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Lecture 4

PSYC 367 Lecture Notes - Winter 2018 Lecture 4 - Receiver operating characteristic, Fundamental frequency, Detection theory

Course Code
PSYC 367
Deborah Giaschi

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Learning objectives:
- State the difference between sensitivity (d’) and criterion, and describe the effect of stimulus
probability on each
- Describe signal detection theory in terms of the hypothetical distributions underlying
- Show how d’, criterion, hits, false alarms, misses and correct rejections are represented on noise
and signal + noise distributions
- Indicate frequency, amplitude and phase on a diagram of a simple sine wave, and define sound
pressure level. List the units of measurement corresponding to each feature and the normal
human range.
- Define Fourier’s theorem and Fourier analysis, and describe the use of sine waves to describe
auditory stimuli. Explain why 2 different musical instruments sound different even when playing
the same note.
Signal Detection Method
Why do observers make false alarms?
- Endogenous noise: spontaneous neural activity; affects measurement of thresholds & sensitivity
- Sensory
- Criterion: response bias within an observer; depends on expectations & motivation
- Non-sensory
- Can manipulate criterion due to expectations by varying stimulus probability
- If they expect a stimulus present, they should say yes
- If they expect no stimulus present, they should say no more often
- Response pattern, but not d’, varies with stimulus probability
- Signal detection theory: endogenous noise has normal distribution
- N represents sensory activity during catch trials
- When signal is present, it adds to noise (S+N)
- Sensory activity for signal + noise is, on average, more intense than noise alone
- Noise can produce sensation as strong as that produced by the signal (could be
endogenous + external noise)
- Criterion needed: level above which sensation is attributed to signal and not to noise
- Correct rejection - signal absent; activity to the left of criterion
- Hit - signal present; sensory activity to the right of criterion
- Miss - signal present; activity to the left of criterion
- False alarm - signal absent; sensory activity to the right of criterion
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