1: Principles of Perceptual Measurement Flashcards
Stimulus
An object or event in the physical world that may be perceived through stimulation of one of the sensory systems
Absolute threshold
The minimum physical intensity that is required for a stimulus to be detected.
Correct rejection
When no stimulus is present in a trial and the subject answers NO.
Criterion
(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.
Cross-modality matching
The use of stimuli from different domains to make comparison of the relative magnitude that are produced in different sensory system.
D’ (d prime)
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.
Difference threshold
The minimum change in physical intensity that is required for a noticeable change in sensation. Difference thresholds are always determined at suprathreshold levels.
Discrimination scaling
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.
Ekman’s law
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.
False alarm
When no stimulus is present in a trial and the subject says YES.
Fechner’s law
The logarithmic relationship between stimulus intensity and sensation magnitude proposed by Gustav Fechner in 1860.
Function
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.
Hit
When a stimulus is present in a trial and the subject says YES
Ideal detector
A detector that can always detect a stimulus and always fails to detect it when it’s a below a certain defined level.
Intramodal matching
Comparing different aspects of a stimulus within a particular sensory domain or modality.
Just noticeable difference JND
A change in sensation that is sufficient to allow that mental event to be just detected.
Magnitude estimation
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.
Metathetic
Sensations that rely on a substitutive process such that changing some aspect of the stimulus alters the quality of the sensory impression.
Method of adjustment
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.
Method of constant stimuli
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.
Method of limits
A psychophysical method in which stimulus intensity is systematically increased or decreased by the experimenter until the subject gives a change in response.
Miss
When a stimulus is present and the subject says NO
Multi-dimensional scaling
A representation on a spatial map based on the similarity or dissimilarity of the sensory impression produced by metathetic stimuli.
Noise
Background activity that is unrelated to the stimulus and which can interfere with its detection.
Ogive
An s-shaped response function that is typically seen in psychophysical experiments where detection or discrimination performance is measured.
Power law
The relationship deduced by Stevens in which sensory magnitudes are related to stimulus intensity raise to some exponent.
Prothetic
Sensations that rely on an additive process where changing some aspect of the stimulus alters the magnitude of the sensory impression.
Psychometric function
The relationship between performance on a psychophysical task and some feature of the stimulus.
Psychophysics
The study of quantitative relationships between physical events and psychological experiences.
Ratio scaling
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.
Receiver scaling characteristic ROC
A graphical plot of hits vs. false alarms that shows how these values change with respect to each other at all possible criterion levels.
Response bias
The influence of factors unrelated to the sensory stimulus in the decision-making process that leads to judgements about that stimulus.
Scaling
A general psychophysical procedure to estimate the amount of magnitude of something related to perception or some other aspect of psychology.
Sensory transducer theory
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.
Signal
An event, action, or object that serves as a stimulus for detection or discrimination.
Signal detection theory SDT
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.
Staircase procedure
This is an example of an adaptive procedure in which the sequence of stimulus presentations is varied according to the subject’s responses.
Step function
A response function that makes an abrupt transition from one level to another.
Subthreshold
Physical intensity values that are below absolute threshold and therefore not detectable.
Suprathreshold
Physical intensity values that are above absolute threshold and therefore generally detectable.
Two-alternative forced choice 2AFC
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.
Weber’s fraction
(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)
Weber’s law
The difference threshold increases in a linear fashion with the intensity (I) at which the sensory discrimination is being made.
