IPL Glossary
activation
The momentary intensity perceived by an observer.
method of adaptation
[psychophysical methods]
An experimental paradigm which presents comparison stimuli which
change slowly until they match the standard stimulus, then continue
changing until the subject detects that there is a difference, and
then change in the other direction until a difference is again detected.
In this way, the
point of subjective equality is crossed several times in each trial.
method of adjustment
[psychophysical methods]
An experimental paradigm which allows the subject to make small
adjustments to a comparison stimulus until it matches a standard
stimulus.
ambiguous
A stimulus which can be interpreted in more than one way. This
example
can be seen as 1. a box in the corner of a room; 2. a solid object with
a cubical hole; or 3. two solid objects joined at one edge.
ascending trial
[psychophysical methods] Enlarging
a small comparison stimulus until it matches or exceeds the associated
standard.
ballistic (movement)
A movement which is completely determined (excepting environmental
influences) before it is begun, and cannot be changed while it is occurring.
comparison stimulus
[psychophysical methods] An
experimental stimulus to be compared to a standard.
control condition
The comparison condition in a within-subjects
design.
-A condition designed as a standard for comparison. All variables are set
at reasonable values; the test condition(s) will attempt to vary only
the independent variables whose effects are to be tested.
cones
One type of light-sensitive cell (photoreceptor) located in the
human eye. (The other type is rods.) Cones allow
color vision; each cone responds most strongly to either red, green, or
blue wavelengths. They are concentrated in the fovea
of the human eye.
method of constant stimuli
[psychophysical methods]
An experimental paradigm which presents, in random order, various
stimuli to be compared to previously presented standard stimulus.
context effects
A familiar object or relationship can influence the perception
of a novel stimulus object.
correct rejection
[signal detection theory] The observer
correctly decides that the target signal
was not present.
criterion
[signal detection theory]The minimum level of
activation necessary for an observer to claim
detection of a signal.
d' [d-prime]
[signal detection theory] A measure of
the average intensity difference perceived by an observer between
samples including a signal
and samples not including a signal.
dependent
-Variables whose values are generated by an experiment, which are
expected to show the effect of the experimental manipulation.
dependent variable
The variable measured and recorded by the experimenter.
depth cues
Effects such as interposition, size changes, vanishing points, and
height in the plane used to make 2 dimensional images seem 3 dimensional.
descending trial
[psychophysical methods] Reducing
a large comparison stimulus until it matches or exceeds the associated
standard.
expectation
The expected result of an action weighted by the probability of
its occurence.
false alarm
[signal detection theory] The observer
incorrectly claims that the target signal
was presented.
feedback
Information about an action gained by an organism during or after
the performance of the action.
fovea
The part of the retina which contains the highest density of
cones and therefore has the best visual acuity.
framing effect
An object which seems to fill a bounding outline looks larger
than the same object within a larger outline.
hit
[signal detection theory] The observer
correctly claims that the target signal
was presented.
Horizontal-Vertical Illusion
More description
Run
experiment
A vertical line appears longer than a horizontal line of the same length.
independent
-A random event.
-Variables in an experiment whose manipulation by the experimenter is
expected to explain the variance in the results of the experiment
(the dependent variables). All other
variables which might affect the results are either held constant
or counterbalanced (randomly, or by design) to cancel out their effects.
independent variable
The variable manipulated by the experimenter.
interaction effects
Experimental results that occur when the effects of one
independent variable depend on the values of other independent variables.
interval scale
A numerical scale in which a difference of one unit always reflects the
same amount of physical difference. (Others are nominal,
ordinal, and ratio.)
just noticeable difference [jnd]
The minimum subjective difference required for a subject to claim
that two stimuli are different on half the presentations.
method of limits
[psychophysical methods]
An experimental paradigm which presents comparison stimuli in
either increasing (ascending) or decreasing (descending) order until
the subject indicates that the standard has been matched.
main effect
The effect of one independent variable independent of the values
of another independent variable.
mean
The arithmetic average of a group of numbers (v1+v2+.../no. of values).
median
The center value in an ordered list of numbers.
miss
[signal detection theory] The observer
incorrectly claims that the target signal
was not presented.
mode
The most common value in a group of numbers.
motivation
A feeling or state of mind that influences one's actions.
Müller-Lyer illusion
More description
Run
experiment
Lines segments of equal length seem different because of inward or
outward pointed arrowheads on their ends.
noise
[signal detection theory]Any
stimulus, internal or external, other than the
signal to which one
wishes to attend.
nominal scale
A numerical scale in which the numbers are only distinguishing labels.
(Others are ordinal, interval,
and ratio.)
normal distribution
The expected distribution of most variables across a population, where
the values cluster near the center and are sparser at the extremes. The
mean, median, and
mode of a normal distribution are the same; if
the distribution is skewed, the mean and median will be
shifted in the direction of the skew; the mean will be shifted farther.
ordinal scale
A numerical scale in which the numbers show relative ordering.
(Others are nominal, interval,
and ratio.)
Poggendorff illusion
More description
Run experiment
The collinear segments of a line whose center seems to be obscured by an
object appear to be misaligned.
point of subjective equality
The point at which a subject, half of the time, will call a
comparison stimulus greater than the standard.
Ponzo illusion
More description
Run experiment
Identical lines appear to be different sizes due to depth cues in
the image.
psychophysical Methods
More description
Standard procedures used to make experimental measurements of
perception.
random
An event whose probability of occurrence is
independent of surrounding events.
ratio
A numerical, interval scale in which the zero
means absence of the property of interest, and the proportion of two
scale values reflects the proportional difference in the property.
(Others are nominal and ordinal.)
receiver operating characteristic curves (ROC curves)
[signal detection theory] A graphical presentation
of the relationship between hits and
false alarms for different signal
probabilities and different levels of sensitivity.
rods
One type of light-sensitive cell (photoreceptor) located in the
human eye. (The other type are cones.) Rods
respond to the overall intensity of the light falling on them,
producing black-and-white vision. They are located outside of the
fovea.
saccade
A very fast, ballistic movement of the
eye. Because the human eye can focus clearly only a very small visual
angle, the eyeball must make many movements to interpret the visual world.
Perception of new information is suppressed during the movement, allowing
the perception of a stable world.
sensitivity
[signal detection theory] A measure
of how strongly an observer reacts to a signal,
usually called d'.
shuffled randomly
Randomly chosen from a set, without replacement.
signal
[signal detection theory] A target
stimulus, usually recurring.
Signal Detection theory
More description
Run
experiment This theory attempts to quantify the reaction of an
observer to the presentation of a signal in an environment
containing noise. The parameters resulting from a series of
presentations are sensitivity (d') and
criterion (ß) of the observer.
skew distribution
One of the tails of the distributions contains more observations
than the other. The skew is toward the longer tail, and the
mean and, to a lesser degree, the
median shift toward that tail.
standard stimulus
[psychophysical methods] An
experimental stimulus which serves as a standard for comparison
for other stimuli.
systematic
A correlation exists between the given variables; they are not
independent.
visual fixation
An eye movement that causes the image of an object or location to
focus at the fovea of the eye.
within-subjects design
An experimental design in which each subject is tested under more than
one level of the independent variable.
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