Figure 3.

Sparseness measures for eight hypothetical response distributions. A, A Gaussian distribution with mean response of zero should have kurtosis and entropy of zero, by definition. B, The same distribution as in A, but with all negative values set to zero; such “half-wave rectification” is a stylized model of the responses of simple cells with no spontaneous activity. C, The same distribution as in A, but with all negative values made positive and reflected through zero; such “full-wave rectification” is a stylized model of the responses of complex cells with no spontaneous activity. D, A stylized model of the response distribution of a simple cell with spontaneous level of activity equivalent to a response of “5 units”: 5 is added to the Gaussian distribution of A and all negative values are then set to zero. E, A leptokurtic distribution (exponential) with the same mean (zero) and variance as in A. F, G, Half-wave rectified and full-wave rectified versions of the exponential distribution in E. H, A stylized model of the responses of a simple cell with no spontaneous activity and with a response threshold equivalent to a response of “5 units”: 5 is subtracted from the Gaussian distribution of A, and all negative values are then set to zero.