PSB CH5 - VISION

Law of Specific Nerve Energies

A principle stating that whatever excites a particular nerve always sends the same kind of information to the brain.

Function of Receptors

Receptors absorb specific types of energy and transduce it into an electrochemical pattern in the brain, with different receptors indicating light or sound.

Brain Coding

The brain codes information received from receptors, but the coding does not resemble what is actually seen until interpreted.

Frequency of Response

The rate at which a neuron fires, which controls the intensity of sensations, such as pain.

Pupil

An opening in the center of the iris that allows light to enter the eye, focused by the lens and cornea.

Retina

The rear surface of the eye lined with visual receptors where light is processed; light from the left strikes the right half and vice versa.

Bipolar Cells

Neurons located close to the center of the eye that receive messages from visual receptors and send them to ganglion cells.

Ganglion Cells

Neurons located even closer to the center of the eye that receive messages from bipolar cells and send their axons to the brain, forming the optic nerve.

Amacrine Cells

Cells that receive information from bipolar cells and send it to other bipolar cells, amacrine cells, or ganglion cells; important for complex processing of visual information.

Optic Nerve

The nerve formed by the axons of ganglion cells that carries visual information from the retina to the brain.

Blind Spot

The point at which the optic nerve leaves the eye; it has no visual receptors.

Fovea

The central portion of the macula specialized for acute, detailed vision, with least impeded vision due to the absence of blood vessels and ganglion cells.

Midget Ganglion Cells

Small ganglion cells in the fovea that each receive input from a single cone, crucial for detail perception, providing 70% of the brain's input.

In the ___ , each cone has its own line to the brain.

fovea

In the ___ , each receptor shares a line with tens or hundreds of others.

periphery

Rods

Type of visual receptor abundant in the periphery of the retina, involved in peripheral and night vision.

Cones

Type of visual receptor found primarily in the fovea, involved in visual acuity and color vision.

Rods to Cones Ratio

In humans, the ratio of rods to cones is approximately 20-to-1.

Photopigments

Chemicals in rods and cones that release energy when struck by light, consisting of 11-cis-retinal bound to proteins called opsins.

What is required for color vision in animals?

Color vision requires comparing the responses of different kinds of cones.

Why can't animals like rats discriminate colors?

Rats have only one type of cone, preventing them from distinguishing different colors.

What are the shortest visible wavelengths perceived as in the human visual system?

The shortest visible wavelengths (about 350 nm) are perceived as violet.

What colors are perceived as wavelengths progressively longer than violet?

Progressively longer wavelengths are perceived as blue, green, yellow, and red (near 700 nm).

What are the two major theories of color vision proposed in the 1800s?

The two major theories are the trichromatic theory and the opponent-process theory.

Trichromatic Theory

A theory of color vision stating that humans have three types of cones, each sensitive to different wavelengths of light, and color is perceived by the ratio of activity across these cones.

Visual Field

The part of your world that you see.

Opponent-process theory

A theory explaining color perception in terms of paired opposites (e.g., red-green, yellow-blue), stating that negative afterimages result from the fatigue of opponent-process cells.

Retinex Theory

A theory proposed to explain color constancy; it suggests that when information from various parts of the retina reaches the cortex, the cortex compares inputs to determine brightness and color perception for each area.

Color Constancy

The ability to recognize the color of objects despite changes in lighting, which is not explained by the trichromatic theory or opponent-process theory.

Color Vision Deficiency

Also known as color blindness, characterized by the inability to perceive color differences. Complete colorblindness (only seeing black and white) is rare. Red-green color blindness is the most common form, primarily seen in males.

Lateral Inhibition

The reduction of activity in one neuron by activity in neighboring neurons; a technique of the retina to sharpen the boundaries of visual objects.

In the vertebrate retina, which cells are responsible for lateral inhibition?​

Horizontal cells.

Receptive Field

The portion of the visual field that excites or inhibits a specific cell in the visual system of the brain.

Parvocellular Neurons

Small cell bodies located in or near the fovea, with small receptive fields that respond best to visual details and color.

Magnocellular Neurons

Larger cell bodies distributed evenly throughout the retina, with larger receptive fields that respond best to moving stimuli.

Koniocellular Neurons

Neurons similar in size to parvocellular neurons, distributed throughout the retina, with several different functions.

Primary Visual Cortex (Area V1)

Located in the occipital cortex, responsible for the first stage of visual processing; damage to this area results in loss of conscious vision.

Blindsight

The ability to respond to visual information after damage to area V1; individuals can react to

Simple Cells

Neurons in the primary visual cortex (V1) with fixed excitatory and inhibitory zones, typically having bar-shaped or edge-shaped receptive fields.

Complex Cells

Neurons located in V1 or V2 that respond to particular orientations of light and receive input from simple cells; their receptive fields cannot be mapped into fixed excitatory and inhibitory zones.

End-stopped (Hypercomplex) Cells

Neurons resembling complex cells but possessing a strong inhibitory area at one end of their bar-shaped receptive field.

The one additional feature that hypercomplex cells have that complex cells do not is that hypercomplex cells…

have an additional inhibitory area at one end of their receptive field.

What is the Columnar Organization of the Visual Cortex?

Cells in the visual cortex are grouped together in columns perpendicular to the surface based on their responsiveness to specific stimuli.

How do cells in the visual cortex respond in terms of eye input?

Cells in a particular column may respond only to visual input from the left or right eye, or from both eyes about equally.

What kind of stimuli do some columns in the visual cortex respond to?

Some columns respond best to stimuli of a single orientation.

Feature Detectors

Neurons whose responses indicate the presence of a particular feature; prolonged exposure decreases sensitivity to that feature, exemplified by the waterfall illusion.