Neuro test 2

Small Cone (S)

Small Cone (S)

shorter wavelength (blue cone)

Medium Cone (M)

Medium Wavelengths (green cone)

Large Cone (L)

Large wavelength (red cone)

What is trichromatic color perception?

Perception of three different types of cones in the retina

How many types of cones are involved in trichromatic color vision?

3

Which three types of cones are responsible for trichromatic color perception?

Short-wavelength, medium-wavelength, long-wavelength

What does trichromatic color perception rely on for accurate color discrimination?

Relative responses of the three types of cones

Metamers

Two different things that can look different but produce the same response to the three cone types in our eyes.

Single Cone Type

A single type of cone in the eye responsible for detecting a specific range of wavelengths. It alone cannot provide full color vision.

Color Blindness

A condition where individuals have difficulty distinguishing between certain colors. The most common type involves a deficiency in either the L or M pigment, which are responsible for perceiving red and green colors.

Ishihara Color Plate

A test for color blindness that uses patterns composed of dots in different colors and sizes. It is used to diagnose the type and severity of color vision deficiency.

Opponent Channels

Three pairs of color channels (red-green, blue-yellow, black-white) in the visual system that are responsible for processing color information. They compute the difference between responses in the three cone types.

Adaptation

After prolonged exposure to a color, the visual system adjusts, and you may start to perceive the opposite color in that location in your visual field.

Color Equivariance

The phenomenon in where some pairs of colors appear identical to a dichromat, even though they are distinguishable to a trichromatic individual. This occurs due to the limited color discrimination abilities of dichromats compared to trichromats.

Three-stage Retinal Processing

The sequential flow of visual information in the retina: Photoreceptor → Bipolar cell → Ganglion cell.

Retinal Cells

types of cells in the retina, including photoreceptors, bipolar cells, ganglion cells, horizontal cells, and amacrine cells.

Horizontal Cells

Improve clearness and sharpness of what you see by having some cells in your eye slow down others nearby through a process called lateral inhibition. This helps highlight edges and differences in what you're looking at.

lateral inhibition

A neural mechanism in the retina where activated photoreceptors inhibit neighboring ones, enhancing the perception of edges and contrasts in visual stimuli.

Ganglion Cells

Neurons in the retina that transmit processed visual information to the brain via the optic nerve, playing a vital role in visual perception.

Pathway to Primary Visual Cortex

retina -> lateral geniculate body of thalamus -> primary visual cortex

V1 (Primary Visual Cortex)

The first cortical area responsible for processing visual information, located in the posterior part of the brain and comprising six layers.

Striate Cortex

primary visual cortex

Optic Chiasm

the point in the brain where the visual field information from each eye "crosses over" to the appropriate side of the brain for processing

• where axons of ganglion cells cross to opposite hemisphere of the brain

Lateral Geniculate Nucleus (LGN)

A structure within the thalamus that receives axons from the optic nerve and serves as a relay station for visual information.

Optic Radiation

Nerve fibers that carry visual information from the LGN to the primary visual cortex (V1) in the occipital lobe.

Layer 4 in V1

Receives the majority of information from LGN (Lateral Geniculate Nucleus).

Layer 6 in V1

Guides attention, filters stimuli for goals, and directs thalamus via corticogeniculate pathway. directs attention by instructing the thalamus to filter out irrelevant visual information, prioritizing stimuli related to immediate goals, such as finding food.

Neurons in V1

Respond to edges of specific orientations on specific regions of the retina. Called "simple cells". Play a fundamental role in perceiving objects and their orientations.

Columns in the Visual Cortex

Neurons in the primary visual cortex (V1) organize into specialized groups called columns, each with similar receptive fields.

Orientation Columns

Respond specifically to lines of the same orientation.

Ocular Dominance Columns

Respond to input from either the left or right eye.

Functional Areas for Color, Movement, and Shape

Various regions in the brain specialize in processing different aspects of visual information.

Dorsal Stream Area MT:

Critical for detecting motion direction.

Ventral Stream Areas V4 and TEO

Specialize in perceiving color.

Ventral Stream Area TE

Processes object shapes; contains FFA (fusiform face area) dedicated to face recognition.

Prosopagnosia

Condition resulting in the loss of ability to identify faces.

Depth Perception

Our ability to perceive depth relies on visual cues, both monocular and binocular.

Monocular Cues

Include objects blocking views and relative size.

Binocular Cues

Such as retinal disparity, which involves the different views from both eyes.

Retinal Disparity

The difference between two different retinal locations.

Scotoma

A blind area in the visual field.

Effects of Damage to V1

Leads to scotomas and specific visual loss areas.

Blindsight

The ability of individuals to respond to visual stimuli without conscious awareness, often due to alternative pathways bypassing V1.

Image reflection on retina

image on retina is upside down and flipped left-right, relative to the orientation of objects in the world.

Color Perception

The ability of the visual system to distinguish and interpret different wavelengths of light, resulting in the perception of various colors.

Rod Cells

Photoreceptor cells in the retina that are specialized for low-light conditions and do not perceive color.

• periphery of the retina

• large # of rods send their combine output to individual receiving neurons (output of many rods converge to influence neurons)

Cone Cells

Photoreceptor cells in the retina that are responsible for color vision and function best in bright light.

• found in fovea

• high acuity (sharp vision): one to one connections between cones and cells that receive the cones signal

Opponent-Process Theory

A theory of color vision proposing that the visual system processes color information in opposing pairs (red-green, blue-yellow, and black-white), creating the perception of complementary colors.

Perceptual Constancy

A neurological condition characterized by the inability to recognize or identify objects or people visually, despite having normal vision.

Which side of the brain receives information from the right visual field?

The left side of the brain.

Where do optic nerve axons synapse after the optic chiasm?

Lateral geniculate nucleus of the thalamus (LGN).

Journey from eyes to brain

eyes → optic nerve → optic tract → LGN → primary visual cortex.

Where is the Primary Visual Cortex (V1) located?

In the occipital lobe.

What is the name of the pathway that LGN neurons use to send information to V1?

Optic Radiation.

What is the role of bipolar cells in vision?

convey information about changes in light to ganglion cells.

binocular vision field.

what both your eyes can see.

What is the difference between binocular and monocular vision?

Binocular vision is what both eyes can see, while monocular vision is what one eye can see.

Describe the receptor density across the retina.

There are fewer photoreceptors at greater eccentricity (distance from fovea).

What is the fovea and what is its significance in vision?

The fovea is the very center of the retina where cones are densely packed. It is essential for detailed central vision.

How does convergence differ between the periphery and the fovea?

There is more convergence in the periphery. Ganglion cells pool input over multiple photoreceptors.

Explain the difference in connections between cones and rods.

Cones have one-to-one connections, while rods exhibit convergence.

What is the blind spot or optic disk?

It is the area on the retina where there are no photoreceptors.

What is the advantage and disadvantage of increased convergence in rods?

What is the advantage and disadvantage of increased convergence in rods?

Receptive fields of neurons in the retina

Bipolar and ganglion cells have small, roughly circular RFs that correspond roughly to where the cell body lives on the retina.

Off center bipolar cells

Excited by neurotransmitter (glutamate), that is released by photoreceptors, and thus more active in the dark.

Center surround structure

Light in one part of the RF excites the cells, light in the other part inhibits it.

What is saturated and unsaturated light?

Saturated: light made of a single wavelength (rich) Unsaturated: mix of wavelengths

What makes a light brighter?

Amplitude/height

Pupil

The diameter controls the amount of light that enters

Cornea

refracts (bends) the entering light before it enters pupil

Lens

After light pass through pupil, bends further as it passes through lens. Tiny muscles can elongate or shorten the lens in order to focus incoming image upon retina

Retina

Thin layer of tissue at back of eye that has neurons that transduce light into patterns of neural activity

Dark current

Excitatory inflow of Na+ ions, along with small inflow of calcium ions

• Na+ enters and depolarizes both the rods and cones in the dark

Bipolar cells

eye neurons that receive information from the retinal cells and distribute information to the ganglion cells (which then passes to brain)

Amacrine cells

receive visual input from bipolar cells, and send signals to retinal ganglion cells

• allows ganglion cells to respond to images falling on regions of the retina larger than that which drives the activity of a single bipolar cell

superior colluculi (mound atop the midbrain)

One bundle of axons leaving the retina terminates here, shifts the gaze toward significant visual stimul

• do not contribute to higher-level aspects of visual perception

Suprachismatic nucleus (SCN) body's internal clock

subcortical region in hypothalamus receives input from the retina

• optic nerve alerts SCN when light has arrived

• linking sleep-wake cycles to environmental light cues

lateral geniculate nucleus (LGN) relay nucleus

Structure in thalamus that connects the eye and retina to the primary visual cortex where higher-order analysis of visual input begins

• largest portion of the retinal axons travels via the optic tract to LGN

Six layers of LGN

2 bottom: magnocellular (large neurons)

• one layer receives input from the left and eye and other from right 4: parvocellular: small bodies Tucked in between: koniocellular

Simple cell V1

Cells in v1 that respond to lines of a specific orientation falling upon a particular region of the retina

What is the corticogeniculate pathway?

cortex to lateral geniculate nucleus

Complex cells V1 and V2

Neuron that respond to lines of specific orientation, but will respond to movement of the line in a specific direction. ability to detect when object is moving

Fusiform face area (FFA)

responds to very specific kinds of shapes, such as faces

• face recognition FFA in the right hemisphere

• prosopagnosia (damage to this area)

Synthesis

combining of senses: often merge between vision and another sensory experiences

• caused maybe by unusual connections between brain areas

Primary Somatosensory Cortex

Receives initial sensory information

Body Part Representations

Largest areas in PSC correspond to body parts with highest touch sensitivity

Shared Features of Sensory Systems

Sensory receptors respond to external energy changes, transduction, neural pathways, PSC, higher cortical areas

Mechanoreceptors

Sensitive to touch and pressure

Merkel's Disks

Respond to light touch

Meissner's Corpuscles

Respond to touch and slow vibrations

Ruffini Endings

Respond to skin stretching (pressure) and warmth

Pacinian Corpuscles

Respond to brief, deep pressure and rapid vibrations

Nociceptors

Sensitive to painful stimuli

Thermal Nociceptors

Respond to intense heat

Chemical Nociceptors

Detect chemical toxins

Mechanical Nociceptors

Respond to intense pressure (pinch, scratch, cut)

Polymodal Nociceptors

Receptors that can detect more than one type of noxious stimulus

Aδ and C Fibers

Nociceptors transmit pain signals to the CNS via Aδ fibers (sharp pain) and C fibers (dull, long-lasting pain)

Locations of Nociceptors

Found in the skin, joints, and visceral organs

Configuration of Receptor Cells

Somatosensory receptor cells have a long axon with one end in the skin and the other end in the spinal cord