Stiles–Crawford effect

Stiles–Crawford effect

The Stiles–Crawford effect (or Stiles–Crawford effect of the first kind [cite book | title = Visual Perception: A Clinical Orientation | author = Steven H. Schwartz | publisher = McGraw-Hill Professional | year = 2004 | ibsn = 0071411879 | url = http://books.google.com/books?id=Oyk0faySQfUC&pg=PA51&dq=%22Stiles-Crawford+effect%22&lr=&as_brr=0&sig=jFnA67AvVsj4VseudpM8JJCHOs8 ] ) is a property of the cone photoreceptors of the human eye.Walter Stanley Stiles and Brian Hewson Crawford (1933), " [http://www.jstor.org/pss/81711 The luminous efficiency of rays entering the eye pupil at different points] ," "Proc. R. Soc. Lond" B 112:428-450.] It refers to the directional sensitivity of the cone photoreceptors; specifically to the phenomenon that light passing near the edge of the pupil is less efficient at evoking sensation than light passing through the center of the pupil. That is, the retina is not lambertian, and the effective acceptance angle of the cones is smaller than that subtended by the pupil.

A stimulus' peak effectiveness is at the center of the pupil (for the normal eye) and falls in effectiveness in a symmetrical pattern.

Rays of light passing through the centre of the pupil are less oblique to the cone after refraction and stimulate them more strongly than rays passing through peripheral areas of the pupil. A photoreceptor acts like a retinal optic fibre, it captures light that hits it at a narrow angle from its normal. The acceptance angle of a cone is narrow, approximately 5°, rods have larger acceptance angles.

The "Stiles-Crawford" effect reduces the detrimental effects of light scatter on the retina at photopic levels. [cite book|title=Adaptive Optics Engineering|first=Robert K.|last=Tyson|publisher=Marcel Dekker|year=2000|id=ISBN 0-8247-8275-5p. 309]

Background

Stiles and Crawford devised an experiment whereby a double pinhole grating was placed before the eyes, one pinhole would be at the centre of the eye, the other at the periphery. A variable filter is placed in front of the central pinhole, this reduced transmission, until the two beams of light appeared equally bright. The difference in brightness is recorded as the relative efficiency of the two pupillary points. This value differs depending whether or not the conditions were photopic or scotopic. Under scotopic conditions, the relative efficiency is much less prominent, different entry points in the pupil are almost equally effective.

References


Wikimedia Foundation. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • Stiles-Crawford effect — Stiles Craw·ford effect .stīlz krȯ fərd n an optical phenomenon in which light passing through the center of the pupil is perceived as more intense than light passing through the periphery of the pupil Stiles Walter Stanley (1901 1985), and… …   Medical dictionary

  • Stiles-Crawford-Effekt — Der Stiles Crawford Effekt der ersten Art (SCE I) beschreibt den empfundenen Helligkeitsunterschied, wenn ein Lichtstrahl durch die geöffnete Pupille wandert. Das Helligkeitsempfinden gleicht einer Gauß Kurve, d. h. am nasalen und temporalen Rand …   Deutsch Wikipedia

  • effect — The result or consequence of an action. [L. efficio, pp. effectus, to accomplish, fr. facio, to do] abscopal e. a reaction produced following irradiation but occurring outside the zone of actual radiation absorption. additive e. an e. wherein two …   Medical dictionary

  • Crawford — Brian H., British physicist, *1906. See Stiles C. effect …   Medical dictionary

  • Stiles — Walter S., English physicist, 1901–1985. See S. Crawford effect …   Medical dictionary

  • Cone cell — Neuron: Cone Cell Normalized responsivity spectra of human cone cells, S, M, and L types NeuroLex ID …   Wikipedia

  • СТАЙЛСА—КРОУФОРДА ЭФФЕКТ — (англ. Stiles Crawford effect) различие в восприятии яркости одного и того же пучка света в зависимости от того, как он проникает в центральную ямку сетчатки. Свет кажется более ярким, если он проходит через центр зрачка, и менее ярким, если он… …   Большая психологическая энциклопедия

  • performing arts — arts or skills that require public performance, as acting, singing, or dancing. [1945 50] * * * ▪ 2009 Introduction Music Classical.       The last vestiges of the Cold War seemed to thaw for a moment on Feb. 26, 2008, when the unfamiliar strains …   Universalium

  • Cat — For other uses, see Cat (disambiguation) and Cats (disambiguation). Domestic cat[1] …   Wikipedia

  • HEBRAISTS, CHRISTIAN — (1100–1890). Factors governing gentile enterprises in Hebrew scholarship prior to the latest phase of more widespread secular attitudes may be distinguished as (1) motivation; (2) scholarly facilities; and (3) occasion; appreciation and… …   Encyclopedia of Judaism

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”