| analytic introspection | A method for studying perception in which trained people attend to and describe the experiences evoked by some stimulus.
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| closure | The Gestalt principle of organization referring to the tendency of the visual system to obscure small breaks or gaps in objects. See proximity, similarity.
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| configural superiority effect | The finding that, under some circumstances, a complex figure, or part of a complex figure, may be seen more readily than one of its parts presented in isolation.
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| contrast | The difference in light intensity between an object and its immediate surroundings; also, the intensity difference between adjacent bars in a grating.
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| contrast normalization | The process by which the limited dynamic range of neurons' responsiveness to contrast can be adjusted to the prevailing level of contrast.
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| contrast sensitivity function (CSF) | A graph depicting a person's ability to see targets of various spatial frequency; on the x-axis is the spatial frequency of the test target; on the y- axis is sensitivity, the reciprocal of the minimum contrast needed to see the test target.
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| contrast threshold | The minimum contrast needed to see some target.
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| cutoff frequency | The spatial frequency at which a lens's transfer function falls to zero; the highest frequency that a lens can image; the highest frequency to which a visual system can respond.
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| detection | The process by which an object is picked out from its surroundings; also, the process by which the presence of some object is perceived.
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| discrimination | The process by which one object is distinguished from another.
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| Fourier analysis | A method for calculating the frequency content of any temporal or spatial signal; can be used to determine the spatial frequency content of a visual scene or the temporal frequency content of a sound.
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| Gestalt principles of organization | Certain stimulus properties that control the perceptual grouping of objects. See bclosure, good continuation, proximity, similarity.
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| good continuation | The tendency to see neighboring elements as grouped together when they are potentially connected by straight or smoothly curving lines.
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| grating | A target consisting of alternating darker and lighter bars, used to study spatial vision. See sinusoidal grating.
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| identification | The cognitive process of distinguishing a particular object. Contrast with categorization.
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| metamers | Two or more objects that appear identical despite acute physical differences.
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| multichannel model | The hypothesis that spatial vision is the product, in part, of sets of neurons responsive to different spatial frequencies.
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| orientation | The degree of inclination of a contour within a two-dimensional plane.
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| proximity | The Gestalt principle of organization referring to the perceptual tendency to group together objects that are near one another. See closure, similarity.
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| scale | Relative size or extent.
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| selective adaptation | A method of studying mechanisms of perception, in which a person's sensitivity to particular targets is depressed by prolonged exposure to one particular target.
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| similarity | The Gestalt principle of organization referring to the perceptual tendency to group together objects that are similar to one another in texture, shape, and so on. See closure, proximity.
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| sinusoidal grating | A target in which the intensity of darker and lighter bars varies sinusoidally over space. See grating.
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| size aftereffect | A change in the apparent size of an object following inspection of an object of a different size.
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| spatial frequency | For a grating target, the number of pairs of bars imaged within a given distance on the retina; units of spatial frequency are cycles/mm or, equivalently, cycles/degree of visual angle.
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| spatial phase | The position of a grating relative to some visual landmark.
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| symmetry | Tendency for parts of an object centered about a given axis of orientation to be highly similar in shape, texture, and/or color.
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| texture contrast | Adjacent regions of a visual scene distinguished by differences in texture.
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| transfer function | A graph showing, for various target spatial frequencies, the contrast contained in an image.
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| window of visibility | The range of spatial frequencies that, with sufficient contrast, an observer can see.
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