argued that critical for polymodal conjunctions of features the PPA poses a double threat to language that (leg þ torso þ head) that are fundamental for consists of associative visual agnosia (i.e., discriminating objects.36 Consistent with this matching a stored visual object description to view of fine-grained visual specificity, Tyler a concept) and aphasia. One strength of Mes- and colleagues speculate that damage to peri- ulum’s theory is that it makes an explicit, rhinal cortex may underlie deficits in patient testable prediction. Specifically, core semantic populations such as individuals with SD and knowledge is maintained in the context of herpes simplex viral encephalitis.35 Specifically, modality-specific access deficits in vision and a progressive loss of fine-grained visual specif- language. By this account, it should be possible icity should produce characteristic naming to access knowledge in an alternate modality impairments where general information about that is neither linguistically nor visually medi- object domain is retained but distinctions ated. For example, one should be able to within specific category coordinates (e.g., CAT recognize a rose by its distinctive odor or a vs. DOG) are lost. thunderstorm by its sound. On the surface, this perspective fits theo-

It is precisely this notion of a modality- ries of hierarchical semantic organization in Downloaded by: University of Pennsylvania Library. Copyrighted material. specific access impairment that theoretical op- healthy, normal adults. SD patients typically ponents have challenged. Counter to the pre- show impairment for distinguishing between diction of modality-specific theory, SD patients basic-level concepts, tending to make coordi- tend to produce consistent performance across nate and superordinate semantic naming errors representational formats and tasks (e.g., se- (e.g., ‘‘horse’’ or ‘‘animal’’ for dog).5,32,37–40 The mantic categorization of words vs. pictures, same hierarchical taxonomic loss is evident in naming, word-to-definition matching). An ex- concept definitions and in delayed picture ample of such homogeneity was demonstrated copying tasks where SD patients have been by Bozeat et al,30 who tested the ability of SD observed to assign prototypic features to a patients to identify environmental sounds. Pa- particular exemplar. For example, Bozeat et al tients were impaired on this task, showing no report the case of an SD patient who showed a significant advantage for audition over words or striking prototypicality effect in delayed picture pictures.30 Other lines of research have dem- drawing/copying—adding four legs to a picture onstrated that SD patients show increasing of a duck.41 The authors attributed this ‘‘bot- impairment in demonstrating the appropriate tom up’’ loss of specificity squarely within the 36 SEMINARS IN SPEECH AND LANGUAGE/VOLUME 29, NUMBER 1 2008

semantic system rather than isolating the effect one would expect to observe cortical activation to higher-level visual processing. Therefore, in each of the sensory domains. Importantly, although promising, Moss and Tyler’s theory this coactivation is expected to occur regardless of fine-grained visual specificity awaits further of how the concept is activated. For example, a empirical support in brain-behavior correla- word that has strong auditory associations (e.g., tions with SD patients. THUNDER) should recruit brain regions involved in auditory perception, even when read silently. The distributed/embodied approach is sup- THEORIES OF KNOWLEDGE LOSS IN ported by functional neuroimaging studies SD: WHAT DEGRADES? that demonstrate a strong link between percep- There is general consensus that SD is not a tion and conceptual representation, such as the disorder of higher-level visual perception or finding that pictures of appetizing food engage aphasia but, rather, a progressive loss of seman- gustatory cortex55 or that pictures of tools tic knowledge.42–50 The organization of such activate cortical areas dedicated to grasp in knowledge, however, remains an issue of the- premotor cortex.56,57 oretical contention. The theoretical distinc- Although fully distributed or embodied tions are valuable for a clinician to understand approaches to semantic cognition are appealing because familiarity with basic theories of se- in their parsimony, SD presents a puzzle for mantic organization is essential toward devel- such theories. SD patients with intact auditory oping intervention strategies for semantically and premotor cortex do not typically show based language disorders. If, for example, one processing advantages for concepts with highly assumes that knowledge is intact but inacces- salient features in domains such as environ- sible, strategies for language rehabilitation can mental sounds or tools.30 One way to account focus on circumventing the impaired route for such uniform degradation of knowledge is or strengthening weakened associations (see to assume that semantic memory involves a set Kiran and Bassetto,51 this issue). However, of abstract, modality-neutral representations. degraded core knowledge is not amenable to That is, the original sensory features that com- such approaches and may require more exten- pose an object are encoded in more of an sive ‘‘reconstruction’’ of large-scale semantic abstract, propositional form. Such an approach, networks. inspired in large part by SD patients’ perform- Dominant theories of semantic memory ance, has been advanced by Rogers and col- are subsumed under two general approaches. leagues, who propose that information from For brevity, we term these approaches distrib- different sensory modalities ultimately con- uted/embodied and amodal. Distributed/embod- verges with other types of affective and verbally ied theories assume that the brain decomposes mediated knowledge.14,49,58–60 The authors

objects into different features (e.g., DOG ! tail, have hypothesized that such convergence oc- Downloaded by: University of Pennsylvania Library. Copyrighted material. fur, barking, etc.) and that these constituent curs in anterior temporal cortex (i.e., the tem- features are stored in cortical regions related poral pole), the cortical region where SD to modality-specific perceptions that are patients typically show the greatest degree of also active during actual perception of the atrophy (J. Reilly et al, unpublished data, object.52–54 The coactivation of these regions 2008).12,13,61,62 is necessary for remotely evoking the original Figure 2 provides a schematic of three concept. For example, one’s concept of a dog models of semantic cognition. In a fully dis- may include visual information, auditory infor- tributed approach shown in Fig. 2A, perceptual mation, olfactory detail, and so forth. Accord- information activates regions of modality-spe- ing to distributed/embodied theories, visual cific cortex, and conceptual knowledge is the information associated with DOG would be concurrent activation of a unique combination stored in areas important for perceiving visual of these nodes. A strong amodal account, features along the ventral temporal lobe and illustrated in Fig. 2B, hypothesizes that per- auditory information near primary auditory ceptual information feeds into central semantic areas. When the concept of DOG is activated, store where semantic memory is stored. We EFFECTS OF SEMANTIC IMPAIRMENT IN SD/REILLY, PEELLE 37

Figure 2 Schematic illustrations of three models of semantic representation. (A) In a fully distributed/ embodied model, perceptual input activates modality-specific areas of cortex; this coactivation is in itself the conceptual representation. (B) In an amodal view of semantics, perceptual information activates modality-specific regions of cortex, which feed into an amodal store where the concept is represented. (C) A hybrid approach to object representation, advocated in the current article, posits that sparse

representation of a concept is stored amodally but that modality-specific regions of cortex must be Downloaded by: University of Pennsylvania Library. Copyrighted material. activated for detailed perceptual information.

have proposed a theory of semantic organiza- because it has access to the original perceptual tion that synthesizes the fully distributed and features of an object. To enrich this sparse modality-neutral approaches, shown in representation, it is necessary to index modal- Fig. 2C. We hypothesize that object concepts ity-specific regions of cortex, and this indexing are stored in lateral temporal cortex as modal- is governed by external task demands. For ity-neutral representations.50,52 We agree that example, if we ask the reader to make a relative information from different modalities (verbal size judgment of two animals presumably not knowledge, hearing, vision) converges upon a in view—‘‘Is a Labrador retriever larger than a single, unitary representation (e.g., CAT). How- poodle?’’—we expect her to access abstract ever, this representation is ‘‘sparse’’ in that it is semantic representations of ‘‘retriever’’ and stripped of its original sensory detail. It is not ‘‘poodle’’ and then recruitment of visual asso- equivalent to encyclopedic or verbal knowledge ciation cortex to aide in making a relative size 38 SEMINARS IN SPEECH AND LANGUAGE/VOLUME 29, NUMBER 1 2008

judgment. However, if asked, ‘‘Is a Labrador concrete and abstract words. Moreover, the retriever friendlier than a poodle?’’ we predict additional impairment for concrete words less recruitment of visual association cortex and sometimes seen in SD is also consistent with more activation of cortical regions dedicated to loss of visual feature knowledge stored in mo- affective knowledge (e.g., amygdala). Thus, we dality-specific regions of inferior temporal cor- hypothesize that there is dynamic interactivity tex (i.e., the ventral visual pathway). in semantic memory between modality-neutral and modality-specific components (J. Reilly et al, unpublished data).61 NAMING AND KNOWING IN SD Profound naming difficulties are a common feature of SD.6,11,14,69–71 A central question MODALITY-SPECIFIC AND concerns whether associated naming deficits MODALITY-NEUTRAL LOSS IN SD result from the loss of conceptual knowledge We believe that semantic impairment in SD (semantic anomia), lexical degradation, or an reflects compromise of two major systems: (1) inability to link phonologic word forms to abstract semantic representations stored in lat- their corresponding semantic representations eral temporal cortex; and (2) visual semantic (pure anomia). Evidence that SD reflects true feature knowledge stored in the ventral tem- semantic anomia is derived from several ele- poral pathway of visual object recognition. By gant lines of research demonstrating strong this account, as SD progresses patients would correlations between semantic knowledge and be expected to lose core concepts that support naming ability. Lambon Ralph and colleagues, language. Moreover the additional loss of visual for example, contrasted quality of the content association cortex should differentially impact of concept definitions for successfully named concepts with high visual salience. Relative wordsversuswordsforwhichpatientswere processing differences for abstract and concrete anomic.47 SD patients consistently produced words in SD provide evidence for this dual richer definitions for objects that they were component loss. able to name successfully, thus demonstrating Healthy adults typically show advantages a strong correlation between ‘‘naming’’ and for concrete words (e.g. dog) over abstract ‘‘knowing.’’ words (e.g., love). This advantage, referred to Patterson and colleagues have argued that as the word concreteness effect, is apparent across the relation between naming and knowing in many domains, including speed and accuracy of SD reflects a strong frequency-by-typicality word recognition,62 word list recall,63 age of interaction in semantic memory.19,48 That is, acquisition,64 and reading.65 Theories of se- low-frequency, atypical members of semantic mantic memory differ in their explanations of categories (e.g., penguins) are most vulnerable

the word concreteness effect, but one common to semantic degradation, whereas high-fre- Downloaded by: University of Pennsylvania Library. Copyrighted material. assumption is that the additional visual salience quency, prototypical category members (e.g., associated with concrete words facilitates their robins) prove more resilient to such loss. processing over abstract words.66 Some SD Lambon Ralph accordingly hypothesized that patients have been reported to show striking as SD progresses, this loss of bottom-up spe- reverse concreteness effects in their language proc- cificity causes category exemplars to merge into essing (i.e., advantages for abstract over con- their most frequent prototypes. For example, crete words). This controversial effect has been ‘‘cat’’ is a prototypical small animal, and SD reported in naming,67 word-to-definition patients may use the label for other small matching,68 lexical decision latencies,61 and animals. This loss of specificity ultimately com- single-word semantic judgments.20 In our promises semantic memory so that patients work, we have found that these abstract word name exemplars at a very nonspecific level advantages are relative in that both word types (e.g., producing ‘‘animal’’ or ‘‘thing’’ in place of are subject to impairment. This degree of uni- bird).14 formity is consistent with the degradation of Several SD case studies support these pre- core semantic knowledge that underlies both dictions. Hodges et al reported the longitudinal EFFECTS OF SEMANTIC IMPAIRMENT IN SD/REILLY, PEELLE 39 case of an SD patient who could successfully Using a different method of eliciting dis- name a cat and an elephant, but less than 2 years course, Ash and colleagues examined SD dis- later he called both ‘‘animal.’’38 This lack of course by asking patients to narrate a wordless specificity is also apparent in picture drawing, children’s picture book.73 This task permitted where patients are asked to reproduce a picture the investigators to examine several factors, from memory after a brief delay. SD patient including global connectedness of events, con- D.S. could accurately copy a rhinoceros when veyance of story gist, and referencing tempo- directly viewing the picture. However, the rally remote events. Not surprisingly, SD picture was removed from sight and after a patients had great difficulties narrating the 10-second delay, the patient’s reproduction was story. Output was reduced relative to age- conspicuously missing distinctive features such matched controls (SD ¼ 81 words per minute as horns and armor.48 Again, this is consistent [wpm]; controls ¼ 142 wpm), and patients with a loss of hierarchical specificity: the patient were observed to provide many nonspecific recognizes the drawing as a type of animal but references (e.g., ‘‘that thing’’). Ash et al also not as the distinct subordinate ‘‘rhinoceros.’’41 noted the predominance of nonspecific prono- minal references (e.g., ‘‘he’’ for main characters) and general superordinate terms (e.g., ‘‘animal’’ DISCOURSE PRODUCTION IN SD or ‘‘critter’’ instead of ‘‘dog’’ and ‘‘frog’’). De- One of the most striking characteristics of SD spite severe anomia, patients were able to is preserved functioning in nonsemantic do- demonstrate knowledge of global connectivity mains. Anecdotally, it is often difficult to detect across the episodes of the story, suggesting at impairment in casual conversation with an SD least some degree of preservation of story gist. patient. Individuals with SD tend to produce fluent, well-formed utterances and pepper their conversations with overlearned phrases (e.g., PHONOLOGIC PRESERVATION ‘‘Oh, I’m doing just fine.’’). Yet, closer scrutiny IN SD reveals that language content is remarkably Phonology remains a clear strength until the empty and circumlocutory. very latest stages of SD,19,74 suggesting that A handful of studies have examined the SD patients may show increasing reliance upon quality of discourse production in SD. Bird et phonology to process language as their lexical- al described both the content and form of SD semantic systems decline.75–77 This hypothesis narratives elicited through the ‘‘Cookie Theft’’ has a basis in the characteristics of speech picture description of the Boston Diagnostic perception of healthy adults, who make active Examination of Aphasia in a longitudinal case use of phonologic cues in the speech stream to study of three SD patients.40,72 Speech rate in speed the efficiency of language processing. For patients was comparable with that of age- example, word length and syllable stress pat- Downloaded by: University of Pennsylvania Library. Copyrighted material. matched controls, but patients showed signifi- terns provide listeners with probabilistic cant content differences. Consistent with the markers of grammatical class (i.e., nouns longer authors’ theory of a frequency-by-typicality than verbs, nouns hold initial syllable stress).78 interaction, SD patients produced fewer low- Similar phonologic differences may aide listen- frequency nouns (e.g., ‘‘fork’’) as a function of ers in making rapid semantic distinctions (ab- disease severity. These individuals did, how- stract words are longer and more derivationally ever, retain highly frequent closed class words complex than concrete).78,79 (e.g., ‘‘the’’) and verbs (e.g., ‘‘went’’). Bird and In a series of experiments, we examined colleagues found that the overall level of mean- such ‘‘bootstrapping effects’’ in SD. Perhaps the ingful content in SD narratives showed a linear most striking example came from a study of decline across time. Narrative was thus marked single-word semantic judgments in which we by the production of large amounts of closed varied words by both their meaning and form.20 class words (e.g., ‘‘the,’’ ‘‘this’’) and generic SD patients made forced-choice judgments of verbs (e.g., ‘‘went’’) in the context of a sweeping meaning for words that differed by length (one loss of nouns from the narrative repertoire. or three syllables), grammatical class (verb or 40 SEMINARS IN SPEECH AND LANGUAGE/VOLUME 29, NUMBER 1 2008

noun), and concreteness (abstract or con- SD is the dynamic nature of the disease. In crete).20 Patients heard each word and an- aphasia resulting from stroke, the associated swered yes/no to the question, ‘‘Can you see, language impairment is typically static or im- hear, or touch this?’’ In this task, SD patients proving, whereas SD is associated with pro- showed relative sensitivity to word form in the gressive deterioration. This fundamental context of insensitivity to the experimental difference necessitates a very different approach manipulation of word meaning. Patients often to language treatment in these populations. misclassified longer concrete words (e.g., One naı¨ve strategy is to attempt to retrain ‘‘apartment’’) as abstract and shorter abstract the structure of forgotten concepts in SD as words (e.g., ‘‘truth’’) as concrete. From this these difficulties emerge. As patients become response pattern, we concluded that SD pa- anomic for specific items, training would focus tients exercise sensitivity to a phonologically on rebuilding that particular concept. We (and mediated property of English word meaning. others) have argued that this reactive approach is inherently flawed, because while training is occurring on a recently lost concept, other READING AND WRITING IN SD concepts are concurrently being lost (J. Reilly The relative preservation of phonology in SD is et al, unpublished data; Kwok et al74). Instead, also evident in the domain of written language. we have proposed that maintenance of a care- Reading and writing difficulties are prevalent, fully structured set of core vocabulary is likely manifesting as surface dyslexia and dysgraphia to produce the best functional results for SD. in SD.80–83 These disorders are characterized Rather than reacquisition of forgotten con- by impairment in reading and spelling ortho- cepts, patients should focus on preserving a graphically irregular words, a pattern com- strongly combinatorial set of known words as monly interpreted to reflect overreliance upon the disease progresses. Jokel and colleagues grapheme-to-phoneme conversion (i.e., letter- have shown very promising results applying a by-letter reading). Thus, when words conform similar maintenance strategy to SD.86 A neces- to orthographic regularity (e.g., ‘‘cat’’), SD sary requirement of this approach is the iden- patients are often able to produce the target tification of key items early on in the disease correctly. However, in situations where lexical- process so that these concepts and their usage semantic knowledge is necessary to overcome can be reinforced. imperfect grapheme-phoneme correspondence (e.g., ‘‘yacht’’), SD patients show marked im- pairment.84,85 Surface dyslexia has thus been CONCLUSION described as ‘‘reading without semantics.’’ Our goal in this review was to describe of the profile of SD within the context of a broader

theory of semantic knowledge. We hypothesize Downloaded by: University of Pennsylvania Library. Copyrighted material. FUTURE DIRECTIONS FOR that semantic memory involves active coordi- BEHAVIORAL TREATMENT nation between modality-specific and modal- Here we have described the unique profile of ity-neutral representations and that SD likely semantic impairment associated with SD. This compromises the integrity of both components neurodegenerative disease presents an in vivo (J. Reilly et al, unpublished data). This includes model for discerning the structure and deteri- progressive degradation of abstract, modality- oration of semantic memory, and for this rea- neutral representations in lateral temporal cor- son there is great interest in this population tex, and the additional loss of modality-specific within the cognitive neuroscience community. regions of visual association cortex critical for Unfortunately, this interest has produced only the storage of visual feature knowledge. The marginal spillover toward the development of a progressive decline of lexical and semantic language intervention for this population (see knowledge in SD differentiates this disease Jokel et al86 and Snowden and Neary71 for from other forms of dementia and aphasia. noteworthy exceptions). Perhaps the most sig- We argue accordingly that there is a need for nificant challenge to developing a treatment for an etiology-specific treatment approach for this EFFECTS OF SEMANTIC IMPAIRMENT IN SD/REILLY, PEELLE 41 population. Although there is not yet an ac- 12. Galton CJ, Patterson K, Graham K, et al. cepted best practice for behavioral treatment, Differing patterns of temporal atrophy in Alz- recent developments in elucidating the organ- heimer’s disease and semantic dementia. Neurol- ization of semantic knowledge in this popula- ogy 2001;57:216–225 13. Mummery CJ, Patterson K, Price CJ, Ashburner J, tion offer encouraging targets for intervention. Frackowiak RSJ, Hodges JR. 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