Vernier acuity (from the term "

vernier scale A vernier scale, named after Pierre Vernier, is a visual aid to take an accurate measurement reading between two graduation markings on a linear scale by using mechanical interpolation, thereby increasing resolution and reducing measurement unc ...

", named after astronomer Pierre Vernier) is a type of

visual acuity Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. (1) the sharpness of the retinal ...

– more precisely of

hyperacuity The sharpness of our senses is defined by the finest detail we can discriminate. Visual acuity is measured by the smallest letters that can be distinguished on a chart and is governed by the anatomical spacing of the mosaic of sensory elements on ...

– that measures the ability to discern a disalignment among two line segments or gratings. A subject's vernier (IPA: ) acuity is the smallest visible offset between the stimuli that can be detected. Because the disalignments are often much smaller than the diameter and spacing of retinal receptors, vernier acuity requires neural processing and "pooling" to detect it. Because vernier acuity exceeds acuity by far, the phenomenon has been termed

. Vernier acuity develops rapidly during infancy and continues to slowly develop throughout childhood. At approximately three to twelve months old, it surpasses grating acuity in

fovea Fovea () (Latin for "pit"; plural foveae ) is a term in anatomy. It refers to a pit or depression in a structure. Human anatomy * Fovea centralis of the retina * Fovea buccalis or Dimple * Fovea of the femoral head *Trochlear fovea of the f ...

l vision in humans. However, vernier acuity decreases more quickly than grating acuity in

peripheral vision Peripheral vision, or ''indirect vision'', is vision as it occurs outside the point of fixation, i.e. away from the center of gaze or, when viewed at large angles, in (or out of) the "corner of one's eye". The vast majority of the area in the ...

. Vernier acuity was first explained by

Ewald Hering Karl Ewald Konstantin Hering (5 August 1834 – 26 January 1918) was a German physiologist who did much research into color vision, binocular perception and eye movements. He proposed opponent color theory in 1892. Born in Alt-Gersdorf, Ki ...

in 1899, based on earlier data by Alfred Volkmann in 1863 and results by Ernst Anton Wülfing in 1892. Vernier acuity is resistant to defocus, motion, and

luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls withi ...

, but is subject to practice effects and changes in

attention Attention is the behavioral and cognitive process of selectively concentrating on a discrete aspect of information, whether considered subjective or objective, while ignoring other perceivable information. William James (1890) wrote that "Att ...

. After training, observers' threshold has been shown to improve as much as 6 fold.

Testing

Vernier acuity is measured by asking participants to judge the offset between two parallel line segments with both eyes (

binocular vision In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an ...

) or with each eye individually (

monocular vision In human species Monocular vision vision is known as seeing and using only one eye in the human species. Depth perception in monocular vision is reduced compared to binocular vision, but still is active primarily due to accommodation of the eye ...

). Vernier measures in infants and non-verbal children can be done using the preferential-looking technique or by electrophysiological techniques.

References

{{reflist Ophthalmology Visual perception

Testing

See also

References