psychophysics

1
psychophysics

• Connects psyche (psycho) to body (physics)
• threshold cutoff point, something different
  happens above point than below point

2
Threshold for detecting light

• How much light is necessary for you to detect
  that there is light?
• Stimulus above threshold (e.g., room lights) is
  called supraliminal (supra above liminal
  threshold)
• stimulus below threshold (e.g., light too weak to
  see) is called subliminal

3
Mind/body connection

• If we measure threshold, then we show a
  relationship between a physical stimulus and your
  psyche (in other words, psychophysical
  relationship)

4
Sample psychophysical study

• Having various stimuli (in this case, light), of
  different strengths
• weak stimuli (low light) and medium stimuli and
  strong stimuli (strong lights)
• sometimes, cases with no light (no stimulus)
• participants response yes or no, can they see a
  light?

5
Low vs. high threshold

• Low threshold good at detecting light, so would
  say yes to weak stimulus
• high threshold bad at detecting light, so would
  say no to a weak stimulus

6
Graphical representation of threshold

• Threshold point at which S detects stimulus 50
  of the time

Supra- liminal
detection
threshold
Sub- liminal
Signal strength
7
How to interpret threshold?

• Threshold is a measure of your awareness of a
  stimulus, or a measure of your consciousness of a
  stimulus
• threshold is dividing line between unconscious
  and conscious
• below threshold unconscious
• above threshold conscious

8
perception

• Making sense of a stimulus
• e.g., knowing that the room lights are turned on
  when they are turned on
• e.g., FRIED -gt perceived to be the word fried
• applies to all senses

9
Perception

• Aka, identification, recognition, pattern
  recognition
• percept the idea of what the stimulus is
• conscious experience of a stimulus
• unconscious perception processing or
  identifying a subliminal stimulus

10
Measuring perception

• Perception is very rapid (usually less than a
  second)
• typically, use a computer and measure reaction
  time
• show two objects, either same or different, and
  person responds same or different by pressing
  one of two different keys

11
Measuring perception (cont.)

• RT measures how long it takes to decide if the
  objects are the same or different
• but also first must perceive the objects before
  you can compare them
• also measures time it takes to remember which key
  to press

12
Choice RT

• Choice RT having to decide between two or more
  options and having to decide between two or more
  responses (which key to press)
• e.g., choice is between same or different

13
Paper-and-pencil version

• Give a whole set of pairs of letters on a sheet
  of paper
• S marks answer -- same or different -- on sheet
  of paper next to each pair of letters
• measure RT from when they start on the first
  letter pair and finish with the last letter pair