/sa kahd", seuh-/, n.
1. the act of checking a horse quickly with a single strong pull of the reins.
2. Ophthalm. the series of small, jerky movements of the eyes when changing focus from one point to another.
[1720-30; < F saccade jerk, jolt, orig., movement of a horseman who abruptly pulls the reins, equiv. to MF saqu(er) to pull violently (N dial. var. of OF sachier, ult. deriv. of sac SACK1, hence presumably with sense "withdraw from a sack") + -ade -ADE1]

* * *

      fast, intermittent eye (eye, human) movement that redirects gaze. Saccades may involve the eyes alone or, more commonly, the eyes and the head. Their function is to place the fovea, the central region of the retina where vision is most acute, onto the images of parts of the visual scene of interest. Their duration and peak velocity vary systematically with their size. The smallest “microsaccades” move the eye through only a few minutes of arc (one minute of arc equals one-sixtieth of one degree). They last about 20 milliseconds and have maximum velocities of about 10 degrees per second. The largest saccades (excluding the contributions of head movements) can be up to 100 degrees, with a duration of up to 300 milliseconds and a maximum velocity of about 500–700 degrees per second.

      During saccades, vision is seriously impaired for two reasons. First, during large saccades, the image is moving so fast that it is blurred and unusable. Second, an active blanking-off process, known as saccadic suppression, occurs, and this blocks vision for the first part of each saccade. Between saccades, the eyes are held stationary in fixations. It is during these periods, which last on average about 190 milliseconds, that the eyes take in visual information. Saccades can be reflexive in nature; for example, when an object appears in one's peripheral field of view. However, as Russian psychologist Alfred L. Yarbus showed, saccades are often information-seeking in nature, directed to particular objects or regions by the requirements of ongoing behaviour.

Michael Land

* * *

Universalium. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • saccade — [ sakad ] n. f. • 1534; de saquer « tirer », forme dial. de l a. fr. sachier « secouer », de 1. sac 1 ♦ Équit. Brusque secousse donnée aux rênes d un cheval. 2 ♦ (1617) Cour. Mouvement brusque et irrégulier. ⇒ à coup, heurt, secousse, soubresaut …   Encyclopédie Universelle

  • saccadé — saccade [ sakad ] n. f. • 1534; de saquer « tirer », forme dial. de l a. fr. sachier « secouer », de 1. sac 1 ♦ Équit. Brusque secousse donnée aux rênes d un cheval. 2 ♦ (1617) Cour. Mouvement brusque et irrégulier. ⇒ …   Encyclopédie Universelle

  • saccadé — saccadé, ée (sa ka dé, dée) part. passé de saccader. 1°   Un cheval saccadé par un cavalier inexpérimenté. 2°   Qui va par saccades, qui est irrégulier. Mouvements saccadés.    Terme de vétérinaire. La respiration est saccadée dans la pousse,… …   Dictionnaire de la Langue Française d'Émile Littré

  • saccade — mid 18c., from Fr. saccade “a jerk,” from obsolete saquer “to shake, pull,” dialectal variant of O.Fr. sachier, ultimately from L. saccus “sack.” …   Etymology dictionary

  • Saccade — Sac*cade , n. [F.] (Man.) A sudden, violent check of a horse by drawing or twitching the reins on a sudden and with one pull. [1913 Webster] …   The Collaborative International Dictionary of English

  • Saccade — (v. fr.), 1) ein Ruck, welchen der Reiter dem Pferde mit dem Zügel gibt, wenn dasselbe auf die Faust dringt; 2) so v.w. Verweis …   Pierer's Universal-Lexikon

  • Saccade — (sakad), frz., heftiger Ruck, den man dem Pferde mit dem Zaume gibt; Verweis …   Herders Conversations-Lexikon

  • saccade — [sa käd′] n. [Fr, a jerk < obs. saquer, to shake, pull, dial. var. of OFr sachier < VL * saccare, to pull from a sack < L saccus, SACK1] any of the rapid, involuntary jumps made by the eyes from one fixed point to another, as in reading… …   English World dictionary

  • Saccade — A saccade is a fast movement of an eye, head or other part of an animal s body or device. It can also be a fast shift in frequency of an emitted signal or other quick change. However, this article deals with saccadic eye motion. Eye saccades are… …   Wikipedia

  • saccade — (sa ka d ) s. f. 1°   Mouvement subit communiqué aux rênes par les mains du cavalier ou du conducteur. •   Le cheval ayant levé la tête pour une furieuse saccade que l imprudent lui donna, SCARR. Rom. com. I, 19. •   Son maître a beau tourner la… …   Dictionnaire de la Langue Française d'Émile Littré

  • SACCADE — s. f. Brusque et rude secousse qu on donne à un cheval en lui tirant la bride. Les saccades gâtent la bouche d un cheval. Donner des saccades à un cheval. Rude saccade.   Il se dit figurément d Une secousse violente qu on donne à quelqu un en le… …   Dictionnaire de l'Academie Francaise, 7eme edition (1835)

Share the article and excerpts

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