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Experience-Dependent Representation of Visual Categories in Parietal Cortex David J. Freedman and John A. Assad

Summary: Experience-Dependent Representation of Visual Categories in Parietal Cortex
David J. Freedman and John A. Assad
Supplementary Methods
Computation of BCD, WCD and category-tuningindex values. The strength of neuronal
category-tuning was estimated by a category-tuning index that was computed from two values: (1)
the average within-category difference (WCD) in firing rates between pairs ofdirections in the
same category, and (2) the average between-category difference (BCD) in firing rates between
pairs of directions in different categories. Our goal was to have equal numbersof paired
comparisons forthe BCD and WCD calculations, and to only include comparisons that were
represented in both BCD and WCD calculations. For these reasons,both BCD and WCD values
were determined by computing the averageabsolute firing-rate differences for 18 pairs of
directions, including comparisons across 30, 60, 90, 120, and 150 intervals. 180 was
excluded fromthe BCD calculation because therewere no corresponding pairs of directions for the
WCD calculation that were 180 apart and in the same category (although, including the 180 BCD
interval gave qualitatively similar results). The 18 pairs used for the WCD calculations were
identical in structure to the 18 pairs used forthe BCD, except that they were all rotated 90 with
respect to the category boundary. In other words, we used the 18 within-category pairs of
directions (nine in each category) for the WCD calculation that, when rotated 90,crossed the
category boundary. For example, the 30 BCD value was computed across the two pairs of
directions that were 30 apart and crossed the category boundary (i.e. 120 - 150 and 300 - 330;


Source: Andrzejak, Ralph Gregor - Departament de Tecnologia, Universitat Pompeu Fabra


Collections: Computer Technologies and Information Sciences