Midterm 1 Flashcards
What is sensation?
Initial steps in the perceptual process, where physical features of the environment are converted into electrochemical signals that are sent to the brain for processing
What are senses?
Physiological functions for converting particular environmental features into electrochemical signals
What is perception?
Later steps in the perceptual process, knowing what the senses are and recording them to memory
What are representations?
Information in the mind and brain used to identify objects and events (recognize)
What is stimuli?
Objects and events that are perceived and the physical phenomena they produce
What are distal stimuli?
Perceived object or event in the world (hearing a voice)
What are proximal stimuli?
Physical phenomenon evoked by a distal stimulus (sound waves, air)
What is the process of perception?
- Distal stimuli (your phone)
- Proximal stimuli (light, sound)
- Proximal stimuli converted into neural signals that are sent to the brain
- Signal processing in the brain
- Conscious awareness
What is psychophysics?
The systematic study of sensory capacities, by varying the physical characteristics of a stimulus (contrast of an image, dimmest light, quietest sound)
What are absolute thresholds?
Minimum adjustment or change in a stimuli that can be perceived (whether or not you perceive it)
What is the method of adjustment?
The participant observes a stimulus and adjusts a knob that directly controls the intensity of the stimulus
What is the method of constant stimuli?
The participant is presented with a fixed set of stimuli covering a range of intensities that are presented repeatedly in random order, and the participant must indicate whether or not each stimulus was detected (lots of time, more mathematically and scientifically accurate)
What is the staircase method?
The participant is presented with a stimulus and indicates whether it was detected, and based on that information, wether it was one step up or one step down in intensity
Where is the absolute threshold in the method of constant stimuli?
The point where they say “yes” 50% of the time
What is the absolute threshold for the staircase method?
The average intensity of all reversals (trials)
What are difference thresholds?
Just noticeable difference or the minimum difference between 2 stimuli to allow you to perceive that the 2 stimuli are different
How do you determine just noticeable different with the method of constant stimuli using curves?
Sharp curve means you notice the difference quickly (smaller JND)
Shallow curve means it’s hard to notice the difference (larger JND)
What is Weber’s law?
The relationship between the intensity of the standard stimuli and the JND is linear
What do the values of Weber’s fraction tell us?
Lower fraction = sharp curve = easy to notice differences
Higher fraction = shallow curve = harder to notice differences
What is psychophysical scaling?
Non linear relationship between actual intensity and perceived intensity of a stimulus
What is Fechner’s Law?
There is a logarithmic relationship between physical intensity of a stimulus and perceived intensity of a stimulus (increase in physical intensity needed to produce a difference is larger for high-intensity stimuli than low-intensity stimuli)
What is Steven’s power equation?
The relationship between perceived intensity and physical intensity is different for different perceptual dimensions
What are neurons made up of from top to bottom?
- Dendrites
- Nucleus
- Cell Body
- Axon
- Axon terminals
What are dendrites?
Receive input/signals from other neurons
What is a cell membrane?
Outer structure of the cell made of a lipid bilayer (separates what’s inside the cell from what’s outside)
What is an axon?
Projection that emanates from the cell body of a neuron and that conducts neural signals to the axon
What are action potentials?
Basic unit of informational protection, message that’s being sent within a neuron
What is the cerebral cortex?
Outermost layer of the cerebral hemispheres
How do action potentials occur?
When a neuron receives a signal from another neuron, the receiving neuron undergoes an abrupt change in membrane potential, which causes voltage-gated sodium channels to open
This allows extracellular sodium ions to flow into the axon
What is gray matter?
Cell bodies of neurons making up the cerebral cortex
What is white matter?
Where axons lie
What is the thalamus?
Takes in information and sends it to the right places, all sensory information goes into thalamus first (most important subcortical structure)
What is modularity?
Idea that the human mind and brain consist of a set of distinct modules, each of which carries out one or more specific functions
What is functional modularity?
Brain region that does something (not where they are but what they do, Broca’s area)
What is anatomical modularity?
Certain brain areas have a cognitive function
What is light?
Visual illumination; corresponding to a small slice of wavelengths in the middle of the electromagnetic spectrum
What is the electromagnetic spectrum?
Entire range of wavelengths of electromagnetic radiation
What is electromagnetic radiation?
Particle (photon) or a wave
What is a wavelength?
Distance between two successive peaks of a wave; different types of electromagnetic radiation are defined by their differences in wavelength
What are photons?
Single particles of light; smallest possible quantity of electromagnetic radiation
What do lower wavelengths have?
Higher frequency (purple)
What do higher wavelengths have?
Lower frequency (red)
What is an optic array?
The structured pattern of light that reaches the observer; changes over time
Where are eyes in humans and what does that mean?
Front of head; narrow field of view; high-resolution depth perception
Where are predators’ eyes and what does that mean?
Placed frontally; narrow field of view; good depth perception
Where are preys’ eyes and what does that mean?
Place laterally; better ability to see predators; wider field of view; worse depth perception
They eye is encased in what 3 layers of membrane?
Sclera, Choroid, Retina
What is the sclera?
Outer membrane of the eye; tough protective covering; white of the eye and transparent cornea at the front of the eye
What is the choroid?
Middle membrane of the eye; contains most of the blood vessels
What is the retina?
Inner membrane (very back) of the eye; made up of neurons, including the photoreceptors that convert the light entering the eye into neural signals
What muscles move the eye up and down?
Superior and Inferior rectus
What muscles move the eye from side to side?
Medial and lateral rectus
What muscles rotate the eye?
Superior and inferior oblique
What is the optic axis?
Diameter from center of lens to back of the eye and meets at fovea
What is the cornea?
Transparent membrane at the front of the eye; light enters the eye by first passing through the cornea, which sharply refracts the light
What is the iris?
Muscle in the eye, pulls on pupil to allow more or less light in; colored part of the eye
What is the pupil?
Opening in the middle of the iris, through which light enters the eye
What is the pupillary reflex?
Automatic process by which the iris contracts and relaxes to control the size of the pupil in response to the relative brightness of light entering the eye
What is the aqueous humor?
Clear, thin fluid filling the anterior and posterior chambers of the eye
What is the vitreous chamber?
The main interior portion of the eye, filled with vitreous humor
What is vitreous humor?
Thick gel-like, hard
What is intraocular pressure?
Pressure of the fluids in the 3 chambers of the eye (too much causes glycoma)
What are the 3 chambers in the eye?
Anterior, posterior, and vitreous chambers
What is the anterior chamber?
Between cornea and iris; filled with aqueous humor
What is the posterior chamber?
Smaller space between iris and lens; filled with aqueous humor
What are zonule fibers?
Fibers that connect the lens to the choroid
What are ciliary muscles?
Tiny muscles attached to the choroid; control lens to control focus of the eye
What is the lens?
Allows rays of light to be focused (bend/refracted towards a certain focal point)
What does a weak lens do?
Bends light toward farther focal point; small angle of refraction
What does a strong lens do?
Bends light toward closer focal point; large angle of refraction
What is focal length?
Distance from a lens to the focal point
What are diopters?
Units used to express the power of a lens
What does a thinner lens do?
Flat; ciliary muscle relaxed; focus on distant object; long focal length
What does a thicker lens do?
Ciliary muscle contracted; focus on closer object; shorter focal length
What is accommodation?
Human eye adjusts the shape of the lens to change its focal length
What is retinal image?
Image that retina sees; is flipped, lens flips object
How is object flipped in retina?
Light from top of object is refracted to bottom of retina and vice versa
What is the optic disk (or blind spot)?
Location on retina where the axons of RGCs exit the eye; contains no photoreceptors
What is the optic nerve?
Nerve formed by the bundling together of the axons of RGCs; exits the eye into the brain
What is the fovea?
Region in the center of the retina; at the center of our gaze; contains no rods and a very high density of cones; has axons
What are the 3 main retinal layers?
Outer nuclear layer, inner nuclear layer, and ganglion cell layer
What are photorecpetors?
Retinal neurons (rods and cones) that transduce light into neural signal
What are rods?
Long shape; scotopic (night) vision
What are cones?
SML cones; photopic (day) vision
What cells are involved in the through pathway?
Cones, Bipolar cells and Retinal ganglion cells
What cells are involved in the lateral pathway?
Cones, Horizontal cells and Amacrine cells
What are SML cones?
Defined by wavelengths they absorb
What is photoisomerization?
Process of adapting to the light or to the dark
How are rods distributed?
Not in fovea, mostly in periphery (color is poor mainly made up in brain)
What happens in photoisomerization?
Begins in bent state (11-cis-retinal) then light is absorbed and goes into straight form (all-trans-retinal) then gets regenerated (your eyes adjust)
How are cones distributed?
Mainly in fovea or central vision; responsible for color vision
How long does light adaptation take?
Takes place in only a few minutes; whole process takes 10 minutes
How long does dark adaptation take?
Whole process takes up to 30 minutes
What are the RGCs firing rates for darkest vs brightest?
Lowest firing rate for whatever’s darkest
Highest firing rate for whatever’s brightest
What does the dark adaptation curve for rods only show?
Begins with poorest amount of vision; slower gradual adaptation
What does the dark adaptation curve for cones only show?
Adapts quickly then bottoms out; not as sensitive as rods
What does the dark adaptation curve for rods and cones combined show?
1st cones adapt, then rods which take longer
What colors are rods more sensitive to?
Blues and purples
What is convergence?
Property of retinal circuits in which multiple photoreceptors send signals to one RGC
What is spatial summation?
Consequence of convergence; firing rate of RGC increases as the number of photoreceptors that are activated by light increases
What does a higher degree of convergence mean?
Larger receptive field, high firing rate, lower visual acuity, more sensitive to light
What does a lower degree of convergence mean?
Low firing rate; better sense of shape (higher visual acuity)
What is a receptive field?
A region of retinal or visual space that a neuron responds to (when retina moves receptive field moves)
What are midget ganglion cells?
They are smaller cells with smaller receptive fields and less convergence
What are parasol ganglion cells?
They are larger cells with larger receptive fields and more convergence
What is a center-surround receptive field?
RGC receptive fields in which the center of the receptive field responds differently to stimulation than does the surrounding portion of the field
What are on-center receptive fields?
The RGCs increase their firing rate when the amount of light striking the center of the receptive field increases relative to the amount of light striking the surround
What is a preferred stimulus?
Type of stimulus that produces a neuron’s maximum firing rate
What is the process of lateral inhibition?
When bipolar cell receives input from the center and then gives input to RGC. Surround feeds into horizontal cells and they inhibit the signal
What is edge enhancement?
Process by which the visual system makes edges as visible as possible, facilitating perception of where one object or surface ends in the retinal image and another begins
What is Strabismus?
Disorder of the extraocular muscles in which the two eyes are not aligned with one another resulting in a double image and stereoblindness
What is steroblindness?
Impairment of binocular depth perception; don’t fuse images between the 2 eyes
What is Amblyopia?
Condition in which both eyes develop normally but the neural signals from one eye aren’t processed properly, so that fine vision does not develop in that eye
What is myopia or nearsightedness?
Eye/optic axis is longer which means light comes into focus in front or retina; person can see nearby objects but not distant ones
What is hyperopia or farsightedness?
Eye/optic axis is too short which means that light comes into focus behind the retina; person can see distant objects but not nearby ones
What is functional specialization?
Specialization of different neural pathways and different areas of the brain for representing different kinds of information
What is retinotopic mapping?
Arrangement of neurons in the visual system whereby signals from retinal ganglion cells with receptive fields that are next to each other on the retina travel to neurons that are next to each other in each visual area of the brain
What information is sent to the right hemisphere?
Information from the left half of the visual field; right temporal retina and the left nasal retina
What information is sent to the left hemisphere?
Information from the right half of the visual field; left temporal retina and right nasal retina
What information crosses over at the optic chiasm?
Left nasal retina and right nasal retina
What is the optic chiasm?
Location where the optic nerves from the 2 eyes split in half and cross over to the other hemisphere of the brain
What is the optic tract?
Continuation of the optic nerve past the optic chiasm
What is contralateral organization?
Opposite side organization; stimulation of neurons on one side of the body or sensory organ is represented by the activity in the opposite side of the brain
What is the lateral geniculate nucleus (LGN)?
Part of the thalamus (one in each hemisphere); receives visual signals via the axons of retinal ganglion cells (1st stop in receiving visual information)
What are magnocellular layers?
Layers 1 and 2 of LGN containing parasol RGCs (movement changes in light)
What are parvocellular layers?
Layers 3 to 6 of LGN containing midget RGCs (high acuity - shape, sharp edges, form, high spatial frequency)
What are koniocellular layers?
Located between magnocellular and parvocellular layers
Magnocellular layers best respond to information about…
Movement
Parvocellular layers best respond to information about…
Shape
What is the superior colliculus?
One in each hemisphere of the brain; helps control eye movements to visual stimuli
What is the Primary Visual Cortex (V1)?
First cortex area to receive visual information; high organized with columns for ocular dominance and orientation; has simple and complex cells
Cells in V1 are most effectively stimulated by…
bars or edges with narrow ranges of orientations
What is a simple cell?
Type of neuron in area V1 that responds best to a stimulus with a particular orientation in the location of its receptive field
What is preferred orientation?
Stimulus orientation that tends to produce the strongest response
What is an orientation tuning curve?
Curve on a graph that shows the average response of an orientation-tuned neuron (peak that they prefer the most, then drops off from there)
What is a population code?
Used to compute perceptual features such as the orientation of a visual stimulus; a consistent difference in the patterning of the relative responses of a population of differently tuned neurons
What are complex cells?
Don’t care where their preferred stimulus is, as long as it’s within their receptive fields
What do simple and complex cells have tuning for?
Luminance, color, orientation, spatial frequency, depth, motion
What is spatial frequency?
Blurry vs fine detail
What is layer 4?
Layer 4 of area V1 also called the Stria of Gennari; receives so much input from LGN that V1 is identifiable from a light microscope
What are cortical columns?
Consists of neurons that respond to similar types of stimuli and that have highly overlapping receptive fields
What ocular dominance columns?
Consist of neurons that receive signals from one eye only; preferences for left or right eye
What are orientation columns?
Cortical columns consisting of neurons with the same or very similar orientation tuning
What is retinotopic mapping?
Third type of organization in V1 involves receptive field locations of neurons at adjacent locations in the cortex
What is cortical magnification?
Nonuniform representation of visual space in the cortex; amount of cortical territory devoted to the central part of the visual field is much greater than the amount devoted to the periphery
What is the dorsal pathway from LGN to the brain’s visual areas?
Neurons in magnocellular layers of the LGN (receive parasol input from the retina) send signals to layer 4Ca of V1; from there, signals flow to the thick bands of V2 and then to MT (motion) and then to parietal cortex
What is the ventral pathway from LGN to the brain’s visual areas?
Neurons in the parvocellular layers of the LGN (get input from midget cells in the retina) send signals to layer 4Cb of V1; from there, signals flow to the blobs and the interblob regions of layers 2/3 of V1 and then to the thin and pale bands of V2 and to V4 and then to inferotemporal cortex
What is another name for the dorsal pathway?
Where pathway
What is another name for the ventral pathway?
What pathway
What is area V4 involved in?
Color perception and perceiving curvature of edges
What is area MT involved in?
Motion perception
What is the lateral occipital cortex and inferotemporal cortex involved in?
Object recognition
What did the landmark task tell us about the dorsal pathway?
Lesions in parietal cortex meant participants were unable to find where food was when it was closer to a landmark (but were able to complete what task)
What did the object task tell us about the ventral pathway?
Lesions in inferotemporal cortex meant participants were unable to find food under an object (object recognition) but could complete landmark task
What does the perceptual matching test tell us?
Lesions to inferotemporal cortex led patient unable to complete perceptual matching task, but where able to complete posting task
