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When an object is too small or too far off in the distance, we cannot identify it visually. We can detect its presence but cannot make out its features. This inability to make out small features is caused by the limited spatial acuity (or spatial resolution) of the visual system. Our visual acuity is tested, using a so-called Snellen chart, by determining what the smallest identifiable letter is. Eye exams are, in effect, tests of how small visual features can be before we can no longer discern them.

The sense of touch is also subject to limited resolution. Indeed, when we run our fingers across surfaces with large features, such as the number pad on a phone, we can discern individual features (e.g., the buttons on ...

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