Academic journal article Cognitive, Affective and Behavioral Neuroscience

Understanding the Effects of Task-Specific Practice in the Brain: Insights from Individual-Differences Analyses

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Understanding the Effects of Task-Specific Practice in the Brain: Insights from Individual-Differences Analyses

Article excerpt

We used functional magnetic resonance imaging to study practice effects in different mental imagery tasks. The study was designed to address three general questions: First, are the results of standard group-based analyses the same as those of a regression method in which brain activation changes over individual participants are used to predict task performance changes? With respect to the effects of practice, the answer was clear: Group-based analyses produced different results from regression-based individual-differences analyses. Second, are all brain areas that predict practice effects consistently activated across participants? Again, the answer was clear: Most areas that predicted the effects of practice on performance were not activated consistently over participants. Finally, does practice affect different areas in different ways for different people in different tasks? The answer was again clear: The areas that predicted changes in performance with practice varied for the different tasks, but this was more dramatically and clearly revealed by the individual-differences analyses. In short, individual-differences analyses provided insights into the relation between changes in brain activation and changes in accompanying performance, and these insights were not provided by standard group-based analyses.

Neuroimaging has revealed that even apparently simple perceptual and cognitive tasks are carried out by numerous interconnected brain areas and that different tasks typically rely on partially overlapping sets of brain areas (e.g., Kandel & Squire, 2000; Kosslyn, Thompson, & Alpert, 1997; Smith & Jonides, 1997). Research has also revealed that the more similar the tasks, the more brain areas are activated in common; for example, when participants performed different judgments with different stimuli in imagery and perception tasks, about two thirds of the same areas were activated in common (Kosslyn et al., 1997), whereas when participants performed the same judgment on imagined and visually perceived versions of the same stimuli, over 90% of the same brain areas were activated (Ganis, Thompson, & Kosslyn, 2004). The pattern of commonalities and differences between brain regions active in different tasks provides a plausible explanation for the pattern of impairments exhibited by neurological patients. For instance, consistent with the overlap between the neural activation elicited by visual imagery and visual perception, damage to the ventral temporal cortex often leads to parallel impairments in visual imagery and visual perception (Ganis, Thompson, Mast, & Kosslyn, 2003). Conversely, the lack of common activation in some brain regions can explain why brain damage sometimes results in a dissociation between impairments in visual imagery and visual perception (Ganis et al., 2003).

Understanding which brain areas are recruited during specific tasks is important not only if we are to understand the effects of brain damage, but also if we are to understand many fundamental aspects of the relation between mind and brain-such as how drugs selectively affect performance and how genes affect cognition and affect. However, the neuroimaging findings that document the networks of areas activated while participants perform specific tasks rely on a number of key assumptions, and these assumptions may, at least sometimes, lead us to mischaracterize the pattern of brain activation that underlies task performance. In the present article, we will consider implications of three general methodological assumptions that characterize most neuroimaging studies.

First, most neuroimaging studies employ a subtraction logic, which entails comparing results from test and baseline (control) tasks. This logic is not new: It was originally developed over 100 years ago to study response times (RTs; Donders, 1868/1969) and has been used extensively in mental chronometry studies to infer the duration of mental processes (Posner, 1978). …

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