Investigating the modality speci W city of response selection using a temporal X anker task

The neurocognitive architecture for response selection is uncertain. Some theorists suggest that it is mediated by an amodal central mechanism, whereas others propose a set of independent control mechanisms. In a functional neuroimaging experiment, we investigated the nature of response selection by examining how its underlying brain mechanisms are aVected by stimulus modality. To do this, we used a modiWed Xanker task, in which the target and Xanker (distractor) stimuli diVered in time rather than space, making it accessible for both visual and auditory stimuli. As in the traditional Xanker task, larger reaction times were observed for incongruent than congruent trials (i.e., a congruency eVect) for both modalities. Congruency aVected brain activation for both modalities in prefrontal cortex, parietal cortex, and the putamen. Modality-dependent activation was found in additional prefrontal and parietal regions for the visual modality and in left inferior prefrontal cortex for the auditory modality. Modality-dependent activity speciWcally related to response congruency was also found in sensory cortical regions. These data suggest that modality aVects the brain regions throughout the cortex mediating response selection even for conceptually identical stimuli and tasks. They are consistent with the hypothesis that (at least partially) independent brain networks mediate response selection and that input modality may be a powerful factor for organizing neural activity to support task performance. Introduction Response selection is the cognitive process, or collection of processes, that activate a response representation based on a particular stimulus representation and a set of stimulus– response (S–R) rules. How responses are selected based on stimulus inputs is controversial. Many theorists consider response selection a processing stage distinct from modality-speciWc stimulus encoding and response production stages (for reviews see Meyer & Kieras, 1997a; Pashler, 1994; Pashler & Johnston, 1998). Other theorists (e.g., Cohen & Feintuch, 2002; Magen & Cohen, 2010; Wickens & Liu, 1988; Wickens, Mountford, & Schreiner, 1981) emphasize the eVect on response selection of input and output modalities (and the pairings between them). The current functional magnetic resonance imaging (fMRI) experiment investigates the eVect of manipulating stimulus modality on response selection within an otherwise identical task. In this way we may isolate the eVect of modality on the brain mechanisms underlying response selection. According to the amodal view of response selection (e.g., Byrne & Anderson, 2001; Pashler, 1994; Pashler & Johnston, 1998), a unitary mechanism applies the abstract S–R rules and selects appropriate responses for all incoming task-relevant stimuli. Evidence for this hypothesis comes mainly from behavioral experiments, in which the eVect on behavioral dependent variables (viz., reaction time, RT, and accuracy) of performing two tasks simultaneously (or nearly so) are measured. These experiments typically show that processing of the secondary task stimulus is delayed by processing of the primary task stimulus— even when the tasks do not share stimulus or response modalities (e.g., Pashler, 1990). Additional experimental manipulations have been used to suggest that a bottleneck in response selection processing (i.e., response selection E. H. Schumacher (&) · H. Schwarb · E. Lightman School of Psychology, Georgia Institute of Technology, 654 Cherry Street, Atlanta, GA 30332, USA e-mail: eschu@gatech.edu E. Hazeltine Department of Psychology, University of Iowa, E111 Seashore Hall, Iowa City, IA 52242, USA e-mail: eliot-hazeltine@uiowa.edu