chapter 2 Flashcards
visual perception two phases
-an early phase in which shapes and objects are extracted from the visual scene
-a later phase in which the shapes and objects are recognized.
explain the cortical structures involved in visual and audition
early visual processing goes on in the occipital cortex, later processing takes one of two paths
-might have activity going into the temporal lobe, the “what” visual pathway, trying to identify what you are seeing (ventral)
-might have activity going into the “where” visual pathway, understanding the spatial relationship between things, focusing more on where things are (dorsal)
explain visual agnosia
Inability to recognize visual objects, which is neither a function of general intellectual loss nor a loss of basic sensory abilities
Two types:
-Apperceptive
-Associative
what is apperceptive agnosia
-Inability to recognize simple shapes or draw shapes that are shown
-Early processing problems
-As soon as information gets into the occipital lobe, you have trouble dealing with it
what is associative agnosia
-Ability to recognize simple shapes and copy drawings of complex objects, but not to recognize complex objects
-Later processing problems
-Ex. Able to copy a picture of an anchor, but unable to say what it is
early visual processing overview
Early visual information processing begins in the eye.
Light passes through the lens and the vitreous humor and falls on the retina at the back of the eye.
The retina contains the photoreceptor cells, which are made up of light-sensitive molecules that undergo structural changes when exposed to light.
Light is scattered slightly when passing through the vitreous humor, so the image that falls on the back of the retina is not perfectly sharp.
-The right and left nerves coming from the eyes cross over within the brain, right and left genicular regions receive information from opposite eye
-Eg. Left visual field goes to the right occipital lobe
One of the functions of early visual processing is to sharpen that image.
what is the fovea
You have the most visual acuity when you hold things in front of your fovia, the center of your eyes
-A small area in the center of the retina, composed primarily of cones
-Where visual information is most sharply focused
what are rods
-Long, thin, blunt sensory receptors of the eye that are highly sensitive to light, but not to color
-Primarily used for peripheral and night vision
what are cones
-Short, thick, pointed sensory receptors of the eye that detect color
-Responsible for color vision and visual acuity
what is the optic disk
-Area of the retina without rods or cones
-Where the optic nerve exits the back of the eye
what is the optic nerve
-The thick nerve that exits from the back of the eye
-Carries visual information to the visual cortex and brain
what are the ganglion cells
-In the retina, the specialized neurons that connect to the bipolar cells
-Bundled axons of the ganglion cells form the optic nerve.
what is the blind spot
The point at which the optic nerve leaves the eye, producing a small gap in the field of vision
explain neural pathways from the eye to the brain
Neural Pathways from the Eye to the Brain
-Optic nerves meet at the optic chiasma
explain depth cues
-Information from the retina is 2-D, but 3-D representation is needed.
The visual system uses cues to infer distance:
-Texture gradient
-Stereopsis
-Motion parallax
explain texture gradiant
Elements tend to appear more closely packed together as the distance from the view increases.
what is stereopsis
The ability to perceive 3-D because two eyes receive slightly different view of the world
what is motion parallax
-Provides information about a 3-D scene when you are in motion
-More distant points move more slowly across the retina than closer points
what are the gestalt principles of organization, how they explain the brain segments visual scenes into objects
Principle of proximity
-Lines picture, brain organizes them into four bars rather than 8 lines, the lines are closer together and our brain thinks that things that are closer together go together
Principle of similarity
-Lines of circles and x’s rather than alternating shapes that make up columns, we group similar objects together
Principle of good continuation
-Two lines crossing each other, one from A to B and one from D to C, we try to maintain continuity
Principle of closure
-Two circles overlapping each other rather than seeing a jagged line, we see whole objects
what is object perception
-Gestalt principles tend to organize even novel stimuli into units.
Palmer (1977) found that participants could recognize the parts most rapidly when they were the segments predicted by the gestalt principles.
-Psychological reality/purpose of why we follow the gestalt principles
explain template matching theory (how we recognize things)
Image of an object is faithfully transmitted to the brain
an attempt is made to compare it directly with various stored patterns
-These patterns are called templates
An attempt is made to achieve correspondence between the retinal cells stimulated and the retinal cells specified for a template pattern.
Used in machine pattern recognition
what is feature analysis
Stimuli are thought of as combinations of elemental features.
What we store in our long-term memory are its parts/features.
Compare retinal image to objects in long-term memory
Look for corresponding features
Advantages over template model
-Features are simpler, and it is easier to extract the separate features.
-Can specify those relationships among the features that are most critical to the pattern.
-The use of features rather than large patterns will reduce the number of templates needed.
explain disintegration of an image that is stabilized on the eye
Display the combined image so that is completely still in front of the eye, overtime pieces of the letter or image you are staring at will disappear; so they set up things so that the eye could not get fatigued
-You are always moving a little bit and your eye has a slight tremor, over time it will be fatigued and not work
-People would report the letters or shapes they saw, H, B, 3, 4, kept track of which features of the original image disappeared
explain recognition by components theory
Biederman proposes three substages:
1) The object is segmented into a set of basic subobjects using early visual processing.
2) Once an object has been segmented into basic subobjects, one can classify the category of each subobject.
-36 basic categories of subobjects, called geons
3) Having identified the pieces out of which the object is composed and their configuration, one recognizes the object as the pattern composed from these pieces.
