Chapter 6 Vision Notes

Connecting to Research: Hubel and Wiesel Map the Visual Cortex

Hubel and Wiesel explored the activity of single cells in the visual cortex using anesthetized cats.
They identified simple cortical cells, complex cortical cells, orientation columns, and ocular dominance columns.
Their research demonstrated that larger areas of the cortex respond to light in the fovea compared to the periphery.

Behavioral Neuroscience Goes to Work: 3-D Animation

3-D movies utilize special cameras with two lenses to mimic human binocular vision.
Projectors display polarized light that requires 3-D glasses to combine images, creating depth perception.
Tilting the head while watching a 3-D film with linear polarizing glasses can distort the image.

Thinking Ethically: Inclusive Web Design

Web designers should avoid certain color combinations to accommodate viewers with color deficiencies.
Color should not be the only cue in web features; additional cues like text or symbols should be included.
Websites can be scanned for accessibility to ensure compliance with standards like the Americans with Disabilities Act.

Neuroscience in Everyday Life: Are You a Super-Recognizer?

Super-recognizers possess exceptional facial recognition skills, remembering a high percentage of faces they see.
Law enforcement agencies hire super-recognizers to identify individuals in poor-quality videos and photos.
Super-recognizers process all facial features in depth, while individuals with prosopagnosia process less information.

Chapter 6 Vision - Key Concepts and Objectives

L01: Differentiate between sensation and perception.
L02: Discuss visible light as a stimulus.
L03: Explain the features and functions of the eye, retina, and photoreceptors.
L04: Identify information pathways from photoreceptors to the secondary visual cortex.
L05: Summarize visual object perception, depth perception, and color vision.
L06: Describe developmental changes in the visual system across the lifespan.
L07: Differentiate between major disorders affecting human vision.

From Sensation to Perception

Objective physical reality exists, but our perception is based on our sensory systems.
Sensory systems transduce information into action potentials for the nervous system to process.
Each organism has sensory capacities tailored to its survival needs.
Sensation brings information to the central nervous system (CNS).
Perception interprets sensory signals sent to the brain, guided by attention.
Attention focuses consciousness on relevant stimuli, both consciously and automatically.
Unfamiliar, changing, and high-intensity stimuli naturally attract attention.
Bottom-up processing combines simpler meanings to construct complex meanings.
Top-down processing uses knowledge and expectations to interpret meanings.

The Visual Stimulus: Light

Vision is a primary sensory system; 50% of cerebral cortex neurons respond to visual information.
Vision begins with light energy reflected from objects.
Visible light is a form of electromagnetic energy.
Transduction: Transformation of sensory information into neural signals.
Sensation: Process of obtaining environmental information and transmitting it to the brain.
Perception: Process of interpreting sensory signals sent to the brain.
Attention: A narrow focus of consciousness.
Bottom-up processing: Combining simple meanings to construct more complex ones.
Top-down processing: Using knowledge and expectations to interpret meanings.
Electromagnetic energy: Light energy emitted by stars and artificial sources.

The Advantages of Light as a Stimulus

Electromagnetic energy is abundant.
It travels quickly, allowing near-instantaneous sensing of events.
It travels in straight lines, minimizing distortion.

The Electromagnetic Spectrum

Visible light occupies a small portion (400-700 nm) of the electromagnetic spectrum.
Shorter wavelengths (around 400 nm) are perceived as violet and blue.
Longer wavelengths (around 700 nm) are perceived as red.
Gamma rays, X-rays, UV rays, infrared rays, microwaves, and radio waves are outside human visibility.
Some insects and birds can see parts of the ultraviolet spectrum.
Some snakes use infrared radiation to “see” body heat.
Wavelength: Distance between successive peaks of a wave; determines color or shades of gray.
Amplitude: Height of a wave; determines brightness.
Nanometers: Unit of measurement equaling $10^{-9}$ m, used to measure light wave frequency.

Light Interacts With Objects

Objects absorb, reflect, or refract electromagnetic energy.
The color of an object is determined by the wavelengths of light it reflects.
Light-colored clothing reflects more energy, keeping us cooler.
Dark clothing absorbs more energy, keeping us warmer.
Air and water refract light differently.
Human eyes are adapted for use in air, requiring goggles underwater.
Fish eyes are adapted to focus light refracted by water, with rippled outer surfaces and spherical lenses.
Absorption: The ability to retain something rather than reflect or transmit it.
Reflection: The bending back of light toward its source.
Refract: The deflection, or changing of direction, of light at a boundary such as that between air and water.

The Structure and Functions of the Visual System

Eye placement varies among species: front for predators (depth perception), sides for prey (wide scanning).

The Human Eye

The eye is a sphere with a diameter of about 24 mm.
Sclera: The “white” of the eye, a tough outer covering that maintains the eyeball’s shape.
Cornea: A transparent outer layer that begins directing light to form an image. It obtains nutrients from aqueous humor and has a high density of pain receptors.
Anterior Chamber: Contains aqueous humor fluid, which nourishes the cornea and lens.
Aqueous Humor: Fluid in the anterior chamber that nourishes the cornea and lens.
Pupil: An opening formed by the iris, adjusting to light amount and emotional state.
Iris: Circular muscle controlling pupil opening, influenced by melanin pigment (color).
Lens: Focuses light on the retina, adjusting for near or far objects through accommodation.
Accommodation: Ability of the lens to change shape to adjust to the distance of the visual stimulus.
Vitreous Chamber: Large inner cavity filled with vitreous humor (jellylike substance).
Vitreous Humor: Jellylike substance in the vitreous chamber.
Retina: Network of photoreceptors and interneurons sensing light; part of the diencephalon.
- Projects an upside-down and mirrored image relative to actual object orientation.

The Layered Organization of the Retina

Ganglion Cell Layer: Innermost layer containing ganglion cells, whose axons form the optic nerve.
Ganglion Cell: Retinal cell in the ganglion cell layer whose axon leaves the eye as part of the optic nerve.
Inner Plexiform Layer: Contains connections between ganglion, bipolar, and amacrine cells.
Amacrine Cell: Retinal interneuron integrating signals across adjacent retina segments.
Bipolar Cell: Cell in the inner nuclear layer forming a straight pathway between photoreceptors and ganglion cells.
Inner Nuclear Layer: Contains cell bodies of bipolar, amacrine, and horizontal cells.
Outer Plexiform Layer: Connects bipolar cells with horizontal cells and photoreceptors.
Horizontal Cell: Retinal interneuron integrating signals across the retina surface.
Outer Nuclear Layer: Contains cell bodies of photoreceptors.

The Photoreceptors

Rods:
- Approximately 120 million per eye.
- Long, cylinder-shaped outer segment with rhodopsin photopigment.
- Responsible for sensing movement and scotopic vision (dim light vision).
- Do not provide color information or sharp images; vision at night is approximately 20/200.
Cones:
- Approximately six million per eye.
- Responsible for photopic vision (bright light vision).
- Shorter, more pointed outer segment.
- Store one of three different photopigments for color vision and excellent clarity.
- Three classes of cones respond maximally to different wavelengths:
  - Blue (short-wavelength, cyanolabe): 420 nm.
  - Green (middle-wavelength, chlorolabe): 534 nm.
  - Red (long-wavelength, erythrolabe): 564 nm.
Rods respond maximally to wavelengths of 498 nm (bluish-green).
Rods and cones require different amounts of light to respond.
- Rhodopsin responds to very little light.
- Cone photopigments are more resistant and require bright light.
- Rod: A photoreceptor that responds to low levels of light but not to color.
- Cone: A photoreceptor that operates in bright conditions and responds differentially to color.
- Outer segment: The portion of a photoreceptor containing photopigments.
- Photopigment: A pigment contained in the photoreceptors of the eye that absorbs light.
- Rhodopsin: The photopigment found in rods.
- Scotopic vision: The ability to perceive visual stimuli in near darkness due to the activity of rods.
- Photopic vision: The ability to perceive visual stimuli under bright light conditions due to the activity of cones.

The Dark Current

Photoreceptors transduce light energy into electrical signals.
Rhodopsin consists of opsin and retinal (made from vitamin A).
Absorption of light energy changes the shape of retinal, causing rhodopsin to break apart.
Resting potential of a rod outer segment in complete darkness is about -30mV (relatively depolarized).
Sodium ions constantly enter photoreceptors via the dark current.
cGMP keeps sodium channels open in the dark.
Light absorption releases enzymes that break down cGMP, closing sodium channels and hyperpolarizing the photoreceptor.
Photoreceptors produce graded potentials (signals that vary in size) rather than action potentials.
Bright light leads to greater hyperpolarization, while dim light leads to less.
Photoreceptors release glutamate when depolarized (largest amounts in the dark; less with light exposure).

Processing by Retinal Interneurons

Photoreceptors (rods and cones) are the only true receptor cells in the visual system.
Bipolar and ganglion cells provide a direct pathway from photoreceptors to the brain.
Horizontal and amacrine cells integrate information across the retina surface.

Horizontal Cells

Receive input from photoreceptors and output to bipolar cells.
Combine information from nearby photoreceptors to help locate edges and borders.
Communicate through graded potentials.

Bipolar Cells

*Receive input from photoreceptors and horizontal cells; communicate with amacrine and ganglion cells.
*Produce graded potentials.
*Different types support various levels of color and detail: rod bipolar cells, midget bipolar cells, blue cone bipolar cells, diffuse bipolar cells, and giant bipolar cells.
*Compare the amount of light falling on different parts of the retina using receptive fields.
* Receptive field: The location on the retina at which light affects the activity of a particular visual neuron.

Amacrine Cells

Form connections with bipolar cells, ganglion cells, and other amacrine cells.
- Releases inhibitory neurotransmitters (GABA and glycine).

Ganglion Cells

Output cells of the retina; receive input from bipolar and amacrine cells.
Axons form the optic nerve, traveling to higher levels of the brain.
Produce conventional action potentials.
- Continues the process of evaluating information in rods and cones.
- Contains photopigment melanopsin and act as photoreceptors themselves

Ganglion Receptive Fields

Receptive fields in the shape of doughnuts.
Midget ganglion cells are the most common type of human ganglion cells.
- Parasol ganglion cells receive input from diffuse and giant bipolar cells.
- Small bistratified ganglion cells connect to bipolar cells that, in turn, make connections with blue photopigment cones.
  - Demonstrate blue-on, yellow-off responses.
- Midget ganglion cell: Small ganglion cell that responds to high contrast and color.
- Parasol ganglion cell: Large ganglion cell that responds to all wavelengths regardless of color, subtle differences in contrast, and stimuli that come and go rapidly.
- Small bistratified ganglion cell: A ganglion cell that processes blue and yellow.

Visual Pathways

Ganglion cell axons exit through the optic disk, forming the optic nerve.
- Partially crosses the optic chiasm.
  *Almost 90 percent of the axons in the optic tract proceed to the thalamus, which, in turn, projects to
the primary visual cortex located in the occipital lobe of the brain.

The Superior Colliculus

*The superior colliculus also receives input from the visual cortex, which moderates its activity.

The Lateral Geniculate

The LGN possess the same doughnut-shaped, antagonistic center-surround organization of receptive fields that we observed in the retinal bipolar and ganglion cells.

The Striate Cortex

*In the striate cortex, located in the occipital lobe, cortical mapping of the visual world returns to figure 6.18, you can trace the pathways from the eye,
*Striate cortex cortical receptive fields are capable of assessing much more complex features, such as moving bars of light

Connecting to Research Hubel and Wiesel Map the Visual Cortex

*Hubel and Wiesel knew from previous research that retinal cells and cells in the LGN had on- and off-center receptive fields, yet no such organization had ever been demonstrated in the cerebral cortex.
* Complex Cortical Cells respond to all stimuli shape and orientation without reference to the stimuli location or appearance in the receptive field.

Cortical Columns

*Cortical Neurons are formed into columns perpendicular to the surface of the brain neurons in cortical columns communicate with one another from about 0.5 mm away

*One type of column found in the striate cortex is known as ocular dominance column
* Neurons in areas with high concentrations of cytochrome oxidase appear to process information regarding color.

Cortical Modules

*At some point, our visual system puts these separate characteristics back together to form coherent images.
*We have about 1,000 modules and each one makes up approximately 2mm.

Visual Analysis Beyond the Striate Cortex

*At least a dozen additional area of the human cerebral cortex participate in visual processing because these areas are not inclusive in the striate cortex they are often referred to as extra striate areas These areas are also referred to as secondary visual cortex
*Next to the striate cortex is an area known as V2.

Information about movement and the location of objects is processed further by the dorsal stream
while information about object recognition is processed further by the ventral stream.
Patients with damage to Area MT have a condition called akinetopsia, which results in their seeing the visual scene as a series of still photographs instead of an ongoing flow of information.
Most of the cells in area MT respond to movement in a particular direction.

The Visual Cortex

Simple cortical cell: A cortical interneuron that responds to stimuli in the shape of a bar or edge with a particular slant or orientation in a particular location on the retina.
Complex cortical cell: A cortical interneuron that has a preferred stimulus size and orientation, and in some cases, direction of movement, but not location within the receptive field.
End-stopped cells respond most vigorously to a stimulus that does not extend beyond the boundaries of its receptive field.

Cortical Columns

Ocular dominance columns that respond to input from either the right eye or the left eye but not both.
Orientation columns respond to lines of the same angle. Adjacent columns respond to angles shifted about 10 degrees. A set of these columns that responds to a complete rotation of 180 degrees is referred to as a hypercolumn.

Visual Analysis Beyond the Striate Cortex

*It begins but by no means finishes the task of processing visual input. At least a dozen additional areas of the human cerebral cortex participate in visual processing. Because these areas are not included in the striate cortex they are often to as extra striate areas.

Dorsal stream: A pathway leading from the primary visual cortex in a dorsal direction that is thought to participate in the perception of movement and object location.
Ventral stream: A pathway of information from the primary visual cortex to the inferior temporal lobe that is believed to process object recognition.

Visual Perception

The interpretation of this incoming data recruits the memories, experiences and expectations.

Bottoms up or top down?

The model implies a bottom up and structural organization of which simple so contributes input to increasingly complex cells. At each level of processing cells are more complex because from simpler responses
*One patient had a cell that fired in response to all images that included actress Jennifer Aniston, but not at all to images of other faces, landmarks, or objects.

Visual spatial Frequencies

Striate cortex may respond to patterns of lines instead of isolated lines and bars such the simplest patterns of lines or as grated which has many bars in a given distance.

*A small minority about 5 - 10 percent of the population have difficulty with this procedure because they rely so much in color so with the goal the contrast can be more beneficial for people with low vision.
*The perception is a process of steps to contribute to both top down and bottom up effects .

Contrast sensitivity function

*It is measuring how much contact is needed for grating to look different from a uniformly colored disc as a function of spatial frequency.

The human eye may be easily available to adapt the darkness compared to a cat's or vice versa.

The perception of depth

Monocular requires the use of only one eye, there are several of these techniques that are known now and we have binocular a two way depth Q is that are even more effective than singular ones.
*We can also use retinal disparity to give us even more illusion than the image can project. The degree of the cells with their own activities to judge better results.

Coding Color

*They can be mixed to generate all colors in missing them together will give you a white light consequently the primary colors are red green and blue.

The trichromatic theory which is based on humans is a series of tasks which proposed his theory in 1807
The theory of opponent processes states that when mixing blue and yellow lights yielded the sensation of gray

Color deficiency

*When a body has 3 cone pigments however the cones week from the sun occurs at slightly different wavelengths than is typical then the condition is called anomalous rich mommy
*Individuals match colors so and almost similar as a normal people do But they had some exceptions and problems with what they are doing In conclusion it might be easier to to find them unusual compared normal humanoids

Color contrast and color constantly

*Like color contrast a color may look different against another background or color
*colors did not appear to change even if something changes with them it it is called color constantly which means the brain compensates

Thinking Ethically

Inclusive Web Design has the goal, to accommodate the need or wants for different people that may see the colors different depending on the different types of light .
*When the designer should try to avoid the mistakes of the potential viewers that could see those colors different depending some choices.

The life Span development of the visual system .

We can't ask or investigate about one's thought when their are infants but we can ask about contrast. .
*Beginning from middle age harder of the lessons to a near side objects the vision reduces
But the person may require extreme strong glasses when getting a artificial eye it requires different Vision of some ethnic for there is. Also a different to the view that can see Nearly any vision

The older eye can't be respond to the lighting as the lenses have that ability . However there so that provide of this there that might effect the aging in future can get hard

The development of what will increase their abilities of them in there orientation or social interactions.

Disorders of the visual system

*Can interfere with vision there vision can be lost because problems of the eye and retina.
*The brain won't ever notice it. Macular degeneration which cell begins to die is the leading causes of brain injuries when older.
*They see they are in normal area to function in the Cortical area which. Has a Scotona there were often demonstrate of this vision

Visual Agnosias

*are disorder in which people can seem a stimulus
*Prosopagnosia is and vision is and cannot face and there and this cannot recognise the well , the famous known area is and this is due to stroke or the accident

Neuroscience in everyday life are you a super recognizer

Face recognition skills varies on the population who have it and on the way , you can also can and find this online by a number of online test designs .
The main difference is of people that are with this , because of how process as amount of many process the information. that is around them.