Psychophysics & Signal Detection Theory Jonathan Pillow - - PowerPoint PPT Presentation

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Psychophysics & Signal Detection Theory Jonathan Pillow - - PowerPoint PPT Presentation

Apr 18, 2023 417 likes •671 views

Psychophysics & Signal Detection Theory Jonathan Pillow Perception (PSY 345 / NEU 325) Princeton University, Spring 2019 Lec. 3 Chapter 1 1 Outline for today: Stephens power law psychophysics Signal Detection Theory 2

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Psychophysics & Signal Detection Theory

Jonathan Pillow Perception (PSY 345 / NEU 325) 
 Princeton University, Spring 2019

  • Lec. 3

Chapter 1

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Outline for today:

  • Stephen’s power law
  • psychophysics
  • Signal Detection Theory

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Stevens’ Power Law

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(my rating: “meh”)

  • subjective
  • based on rating data
  • no “right” answer: just a mapping between
  • ne unknown scale (‘pain’) and another

unknown scale (‘numbers’) Stevens’ Power Law

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A C B Test yourself: at which intensity are changes most detectable?

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For this stimulus/sensation relationship, which stimulus changes are most detectable?

A B C

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How to measure perception?

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müller-lyer illusion

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“percept” “percept” is internal

müller-lyer illusion

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Psychophysics

  • detection (yes/no)
  • discrimination (e.g., bigger than)
  • estimation (report the stimulus exactly)

All provide indirect measure of internal mental state!

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Detection

perfect threshold

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Detection

noise perfect threshold

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psychometric function

  • relates physical quantity to the probability of detecting it

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Signal detection theory: A psychophysical theory that quantifies the response of an observer to the presentation of a signal in the presence of noise ( On board )

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Detecting a stimulus using the signal detection theory (SDT)

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Detecting a stimulus using the signal detection theory (SDT)

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Sensitivity to a stimulus: The separation between the distributions of response to noise alone and to signal plus noise

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For a fixed dʹ, shifting the response criterion

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Signal detection theory Hit: Stimulus is presented and observer responds “Yes” Miss: Stimulus is presented and observer responds “No” False alarm: Stimulus is not presented and

  • bserver responds “Yes”

Correct rejection: Stimulus is not presented and

  • bserver responds “No”

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Signal Detection Theory Terms to know: “noise” distribution: values arising when stimulus not present “signal” distribution: values arising when signal + noise present Type I error: rate of “false alarms”, or false positives Type II error: rate of “misses”, or false negatives psychometric function: describes probability of saying “I heard it” as function of stimulus intensity

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Chapter 1 Summary

  • Weber-Fechner law
  • Stevens’ power law
  • psychophysics
  • psychometric function
  • signal detection theory: threshold, criterion, Hit/

Miss, FA/CR, d’ (i.e., “d-prime”)

  • spikes, synapses, neurotransmitter

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You can safely ignore (for now)

  • method of constant stimuli / method of adjustment
  • ROC curves
  • Fourier analysis (though we will come back to it!)
  • Cranial nerves (Fig 1.20)
  • brain anatomy (Fig 1.21, but we will come back as

needed)

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Next: Read Chapter 2

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