Author's personal copy Brain & Language 117 (2011) 53–68 Contents lists available at ScienceDirect Brain & Language journal homepage: www.elsevier.com/locate/b&l Theories of spoken word recognition deficits in Aphasia: Evidence from eye-tracking and computational modeling ⇑ Daniel Mirman a, ,1, Eiling Yee b,1, Sheila E. Blumstein c,d,e,f, James S. Magnuson g,h a Moss Rehabilitation Research Institute, 50 Township Line Rd., Elkins Park, PA 19027, USA b Department of Psychology, University of Pennsylvania, Philadelphia, PA 19104, USA c Department of Cognitive, Linguistic, and Psychological Sciences, Brown University, USA d Research Service, Department of Veterans Affairs Medical Center, Providence, RI 02908, USA e Boston University Harold Goodglass Aphasia Research Center at the VA Boston Healthcare System, Boston, MA 02130, USA f Research Service, VA Boston Healthcare System, Boston, MA 02130, USA g Department of Psychology, University of Connecticut, Storrs, CT 06269, USA h Haskins Laboratories, New Haven, CT 06511, USA article info abstract Article history: We used eye-tracking to investigate lexical processing in aphasic participants by examining the fixation Accepted 23 January 2011 time course for rhyme (e.g., carrot–parrot) and cohort (e.g., beaker–beetle) competitors. Broca’s aphasic Available online 2 March 2011 participants exhibited larger rhyme competition effects than age-matched controls. A re-analysis of pre- viously reported data (Yee, Blumstein, & Sedivy, 2008) confirmed that Wernicke’s aphasic participants Keywords: exhibited larger cohort competition effects. Individual-level analyses revealed a negative correlation Spoken word recognition between rhyme and cohort competition effect size across both groups of aphasic participants. Computa- Aphasia tional model simulations were performed to examine which of several accounts of lexical processing def- Eye-tracking icits in aphasia might account for the observed effects. Simulation results revealed that slower Computational models Growth curve analysis deactivation of lexical competitors could account for increased cohort competition in Wernicke’s aphasic participants; auditory perceptual impairment could account for increased rhyme competition in Broca’s aphasic participants; and a perturbation of a parameter controlling selection among competing alterna- tives could account for both patterns, as well as the correlation between the effects. In light of these sim- ulation results, we discuss theoretical accounts that have the potential to explain the dynamics of spoken word recognition in aphasia and the possible roles of anterior and posterior brain regions in lexical pro- cessing and cognitive control. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction Broca’s and Wernicke’s aphasia exhibit different patterns of perfor- mance in lexical processing tasks. These differences have led to It has been long recognized that individuals with aphasia have considerable debate about the nature of the functional deficits of lexical processing impairments. Particular focus has been on the these individuals and their underlying neurobiological substrates. two classical clinical types, Broca’s and Wernicke’s aphasia, with Given that word recognition calls on many different aspects of the goal of understanding the neurobiological substrates of word cognitive processing, impairments of any of these aspects could recognition. Individuals with Broca’s aphasia typically have left give rise to word recognition deficits. Much research has investi- frontal lesions including the inferior frontal gyrus (IFG). In contrast, gated potential deficits at different points in the processing stream. individuals with Wernicke’s aphasia typically have left posterior A classic method for investigating lexical access is semantic prim- lesions including the posterior portion of the superior temporal ing using the lexical decision paradigm. In general, individuals gyrus (STG) and often extending into inferior parietal areas. with Broca’s and Wernicke’s aphasia both show semantic priming Although the mapping between clinical diagnosis and underlying in a lexical decision task, suggesting that they are able to map neuropathology is far from perfect, as we will discuss, there is a sound structure onto the lexicon and access lexical-semantic rep- rich literature demonstrating that individuals diagnosed with resentations (e.g., Blumstein, Milberg, & Shrier, 1982; Milberg & Blumstein, 1981). However, their priming is not completely nor- ⇑ Corresponding author. Fax: +1 215 663 6783. mal. Several studies have demonstrated that in Broca’s aphasia, E-mail address: [email protected] (D. Mirman). priming fails to emerge under some conditions in which controls 1 The two first authors contributed equally to this manuscript. exhibit priming, e.g., with acoustic modifications and at various 0093-934X/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.bandl.2011.01.004 Author's personal copy 54 D. Mirman et al. / Brain & Language 117 (2011) 53–68 interstimulus intervals (Milberg, Blumstein, & Dworetzky, 1988; competing alternatives could also be argued to account for fragile Misiurski, Blumstein, Rissman, & Berman, 2005; Prather, Zurif, priming, particularly under conditions of lexical competition. Like- Stern, & Rosen, 1992; Utman, Blumstein, & Sullivan, 2001). In wise, in Wernicke’s aphasia, increased activation and delayed Wernicke’s aphasia, in contrast, priming has emerged under more deactivation could both account for priming occurring in more cir- conditions than normal; for example, they show an equal magni- cumstances than normal. The perceptual impairment hypothesis tude of priming when a real word prime is changed to a phonolog- can predict either the Broca’s pattern of reduced priming because ically similar non-word (e.g., gat–dog and wat–dog show as much perceptual noise typically reduces activation (i.e., perceptual cer- priming as does cat–dog), whereas control participants show a tainty) or the Wernicke’s pattern of priming for a wider set of stim- graded reduction in priming (cat > gat > wat)(Milberg et al., 1988). uli because perceptual noise reduces differentiation among similar Although it is clear that Broca’s and Wernicke’s aphasia both speech sounds. cause deficits in lexical processing, there is disagreement about the exact nature of the deficit. The current work aims to provide 1.2. Eye-tracking studies of spoken word processing a fuller picture of lexical processing in aphasia by combining com- putational modeling with data from an eye-tracking paradigm (the Prior studies using the visual world paradigm (VWP) with ‘‘visual world paradigm’’) that provides fine-grained information unimpaired participants have shown that fixations are time locked about the time course of lexical activation. to fine-grained details of ongoing speech, allowing estimates of the time course of processing at phonetic, lexical, and sentence level 1.1. Five accounts of lexical processing deficits in Aphasia time scales (for a review, see Tanenhaus, Magnuson, Dahan, & Chambers, 2000). In VWP studies participants are typically pre- Several theories have been proposed to account for the lexical sented with a four-picture display and asked to ‘‘pick up’’ (i.e., processing impairments in aphasia. Here we briefly state the cen- move with a computer mouse) one of the objects in the display tral hypothesis of each and discuss some challenges in distinguish- (the target). If the name of one of the distractor objects is an onset ing between them. (‘‘cohort’’) competitor of the target word (e.g., beaker–beetle), par- ticipants are initially more likely to fixate on this object than on Degree of activation. The overall activation in the lexicon is objects with phonologically unrelated names. For example, if asked reduced in Broca’s aphasia and increased in Wernicke’s aphasia to ‘‘Pick up the beaker,’’ participants are more likely to fixate a bee- (Blumstein & Milberg, 2000; Janse, 2006; McNellis & Blumstein, tle than an unrelated distractor such as a carriage. If the name of 2001; Milberg, Blumstein, & Dworetzky, 1987; Milberg et al., one of the distractor objects is an offset (‘‘rhyme’’) competitor 1988; Utman et al., 2001). (e.g., beaker–speaker), participants also tend to fixate this object Time course of lexical activation. In Broca’s aphasia, lexical activa- more than phonologically unrelated objects, though the competi- tion is delayed or slowed, leading to a later-than-normal rise tion tends to be weaker and later (Allopenna et al., 1998; time (Prather, Zurif, Love, & Brownell, 1997; Prather et al., Desroches, Joanisse, & Robertson, 2006; Magnuson, Tanenhaus, 1992; Swinney, Prather, & Love, 2000; Swinney, Zurif, & Nicol, Aslin, & Dahan, 2003; for demonstrations of cohort and rhyme 1989). In Wernicke’s aphasia, a failure to inhibit lexical compet- competition effects in other paradigms see Andruski, Blumstein, itors leads to delayed deactivation in the lexical-semantic net- and Burton (1994), Connine, Blasko, and Titone (1993), Marslen- work (Prather et al., 1997). Wilson and Zwitserlood (1989), and Slowiaczek, Nusbaum, and Short-term memory. Aphasic individuals have deficits in short- Pisoni (1987)). Furthermore, as a word unfolds, the likelihood that term memory (or working memory) that cause difficulty main- a participant will fixate on its corresponding picture – and on its taining the activation of lexical representations (Martin, phonological competitors – closely matches each word’s lexical