Task 5 - Mechanisms of low-high-level vision Flashcards
Visual information moves out along two main pathways
- The where pathway: This pathway heads up into the parietal lobe – (visual areas in this pathway seem to be important for processing information relating to the location of objects in space and the actions required to interact with them) – this pathway plays an important role in the deployment of attention
- The what pathway: This pathway heads down into the temporal lobe and appear to the locus for the explicit acts of object recognition
Agnosia
a failure to recognize objects in spite of the ability to see them. Agnosia is typically due to brain damage
Inferotemporal (IT) cortex
Part of the cerebral cortex in the lower portion of the temporal lobe, important in object recognition (the what pathway)
Grandmother cell
any cell that seems to be selectively responsive to one specific object
Homologous regions
brain regions that appear to have the same function in different species
Feed-forward process
a process that carries out a computation (e.g. object recognition) one neural step after another, without need for feedback from a later stage to an earlier stage
Middle (or midlevel) vision
a loosely defined stage of visual processing that comes after basic featured have been extracted from the image (low-level, or early, vision) and before object recognition and scene understanding (high-level vision)
Illusory contours
a contour that is perceived even though nothing changes from one side of it to the other in an image – they are perceived because they are the best guess about what is happening in the world at that location
Structuralists
a school of thought believing that complex objects or perceptions could be understood by analysis of the components
Gestalt
a school of thought stressing that the perceptual whole could be greater than the apparent sum of the parts
Gestalt theory
the perceptual whole is more that the sum of its sensory parts
Gestalt grouping rules
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
Good continuation
a Gestalt grouping rule stating that two elements will tend to group together if they seem to lie on the same contour
Closure
in reference to perception, closure is the name of a Gestalt principle that holds that a closed contour is preferred to an open contour
Texture segmentation
carving an image into regions of common texture properties
Similarity
image chunks that are similar to each other will be more likely to group together – a Gestalt grouping rule stating that the tendency of two features to group together will increase as the similarity between them increases
Proximity
items near each other are more likely to group together than are items more widely separated – a Gestalt grouping rule stating that the tendency of two features to group together will increase as the distance between them decreases
Parallelism
a rule for figure-ground assignment stating that parallel contours are likely to belong to the same figure
Symmetry
a rule for figure-ground assignment stating that symmetrical regions are more likely to be seen as figure
Ambiguous figure
a figure that generates two or more plausible interpretations - a visual stimulus that gives rise to two more interpretations of its identity or structure
Necker cube
an outline that is perceptually bi-stable. Unlike the situation with most stimuli, two interpretations continually battle for perceptual dominance
Accidental viewpoint
a viewing position that produces some regularity in the visual image that is not present in the world (e.g., the slides of two independent objects lining up perfectly)
Figure-ground assignment
the process of determining that some regions of an image belong to a foreground object (figure) and other regions are part of the background (ground)
Surroundedness
a rule figure-ground assignment stating that if one region is entirely surrounded by another, it is likely that the surrounded region is the figure
Relatability
the degree to which two line segments appear to be part of the same contour
Heuristic
a mental shortcut
Nonaccidental features
a feature of an object that is not dependent on the exact (or accidental) viewing position of the observer
Global superiority effect
the finding in various experiments that the properties of the whole object take precedence over the properties of parts of the object
Bayesian approach
a way of formalizing the idea that our perception is a combination of the current stimulus and our knowledge about the conditions of the world - what is and is not likely to occur
Subtraction method
in functional magnetic imaging, brain activity is measured in two conditions: one with and one without the involvement of the mental process of interest. Subtracting the two conditions shows regions of brain specifically activated by that process
Parahippocampal place area (PPA)
a region of extrastriate visual cortex in humans that is specifically and reliably activated more by images of places than by other stimuli
Fusiform face area (FFA)
a region of extrastriate visual cortex in humans that is specifically and reliably activated by human faces
Extrastriate body area (EBA)
a region of extrastriate visual cortex in humans that is specifically and reliably activated by images of the body other than the face
Naïve template theory
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 – difficulty with this model is that too many templates are required
Structural description
a description of an object in terms of the nature of its constituent parts and the relationships between those parts
Geon
in Biederman’s recognition-by-components model, any of the geometric ions” out of which perceptual objects are built
Recognition-by-components model
Biederman’s model of object recognition, which holds that objects are recognized by the identities and relationships of their component parts
Viewpoint invariant
- 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
Entry-level category
for an object, the label that comes to mind most quickly when we identify it (e.g., “bird”). At the subordinate level, the object might be more specifically names (e.g., “eagle”); at the superordinate level, it might be more generally names (e.g., “animal”)
Double dissociation
the phenomenon in which one of two functions, such as hearing and sight, can be damaged without harm to the other, and vice versa
Congenital prosopagnosia
a form of “face blindness” apparently present from birth, as opposed to “acquired prosopagnosia,” which would typically be the result of an injury to the nervous system
