Psychophysics Neuroscience

Psychophysics

• the science of defining quantitative relationships between physical and psychological (subjective) events

  • ex. controlling a physical stimuli, then measuring 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 smallest intensity that can be detected is

• 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 — 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)

• an average threshold of detecting a change between participants

• Data is rarely straightforward — there is 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

• 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 pocket— need to take off gloves and be extra cold. with all of your snow stuff on, it's hard to tell when your phone vibrates over the sound of your gear jostling

Noise

• internal — the static in your nervous system that interferes with your ability to detect a signal

• external — the stimuli surrounding the target signal that interferes with your ability to detect it

• Generally drawn as a normal distribution — 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

  • when moving further down the x-axis — better be sure that the signal is present (minimizes false alarms)

• Can shift reflexively 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)

  greater sensitivity = curve moves closer to top left corner

• Criterion — 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)