Several recent theoretical models for human spatial vision posit that cortical receptive fields act to minimize simultaneously the product of the standard deviation of the sensitivities to position (delta chi) and to spatial frequency (delta omega) in accord with the uncertainty principle from Fourier analysis. The receptive-field functions resulting from this approach--one-dimensional or two-dimensional Gabor elementary functions--have been shown by others to fit measured receptive fields adequately in some species. However, only complex-valued Gabor functions minimize this product, and these cannot be fitted to single-cell receptive fields. We point out that the derivations of others have an implied metric or measure of positional and spatial-frequency uncertainties and that there is an infinitely large class of such metrics, many of which yield other receptive-field functions that are quite plausible biologically. We review neurophysiological measurements of others and analyze psychophysical masking data and find that in many cases receptive-field functions other than Gabor functions fit better. We conclude that there are insufficient theoretical demonstrations and experimental data to favor Gabor functions over any of a number of other plausible receptive-field functions.