Methodological Concerns

For many reasons, the neuroimaging data in their present form do not provide satisfactory or conclusive answers to the question of whether there is differential hemispheric activation in bilinguals and what overlapping patterns of activation might mean. As already noted, the studies have varied widely in their tasks (including overt and covert production vs comprehension tasks, with the unit of language varying from single words to sentences or discourse); however, task parameters have not specifically been addressed in most of the studies. Although proficiency and age of onset of bilingualism have been proposed to explain discrepancies across studies, only two studies specifically compared early versus late proficient bilingual users (controlling for language used), and only one directly compared proficient and nonproficient late bilinguals.

More important, since only 3 of the 38 imaging studies employed monolinguals and only 4 controlled for whether a particular language was the first or the second language, it is not clear to what extent the patterns of activation observed (whether differential or overlapping) simply reflect language-specific effects (e.g., characteristics of the languages' orthographies, phonologies, or grammar). Another problem in interpreting the studies is that task performance was not consistently monitored behaviorally. It is important to do so both to ensure that subjects were complying with instructions and to determine subjects' level of performance on each language. In some cases, where subjects were reported to be slower in performing the task in the second language, their pattern of brain activation showed no difference across languages. In other studies subjects were pretested to be equivalent in their task performance in the two languages and overlapping patterns of brain activation were again observed.

As Paradis cautions, PET and fMRI data may tell us that some cerebral area is activated during the performance of a particular task, but they do not tell us what function is activated in this area, nor is it possible to determine if the areas that are activated in a particular study are crucial or incidental to language. Furthermore, failure to detect activation in a specific area is not evidence that this area is not active—only that it is not revealed by the procedure that is used. The likelihood of observing a change in activation is influenced by both the study design and the image analysis technique employed. That is, areas found to be significantly activated are activated only with reference to the particular task chosen as a baseline (whether this be attentive silence, periods of rest, random noise, word repetition, or backward speech) and with reference to the statistical tools (and cutoff thresholds for significance) and rationale used, regarding what is to be subtracted from what. Indeed, the appropriateness of the practice of using a subtractive logic to study functional activation of language in general has been questioned.

Breaking Bulimia

Breaking Bulimia

We have all been there: turning to the refrigerator if feeling lonely or bored or indulging in seconds or thirds if strained. But if you suffer from bulimia, the from time to time urge to overeat is more like an obsession.

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