Brain and Behaviour - Chapter 5: Vision

Flashcards covering key vocabulary terms, anatomical structures, and visual processing theories from Chapter 5 (Vision) of Biological Psychology by James W. Kalat.

Law of Specific Nerve Energies

A principle stating that exciting activity by a particular nerve always conveys the same type of information to the brain

e.g Impulses in one neuron indicate light, whereas impulses in another indicate sound

How does vision work in organisms?

It depends only on how far the light travels before it strikes the eyes

Discovery of how vision work in organisms?

Philosopher Hasan Ibn al-Haytham observed that when eyes are opened at night, you immediately see the distant stars and reasoned that if you saw by sending out sight rays, they couldn’t get to the stars that fast.

Pupil

An opening in the center of the iris through which light enters the eye.

Retina

The rear surface of the eye lined with visual receptors onto which light is focused by the (adjustable) lens and (unadjustable) cornea.

Retina (con’t)

• Light from the left side of the world strikes the right half of the retina, and vice versa

• Light from above strikes the bottom half of the retina, and light from below strikes the top half.

Bipolar Cells

A type of cell located in the retina that receives direct signals from retinal photoreceptors and transmits them to ganglion cells.

Ganglion Cells

Retinal cells located closer to the center of the eye whose axons join together to form the optic nerve.

Ganglion Cells (con’t)

Type of neuron in the retina that receives input from the bipolar cells

Optic Nerve

A structure formed by the bundled axons of ganglion cells that exit through the back of the eye and travel to the brain.

Amacrine cells

Retinal cells that get information from bipolar cells and send it to bipolar cells, ganglion cells, and other amacrine cells.

Amacrine cells (con’t)

Refines the responses of bipolar and ganglion cells, enabling certain ones to respond mainly to shapes, directions of movement, color, or other visual features

Blind Spot

The point at which the optic nerve leaves the eye and blood vessels enter and leave, containing no photoreceptors.

Fovea (pit)

The tiny central portion of the retina that allows for acute and detailed vision, tightly packed with receptors (almost exclusively cones).

Fovea (pit) [con’t]

It has nearly unimpeded vision as blood vessels and ganglion cell axons are almost absent near the fovea

Midget Ganglion Cell

A single ganglion cell located in the fovea that connects to a single bipolar cell and a single cone

Midget Ganglion Cell (con’t)

Provides a direct line to the brain to register the exact location of light input.

Transduction

The process by which photoreceptors convert physical energy (light) into neuronal signals through chemical breakdown.

Rods

Visual retinal photoreceptors are that most abundant in the periphery of the retina ($120\,\text{million}$ per retina) that detect and respond to faint light.

Cones

Visual retinal photoreceptors most abundant in and around the fovea ($6\,\text{million}$ per retina) essential for color vision and bright light perception.

Cones (con’t)

They provide 90% of the brain’s input

The ratio of rods to cones

20 rodes to 1 cone

Photopigments

Chemicals contained by rods and cones, consisting of 11-cis-retinal (vitamin A derivatives) bound to opsin proteins that release energy when struck by light.

Trichromatic (Young-Helmholtz) Theory

A theory proposing that colour perception occurs through the relative rates of response across three kinds of cones:

• Short-wavelength,

• Medium-wavelength

• Long-wavelength.

Trichromatic (Young-Helmholtz) Theory (con’t)

Humans discriminate among wavelengths by the ratio of activity across the three types of cones.

e.g. Light at 550 nm excites the medium-wavelength and long-wavelength receptors about equally, and the short-wavelength receptor almost not at all (determines a perception of yellow-green).

Wavelengths and light

We call these wavelengths “light” only because the receptors in our eyes are tuned to detecting them

Wavelengths and colour

We perceive the shortest visible wavelengths as violet, while progressively longer wavelengths are perceived as blue, green, yellow, orange, and red

Visual field

Area of the world that an individual can see at any time

Negative colour afterimage

The result of staring at a colored object for a prolonged length of time and then looking at a white surface

Opponent-Process Theory

A theory suggesting that we perceive colour in terms of paired opposites along a continuum from red to green and yellow to blue.

i.e. The brain has a mechanism that perceives color on a continuum from red to green, another from yellow to blue, and another from white to black

Color Constancy

The ability to recognize colour despite changes in lighting.

e.g. If you wear green-tinted glasses you still identify bananas as yellow, paper as white

Retinex Theory

A theory suggesting that the cortex compares information from various parts of the retina to determine the brightness and color for each area.

Color Vision Deficiency

An X-chromosome-linked impairment in perceiving colour differences, most commonly caused by long and medium-wavelength cones sharing the same photopigment.

How does Color Vision Deficiency develop?

It results when people with certain genes fail to develop one type of cone, or develop an abnormal type of cone

e.g. In red-green colour deficiency, people have trouble distinguishing red from green because their long-and medium-wavelength cones have the same photopigment instead of different ones.

What’s the correct order for the visual pathway?

1. Receptors

2. Bipolar cells

3. Retinal ganglion cells

Horizontal Cells

Cells in the eye that get inputs from the receptors and deliver inhibitory contact onto bipolar cells.

Optic Chiasm

The location where the two optic nerves meet, where half of the axons from each eye cross to the opposite hemisphere in humans.

Lateral geniculate nucleus

Thalamic nucleus that receives incoming visual information

Lateral Inhibition

The reduction of activity in one neuron caused by activity in neighbouring neurons, which sharpens contrasts to emphasize object borders.

Lateral Inhibition’s process

The receptors send messages to excite nearby bipolar cells and they also send messages to horizontal cells that slightly inhibit those bipolar cells and the neighbours to their sides.

The result heightens the contrast between an illuminated area and its darker surroundings.

Receptive Field

The part of the visual field or point in space that either excites or inhibits a cell in the visual system.

e.g. When one keeps track of activities on their block, that’s their receptive field, and reports any findings to a supervisor, whose receptive field is the whole street

How to locate a cell’s receptive field

An investigator records from the cell while shining light in various locations; if light on a particular spot excites or inhibits the neuron, then that location is part of the neuron’s excitatory or inhibitory receptive field.

Ganglion cells receptor fields

A ganglion cell’s receptive field has a circular center and an antagonistic doughnut-shaped surround, and are spaced out evenly across the retina, usually alternating excitatory-inhibitory

Parvocellular Neurons (small celled)

Primate ganglion cells located mostly in or near the fovea with smaller cell bodies and receptive fields, highly sensitive to color and fine visual detail.

Magnocellular Neurons (large celled)

Primate ganglion cells distributed evenly throughout the retina with larger cell bodies and receptive fields, highly sensitive to moving stimuli and large overall patterns.

Koniocellular Neurons (dust-celled)

Primate ganglion cells with granular appearances and small cell bodies found occurring throughout the retina that serve several functions, and terminate in many different locations.

Primary Visual Cortex (Area V1 or striate cortex)

The cortical area that receives information from the lateral geniculate nucleus of the thalamus and carries out the first stage of visual processing.

Primary Visual Cortex (Area V1 or striate cortex) [con’t]

Activity from it projects to the frontal cortex, which within 100–200 milliseconds sends information back to modify the activity in it and other visual areas

Primary Visual Cortex (Area V1 or striate cortex) [III]

The activity in it corresponds to your conscious visual experience, and damage in and around area report no conscious vision, no visual imagery, and no visual dreams

Aphantasia

When people have little or no auditory imagery or other types of sensory imagination

Aphantasia (con’t)

Sufferers tend to be attracted toward math and science

Hyperphantasia

People who can imagine a visual scene almost as vividly as actually seeing it

Blindsight

An ability of some people with damage to area V1 to respond to visual stimuli that they report not consciously perceiving

Continuous flash suppression

A procedure where rapidly changing stimuli captures attention

Simple Cells

Neurons in the visual cortex with bar or edge-shaped receptive fields that have fixed excitatory and inhibitory zones.

Simple Cells (con’t)

Light in the excitatory zone increases responses and light in the inhibitory zone decreases it

Simple Cells (III)

Responds to a stimulus in only one location

Complex Cells

Cells in areas V1 and V2 with large receptive fields without fixed zones, responding best to a pattern of light in a particular orientation, especially moving stimuli.

e.g. A vertical bar moving left to right.

Complex Cells (con’t)

Responds anywhere within a larger area is a complex cel

End-Stopped (Hypercomplex) Cells

Neurons in V1 and V2 similar to complex cells but possessing a strong inhibitory area at one end of their bar-shaped receptive field.

Feature Detectors

Neurons in the visual cortex whose responses indicate the presence of a particular visual feature or stimulus.

Sensitive period

A time early in development when experiences have a particularly strong and enduring influence

Sensitive period (con’t)

It depends on inhibitory neurons

Stereoscopic Depth Perception

A method of perceiving distance in which the brain compares slightly different visual inputs from both eyes using retinal disparity.

Retinal Disparity

The discrepancy between what the left eye and the right eye see.

Strabismus (lazy eye)

A condition in which the eyes do not point in the same direction, impairing stereoscopic depth perception as no cell in the visual cortex gets matched inputs from the two eyes

Astigmatism

A blurring of vision for lines in one direction caused by an asymmetric curvature of the eyes.

e.g. Horizontal, vertical, or one of the diagonals

Astigmatism statistics

About 70% of all infants have it

Secondary Visual Cortex (Area V2)

The brain area that receives visual information from area V1, processes it further, and transmits it to other areas.

Secondary Visual Cortex (Area V2) [con’t]

Its receptive fields are more elongated than those of V1, with many cells that respond to corners, textures, or complex shapes

Ventral Stream (the 'what' path)

The visual pathway through the temporal cortex specialized for identifying and recognizing objects.

Dorsal Stream (the 'how' and ‘where’ path)

The visual pathway in the parietal cortex important for visually guided movements.

Inferior temporal cortex

A portion of the cortex where neurons are highly sensitive to complex aspects of the shape of visual stimuli within very large receptive fields

Visual Agnosia

The inability to recognize objects despite satisfactory basic vision, usually caused by damage to temporal cortex pattern pathways

Visual Agnosia (con’t)

Is brought on by damage to the ventral pathway of the cortex, leading to specialized deficits

Fusiform Gyrus

An area of the inferior temporal cortex containing cells that are especially active during the recognition of faces.

Prosopagnosia

The impaired ability to recognize faces, occurring after damage to or incomplete development of the fusiform gyrus of the inferior temporal cortex.

Prosopagnosia (con’t)

It has nothing to do with memory or visuals, as sufferers can recognize people’s voices, read, and recognize emotions

Middle-Temporal Cortex (MT/V5)

A middle temporal lobe that is important for perception of visual motion

Middle-Temporal Cortex (MT/V5) [con’t]

Its cells detect acceleration or deceleration as well as absolute speed and they respond to motion in all three dimensions

Middle-Temporal Cortex (MT/V5) [III]

Responds to photographs that imply movement

e.g. A photo of people running

Medial Superior Temporal Cortex (MST)

A temporal cortex area that responds best to the expansion, contraction, or rotation of a visual display

Medial Superior Temporal Cortex (MST) [con’t]

The dorsal part of area MST respond to more complex stimuli

e.g. The expansion, contraction, or rotation of a scene

Motion Blindness

The inability to determine the direction, speed, and movement of objects, typically caused by damage to the middle-temporal cortex

Motion Blindness (con’t)

Sufferers are better at reaching for a moving object than at describing its motion

Saccades

Voluntary rapid eye movements during which visual cortical activity and blood flow (specifically in the middle-temporal cortex and parietal cortex) are suppressed.