Aim 2: The influence of memory capacity vs language knowledge on sentence processing

Experiments 1 to 4 demonstrated that in the immediate years that follow an early appreciation for the meaning of the connective, performance was not uniform across sentence structures. One possibility is that performance on some structures was poor because of

differences in the processing demands of those sentence structures. As noted, the design of the experimental work in this thesis contrasted the role of working memory resources versus language knowledge on processing. This enabled a test of whether processing difficulties were best explained by a memory capacity account (e.g., Just & Carpenter, 1992) or a language-based account (e.g., Van Dyke et al., 2014). A memory capacity account posits that performance will be driven by an individual’s working memory capacity and that processing ease will be influenced by the amount of information that must be held in working memory for a specific sentence structure. A language-based account posits that an individual’s performance is not dependent on their working memory capacity per se, rather, it is

dependent on the support for an accurate representation of information in working memory that is provided by language knowledge. These accounts are discussed in turn.

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5.2.1. Evidence in support of memory capacity accounts

In the two comprehension experiments (1 and 2), children aged 5 years and older were above chance for each sentence structure, so demonstrated an appreciation for the meaning of the connective. However, these children were typically most accurate (Experiment 1) and fast at processing (Experiment 2) sentences in a chronological order linked medially by before (e.g., He put on the sandals before he ate the burger) compared to the other sentence types. This superior performance for before-chronological sentences has been explained in relation to the additional demands that are made on working memory when a sentence has a reverse order (Ye et al., 2012), a more difficult vocabulary (Gunter et al., 2003), or an initial position for the connective (Diessel, 2004). Before-chronological sentences carry none of these additional demands, and afford incremental processing. Conversely, before-reverse (reverse order, initial position), after-chronological (initial position, difficult connective), and after-reverse (reverse order, difficult connective) sentences each carry two of these additional demands, so require the comprehender (or speaker) to maintain more information in working memory whilst constructing their mental representation (see Table 1.2, relevant section reproduced here for ease of reference).

CHAPTER 5: GENERAL DISCUSSION.

143 Table 1.2.

Sentence structures and their additional working memory load as influenced by a reverse order of mention of events, a later acquired connective, and an initial position of the connective.

Additional working memory load

Reverse order Later acquired connective

Initial position

Before-chronological No No No

After-chronological No Yes Yes

Before-reverse Yes No Yes

After-reverse Yes Yes No

Critically, in both comprehension experiments, the advantage reported for before- chronological sentences was predicted by performance on an independent measure of working memory. Therefore, the overall findings for comprehension support a memory capacity account (Just & Carpenter, 1992), such that children’s comprehension of two-clause sentences containing before and after is influenced by an individual’s memory capacity resulting in poorer performance for sentence structures that carry additional memory load (Just & Carpenter, 1992; Pyykkönen & Järvikivi, 2012; Ye et al., 2012).

In contrast to the comprehension experiments, the production studies (Experiments 3 and 4) did not provide support for a memory capacity account: children did not display an advantage for before-chronological sentences, and the independent measure of working memory did not predict unique variance in performance. The production data support the

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predictions of a language-based account (e.g., Van Dyke et al., 2014), discussed further below.

5.2.2. Evidence in support of language-based accounts

Although the comprehension experiments provide strong support for a memory capacity account (Just & Carpenter, 1992), some of those findings can be explained by language knowledge. For example, the advantage for chronological sentences displayed by the younger children, suggests that when children do not have an appreciation for the meaning of a temporal connective, they will use a non-linguistic strategy to understand and represent the relation between two events. Also, a general advantage found for before in both comprehension experiments, supports a simple form of a language-based account, such that language knowledge (of the connective) directly influences ease of processing.

As detailed in the literature review (Chapter 1), a language-based account that acknowledges the influence of memory proposes that the relation between memory and sentence processing is indirect and that, rather, good language skills modulate the accurate representation of information in verbal working memory (e.g., Van Dyke et al., 2014). According to this account, working memory should not explain unique variance in

performance after individual differences in language knowledge have been taken into account (Klem et al., 2015). The comprehension experiments did not support these predictions: in Experiments 1 and 2, an independent measure of working memory explained unique variance in performance over and above an independent measure of language knowledge.

In contrast to comprehension, the production experiments (Experiments 3 and 4) support a language-based account of the role of working memory in sentence processing (Van Dyke et al., 2014). In both a sentence repetition task (Experiment 3) and an elicited

production task (Experiment 4), children were significantly less accurate at producing target sentences when the presentation order of the two clauses did not match the chronological

CHAPTER 5: GENERAL DISCUSSION.

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order of events, but this difficulty was specific to target sentences linked by after. Further, in elicited production, vocabulary explained unique variance in this pattern of performance. Critically, as noted in Section 5.2.1, an independent measure of working memory did not explain unique variance in either of the production experiments. Together these findings suggest that language knowledge modulated children’s ability to cope with the cognitive demands of producing reverse order sentences.

5.2.3. Does position of connective provide an adequate explanation for the difficulty in producing after-reverse sentences?

It should be noted that an additional influence on children’s specific difficulty in producing reverse order sentences linked by after (Experiments 3 and 4), may be the position of the connective. In reverse order sentences linked by after, the connective appears in the medial position(He ate the hotdog, after he put on the jumper); when linked by before, the connective appears in the initial position (Before he ate the hotdog, he put on the jumper).

Although a medial position is generally proposed to carry lower demands on working

memory than an initial position (Diessel, 2005), speakers may have a pragmatic preference to place the connective in the initial position in order to foreground critical information that can guide the listener’s understanding (see Chafe, 1984; Gernsbacher, 1997; Junge, Theakston, & Lieven, 2013; Myachykov, Garrod, & Scheepers, 2012; Silva, 1991). Therefore, there may be two reasons why a reverse order sentence presents difficulties only in production when it is linked by after. First, as argued by a language-based account, after is the later-acquired connective and is used less consistently as a connective than before. Second, a reverse order of events signalled by after is difficult to plan and produce because the speaker only provides the critical information that the events occur in reverse order, part way through the sentence.

This explanation fits the findings in Experiment 1 and 2 that children are most

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However, it does not account for the pattern of results in Experiments 3 and 4 as adequately as the explanation that is provided by the language-based account in section 5.2.2. The first reason for this was that corpus and experimental work suggest positioning the connective in the medial position enables incremental processing (Cain & Nash, 2011; Diessel, 2004). As a result, medially placed connectives in after-reverse sentences should not be problematic for the speaker (or comprehender). Second, if the late (medial) signalling of reverse order in after

sentences is the true explanation for the results, it should tax working memory resources because more information has to be held in working memory while the mental representation is revised. However, as noted, working memory did not explain unique variance over and above language knowledge. I return to the issue of determining the influence of connective position on sentence processing in Section 5.3 and in Section 5.4.2.