On-line language processing in older adults

Transcriptie

1 MA thesis On-line language processing in older adults The case of pronominal relations Inger Seits First supervisor: Esther Ruigendijk (Utrecht University) Second supervisor: Sergey Avrutin (Utrecht University) Submitted to the Faculty of Arts of Utrecht University The Netherlands

2 Doctoraalscriptie van Inger Seits (st. nr.: ) Faculteit der Letteren, Universiteit van Utrecht Opleiding Algemene Taalwetenschap Specialisatie Taalontwikkeling en Taalvariatie 1 e scriptiebegeleider: Esther Ruigendijk (Universiteit van Utrecht) 2 e scriptiebegeleider: Sergey Avrutin (Universiteit van Utrecht) mei

3 Acknowledgments Finally I have written my thesis and finished my study in Linguistics. It was a tough route, especially the last few months, and I learned a lot. I would like to thank a few people who supported and helped me throughout the course of writing my thesis. Without their help I would have been lost in this thesis-world. First of all, I appreciate all the supporting conversations, help, patience and confidence Stefan gave me. Furthermore, I m very grateful to my parents for their belief in me, and their psychological and financial support. At the university, I am especially grateful to my supervisor Esther Ruigendijk for sharing her knowledge, for her valuable comments on the earlier versions of my thesis, her help with the statistical analysis and her suggestions regarding my research goal and research question. Without her my thesis would have been very chaotic and way too long. Thank you, I have learned so much from you. I also want to thank Sergey Avrutin for being my second supervisor. I am very grateful Petra Burkhardt for giving me permission to use her data on pronominal interpretation in younger adults. And last but not least, I would like to thank my friends who always showed interest in the progression of my thesis, and who were always able to cheer me up when something went wrong and I felt I got stuck. 3

4 Contents Acknowledgements.3 Contents.4 Summary 6 Chapter 1 - Introduction.7 Chapter 2 - Theoretic Background 2.1 Off-line and on-line sentence processing in older adults Linguistic processing and general cognitive processing Processing differences in establishing reflexive/pronoun antecedent relations Summary theoretic background..25 Chapter 3 - Research goal, research questions and expectations..26 Chapter 4 - Methods 4.1 Paradigm Subjects Materials Procedure Analysis...35 Chapter 5 - Results 5.1 Results coargument condition vs. logophoric condition Results referring pronoun condition vs. bound variable pronoun condition 37 Chapter 6 - Discussion 6.1 Results coargument condition vs. logophoric condition Results referring pronoun condition vs. bound variable pronoun condition Reflection and criticism Criticism regarding the iedereen ( everyone ) sentences.46 4

5 Chapter 7 - Summary, conclusions and suggestions for further research 7.1 Summary Answering the research question Suggestions for further research 58 References..60 Appendices Appendix I - Experimental and filler sentences..66 Appendix II - The off-line tasks. 74 5

6 Summary This study investigates on-line language processing in older adults. It is hypothesized that older adults show a decline in their processing resources that can be employed during language processing, resulting in differences between younger and older adults when their on-line sentence interpretation is tested. Such differences might be observed in sentences that exert a higher demand on processing resources for interpretation. Two on-line experiments are performed, examining reaction times in a lexical decision task. In this task, varying interpretive demands are imposed by different pronoun and reflexive-antecedent relations (logophoric reflexive - antecedent relations vs. coargument reflexive - antecedent relations and bound variable pronoun - antecedent relations vs. referring pronoun - antecedent relations). Since the interpretation of logophoric reflexives and bound variable pronouns is assumed to cause a higher load on the processing system, these pronominal relations are expected to give rise to longer reaction times already in younger subjects, and to disproportionate longer reaction times in older adults. The results show that the reaction times of the older adults are not significantly longer for the more demanding sentence types compared to the younger subjects. The hypothesis of an age related decline in language processing cannot be confirmed; the older adults are slower, but they are slower on all sentence types. This suggests an age related slow down in the execution of general cognitive tasks, not attributable to language processing per se. However, some results tend to suggest that the hypothesized age related decline is not observable in terms of longer reaction times for older adults, but in terms of a delayed syntactic processor in older adults. In that case, the effects of interpreting sentence types that impose a higher load to the system will be observable at some later point during sentence interpretation. This is an interesting point for further research. 6

7 Chapter 1 Introduction In recent psycholinguistic research, the focus is on language processing in patients with agrammatic Broca s Aphasia. Investigation in the linguistic abilities and impairments of these speakers can give insight into leading questions in psycholinguistics. In such studies, the linguistic performance of the aphasic speakers is often compared to that of a control group, consisting of healthy, non-aphasic adult speakers. It is often recommended that this control group should be matched in age to the aphasic speakers. Since aphasic patients are in most cases elderly adults, who have suffered from a trauma or stroke, control groups should also consist of elderly adults. The reason for this is to avoid that the data show differences between aphasic speakers and controls not due to the Aphasia, but due to an age-effect. Several comments can be made regarding this issue. First, although most researchers agree that controls should be age-matched and therefore make use of elderly control groups, in recent literature age effects on linguistic processes are not well documented. One can wonder whether age effects will occur in the first place. Second, if there is an age-effect, and elderly adults indeed differ from younger adults in linguistic processing, then another issue raises: a control group consisting of elderly adults is a good reflection of age matched healthy, non-aphasic speakers. However, one should be careful in extending results of such studies to normal speakers in general, since these also contain young adults. Third, some age-matched control groups used in experiments testing language processing in subjects with Broca s Aphasia exist of older ánd younger subjects, because there are also some younger aphasic patients. In such control groups, there is quite a spread in age range (35-75), and if language processing is affected by aging, then the results of such control groups are less accurate. The goal of this study is to investigate whether there is a difference in linguistic processing between elderly adults and young adults. A difference between these two subject groups can be observed in cognitive functions like memory, attention and information processing speed. Studies on cognitive aging show that there is a mild age-related decline in these functions (Salthouse, 1991 for a review; Kandel, Schwarz and Jessell, 2000). Elderly adults perform poorer on memory-span tasks and other cognitive tasks; they often take longer time to perform the actions they plan, to answer questions or to give a solution to a difficult mathematic problem. In the literature different accounts are given for this age related decline. Some researchers subscribe it to a slow-down in the execution of cognitive tasks (Salthouse, 1996). Others claim that this decline is caused by a limitation in working memory capacity (Craik, 1986). The third account is that of an attentional deficit: elderly adults are less able to 7

8 select their attention (i.e. activate in working memory) only to current relevant information; they have problems inhibiting no-longer relevant information (Hasher and Zacks, 1988). Since language is one of the human cognitive functions, it might be subject to the age-related cognitive deterioration. However, various linguists assume that language processing is different from other types of verbally mediated cognitive processing, like problem solving, remembering a string of words or important chronological dates and logical reasoning. These researchers believe that that there is a special language processor in the human brain, which takes care of the structuring and comprehension of sentences (e.g. Rochon, Waters and Caplan, 1994; Waters and Caplan, 1996; Caplan and Waters, 1999). Other researchers believe that language processing and verbally mediated cognitive processing both rely on the same processing resources, and that higher processing demands imposed by one of the two has an effect on the processing efficiency of the other one (King and Just, 1991; Just and Carpenter, 1992). There are some early studies on linguistic skills of elderly adults, which suggest that the performance of older subjects deviates from the performance of younger subjects (Walsh and Baldwin, 1977; Feier and Gerstman, 1980; Emery, 1985; Kemper, 1986; Davis and Ball, 1989; Obler et al., 1992; Zurif et al., 1995) 1. In these studies, elderly adults are indeed performing poorer on tasks assessing linguistic skills than the younger adults, but in many cases the experiments are designed in such a way that additional task-demands or additional conditions are added. Therefore the declined performance of the older adults may not be due to impaired language processing, but to the additional task demands, that could have obscured the results. Furthermore, almost all of these studies investigating the effect of age on sentence interpretation use off-line techniques. They test comprehension after the sentence is presented. Therefore the results do not tell us much about age effects on linguistic processing during sentence presentation. Yet, recent psycholinguistic research that makes use of an experimental Broca s Aphasia patients group and an age matched control group, very often measures language processing during sentence presentation. Findings of on-line language processing in older healthy adults could be of importance for these kinds of psycholinguistic research. Thus, although the off-line studies indicate that elderly adults may have problems with the comprehension of complex sentences in off-line tasks, the on-line evidence is scarce. 1 See also chapter 2 8

9 Yet a difference between younger and older adults in on-line sentence processing is not unlikely, since an age related difference has been observed for on-line cognitive tasks. Furthermore, an on-line difference in sentence processing has been observed for aphasic speakers as compared to healthy speakers (Love et al., 1998; Love, Swinney and Zurif, 2001; Piñango and Burkhardt, 2001, 2003; Burkhardt and Piñango, 2002; Burkhardt, 2004). It is in principle possible that there are also differences in on-line sentence processing between younger and older subjects. Regarding the healthy subject-aphasic patient dissociation in on-line linguistic tasks, various proposals have emerged. One proposal assumes that aphasic speakers are less able to handle linguistic structures where information from different modalities is needed for interpretation (Avrutin 1999). It is argued that shifting from one linguistic modality to another and establishing the link between two systems asks too much of Broca s patients, because their resources pool for linguistic processing is decreased. Another proposal considers the linguistic problems of aphasic speakers to be a consequence of a slowed-down syntactic processor (Piñango, 1999, 2002). So, in work on aphasic speakers, the notion of a decreased pool of processing resources figures prominently, although there is some discussion about the nature of the limitation. It may be the case that aging also causes a limitation in processing resources, although not as dramatically as is the case in subjects suffering from Broca s Aphasia. In this study, processing resources are regarded as resources required for speech production and comprehension, similar to energy resources that are required for any other biological process. Speakers have to employ resources in order to implement their knowledge of linguistic rules in real time, during the course of speech production and interpretation. Regarding the specificity-issue (is there a separated language processor, or are language processing and verbally mediated cognitive processing served by the same process), there are globally three possibilities: (1) either older adults have a limited processing capacity for cognitive processing, and this influences their language interpretation processes, (2) or older adults have a limited cognitive processing capacity but this does not influence their language interpretation processes, only extra linguistic skills, like reasoning, can be affected, (3) or their language interpretation processes itself are impaired. Whatever the precise characterization of any decline in processing resources in older adults might be, I am interested in the question whether differences can be observed between older and younger subjects in on-line sentence processing tasks. This study investigates on-line reflexive and pronoun interpretation in elderly adults and gathers data that can tell us more about this issue. 9

10 The outline of this study is as follows. Chapter 2 aims to give a theoretical background that is necessary to understand the experiment on on-line reflexive and pronoun interpretation in younger and older adults. Theoretical issues concerning sentence comprehension in older adults, specializations of cognitive functions and language processing resources are discussed and pronominal relations are described that exert different demands on processing resources and can therefore be used to study processing differences in younger and older adults. In chapter 3, I introduce the research goal, the research questions and my expectations. The methods and materials used in the experiment on reflexive and pronoun interpretation in younger and older adults are discussed in chapter 4. Chapter 5 presents the results of the experiment and in chapter 6, a discussion of the results is given. Finally, in chapter 7, the main findings and conclusions of the present study are summarized and I point out some directions that might be interesting for further research. 10

11 Chapter 2 Theoretic background Not much work is done on the subject of on-line linguistic processing in elderly adults. Furthermore, not much reliable work is done on off-line linguistic performance of elderly adults either. In section one of this chapter, I review the off-line and on-line work done so far. Because this study investigates on-line language processing in older adults, in section two, language-processing considerations are discussed. I discuss the notion of processing resources, the possibility of specializations in the processing resource pool, and how a limitation in processing resources could look like. In section three, I examine linguistic contrasts that can be used to measure on-line processing cost, and therefore, can be used to investigate differences between age groups. Finally, in section four, I summarize the results of this chapter. 2.1 Off-line and on-line sentence processing in older adults Various reports describe comprehension of spoken sentences by older adults. The effects of aging on sentence comprehension abilities have been examined using several tasks. These are mainly off-line studies, using a variety of tasks such as object manipulation (Feier and Gerstman, 1980), question answering (Emery, 1985; Davis and Ball, 1989) and acceptability judgment (Kemper, 1986). These tasks tap comprehension of a sentence after the sentence is heard, or measure reaction times between the ending of the sentence and the response of the subject. Davis and Ball (1989) presented younger and older healthy subjects (aged 25-79) with two types of sentences, varying in complexity (sentences with center-embedded- and with right branching subordinate clauses 2 ). In both conditions, semantically plausible as well as semantically implausible sentences were presented and subjects had to answer questions about who is doing what in the sentences. All subjects did well on all plausible sentences. In the implausible condition, both groups performed poorer, and the older subjects did less well on the complex sentences than did the younger subjects. Davis and Ball argued that older adults let their world-knowledge exert more influence on their understanding of complex sentences than younger adults do, which may point to a weakening of the syntactic component when sentences convey implausible information. However, since the older 2 Respectively: The policeman that handcuffed the kidnapper untied the woman The judge imprisoned the mother that abandoned her child 11

12 subjects did very well on plausible complex sentences, the age-related decline in comprehension of complex implausible sentences cannot be attributed in a straightforward way a weakening of the syntactic processor. Why would a syntactic processor be weakened in one case and work well in the other? It is more likely that there is something about implausibility that is susceptible to old age. Old-age comprehension of center-embedded and right branching sentences was also investigated by Feier and Gerstman (1980). In this experiment, subjects had to act out the sentences by manipulating animal dolls. The older subjects made significantly more errors with the act-out of both types of sentences compared to the younger subjects. However, they were not differentially impaired on the syntactically more complex sentences. The results may therefore indicate a more general deficit, maybe older adults are less able to act out situations with dolls then younger adults are. The extra task may be too demanding for older subjects. The same observations can be made regarding a study of Emery (1986). She used three tests 3, assumed to test comprehension and linguistic patterning of syntactically complex sentences. The older adults performed worse than the younger adults, especially on more complex sentences, and Emery concluded that the results of the study point to a direct relationship between language deficits and age and a direct relationship between language deficits and linguistic complexity. However, examining the tests used (see footnote), it seems obvious that these tests do not measure straightforward linguistic processing, but the ability to use the information of (already processed) sentences to a variety of (often cognitive complex) tasks. Obler et al. (1992) used a question-answering task (subjects had to answer with yes or no by pressing a button) and tested comprehension of sentence types of varying complexity. All sentence types were presented in a plausible and implausible form. They found a general increase for all sentence types in both reaction times (RT s) and errors in the older subjects. The older adults made disproportionately more errors with implausible sentences than the 3 Token test. Verbal instructions of increasing linguistic complexity. Examples: show me a circle, show me a blue circle, show me the small blue square, touch the blue circle with the red square, move the green square away from the yellow square. Emery Test for Syntactic Complexity. Questions that deal with various complex syntactic relations. Examples: do you put on your stockings before your shoes, what season comes before Spring and after Autumn, the dog was bitten by the cat, which animal bit the other and which was bitten, what is the relationship of your mother s sister / uncle s daughter / daughter s uncle to you, John and Mary run to the store really fast John runs faster than George but slower than Humphrey. Chomsky test of syntax. Instructions based on conditions under which maximal complexity occurs. Examples: Participant is presented with a blindfolded doll and asked, is this doll easy to see or hard to see, participant is presented with figures of Mickey Mouse and Donald Duck and is asked, Mickey tells Donald to hop up and down; make him hop, ask him what to do, tell him what to do, Donald knew that Mickey was tired; who was tired and who knew it, Mickey was six years old when he started school; who was six years old and who started school. 12

13 younger adults did. Obler et al. suggested, as Davis and Ball (1989), that older adults, more than younger adults, tend to use their knowledge of what is most likely to be true. The results are indeed comparable with the results of Davis and Ball (1989), but, again, the tasks on which the older subjects have shown such effects are ones that require non-linguistic processing, in this case, interpreting implausible sentences. The age related increase in both RT s and error rates was not differently affected by more complex syntactic structures, and therefore this may reflect a generalized slowing in cognitive non-linguistic functioning in older adults instead of a decrease in syntactic processing. Apparently, in the results of many of these off-line studies testing the comprehension of elderly adults, the effect of age may be attributed to difficulties subjects have with processes other than those involved in sentence interpretation. The techniques used in these studies may conflate on problems that arise in a later stage, when the subjects have to use the form and content of the sentence for an appropriate response. A study of Kemtes and Kemper (1996) also suggest that difficulties older people have with off-line tasks may be attributable to task demands, and disappear when using an on-line measure. They found differences between older and younger adults in an off-line test where subjects had to answer questions about ambiguous sentences, while they failed to find differences between the two age groups in an on-line measure testing the effect of syntactic ambiguity on word-by-word reading times. A study of Baum (1991) and Waldstein and Baum (1992) also failed to find on-line differences. Using a word monitoring paradigm, where subjects had to monitor for a word following an ungrammaticality in the sentence, they found that RT s and error rates of older adults were higher overall, but found no evidence that elderly subjects were more reliant on sentential context or that they were less sensitive to ungrammaticalities. Zurif et al. (1995), however, did find on-line differences between older and younger adults using a Cross Modal Lexical Priming (CMLP) paradigm. Subjects heard subject- and object relative sentences 4 through headphones, and immediately after the gap position, where the antecedent (the moved constituent) is supposed to be reactivated (Swinney and Fodor, 1989), either a semantically related (to the antecedent) or a semantically unrelated word appeared on a computer screen. Subjects had to decide whether this word was a word of English or not, and in the semantically related cases, the RT to this decision should be shorter, because the semantically related antecedent is activated and this constituent should prime the recognition of the word. This was the case for older adults with the subject relative sentences, but no shorter RT s were observed after a semantically related word in object 4 Respectively: The gymnast loved the professori from the North western city who (tri) complained about the bad coffee The tailor hemmed the cloaki that the actor from the studio needed (tri) for the performance 13

14 relative sentences, where the antecedent is extracted from object position and which are considered harder to compute. It was shown that this had nothing to do with processing inefficiency of the more complex construction. The object relative sentences contained more words between gap and antecedent than the subject-relatives did, and when they controlled for this factor, the differences between RT s on subject vs. object relative sentences disappeared. Zurif et al. concluded that the system responsible for assigning phrase structure is unaffected by age (the older subjects were able to process subject- as well as object relatives) and that the system responsible for establishing dependency relations decreases in storage capacity when people get older. The studies discussed in this section do not provide convincing evidence that older adults experience a decline in syntactic processing. It only suggests that older adults observe some cognitive deficits, which may influence their use of already processed linguistic information. However, results of Zurif et al. (1995) suggest that there are some differences in language processing between younger and older adults. Zurif et al. (1995) made a distinction between a system assigning phrase-structure and a system establishing dependency relations. Their results point to an age-related limitation in this latter system 5. And recent psycholinguistic research investigating the underlying cause of linguistic problems of patients suffering from agrammatic Broca s Aphasia use tasks testing on-line establishment of dependency relations (for instance, reflexive- and pronoun - antecedent relations). Control groups in such studies consist of age matched, therefore, usually, elderly healthy persons. Moreover, in control groups with older ánd younger subjects, there is quite a spread in age range. If language processing is affected by age, then the results of such control groups are less accurate. Since we have seen in this section that there is only little work done on on-line linguistic processing in older adults, more information about how healthy older adults establish dependency relations can be useful. 5 However, one limitation of the work of Zurif (1995) is that they only tested older adults, and used data of a group of younger healthy adults obtained in a study of Swinney (1988) as their control data. This control group, although presented with the same paradigm, was not tested on the same materials as the older group, and this weakens the results of Zurif et al. (1995). 14

15 2.2 Linguistic processing and general cognitive processing One theoretical question concerning research investigating linguistic processing in healthy older adults is whether linguistic processing is substantially different from other types of cognitive processing. Why would we otherwise be concerned with the issue of linguistic processing in older adults in the first place? There is substantial evidence that older adults observe a mild decline in various non-linguistic cognitive tasks, measuring memory- and cognitive capacities like reasoning, spatial abilities, speed of learning and problem solving (Craik, 1986; Botwinick, 1984; Salthouse, 1991, 1996; Schaie and Willis 1993; Kandel, Schwartz and Jessel, 2000). Various researchers assume that this is due to an age related decrease in the processing resource pool for cognitive processing (Salthouse, 1996; Craik and Jennings, 1992). None of the studies testing cognitive abilities of older adults also considered linguistic processing. However, it seems plausible that the language processing abilities of older adults are also declined, since language processing is a form of cognitive processing. In this study I hypothesize that the processing resource pool of older adults is decreased, resulting in a decline in on-line language processing abilities. However, I cannot simply hypothesize this without mentioning the debate in the literature about possible specializations in this processing resource pool. Whereas it seems likely to assume that older adults are declined in language processing since they are declined in cognitive processing, some researchers believe that language processing is substantially different from cognitive processing, and that both processes draw on different resource pools. Another issue that needs to be addressed is how we should conceptualize a processing resource pool, and furthermore, how we should think of a decline in such a resource pool. In this section, I discuss these issues, and describe the different views that can be found in the literature. Baddeley (1976) first introduced the notion of a resource pool for cognitive processing: a working memory, a short-duration system in which small amounts of information are simultaneously stored and manipulated in the service of accomplishing a task, to be separated from long term memory. Research in psychology provided considerable evidence for such a division; in the long-term memory memories of large numbers of facts and autobiographical events are maintained for up to years, and the short-term memory is capable of retaining small amounts of information for very short periods of time (Squire and Zola-Morgan, 1991). Baddeley and his colleagues suggested that the appropriate way to characterize this short-term memory is as a "working memory" system (Baddeley, 1976, 1995) and both normal as well as impaired cognitive functions are accounted for by the 15

16 notion of a limited-capacity working memory system (Just and Carpenter, 1992; Gathercole and Baddeley, 1993). There is a limit to the amount of information you can process simultaneously; and for cognitively impaired subjects, the working memory system is even further restricted. Another way of speaking about working memory is in terms of processing resources. In a physical approach to the notion of processing resources, cognitive functions, like all other biological processes, require a certain amount of energy resources to execute the processes that lead to successful implementation of the cognitive information, just as energy resources are needed in order for our metabolic system to work. Humans have to draw on their pool of processing resources during the execution of cognitive tasks and during language interpretation processes. In the literature, different views can be noticed regarding possible specializations in the processing resource pool. Most researchers agree that a distinction must be made between language processing and other types of verbally mediated cognitive processing (or general cognitive processing ) (Fodor, 1983; Caplan and Waters, 1996; Frazier, 1990). Language processing is an unconscious process of extracting meaning from a linguistic signal and consists of lexical, semantic, syntactic and discourse processes 6. Caplan and Waters (1996) call this type of processing interpretive processing. General cognitive processing uses the outcome of the interpretive processes (i.e., the meaning of the linguistic input) to accomplish other tasks such as storing information in long term memory, reasoning, planning actions, and other cognitive functions ( post-interpretive processing, in terms of Caplan and Waters). This is assumed to be a conscious process. Researchers disagree with respect to the issue of whether language processing and general cognitive processing draw from the same pool of processing resources or not. Some researchers argue that humans have a set of working memory processing resources that can be devoted to both language- and general cognitive processes (Just and Carpenter 1992; King and Just 1991; Miyake, Just and Carpenter, 1994). I will refer to this model as the oneresource model. Others believe that language processing is substantially different from general cognitive processing, and that it constitutes a separate specialization in working memory: a separated language processing resource pool (Rochon, Waters and Caplan, 1994; Caplan and Waters, 1996; Waters and Caplan, 1999). I will refer to this model as the separate-resource model. 6 This is a rather rough classification of interpretive processes ( all lexical, semantic, syntactic and discourse processes), but in the literature many researchers suggest a similar distinction. 16

17 The two models make different predictions with respect to the performance of healthy subjects and cognitively impaired subjects. First, whereas the one-resource model predicts that healthy subjects with different working memory capacities 7 should exhibit differences in efficacy of language processing (subjects with a lower working memory capacity have fewer resources available for language processing), the separate-resource model predicts that subjects with a low working memory capacity will be as efficient in language processing as subjects with a high working memory capacity, since language processing draws from a separate resource pool. Second, the one-resource model predicts decreased processing of complex sentences when a concurrent memory load is added (a complexity*load interaction), while the separate-resource model predicts no such effect. And finally, the two models make different predictions with regard to the language processing capacities of subjects with a working memory deficit, like patients with Dementia of the Alzheimer type or Parkinson s Disease. These subjects have been found to have a reading span of one or less, which indicates that they have a very low working memory capacity (Caplan and waters, 1999). The one-resource model predicts that these patients differ from healthy subjects in processing syntactic complex sentences, especially when a concurrent memory load is added. The separate-resource model predicts that these patients do not differ from healthy subjects. Different studies have investigated the truth or falsity of either the one-resource model or the separated-resource model. However, results of these studies are rather mixed. Some studies find complexity*load interactions and decreased language processing capacities in healthy and cognitively impaired subjects with low working memory capacities (Emery, 1985; King and Just, 1991; Grossman et al., 1992; Waters and Caplan, 1996), pointing to a oneresource hypothesis of the working memory. Results of other studies suggest that the language processing capacities are unaffected in healthy and impaired subjects and are unaffected by a concurrent memory load (Lalami et al., 1996; Caplan and Waters, 1999; Rochon, Waters and Caplan, 2000), pointing to a separate-resource hypothesis of the working memory. In this study, I will be neutral with respect to this issue. I hypothesize that on-line language processing capacities will be affected by age and that this is due to an age related decline in processing resources. However, whether this is a decline in a general cognitive resource pool or in a specialized language resource pool, is not of concern. I leave this question open, 7 Working memory is often assessed by the Daneman and Carpenter reading task. In this task, subjects are required to read aloud increasingly longer sequences of sentences and to recall the final word of all the sentences in each sequence. A subject's working memory capacity is defined as the longest list length at which they are able to recall the sentence-final words on the majority of trials (Caplan and Waters, 1996). 17

18 and only argue that there are three possibilities, which I already discussed in the introductory chapter and which I repeat here: (1) either older adults have a limited processing capacity for cognitive processing, and this influences their language interpretation processes, (2) or older adults have a limited cognitive processing capacity but this does not influence their language interpretation processes, only extra linguistic skills, like reasoning, can be affected, (3) or their language interpretation processes itself are impaired. Because I hypothesize that any on-line differences between younger and older adults are due to an age related decline in the processing resource pool (whatever its specificity), it is important to note that there are various views on the nature of such a decline. Both in the cognitive and in the linguistic field the view of a limitation in the processing resource pool is adopted by many researchers. In the linguistic field, for patients suffering from agrammatic Broca s Aphasia and for children it is proposed that they suffer from a limitation in their processing resources for language processing (Grodzinsky et al., 1993; Avrutin, 1999). In aphasic patients this may be due to brain damage, while in children the processing limitation could be related to the yet immature state of their brains. However, there is considerable discussion about the nature of the limitation. In what way are processing resources limited? Caplan and colleagues (e.g., Caplan and Hildebrandt, 1988: Waters and Caplan, 1996) conceive of this deficit as a restriction in syntactic workspace. Miyakes et al. (1994) propose that there is a limitation in the total pool of activation, or energy pool that is available for language processing. They do not have as much energy for language processing as normal adults. In the work of Kolk and colleagues (e.g., Kolk 1995), it is assumed that all speakers have a certain amount of internal time in which they have to execute the processes involved in sentence comprehension. To execute these processes, syntactic information is needed and must be activated and reached above rest level. These syntactic activation processes may take longer in agrammatics and therefore they cannot handle syntactic processing it in the available time. Next, an activated element may drop below its critical activation threshold too soon, so that the element is not available any more, and syntactic processing is disrupted. Thus, the notion of limited language processing resources has centered around three metaphors: space or capacity (Caplan and Hildebrandt 1988), energy (Miyakes et al. 1994) and time (Kolk 1995). Although there are various ways to look at the specific nature of the limitation in language processing resources, for the present study, it does not make a difference whether we start off from space, energy, or time. Therefore, in this study, I will be neutral with respect to the issue of the exact nature of the language processing resources limitation. 18

19 2.3 Processing differences in establishing reflexive/pronoun - antecedent relations In section 2.1 we saw that the evidence that older adults differ from younger adults in comprehending complex sentences in off-line studies is limited. In one on-line study (Zurif et al, 1995), a difference between older and younger adults in reaction times in a CMLP paradigm was observed for complex sentences (involving constituent movement). No difference was observed for the less complex sentences without moved constituents. The same observations are made for agrammatic aphasic subjects and children; they have problems with the interpretation and production of complex sentences, where constituents have been moved (Caplan et al., 1985; Zurif and Swinney, 1995; Hartsuiker and Kolk, 1998; Avrutin, 1999; Love, Swinney and Zurif, 2001; Burkhardt, Piñango and Avrutin, 2003). Processing of simple sentences does not exceed their limited resources pool. If older healthy adults differ from younger adults, the difference will therefore only be noticeable in complex sentences where movement is involved. Differences are further expected in sentences where information from different linguistic modules needs to be integrated. These sentences are also assumed to place a higher demand on processing resources than do sentences where only syntactic information is needed, and are shown to exceed the limited resources of children and agrammatic aphasics (Grodzinsky et al., 1993; Hickok and Avrutin, 1995; Love et al., 1998; Piñango, Zurif and Jackendoff, 1999; Avrutin, 1999; Shapiro, 2000; Piñango and Burkhardt, 2001, 2003; Burkhardt and Piñango, 2002; Burkhardt, 2004). Moreover, several recent studies using on-line measurements of reaction times have shown that these sentences are more costly for healthy younger adults as well (Shapiro et al., 1991; Shapiro and Levine, 1990; De Vincenzi, 1996; Shapiro, 2000; Piñango et al., 2001; Burkhardt, Piñango and Avrutin, 2003; Burkhardt, 2002, 2004). Testing older healthy adults on-line on these high demanding structures can tell us whether they differ from younger adults. Will older adults show longer RT s than younger adults 8? Off course, if there is a difference, this difference will not be as large as the difference between younger adults and agrammatic aphasic subjects, since healthy older adults are not brain damaged, while the brains of patients with agrammatic Broca s Aphasia are injured and lesioned due to a trauma or stroke. Brains of healthy older adults become less plastic, brain weight decreases, some populations of neurons may be reduced in number through cell death and some connections between neurons are lost, but there is no huge loss of brain tissue (Kandel, Schwarz and Jessell, 2000). 8 Not due to an age-related slow down of general cognitive functions like decision-making and motor functions like pressing a yes or a no button (Salthouse, 2000). 19

20 In this study, older adults are tested on linguistic distinctions that are related to reflexive and pronoun interpretation 9. I argue that these distinctions are observable in the form of cost to the processing system in younger healthy subjects; pronominal 10 dependencies where discourse information needs to be accessed exert a higher cost to the system than pronominal dependencies where syntactic knowledge is sufficient. I hypothesize that for older subjects, the interpretation of a high demanding pronominal dependency requires relatively more of their limited processing system as it does of the intact system of younger subjects. The linguistic distinctions examined are based on two contrasts: 1) referring pronouns vs. pronouns as bound variables, and 2) coargument reflexives vs. logophoric reflexives. I what follows, I discuss representational and processing considerations of these two contrasts. 1) Referring pronouns vs. pronouns as bound variables Consider the following contrast in sentences (1)a and b. (1)a. The boyi hopes that the funny girl likes himi (1)b. Everyonei hopes that the funny girl likes himi Within the standard government and binding theory (Chomsky, 1981), no distinction is made between referring pronouns ((1)a) and bound variable pronouns ((1)b). However, the interpretation of both pronouns is different: whereas in (1)a the pronoun is interpreted as denoting an individual; in (1)b it is interpreted as denoting a set. Reinhart (1983) outlines the distinction between referring pronouns and bound variable pronouns. She assumes that there are two types of dependencies: binding and coreference. In the case of R-expression 11 antecedents, as in (1)a, pronoun and antecedent establish a coreference relation; both refer to the same individual in the outside world. This requires accessing the level of discourse information (Heim, 1982; Avrutin, 1999). When the antecedent is a quantified expression, as 9 Pronominal and reflexive entities (e.g. she, you, her, our, himself, themselves and Dutch zich ) are referentially dependent elements. Their interpretation is not sufficiently determined by their own lexical content. They do not pick out one unique referent in the universe of discourse or, in the outside world and have no interpretation of their own. Therefore, these elements must establish a dependency relation with another entity, an antecedent, to obtain referential content and to be interpreted. 10 In this study, pronominal elements are both reflexives ( himself, themselves ) and pronouns ( him, them ) 11 Referential Expressions expressions that select one unique referent from the universe of discourse, they have independent reference, such as proper names and NP s like the detective. 20