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Sensitivity versus response bias: Psychophysical techniques

Sensitivity versus response bias: Psychophysical techniques. The experimental context. The kinds of questions you may want to address: tone 1 versus tone 2 (or faces, or line length etc…) tone 1 versus noise (or face versus standard face etc…)

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Sensitivity versus response bias: Psychophysical techniques

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  1. Sensitivity versus response bias: Psychophysical techniques

  2. The experimental context • The kinds of questions you may want to address: • tone1 versus tone2 (or faces, or line length etc…) • tone1 versus noise (or face versus standard face etc…) • new words versus old words (or faces etc…) • You may face a situation where the stimuli are insufficiently discriminable for response latency to be a reasonable independent variable • In any of these cases Psychophysical techniques are a reasonable method to use.

  3. Stimulus 2 Stimulus 1 Stimulus representation Decision axis (z units) The technique • Method: (the simplest) • one interval • one of two stimulus alternatives are presented • participant identifies stimulus alternative • response accuracy is independent variable

  4. Decision axis (z units) The technique… • We consider the response matrix from the point of view of one response type • We use the number of Hits (H) and False Alarms (F) • Sensitivity d’= z(H)-z(F) • Response bias c = -0.5[z(H)+z(F)]

  5. Decision axis (z units) Importance of response bias • If you concentrate on response accuracy without taking into account response bias, you may get a misleading idea • Important in cases where response bias is crucial – for example histological examinations for precancerous cells, x-ray examinations etc…

  6. References • The classic text: • Green, D.M., and Swets, J.A., (1966). Signal Detection Theory. Wiley: London • A user friendly text: • Macmillan, N.A., and Creelman, C.D., (1991). Detection Theory: A user’s guide. Cambridge University Press. • Know of anything more up to date, please let me know…

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