Neuropsychologia 50 (2012) 723–732 Contents lists available at SciVerse ScienceDirect Neuropsychologia jo u rn al hom epa ge : www.elsevier.com/locate/neuropsychologia Paced reading in semantic dementia: Word knowledge contributes to phoneme binding in rapid speech production Elizabeth Jefferies a,∗ , John Grogan a , Cristina Mapelli b , Valeria Isella b a Department of Psychology, University of York, York YO10 5DD, UK b Department of Neurosciences, School of Medicine, University of Milan Bicocca, Italy a r t i c l e i n f o Article history: Received 9 September 2011 Received in revised form 8 December 2011 Accepted 3 January 2012 Available online 11 January 2012 Keywords: Semantic dementia Phoneme binding Verbal short-term memory a b s t r a c t Patients with semantic dementia (SD) show deficits in phoneme binding in immediate serial recall: when attempting to reproduce a sequence of words that they no longer fully understand, they show frequent migrations of phonemes between items (e.g., cap, frog recalled as “frap, cog”). This suggests that verbal short-term memory emerges directly from interactions between semantic and phonological systems, allowing semantic knowledge to make a critical contribution to the stability of phonological sequences. According to this standpoint, SD patients should show phoneme binding deficits in additional language tasks beyond standard assessments of verbal short-term memory: for example, these errors should emerge in paced reading, which also requires the rapid production of semantically degraded words in order. To test this hypothesis, we examined a cyclical paced reading task in three SD patients for the first time. Every patient showed deficits in phoneme binding: they were more vulnerable than a set of age- matched controls to phoneme competition effects following the repetition of a small set of words across several cycles. They also showed substantially elevated numbers of phoneme migration, substitution and omission errors, despite being able to read the individual words almost without error. These findings confirm that the semantic contribution to phoneme binding is disrupted in SD patients across tasks. In line with the view that verbal short-term memory emerges from interactions between basic phonological and semantic components, these effects occur both within classic short-term memory paradigms, such as immediate serial recall, and tasks without explicit memory demands, such as paced reading. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction When we speak or comprehend a sequence of words, we are required to maintain their constituent phonemes in order – a ‘half formed wish’ is not the same as ‘a half warmed fish’! This ability to preserve ordered language information is crucial for many every- day activities, such as holding a conversation, learning new words and verbal reasoning, but there is controversy about the precise mechanisms involved. In particular, there is ongoing debate about the relationship between verbal short-term memory (STM) and language representations, and the nature of the serial order mech- anisms in each of these domains (Acheson & MacDonald, 2009b; Jefferies, Frankish, & Lambon Ralph, 2006a; Martin & Saffran, 1997; Patterson, Graham, & Hodges, 1994). Previous work has shown that linguistic knowledge has little influence on serial order mem- ory, at least when immediate serial recall (ISR) is examined at the level of whole items (as in the overwhelming majority of studies; Gathercole, Pickering, Hall, & Peaker, 2001; Hulme et al., 1997; ∗ Corresponding author. Tel.: +44 01904 434368. E-mail address: ej514@york.ac.uk (E. Jefferies). Poirier & Saint-Aubin, 1995; Saint-Aubin & Poirier, 1999; Walker & Hulme, 1999). Lexical and semantic factors such as word fre- quency and imageability (i.e., whether targets refer to imageable or abstract concepts) affect memory for the items themselves, rather than their order, in line with the dominant view in the STM liter- ature that lexical knowledge is used to reconstruct familiar items during a process of “redintegration” at recall (Baddeley, Gathercole, & Papagno, 1998; Hulme, Maughan, & Brown, 1991; Schweickert, 1993). However, when ISR is examined at the level of individual phonemes, there is a clear effect of linguistic knowledge on order memory which cannot be readily explained by the redintegration account (e.g., Jefferies et al., 2006a; Jefferies, Frankish, & Lambon Ralph, 2006b; Patterson et al., 1994). We have proposed that a com- mon mechanism can account for both of these patterns of data, because when phonemes migrate, the identity of items is changed. Therefore, if lexical and semantic knowledge influences phoneme sequencing, manipulations of these variables should affect identity rather than order errors at the level of whole items. Much of the work suggesting a role for word knowledge in the maintenance of phoneme order in ISR has examined patients with semantic dementia (SD). These patients show a progressive and highly selective impairment of conceptual knowledge which affects 0028-3932/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuropsychologia.2012.01.006