Neuroscience: Vision

Vision

The sensory system that allows humans to detect and interpret light from the environment.

Visual System

The brain and eye structures responsible for processing visual information.

Light

A form of electromagnetic energy detected by the eyes.

Photoreceptor

A specialized cell in the retina that detects light.

Retina

The light-sensitive layer at the back of the eye.

Pupil

The opening in the eye that allows light to enter.

Iris

The colored part of the eye that controls pupil size.

Cornea

The transparent front surface of the eye that helps focus light.

Lens

A structure that focuses light onto the retina.

Optic Nerve

The bundle of axons that carries visual information from the retina to the brain.

Fovea

The area of the retina responsible for the sharpest vision.

Blind Spot

The location where the optic nerve exits the eye and contains no photoreceptors.

Function of the Pupil

Regulates how much light enters the eye.

Function of the Iris

Expands or contracts to adjust pupil size.

Image Formation

Light is focused onto the retina before visual processing begins.

Why the Eye Is Not a Camera

The brain must interpret visual signals rather than simply view an image.

Phototransduction

The conversion of light energy into electrical signals.

125 Million Photoreceptors

The approximate number of photoreceptors in the human retina.

Retinal Ganglion Cells

Output neurons of the retina whose axons form the optic nerve.

Function of Retinal Ganglion Cells

Send visual information from the retina to the brain.

Bipolar Cells

Retinal neurons that connect photoreceptors to ganglion cells.

Horizontal Cells

Retinal neurons involved in processing visual information.

Amacrine Cells

Retinal neurons that help modify visual signals before they leave the eye.

Rods

Photoreceptors specialized for dim-light vision.

Cones

Photoreceptors specialized for color vision and daytime vision.

Rod Function

Allow vision in low-light conditions.

Cone Function

Provide color vision and high visual acuity.

Rod Sensitivity

Rods are about 1000 times more sensitive to light than cones.

Night Vision

Primarily depends on rods.

Day Vision

Primarily depends on cones.

Three Types of Cones

Cones are sensitive to different wavelengths of light.

Color Vision

Depends heavily on cone activity.

Color Adaptation

Temporary reduction in sensitivity after prolonged exposure to a color.

Visual Pigment

A light-sensitive molecule found in photoreceptors.

Color Blindness

A condition caused by the absence of certain visual pigments.

Genetic Basis of Color Blindness

Missing or altered cone pigments affect color perception.

Magnocellular (M-Type) Cells

Large retinal ganglion cells specialized for certain visual functions.

Importance of M-Type Cells

May play a role in some cases of dyslexia.

Optic Chiasm

The structure where some optic nerve fibers cross to the opposite side of the brain.

Optic Tract

The pathway carrying visual information after the optic chiasm.

Lateral Geniculate Nucleus (LGN)

A thalamic relay station for visual information.

Function of the LGN

Relays visual signals from the retina to the cortex.

Visual Representation

The brain's internal map of visual space.

Contralateral Visual Processing

The left visual field is processed in the right hemisphere and vice versa.

Left Visual Field

Processed mainly by the right hemisphere.

Right Visual Field

Processed mainly by the left hemisphere.

Binocularity

The ability of neurons to respond to input from both eyes.

Binocular Vision

Vision that combines information from both eyes.

Visual Cortex

The cortical regions responsible for processing visual information.

Area V1

The first stage of cortical visual processing.

Area V2

A visual processing area that receives input from V1.

Area V4

A visual area strongly involved in color perception.

Area MT (V5)

A visual area specialized for processing motion.

Function of V1

Detects basic visual features such as lines and edges.

Function of V4

Processes aspects of color perception.

Function of V5 (MT)

Processes motion and movement.

Receptive Field

The area of the retina that influences the activity of a neuron.

Orientation Selectivity

The tendency of neurons to respond best to lines at specific angles.

Orientation Column

A group of neurons that respond to the same line orientation.

Columnar Organization

The arrangement of neurons into columns with similar response properties.

Visual Cortex Plasticity

The ability of the visual cortex to change with experience.

Plasticity

The brain's ability to reorganize with experience.

Hubel and Wiesel

Scientists who discovered orientation selectivity and columnar organization.

Hubel and Wiesel Nobel Prize

Awarded for discoveries about visual cortex organization.

Visual Illusion

A perception that differs from physical reality.

Purpose of Visual Illusions

Reveal how the brain interprets sensory information.

Kanizsa Triangle

An illusion in which the brain perceives a triangle that is not actually present.

Cafe Wall Illusion

An illusion in which straight lines appear tilted.

Dalmatian Dog Illusion

Demonstrates how prior knowledge helps interpret visual scenes.

Visual Interpretation

The brain's process of making sense of sensory information.

Decision Making

The process of evaluating information and selecting a response.

Visual Decision Making

The process of interpreting visual stimuli and choosing an action.

Cognitive Processing

The thinking and reasoning involved in decision making.

Sensory Evidence

Information gathered through the senses.

Role of Experience in Decision Making

Past knowledge helps interpret current sensory information.

Visual Motion

The perception of movement within the visual field.

Importance of Motion Detection

Helps identify objects and changes in the environment.

Motion-Sensitive Neurons

Neurons that respond selectively to movement.

Motion Processing Area

V5 (MT).

Preferred Direction

The specific direction of motion that excites a neuron most strongly.

Motion Coherence

The percentage of dots moving in the same direction.

Motion Detection Task

A task requiring identification of the overall direction of moving dots.

Relationship Between V5 Activity and Motion

Neural activity increases as coherent motion increases.

Microstimulation

The activation of neurons using small electrical currents.

Effect of Microstimulation in V5

Can bias an animal's judgment of motion direction.

Neural Correlate of Perception

Brain activity associated with a specific perception.

Perceived Motion

The motion that a person experiences, regardless of actual stimulus movement.

Believing Is Seeing

The idea that perception can differ from physical reality.

True Color Perception

Depends on cortical interpretation rather than wavelengths alone.

Color-Sensitive Cells

Neurons that respond selectively to perceived colors.

Mondrian Experiment

Demonstrated that color perception depends on context.

V1 and Color

V1 responds to wavelengths but may not directly encode perceived color.

V4 and Color

V4 neurons respond to perceived color categories.

Conscious Vision

Visual information that reaches awareness.

Blindsight

The ability to respond to visual stimuli without conscious awareness.

Cause of Blindsight

Damage to the primary visual cortex while other visual pathways remain functional.

Significance of Blindsight

Shows that some visual processing occurs unconsciously.

Functional Blindsight

Using visual information without conscious awareness during everyday tasks.

Parallel Visual Pathways

Multiple visual routes from the eye to different brain regions.

Visual Awareness

Conscious perception of visual stimuli.