Coletta & Williams were first to point out that performance for the two resolution tasks of direction discrimination and orientation discrimination have different endpoints. As illustrated in the right hand graph, the psychometric function of the orientation task is further to the right, indicating a higher acuity. But this leads to a methodological problem: which resolution limit should be used for the purpose of estimating the sampling density of the underlying array? Alternatively, might there be different neural arrays responsible for performing the different visual tasks?

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