Poster Winner, Margaret Gullick!
Congratulations to graduate student Margaret Gullick, in the Psychological and Brain Sciences Department, who was one of four winners of the Graduate Poster Session held recently at the Top of the Hop! Margaret will soon be moving to Northwestern University, where she has accepted a postdoctoral fellowship aimed at examining the neural basis of dyslexia using functional and structural brain imaging. Enjoy your winnings, Margaret! (Read on for a summary of Gullick’s poster.)
Poster title: “Understanding less than nothing: A developmental fMRI study of negative number comparisons”
Negative numbers are a counterintuitive mathematical concept: they are worth literally less than nothing, and yet represent some quantitative value. While we eventually come to work with these numbers fluently after years of practice, it is unknown whether we end up processing them like positive numbers (which represent amounts of real things in the world) or if we invoke different strategies or rules. I investigated the brain systems involved in understanding these difficult values across age using functional magnetic resonance imaging (fMRI).
The intraparietal sulcus (IPS), a groove in the brain within the parietal lobe, has evolved a particular sensitivity to positive numbers and the amounts they represent. Further, when we compare pairs of numbers, activity in this region increases as the difference between the comparators decreases (e.g., as the comparisons get harder). I wanted to determine whether the IPS was similarly sensitive to comparator difference for negative number pairs, which involves choosing between two less-than-zero amounts. I also wanted to investigate how this processing changes across age and instruction.
Therefore, I examined the brain activity underlying these comparisons in adults (college students), seventh-graders (who had at least one year of school instruction on negative numbers), and fifth-graders (who had no formal experience with negatives). All age groups showed a typical effect of comparator difference on IPS activity, where activity increased as the difference decreased, for both positive and negative number pairs. Negative number processing thus appears to draw on the same number-sensitive region in the same manner as positive numbers even before instruction. Second, the size of this effect for negative number comparisons in fifth graders was significantly predicted only by children’s accuracy on the positive comparison pairs: children with better positive accuracy showed a stronger effect. This relationship implies that before formal instruction on the topic, children who better understand positive numbers may have a better basis for understanding negative numbers, allowing more fluent use.
Such investigations help us understand the flexibility of the mental number system and its ability to incorporate non-intuitive values by determining the extent to which number-sensitive regions of the brain area responsive to negative amounts, and can more generally inform us about how best to teach these concepts.
poster summary by Margaret Gullick