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ef·fect(e-fekt'), Do not confuse this word with affect.
effect/ef·fect/ (ĕ-fekt´) the result produced by an action.
effectIn the context of evidence-based medicine and clinical trials, a change attributed to a treatment, which is compared to a similar event or lack thereof in another treatment “arm”.
effectconsequence of drug action
additive effect total effect over time is the same as the sum of the individual effects
cumulative effect repeated administration of a drug produces more marked effects than effects produced by the first dose (i.e. opposite of habituation)
Aubert's effect See Aubert's phenomenon.
Bezold-Brücke effect See Bezold-Brücke phenomenon.
Broca-Sulzer effect The brightness produced by a flash of a given luminance depends upon its duration. It is maximum for durations around 30-40 ms when the flash luminance is photopic.
Brücke-Bartley effect An increased brightness produced by an intermittent light source (usually around 8-10 Hz) compared to the same light source viewed in steady illumination. Syn. brightness enhancement.
Cheshire cat effect A form of binocular rivalry in which a moving object seen by one eye can cause the entire image, or parts of the image, of a stationary object seen by the other eye to disappear. The effect can be observed by dividing the field of vision with a mirror placed edge-on in front of the nose at a slight angle. One eye looks straight at a stationary object, such as a sleeping cat, while the other eye sees a reflection through the mirror of a white wall or background. If a hand is waved on the mirror side in the region of the field where the cat is seen, the whole cat or part of it may be seen to disappear. See retinal rivalry.
Craik-O'Brien-Cornsweet effect A phenomenon in which the brightness of an area on one side of a transition strip appears greater than the brightness of the area on the other side of the strip, although both areas outside the transition strip have exactly the same luminance. The transition strip consists of two opposing luminance gradients that meet along a linear edge (called Cornsweet edge); on one side the luminance gradually increases to the edge and on the other side the luminance gradually decreases to the edge. The area adjoining the gradient of increasing luminance appears brighter than the area adjoining the gradient of decreasing luminance. One possible explanation is that the edge information predominates and the visual system and brain 'fill-in' the area next to it to construct a higher brightness percept. Note: by covering the transition strip it is easy to confirm that the two areas have the same luminance. Syn. Craik-O'Brien-Cornsweet illusion; Cornsweet illusion.
crowding effect See crowding phenomenon.
differential prismatic effect The difference in prism power induced by a pair of ophthalmic lenses of different power when the eyes look in various directions of gaze (except through the optical centres). Large amounts of differential prismatic effect can hinder fusion and give rise to diplopia. Example: A patient's right eye is corrected by +5 D, the left eye by +2 D. When the eye rotates upward so that the visual axes intersect the lenses 1 cm above the optical centres, the induced prism power becomes 5 Δ base down on the right and 2 Δ base down on the left. The differential prismatic effect is 3 Δ base down in front of the right eye, probably too large for fusion to be maintained. Syn. prismatic imbalance; relative prismatic effect. See anisophoria; Prentice's law.
Gelb effect In a faintly illuminated room a piece of black paper (or a rotating black disc) is illuminated by a high intensity projector. The beam of the projector falls exactly on the area of the black surface. The paper or disc will then appear to be white. A reversal of the perception is accomplished by placing a small piece of white paper near the disc in front of the projected light, at which time the paper or disc reappears in its true colour, i.e. black.
kinetic depth effect An impression of a three-dimensional structure of a moving two-dimensional shadow cast by a three-dimensional object. It is most easily demonstrated by casting a shadow onto a translucent screen.
Mandelbaum effect A tendency for the accommodative response to be altered when interposing a conflicting visual stimulus to the one being viewed. If the eyes are viewing a distant object through a dirty window or a wire fence, the actual accommodative response will tend to be raised. If the eyes are viewing a near object in front of a dirty window or wire fence the actual accommodative response will be less than if there were no conflicting stimulus.
McCollough effect A visual after-effect of colour that is seen when viewing, for a minute at least, two differently oriented and differently coloured gratings, such as a vertical grating with blue and black stripes and a horizontal grating with orange and black stripes. After adapting to these the subject looks at a figure containing a grating of vertical black and white stripes and a grating of black and white horizontal stripes of the same size as the original coloured gratings. The white stripes will then appear to be of the complementary colour, that is, the vertical stripes appear pinkish and the horizontal stripes appear bluish.
moiré effect An illusory shimmering movement produced by moving one pattern superimposed on another pattern very similar to it. The phenomenon occurs because parts of the periodic patterns are in phase in some locations, and out of phase in other locations. Examples: passing by a set of railings; if a transilluminated square wave grating is superimposed on an identical grating but cross each other at an angle of less than 45º, moiré fringes will appear at the intersections. Syn. moiré pattern. See Toposcope.
oblique effect In central vision, contours with oblique orientations are perceived and discriminated less easily than those close to the horizontal or vertical.
Pulfrich effect See Pulfrich stereophenomenon.
Raman effect In certain substances scattered light may be of a slightly different wavelength from that of the incident light.
Stiles-Crawford effect Variation of the luminosity of a pencil of light stimulating a given receptor with the position of entry of the pencil through the pupil. The maximum luminosity occurs for pencils passing through the centre of the pupil and stimulating the receptor along its axis. This phenomenon is attributed to the particular shape of the cone cells of the retina and occurs only in photopic vision.
Tyndall effect Diffusion of light by the particles present in a liquid or gas. It is because of this effect that heterogeneities (e.g. increased proteins) of the media of the eye can be seen, as occurs in iris and/or ciliary body inflammation. Syn. Tyndall scatter. See aqueous flare.
sunburst appearance, effect
Patient discussion about effect
Q. Do they have any side effects? what are the benefit of drugs like Divalproex and Carbamazepine over lithium for acute mania patients? Do they have any side effects?
Q. How long does Viagra's effect last? My Husband got Viagra from his Doctor and wants to start taking it. How long does the effect last?
Q. Does it carry any side effects? I am pregnant and in my second trimester. I am having flu infections. I am prescribed with Sudafed. Does it carry any side effects?