Signal detection

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Signal detection

• Psychophysics

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Psychophysics The study of the relationship
between physical stimulation and subjective
sensations. Signal-Detection Theory The theory
that detecting a stimulus is jointly determined
by the signal and the subjects response
criterion.
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Psychophysics

• The formal study of the relationship between the
  properties of stimuli as measured by a physical
  scale and the psychological impressions of those
  stimuli.
• Lawful relationships were uncovered between
  stimulus differences, measured on a physical
  scale, and experienced differences.
• Measurable stimulus values were observed below
  and above the threshold of awareness

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Psychophysics

• Relationship between physical stimuli and
  percepts
• Objective measurement of stimuli
• Eg varying light intensity, frequency of tones
• What can you hear see taste smell etc???

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Psychophysics

• Method of limits descending and ascending
• Method of constant stimuli random level
• Method of adjustment - control
• 2AFC (2 alternative choice or 3..)
• Gono go
• 2IFC (2 interval choice or 3..)

demos
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The Method of Limits

• A psychophysical method where a standard stimulus
  is compared with various values of comparison
  stimuli presented in both ascending and
  descending series. The task of the subject is to
  specify when the standard and the variable appear
  to be the same.

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The Method of Constant Stimuli

• A psychophysical method where a standard stimulus
  is judged against comparison stimuli. Various
  values of the comparison stimuli above and below
  the standard stimulus are presented on a random
  basis. The task of the subject is to specify
  whether the comparison is , lt, gt standard.

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Absolute Threshold The smallest amount of
stimulation that can be detected Just Noticeable
Difference The smallest amount of change in a
stimulus that can be detected
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• Regardless of the sensory domain, there are three
  main topics in the psychophysical classification
  scheme
• absolute thresholds
• discrimination thresholds
• scaling
• Typically small n experiments

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Signal Detection Theory

• Find the signal in the noise

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Gives all possible choices and we can determine
the sensitivity and response bias
Stimulus present Noise present
Responds stimulus Hits False alarm
Responds noise Miss Correct rejection
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Criterion of decision
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d or how much separation?d' separation /
spread
d' ZFA - ZHit
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Signal detection applet