The orientation selectivity index (OSI) was calculated for visually responsive cells16,30. First, the preferred orientation (θpref) of the cell was determined as the stimulus that produced the strongest response. The orientation tuning curve was constructed by measuring the mean ΔF/F0, averaged over the stimulus period, for each orientation. We then fitted the tuning curve with the sum of two Gaussians centered on θpref and θpref + π, both with width σ (constrained to >15°), amplitudes A1 and A2, and a constant baseline B. The OSI was defined as OSI=(Rpref-Rortho)/(Rpref+Rortho), where Rpref and Rortho are the response amplitudes at the preferred (θpref) and the orthogonal orientation (θpref + π/2) respectively.
