01. Psychophysics & research methods

Question 1

What is single-cell recording?

Answer 1

• electrode measures activity of one cell in response to different stimuli
• stimuli = light bars at different angles
• each cell responds to only one specific angle

Question 2

Types of brain imaging?

Answer 2

• PET scans
  -fMRIs
  -Diffuse optical tomography (DOT)

Question 3

PET scans?

Answer 3

• one of the first types of brain imaging
• measures bloodflow to see brain activity during different actions
  Problems:
• same action/stimuli for a long time to be accurate
• involves radiation

Question 4

fMRI?

Answer 4

• more modern
• oxygen level in blood
• more activity = more oxygen
• better spatial resolution

Question 5

DOT?

Answer 5

• diffuse optical tomography
• oxygen in brain by detecting light reflected by brain
• temporal resolution = fMRI, spatial resolution is a little worse
• Portable equipment!!

Question 6

Psychophysics def

Answer 6

study of relationship between physical energy in a stimulus and the perceptual experience it produces

helps make inferences without directly observing brain activity

Question 7

Absolute threshold def

Answer 7

• minimum intensity of a stimulus required to produce a sensation
• defined as stimulus detected 50% of the time

Question 8

Difference threshold def

Answer 8

minimum difference in intensity that can be detected
–> Just noticeable difference (JND)

Question 9

Method of limits?

Answer 9

1. present series of stimulus intensities IN ORDER
2. ask if they detect it at each presentation
3. Threshold = midpoint between where the response changed

Question 10

2 potential problems of method of limits (and solutions)?

Answer 10

1. they keep reporting that they heard it –> error of habituation (present ascending and descending series)
2. they remember how many stimuli they detect (start the series at a different point each trial)

Question 11

Method of adjustment

Answer 11

• same as limits
• except the subject (or experimenter) CONTINUOUSLY adjusts the stimulus until they can’t detect it

Question 12

Method of constant stimuli

Answer 12

• more accurate than limits, but more trials needed
• fixed set of stimulus intensities, including extremes
• presented in RANDOM order
• each intensity is presented several times
• graph is an elongated S curve

compare “classical threshold theory” graph to actual “psychophysical function”

Question 13

Staircase method

Answer 13

• begin at an extreme (far above/below) threshold
• increase 1 step if not detected, decrease 1 step if detected
• stop after a predetermined number of response reversals
• threshold = average intensity at response reversal
• more efficient than constant stimuli (don’t waste trials on stimuli we know they will/won’t detect)

Question 14

Method of constant stimuli for difference threshold

Answer 14

• use pre-selected stimulus intensities presented RANDOMLY
• on each trial, present TWO stimuli
  –> one standard (reference stimuli)
  –> one comparison (varies each trial)
• possible responses:
  –> C is bigger/brighter/heavier than S
  –> C is smaller/dimmer/lighter than S

Key terms:
- point of subjective equality: stimulus intensity judged greater/less than standard 50% of the time
- point of objective equality: actual value of standard
- constant error: diff. btw PSE & POE
- Diff threshold –> 1/2(75%-25%)

Look at powerpoint 01.methods for ex

Question 15

Size-weight illusion

Answer 15

• the larger of 2 equal-weight objects feels lighter
• context influencing perception
  ex –> envelopes with coins

Question 16

Metamers?

Answer 16

any 2 stimuli that are physically different, but perceived as identical