Psychophysics

Absolute threshold

the minimum stimulus energy necessary for an observer to detect a stimulus

Bias

a measure for the extent to which one response is more probable than another. Bias is independent of sensitivity

Correct rejection

in a signal detection experiment saying ‘no I don’t detect a signal’ on a trial in which the signal is not presented (correct response)

False alarm

saying ‘yes I detect’ when it is not presented (incorrect response)

Fechners law

a principle stating the relationship between a stimulus and the resulting sense action that says the magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity

Hit

In a signal detection experiment, saying “Yes, I detect the signal” on a trial in which the signal is present (a correct response).

Miss

In a single detection experiment, saying “No, I don’t detect a signal” on a trial in which the signal is present (an incorrect response).

Psychophysics

traditionally refers to quantative methods of measuring the relationship between properties of the stimulus and the subjects experience

Receiver operating characteristic (ROC) curve

In a signal detection experiment, the graphical plot of the hit rate as a function of the false alarm rate. If these are the same, observers cannot distinguish between signal and noise. As the observer’s sensitivity increases, the curve bows toward the upper left corner –a point that represents perfect sensitivity.

Response criterion

in a signal detection experiment, the subjective attitude of a stimulus above which the participant will indicate that the stimulus is present

Sensitivity

a measure for how hard or easy it is for a subject to detect that a target stimulus is present. It can be computed based on hit-and false alarm rates. Also call d’ (pronounced Dee prime)

Signal detection theory

theory stating that the detection of a signal depends both on participants sensitivity to the signal and on the participants response bias

Webers law

a law stating that the ratio is the difference threshold (DI) to the stimulus intensity (I) is constant. According to this relationship, doubling the value of the stimulus intensity will cause a doubling of the difference threshold. The ratio DI/I is called Weber’s fraction.