cognition, 36 (1990) 129-153 Processing distinctions between stems and affixes: Evidence from a non-fluent aphasic patient* LORRAINE K. NLER SUSANBEHRENS HOWARD COBB University of Cambridge WlLLlAM MARSLEN-WILSON MRC Applied Psychology Unit, Cambridge Received June 2, 1989, final revision accepted February 19, 1990 Abstract Tyler, L.K., Behrens, S., Cobb, H., and Marsten-Witson, W., 1990. Processing distinctions between stems and affixes: Evidence from a non-fluent aphasic patient. Cognition, 36: 129-153. In this paper, we study the ability of a non-fluent aphasic patient, BX, to comprehend morphologically complex words when they appear in utterance contexts. Wefirst establish that he is insensitive to the contextual appropriateness of both derived and inflected words. In a further experiment we show that he has no difficulty processing the stems of complex words and conclude th-zt his problem is with the bound morphemes themselves. We then ask whether this problem is due to his inability to access either the phonological form of a morphologically complex word or its semantic andlor syntactic content. We find that only the access of semantic and syntactic content is impaired. We conclude from these six studies that: (a) BN presents a counter-example to the claim that non-fluent patients have particular dificulty with those aspects of morphology which have a syntactic function; (b) BN processes both derived and inflected words by mapping the sensory input onto the entire full-form of a complex word, but the semantic and syntactic content of the stem alone is accessed and integrated into the context. The semantic and syntactic implica- tions of the suffix are never evaluated. This implies separate representation of the stems and sufSixes of some types of morphologicully complex words. *We thank Paul Warren for his help with these experiments. This research was supported by an MRC ?ragramme grant to L.K.T. and W.M.W. Requests for reprints should be addressed to Lorraine K. Tyler. Department of Experimental Psychology. University of Cambridge, Downing Street, Cambridge CB2 3EB. U.K. 0010-0277/90/$8.00 O 1990-Elsevier Science Publishers B.V. 130 L. K. Tylar at al. Introduction There are a number of reports in the literature of aphasic patients who have particular problems in producing morphologically complex words (e.g., De- Villiers, 1978; Goodglass & Berko, 1960; Goodglass, Gleason, Ackeman, & Hyde, 1972; Miceli & Caramazza, 1987). English-speaking patients of this type rarely spontaneously produce morphologically complex words and also tend to omit the free-standing grammatical morphemes (such as "the" "and" "but"). Furthermore, they are less likely to produce inflected than derived words. Problems with morphologically complex \vords show up even more clearl;. in the spontaneous speech of patients who are native speakers of languages like Italian and Hebrew, which have a richer inflectional system than English. Although Italian and Hebrew patients produce inflected words (presumably because an uninflected root is a non-word in these languages), the inflections tend to be inappropriate for the context (Grodzinsky, 1984; Miceli & Caramazza, 1987). There are indications that the same kind of difficulty with morphoZogically complex words also occurs in comprehension, although the data here are much more sparse (e.g., Eling, 1986; Patterson, 1979; Tyler & Cobtb, 1987). Although most of this research does not distinguish inflected from derived words, the studies that do (e.g., Tyler & Cobb, 1987) reveal the same kind of poor performance for inflected words in comprehension as in production. Although it is rarely the case that such patients only have problems with the closed class morphology, it has been claimed that difficulties with this particular type of linguistic element is at the heart of their language disorder because of the syntactic role which the closed class morphology plays in many languages. Free-standing grammatical morphemes and the inflectional inor- phology, in particular, contribute to the construction of a syntactic represen- tation of an utterance (e.g., Anderson, 1982). The ciaim is that agammatic patients have problems with these linguistic elements because they do not have "knowledge of the structural roles played by grammatical markers ... (and) ... they are thereby unable to use these items as markers of phrasal constituents" (Cooper & Zurif, 1383). This pattern of impaired performance is consistent with models of the unimpaired processing system, such as Garrett's production model (1980), or Miceli and Caramazza's (1987) m~delof the structure of the lexicon, which stress the functional relationship between the closed class morphology and the syntactic structure of an utterance. In Garrett's model, for example, function words and grammatical morphemes are inserted into the sentence frame at the positional level so as to define the grammatical structure of an utterance. This accounts for the frequently observed CO-occurrenceof syntac- Processing distinctions between srems and ames 131 tic and morphological deficits in "agrammatic" patients (but see Berndt & Caramazza, 1980, Goodglass & Men, 1985; Martin, Blossom-Stach, & Feher, 1989). Errors in this stage of the process result in two types of errors involving affixes - omissions and substitutions -which are the types of errors found in "agrammatic* speech. For production deficits involving closed class morphemes, theory and data neatly converge. However, the situation is not quite so clear-cut when we consider comprehension deficits. There is little evidence bearing directly on the claim that when patients have problems in comprehension which involve morphologically complex words, it is because they have a general syntactic deficit. This is because there are no studies (with the exception of Lukatela, Crain, & Shankweiler, 1988; Tyler & Cobb, 1987) testing the comprehension of bound grammatical morphemes in sentence contexts. Instead, experiments typically involve presenting morphologically complex words in isolation - usually for the patient to read (Eling, 1986; Patterson, 1979). The only work which has examined the processing of grammatical markers in context has focused on the free-standing morphemes (e.g., Goodenough, Zurif, & Wein- traub, 1977; Grossman, Carey, Zurif, & Diller, 1986). This neglect is surpris- ing, since the only way to determine whether a patient can exploit the syntac- tic (or semantic) properties of a bound morpheme - whether an inflected or derived form - is to place it in a context which allows the functional signifi- cance of those properties to have an effect. This means that the morpholog- ically complex word should appear in a sentential context rather than in an unstructured word list. However, to determine whether a patient has problems comprehending morphologically complex words, we have to do more than just look at his or her difficulty in processing such words when they appear in sentential con- texts. We have to try to tease apart the possible underlying causes of the problem. This can be complex because there are a number of ways in which the piocess of comprehending a derived or inflected word can be disrupted. We assume here a three-stage process. The first stage involves mapping the senwry input onto mental representations of the plrcse!ogca! farm of a worct. In the absence of any data to the contrary, we assume that this process is the same for both simple and suffixed words - that is, the sensory input is mapped onto the entire form of the word. The second stage occurs after these form representations have been activated. This is when the syntactic and semantic properties of the word (i.e., its "lexical content") are accessed. The process of accessing this information may differ, depending on whether the meaning of the word represented in a decoinposed or whole form in the mental lexicon (e.g., Butterworth, 1983; Stemberger & McWhinney, 1986). The third stage is when the semantic and syntactic properties of a morpholog- 132 L.K. Tyler et al. ically complex word are used in parsing and interpretation. Although it is possible in principle to distinguish between the access of content and its use in sentence interpretation (stages two and three), in practice this is very difficult and the experiments reported in this paper do not do so. In principle, patients may have problems with any of these stages. First, they may have difficulty mapping the sensory input onto mental representa- tions of lexical form. This may be a general problem, involving both mor- phologically simple and complex words, or it may be confined to complex words. Second, they may have no problems with form mapping but the access of lexicd content may be impaired. They may be unable to process the syn- tactic andlor semantic proporties of morphologically complex words - either because they are unable to access the component morphemes, or combine them appropriately. Third, although they uay be able to access the content of morphemes, they may be unable to use them for parsing and interpreta- tion. To further complicate the picture, deficits in the ability to access either lexical form or lexical content may bd confined to either derived or inflected words. To try to separate out these various factors, we carried out a series of experiments on a non-fluent aphasic patient, BN. These studies focused on different aspects of the invofved in comprehending morphologically comp!ex words. The first study was designed as a general test of BN's ability to inflected and derived words ihen they appear in sentential con- texts. Since he performed poorly in this experiment, we then asked whether this was due to his inability to access the phonological form of such words, oi to his inability to access their semantic andor syntactic content. To answer these questions, we designed a series of studies in which morphologically complex words were either heard in an unstructured list of words or appeared in different kinds of sentential contexts. We designed the experiments so as to be able to tease apart BN's ability to process inflectional and derivational affixes as opposed to either the full-form of an affix-bearing word or its stem.