- Email: [email protected]
Platform Session 2
Brain and Language 79, 21–31 (2001) doi:10.1006/brln.2001.2574, available online at http://www.idealibrary.com on
PLATFORM SESSION 2: THE LEXICON Phonological Neighborhood Effects: Evidence from Aphasia and Connectionist Modeling
Jean K. Gordon and Gary S. Dell University of Illinois at Urbana–Champaign
The processes of lexical access in aphasic speech production have been elucidated by two converging sources of evidence: spontaneously occurring speech errors, and the simulation of such errors in connectionist models. Both types of evidence have highlighted similarities between normal and disrupted lexical access. Aphasic speech errors have been found to be constrained by the same factors noted to influence normal speech errors. Connectionist modeling approaches have illustrated that aphasic patterns of errors can be produced through quantitative alterations of a model constructed to simulate normal errors (Dell, Schwartz, Martin, Saffran, & Gagnon, 1997). Recent studies have shown that lexical access in normal speech production is facilitated, not only by the frequency of occurrence of the target, but also by the number of phonological neighbours it has. Although neighborhood density has been shown to inhibit accurate word recognition (e.g., Luce & Pisoni, 1998), it appears to facilitate lexical access during normal speech production (Harley & Bown, 1998; Vitevitch, in preparation). Similar results have been shown in a preliminary analysis of aphasic speech errors (Gordon & Baum, 1999). In the current study, these results are extended to speech errors produced by a larger group of aphasic subjects in spontaneous and structured tasks, and the facilitative effects of neighborhood density are reproduced in both normal and ‘‘lesioned’’ simulations using the interactive activation lexical access model of Dell and colleagues (1997). PATIENT STUDY Methods
Thirty-six subjects with aphasia, both fluent and nonfluent, participated in the experiment. All were native English speakers with a primary diagnosis of aphasia, at least three months post-onset. Subjects performed two tasks: in the first, subjects described Normal Rockwell (NR) pictures; in the second, subjects performed the Philadelphia Naming Test (PNT). Responses were tape-recorded and transcribed, and errors were identified. Targets of the errors were examined to assess the influence of three variables—frequency of occurrence, neighborhood density, and length (number of syllables)—on accuracy of production. Results NR task. Target words containing phonological errors (error-targets) were compared to a set of targets produced accurately (control-targets), pseudo-randomly selected from the speech samples to match the error-targets on grammatical class and 21 0093-934X/01 $35.00 Copyright 2001 by Academic Press All rights of reproduction in any form reserved.
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number of syllables. The mean frequency of the error-targets was 423/million, compared to 527/million for the control-targets (t (503) ⫽ ⫺8.04, p ⬍ .001); the mean densities were 11.4 neighbors for the error-targets, and 13 neighbors for the controltargets (t (503) ⫽ ⫺4.42, p ⬍ .001). Thus, higher frequency words from denser neighborhoods were more likely to be produced correctly. Moreover, this effect cannot be attributed to word-length or grammatical class, because these variables were held constant. PNT. The accuracy rates of individual items were correlated with their neighborhood characteristics. Moderate negative correlations were found for frequency (r ⫽ ⫺0.44) and density (r ⫽ ⫺0.41), and a moderate positive correlation for length (r ⫽ 0.40), illustrating that shorter, more frequent words with more neighbours are more likely to be produced accurately. Because density is confounded with length (r ⫽ ⫺0.76 for this stimulus set), the effect of density was examined separately for one-, two-, and three-syllable targets. Accuracy was significantly enhanced by density for both two-syllable (r ⫽ 0.28) and three-syllable (r ⫽ 0.42) targets.
MODELLING STUDY The Model
The interactive spreading activation model of production (Dell et al., 1997) includes three levels—semantic, lemma, and phoneme nodes—among which activation spreads bidirectionally. Lemma access and phonological access occur in two consecutive steps, but feedback from phonological nodes serves to facilitate correct lemma access. In the present study, neighborhood density was manipulated by modifying the lexicon. In the dense neighborhood, the target (CAT) had two phonological neighbours (HAT and MAT). A sparse neighborhood was created by eliminating one neighbor, and an ‘‘empty’’ neighborhood by eliminating both. The model was run first with normal parameters, then with reduced connection weights or an increased decay rate to explore the impact of these ‘‘lesions’’ on observed neighborhood effects. Normal simulations. Although accuracy was generally very high, more errors were produced as the neighborhood became more sparse, in keeping with facilitative effects of density shown for normal subjects. As seen in Table 1, facilitation is evident in the accuracy of lemma and phoneme selection, illustrating that density operates at sublexical and lexical levels. Both can be explained by the interactive nature of the model: activation spreads from the target to its neighbors through their shared phonemes, which provide feedback to reinforce the target lemma, and also the activation of the target phonemes. Aphasic simulations. Each lesion type was simulated at three arbitrarily chosen levels of severity (Table 1). In the decay-lesioned model, facilitative effects of density were preserved at both lemma and phonological levels, except for a competitive effect of density at the lemma level for the severe lesion. In the weight-lesioned model, density exhibited opposing effects at the two levels. As density decreased, phonological accuracy decreased, indicating facilitation, but lemma accuracy increased slightly, indicating competition. Thus, facilitative effects of density on phonological access were present in all the models, but were quite small in the weight-lesioned models. This is because weight lesions reduce the interactive feedback between phonemes and words, which is the mechanism for neighborhood facilitation. The competitive effect seen at the lemma level simply shows that, when target activation is low (either due to lesion severity
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TABLE 1 Accuracy as a Function of Phonological Neighborhood Density
Normal model (p ⫽ 0.1; q ⫽ 0.5) Decay-lesioned model Mild (q ⫽ 0.8) Moderate (q ⫽ 0.9) Severe (q ⫽ 0.94) Weight-lesioned model Mild (p ⫽ 0.0085) Moderate (p ⫽ 0.0033) Severe (p ⫽ 0.0025)
Level
Dense (%)
Sparse (%)
Empty (%)
Lemma Phonol.
97.9 99.9
97.8 99.8
97.6 99.3
Lemma Phonol Lemma Phonol. Lemma Phonol.
92.0 98.3 66.6 71.7 39.6 44.8
91.5 97.2 66.0 60.9 42.2 29.5
88.8 88.8 65.0 39.1 45.8 17.1
Lemma Phonol. Lemma Phonol. Lemma Phonol.
94.6 94.8 62.5 54.0 50.8 40.5
94.8 94.8 65.6 53.4 54.5 39.5
94.9 94.7 68.7 52.9 58.5 38.8
Note. Phonological accuracy represents the proportion of correctly selected lemmas which are also correctly specified phonologically.
or reduced connection weights), neighboring lemmas can be mistakenly selected; the larger the neighborhood, the greater the opportunity for such errors.
DISCUSSION
The convergent findings of facilitative neighborhood density effects in both naturally occurring and simulated errors provides support for the interactive activation model of lexical access in speech production and its theory of lexical access deficits in aphasia (Dell et al., 1997). The mechanism of the effect is further clarified by the combined, and sometimes antagonistic, effects at lemma and phoneme levels. These findings make predictions, to be investigated in future studies, about the influence that neighborhood density might exert on different types of errors and on error patterns exhibited in different types of aphasic deficits.
REFERENCES Dell, G. S., Schwartz, M. F., Martin, N., Saffran, E. M., & Gagnon, D. A. (1997). Lexical access in aphasic and nonaphasic speakers. Psychological Review, 104(4), 801–838. Gordon, J. K., & Baum, S. R. (1999). The role of the phonological neighbourhood in aphasic speech errors. Poster presented at the Academy of Aphasia, Venice, Italy. Harley, T. A., & Bown, H. E. (1998). What causes a tip-of-the-tongue state? Evidence for lexical neighbourhood effects in speech production. British Journal of Psychology, 89, 151–174. Luce, P. A., & Pisoni, D. B. (1998). Recognizing spoken words: The Neighborhood Activation Model. Ear & Hearing, 1–36. Vitevitch, M. S. (in preparation). The influence of phonological similarity neighbourhoods on speech production.
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Processing of Verb–Argument Structure and Subcategorization Information in Brain-Damaged Patients: Event-Related Potential Evidence
Sonja A. Kotz,* Stefan Frisch,† and Angela D. Friederici* *Max-Planck-Institute of Cognitive Neuroscience; †University of Potsdam
Introduction The processing of verbs is characterized by the fact that verbs can (or must) take complements. These complements are semantically as well as syntactically specified in the lexical entry of each verb. Semantically speaking, a verb such as ‘‘besuchen’’ (to visit) expresses an event which has two participants, one doing the visiting (agent) and one who is visited (patient). Syntactically speaking, the verb ‘‘besuchen’’ needs two expressions as complements in order to form a grammatical sentence, namely two noun phrases (e.g., ‘‘Der Junge besucht den Mann’’/The boy visits the man). ERP recordings of verb argument violations (e.g., ‘‘Der Junge grinst den Mann’’/ The boy grins the man) elicit a biphasic event-related potential (ERP) pattern, namely a negativity (resembling an N400 component) and a positivity (P600) (e.g., Frisch, 2000; Friederici and Frisch, 2000). This pattern suggests that violations of this type involve semantic as well as syntactic processing. Processing of verb complements also play a central as well as a controversial role in the discussion of agrammatism (e.g., Grodzinsky, 2000; Friederici & Gorrell 1998; Frisch, Saddy, & Friederici, 2000). It is assumed that Broca’s aphasics detect argument structure violations (e.g., complements), but their detection may rely on semantic aspects inherent to an argument structure violation. On the other hand, Wernicke’s aphasics seem not to be able to detect an argument structure violation possibly due to missing the semantic aspect of the verb argument structure. We therefore set out to test verb argument violations in patients with anterior (including Broca’s area) and temporo-parietal lesions measuring ERPs. Subjects A group of 7 patients (3 female) with left anterior lesions (including Broca’s) area and a mean age of 43.50 years and 6 patients with left temporo-parietal lesions (2 female) and a mean age of 52.33 years were tested in the experiment. In addition, a respective age- and gender-matched control group was tested. None of the control subjects had a history of physical or neurological disease. The mean age of the left anterior control group was 43.50 years and for the left temporo-parietal control group was 52.33 years. All subjects gave informed written consent to participate in the study. Methods Event-related brain potentials were recorded from 21 electrode-sites placed according to the International 10–20 system and referenced to the left mastoid while all patients and controls listened to 160 auditorily presented sentences. There were two critical sentence conditions: correct sentences (Im Institut wurde viel gesteikt und kritisiert./In the institute was a lot of striking and criticizing. [literal translation]) and incorrect sentences based on number of argument violations (Das Insitut wurde viel gestreikt und kritisiert./The institute was striked and criticized [literal translation]). There were also filler conditions to balance the experimental design.
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Results/Discussion Preliminary results indicate that the biphasic pattern of a negativity followed by a positivity in the ERP is modulated as a function of lesion site. While patients with anterior lesions display a negativity, but no positivity, patients with temporo-parietal lesions show the reversed picture. Age- and gender matched controls showed the expected biphasic pattern of an N400 followed by a P600. However, the N400 in the temporo-parietal control group was reduced. This reduced effect can be related to a typical aging effect that modulates the amplitude and/or the latency of the N400. Functionally speaking, the current results provide evidence for differential sensitivities towards the semantic and syntactic aspects of verb-argument structure processing in the two groups of aphasic patients as reflected in the ERP. REFERENCES Friederici, A. D., and Gorrell, P. (1998). Structural prominence and agrammatic theta-role assignment: A reconsideration of linear strategies. Brain and Language, 65, 253–275. Friederici, A. D., and Frisch, S. (2000). Verb-argument structure processing: The role of verb-specific and argument-specific information. Journal of Memory and Language, 43, 476–507. Frisch, S. (2000). Verb-Argument-Struktur, Kasus und thematische Interpretation beim Sprachverstehen. Unpublished dissertation, MPI Series, Leipzig, Germany. Frisch, S., Saddy, D., and Friederici, A. D. (2000). Cutting a long story (too) short, Behavioral and Brain Sciences, 23, 34–35. Grodzinsky, Y. (2000). The neurology of syntax: Language use without Broca’s area. Behavioral and Brain Sciences, 23, 01–71.
Effects of Lexical Competition and Phonetic Degradation on Lexical Processing in Aphasia
Cara Misiurski,* Daniel Berman,* Jesse Rissman,* and Sheila E. Blumstein*,† *Brown University; and †VA Medical Center, Boston
Introduction We have proposed that Broca’s and Wernicke’s aphasics have deficits in the dynamics of lexical activation. This interpretation is based on a series of studies showing ‘‘pathological’’ patterns of semantic priming in the presence of lexical competition. In particular, both normal subjects and Broca’s aphasics showed a reduction in the magnitude of semantic priming for dog when the semantically related prime stimulus cat contained a poor exemplar of [k] that was closer to the voiced phonetic category boundary. In this case, despite the manipulation of the initial voiceless stop [k], there is no voiced lexical competitor (i.e., gat is not a word). However, under similar conditions of phonetic degradation, Broca’s aphasics failed to show any priming when the prime stimulus had a real word voiced competitor (i.e., t*ime, with the voiced lexical competitor, dime, failed to prime clock). In contrast to both normal subjects and Broca’s aphasics, Wernicke’s aphasics showed a similar magnitude of priming irrespective of phonetic manipulation or lexical competition. Our explanation for the competitor effects that emerged in the aphasic patients rests on the assumption that a poor exemplar of a stimulus word will partially activate not only its lexical representation but also its voiced lexical competitor (cf. also Connine et al., 1994). If this is true, then an acoustically modified t*ime should partially
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activate dime, and hence t*ime should prime penny. Results in our lab with normal subjects have demonstrated this mediated priming effect. Given our hypotheses concerning the dynamics of lexical activation, Broca’s aphasics should show priming for penny when it is preceded by the semantically related prime stimulus dime, but fail to show priming when it is preceded by t*ime. In contrast, Wernicke’s aphasics should show a similar magnitude of semantic priming for penny whether it is preceded by dime or t*ime.
Participants Nine Broca’s aphasics, 6 Wernicke’s aphasics, and 16 young normal adults served as subjects. All participants were right-handed, native English speakers with no known hearing impairments.
Method Test stimuli consisted of 21 real word targets preceded by real words in three priming conditions. In the first condition, the prime was semantically related to the target and began with a voiced stop consonant, e.g., dime-penny. In the second condition, the prime was a voiceless competitor to the voiced prime in the first condition, and its initial voice-onset time was reduced by 2/3, e.g. acoustically modified t*imepenny (cf. Andruski et al., 1994). In the third condition, the real word prime was both phonologically and semantically unrelated to the target, e.g. nose-penny. A set of 21 nonword targets, also preceded by real word ‘primes’, was created in an analogous fashion. In order to explore the time course of the priming effects, the stimulus pairs in the lexical decision task were presented in two ISI conditions: 50 ms and 250 ms. The intertrial interval was 3 s. A discrimination task was administered as a posttest to ensure that the acoustically modified prime stimuli were still perceived as the same word as the unmodified stimuli. That is, acoustically modified t*ime should be perceived as time and not dime. Subjects were instructed to determine whether the two words were the same or not by pressing the appropriate key on a response board.
Results Only the reaction time scores for correct responses to real word targets were used in the data analysis. All subjects, whether aphasic or normal, were significantly faster at responding to the real word target when it was semantically related to the prime than when it was unrelated. The interesting differences between the three subject groups were in the magnitude of priming elicited by acoustically modified competitors of these semantically related primes. In both ISI conditions, normal controls showed significant RT facilitation for targets preceded by modified primes, but the magnitude of this priming effect was significantly less than that produced by related primes. Unlike normals, Broca’s aphasics did not show significant priming in the modified condition at either of the two ISIs. Wernicke’s aphasics, while showing no significant priming in any condition for stimuli presented at the 50 ms ISI, showed significant RT facilitation for both related and modified primes at the 250 ms ISI. Moreover, their RT means for these two conditions were not found to be significantly different from each other. Results from the discrimination post-test confirmed that for all subject groups, the acoustically modified prime stimuli were perceived as voiceless, i.e., t*ime was perceived as time.
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Discussion These results are consistent with our hypothesis that the neuropathological changes that characterize Broca’s and Wernicke’s aphasia affect the processing mechanisms underlying lexical activation. We have demonstrated that normal subjects show reduced, but significant, RT facilitation when presented with a prime stimulus that is not itself semantically related to the target, but is a phonetically degraded lexical competitor of a semantically related prime. The failure of Broca’s aphasics to show any priming for targets preceded by such primes suggests that these degraded primes may not be activating lexical candidates enough to reach the threshold necessary for semantic facilitation. In contrast to Broca’s aphasics, Wernicke’s aphasics did show significant priming in the modified condition. However, unlike normals, the magnitude of this priming effect was statistically equal to that elicited by standard related primes. These findings add support to our proposal that Wernicke’s aphasics may have an overactivated lexicon, possibly due to decreased lexical activation thresholds, while Broca’s aphasics may have a generalized reduction of lexical activation levels. REFERENCES Andruski, J., Blumstein, S. E., & Burton, M. (1994). The effects of subphonetic differences on lexical access. Cognition, 43, 336–348. Connine, C. M., Blasko, D. G., & Wang, J. (1994). Vertical similarity in spoken word recognition: multiple lexical activation, individual differences, and the role of sentence context. Perception & Psychophysics, 56, 624–636.
Typicality of Category Exemplars in Aphasia: Evidence from Reaction Time and Treatment Data
Swathi Kiran and Cynthia K. Thompson Northwestern University
Numerous studies have shown that representation of and access to semantic categories are influenced by the typicality of category exemplars in normal subjects. Typical exemplars (e.g., robin, sparrow) represented close to the center of the semantic category and having similar features to one another and the category prototype, yield faster reaction times as compared to atypical examples (e.g., penguin, ostrich) which are at the periphery of the category boundary and have fewer features in common (e.g., Rosch & Mervis, 1975). Little evidence, however, exists regarding typicality in individuals with aphasia (Grossman, 1981), the interpretation of these deficits with reference to theoretical models of typicality, or the applicability of typicality of category exemplars to treatment of naming deficits. Two experiments were conducted to investigate the nature of category typicality in patients with aphasia. In the first experiment, an online category verification task was performed with aphasic and normal individuals. In the second experiment, four fluent aphasic patients were trained on either typical or atypical examples of selected categories while generalization to untrained examples of the category was examined. Experiment 1
Methods Normal young (N ⫽ 9), elderly (N ⫽ 9), Broca’s (N ⫽ 7) and Wernicke’s aphasic (N ⫽ 7) individuals participated in an online category verification task. Primes were
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superordinate labels of three categories (bird, vegetable, fish) while targets were typical and atypical examples of the categories and nonmembers. Norms for typicality of category exemplars were developed prior to initiation of the experiment. Participants viewed written words presented on a computer screen and judged whether each example belonged to the preceding superordinate category.
Results Wernicke’s aphasic patients made the greatest number of errors on the task (22.1%). In comparison, Broca’s aphasic patients (8.67%), young (4.2%) and elderly groups (2.7%) made fewer errors. Separate analyses were performed for each participant group using a 3 ⫻ 3 (typicality ⫻ category) repeated measures ANOVA performed on item mean reaction times. Only results for typicality are discussed here. A significant main effect for typicality was noted in three of the four groups: young (F(2, 170) ⫽ 14.64, MS e ⫽ .4158, p ⬍. 001), elderly (F(2, 170) ⫽ 8.47, MS e ⫽ .4005, p ⬍ .001) and Broca’s aphasic patients (F(2, 170) ⫽ 20.924, MS e ⫽ 4.84, p ⬍ .001). For all three groups reaction times for typical examples and nonmembers were faster than atypical examples ( p ⬍ .01, p ⬍ .01), supporting previous studies on normal individuals. No significant main effect for typicality was observed for Wernicke’s aphasic patients.
Discussion Results of Experiment 1 demonstrated that Wernicke’s aphasic patients have impaired category representations as evinced by the greater numbers of errors on this task. Second, the lack of a significant typicality effect for Wernicke’s aphasic patients suggests that representation of categories in terms of category prototypes is diminished in these patients. We hypothesize that access of exemplar semantic features is impaired in this population, thus providing justification for the second experiment.
Experiment 2
In the second experiment, four Wernicke’s aphasic individuals from the previous experiment received a semantic feature treatment to improve naming of either typical or atypical examples, while generalization was tested on the untrained examples of the category. Based on a connectionist simulation by Plaut (1996), we hypothesized that training aphasic individuals to produce atypical examples from a category would result in generalization to typical examples of the category. Training typical examples was predicted to result in no improvements in atypical examples.
Methods The four participants, aged 63–75 years presented with severe naming deficits. Based on standardized language testing, the locus of naming deficit was attributable to impairments in accessing the semantic representation of the target, and/or in accessing its phonological form. Based on prior norms developed, examples for two categories (bird, vegetable) were divided into three groups, typical, intermediate and atypical. The two categories consisted of 24 examples each (N ⫽ 8 for each typicality group) that were matched for frequency, number of syllables and distinctiveness.
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Design and Treatment A single subject experimental design with multiple baselines across behaviors and participants was employed. Prior to application of treatment, naming of all 24 examples for each category was tested during baseline. Confrontation naming was then trained using selected examples of one superordinate category, with the order of categories and exemplar typicality counterbalanced across participants. For each participant, all eight examples in the subset (e.g., atypical) of the category were trained simultaneously. Treatment steps for each item included: (1) naming the picture, (2) sorting pictures of the target category with distracters, (3) identifying semantic attributes for the target example and, (4) answering yes/no questions regarding semantic features of the target example. Results Participant 1 received treatment for typical examples of birds, while participant 3 received treatment on typical examples of vegetables. Both participants demonstrated improvements on the trained typical examples to criterion (85% naming accuracy on two consecutive sessions), while no improvements were observed on the untrained intermediate and atypical examples. Treatment was then shifted to intermediate examples, following which improvements were observed on those items. When treatment was finally shifted to atypical examples improvements were noted on those examples (see Fig.1). Participant 2 received treatment for atypical examples of birds, while participant 4 received treatment on atypical example of vegetables. Improvements were noted for both participants on the trained atypical items while generalization to naming of intermediate and typical items was also noted (see Fig. 1). Treatment was then shifted to the second category for each participant (P2: vegetables, P4: birds). Once again, naming of the trained atypical examples improved, while generalization was observed to the untrained intermediate and typical examples (not illustrated). Discussion Results of this experiment showed that training atypical examples of a category and their semantic features resulted in generalization to naming of intermediate and typical examples of the category. Training typical examples and their semantic features, however, did not result in generalization to the intermediate and atypical examples. It is hypothesized that since atypical examples are dissimilar to one another and to the category prototype, they collectively convey more information about the variation of semantic features that can occur within the category than do typical examples. Therefore, training features of atypical examples facilitate access to those of typical examples, resulting in improved activation and naming. While current models of typicality explain possible differences in the representation of typical and atypical examples, in that categories are either represented by a set of features that may carry more or less weight compared to the prototype (Hampton, 1979) or as specific instances that have been previously encountered (Heit & Barsalou, 1996), these models do not explain the results of the present treatment. Instead, an interactive activation based model is proposed in which the connections between semantic and phonological representations are excitatory. At the semantic level, each example of a category is a summary representation of weighted semantic features. Due to their similarity with the category prototype, typical items exert greater lateral inhibition on other examples within the category whereas atypical ex-
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FIG. 1. Percent naming accuracy on typical, intermediate, and atypical examples for Participant 1 (P1) and Participant 3 (P3) who received treatment on typical examples and for Participant 2 (P2) and Participant 4 (P4) who received treatment for atypical examples.
amples exert less lateral inhibition. Training atypical examples improves access to atypical examples while not changing the amount of lateral inhibition exerted on intermediate and typical examples, and thus, naming of these examples are also facilitated following treatment. In contrast, training typical examples improves access to typical examples while increasing the amount of lateral inhibition exerted on interme-
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diate and atypical examples, therefore, no improvements in naming of these items are observed. Results of both experiments reported here provide insights into the representations of typicality in fluent aphasia. Although counter-intuitive to traditional treatment approaches, these results suggest that training naming of atypical examples is a more efficient method of improving naming of items within a category than training typical items. These data support the notion advanced by Thompson et al. (1997) that training more complex items which encompass variables relevant to simpler items enhance generalization. REFERENCES Grossman, M. (1981). A bird is a bird: Making references within and without superordinate categories. Brain and Language, 12,313–331. Hampton, J. A. (1979). Polymorphous concepts in semantic memory. Journal of Verbal Learning and Verbal Behavior, 18, 441–461. Heit, E., & Barsalou, L. (1996). The instantiation principle in natural language categories. Memory, 4, 413–451. Plaut, D. C. (1996). Relearning after damage in connectionists networks: Toward a theory of rehabilitation. Brain and Language, 52, 25–82. Rosch, E., & Mervis, C. (1975). Family resemblances: Studies in internal structure of categories. Cognitive Psychology, 7, 573–604. Thompson, C. K., Shapiro, L. P. Ballard, K. J., Jacobs, B., Schnieder, S. L., & Tait, M. (1997). Training and generalized production of wh and NP movement structures in agrammatic aphasia. Journal of Speech and Hearing Research, 40, 228–244.
PLATFORM SESSION 2: THE LEXICON Phonological Neighborhood Effects: Evidence from Aphasia and Connectionist Modeling
Jean K. Gordon and Gary S. Dell University of Illinois at Urbana–Champaign
The processes of lexical access in aphasic speech production have been elucidated by two converging sources of evidence: spontaneously occurring speech errors, and the simulation of such errors in connectionist models. Both types of evidence have highlighted similarities between normal and disrupted lexical access. Aphasic speech errors have been found to be constrained by the same factors noted to influence normal speech errors. Connectionist modeling approaches have illustrated that aphasic patterns of errors can be produced through quantitative alterations of a model constructed to simulate normal errors (Dell, Schwartz, Martin, Saffran, & Gagnon, 1997). Recent studies have shown that lexical access in normal speech production is facilitated, not only by the frequency of occurrence of the target, but also by the number of phonological neighbours it has. Although neighborhood density has been shown to inhibit accurate word recognition (e.g., Luce & Pisoni, 1998), it appears to facilitate lexical access during normal speech production (Harley & Bown, 1998; Vitevitch, in preparation). Similar results have been shown in a preliminary analysis of aphasic speech errors (Gordon & Baum, 1999). In the current study, these results are extended to speech errors produced by a larger group of aphasic subjects in spontaneous and structured tasks, and the facilitative effects of neighborhood density are reproduced in both normal and ‘‘lesioned’’ simulations using the interactive activation lexical access model of Dell and colleagues (1997). PATIENT STUDY Methods
Thirty-six subjects with aphasia, both fluent and nonfluent, participated in the experiment. All were native English speakers with a primary diagnosis of aphasia, at least three months post-onset. Subjects performed two tasks: in the first, subjects described Normal Rockwell (NR) pictures; in the second, subjects performed the Philadelphia Naming Test (PNT). Responses were tape-recorded and transcribed, and errors were identified. Targets of the errors were examined to assess the influence of three variables—frequency of occurrence, neighborhood density, and length (number of syllables)—on accuracy of production. Results NR task. Target words containing phonological errors (error-targets) were compared to a set of targets produced accurately (control-targets), pseudo-randomly selected from the speech samples to match the error-targets on grammatical class and 21 0093-934X/01 $35.00 Copyright 2001 by Academic Press All rights of reproduction in any form reserved.
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number of syllables. The mean frequency of the error-targets was 423/million, compared to 527/million for the control-targets (t (503) ⫽ ⫺8.04, p ⬍ .001); the mean densities were 11.4 neighbors for the error-targets, and 13 neighbors for the controltargets (t (503) ⫽ ⫺4.42, p ⬍ .001). Thus, higher frequency words from denser neighborhoods were more likely to be produced correctly. Moreover, this effect cannot be attributed to word-length or grammatical class, because these variables were held constant. PNT. The accuracy rates of individual items were correlated with their neighborhood characteristics. Moderate negative correlations were found for frequency (r ⫽ ⫺0.44) and density (r ⫽ ⫺0.41), and a moderate positive correlation for length (r ⫽ 0.40), illustrating that shorter, more frequent words with more neighbours are more likely to be produced accurately. Because density is confounded with length (r ⫽ ⫺0.76 for this stimulus set), the effect of density was examined separately for one-, two-, and three-syllable targets. Accuracy was significantly enhanced by density for both two-syllable (r ⫽ 0.28) and three-syllable (r ⫽ 0.42) targets.
MODELLING STUDY The Model
The interactive spreading activation model of production (Dell et al., 1997) includes three levels—semantic, lemma, and phoneme nodes—among which activation spreads bidirectionally. Lemma access and phonological access occur in two consecutive steps, but feedback from phonological nodes serves to facilitate correct lemma access. In the present study, neighborhood density was manipulated by modifying the lexicon. In the dense neighborhood, the target (CAT) had two phonological neighbours (HAT and MAT). A sparse neighborhood was created by eliminating one neighbor, and an ‘‘empty’’ neighborhood by eliminating both. The model was run first with normal parameters, then with reduced connection weights or an increased decay rate to explore the impact of these ‘‘lesions’’ on observed neighborhood effects. Normal simulations. Although accuracy was generally very high, more errors were produced as the neighborhood became more sparse, in keeping with facilitative effects of density shown for normal subjects. As seen in Table 1, facilitation is evident in the accuracy of lemma and phoneme selection, illustrating that density operates at sublexical and lexical levels. Both can be explained by the interactive nature of the model: activation spreads from the target to its neighbors through their shared phonemes, which provide feedback to reinforce the target lemma, and also the activation of the target phonemes. Aphasic simulations. Each lesion type was simulated at three arbitrarily chosen levels of severity (Table 1). In the decay-lesioned model, facilitative effects of density were preserved at both lemma and phonological levels, except for a competitive effect of density at the lemma level for the severe lesion. In the weight-lesioned model, density exhibited opposing effects at the two levels. As density decreased, phonological accuracy decreased, indicating facilitation, but lemma accuracy increased slightly, indicating competition. Thus, facilitative effects of density on phonological access were present in all the models, but were quite small in the weight-lesioned models. This is because weight lesions reduce the interactive feedback between phonemes and words, which is the mechanism for neighborhood facilitation. The competitive effect seen at the lemma level simply shows that, when target activation is low (either due to lesion severity
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TABLE 1 Accuracy as a Function of Phonological Neighborhood Density
Normal model (p ⫽ 0.1; q ⫽ 0.5) Decay-lesioned model Mild (q ⫽ 0.8) Moderate (q ⫽ 0.9) Severe (q ⫽ 0.94) Weight-lesioned model Mild (p ⫽ 0.0085) Moderate (p ⫽ 0.0033) Severe (p ⫽ 0.0025)
Level
Dense (%)
Sparse (%)
Empty (%)
Lemma Phonol.
97.9 99.9
97.8 99.8
97.6 99.3
Lemma Phonol Lemma Phonol. Lemma Phonol.
92.0 98.3 66.6 71.7 39.6 44.8
91.5 97.2 66.0 60.9 42.2 29.5
88.8 88.8 65.0 39.1 45.8 17.1
Lemma Phonol. Lemma Phonol. Lemma Phonol.
94.6 94.8 62.5 54.0 50.8 40.5
94.8 94.8 65.6 53.4 54.5 39.5
94.9 94.7 68.7 52.9 58.5 38.8
Note. Phonological accuracy represents the proportion of correctly selected lemmas which are also correctly specified phonologically.
or reduced connection weights), neighboring lemmas can be mistakenly selected; the larger the neighborhood, the greater the opportunity for such errors.
DISCUSSION
The convergent findings of facilitative neighborhood density effects in both naturally occurring and simulated errors provides support for the interactive activation model of lexical access in speech production and its theory of lexical access deficits in aphasia (Dell et al., 1997). The mechanism of the effect is further clarified by the combined, and sometimes antagonistic, effects at lemma and phoneme levels. These findings make predictions, to be investigated in future studies, about the influence that neighborhood density might exert on different types of errors and on error patterns exhibited in different types of aphasic deficits.
REFERENCES Dell, G. S., Schwartz, M. F., Martin, N., Saffran, E. M., & Gagnon, D. A. (1997). Lexical access in aphasic and nonaphasic speakers. Psychological Review, 104(4), 801–838. Gordon, J. K., & Baum, S. R. (1999). The role of the phonological neighbourhood in aphasic speech errors. Poster presented at the Academy of Aphasia, Venice, Italy. Harley, T. A., & Bown, H. E. (1998). What causes a tip-of-the-tongue state? Evidence for lexical neighbourhood effects in speech production. British Journal of Psychology, 89, 151–174. Luce, P. A., & Pisoni, D. B. (1998). Recognizing spoken words: The Neighborhood Activation Model. Ear & Hearing, 1–36. Vitevitch, M. S. (in preparation). The influence of phonological similarity neighbourhoods on speech production.
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Processing of Verb–Argument Structure and Subcategorization Information in Brain-Damaged Patients: Event-Related Potential Evidence
Sonja A. Kotz,* Stefan Frisch,† and Angela D. Friederici* *Max-Planck-Institute of Cognitive Neuroscience; †University of Potsdam
Introduction The processing of verbs is characterized by the fact that verbs can (or must) take complements. These complements are semantically as well as syntactically specified in the lexical entry of each verb. Semantically speaking, a verb such as ‘‘besuchen’’ (to visit) expresses an event which has two participants, one doing the visiting (agent) and one who is visited (patient). Syntactically speaking, the verb ‘‘besuchen’’ needs two expressions as complements in order to form a grammatical sentence, namely two noun phrases (e.g., ‘‘Der Junge besucht den Mann’’/The boy visits the man). ERP recordings of verb argument violations (e.g., ‘‘Der Junge grinst den Mann’’/ The boy grins the man) elicit a biphasic event-related potential (ERP) pattern, namely a negativity (resembling an N400 component) and a positivity (P600) (e.g., Frisch, 2000; Friederici and Frisch, 2000). This pattern suggests that violations of this type involve semantic as well as syntactic processing. Processing of verb complements also play a central as well as a controversial role in the discussion of agrammatism (e.g., Grodzinsky, 2000; Friederici & Gorrell 1998; Frisch, Saddy, & Friederici, 2000). It is assumed that Broca’s aphasics detect argument structure violations (e.g., complements), but their detection may rely on semantic aspects inherent to an argument structure violation. On the other hand, Wernicke’s aphasics seem not to be able to detect an argument structure violation possibly due to missing the semantic aspect of the verb argument structure. We therefore set out to test verb argument violations in patients with anterior (including Broca’s area) and temporo-parietal lesions measuring ERPs. Subjects A group of 7 patients (3 female) with left anterior lesions (including Broca’s) area and a mean age of 43.50 years and 6 patients with left temporo-parietal lesions (2 female) and a mean age of 52.33 years were tested in the experiment. In addition, a respective age- and gender-matched control group was tested. None of the control subjects had a history of physical or neurological disease. The mean age of the left anterior control group was 43.50 years and for the left temporo-parietal control group was 52.33 years. All subjects gave informed written consent to participate in the study. Methods Event-related brain potentials were recorded from 21 electrode-sites placed according to the International 10–20 system and referenced to the left mastoid while all patients and controls listened to 160 auditorily presented sentences. There were two critical sentence conditions: correct sentences (Im Institut wurde viel gesteikt und kritisiert./In the institute was a lot of striking and criticizing. [literal translation]) and incorrect sentences based on number of argument violations (Das Insitut wurde viel gestreikt und kritisiert./The institute was striked and criticized [literal translation]). There were also filler conditions to balance the experimental design.
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Results/Discussion Preliminary results indicate that the biphasic pattern of a negativity followed by a positivity in the ERP is modulated as a function of lesion site. While patients with anterior lesions display a negativity, but no positivity, patients with temporo-parietal lesions show the reversed picture. Age- and gender matched controls showed the expected biphasic pattern of an N400 followed by a P600. However, the N400 in the temporo-parietal control group was reduced. This reduced effect can be related to a typical aging effect that modulates the amplitude and/or the latency of the N400. Functionally speaking, the current results provide evidence for differential sensitivities towards the semantic and syntactic aspects of verb-argument structure processing in the two groups of aphasic patients as reflected in the ERP. REFERENCES Friederici, A. D., and Gorrell, P. (1998). Structural prominence and agrammatic theta-role assignment: A reconsideration of linear strategies. Brain and Language, 65, 253–275. Friederici, A. D., and Frisch, S. (2000). Verb-argument structure processing: The role of verb-specific and argument-specific information. Journal of Memory and Language, 43, 476–507. Frisch, S. (2000). Verb-Argument-Struktur, Kasus und thematische Interpretation beim Sprachverstehen. Unpublished dissertation, MPI Series, Leipzig, Germany. Frisch, S., Saddy, D., and Friederici, A. D. (2000). Cutting a long story (too) short, Behavioral and Brain Sciences, 23, 34–35. Grodzinsky, Y. (2000). The neurology of syntax: Language use without Broca’s area. Behavioral and Brain Sciences, 23, 01–71.
Effects of Lexical Competition and Phonetic Degradation on Lexical Processing in Aphasia
Cara Misiurski,* Daniel Berman,* Jesse Rissman,* and Sheila E. Blumstein*,† *Brown University; and †VA Medical Center, Boston
Introduction We have proposed that Broca’s and Wernicke’s aphasics have deficits in the dynamics of lexical activation. This interpretation is based on a series of studies showing ‘‘pathological’’ patterns of semantic priming in the presence of lexical competition. In particular, both normal subjects and Broca’s aphasics showed a reduction in the magnitude of semantic priming for dog when the semantically related prime stimulus cat contained a poor exemplar of [k] that was closer to the voiced phonetic category boundary. In this case, despite the manipulation of the initial voiceless stop [k], there is no voiced lexical competitor (i.e., gat is not a word). However, under similar conditions of phonetic degradation, Broca’s aphasics failed to show any priming when the prime stimulus had a real word voiced competitor (i.e., t*ime, with the voiced lexical competitor, dime, failed to prime clock). In contrast to both normal subjects and Broca’s aphasics, Wernicke’s aphasics showed a similar magnitude of priming irrespective of phonetic manipulation or lexical competition. Our explanation for the competitor effects that emerged in the aphasic patients rests on the assumption that a poor exemplar of a stimulus word will partially activate not only its lexical representation but also its voiced lexical competitor (cf. also Connine et al., 1994). If this is true, then an acoustically modified t*ime should partially
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activate dime, and hence t*ime should prime penny. Results in our lab with normal subjects have demonstrated this mediated priming effect. Given our hypotheses concerning the dynamics of lexical activation, Broca’s aphasics should show priming for penny when it is preceded by the semantically related prime stimulus dime, but fail to show priming when it is preceded by t*ime. In contrast, Wernicke’s aphasics should show a similar magnitude of semantic priming for penny whether it is preceded by dime or t*ime.
Participants Nine Broca’s aphasics, 6 Wernicke’s aphasics, and 16 young normal adults served as subjects. All participants were right-handed, native English speakers with no known hearing impairments.
Method Test stimuli consisted of 21 real word targets preceded by real words in three priming conditions. In the first condition, the prime was semantically related to the target and began with a voiced stop consonant, e.g., dime-penny. In the second condition, the prime was a voiceless competitor to the voiced prime in the first condition, and its initial voice-onset time was reduced by 2/3, e.g. acoustically modified t*imepenny (cf. Andruski et al., 1994). In the third condition, the real word prime was both phonologically and semantically unrelated to the target, e.g. nose-penny. A set of 21 nonword targets, also preceded by real word ‘primes’, was created in an analogous fashion. In order to explore the time course of the priming effects, the stimulus pairs in the lexical decision task were presented in two ISI conditions: 50 ms and 250 ms. The intertrial interval was 3 s. A discrimination task was administered as a posttest to ensure that the acoustically modified prime stimuli were still perceived as the same word as the unmodified stimuli. That is, acoustically modified t*ime should be perceived as time and not dime. Subjects were instructed to determine whether the two words were the same or not by pressing the appropriate key on a response board.
Results Only the reaction time scores for correct responses to real word targets were used in the data analysis. All subjects, whether aphasic or normal, were significantly faster at responding to the real word target when it was semantically related to the prime than when it was unrelated. The interesting differences between the three subject groups were in the magnitude of priming elicited by acoustically modified competitors of these semantically related primes. In both ISI conditions, normal controls showed significant RT facilitation for targets preceded by modified primes, but the magnitude of this priming effect was significantly less than that produced by related primes. Unlike normals, Broca’s aphasics did not show significant priming in the modified condition at either of the two ISIs. Wernicke’s aphasics, while showing no significant priming in any condition for stimuli presented at the 50 ms ISI, showed significant RT facilitation for both related and modified primes at the 250 ms ISI. Moreover, their RT means for these two conditions were not found to be significantly different from each other. Results from the discrimination post-test confirmed that for all subject groups, the acoustically modified prime stimuli were perceived as voiceless, i.e., t*ime was perceived as time.
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Discussion These results are consistent with our hypothesis that the neuropathological changes that characterize Broca’s and Wernicke’s aphasia affect the processing mechanisms underlying lexical activation. We have demonstrated that normal subjects show reduced, but significant, RT facilitation when presented with a prime stimulus that is not itself semantically related to the target, but is a phonetically degraded lexical competitor of a semantically related prime. The failure of Broca’s aphasics to show any priming for targets preceded by such primes suggests that these degraded primes may not be activating lexical candidates enough to reach the threshold necessary for semantic facilitation. In contrast to Broca’s aphasics, Wernicke’s aphasics did show significant priming in the modified condition. However, unlike normals, the magnitude of this priming effect was statistically equal to that elicited by standard related primes. These findings add support to our proposal that Wernicke’s aphasics may have an overactivated lexicon, possibly due to decreased lexical activation thresholds, while Broca’s aphasics may have a generalized reduction of lexical activation levels. REFERENCES Andruski, J., Blumstein, S. E., & Burton, M. (1994). The effects of subphonetic differences on lexical access. Cognition, 43, 336–348. Connine, C. M., Blasko, D. G., & Wang, J. (1994). Vertical similarity in spoken word recognition: multiple lexical activation, individual differences, and the role of sentence context. Perception & Psychophysics, 56, 624–636.
Typicality of Category Exemplars in Aphasia: Evidence from Reaction Time and Treatment Data
Swathi Kiran and Cynthia K. Thompson Northwestern University
Numerous studies have shown that representation of and access to semantic categories are influenced by the typicality of category exemplars in normal subjects. Typical exemplars (e.g., robin, sparrow) represented close to the center of the semantic category and having similar features to one another and the category prototype, yield faster reaction times as compared to atypical examples (e.g., penguin, ostrich) which are at the periphery of the category boundary and have fewer features in common (e.g., Rosch & Mervis, 1975). Little evidence, however, exists regarding typicality in individuals with aphasia (Grossman, 1981), the interpretation of these deficits with reference to theoretical models of typicality, or the applicability of typicality of category exemplars to treatment of naming deficits. Two experiments were conducted to investigate the nature of category typicality in patients with aphasia. In the first experiment, an online category verification task was performed with aphasic and normal individuals. In the second experiment, four fluent aphasic patients were trained on either typical or atypical examples of selected categories while generalization to untrained examples of the category was examined. Experiment 1
Methods Normal young (N ⫽ 9), elderly (N ⫽ 9), Broca’s (N ⫽ 7) and Wernicke’s aphasic (N ⫽ 7) individuals participated in an online category verification task. Primes were
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superordinate labels of three categories (bird, vegetable, fish) while targets were typical and atypical examples of the categories and nonmembers. Norms for typicality of category exemplars were developed prior to initiation of the experiment. Participants viewed written words presented on a computer screen and judged whether each example belonged to the preceding superordinate category.
Results Wernicke’s aphasic patients made the greatest number of errors on the task (22.1%). In comparison, Broca’s aphasic patients (8.67%), young (4.2%) and elderly groups (2.7%) made fewer errors. Separate analyses were performed for each participant group using a 3 ⫻ 3 (typicality ⫻ category) repeated measures ANOVA performed on item mean reaction times. Only results for typicality are discussed here. A significant main effect for typicality was noted in three of the four groups: young (F(2, 170) ⫽ 14.64, MS e ⫽ .4158, p ⬍. 001), elderly (F(2, 170) ⫽ 8.47, MS e ⫽ .4005, p ⬍ .001) and Broca’s aphasic patients (F(2, 170) ⫽ 20.924, MS e ⫽ 4.84, p ⬍ .001). For all three groups reaction times for typical examples and nonmembers were faster than atypical examples ( p ⬍ .01, p ⬍ .01), supporting previous studies on normal individuals. No significant main effect for typicality was observed for Wernicke’s aphasic patients.
Discussion Results of Experiment 1 demonstrated that Wernicke’s aphasic patients have impaired category representations as evinced by the greater numbers of errors on this task. Second, the lack of a significant typicality effect for Wernicke’s aphasic patients suggests that representation of categories in terms of category prototypes is diminished in these patients. We hypothesize that access of exemplar semantic features is impaired in this population, thus providing justification for the second experiment.
Experiment 2
In the second experiment, four Wernicke’s aphasic individuals from the previous experiment received a semantic feature treatment to improve naming of either typical or atypical examples, while generalization was tested on the untrained examples of the category. Based on a connectionist simulation by Plaut (1996), we hypothesized that training aphasic individuals to produce atypical examples from a category would result in generalization to typical examples of the category. Training typical examples was predicted to result in no improvements in atypical examples.
Methods The four participants, aged 63–75 years presented with severe naming deficits. Based on standardized language testing, the locus of naming deficit was attributable to impairments in accessing the semantic representation of the target, and/or in accessing its phonological form. Based on prior norms developed, examples for two categories (bird, vegetable) were divided into three groups, typical, intermediate and atypical. The two categories consisted of 24 examples each (N ⫽ 8 for each typicality group) that were matched for frequency, number of syllables and distinctiveness.
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Design and Treatment A single subject experimental design with multiple baselines across behaviors and participants was employed. Prior to application of treatment, naming of all 24 examples for each category was tested during baseline. Confrontation naming was then trained using selected examples of one superordinate category, with the order of categories and exemplar typicality counterbalanced across participants. For each participant, all eight examples in the subset (e.g., atypical) of the category were trained simultaneously. Treatment steps for each item included: (1) naming the picture, (2) sorting pictures of the target category with distracters, (3) identifying semantic attributes for the target example and, (4) answering yes/no questions regarding semantic features of the target example. Results Participant 1 received treatment for typical examples of birds, while participant 3 received treatment on typical examples of vegetables. Both participants demonstrated improvements on the trained typical examples to criterion (85% naming accuracy on two consecutive sessions), while no improvements were observed on the untrained intermediate and atypical examples. Treatment was then shifted to intermediate examples, following which improvements were observed on those items. When treatment was finally shifted to atypical examples improvements were noted on those examples (see Fig.1). Participant 2 received treatment for atypical examples of birds, while participant 4 received treatment on atypical example of vegetables. Improvements were noted for both participants on the trained atypical items while generalization to naming of intermediate and typical items was also noted (see Fig. 1). Treatment was then shifted to the second category for each participant (P2: vegetables, P4: birds). Once again, naming of the trained atypical examples improved, while generalization was observed to the untrained intermediate and typical examples (not illustrated). Discussion Results of this experiment showed that training atypical examples of a category and their semantic features resulted in generalization to naming of intermediate and typical examples of the category. Training typical examples and their semantic features, however, did not result in generalization to the intermediate and atypical examples. It is hypothesized that since atypical examples are dissimilar to one another and to the category prototype, they collectively convey more information about the variation of semantic features that can occur within the category than do typical examples. Therefore, training features of atypical examples facilitate access to those of typical examples, resulting in improved activation and naming. While current models of typicality explain possible differences in the representation of typical and atypical examples, in that categories are either represented by a set of features that may carry more or less weight compared to the prototype (Hampton, 1979) or as specific instances that have been previously encountered (Heit & Barsalou, 1996), these models do not explain the results of the present treatment. Instead, an interactive activation based model is proposed in which the connections between semantic and phonological representations are excitatory. At the semantic level, each example of a category is a summary representation of weighted semantic features. Due to their similarity with the category prototype, typical items exert greater lateral inhibition on other examples within the category whereas atypical ex-
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FIG. 1. Percent naming accuracy on typical, intermediate, and atypical examples for Participant 1 (P1) and Participant 3 (P3) who received treatment on typical examples and for Participant 2 (P2) and Participant 4 (P4) who received treatment for atypical examples.
amples exert less lateral inhibition. Training atypical examples improves access to atypical examples while not changing the amount of lateral inhibition exerted on intermediate and typical examples, and thus, naming of these examples are also facilitated following treatment. In contrast, training typical examples improves access to typical examples while increasing the amount of lateral inhibition exerted on interme-
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diate and atypical examples, therefore, no improvements in naming of these items are observed. Results of both experiments reported here provide insights into the representations of typicality in fluent aphasia. Although counter-intuitive to traditional treatment approaches, these results suggest that training naming of atypical examples is a more efficient method of improving naming of items within a category than training typical items. These data support the notion advanced by Thompson et al. (1997) that training more complex items which encompass variables relevant to simpler items enhance generalization. REFERENCES Grossman, M. (1981). A bird is a bird: Making references within and without superordinate categories. Brain and Language, 12,313–331. Hampton, J. A. (1979). Polymorphous concepts in semantic memory. Journal of Verbal Learning and Verbal Behavior, 18, 441–461. Heit, E., & Barsalou, L. (1996). The instantiation principle in natural language categories. Memory, 4, 413–451. Plaut, D. C. (1996). Relearning after damage in connectionists networks: Toward a theory of rehabilitation. Brain and Language, 52, 25–82. Rosch, E., & Mervis, C. (1975). Family resemblances: Studies in internal structure of categories. Cognitive Psychology, 7, 573–604. Thompson, C. K., Shapiro, L. P. Ballard, K. J., Jacobs, B., Schnieder, S. L., & Tait, M. (1997). Training and generalized production of wh and NP movement structures in agrammatic aphasia. Journal of Speech and Hearing Research, 40, 228–244.