Topic 2: Early Visual Processing Flashcards
Neuron
the structure that transmits electrical signals in the body
key components are the cell body, dendrites, and the axon or nerve fiber
Cell Body
the part of a neuron that contains the neuron’s metabolic machinery and that receives stimulation from other neurons
Dendrites
nerve processes on the cell body that receive stimulation from other neurons
Axon
the part of the neuron that conducts nerve impulses over distances
also called the nerve fiber
Nerve Fiber
in most sensory neurons, the long part of the neuron that transmits electrical impulses from one point to another
also called the axon
Resting Potential
the difference in change between the inside and the outside of the nerve fiber when the fiber is not conducting electrical signals
most nerve fibers have resting potentials of about -70 mV, which means the inside of the fiber is negative relative to the outside
Action Potential
rapid increase in positive change in a nerve fiber that travels down the fiber
also called the nerve impulse
Propagated Response
a response, such as a nerve impulse, that travels all the way down the nerve fiber without decreasing in amplitude
Refractory Period
the time period of about 1/1000th of a second that a nerve fiber needs to recover from conducting a nerve impulse
no new nerve impulses can be generated in the giber until the refractory period is over
Spontaneous Activity
nerve firing that occurs in the absence of environmental stimulation
Ions
charged molecules
sodium, potassium, and chlorine are the main ions found within nerve fivers and in the liquid that surrounds nerve fibers
Permeability
a property of a membrane that refers to the ability of molecules to pass through it
if permeability to a molecule is high, the molecule can easily pass through the membrane
Depolarization
when the inside of a neuron becomes more positive, as occurs during the initial phases of the action potential
depolarization is often associated with the action of excitatory neurotransmitters
Rising Phase of the Action Potential
in the axon, or nerve fiber, the decrease in negativity from -70 mV to 140 mV (the peak action level) that occurs during the action potential
this increase is caused by an inflow of Na+ ions into the axon
Hyperpolarization
when the inside of a neuron becomes more negative
is often associated with the action of inhibitory neurotransmitters
Falling Phase of the Action Potential
in the axon, or nerve fiber, the increase in negativity from 140 mV back to -70 mV (the resting potential level) that occurs during the action potential
this increase in negativity is associated with the flow of positively charged potassium ions out of the axon
Synapse
a small space between the end of one neuron (the presynaptic neuron) and the cell body of another neuron (the postsynaptic neuron)
Neurotransmitters
a chemical stored in synaptic vesicles that is released in response to a nerve impulse and has an excitatory or inhibitory effect on another neuron
Receptor Sites
small area on the postsynaptic neuron that is sensitive to specific neurontransmitter
Excitatory Response
the response of a nerve fiber in which the firing rate increases
Inhibitory Response
occurs when a neuron’s firing rate decreases due to inhibition from another neuron
Sensory Coding
how neurons represent various characteristics of the environment
Specificity Coding
type of neural code in which different perceptions are signaled by activity in specific neurons
Grandmother Cell
a highly specific type of neuron that fires in response to a specific stimulus, such as a person’s grandmother
Sparse Coding
the idea that a particular object is represented by the firing of a relatively small number of neurons
Population Coding
representation of a particular object or quality by the pattern of firing of a large number of neurons
Phenology
belief that different mental faculties could be mapped onto different brain areas based on the bumps and contours on a person’s skull
Modularity
the idea that specific areas of the cortex are specialized to response to specific types of stimuli
Module
a structure that processes information about a specific behavior or perceptual quality
often identified as a structure that contains a large proportion of neurons that respond selectively to a particular quality, such as the fusiform face area, which contains many neurons that response selectively to faces
Broca’s Area
an area in the frontal lobe that is important for language perception and production
one effect of damage is difficulty in speaking
Wernicke’s Area
an area in the temporal lobe involved in speech perception
damage to this area causes Wernicke’s aphasia, which is characterized by difficulty in understanding speech
Neuropsychology
the study of the behavioral effects of brain damage in humans
Brain Imaging
procedures that make it possible to visualize areas of the human brain that are activated by different types of stimuli, tasks, or behaviors
Magnetic Resonance Imaging (MRI)
brain scanning technique that makes it possible to create images of structures in the brain
Functional Magnetic Resonance Imaging (fMRI)
a brain imaging technique that indicates brain activity in awake, behaving organisms
the fMRI response occurs when the response to a magnetic field changes in response to changes in blood to the brain
Distributed Representation
occurs when a stimulus causes neural activity in a number of different areas of the brain, so the activity is distributed across the brain
Structural Connectivity
the structural “road map” of fibers connecting different areas of the brain
Functional Connectivity
neural connectivity between two areas of the brain that are activated when carrying out a specific function
Task-Related fMRI
fMRI measured as a person is engaged in a specific task
Resting-State fMRI
the signal recorded using functional magnetic resonance imaging when the brain is not involved in a specific task
Resting-State Functional Connectivity
a method in which resting-state fMRI is used to determine functional connectivity
Seed Location
location on the brain that is involved in carrying out a specific task and which is used as a reference point when measuring resting-state functional connectivity
Test Location
resting-state fMRI measured at a location other than the seed location
Mind-Body Problem
one of the most famous problems in science
how do physical processes such as nerve impulses or sodium and potassium molecules flowing across membranes (the body part of the problem) become transformed into the richness of perceptual experience (the mind part of the problem)
What is visible light?
Isaac Newton (1704): light acts like a particle
James Clerk Maxwell (1873): light has wavelike properties (produces diffraction patterns)
light is electromagnetic radiation (like gamma rays, radio, radar, etc.)
visible from ~380 to ~760 nm (billionths of a metre)
the eye transduces light energy –> neural impulses
Who was Hasan Ibn al-Haytham?
called the “father of optics” and a “pioneer of modern optics”
wrote Book of Optics: vision produced by light reflecting from surfaces into the eye, visual perception occurs in the brain, perception is subjective and affected by individual experience
laid the foundation for the scientific method
What is the path of light in the eye?
light first strikes cornea: concentrates light rays
passes through aqueous humour
passes through pupil (hole in centre of the iris)
passes through crystallin lens
passes through vitreous humour to retina
What is the pupil?
pupil dilates (gets larger) in the dark to let in more light
contracts in bright light to protect the eye
sunglasses should have UV protection to guard against retinal and corneal damage
What is accommodation of the crystallin lens?
ciliary muscles change shape of the lens, altering its focal length, which keeps image focused on retina
What is the retina?
receptors (rods and cones) point to the back of the eye
synapse with bipolar cells (have two long extensions)
which connect to ganglion cells (2 types): P-cells and M-cells
What are horizontal cells?
make lateral connections among receptors and bipolar cells
What are amacrine cells?
laterally connect among bipolar and ganglion cells
What is duplex retina theory?
using microscope, saw two different types of structures in the retina
What is duplicity theory?
believed that rods and cones differed not only in structure, but also in function
What are the characteristics of rods?
number: ~120-125 M
location: periphery only
sensitivity: high
vision: scotopic (dark)
characteristics: black & white
What are the characteristics of cones?
number: ~5-6 M
location: fovea & periphery
sensitivity: low
vision: photopic (light)
characteristics: color
What is the fovea centralis?
used for directed looking
densest concentration of receptors in the eye
only has cones (peripheral retina contains rods & cones)
What are the functional differences between rods and cones?
dark adaptation
ambient illumination changed from light to dark
after a while, eyes adapt: sensitivity increases
What is the dark adaptation curve experiment?
procedure: room lights go out; test light shined in observer’s periphery (rods & cones)
test light adjusted to absolute threshold repeatedly as time passes
result: threshold decreases (sensitivity increases) with time
What is the cone adaptation experiment?
repeat experiment one, but shine light on fovea
result: explains part of the curve
What is the rod adaptation experiment?
problem: how do you measure rods alone?
solution: rod monochromats, due to genetic defect, have only rods on their retinas
What causes the difference between cone and rod adaptation?
different pigments in rods and cones
Boll (1876) found photosensitive pigments in rods: bleached in the light and regenerated in the dark
rhodopsin comprised of retinal and opsin
when hit by light, retinal changes shape (isomerization), causing a chain of events that culminates in a neural signal
What is the absorption spectrum?
amount of each wavelength absorbed by each type of pigment
What is the Hecht, Shlaer, & Pirenne (1942) study on the measure of absolute threshold?
observers detected a flash of light of 100 photons
50 reached retina (rest bounced out/absorbed)
only 7 photons absorbed by pigment molecules
but… flash distributed over an area with 500 receptors
likely that each photon hit a different receptor
thus, one photon is the minimum to change the shape of a pigment molecule
What is the Rushton (1961) study on measured pigment regeneration using retinal densitometry?
shone thin, dim beam of light onto the retina
some bounces off the back of the eye and is reflected out
receptor pigment absorbs light – until it bleaches out, causing more light to be reflected out
measured amount of reflected light over time: indicates time for pigment to regenerate
results: cones take 6 min., rods take 30 min.
pigment is re-formed, with the help of (beta carotene –>) vitamin A + enzymes
What are neurons?
specialized cells that transmit information within the body
What are receptors?
specialized neurons that transduce (convert) environmental energy or chemical into electrical energy
What is resting potential?
there are more negatively charged ions inside the neuron (vs. outside), resulting in a potential difference of -70 mV
What is an action potential?
when a neuron receives sufficient input from other neurons, it becomes “activated”
depolarization: Na+ enters neuron; inside becomes more positive
followed by repolarization: K+ exits neuron; inside becomes more negative to restore resting potential
changes in charges (i.e. voltage) can be measured using microelectrodes
neurons fire spontaneously; have a baseline response rate
firing rate may increase or decrease in frequency
maximum determined by refractory period: interval during which neuron is unable to fire again (~1 ms)
What is the synapse?
gap between axon terminal of one neuron and dendrite (or soma) of another; ~2.0 x 10^-8 m wide
What are neurotransmitters?
chemical messengers released by traveling charge in the axon
fit into specific receptor sites after traversing the synapse
threshold: minimum input required to activate a neuron
excitation vs. inhibition: neurotransmitter may either increase or decrease likelihood that post-synaptic cell fires
inhibition is due to hyperpolarization: K+ exits or Cl- enters neuron; inside becomes more negative
What is specificity coding?
one specific neuron is activated by a particular stimulus
What is a “grandmother cell”?
only fires when you see your grandmother – regardless of viewing angle or point of view
What is sparse coding?
a small number of neurons used to encode a stimulus
What is population coding?
stimulus encoded by pattern of activity across a large number of neurons
What is temporal coding?
timing of neural impulses encodes the stimulus
What is temporal synchronicity coding?
firing of neurons is synchronized over time
Do “grandmother cells” actually exist?
cells are not absolutely exclusive (significantly weaker responses to other stimuli)
unlikely that there’s exactly one “Halle Berry” neuron
MTL involved in emotion, which may influence neural activity
although MTL structures implicated in storage of memories, they are not the ultimate “storage area”
