Vision and Anatomy of the Eye: Key Concepts

Sensation

Detection of stimuli from the environment.

Perception

Conscious experience and interpretation of information from the senses by neurons in the CNS.

Wave

Disturbance or oscillation that transfers energy from one place to another.

Wave properties

1. Wavelength (nm), 2. Frequency (Hz), 3. Amplitude (Volts)

what is the electromagnetic spectrum?

the range of wavelengths (in nanometers) or frequencies over which electromagnetic radiation extends.

what are the dimensions of light?

Hue: color determined by wavelength

Saturation (purity): determined by the # of wavelengths in the perceived light.

Intensity (brightness): determined by the intensity of the electromagnetic radiation.

Hue

Color determined by wavelength.

Saturation

Purity determined by the number of wavelengths in the perceived light. example is that red is high in saturation and pink is low in saturation.

Intensity

Brightness determined by the intensity of the electromagnetic radiation.

Fibrous layer

The outer layer of the eye that includes the sclera and cornea.

Orbits

Orbits are the bony pockets in the front of the skull in which the eyes are suspended.

Sclera

White outer coat of the eye to which six extraocular muscles are attached.

Cornea

Transparent part of the eye that helps to focus light on the retina.

what are the layers of the eye?

Fibrous layer - sclera and cornea

vascular layer - choroid, ciliary body, iris

nervous layer - retina

Vascular Layer

choroid, ciliary body, iris

Choroid

a layer of blood vessels and connective tissue located in the eye, plays a crucial role in providing nutrients and oxygen to the inner parts of the eye, particularly the outer retina

Iris

color part of the eye that regulates the amount of light that enters the eye by adjusting the size of the pupil

Ciliary body

Produces aqueous humor and contains muscles that change the shape of the lens for focusing (accommodation).

Conjunctiva

Clear, thin tissue that covers the inside of the eyelid and the white of the eye (sclera).

Lens

Focuses light and adjusts focus (accommodation).

Retina

Contains photoreceptor cells called rods and cones that convert light into electrical signals.

vitreous humor

the transparent jellylike tissue filling the eyeball behind the lens.

Nervous layer

retina which captures light through photoreceptors, converts light into electrical signals, then sent to the brain via the optic nerve.

process of vision

Stimuli > Sensory receptors > Sensory transduction > Receptor potentials

Rods

peripheral, sensitive to low levels of light, monochromatic information, poor visual acuity

Cones

found in the fovea, sensative to high levels of light, color/ hue, high visual acuity

how many rods and cells are there?

there are 120 million rods and 6 million cones.

Optic disc

"blind spot" - The exit point for the axons of the ganglion cells, which carry visual information from the retina to the brain.

what are the layers of the retina?

photoreceptors (rods and cones) , bipolar cells (horizontal and amacrine) , ganglion cells

Photopigments

Rhodopsin that turns light into action potential (energy > chemical > electrical).

Transduction

The process by which photoreceptors convert light into electrical signals.

what causes hyperpolarization during transduction?

The photoreceptor splits causes hyperpolarization, then reduces glutamate release which signals transmitted to bipolar cells, then ganglion cells

Darkness detectors

Photoreceptors depolarize with darkness glutamate is also released and hyperpolarize with light and NT glutamate releases

Bipolar cells response to glutamate

light ON - hyperpolarization; dark OFF - depolarization

Neuron's receptive field

the part of the visual field to which the neuron responds

saccadic eye movement

a rapid, jerky movement from one fixation to the next

vergence eye movements

move your two eyes in unison to focus on a single chosen image

pursuit eye movement

smooth following of a moving target

Visual pathway

Includes Retina (optic nerve), Optic chiasm, dLGN (part of the thalamus), Optic radiations, Primary visual cortex (V1, striate cortex), Visual association cortex (V2, extrastriate cortex)

Lateral geniculate nucleus (LGN)

Six layers of neurons; Each layer receives information from ganglion cells of one eye.

Lateral Geniculate Nucleus Layers 1,4,6

Layers 1,4,6 > contralateral eye

Lateral Geniculate Nucleus Layers that are ipsilateral eye

2,3,5

Magnocellular layers

layers 1 & 2; large cell bodies; sensitive to motion

Contrast-sensitive High temporal resolution

Parvocellular layers

Layers 3, 4, 5, and 6 of the LGN, small cells, which get information from P-ganglion cells and process color, shapes, and details.

Detect fine details but respond slow

koniocellular division

These layers are found between the other layers and contain very small cells. They receive input from ganglion cells that signal average illumination and are thought to play a role in color perception and other visual functions.

Striate cortex (V1)

The first region to combine visual information from several sources.

Striate cortex fovea processing

25-50% of striate cortex devoted to fovea processing (1% of retina)

Cytochrome oxidase (CO) blobs

blob-like structures within primary visual cortex (V1) that are thought to be involved in the color processing pathway. Similar structures are also seen in V2 (stripes) and V4 (globs), both of which are visual areas also involved in color processing

Blobs in V1

Located in layers 2 & 3 (5 & 6) of V1

Module of striate cortex

A specialized and relatively self-contained group of neurons or brain regions that work together to perform a specific function.

Information in each module (column) in the striate cortex

Contains information about Orientation selectivity, Spatial frequency, Color, Motion

Extrastriate cortex (V2-V5)

Combines information from modules in the striate cortex to form representations of objects and visual scenes.

Ventral stream

What information (physical form of the object)

Dorsal stream

Where information (location and place of the object in space)

Ventro-dorsal stream

skilled object use ex: grasping

ON cells

Excited by light in center Inhibited by light in periphery

OFF cells

Excited by light in periphery Inhibited by light in center

ON/OFF cells

Excited by light turning on or off

Response to moving or suddenly appearing objects

Difference between rebound effect and on/off cells

ON/OFF cells are a type of neuron that respond to changes in light intensity, with ON cells increasing their firing rate when light turns on and OFF cells increasing their firing rate when light turns off. The rebound effect, on the other hand, refers to a phenomenon where a neuron's firing rate returns to or exceeds its baseline level after a period of inhibition or hyperpolarization.

Trichromatic theory

theory of color vision that proposes three types of cones: red, blue, and green

Opponent color system theory

Cones are linked together in opposing pairs, like red-green, blue-yellow, and black-white, and only one cone in each pair can signal the brain at a time.

Photoreceptors in the retina use which color theory?

trichromatic system - three types of cones: red, blue, and green

Protanopia

lack of functioning red cones

opsin

the protein portion of visual pigment molecules

Deuteranopia

lack of functioning green cones

Tritanopia

lack of functioning blue cones, monochromatic vision

Ganglion cells in the retina use the x color system

opponent color system

explain how the ganglion cells in the retina use the opponent color system?

The retina contains three types of cone photoreceptors: those sensitive to short (blue), medium (green), and long (red) wavelengths of light. Ganglion cells don't simply respond to the presence of one color. Instead, they are excited by one color within a pair and inhibited by its complementary color. A cell might be excited by red and inhibited by green, or excited by blue and inhibited by yellow.

ganglion types of opponent cells of red-green

Red-Green Opponent Cells: These cells respond positively to red light and negatively to green light.

ganglion types of opponent cells of blue-yellow

Blue-Yellow Opponent Cells: These cells respond positively to blue light and negatively to yellow light.

explain the phenomenon of negative afterimage and rebound effect

The retina has different photoreceptor types that respond to different wavelengths of light (e.g., red, green, blue). When one type of photoreceptor is fatigued, the other types, which respond to the complementary color, become more active.

striate cortex and extrastriate cortex and color formation

Both the striate and extrastriate regions are crucial for color perception, with V1 handling the initial processing and extrastriate areas like V2 and V4 contributing to higher-order color processing.

striate cortex and form perception

receives visual input from the thalamus and processes basic visual features like edges, lines, and orientations.

extrastriate cortex and form perception

ventral stream of the extrastriate cortex is involved with the "what" the objects are

V4: Involved in color processing and shape perception

striate cortex

Initial Visual Processing (from LGN)

Retinotopic Mapping:

It maintains a precise spatial representation of the visual field, allowing for the accurate perception of object locations.

Feature Detection:

specific visual features, such as edges, orientation, and direction of motion.

Binocular Vision:

neurons have receptive fields that integrate information from both eyes.

Input to Extrastriate Areas:

sends processed visual information to other visual areas (extrastriate cortex) for further analysis.

conscious processing of visual stimuli, meaning it is necessary for visual perception.

Blindness from Damage:

Damage to the striate cortex can lead to blindness in the corresponding regions of the visual field.

Sine-wave grating

A series of fuzzy parallel bars.

Spatial frequency

Variation in brightness measured in cycles per degree of visual angle.

inferior temporal (IT) cortex

encompassing areas TEO and TE, is a critical part of the visual processing system in the brain, particularly involved in object and face recognition. Located in the temporal lobe, it receives input from other visual areas and is known for its role in higher-level visual processing.

Visual agnosia

Inability to recognize objects despite intact vision. they can recognize items through other senses. due to damage in the occipital lobe

Prosopagnosia

inability to recognize faces; face blindness. damage in the fusiform face area (FFA)

The fusiform face area (FFA)

A region of extrastriate visual cortex in humans that is specifically and reliably activated by human faces.

Congential prosopagnosia

a lifelong face recognition impairment that is present from birth, without any other neurological damage or developmental delays. Due to smaller anterior FFA and decreased connectivity within temporal-occipital cortex

Extrastriate body area (EBA)

An area in the temporal cortex that is activated by pictures of bodies and parts of bodies, but not by faces or other objects.

Parahippocampal place area (PPA)

Activated by scenes and backgrounds.