Journal of Memory and Language Journal of Memory and Language 54 (2006) 81–98 www.elsevier.com/locate/jml Lexical and semantic binding in verbal short-term memory Elizabeth Jefferies a,*, Clive R. Frankish b, Matthew A. Lambon Ralph a a University of Manchester, UK b University of Bristol, UK Received 8 February 2005; revision received 30 August 2005 Available online 15 November 2005 Abstract Semantic dementia patients make numerous phoneme migration errors in their immediate serial recall of poorly comprehended words. In this study, similar errors were induced in the word recall of healthy participants by presenting unpredictable mixed lists of words and nonwords. This technique revealed that lexicality, word frequency, imageability, and the ratio of words to nonwords all influence the stability of the phonological trace. These factors affected phoneme migrations and phoneme identity errors for both the words themselves and the nonwords they were presented with. Therefore, lexical/semantic knowledge encourages the phonological segments of familiar words to emerge together in immediate serial recall. In the absence of such knowledge, the elements of a particular item are more likely to recom- bine with the phonemes of other list items. These findings demonstrate the importance of lexical and semantic binding in verbal short-term memory. Ó 2005 Elsevier Inc. All rights reserved. Keywords: Redintegration; Semantic binding; Semantic dementia; Verbal short-term memory; Immediate serial recall It is well established that verbal short-term memory is better for: (1) words vs. nonwords (e.g., Brener, 1940; (STM) draws heavily on a phonological code, account- Hulme, Maughan, & Brown, 1991); (2) high compared ing for the occurrence of phonological errors in immedi- with low frequency words (Gregg, Freedman, & Smith, ate serial recall tasks (Conrad, 1964) and the poorer 1989; Hulme et al., 1997; Roodenrys & Quinlan, 2000; recall of lists of phonologically similar than dissimilar Watkins & Watkins, 1977); (3) imageable/concrete items (Conrad & Hull, 1964). In line with these findings, words vs. abstract words (Bourassa & Besner, 1994; the highly influential working memory model proposes Walker & Hulme, 1999); (4) semantically grouped vs. that verbal STM is underpinned by a phonological loop ungrouped words (Poirier & Saint-Aubin, 1995; Saint- subsystem that operates independently of long-term Aubin & Poirier, 1999). memory (Baddeley, 1986; Baddeley & Hitch, 1974). Neuropsychological evidence also points to the role However, research has indicated that stable lexical and of lexical–semantic representations in immediate recall. semantic representations also make an important contri- Semantically impaired aphasic patients show reduced ef- bution to immediate serial recall. Immediate serial recall fects of frequency and imageability in immediate serial recall (Martin & Saffran, 1997). In addition, semantic dementia patients, who show a specific and progressive * Corresponding author. Fax: +44 161 275 2588. decline in semantic memory, have better immediate E-mail address: beth.jeff[email protected] (E. Jeff- recall of words that they understand relatively well eries). compared with words whose meanings have become 0749-596X/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jml.2005.08.001 82 E. Jefferies et al. / Journal of Memory and Language 54 (2006) 81–98 degraded over the course of the disease (Jefferies, Jones, these constraints might allow phonemes to migrate be- Bateman, & Lambon Ralph, 2004; Jefferies, Jones, Bat- tween items. This hypothesis posits distinct semantic eman, & Lambon Ralph, 2005; Knott, Patterson, & and phonological representations but no separate lexical Hodges, 1997, 2000; Patterson, Graham, & Hodges, level, in line with the parallel distributed processing 1994). Immediate serial recall differences between rela- (PDP) models of, for example, Seidenberg and McClel- tively well-known and semantically degraded words land (1989). ÔLexicalÕ constraints on phonology result have also been reported in semantically impaired pa- from a combination of long-term learning of frequently tients following cerebrovascular accident (Forde & co-occurring phonemes and stable associations between Humphreys, 2002) and herpes simplex encephalitis phonological and semantic representations. (Caza, Belleville, & Gilbert, 2002). The semantic binding account suggests that verbal Although it is widely accepted that lexical/semantic STM emerges from the language system; therefore, lex- factors contribute to verbal STM, there is still consider- ical and semantic constraints are integral to it. Several able controversy about the mechanisms involved. The other researchers have also advocated this view: for recall errors of patients with semantic dementia appear example, Martin and Saffran (1997) suggested that ver- to offer an intriguing insight into this issue. Semantic bal STM results from interactive activation between dementia patients make numerous phoneme migration phonological, lexical, and semantic nodes following Dell errors in immediate serial recall, particularly for words and OÕSeaghdaÕs (1992) model of speech production. In that they understand poorly (Patterson et al., 1994). This addition, Gathercole and Martin (1996) likened the finding suggests that in healthy individuals, stable operation of phonological STM to McClelland and El- semantic representations help to maintain the correct manÕs (1986) TRACE model of speech perception. configuration of phonological elements in STM. Patter- A rather different account of the long-term memory son et al. (1994) found that immediate serial recall errors contribution to verbal STM proposes that two separate in semantic dementia typically consisted of incorrect mechanisms underlie immediate serial recall perfor- combinations of phonemes from different words that mance (Baddeley, Gathercole, & Papagno, 1998; Hulme largely preserve onset/rime syllable structure (e.g., the et al., 1991, 1997; Schweickert, 1993). (1) There is a rap- onsets in the words Ômint, rugÕ were exchanged to pro- idly decaying phonological STM store, which is initially duce the response Ôrint, mugÕ). Treiman and Danis inert to the effects of lexical and semantic factors. (2) (1988) observed a similar pattern of phoneme migration There is a later reconstructive process that compares errors in normal participantsÕ recall of lists of nonwords the degraded STM trace with separate long-term phono- (e.g., Ôgir, vang, kusÕ recalled as Ôgir, kang, vusÕ). In con- logical–lexical representations during recall to reinstate trast, healthy participants rarely make phoneme migra- the correct phonological activation for words. Although tion errors in word recall. Instead, whole-item order this reconstructive process is underpinned by phonolog- errors constitute the majority of immediate serial recall ical–lexical representations, the model can account for errors in many studies (e.g., Henson, Norris, Page, & semantic effects in immediate serial recall by assuming Baddeley, 1996; Pickering, Gathercole, & Peaker, that semantic activation contributes to the selection of 1998), particularly when a small pool of repeating items lexical candidates for reconstruction (Poirier & Saint- is used to construct the lists for recall (Coltheart, 1993; Aubin, 1995). This view, which has largely emerged Gathercole, Pickering, Hall, & Peaker, 2001). from research on normal participants, suggests that the This striking association between a lack of semantic long-term memory contribution to verbal STM is late- support and the emergence of phoneme migration errors stage and item specific. As the redintegration of each led Patterson et al. (1994) to propose that semantic item is predicted to occur at a late stage, there is no memory makes a major contribution to the coherence mechanism by which lexical/semantic factors pertaining of phonological representations in STM. According to to one item can influence the phonological decay and this ‘‘semantic binding hypothesis,’’ there are two sourc- reconstruction of other list items (see Schweickert, es of constraint that contribute to the phonological 1993). In line with this proposal, several computational coherence of words. First, the constituents of words be- models of immediate serial recall suggest (or, if extend- come associated in the phonological system because they ed, would suggest) that lexical-level representations are always activated together during speech production/ restore the appropriate phonological activation for indi- comprehension; as a result, they are more likely to vidual words at an output stage, after order and partial emerge together in immediate serial recall. Secondly, be- item information has been recovered (Brown, Preece, & cause specific semantic activation frequently co-occurs Hulme, 2000; Burgess & Hitch, 1999; Henson, 1998; with the phonology of words, semantic constraints Page & Norris, 1998). It is important to acknowledge, encourage word phonemes to emerge together in the however, that not all redintegrative theories predict that correct order in immediate serial recall. As immediate late-stage reconstruction is specific to individual items. serial recall tasks require subjects to maintain a phono- For example, the feature model (Nairne, 1990) proposes logical trace of an entire list of items, a loosening of that degraded representations in primary memory are E. Jefferies et al. / Journal of Memory and Language 54 (2006) 81–98 83 matched to possible responses in secondary