Final Flashcards
Vision-energy type?
Electromagnetic
Vision
Electromagnetic Photons captured From extrastriate-->what/where pathways Cones. Rods. Photoreceptors. To measure optical power-diopter. Topographical mapping. Cortical rep of fovea greatly magnified compared to cortical rep of peripheral vision.
Audition
Mechanical forces
Energy-captured as air pressure.
Pathway for audition
Air pressure wave Pinnae Ear canal Tympanic membrane Ossicles Malleus Incus Stapes Oval window Vestibular Tectorial membrane Organ of corti Steric ilia Neurotransmitter- initiates action potentials in auditory nerve fibers that carried out to the brain
Decibel measures
Physical intensity of sound
Hertz
Frequency
Receptors in ears
Hair cells
Stereocilia
Ear organization
Tonotopic
Touch
Mechanical forces
Soma topically
Homonculus
Touch pathways
Skin and muscles-> spinal cord-
Spinothalamic
Temp pain
Dcml
Tactile
Smell is the only ________
Ipsilateral
Smell mapping
Topographical
Smell pathway
Odorants Receptor Olfactory cilia OSN Cribiform plate (olfactory bulb) Olfactory nerves Glomerulus Mitral Primary olfactory cortex/ other brain structures
Fourier analysis
Any complex sound can be broken down into individual sine wave components through this process.
taste
○ Type of energy: chemical diffusion
○ What form of energy captured: chemical senses
○ Sensory organ: tongue
○ Receptor: microvilli
○ Mapping:
○ Pathway: chewing breaks down food substances into molecules, dissolved in saliva → papillae which have taste buds embedded in them → Microvilli → cranial nerves → medulla → thalamus → insular cortex → orbitofrontal cortex
Vestibular (sense of balance)
○ Sensory organ: ear
■ 5 total: 3 semicircular and 2 otolith
Proprioception
(sense of limb positions)
○ Type of energy: mechanical forces
○ Sensory organ: muscles
Sound
■ different locations of cochlea for different frequencies
■ pressures relieved by round window
if I ask a ganglion cell, what do you know, what can you tell me about the visual word as opposed to a simple cell in v1,
all I know is if theres a spot of light in this one spot or not
● Index of Refraction
Indicates how much light ‘bends’ when it goes from one medium to another.
Responsible for image formation and rainbows
Cornea:
The front part of the eye; a transparent “window” into the eyeball
-● Presbiopia
“old sight”. Hardening of the crystalline lens. The lens becomes sclerotic (harder) and the capsule that encircles the lens (enabling it to change shape) loses its elasticity-
● Hyperopia:
When light entering the eye is focused behind the retina; farsightedness
● Myopia:
When light entering the eye is focused in front of the retina, and distant objects cannot be seen sharply; nearsightedness
diopter
unit of measurement of the optical power of a lens (or curved mirror). Reciprocal of focal length (in meters). D = 1/f(m)
Emmetropia:
No refractive error (no need for corrective eyewear)
Accommodation (change in focus):
The process in which the lens shape is changed, by the ciliary muscle, thus altering its refractive power
Retina:
A light-sensitive membrane in the back of the eye that contains rods and cones (and other neurons, supporting vessels, and structures), which receives an image from the lens and sends it to the brain through the optic nerve
● Aqueous Humor:
The watery fluid in the anterior chamber (between cornea and lens)
o Provides oxygen & nutrients; and,
o Removes waste from cornea & lens
● Crystalline Lens:
The lens inside the eye, which allows changing focus (Accommodation)
Pupil-
The circular opening (aperture) at the center of the iris in the eye, where light enters the eye
Iris:
The colored part of the eye, between the sclera (white part) and the pupil, consisting of a muscular diaphragm surrounding the pupil and regulating the light entering the eye by expanding and contracting the pupil
Vitreous Humor:
The transparent fluid that fills the large (vitreous) chamber in the posterior part of the eye (i.e., between the lens and the retina)
o Where floaters occur
● Astigmatism:
A visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye, usually the cornea (requiring cylinder correction)
● Photoreceptors:
Cells in the retina that initially transduce light energy into neural energy
● Rods:
●
● :
●
● Horizontal Cells: located between photoreceptors and bipolar cells. Perform lateral inhibition. Responsible for center-surround receptive fields.
● Bipolar Cells: bridge between photoreceptors and ganglion cells. Two types: midget, 1:1 cone : ganglion (giving low convergence); and diffuse: connected to several photoreceptors (giving high convergence)
Photoreceptors that are specialized for night vision
o Respond well in low luminance conditions
o Do not process color
cones
-Photoreceptors that are specialized for daylight vision, fine visual acuity, and color
o Respond best in high luminance conditions
Duplex Retina
retina with cones and rods for day and night vision
● Pigment Epithelium:
Provides nutrients to photoreceptors. Usually opaque, sometimes reflective.
● Photoreceptors:
Rods: dim light, larger, more numerous, more sensitive, not in fovea; & Cones: better acuity, daylight, mostly in fovea, few in periphery, usu. 3 types (S, M, & L)
Horizontal Cells:
located between photoreceptors and bipolar cells. Perform lateral inhibition. Responsible for center-surround receptive fields.
● Bipolar Cells:
bridge between photoreceptors and ganglion cells. Two types: midget, 1:1 cone : ganglion (giving low convergence); and diffuse: connected to several photoreceptors (giving high convergence)
● Amacrine Cells:
● Ganglion Cells: Connection between eye and brain. Recieves information from bipolar cells (and amacrine cells) and sends info via the optic nerve.
● Age-related Macular Degeneration (AMD): A disease associated with aging that affects the macula. AMD gradually destroys sharp central vision
● Macula: The central part of the retina containing the fovea
● Scotoma: AMD causes central vision loss, resulting in a blind spot in this visual field
● Wet AMD: Abnormal blood vessels grow under the macula and can leak blood and fluid, raising the macula and impairing central vision. As the macula is displaced, straight lines may look wavy
● Dry AMD: More common. Occurs when macula cones degenerate. Sometimes dry AMD turns into wet AMD. Once dry AMD is advanced, no treatment can reverse the loss of vision.
less well understood. Seem to integrate information from groups of bipolar cells and communicate to ganglion cells.
Rhodopsin
-protein in rods
OFF-center ganglion cells
Inhibited by light falling on center, excited by light falling on surround
ON-center ganglion cells
Excited by light falling on center, inhibited by light falling surround
Cataracts
-loss of transparency in lens (solved with silicone implants)
Retinitis pigmentosa (RP):
Family of hereditary diseases involving the progressive death of photoreceptors and degeneration of the pigment epithelium
Receptive Field:
The region on the retina in which stimuli influence a neuron’s firing rate
Magnocellular
pathway is involved in motion processing. Excellent temporal resolution but poor spatial resolution
● M ganglion cells: Connect to the magnocellular pathway
o Receive input from diffuse bipolar cells
● P ganglion cells:
Connect to the parvocellular pathway
o Receive input from midget bipolar cells
o Parvocellular (“small cell”) pathway is involved in fine visual acuity, color, and shape processing. Poor temporal resolution but good spatial resolution
Vertical Pathway:
Photoreceptors, bipolar cells, and ganglion cells
Midget bipolar cell:
A small bipolar cell that receives input from a single cone
Diffuse bipolar cell:
A bipolar cell that receives input from multiple photoreceptors
Bipolar cell:
A retinal cell that synapses with one or more rods or cones (not both) and with horizontal cells, and then passes the signals on to ganglion cells
Amacrine cells: cells
●
These cells synapse horizontally between bipolar cells and retinal ganglion
Horizontal Pathway:
Horizontal cells & amacrine cells
● Horizontal cells:
Specialized retinal cells that run perpendicular to the photoreceptors and make contact with photoreceptors and bipolar cells
o Responsible for lateral inhibition, which creates the center–surround receptive field structure of retinal ganglion cells
● Ganglion Cells:
Connection between eye and brain. Recieves information from bipolar cells (and amacrine cells) and sends info via the optic nerve.
Age-related Macular Degeneration (AMD):
A disease associated with aging that affects the macula. AMD gradually destroys sharp central vision
Macula
-The central part of the retina containing the fovea
Scotoma
-AMD causes central vision loss, resulting in a blind spot in this visual field
Wet AMD:
Abnormal blood vessels grow under the macula and can leak blood and fluid, raising the macula and impairing central vision. As the macula is displaced, straight lines may look wavy
Dry AMD:
More common. Occurs when macula cones degenerate. Sometimes dry AMD turns into wet AMD. Once dry AMD is advanced, no treatment can reverse the loss of vision.
● Acuity:
the smallest spatial detail that can be resolved
● Measuring visual acuity
○ eye doctors use distance (20/20)
■ Numerator: the distance at which you can just identify the letters
■ Denominator: the distance at which a person with “normal” vision can just identify letters
■ 20/20 isn’t perfect, but normal
■ 20/8 is the physiological limit of human vision
● based on cone density
■ 20/200 while wearing corrective lens is legally blind in the US
○ Vision scientists use the smallest visual angle of a cycle of a grating
○ Other countries use Landolt Rings
Spatial Frequency and Contrast
● Spatial Frequency: the number of cycles of a grating per unit of visual angle
○ usually specified in degrees
● Contrast: the difference in illumination between a figure and its background
● Oriented grating appears to be gray if you’re far enough away because:
○ this striped pattern is a “sine wave grating”
○ the visual system “samples” the grating discretely
Threshold and Sensitivity
○ the minimum change in a stimulus that enables it to be correctly judged as different
● Sensitivity: a value that defines the ease with which an observer can tell the difference between either:
○ the presence or absence of a stimulus
○ the difference between stimulus 1 and 2
● Just Noticeable Difference (JND): a difference threshold
○ the smallest detectable difference between two stimuli
● Thresholds________ are to sensitivity
inversely proportional
● Contrast Sensitivity Function (CSF):
a plot of the threshold contrast to detect the grating (as opposed to seeing a uniform gray) as a function of spatial frequency
○ developed by Otto Schade
○ inverse of Contrast Threshold
○ if CT = 0.01, then contrast sensitivity is 1/0.01 = 100
○ For photopic vision, the CSF peaks around 2 to 4 cycles per degree
○ note how sensitivity is reduced for mesopic or scotopic vision
○ Photopic: daylight vision
○ Mesopic: twilight vision
○ Scotopic: nighttime vision
○ Contrast sensitivity is quite poor at birth, improves gradually with development
○ Contrast sensitivity is reduced with aging, primarily for high spatial frequencies
● Cycles per Degree:
the number of dark and bright bars per degree of visual angle
● Contrast Threshold:
the minimum difference in contrast for you to detect a pattern
Retinal Ganglion Cell
● Retinal cells like spots of light
● Low frequency yields weak responses
● Medium frequency yields strong responses
● High frequency yields weak responses
● Spatial frequency is important, but so is the phase
○ Phase: the phase of a grating refers to its position within a receptive field
Lateral Geniculate Nucleus
●
Two Lateral Geniculate Nuclei (LGNs): axons of retinal ganglion cells synapse there ● Two types of layers in LGN ○ Magnocellular ■ M Ganglion cells (Parasol cells) ■ Fast, large moving objects ○ Parvocellular ■ P Ganglion cells (Midget cells) ■ Details of static objects
● RETINAL PROJECTION
● The world is divided at the LGN:
○ Left side of space goes right
○ Right side of space goes left
● Each layer: input from ONE eye
○ Each layer = organized map of half of the visual world
● This is TOPOGRAPHICAL MAPPING
● LGN is not only a “relay” between eyes and visual cortex, but it also receives info from a number of other brain areas, functioning as a gate to the cortex
● Ipsilateral: referring to the same side of the body (or brain)
● Contralateral: referring to the opposite side of the body (or brain)
Striate Cortex
● Also known as the Primary Visual Cortex, area 17, or V1
● Major transformation of visual info takes place in striate cortex
○ Topographical Mapping
■ the organization of sensory surface matches the organization of the sensory world
● Neighboring “stuff” in the visual field will be processed by neighboring cells
○ Cortical Magnification
■ the dramatic scaling of info from different parts of visual field
■ 1 degree of visual angle at fovea is processed by 15 times more neurons than 1 degree of visual angle just 10 degrees away from fovea.
● Visual acuity declines in an orderly fashion with______
eccentricity
Receptive Field
●
Selective Responsiveness: orientation tuning: tendency of neurons in striate cortex to respond optimally to certain orientations and less to others
● Many cortical cells respond especially well to:
○ moving lines
○ bars
○ edges
○ gratings
○ certain motion directions
● Simple Cells
○ responds primarily to oriented edges and grating
○ simple cells in the primary visual cortex can be formed by the linking of outputs from concentric lateral geniculate nucleus cells with adjacent receptive fields
● Complex Cell
○ responds primarily to oriented edges and gratings, however it has a degree of spatial invariance
○ respond to bar, regardless of exact positioning within RF
● Each LGN cell responds to one eye or the other, but never to both
● End Stopping:
process by which cells in the cortex first increase their firing rate as the bar length increases to fill up its receptive field, and then decrease their firing rate as the bar is lengthened further
● Column:
a vertical arrangement of neurons
Hypercolumn
-a 1 x 1 mm block of striate cortex containing “all the machinery necessary to look after everything the striate cortex is responsible for, in a certain small part of the visual world” ●
Method of Adaptation-
the diminishing response of a sense organ to a sustained stimulus
Selective Adaptation
●
Tilt Aftereffect: perceptual illusion of tilt, provided by adapting to a pattern of a given orientation
○ supports the idea that the human visual system contains individual neurons selective for different orientation
● Selective Adaptation: evidence that human visual system contains neurons selective for specific stimulus properties
○ if adaptation to a stimulus occurs, then it must be that a group of neurons was coding that stimulus and became fatigued
● Adaptation experiments provide strong evidence that orientation and spatial frequency are coded by neurons somewhere in the human visual system
○ Cats, Monkeys: striate cortex, not in retina or LGN
○ Humans operate the same way as cats and monkeys with respect to selective adaptation
Sine waves
● Many stimuli can be broken down into a series of sine wave components using Fourier analysis
○ any sound, including music and speech
○ any complex image, including photographs, movies, objects, and scenes
○ any movement, including head and limb movements
● Our brains seem to analyze stimuli in terms of their sine wave components
○ vision
○ audition
● Properties:
○ Period or Wavelength: the time or space required for one cycle of a repeating waveform
○ Phase:
■ In vision, the relative position of a grating
■ In hearing, the relative timing of a sine wave
Color Perception
○ Detection: wavelengths of light must be detected in the first place
○ Discrimination: we must be able to tell the difference between one wavelength (or mixture of wavelengths) and another
○ Appearance: we want to assign perceived colors to lights and surfaces in the world and have those perceived colors be stable over time, regardless of different lighting conditions
Color
not a physical property but rather a psychophysical property
○ Most of the light we see is reflected
○ Typical light sources: sun, light bulb
○ Color on the surface depends on the mix of wavelengths that reach the eye from that surface
○ In the electromagnetic spectrum, we perceive light of a wavelength of 700 nm as a red
Four Photoreceptors
■ S- cones, M- cones, L-cones, Rods
○ Photopic:
light intensities that are bright enough to stimulate the cone receptors and bright enough to “saturate” the rod receptors
■ sunlight and bright indoor lighting are both photopic lighting conditions
