Sensory Process Terms

why measure perception

offers clues about nature of the brain, how it processes information, and the biological reasons that lead to sensation and perception.

perception

subjective, private experience of stimuli

physical stimuli

quantifiable, real, can be measured

threshold

minimum amount of detectable stimuli

scaling

measuring private experience

signal detection theory

measuring difficult decision ex. did you see a light or was it your imagination

sensory neuroscience

how do sensory nerves and receptors underlie our perceptual experiences

neuroimaging

what parts of the brain are active during different tasks

computational methods

can we create models of sensory systems that adapt and learn like humans do

charles Darwin contributions

theory of evolution, suggested continuity in structure and function of senses and nervous systems

johannes muller contributions

doctrines of specific nerve energies, we are only aware of the activity in our nerves, and cannot be directly aware of the world itself, it is most important which nerve is stimulated not how

Hermann van helmholtz contributions

first to effectively measure how fast neutrons transmit their signals, neutrons obey laws of physics

Santiago Ramon y Cajal contributions

made drawing soft neurone and their connections, suggested that neutrons are discrete entities that don't actually ouch each other, neuron doctrine

sir charles sherrington contributions

coined the term synapse (to clasp)

otto loewi contributions

discovered the first ever neurotransmitter (acetylcholine), two prove that neutrons use chemical not electrical signals

sir alan hodgkin and sir andrew huxley contributions

used squid models to discover the ionic basis of the resting potential and action potential

afferent

signals travelling towards the CNS

efferent

signals travelling away from the CNS

transduction

starts the process of all sensation, conversion of external energy into an electrical signal (receptor potential), always mediated by opening/closing ion channels which changes the membrane potential

ligand

ion or molecule that bonds reversibly

ligand gated channel

cell is receiving and transducing, opens a channel pore that allows specific ions to pass through membrane

g protein coupled receptor

ligand binds g protein coupled receptor, GPCR activates a g protein, g protein initiates a signal that ultimately opens ion channels

stretch/pressure gated channels

deformation of the membrane causes the protein to change configuration, opens a channel pore that allows specific ions to pass

receptor potential

change in membrane potential of sensory receptor, depolarize cells to reach action potential threshold ex. touch

law of dynamic polarization

unidirectional flow of information within the neuron

synaptic transmission

how sensory signals are relayed to other neuron's

neurotransmitter

chemical messenger packed into vesicles, bind to specific receptors on postsynaptic cells

steps to chemical synaptic transmission

1. synaptic vesicles containing neurotransmitters travel down axon terminal

2. voltage gated Ca2+ channel opens to depolarize cell

3. neurotransmitters are released into the synapse and enzyme and receptors bind to them and absorb into the postsynaptic neuron

4. reuptake molecules recycle neurotransmitters

5. leftover neurotransmitters are diffused out of synaptic cleft

synaptic potential

caused by binding of neurotransmitters to post synaptic receptors

depolarization

excitatory response to membrane potential being above threshold causing action potential to fire

hyper polarization

inhibitory response to the membrane potential being brought down below threshold to inhibit firing of an action potential

bipolar neurons

one axon and one dendrite, generally sensory neurons

pseudo unipolar neurons

peripheral axon to send/receive signals to body, central axon to send signals to CNS, sensory neurons

multipolar neurons

many dendrites emerging from cell body, many places where signals are sent/received, generally motor and interneurons

stimulus location

topographical relationships maintained from sensory organ to primary cortical site

receptive field

each neuron in cortical areas are stimulated only if corresponding sensory area is stimulated

intensity

absolute threshold is largely determined by minimum receptor potential, more intense stimulus=larger receptor potential=greater action potential frequency

adaptation

frequent exposure to a stimulus leads to reduced awareness, adaptation of sensory receptors

modality

sensory receptors are sensitive to a specific type of energy

axes of CNS

long axis has a bend in it, must consider when applying anatomical terms

4 lobes of brain

temporal, frontal, occipital, parietal

gyri

crests of filed cortical issue

sulci

grooves that divide gyri

visual cortex

vison

auditory cortex

hearing

motor cortex

motor movements in body

somatosensory cortex

skin sensations

olfactory cortex

smell

primary receiving area

where all sensory input first arrive in the cerebral cortex

poly sensory

where information from more than one sense is combined

association areas

where sensory information travels after leaving the primary receiving area

cerebral cortex

thin layer of neural tissue that covers the entire cerebrum, made of 6 layers called the neocortex

white matter

axon tracts and commissures

nuclei

local groups of neurons that have roughly similar connections and functions

thalamus

major relay station, all sensory signals except smell travel through thalamus on their way to the cortex

spinal cord

transmits sensory and motor information to and from the brain

brainstem

composed of the pons, medulla and midbrain, relays motor information from the brain

ganglion

local accumulations of neutrons and glia in the PNS

peripheral nerves (31 pairs)

bundles of peripheral axons ensheathed by glial cells

intracellular recording

measures voltage changes across the cell membrane, compares the voltage inside vs outside the cell, can detect small changes in membrane potential

extracellular recordings

measure voltage changes just outside of the cell, compares activity from outside cell membrane to an inactive area, can only detect big changes in MP such as action potentials

pros and cons of electrophysiological recording

can only record one neuron at once, can't be used in humans, good spatial and temporal resolution

neuroimaging

A set of methods that generate images of the structure and/or function of the brain.

EEG

measures electrical activity through dozens of electrodes placed on the scalp, get baseline brain activity, then present stimulus, average responses to stimuli

pros and cons of EEG

can see what parts of brain are active during stimulus presentation, can tell if neural signalling is slow, noninvasive, low spatial resolution, high temporal resolution

MEG

measures changes in tiny magnetic fields across populations of many neurons in the brain. uses a SQUID to localize populations of active neurons

pros and cons of MEG

costly and hard to perform, better at localizing subcortical structures

MRI

patient is placed in a large powerful magnet that influences the way the hydrogen in the brain spins, then radio frequency is pulsed, causes the atoms to spin out of equilibrium, sensors detect energy released after pulse and produces a 3d image of brain

pros and cons of MRI

detailed structural images, no functional information, no radiation, detailed pictures of soft tissues where lots of hydrogen is present

fMRI

magnetic pulses pick up oxygen rich areas in brain, more active neurons need more oxygen rich blood, measures oxygenated blood in the brain then baseline, subtracts baseline from amount of oxygenated blood in areas when stimulus present.

pros and cons of fMRI

delayed responses, indirect measure of activity, shows activity in subcortical structures, non invasive

PET

radioactive tracer injected into bloodstream, camera detects radiation emitted from brain regions which are more metabolically active therefore using more tracer.

pros and cons of PET

low spatial resolution, invasive, subcortical structures visible

mathematical models

use mathematical language, concepts, and equations to closely mimic psychology and neuronal processes

computation models

use mathematical language, and equations to describe steps in psychological or neural processes, can predict processes based off patterns

efficient coding models

assume that sensory systems are predictable in natural environments, economically encode predictable sensory inputs while highlighting less predictable input

bayesian models

assume earlier observations should bias expectations for future events to build a model of the world, predictive coding

linear change in stimulus intensity and perceived sensation

as intensity changes, sensation increases by an equal unit

exponential change in stimulus intensity and perceived sensation

at a high level, a small stimulus intensity change causes a large change in perception

logarithmic change in stimulus intensity and perceived sensation

at a low level, a small stimulus intensity change causes a large change in perception

absolute threshold

minimum stimulus level required to be registered by brain as a sensory event, has to be enough stimulation to activate neuron

sub threshold

below the level of detection

supra threshold

above the level of detection

3 ways to measure thresholds

1. method of adjustment

2. method of limits

3. method of constant stimuli

step function vs psychometric function

step function: always senses supra threshold stimuli, not typic psychophysics results

psychometric function: uncertainty around stimulus intensifies near absolute threshold, s shaped function

why is variability around 50% for psychometric functions?

cognitive functions vary on stimulus baseline and neuronal activity sensitivity

what determines the shape of the psychometric function?

absolute threshold, what the slope is at supra threshold levels, how the slope changes with increasing intensity

just noticeable difference

how much does a stimulus need to change in order to produce a detectable change in perception

how to find the difference threshold

present subject with 2 stimuli ask which is heavier, repeat 50 times. Calculate % of times subject said target was heavier than the reference.

perceptual equivalence point

difference detected on 50% of trials of difference threshold

webers law

delta is a constant proportion of the stimulus intensity. k (webers fraction) must be experimentally determined

what does a k value of 0.07 mean?

change 7% of stimulus to detect a difference, k% of stimulus needs to be added to notice a difference.

what sensory dimension has the lowest k value

pitch

Fechner's Law

assumes that all JND's are perceptually equivalent. for every JND amount added is different, but change in sensation is the same.

scaling

psychophysical procedure to estimate the amount of something related to perception

magnitude estimation

a scaling approach where subjects provide direct ratings of their sensations

power law

sensory experience = scaling constant x initial intensity

value of the power exponent

each sensory experience is related to stimulus intensity by an exponent. The relationship is increasing or decreasing depending on the exponent. pain is exponential

sensory transducer thoery

idea that transduction of the physical stimuli into a biological stimuli is the basis of the power law

cross modality matching

compare stimuli from one sensory modality to stimuli of another sensory modality