Poster A134, Saturday, March 25, 5:00 – 7:00 pm, Pacific Concourse
Intraparietal sulcus codes for auditory quantities
Shipra Kanjlia1, Lisa Feigenson1, Marina Bedny1; 1Johns Hopkins University
Numerical thinking is supported by a fronto-parietal network of which the intraparietal sulcus (IPS) is a key node. During visual number tasks, different numerosities are coded by distinct populations of neurons in the IPS. Spatial patterns of activity in the IPS can distinguish between whether participants are viewing 4, 8, 16 or 32 dots (Eger et al., 2009). Here we asked whether there is also a spatial code in the IPS for quantities conveyed as auditory sequences. Participants (n=14) judged the quantity of auditory tones while undergoing fMRI. Participants heard a sample set of tones (either 4, 8, 16, or 32 beeps), followed by a 6s delay, and then a test set. They decided whether the first or second set had more tones. We asked whether we could decode how many tones participants heard based on the spatial pattern of activity in the IPS during the delay period. A linear support vector machine (SVM) classifier was trained to distinguish between every possible pairing of numerosities (e.g. 4 vs. 8 and 4 vs. 16). SVMs were trained on all but 1 run of data and tested on trials from the remaining run. Classification accuracy was averaged across possible number pairings and across runs. 54% trials were correctly classified by left and right IPS activity (lIPS: p<0.01 (using single sample t-test), p<0.001 (using permutation test); rIPS: p<0.02 (using single sample t-test), p<0.001 (using permutation test)). Thus, in addition to visual quantities, the IPS has a spatial code for auditory quantities.
Topic Area: OTHER