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CogPsych
Tutorial 2: Signal Detection Theory
| Question | Answer |
|---|---|
| What are the assumptions of SDT? | • SDT assumes that the evidence for the presence of a signal as varying continuously • SDT also assumes that the participant’s criteria for deciding a signal was present changes with experimental conditions • Signal and noise distributed normally |
| What does d' represent? What do various values of d' mean? | • Participant’s sensitivity is represented by d’ (d prime) • When d’ (d prime) = 0, it means that participants are responding at chance • The larger the d’ (d prime), the more sensitive the participant is to the signal: 1 is medium, 4 is extremely good |
| What does c represent? | • Participant’s response bias is represented by c (criterion) |
| What do various values of c mean? | When c = 0, the participant is said to be unbiased • When c > 0, the participant is biased towards making a “No” response (i.e., false alarm < misses) • When c < 0, the participant is biased towards making a “Yes” response (i.e., false alarm > misses) |
| What is panpsychism? | The hypothesis that mind exists as a property of all matter, extended not only to animals, but to inanimate things as well. |
| What is the goal of psychophysics? | To formally describe the relationship between sensation (mind) and the energy (matter) that gave rise to the sensation. |
| What is just noticeable difference / difference threshold? | Smallest change in a stimulus that can be detected 50% of the time |
| What is Fechner's law? | S = k log R where S is the psychological sensation, which is equal to the logarithm of the physical stimulus level (log R) multiplied by a constant k. |
| What does Fechner's law represent? | Your psychological experience of the intensity of light, sound, smell, taste, or touch increases less quickly than the actual physical stimulus increases. |
| What are Weber fractions? | For virtually every measure-whether brightness, pitch, or time--constant ratios describe our ability to detect change fairly well. |
| What is absolute threshold? | Minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time. |
| What are the ways of measuring people's sensations | - method of constant stimuli - method of limits - method of adjustment |
| What is the method of constant stimuli? | Creating many stimuli with different intensities in order to find the tiniest intensity that can be detected |
| What is the method of limits? | With this method, the experimenter begins with the same set of stimuli, in this case tones that vary in intensity. Instead of a random presentation, tones are presented in order of increasing or decreasing intensity |
| What is the method of adjustment? | This method is just like the method of limits, except the subject is the one who steadily increases or decreases the intensity of the stimulus. |
| What are some pitfalls of measuring sensations? | Because thresholds are probabilistic, not really absolute, more sophisticated methods are required if we are to measure how sensitive people are to different stimuli. Also, thresholds change from trial to trial as subjects change from trial to trial. |
| What is a receiver operating characteristic (ROC) curve? | The graphical plot of the hit rate as a function of the false alarm rate. If these are the same, points fall on the diagonal, indicating that the observer cannot tell the difference between the presence and absence of the signal. |
| What is Steven's power law? | S = aI^b. It stated that the sensation (S) is related to the stimulus intensity (I) by an exponent (b) |
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