Acuity
u DEFINITION: ability to resolve or see fine details.
u Visual Angle: DEFINITION: Angle formed by object
on retina.
u Types of Acuity: what is meant by acuity depends
upon the stimulus used to measure it.
l Detection:   black bar on white field
l Resolution:   a grating
l Recognition:   e.g. Snellen, where
            you read letters.