Sensation And Perception Ch. 4 Perceiving And Recognizing Objects

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Middle (midlevel) vision

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a loosely defined stage of visual processing come after basic features have been extracted from the image ("early vision") and before object recognitin and scene understanding (high-level vision).

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Illusory contour

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a contour that is perceived, even though nothing changes from one side of the contour to the other in the image.

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Structuralism

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a school of thought that held that complex objects or perceptions could be understood by analysis of the components.

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Gestalt

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from a German word referring to the "whole". In perception, the name of a school of thought that stressed that the perceptual whole could be greater than the apparent sum of the parts.

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Gestalt grouping rules

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a set of rules describing which elements in an image will appear to group together. The original list was assembled by members of the Gestalt school of thought.

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Good continuation

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a Gestalt grouping rule stating that two elements will tend to group together if they seem to lie on the same contour.

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Texture segmentation

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carving an image into regions of common texture properties.

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Similarity

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a Gestalt grouping rule stating that the tendency of two features to group together will increase as the similarity between them increases.

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Proximity

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a Gestalt grouping rule stating that the tendency of two features to group together will increase as the distance between them decreases.

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Parallelism

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a rule for figure-ground assignment stating that parallel contours are likely to belong to the same figure.

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Symmetry

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a rule for figure-ground assignment stating that symmetrical regions are more likely to be seen as a figure.

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Common region

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a Gestalt grouping rule stating that two features will tend to group together if they appear to be part of the same larger region.

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Connectedness

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a Gestalt grouping rule stating that two items will tend to group together if they are connected.

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Common fate

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a Gestalt grouping rule stating that visual elements will tend to group together if they are doing the same thing (e.g. moving together).

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Synchrony

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a general grouping principle stating that if all the items in a set change at the same time, those items will tend to group together, even if they change in different ways.

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Ambiguous figure

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a visual stimulus that gives rise to two or more interpretations of its identity or structure.

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Necker cube

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an outline that is perceptually bistable. Unlike most stimuli, two interpretations continually battle for perceptual dominance.

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Accidental viewpoint

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a viewing position that produces some regularity in the visual image that is not present in the world (e.g., the sides of two independent objects lining up perfectly).

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Figure-ground assignment

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the process of determining that some regions of an image belong to a foreground object (figure) and that other regions are part of the background (ground).

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Surroundedness

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a rule for figure-ground assignment stating that if one region is entirely surrounded by another, it is likely that the surrounded region is the figure.

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Relatability

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the degree to which two line segments appear to be part of the same contour.

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Heuristic

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a mental shortcut.

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Nonaccidental feature

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a feature of an object that is not dependent on the exact (or accidental) viewing position of the observer.

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Global superiority effect

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the finding in various experiments that the properties of the whole object take precedence over the properties of parts of the object.

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Template theory (or naive template theory)

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the proposal that the visual system recognizes objects by matching the neural representation of the image with a stored representation of the same "shape" in the brain.

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Structural description

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a description of an object in terms of the nature of its constituent parts and the relationships between those parts.

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Geons

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in Biederman's "recognition by components" model, the "geometric ions" out of which perceptual objects are built.

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"Recognition by components" model

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Biederman's model of object recognition, which holds that objects are recognized by the identities and relationships of their component parts.

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Viewpoint-invariance

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1. a property of an object that does not change when observer viewpoint changes. 2. a class of theories of object recognition that proposes representations of objects that do not change when viewpoint changes.

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Prosopagnosia

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an inability to recognize faces.

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Double dissociation

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in neuropsychology, the effects of two brain lesions are said to be doubly dissociable if lesion A produces effect X but not Y, while lesion B produces effect Y but not X.

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Extrastriate cortex

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the region of cortex bordering primary visual cortex and containing multiple areas involved in visual processing.

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Lesion

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in neuropsychology: 1. (n) A region of damaged brain. 2. (v) to destroy a section of the brain.

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Agnosia

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a failure to recognize objects in spite of the ability to see them. Agnosia is typically due to brain damage. Compare anomia.

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Inferotemporal (IT) cortex

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part of the cerebral cortex in the lower portion of the temporal lobe, important in object recognition.

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Homologous regions

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brain regions that appear to have the same function in different species.