L3 Psychophysics

Question 1

What is the Psycho-physical Function?

Answer 1

A relationship between physiological (perceived) intensity and physical (actual) intensity of a stimulus.
As physical increases, the amount of change in physical to detect a change in perceptual increases (JND)

Question 2

What is a JND?

Answer 2

The change needed in a physical stimulus to make a noticeable change in percept.

Question 3

What is the Perceptual Threshold?

Answer 3

The smallest amount of physical intensity we are able to detect.

Question 4

Define Sensitivity and Bias.

Answer 4

Sensitivity refers to ones ability to detect a signal.

Bias refers to ones tendency to respond in a certain way

Question 5

Outline the four components of Signal Detection theory.

Answer 5

SDT: a detector needs to decide whether a signal has been detected

                                           Judgement
                  There                                                 Not there signal  

There HIT MISS

Not there F/A CORRECT
REJECTION

Question 6

Talk about the underlying mechanism in SDT

Answer 6

behind SDT are two internal responses, one sends a signal saying ‘yes, there is a signal, the other says ‘no, there is no signal. The Bias we have to answer in a particular way sets the Criterion, which sets the point at which we change our answer from a no to a yes. our Sensitivity is measured by the distance between the peaks of the ‘yes’ ‘no’ distributions and is called D’ (d prime)

Question 7

how is d’ calculated?

Answer 7

d’=Z(HITS)-Z(F/A)

Question 8

what is the ROC curve

Answer 8

‘Receiver operator characteristics’ curve is HITS (sensitivity) plotted against FALSE ALARMS. you move along the curve when you change your BIAS, so your sensitivity cant change.

        !
        !
        !
Hits !
        !
        !
        !\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
                        False alarms

Question 9

state the statistical equivalents to these SDT terms;

• Target present
• Target abscent
• Positive response ‘yes’
• Negative response ‘no’
• Hit
• False alarm
• Miss
• Correct rejection

Answer 9

• True effect
• False effect
• p<0.05, null false
• p>0.05, null true
• p<0.05 and effect is true
• p<0.05 and effect is false (type I error)
• p>0.05 and effect is true (type II error)
• p>0.05 and effect is false