Chapter 1 - Psychophysics

Question 1

Why measure perception

Answer 1

• physical stimuli are real and can be measured
• it is a private experience
• it is subjective BUT it may offer info about the nature of the brain and how it processes info, and the biological processes that lead to sensation and perception

Question 2

Methods used to study sensation and perception

Answer 2

Threshold - faintest sound one can hear
Scaling - measuring private experiences (rates)
Signal detection theory - measuring difficult decisions
Sensory neuroscience - sensory receptors and nerves affect on perceptual experience
Neuroimaging - parts of the brain activated
Computational models - models of sensory systems that adapt and learn like humans

Question 3

What is a function and what are the components

Answer 3

Function - mathematical description of how one variable is related to another
- Linear (slope), exponential, logarithmic,

Question 4

3 Main thresholds

Answer 4

Absolute threshold - minimum stimulus level required to be registered by the brain as a sensory event
- Subthreshold- below level of activation
- Suprathreshold - above level of activation

Question 5

3 Ways to measure thresholds (which one is the best?)

Answer 5

1. method of adjustment - turning up or down
2. method of limits - increased or decreased intensity (the best because it removes the most amount of biases)
3. constant stimuli - random order

Question 6

What is the shape of a psychophysics experiment and why?

Answer 6

• most assume step function but it is a curve, s-haped, ogive
• people do not accurately give same answers during each trial as there is uncertainty around threshold
• variability is around 50% due to biological, environmental and cognitive factors

Question 7

JND

Answer 7

how much a stimulus needs to change in order to produce a change in perception
- 75% of responses are the same = JND
- as stimulus intensity increases, we need to add more to notice a difference
- what determines the shape of the function

Question 8

Webber’s law

Answer 8

focussed heavily on exact ratios and his law thought that the size of detectable change is a constant proportion of the level of stimulus

Question 9

Fechner’s law

Answer 9

• the smallest dectable change in stimulus could be a unit of the mind since its the smallest thing that could be perceived
• our mind increases slower than matter (to increase a consious change in a heavy stim you need to increase it by alot)
• “perceptually equivilent”

Question 10

Stevens Power Law

Answer 10

Scaling - general psychological procedure to estimate the amount of something related to perception
Magnitude Estimation - scaling in which subjects provide direct ratings of sensations

Question 11

sensory transducer theory

Answer 11

transduction of the physical stimulus into a biological stimulus is the basis of the power law

Question 12

cross modality matching

Answer 12

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

Question 13

Signal detection theory

Answer 13

takes into account cognitive factors that may influence a subject’s decision making process

Question 14

Possible outcomes of SDT

Answer 14

Correct rejection – rejected that it’s the phone – the noise is from the noise distribution

Hit – thinking it is the phone and it is the phone

False alarm – think you hear phone and its not phone it was only a part of the noise distribution

Miss – you hear a sound no its not the phone and it is

Question 15

D prime

Answer 15

The relationship of hits to false alarms – sensitivity
- tested to see how far is the signal and noise distribution from the criterion

Question 16

Criterion

Answer 16

threshold that is set by observer – if response is above criterion = hears it – below criterion – does not hear it

Question 17

ROC curve

Answer 17

provides estimate of relative sensitivities of different individuals
- plots hits vs false alarms for a signal or fixed intensity