Variability and fluctuation in behavior and task performance are commonly observed in individuals with developmental disorders (Castellanos et al., 2005). Although most typically associated with ADHD, recent empirical work has demonstrated that individuals with ASD show significantly greater intra-individual response time variability during a simple 2AFC task compared not only to a group of typically developing (TD) matched control participants, but also compared to a group of matched participants with ADHD (Geurts et al., 2008). Intra-individual variability appears to be an important indicator of pathophysiological processing therefore, and its potential to explain a number of task-related behaviors in those with ASD should not be over-looked. However, there are many potential routes to response time variability, including: variability in higher-order cognitive functions such as initiating or generating motor responses (Deutsch and Newell, 2005); transient lapses of attention; and/or variability in early sensory encoding (e.g., Croner et al., 1993; Arieli et al., 1996). The source of intra-participant variability in ASD is therefore unclear.
