Eye chart number). The denominator indicates the distance in feet at which a person with normal vision could stand to correctly identify the same symbols identified by the person tested. For example, a visual acuity of 20/20 is considered normal. Numerous types of eye charts exist and are used in various situations. For example, the Snellen chart is designed for use at 6 meters or 20 feet, and is thus appropriate for testing distance vision. There is often also a need to test a subject's vision at near or occupational tasks (such as reading or computer use). For these situations, a Rosenbaum
Levels-of-processing effect subject does not explicitly recall the stimulus, but the previous stimulus still affects performance. For example, in a word-completion implicit memory task, if a subject reads a list containing the word "dog", the subject provides this word more readily when asked for three-letter words beginning in "d". The levels-of-processing effect is only found for explicit memory tests. One study found that word completion tasks were unaffected by levels of semantic encodings achieved using three words with various levels of meaning in common. Another found that typical level-of-processing effects are reversed in word completion tasks; subjects recalled pictures pairs more completely