1: Principles of Perceptual Measurement

Question 1

Stimulus

Answer 1

An object or event in the physical world that may be perceived through stimulation of one of the sensory systems

Question 2

Absolute threshold

Answer 2

The minimum physical intensity that is required for a stimulus to be detected.

Question 3

Correct rejection

Answer 3

When no stimulus is present in a trial and the subject answers NO.

Question 4

Criterion

Answer 4

(aka beta) A setpoint or cut off point that is internally established by the subject. On those trials where sensory magnitude exceeds beta, the subject will indicate that a detectable sensory event has occurred and will say YES. If the sensory magnitude fails to reach beta, then the subject will respond NO.

Question 5

Cross-modality matching

Answer 5

The use of stimuli from different domains to make comparison of the relative magnitude that are produced in different sensory system.

Question 6

D’ (d prime)

Answer 6

The difference between the means of the noise had signal + noise distributions. According to SDT, d’ can increase either by increasing the strength of the signal or by increasing the sensitivity of the detector.

Question 7

Difference threshold

Answer 7

The minimum change in physical intensity that is required for a noticeable change in sensation. Difference thresholds are always determined at suprathreshold levels.

Question 8

Discrimination scaling

Answer 8

The application of difference threshold measurements to estimate sensory magnitude functions. The theoretical foundation for this approach is based on the motion that JNDs represent a constant unit of sensory change, regardless of the actual operating level.

Question 9

Ekman’s law

Answer 9

The amount of sensory change necessary to produce a JND is not constant, but rather a linear function of the intial or operating level of sensation, This is the physical counterpart to Weber’s law.

Question 10

False alarm

Answer 10

When no stimulus is present in a trial and the subject says YES.

Question 11

Fechner’s law

Answer 11

The logarithmic relationship between stimulus intensity and sensation magnitude proposed by Gustav Fechner in 1860.

Question 12

Function

Answer 12

A mathematical description of how one variable is related to another and generally expressed as a formula. If S represents perceived intensity of sensation and I represents stimulus intensity, then a linear function would have the form S = K x I where k represents the slope of function.

Question 13

Hit

Answer 13

When a stimulus is present in a trial and the subject says YES

Question 14

Ideal detector

Answer 14

A detector that can always detect a stimulus and always fails to detect it when it’s a below a certain defined level.

Question 15

Intramodal matching

Answer 15

Comparing different aspects of a stimulus within a particular sensory domain or modality.

Question 16

Just noticeable difference JND

Answer 16

A change in sensation that is sufficient to allow that mental event to be just detected.

Question 17

Magnitude estimation

Answer 17

A psychophysical scaling procedure developed by Stanley Stevens in which human subjects are required to make numerical estimates of the sensory magnitudes that are evoked by stimuli of different physical intensities.

Question 18

Metathetic

Answer 18

Sensations that rely on a substitutive process such that changing some aspect of the stimulus alters the quality of the sensory impression.

Question 19

Method of adjustment

Answer 19

A psychophysical method in which the subject directly adjusts stimulus intensity to produce a detectable sensation. The threshold is calculated from the mean of several trials.

Question 20

Method of constant stimuli

Answer 20

A psychophysical method in which stimulus intensity values are randomly chosen from a preset rage. The subject’s responses over many trials are stored and later used to generate a response frequency for each intensity level.

Question 21

Method of limits

Answer 21

A psychophysical method in which stimulus intensity is systematically increased or decreased by the experimenter until the subject gives a change in response.

Question 22

Miss

Answer 22

When a stimulus is present and the subject says NO

Question 23

Multi-dimensional scaling

Answer 23

A representation on a spatial map based on the similarity or dissimilarity of the sensory impression produced by metathetic stimuli.

Question 24

Noise

Answer 24

Background activity that is unrelated to the stimulus and which can interfere with its detection.

Question 25

Ogive

Answer 25

An s-shaped response function that is typically seen in psychophysical experiments where detection or discrimination performance is measured.

Question 26

Power law

Answer 26

The relationship deduced by Stevens in which sensory magnitudes are related to stimulus intensity raise to some exponent.

Question 27

Prothetic

Answer 27

Sensations that rely on an additive process where changing some aspect of the stimulus alters the magnitude of the sensory impression.

Question 28

Psychometric function

Answer 28

The relationship between performance on a psychophysical task and some feature of the stimulus.

Question 29

Psychophysics

Answer 29

The study of quantitative relationships between physical events and psychological experiences.

Question 30

Ratio scaling

Answer 30

Direct estimations of sensory magnitudes produced by stimuli of different intensities. The technique is based on the theory that sensory magnitudes fall on a ratio scale and can therefore be directly measured by the perceiver.

Question 31

Receiver scaling characteristic ROC

Answer 31

A graphical plot of hits vs. false alarms that shows how these values change with respect to each other at all possible criterion levels.

Question 32

Response bias

Answer 32

The influence of factors unrelated to the sensory stimulus in the decision-making process that leads to judgements about that stimulus.

Question 33

Scaling

Answer 33

A general psychophysical procedure to estimate the amount of magnitude of something related to perception or some other aspect of psychology.

Question 34

Sensory transducer theory

Answer 34

The notion that transformation of physical energy in the stimulus into the biological signals is the basis of the power law. The power law depends on the sensory mechanisms that are involved with this process.

Question 35

Signal

Answer 35

An event, action, or object that serves as a stimulus for detection or discrimination.

Question 36

Signal detection theory SDT

Answer 36

A theory based on statistical concepts that take into account detection and discrimination sensitivity as well as nonsensory factors that may affect the decision making process.

Question 37

Staircase procedure

Answer 37

This is an example of an adaptive procedure in which the sequence of stimulus presentations is varied according to the subject's responses.

Question 38

Step function

Answer 38

A response function that makes an abrupt transition from one level to another.

Question 39

Subthreshold

Answer 39

Physical intensity values that are below absolute threshold and therefore not detectable.

Question 40

Suprathreshold

Answer 40

Physical intensity values that are above absolute threshold and therefore generally detectable.

Question 41

Two-alternative forced choice 2AFC

Answer 41

An experimental procedure where two presentations are made with only one of them containing the stimulus. The subject's task is to identify the presentation with the stimulus. Criterion effects are minimized in this procedure.

Question 42

Weber's fraction

Answer 42

(k) The proportion by which the difference threshold (delta((I)) increases with intensity to produce a just noticeable difference in sensation. k = delta(I)/(I)

Question 43

Weber's law

Answer 43

The difference threshold increases in a linear fashion with the intensity (I) at which the sensory discrimination is being made.