Perceiving and Recognizing Objects
Perceiving and Recognizing Objects
Templates versus structural descriptions
Naive template theory
Visual system recognizes objects by matching the neural representation of the image with a stored representation "shape" in the brain
Mostly agreed upon. A description of an object in terms of its parts and the relationships between those parts.
Beiderman's model of object recognition
Holds that objects are recognized by the identities and relationships of their component parts.
The "geometric ions" out of which objects are built.
A property of an object that does not change when an observer changes viewpoint.
Advantage of structural description is that "A above B" is equally recognizable from different viewpoints.
Retinal Ganglion Cells + LGN
Primary Visual Cortex
Sophistication beyond V1
What And Where Pathways
Objects in the brain
Brain regions bordering striate cortex that contains other areas involved in visual processing
Respond to visual properties important for perceiving objects.
V2 cells respond to "boundary ownership"
Concerned with locations and shapes of objects but not their names or functions
Names and functions of objects regardless of location
Part of cerebral cortex in lower portion of temporal lobe; object recognition
Region of damaged brain
To destroy a section of the brain
Failure to recognize objects in spite of the ability to see them.
A single neuron responsible for recognizing something specific.
Jennifer Aniston cell
Feed Forward Process
Computation one neural step after another, without
the need for feedback from a later stage to an earlier stage.
A metaphor for how perception works.
Middle vision results from the consensus that emerges from competing principles involved in middle vision.
Perceptual committee made up of "demons"
Formal, mathematical system that combines information about the current stimulus with prior knowledge about the world.
Prior probability: how likely is what you are proposing?
Unicorn vs. Cow
How consistent is each hypothesis with the observation?
Multiple recognition committees?
For an object, the label that comes to mind most quickly when we identify the object. E.g. Building
A more specific term for an object. E.g. High School
A more general term for an object. E.g. Structure
Problems with structural-description theories
Object recognition not completely viewpoint-invariant.
Observers show viewpoint effects in object recognition.
The farther an object is rotated away from a learned view, the longer it takes to recognize
Geons aren't always the best description of objects.
Areas of human cortex specialized in certain types of stimuli
Parahippocampal place area - responds to places, such as pictures of houses.
Fusiform face area - responds to faces more than other objects.
Extrastriate body area - specifically involved in the perception of body parts (arms, legs, etc).
Problems of Perceiving and Recognizing Objects
Pictures were just a bunch of pixels on a screen, but you perceive a house.
How does your visual system move from points of light, to whole entities in the world (like houses)?
How did you recognize all four images as depicting a house?
Loosely defined stage of visual processing. A combo of low-level vision and high-level vision (object recognition and scene understanding).
Involves perception of edges and surfaces
Determines which regions of an image should be grouped together into objects.
Dealing with Occlusion
The degree to which two line segments appear to be part of the same contour (related).
Parts and Wholes
Global Superiority effect
The properties of the whole object take precedence over the properties of parts of the object.
"The whole is greater than the sum of its parts."
Gestalt Grouping Rules
A set of rules that describe when elements in an image will appear to group together.
Two elements will tend to group together if they lie on the same contour.
Carving an image into regions of common texture property
Similar looking items tend to group
Items that are near each other tend to group.
Parallel contours are likely to belong to the same group.
Symmetrical regions are more likely to be seen as a group.
Items will group if they appear to be part of the same larger region.
Items will tend to group if they are connected.
Dynamic Group Principles
Elements that move in the same direction together tend to group together.
Elements that change at the same time tend to group together.
A real world example. Animals exploit Gestalt grouping principles to group themselves into their surroundings.
The process of determining that some regions of an image belong to foreground object and regions are part of the background.
The surrounding region is likely to be ground.
The smaller region is likely to be figure.
A symmetrical region tends to be seen as a figure.
Regions with parallel contours tend to be seen as a figure.
If one region moves in front of another, then the closer region is figure.
A contour that is perceived even though nothing changes from one side of the contour to the other.