Sensation and Perception Exam 3 (Touch, Taste, Vision, Vestibular)

Kinesthesis, Proprioception, and Somatosensation

• Kinesthesis - perception of position and movement of our limbs in space (direction)

• Proprioception - perception mediated by kinesthetic and vestibular receptors

• Somatosensation - collective term for sensory signals from the body

Touch Mechanoreceptors

• specialized structures that respond to mechanical stimulation

• typically embedded on outer layer (epidermis) and underlying layer (dermis)

• many types of touch receptors for different stimulation: vibration, deflection, fast/slow

• Information from mechanoreceptors is transmitted to the brain via A-beta fibers

  • they signal “hey I got touched”

Kinesthetic Receptors and Muscle Spindles

• Kinesthetic Receptors - sense of where limbs are and what kinds of movements are made

  • Ian Waterman - nerves connecting receptors to brain were destroyed, lacked kinesthetic senses had to relearn how to move

• Muscle Spindle - located in muscle and senses tension

  • receptors in tendons → tension in muscles attached to tendons

  • receptors in joints → react when joint is bent to extreme angle

Thermoreceptors

• signal information about changes in skin temperature

• warmth fibers and cold fibers

• body is constantly regulating internal temperature and respond when you make contact with objects warmer/cooler than your skin

Nociceptors + Pain

• transmit information about noxious stimulation that could cause damage to the skin

• transduce impending or ongoing damage to body’s tissue into a specialized neural signal = pain

• Split into 2 groups

  • A-delta fibers - mid-sized, myelinated sensory nerve fibers that transmit pain and temperature signals

  • C fibers - narrow, unmyelinated sensory nerve fibers that transmit pain and temperature signals

• You need to be able to sense pain → Miss C!

How do touch sensations travel?

• passes through spinal cord first then

• Spinothalamic Pathway - carries most information about skin temperature and pain (slower)

• Dorsal column-medial lemniscal (DCML) pathway - carries signals from skin, muscles, tendons, and joints

• In the brain signals arrive at the ventral posterior nucleus of the thalamus (VPN) and then routed to primary somatosensory cortex (S1)

How are touch sensations mapped onto the brain?

• somatotopical representation - adjacent areas on skin connect to adjacent areas in brain

  • similar to retinotopy found in vision!

• Homunculus - a map-like representation of regions of the body in the brain

Phantom Limb

• sensation perceived from a physically amputated limb of the body

• parts of brain listening to missing limbs not fully aware of altered connections

Analgesia and Endogenous Opiates

• Analgesia - decreasing pain sensation during conscious experience (tylenol/advil)

  • body systems actively modulate pain perceptions and shut down pain in emergencies

• Endogenous Opiates - chemicals released in body to block release or uptake of neurotransmitters that transmit pain

  • natural analgesia mechanism

  • externally produced substances like morphine, heroin, and codeine have similar effects

Gate Control Theory

• system that transmits pain that incorporated modulating signals from the brain

• Feedback circuit located in the substantia gelatinosa of dorsal horn of spinal cord

• gate neurons block pain transmission → activated by extreme pressure, cold, or other stimulation

• Rubbing/Holding a body part can activate gate neurons and help relieve pain

Cognitive Aspects of Pain

• experience of pain includes nocieceptive sensation and emotional response

• Cognitive and emotional aspects of pain are experienced in

  • Anterior Cingulate - perceived unpleasantness

  • Prefrontal Cortex - cognition and executive control

Pain Sensitization

• Nociceptors provide signal to damage to body tissue

• once damage occurs site can become more sensitive → Hyperalgesia

• pain as a result of damage to nervous system → Neuropathic

• no 1 pain medicine can alleviate all types of pain

Touch and Spatial Details

• Two-Point Threshold - minimum distance which 2 stimuli are just perceptible as separate

• varies across the body but is most accurate on fingertips, face, and toes

• Fork prong demonstration

• Smallest raised element that can be felt - 1 micrometer high = 75% accurate

Tactile Sensitivity and Acuity

• Touch - differences sensed at 5ms

• Vision - differences of 25ms

• Audition - differences sensed at 0.01 ms

Haptic Perception

• Knowledge of the world from sensory receptors in skin, muscles, tendons, joints (pressing snooze even when tired)

• Geometric properties of objects are most important for visual recognition

• Perception for action - less grip strength is needed after a while of holding

• Acting for perception - metal bat will feel cold

  • Exploratory Procedure - stereotyped hand movement pattern used to contact objects to perceive their properties

Taste vs Flavor

• Taste - sensations specifically from taste buds

• Flavor - multimodal sensation associated with food or drink in the mouth

  • retronasal smell, somatosensation, trigeminal stimulation (spicy), astringency (pucker)

Taste Buds

• bumps on your tongue → papillae

• Filiform Papillae - most bumps on your tongue, have nothing to do with taste

• CONTAIN TASTE BUDS

  • Fungiform Papillae - bumps on edges of your tongue

  • Circumvallate Papillae - V of circles in the back

  • Foliate Papillae - folds on the back edges of your tongue

Taste Buds Structure + Function

• Each taste bud is a collection of taste receptor cells that make a neural response to tastants

• Taste receptor cells extend microvilli into buds taste pore and contain taste receptors that the tastants bind to evoking a neural signal

• Taste receptors determine what compounds each taste receptor cell responds to

• papillae → taste bud → microvilli → taste receptor

Tastants

• any stimulus that can be tasted

• divided into 2 large categories

  • small charged particles that taste salty or sour: small ion channels in microvilli allow some types of charged particles to enter and not others

  • others are perceived via G protein-coupled receptors and taste sweet or bitter

Taste Receptors

• determine what compounds each receptor cell responds to

• salty receptors - ion channels that sodium can pass through depolarizing the cell and causing action potentials → salty

• sour receptors - ion channels that let hydrogen ions pass, depolarizing the cell and causing action potentials → higher levels of acids so = sour

• sweet and bitter receptors - special variety of G-protein coupled receptors that bind molecules with specific molecular shapes and release G-protein + action potentials

Umami

• 5th basic taste - essentially taste of protein

• comes from receptors that detect monosodium glutamate (MSG)

  • almost nobody actually has a bad reaction to eating MSG

• Umami receptors are found in the gut, suggesting the taste isn’t about tasting but knowing the nutrients

Taste Processing in the Central Nervous System

• Pathway: taste buds → cranial nerves → medulla and gustatory thalamus → cortex

• Insular Cortex - primary cortical processing area for taste, first receives taste information and gets olfactory information

• Orbitofrontal Cortex - part of frontal lobe that lies above the bone containing the eyes

  • Receives projections from insular cortex

  • processes temperature, touch, smell, taste = integration area

Light + Vision

Light - wave, stream of photons, tiny particles that each consist of one quantum energy

• Light can be absorbed (taken up/not transmitted), scattered (dispersed in an irregular fashion), reflected (redirected usually back to original point), transmitted (passed on through a surface), refracted (altered as it passes to another medium)

Human Eye

• Cornea - transparent window into the eyeball

• Aqueous Humor - watery fluid in anterior chamber

• Crystalline lens - lens inside eye allows changing focus

• Pupil - dark circular opening in the iris where light enters the eye

• Vitreous Humor - transparent fluid that fills vitreous champer in the posterior of the eye

• Retina - light sensitive membrane in back of the eye and contains rods+cones, send info to brain through the optic nerve

Accomodation

• the lens in the eye refracts light to focus the image on the retina

• Accommodation - process where lens changes shape altering refractive power and focusing on different focal planes in the world

• Using ophthalmoscope doctors can view back of patients eye → fundus

Eye Problems

• Presbyopia - unable to accommodate lens sufficiently to focus on nearby objects, caused by sclerosis (hardening of lens) and loss of elasticity

• Cataracts - opacities in the lens that develop through age/illness

• Emmetropia - no refractive error, image is properly focused on the retina

• Problems with Refraction

  • Myopia - light entering eye is focused in front of retina and distant objects can’t be seen sharply (nearsighted)

  • Hyperopia - light entering the eye is focused behind the retina (farsighted)

  • Astigmatism - unequal curving of one or more refractive surfaces of the eye, usually cornea

Blind Spot + Depth Cues

• Blind Spot - optic disc = place where the nerve leaves the eye

  • your brain fills in the space you can’t actually see so you don’t perceive a gap in your vision

• Pictoral Depth Cues - cue to distance/depth used by artists to depict 3D depth in 2D pictures

• Anamorphosis - use of rules of linear perspective to create a 2D image so distorted it looks correct when viewed from a specific angle or mirror

Photoreceptors

• Photoreceptors - cells in the retina that initially transduce light energy into neural energy

  • Rods - photoreceptors specialized for night vision

    • respond well in low light, no color processing, gather light over large areas

  • Cones - photoreceptors that are specialized for daylight vision and fine visual acuity and color

    • respond best with lots of light, gather light over small areas

  • very poor color vision and spatial resolution in your periphery

Visual Transduction

• Light activates rhodopsin molecules

• Each rhodopsin molecule activates hundreds of transducin molecules

• Each transducin molecule activates hundreds of phosphodiesterase molecules

• Each phosphodiesterase hydrolyzes (inactivates) hundreds of cGMP molecules

• drop in cGMP causes hyperpolarization of photoreceptor

• hyperpolarization reduces transmitter release → neural signal

• light → rhodopsin → transducin → phosphodiestrase → cGMP → hyperpolarization of photoreceptors → neural signal

Photoreceptor Dark Current

• when there is no light cells are constantly depolarized by Na+ and Ca2+ currents in the outer segment

• constantly releasing neurotransmitter glutamate

• Light causes reduction in dark current → decrease in transmitter release

• decrease in neural signals = light on that spot of the retina

Specialization and Parallel Processing

• retinal signals are distributed to many parts of the circuit which all analyze it at the same time → Parallel Processing

• Each part of the circuit is specialized to certain kinds of processing

  • detection of motion, faces, color, absence of light, fine spatial detail

• Path of image processing

  • Eye → photoreceptors, bipolar cells, retinal ganglion cells

  • Lateral geniculate nucleus in the thalamus

  • Primary visual cortex

Receptive Fields

• Receptive Field - region in space which stimuli activate neurons

  • critical conept across all sensory systems!

• Photoreceptors have simple, round receptive fields

  • circular area in space where light will cause them to respond (reduce neurotransmitter release)

  • this sets the limit on how small of a stimulus we can discriminate

  • Ex. stripes or grey block? (both light and dark parts fall into receptive field of cone)

    • size of photoreceptor = limit to what you can see

Retinal Ganglion Cells

• Retinal Ganglion Cells → Center Surround Receptive Field

  • ON-center ganglion cells - excited by light falling on the center and inhibited by light falling in the surround

  • OFF-center ganglion cells - inhibited by light falling on the center and excited by light falling on the surround

    

• Center-surround receptive fields are tuned to respond to sine wave patterns with specific frequencies → specific spatial frequency + phase + place in visual world

Primary Visual/Striate Cortex

• gets input from lateral geniculate nucleus carrying basic info from the eyes

• cells here respond best to bars of light/dark rather than spots

• Topographical Mapping - points in physical space are represented in similar points in the brain (picture mapped onto brain)

• Cortical Magnification - dramatic scaling of information from different parts of visual field

  • amount of cortex devoted to processing the fovea is much more than that devoted to processing periphery

• Orientation Tuning - neurons respond more to bars of certain orientations, response rate falls off with angular difference of bars

Hubel and Wiesel

• cortical neuron responds to oriented bars of light might receive input from several retinal ganglion cells

• string several retinal ganglion cells together → oriented bar

• Cell that is tuned to any orientation you want could be created in cortex by connecting it up with the appropriate retinal ganglion cells

Object Recognition

• Mid-Level Vision - process which edges are identified and linked together to form discrete objects

  • figure-ground assignment - brain decides what is background vs object

  • strongly influenced by expectations about the world

    • brain rejects accidental viewpoints → combinations of visual inputs that are very unlikely

• Object Recognition - process which brain connects visual stimuli with understanding of how objects work

  • naive template matching → doesnt work because same object can look varyingly different (cowiest cow)

Depth Perception

• based on our prior understanding of the world → ex overlapping pennies = 2 pennies

• visual systems use depth cues when interpreting size of objects → most likely explanation based on prior information

  

Calculating Depth Perception

• Binocular Disparity - differences between the two retinal images of the same scene

  • Ex. finger in front different eye different position

• Stereopsis - perception of 3 dimensionality of the world based on binocular disparity (not available with monocular vision)

  • Ex. putting on pen cap with one eye closed

• Motion Parallax - images closer to observer seem to move faster than images farther away → brain uses this information to calculate distances of objects

Color Vision + Problem of Univariance

• Problem of Univariance - infinite set of different wavelength intensity combinations can elicit exact same response from photoreceptor

  • 1 photoreceptor can’t make color discriminations based on wavelength → why you can’t see color with just rods

• Cone photoreceptors come in 3 varieties

  • S-cones - preferentially sensitive to short wavelengths (blue)

  • M-cones - preferentially sensitive to middle wavelengths (green)

  • L-cones - preferentially sensitive to long wavelengths (red)

• Metamers show color is not a physical property but psychophysical instead

Trichromacy + Metamers

• Trichromacy - color of any light is defined in our visual system by relationships of 3 numbers, outputs of 3 recepter types/cones

• Metamers - different mixtures of wavelengths that look identical, any pair of stimuli perceived as identical in spit of physical differences

  • show color is a mental construct not just wavelengths

Middle Vision (Gestalt)

• Gestalt Grouping Rules - describe when elements in an image will appear to group together

  • Similarity + Proximity

• Good Continuation - 2 elements group together if they lie on the same contour

• Texture Segmentation - carving image into regions of common texture properties

  • Parallelism + Symmetry

  • Common Region + Connectedness

Color Perception

• the 7 colors of the rainbow are stupid and made up… what even is indigo