The total area in which visual perception is possible while a person is looking straight ahead.
The visual fields normally extend outwards over an angle of about 90 degrees on either side of the midline of the face, but are more restricted above and below, especially if the eyes are deep-set or the eyebrows are prominent.
The visual fields of the 2 eyes overlap to a large extent, giving binocular vision.
Partial loss of the visual field may occur in glaucoma or stroke.... visual field
Habitat: By waterways; luxuriantly on river islands and banks.
Features ? Stem four- (sometimes six-) sided, up to four feet high. Leaves in pairs, threes or fours, nearly sessile, lanceolate, margins entire, two to five inches long. Flowers (July to September) large, reddish-purple, six to eight in rings round the stalk. Root woody.Part used ? Herb.
Action: Febrifuge, astringent, alterative.
Chiefly in feverish conditions with other herbs. Sometimes as an astringent in diarrhea. Used alone, simmer 1 ounce in 1 1/2 pints water for ten minutes. Dose, wineglassful as required.... purple loose-strife
Stimulation of the retina of the EYE with light causes changes in the electrical activity of the cerebral cortex (see BRAIN). These changes can be measured from outside the skull and can give valuable information about the state of the visual pathway from the retinal ganglion cells to the occipital cortex. Not only can it determine that function is normal, it can also help to diagnose some causes of poor VISION.... visual evoked response
(visual reinforced audiometry, VRA) a behavioural test of hearing for children aged approximately 6 to 30 months in which the subject sits between two calibrated loudspeakers. A sound is generated from one loudspeaker. Children who turn towards the sound are rewarded by brief illumination of a toy adjacent to the loudspeaker. Older children can be tested with headphones, rather than using the loudspeakers, to enable each ear to be tested separately. The test can be adapted for use with older subjects who have learning disabilities.... visual reinforcement audiometry
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