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Chapter 4

PSYB51H3 Chapter Notes - Chapter 4: Principles Of Grouping, Illusory Contours, Extrastriate Cortex

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Matthias Niemeier

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Perception and Cognition
Week 4 – May 29 th
, 2015
Chapter 4:
Extrastriate cortex: the region of cortex bordering the primary visual cortex and containing multiple areas
involved in visual processing.
oV2 cells: care about “boundary ownership”; they might respond to the dark edge of an object but
not to a dark edge created by a light object on a dark background.
oFrom the extrastriate regions of the occipital lobe, visual information moves out along two main
Dorsal stream processes ‘where, how’ information.
oFast but colorblind.
oProjects forward up to the parietal cortex from V1.
oAreas that have to do with spatial information and how to control actions.
oImportant for processing information relating to the location of objects in space and the actions
required to interact with them (moving the hands, eyes, etc.).
oPlays an important role in the deployment of attention.
Ventral stream processes ‘what’ information.
oProjects along the inferior occipital and inferior temporal from V1.
oVentral stream areas:
Lateral occipital lobe (LOC): all other objects
Parahippocampal Place Area (PPA): scenery locations
Fusiform Face Area (FFA): faces
Extrastriate Body Area (EBA): bodies
oAppears to be the locus for the explicit acts of object recognition.
oReceptive fields get much bigger as we move down into the temporal lobes.
Lesion: in reference to neuropsychology, 1. (n) a region of damaged brain. 2. (v) to destroy a section of
the brain.
Agnosia: a failure to recognize objects in spite of the ability to see them.
oIs typically due to brain damage.
oInferotemporal (IT) cortex: part of the cerebral cortex in the lower portion of the temporal lobe,
important in object recognition.
When sections of temporal lobes were lesioned in monkeys, they behaved as though
they could see but did not know what they were seeing.
Grandmother cell: any cell that seems to be selectively responsive to one specific
Maintains close connections with parts of the brain involved in memory formation.
Important because IT cells need to learn their receptive-field properties.
Neurons that respond to grandmother cells can’t be hardwired, unlike in V1
(written into the genetic code).
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.
oBroad generalization: dorsal and ventral streams form cross connections, feedback as well as
Middle (or midlevel) vision: a loosely defined stage of visual processing that comes after basic features
have been extracted from the image (low-level, or early, vision) and before object recognition and scene
understanding (high-level vision).
oCombines features into objects.
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The result is object recognition.
Object recognition: to match a perceived object representation to a representation
encoded in memory.
Prior knowledge that seeps into our object perception.
Memory traces can contain information about categories or particular objects.
Illusory contours: a contour that is perceived even though nothing changes from one side of it to the
other in an image.
oAre perceived because they are the best guess about what is happening in the world at that
oAre able to create contours that don’t exist – occluding an image (e.g., Kaniza figures).
oStructuralism: a school of thought believing that complex objects or perceptions could be
understood by analysis of the components.
An illusory contour challenges this view.
Gestalt (German, literally “form”): a school of thought stressing that the perceptual whole could be
greater than the apparent sum of the parts.
oGestalt grouping rules: a set of rules describing which elements in an image will appear to group
Good continuation: a gestalt grouping rule stating that two elements will tend to group
together if they seem to lie on the same contour.
Smooth contours are more likely than others.
Natural scene statistics explain the gestalt law of good continuation.
Good continuation is at odds with the principle of closure.
Texture segmentation: carving an image into regions of common texture properties.
oCamouflage is an attempt to trick the system.
oSimilarity: a Gestalt grouping rule stating that the tendency of two features to group together will
increase as the similarity between them increases.
Similarities pertaining to color, size, orientation, and form.
oProximity: a Gestalt grouping rule stating that the tendency of two features to group together will
increase as the distance between them decreases.
oParallelism: a rule for figure-grounding assignment stating that parallel contours are likely to
belong to the same figure.
oSymmetry: a rule for figure-grounding assignment stating that symmetrical regions are more
likely to be seen as a figure.
oCommon fate: groups together elements that are moving in the same direction.
oSynchrony: group elements changing at the same time together.
oCommon region: elements perceived to be part of a larger region group together.
Might overrule the gestalt law of proximity.
oConnectedness: elements that are connected to each other group together.
Ambiguous figure: a visual stimulus that gives rise to two or more interpretations of its identity or
oNecker cube: an outline that is perceptually bi-stable.
Unlike the stimulation with most stimuli, two interpretations continually battle for
perceptual dominance.
Accidental viewpoint: a viewing position that produces some regularity in the visual image that isn’t
present in the world (e.g., the sides of two independent objects lining up perfectly).
Perceptual committee models: middle vision similar to a collection of “specialists” for certain features
(feature values) who vote on their opinions.
oParallel processing.
oIdea that many semi-independent processes are working on the input at the same time.
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