Psychophysics Neuroscience

Psychophysics

the science of defining quantitative relationships between physical and psychological (and thus, subjective) events
Can control the physical stimuli, and then measure how a person responds/fails to respond

Method of constant stimuli

measures absolute threshold, test many stimuli of different intensities, to find out what the tiniest intensity that can be detected in
Threshold's in other fields are often all or none (you either hear something or don't), this is NOT how we measure in psychophysics
Does not mean that the stimuli is constantly present, and much of the stimuli is either well above or below the threshold

Method of limits

vary the magnitude/intensity of a stimulus (or difference between two) until participant notices, experimenter adjusts stimuli and samples a scale
Reality of threshold testing; threshold is the point at which you detect it 50% of the time since there are no such "perfect conditions"
Graphed as a Tan function

Method of adjustments

let participant (rather than experimenter) adjust a stimulus until it matches a target (i.e color matching)
There is an average threshold of detecting a change between participants
Data is rarely straightforward, no such thing as "perfect conditions"

Scales

measuring the strength of the sensation rather than the threshold of detection
Not all sensations have the same scale or strength

Magnitude estimation

measures scale, giving participants a sensation and have them rate its strength
Can do freeform or give a starting baseline (baseline is probably more successful)
I.e. how blue or green is this, 1 = very blue, 10 = very green

steven's power law

S = sensation
I = intensity
b = exponent tied to stimulus type
a = constant adjusted to put different scales on the same axis (i.e. adjusting for inches versus centimeters
Sensations have different scales!!!!!!

Signal detection

ability to detect a signal amongst noise, accounts for the amount of noise, the discriminability of the signal, and biases in the person's response patterns
I.e. walking to class in the cold, have a phone in your pocket; to check it, you need to take off gloves and be extra cold. with all of your snow garb on, it's hard to tell when your phone vibrates over the sound of your gear jostling

Noise

the static in your nervous system (internal) that interferes with your ability to detect a signal, or the stimuli surrounding the target signal (external) that interferes with your ability to detect it
Generally drawn as a normal distribution but can be narrow or wider

Criterion

threshold of deciding whether or not you detect a signal, can shift along x-axis, moves towards origin when you are anticipating the signal but when moving further down the x-axis means you had better be sure that the signal is present (minimizes false alarms)
Can shift reflexably on bias

Hit

signal existed and you detected it

Correct rejection

no signal, was not detected

False alarm

no signal but incorrectly detected it

Miss

signal existed but was not detected

Sensitivity

results from signal detection are shifted by this
I.e. how discriminable the target is from the noise
Difference between peaks of signal and situational noise; the larger the difference the better at distinguishing

receiver operating characteristic (ROC) curves

Demonstrate both sensitivity and criterion in one line
Plots Hits versus False Alarms (both Yes responses)
With greater sensitivity, curve moves closer to top left corner
Criterion is represented by a point on the curve

Transduction

translation process; all sensory organs take physical stimuli and convert them to electrical/biochemical signals in our nervous system
The way this occurs is unique to each system but the core tenets are the same

Cellular/Neuronal Neuroscience

From external to internal physics/biochem
The way transduction occurs is unique to each system but the core tenets are the same

Afferent

towards the brain, sensory

Efferent

away from the brain, motor

Systems Neuroscience

Different sensory cortices process different information
McGurk effect states that just because they are different doesn't mean they never interact

EEG

direct measure of electrical activity of large populations of neurons
assesses event-related potentials
good temporal resolution
poor spatial resolution

MRI (structural)

measures shift in magnetic fields to assess atomic structure
indirect measure
good spatial resolution
poor temporal resolution

fMRI

indirect measure
tracks blood oxygen level-dependent signal (BOLD)

PET

similar resolution to fMRI based on metabolism of radiotracer in brain cells

MEG

between EEG and fMRI
measures changes in magnetic activity across large populations of neurons in the brain
good temporal and spatial resolution for the surface of the brain