For a two-dimensional signal such as the retinal image, the penalty of undersampling is that the neural image may misrepresent both the spatial frequency and the orientation of the stimulus pattern, and if the pattern is moving then the direction of motion may also be misrepresented.

In the cartoon at the right I've coded the strength of individual neural responses by the luminance of the circles at each sample point and, as you can see, the neural image indicates the presence of an obliquely oriented pattern with a lower spatial frequency than is actually present on the retina. In other words, a coarse grating lying parallel to the dotted lines at the right would have generated the same pattern of responses in the neural arrray as does the actual stimulus at the left.

This misrepresentation of the spatial features of the stimulus caused by undersampling is called 'aliasing' and so, according to this 'Sampling Theory of Visual Resolution', the limit to visual resolution is marked by the onset of aliasing.

The next slide illustrates neural undersampling for a more naturalistic visual scene.

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WWWaveTM 1996
World Wide Web automated virtual environment TM 1996
Kevin Haggerty, Indiana University.