Cognition Chapter 2

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What are the two problems with perception?

1. Sensory input does not contain enough information to explain our perception, and 2. The world presents us with too much sensory input to include in our coherent perceptions at any given moment

What is the goal of perception?

To take in information about the world and make sense of it

What does vision do?

It tells us what is out there, and where it is

What is the retina?

light-sensitive tissue lining the inner surface of the eye, made up of photoreceptors

What is the layer of cells that respond to light?

retina

What are photoreceptors?

cells that respond to light

What are cells that respond to light?

photoreceptors

What do nerve cells at the back of each eye do?

Convert light into electrochemical signals

What converts light into electrochemical signals?

nerve cells at the back of each eye

How is light transmitted to the brain?

Converted into electrochemical signals by nerve cells at the back of each eye, and then sent via optic nerves to the brain

What do the optic nerves do?

Take light in the form of electrochemical signals to the brain

What takes light in the form of electrochemical signals to the brain?

Optic nerves

What are the optic nerves made up of?

Bundle of long axon fibers of the ganglion cells in the retina

What is the bundle of long axon fibers of the ganglion cells in the retina?

Optic nerves

What do the axons of the optic nerves make contact with?

The neurons of the lateral geniculate nucleus

What do the neurons of the lateral geniculate nucleus make contact with?

The axons of the optic nerves

What is V1?

The primary visual cortex

What is the primary visual cortex called?

V1

What do the axons of the lateral geniculate nucleus do?

Send signals up to the primary visual cortex

What sends signals up to the primary visual cortex?

Axons of the LGN

What is the LGN?

lateral geniculate nucleus

Describe how light gets to the brain.

Patterns of light intensity, edges, and other features form image on retina. Converted to electrochemical signals and sent via optic nerves to the LGN neurons, which send signals up to the primary visual cortex

What two main pathways go beyond the primary visual cortex?

The dorsal pathway and the ventral pathway

Where does the dorsal pathway go?

Reaches up into the parietal lobes

Which pathway goes to the parietal lobes?

The dorsal pathway

Why is the dorsal pathway important?

Helps process information about where items are located and how they might be acted upon, guiding movements

Which pathway goes to the temporal lobes?

The ventral pathway

Where does the ventral pathway go?

The temporal lobes

What is important about the ventral pathway?

Processes information that leads to the recognition and identification of objects

Which pathway is the "what" pathway?

The ventral pathway

Which pathway is the "where" pathway?

The dorsal pathway

Which pathway processes information that leads to the recognition and identification of objects?

The ventral pathway

Which pathway processes information about where items are located and how they might be acted upon?

The dorsal pathway

What does it mean that visual areas have reciprocal connections?

Most visual areas that send output to another area also receive input from that area

What is visual perception a product of?

Top-down and bottom-up processes

What is the product of top-down and bottom-up processes?

Visual perception

What are perceptions?

Interpretations of what we see, representations produced by the interaction of bottom-up and top-down processing

What 2 things are our interpretations of the world around us determined by?

1) Biological structure of our brains, and 2) experience, which modifies that structure

How are visual experiences formed as babies?

As a baby sees something over and over, the lingering memory of each occurrence combines with each new instance, accumulating to form lasting mental representations of people, places, and things. These representations form the basis for subsequent recognition of objects

How does the characteristics of the infants' environment at particular times influence adult capabilities?

If exposure to the natural environment is limited during the designated critical period for a given response, the animal will fail to develop that ability properly. However, the introduction of some prenatal stimulation can impair normal perceptual development later in life as well

What is the critical period for sensory processing?

Different aspects of sensory processing have different critical periods

What does it mean when it is said that there is competition in sensory input?

Different sources and different modalities of sensory input seem to compete for representation in cortex

What happens when one eye is more active than the other?

Cortical resources are redeployed in that direction, and once assigned in infancy, such resources are not easily modified later

What are visual features?

Spots, edges, colors and shapes, movements and textures. The building blocks of perception

What are spots, edges, colors and shapes, movements and textures known as?

Visual features

What are the building blocks of perception?

Visual features

What do photoreceptor cells do?

Convert light energy reflected from various objects in the physical world into an electrochemical signal that can travel through the nervous system

What is the visual field?

the portion of the world that is visible at the given moment

What is the receptive field?

the region of the visual field in which a stimulus will affect the activity of the cell

What is the portion of the world that is visible at the given moment?

visual field

What is the region of the visual field in which a stimulus will affect the activity of the cell?

receptive field

What is the ganglion cell connected to?

Photoreceptor cells

When will the ganglion cell respond to light?

Only when light lands on the photoreceptor cells that the ganglion cell is connected to, or the light in one specific region of the visual field

Where does the ganglion cell get its input from?

The receptors that lie in its receptive field

How does the connection from photoreceptors to the ganglion cell vary?

Light in some portions of the receptive field will excite the cell, whereas light elsewhere will inhibit the ganglion cell

Where does input excite the ganglion cell?

In the central (white) zone of the receptive field

Where does input inhibit the ganglion cell?

In the surrounding (gray) region of the receptive field

What does input to the surrounding(gray) region of the receptive field do to the ganglion cell?

Inhibits it

What does input to the central (white) zone of the receptive field do to the ganglion cell?

Excites it

What happens when the central region of the receptive field is stimulated by a gray area?

Won't be very excited

What happens when the entire receptive field is 100% bright?

The strong excitation of the center would be offset by the strong inhibition from the surrounding

When is the ganglion cell maximally excited?

When a bright spot the size of the central region falls on the central region

What happens when center-surround receptive fields receive inputs across an edge?

One receptive field is mostly on the light side, and another mostly on the dark side. Makes the former a bit lighter and the other "darker-than-dark," enhancing the contrast

What are Mach Bands?

Gray areas are uniform, but each lighter bar appears a bit lighter on the right side, and each darker bar appears a bit darker on the corresponding left side

Why is the visual system tuned to pick out edges?

edge information is important for defining the shape of objects and providing cues for where to direct action

Why are we tricked by the Mach Bands?

Not an unreasonable assumption to believe that image lighter on light side of edge than on darker side. Looks for edges because edge information is important for defining the shape of objects and providing cues for where to direct action

What does throwing out information about intensity of light at every point in space show?

Visual perception efficiently extracts visual features by ignoring some data

What is the fovea?

The part of the retina that has a high concentration of ganglion cells with tiny receptive fields

What is the part of the retina that has a high concentration of ganglion cells with tiny receptive fields?

The fovea

What is the result of having a fovea?

The area is capable of high resolution, and fine details can be perceived

Where are the finest details perceived in the eye?

Fovea

How do receptive fields change according to distance from the point of fixation?

The receptive fields get bigger and bigger the farther away you get

What do the optic nerves form?

The optic chiasm

What is the optic chiasm?

The point at which fibers from each optic nerve cross to opposite hemispheres of the brain

What is the point at which fibers from each optic nerve cross to opposite hemispheres of the brain called?

Optic chiasm

What do cells in the primary visual cortex respond to?

Variations in basic features such as orientation, movement and color

What responds to variations in basic features such as orientation, movement and color?

Cells in the primary visual cortex

What is the striate cortex?

The primary visual cortex

What is the extrastriate cortex?

A collection of visual areas that output from V1 feeds into

What is the collection of visual areas that output from V1 feeds into called?

The extrastriate cortex

What does the extrastriate cortex contain?

Areas whose cells appear to be specialized for the further processing of these basic features and of more elaborate representations, such as faces

What is the visual cortex divided into?

Hypercolumns

What are hypercolumns made up of?

Made up of cells that are activated by stimuli in one small part of the visual field

What are cells in the hypercolumns activated by?

activated by stimuli in one small part of the visual field. Cells in the next hypercolumn will respond to input from a neighboring portion of space

What things do hypercolumns focus on?

More hypercolumns focused on detailed processing of input to the fovea than to cruder processing of more peripheral parts of the visual information

How are hypercolumns organized?

Cells are ordered by their sensitivity to specific aspects of the visual feature, such as edges at a specific orientation

If a cell within a hypercolumn sensitive to edge orientation responds the most to vertical lines, what will the other cells be like?

The next cell over will respond the most to lines tilted a bit more off vertical, and the next one to those even more tilted

How are precise assessments of orientation made?

Made by comparing activity across a population of neurons

What does it mean when it is said that precise assessments of orientation are made by comparing activity across a population of neurons?

If there are neurons that respond to tilts 15 degrees to the left and neurons that respond to tilts 15 degrees to the right, a line that is perceived as vertical would be one that stimulates both of these populations of neurons equally

What is the tilt aftereffect?

...

How do we know that precise assessments of orientation are made by comparing activity across a population of neurons?

If we fixate our gaze on a pattern of lines with the same right tilt, this tires out the neurons specialized for that. Thus, when gaze is switched to a vertical line, it will appear to be tilting to the left because there is more activity in the left neurons. The right neurons are too fatigued to sustain equal activity

How is the value of a particular feature in vision determined?

Determined by comparison between two or more sets of neurons--with different sensitivities--responding to that stimulus

Where is motion detected?

In V5

What does V5 detect?

Motion

What do the cells in V5 detect?

Objects moving in a particular direction

What detects objects moving in a particular direction

cells in area V5

What does damage to area V5 result in?

Akinetopsia

What is akinetopsia a result of?

Damage to area V5

What is akinetopsia?

The loss of the ability to see objects move

What is the loss of the ability to see objects move?

Akinetopsia

What does V4 perceive?

Color

What area perceives color?

area V4

What is achromatopsia a result of?

Damage to area V4

What does damage to area V4 result in?

Achromatopsia

What is achromatopsia?

Cortical color blindness

What is cortical color blindness called?

Achromatopsia

What are the rules that govern the complex process by which we infer the contents of the visual world called?

Gestalt grouping principles

What do the Gestalt grouping principles do?

Guide the visual system and produce our perception of what goes with what

What produces our perception of what goes with what?

Gestalt grouping principles

What are the 5 grouping principles?

Proximity, uniform connectedness, similarity, good continuation, closure

What principle overrides proximity?

Principle of uniform connectedness

What is the principle of proximity?

All things being equal, things that are closer to one another are more likely to be grouped together than things farther apart

Name this principle. Things that are closer to one another are more likely to be grouped together than things farther apart

Principle of proximity

What principle does the principle of uniform connectedness override?

The principle of proximity

What is the principle of colinearity?

Lines group when their orientations are close to that of a neighbor's

What is it called when lines group when their orientations are close to that of a neighbor's?

Principle of colinearity

What does it mean to be occluded?

Hidden

Why do our brains perceive things that are not actually there (i.e., in the case of occlusion)?

It is unlikely that white rectangles and a black one would align just so to produce the image given Instead, it is more likely that one surface (the black rectangle) might occlude another (the long white one)

What is a subjective contour?

a contour that is not physically present int he stimulus, but is filled in by the visual system

What is an illusory contour?

a contour that is not physically present int he stimulus, but is filled in by the visual system

What is a contour that is not physically present int he stimulus, but is filled in by the visual system called?

subjective (illusory) contour

What is the binding problem?

the question of how we associate different features such as shape, color, and orientation so that we perceive a single object

What is the question of how we associate different features such as shape, color, and orientation so that we perceive a single object called?

binding problem

What is part of the answer to the binding problem?

Spatial location can serve as the required "glue"

What is recognition?

The process of matching representations of organized sensory input to stored representations in memory

What is the process of matching representations of organized sensory input to stored representations in memory?

Recognition

What is agnosia?

The inability to recognize objects

What is the inability to recognize objects called?

Agnosia

What is it called when sight is unimpaired, but recognition failed?

Visual agnosia

What is viewpoint dependence?

An object can be viewed from an infinite combination of possible angles and possible distances, each of which projects a slightly different two-dimensional image on a plane

What two challenges are there in recognizing objects?

Viewpoint dependence and exemplar variation

What is exemplar variation?

There are many different instances of each object category

What does an object category consist of?

Many possible examples

What is the term for many different instances of each object category?

Exemplar variation

What four models have been proposed for recognition?

1) Template-matching models, 2) Feature-matching models, 3) Recognition-by-components, 4) Configural models

In short, what is the template matching model?

Matches a whole image to a stored representation of a whole object

In short, what is the feature-matching model?

Extracts important or discriminating features from the image and match them with known features of objects

In short, what is the recognition-by-component model?

Represents three-dimensional structure of objects by specifying their parts and the spatial relations among those parts

In short, what are configural models?

Distinguish among objects that share the same basic parts and overall structure by coding each exemplar according to how it deviates from the average or prototypical object

What model distinguishes among objects that share the same basic parts and overall structure by coding each exemplar according to how it deviates from the average or prototypical object

configural models

What model represents three-dimensional structure of objects by specifying their parts and the spatial relations among those parts?

Recognition-by-component model

What model xtracts important or discriminating features from the image and matches them with known features of objects

feature-matching model

What modelmatches a whole image to a stored representation of a whole object?

Template matching model

What is a template?

a pattern that can be used to compare individual items to a standard

What is a pattern that can be used to compare individual items to a standard

template

When is the template matching model most useful?

The item to be recognized and the template to which the system compares it to are almost identical and different from others

Where do templates fail?

Cannot accommodate variations in object size and orientation

What is the main disadvantage of the template matching model?

Recognition often demands great flexibility, but templates aren't flexible

What is a feature?

Any attribute that distinguishes one object from others

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