Visual Coding and the Eye

Visual Coding

• Vision begins with light, a form of electromagnetic radiation traveling in waves
• Amplitude (wave height) affects the perception of brightness
• Wavelength (distance between peaks) influences color perception
• Humans perceive only a small portion of wavelengths called the visual spectrum
• Turning visual input into neural impulses is crucial for the brain to process visual information
• Purity refers to the mix of wavelengths
• Saturation indicates the whiteness or richness of a color

The Eye: Converting Light

• Eyes channel light towards neural tissue to be received and also house the surrounding tissue

Anatomy of the Eye and Vision Pathway

• Light first enters through the cornea
• The lens focuses light rays onto the retina
• The iris, a colored muscle ring, regulates the amount of light entering the eye by constricting or dilating
• The pupil's size is adjusted by the iris to regulate light intake

The Lens and Accommodation

• Accommodation refers to the lens adjusting curvature to alter visual focus
• Problems with accommodation can lead to nearsightedness or farsightedness
• Nearsightedness results in clear close vision but blurry distant vision due to light being focused in front of the retina
• Farsightedness means distant objects are seen clearly, while close objects appear blurry, with the focus point falling behind the retina

The Retina: Extension of the CNS

• The retina absorbs light, processes images, and transmits visual information to the brain
• The optic nerve carries visual information from the retina to the brain
• The optic disk/blind spot lacks photoreceptors, marking where the optic nerve exits the eye
• Specialized photoreceptor cells in the retina convert light energy into neural energy

Rods and Cones

• Rods mediate black and white/low light vision and are sensitive in dim settings
• Rods are concentrated just outside the fovea to aid peripheral vision
• Rods greatly outnumber cones
• Cones enable color and daylight vision, needing more light than rods
• Cones provide precision through visual acuity

Retina Review

• The retina contains a light-sensitive layer at the back of the eyeball
• Photoreceptors translate light energy into neural impulses and send signals to the brainstem
• Rods are more sensitive to dim light but not to colors and transmit to the midbrain
• Cones respond well to colors but not dim light
• The fovea is an area of sharpest vision on the retina with densely packed cones

Adaptation

• Eyes become more sensitive to light in low illumination, known as dark adaptation
• Dark adaptation completes in 30 minutes, but major progress occurs in the first 10
• Eyes become less sensitive to light in high illumination, termed light adaptation

Visual Information Processing

• Light striking photoreceptors triggers neural impulses, which are then sent to the optic nerve
• Bipolar cells process photoreceptor information, relaying it to ganglion cells
• Ganglion cells consolidate this information into a singular firing rate, which relays to the optic nerve
• Horizontal cells connect receptors
• Amacrine cells facilitates communication between bipolar and ganglion cells

Understanding Receptive Fields

• A receptive field, located on the retina, is the area that affects a particular cell's firing when stimulated
• Receptive fields come in varying shapes and sizes

Lateral Antagonism

• Neural activity in a cell exerts an opposing force on activity in surrounding cells, creating contrast

The Visual Cortex

• After the retina transduces the visual signal, it is sent to multiple higher level processing areas in the brains

Neural Signals

• The light signal is transformed by rods and cones, travels to neural signals, bypass bipolar cells then ganglion cells, the signal is then relayed to the optic nerve, then to the optic chiasm to the opposite half of the brain

Main Pathway

• The pathway travels to the lateral geniculate nucleus (thalamus), and then on to the primary visual cortex (occipital lobe)

Visual Channels

• Magnocellular channels specializes in processing where the object is
• Parvocellular channels processes what the object is

Secondary Pathwys

• The signal is sent to the superior colliculus, the thalamus and then the primary visual cortex

Hubel & Wiesel: Feature Detectors

• Feature detectors discoveries were made in the early 1960s
• Microelectrode recordings of axons in the primary visual cortex of animals were used
• Specific neurons selectively respond to lines, edges, etc

Simple Cells

• Strongly respond to bars of light in the preferred orientation

Complex Cells

• Respond effectively to moving bars of light with the preferred orientation

Hypercomplex Cells

• Optimal response is to moving bars of light containing precise properties/length/angle

Basics of Color Vision: Wavelength and More

• Wavelength measures the perceived color
• Intensity or Amplitude impacts brightness
• Longer wavelengths will produce red whereas shorter ones will be violet
• Brightness is the perceived color
• There is a quantifiable experience with the color which relies on the light stimulus
• The saturation is purity and vividness of color sensations to the human eye
• Brightness is simply how intense the light is
• Psychological sensation is key when deriving the visual perception of light
• Color itself is not an external property

Color Mixing

• Subtractive color mixing involves removing wavelengths of light
• Additive color mixing involves the superimposing of lights to add more light to the mixture

Theories of Color Vision

• Trichromatic theory, by Young and Helmsholtz, proposes how receptors for red, green, and blue can create any color
• Hering proposed an opponent process theory which states color vision arises from 3 systems (Red/green, blue/yellow, black/white)
• Current perspective is that both those theories are necessary
• Visual sensations that linger after the stimulus is removed are called afterimages
• The lingering color is linked to the compliment image of what was originally started at

Color Blindness

• Color blindness describes the inability to distinguish between colors
• Color blindness afflicts more males than females
• Red and green distinctions are the most common form of colorblindness

Perceiving Form Pattern

• Reversible figures elicit two shifting interpretations
• Motivation forces drive what is known as perceptual sets
• Inattentional blindness causes failures to see objects because attention is not focused elsewhere, it is not a lack of vision
• Feature detection has a bottom up process
• Form perception has a top down processing system

Feature Analysis in Form Perception

• Subjective contours describe how contours can be percieved when none exist
• Gestalt Psychologists describe the whole being more than the sum of the parts
• Reversible figures and perceptual sets can help test the concept that perception is easily influenced by a singular visual stimulus

Principles of Perception

• We separate objects or figures to distinguish them from their background environment/ground

Proximity

• Objects are grouped in relation to how close they are to each other
• Example dots placed nearer to each other are easily percieved as a cluster

Similarity

• Similar looking items are grouped together

Continuity

• Visuals with smoother or continuous patterns are better than those that are disjointed
• Example seeing a line cross through a curve, they are easily percieved as two continuous lines rather than disjointed ones

Closure

• The brain easily fills in gaps to form a complete image, visual or otherwise
• A good test is drawing a broken circle, it can be interpretted that it is still a full circle

Simplicity (Pragnanz)

• Complex images can be simplified to the simplest way possible
• For example the Olympic logo is a simple arrangement of overlapping circles not necessarily a complex form on it's own

Recent Research

• Distal stimuli exist outside the body whereas proximal ones exist on the sensory regions themselves

Perceptual Hypotheses

• Rely very heavily on context

Depth & distance

• Binocular cues rely on each eye for accuracy

Retinal Disparity

• Both eyes will see a slightly different image which will be compared by the brain
• This helps gauge the depth to create a better percieved image

Convergence

• The closer an object, the more convergence and inward movement that is required to focus on the object

Monocular Cues

• Depth relies on certain single eyes

Motion Parallax

• Objects closer are faster than those further away
• Example trees closer are fast, the mountains further are slower

Accommodation

• Adjustments from the lens, help perceive objects at distance; this helps indicate depth

Pictorial Depth Cues

• Help create a sense of depth from 2D images
• Lines tend to converge in images to describe distance
• Large objects in comparison to smaller ones help describe relative size and indicate distance
• Closer objects block out further objects, creating overlap
• Higher concentrations of detail are more visible than distant ones which are more blended
• Lower objects appear closer than those further away from the eye

Light and Shadow

• Give more depth to flat images, creating the illusion of 3D shapes and properties

Constancies of Perceptual World

• Stable percieved stimulis help amid changes with the following, the brain normalizes:
  • size
  • shape
  • brightness
  • hue
  • location in space

Optical Illusions

• Optical illusions hinge on discrepancies with physical apperance and real state
• These illusions also relate to cultural differences with perceptual hypotheses at work

Ames Room

• There are distorted rooms to test or create a specific illusion of people growing or shrinking

Muller-Lyer Illusion

• How two lines seem shorter or longer based on the arrow types at the end of the lines

Ponzo Illusion

• There are unequal lengths with horizontal lines because of converging segments to make the brain believe depth is there

Poggendorff Illusion

• How a diagonal line looks misaligned near a shape but it is continuous, causing the brain to percieve false alignments

Zollner Illusion

• Parallel lines appear to divergent because diagonal lines cross each segment

Impossible Figures

• How drawings can represent 3D objects but also defy the physics or perception of existing normally

The Auditory System

• Evolved to detect and make sense of relevant information from our environment

Detection

• Not all sensory information is detected
• We also miss lots of information

A Focus

• Information we focus on tends to be relevant

Audition

• refers to hearing as a sense and process

Waves

• Sound is heard through periodic compressions of water, air, etc

Physics

• Amplitude hinges on the height and subsequent intensity and strength of each particular sound wave
• Loudness comes from that perceived amplitude
• Frequency comes from the compressions per second which is measured as the hertz
• In comparison to wave physics, pitch relates to how sound can travel high or low

The Ear: Anatomy

• Three main types: inner, middle and outer

Outer Ear

• It contains the pinna and contributes the following:
  • aiding in receiving sounds
  • locating the source of it

Middle Ear

• It contains the tympanic membrane which vibrates per the sound waves received

Inner Ear

• It contains the cholea, the snailshell shaped structure, composed of scala and fluid

Receptor

• Receptors here excite auditory hair cells from auditory signals during their displacement

Perception of pitch

• Various theories seek to explain pitch

Frequency Theory

• Axons will create action potentials related with the source basilar rate

Place Theory

• Specific segment or side will be tuned for sound waves

Current Theory

• Combination of the former two theories

Volley Principle

• Axons are capable of doing even more action due to their organization
• A singular axon needs to justify its own rate or frequency

Destination

• Auditory signals are ultimately sent on to the auditory cortex

Function of Auditory Cortex

• Opposites send their signals

Temporal Areas

• Help identify the source of auditory input

Necessary

• Experience is key for a competent auditory cortex

Effects

• Deaf births prevent the growth with auditory axons

Hearing: Function

• An organ is vital for its processing power

Problems and Damage

• Damage must exist in the A1 area as well to cause any sort of real damage

Map

• cells in primary are more active with selected sounds

Some cells

• respond to complex or pure tones

Existent Areas

• Responds or is changed for sound levels

Cells Respond

• animal noises or crying, music, objects

###Initial

• Slow response occurs due to meanings, so the initial response dictates most

Response

• most are still able to hear loud or general noises properly

Impairments

• Issues that can relate to hearing from impairments

Middle Ear

• Conductive bones here fail for signals due to middle ear problems/bones
  • tumor or disease can cause it
  • can be remedied
  • often can vocalize or hear themselves

Nerve Damage

• From hair or auditory nerve
  • can only relate to a certain signal area and often certain noise
  • issues can stem from birth or loud traumatic incidents etc

Ears Ring

• Frequent and non stop, common issues
  • can show up from damaged Cochlea

localization

Humans have an easier time with intensity or frequency differences.

Sound intensity

Easier seen through better sound shadow with high values, as the closer ear should percieve more.

Differences

• Easy seen due to time as both ears measure different arrival time

Localization Phase

• Phases differ for sound sources

Mechanical Senses

• Vibration in the somatosensory system through:
  • pain
  • touch
  • body

Sensors

• Respond to distortion, bending or pressure

Vestibular Sense

Aids in head compensation and directs various functions

• Is near the angular and cochlear joint

Various

• There are specific circular segments to aid with movement in various segments to allow movement
• With fluid and various sensors which assist the process
• Angular gyrus aides communication and connections with multiple sensation centers

Somatosensory system

Aides with body awareness, sense and feeling

• Is discriminate, allows the feeling of pressure along the body for pain and comfort
• Sensors for pressure, touch and position

Skin, Skin, Skin

• They bend membrane using Pacinian sensors, an assistance
  • the CNS, spinal system and overall brain are key

Spinals

Each contains a motor and sensory region

• They have their own region connected via a spinal nerve
• touch and pain are distinct

CNS

• Key portions remain distinct

Impulses

• Thalamus assists impulses that reach the parietal lobe located cortex

Cortex Regions

• Areas respond and damage also depends on which place it's located to what impairment occurs

Pain

• Brain areas, axons and NT are associated with pain including glutamate and substance P
• Relief can be found with opiates preventing the NT

Mechanisms

• Systems exist that deal with similar substances and opioid medicines, blocking Substance P

Synapses

• Genetics explain why sensitivity or lack of pain occurs
• Gate theory aims to help block input too, skin or descension

Gray matters

• Specialized areas such as Periaqueductal grey exist for these regions. Heat or acid receptors are associated

Pain Relief

• Many systems such as hypo,amy or cin come to block it, also with endorphins

Placebo

• It has no pharmacological effect but can impact mental and emotional feeling

Sensitivities

• Some reactions come to raise sensitivity which can relate to
  • high magnitude of sodium gateways per inflammed tissue

Potentiated Receptors

• Cause higher pain if long standing irritation due to chronic irritation

Control with brains

• Brain bombardment or pain itself can increase pain's awareness

Chemical

• Morphine controls slow and certain dull pains

Sharp pain

• Myelinated and unaffected

• inflammation

• Some drugs relieve this

Itch produced by Histamines

• Pathway activated by release of histamine itself, brain to signal and tell about itch
• Pathway also runs slow
• Pain and itch have inhibitors for each other

Sensory

Two type: Line or Across Fiber

Line

• One type of stimuli with line to brain

Across

More stimuli and more contribution together via multiple signals

All systems

• no pure type of function

Information

• Information together through combined responses work better Taste
• Taste itself stimulates a number of factors

The Flavor

is combination of smells

Receptors

modified skin or excited membrane, changed per time

Papillae

Contain structure and range to aid taste

TimeFrames

Are needed for tasting ability as it degrades

Adaption Process

It alters receptors but is needed to identify flavors

Stimulative process

• reduced once exhausted

Taste

sweet sour salty can help provide primary distinction

Mechansims

Potassium closes acids and polarization per sour type chemicals

Action

The processes activates a G protein releases

Receptor

There are types to see cell activity

Taste

• Cell activity and rhythm are essential to see this, which will translate per what is tasted
• We are selective per what we target as a result of our genetics

Convergence

• System then comes to the receptors
• They then help best translate to whatever they are translating as well
• Also relate to area for taste or feel