Neuropsychologia 48 (2010) 2147–2157 Contents lists available at ScienceDirect Neuropsychologia journal homepage: www.elsevier.com/locate/neuropsychologia Localizing the Frequency × Regularity word reading interaction in the cerebral cortex Jacqueline Cummine a,∗ , Gordon E. Sarty b , Ron Borowsky b a Department of Speech Pathology and Audiology, University of Alberta, Canada b Department of Psychology, University of Saskatchewan, 9 Campus Drive, Saskatoon, SK S7N 5A5, Canada article info Article history: Received 17 November 2009 Received in revised form 5 March 2010 Accepted 1 April 2010 Available online 10 April 2010 Keywords: Additive Factors Method Spatial localization Temporal localization Functional magnetic resonance imaging Naming Supplementary motor association cortex abstract The aim of this work is to combine behavioural and functional magnetic resonance imaging (fMRI) data to advance our knowledge of where the Frequency × Regularity interaction on word naming is located in the cerebral cortex. Participants named high and low frequency, regular and exception words in a behavioural lab (Experiment 1) and during an fMRI study (Experiment 2). We used the Additive Factors Method (AFM) to localize the expected overadditive Frequency × Regularity interaction both temporally, through word naming reaction times (whereby low frequency exceptions produce the longest reaction times), and spatially on the cortex, through hemodynamic response measures from fMRI (whereby low frequency exceptions produce the highest activation intensities). Activation maps revealed significant activation for low frequency exception words in the supplementary motor association cortex (SMA). We interpret the SMA activation as increased articulatory preparation, given previous demonstrations of the SMA’s involvement in motor programming. Hemodynamic time courses were extracted from four regions of interest: the middle temporal gyri, SMA, insula and the inferior frontal gyri. Importantly, hemodynamic intensities within the SMA displayed an overadditive interaction pattern parallel to that found with naming reaction times. Thus, we provide an application of the AFM to fMRI intensity measures and evidence that the SMA is a potential cortical source of the Frequency × Regularity interaction during a basic naming paradigm. While the AFM has traditionally been used to localize factors in time we provide evidence that the AFM is useful in understanding how variables influence one another in the brain. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction Donders’ subtractive method provided one of the earliest meth- ods for studying the chronometry of perceptual and cognitive processes (Donders, 1969). By subtracting the reaction time to a task (e.g., identification of a flash of light) from reaction time to a task that involves one additional inserted process (e.g., identifica- tion of the colour of a flash of light), the processing time that it takes for the inserted process could be measured. However, the assump- tion that the additional inserted process was the only change to overall processing, known as the assumption of “pure insertion”, was considered to be problematic (Sternberg, 1969). For example, different decision processes and/or processing streams may also be involved with the additional task requirements. Nonetheless, the subtractive method is still pervasive in the design of neuroimaging experiments (see Culham, 2006 for a review). ∗ Corresponding author at: Department of Speech Pathology and Audiology, Fac- ulty of Rehabilitation Medicine, University of Alberta, 8205 114St, 3-58A Corbett Hall, Edmonton, AB T6G 2G4, Canada. Tel.: +1 780 492 3965; fax: +1 780 492 9333. E-mail address: jcummine@ualberta.ca (J. Cummine). The introduction of Sternberg’s (1969) additive factors method (AFM) provided a new way of looking at reaction times in cognitive experiments. This method has been useful in examining stages or underlying sub-systems of processing and how factors affect a com- mon stage versus separable stages of processing in basic reading tasks (Borowsky & Besner, 1993; Borowsky & Besner, 2006). How- ever, limited research has been conducted which applies the AFM to measures other than reaction time (see Miller & Hackley, 1992; Schweickert, 1989, 1985 for an application of the AFM to lateralized readiness potentials and accuracy, respectively). More specifically, while the AFM has advanced our understanding of when experi- mentally manipulated variables (or factors) influence one another temporally in terms of stages of processing in time, it remains to be seen whether such a method can be useful in our understand- ing of where factors influence one another spatially in terms of the cortex. Research that supports the utility of analyzing men- tal activity with behavioural methodology comes from studies that have demonstrated that a relationship exists between behavioural and neuroanatomical measures. For example, past research has correlated onset measures (e.g., stimulus presentation) with Blood Oxygenated Level Dependent (BOLD) activity onset (e.g., inflection point from baseline; Menon, Luknowsky, & Gati, 1998; Richter, 0028-3932/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuropsychologia.2010.04.006