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Table 1 Nonlinearities g used in FastICA. The nonlinearities probe the non-Gaussianity of the estimated components in different ways.

From: Statistical model of natural stimuli predicts edge-like pooling of spatial frequency channels in V2

g1 (y) = tanh (y) Classic measure of sparseness
g2 (y) = y exp(-y2/2) More robust variant of g1
g3 (y) = y2 Skewness (asymmetry)
g4 (y) = exp(-y2/2) Robust variant of g3