Abstract
BackgroundNeural systems show habituation responses at multiple levels, including relatively abstract language categories. Dishabituation – responses to non-habituated stimuli – can provide a window into the structure of these categories, without requiring an overt task.MethodsWe used an event-related fMRI design with short interval habituation trials, in which trains of stimuli were presented passively during 1.5 second intervals of relative silence between clustered scans. Trains of four identical stimuli (standard trials) and trains of three identical stimuli followed by a stimulus from a different phonetic category (deviant trials) were presented. This paradigm allowed us to measure and compare the time course of overall responses to speech, and responses to phonetic change.ResultsComparisons between responses to speech and silence revealed strong responses throughout the extent of superior temporal gyrus (STG) bilaterally. Comparisons between deviant and standard trials revealed dishabituation responses in a restricted region of left posterior STG, near the border with supramarginal gyrus (SMG). Novelty responses to deviant trials were also observed in right frontal regions and hippocampus.ConclusionA passive, dishabituation paradigm provides results similar to studies requiring overt responses. This paradigm can readily be extended for the study of pre-attentive processing of speech in populations such as children and second-language learners whose overt behavior is often difficult to interpret because of ancillary task demands.
Highlights
Neural systems show habituation responses at multiple levels, including relatively abstract language categories
The goal of the current study is to develop a short interval habituation trial paradigm optimized for event-related fMRI designs that builds on the strengths of currently available methods, and can be applied to a range of populations of interest
In the current study we address a number of these methodological challenges by presenting short interval habituation trials composed of trains of four stimuli
Summary
Neural systems show habituation responses at multiple levels, including relatively abstract language categories. Habituation effects have been observed in a wide range of neural systems from simple sensory responses [1], to higher-order neural representations such as motion-sensitive populations in Area MT [2], and regions responding to written and spoken language [3]. Behavioral and Brain Functions 2005, 1:4 http://www.behavioralandbrainfunctions.com/content/1/1/4 perception under more natural conditions. This is a particular problem for studying speech developmentally, because attention and decision processes develop very slowly [5,6] which may cause us to underestimate children's ability to perceive phonetic contrasts. The goal of the current study is to develop a short interval habituation trial paradigm optimized for event-related fMRI designs that builds on the strengths of currently available methods, and can be applied to a range of populations of interest
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