Extended Data Fig. 8: Population analysis of gratings responses during influence mapping blocks.

a, The orientation information content of all neurons during influence mapping blocks, calculated using the same binning approach used for population decoding. Information is colour coded, and plotted as a function of a neuron’s directional modulation and preferred spatial frequencies estimated during tuning measurement blocks. This demonstrates that tuning estimated in tuning and influence measurement blocks were concurrent (gratings during influence mapping were always 0.04 cycles per degree), but that responses to full-field, low-contrast gratings in influence measurement blocks were sparse. b, Schema indicating the orthogonalization procedure used for population analysis. In brief, because average responses to each grating orientation were not entirely orthogonal, and because photostimulation evoked highly significant changes in response gain in our dataset, we wished to isolate potential changes along alternative population activity dimensions independent of gain changes. To accomplish this, we orthogonalized projections along non-gain dimensions relative to the gain projection observed on individual trials. This ensured that changes in response gain could not trivially produce changes along non-gain population dimensions.