Stimulus shapes strategy: Effects of stimulus characteristics and individual differences in academic achievement on the neural mechanisms engaged during the N-back task.

This fMRI study of 126 youth explored whether the neural mechanisms underlying the N-back task, commonly used to examine executive control over the contents of working memory, are associated with individual differences in academic achievement in reading and math. Moreover, the study explored whether these relationships occur regardless of the nature of the stimulus being manipulated in working memory (letters, numbers, nonsense shapes) or whether these relationships are specific to achievement domain and stimulus type (i.e., letters for reading and numbers for math). The results indicated that higher academic achievement in each of reading and math was associated with greater activation of dorsolateral prefrontal cortex in the N-back task regardless of stimulus type (i.e., did not differ for letters and numbers), suggesting that at least some aspects of the neural mechanisms underlying these academic domains are executive in nature. In addition, regardless of level of academic achievement, prefrontal regions were engaged to a greater degree for letters than numbers than nonsense shapes. In contrast, nonsense shapes yielded greater hippocampal activation than letters and numbers. Potential reasons for this pattern of findings are discussed.

How much is remembered as a function of presentation modality?

According to a widespread claim used for teaching recommendations, students remember 10% of what they read, 20% of what they hear, 30% of what they see, and 50% of what they see and hear. Clearly, the percentages cannot be correct, and there is no empirical evidence for the ordering. To investigate the ordering, in a navigation paradigm, subjects were given messages instructing them to move in a grid of four stacked matrices by clicking a computer mouse. Three modalities were compared presented either once, see (visual arrows), hear (auditory words), read (visual words); twice in succession, see-see, hear-hear, read-read; or in two different successive modalities, see-hear, hear-see, see-read, read-see, hear-read, read-hear. Better performance was found for messages presented twice than once, but messages in the two modalities were not always better than twice in one modality. For the twice-presented messages, performance varied as a function of the second modality, with see best and read worst. However, the ordering for the first modality was not reliable and was inconsistent with the widespread claim. Thus, the widespread claim is clearly wrong, not only in its percentages, but also because of its lack of generality.