Topic A: Psychophysical Methods & TSD Flashcards
Response Compression
the result when doubling the physical intensity of a stimulus less than doubles the subjective magnitude of the stimulus
Response Expansion
the result when doubling the physical intensity of a stimulus more than doubles the subjective magnitude of the stimulus
Power Functions
a mathematical function of the form P=KS^n, where P is perceived magnitude, K is a constant, S is the stimulus intensity, and n is an exponent
Steven’s Power Law
a law concerning the relationship between the physical intensity of a stimulus and the perception of the subjective magnitude of the stimulus
the law states that P=KS^n, where P is perceived magnitude, K is a constant, S is the stimulus intensity, and n is an exponent
Response Criterion
in a signal detection experiment, the subjective magnitude of a stimulus above which the participant will indicate that the stimulus is present
Signal Detection Approach
an approach to detection of stimuli in which subject’s ability to detect stimuli is measured and analyzed in terms of hits and false alarms
the approach can take a subject’s criterion into account in determining sensitivity to a stimulus
Hit
in a signal detection experiment, saying “Yes, I detect a stimulus” on a trial in which the stimulus is present (a correct response)
Miss
in a signal detection experiment, saying “No, I don’t detect a stimulus” on a trial in which the stimulus is present (an incorrect response)
False Alarm
in a signal detection experiment, saying “Yes, I detect the stimulus” on a trail in which the stimulus is not presented (an incorrect response)
Correct Rejection
in a signal detection experiment, saying “No, I don’t detect a stimulus” on a trial in which the stimulus is not presented (a correct response)
Receiver Operating Characteristic (ROC)
a graph in which the results of a signal detection experiment are plotted as the proportion of hits versus the proportion of false alarms for a number of different response criterion
Noise
in signal detector theory, noise is all of the stimuli in the environment other than the signal
Signal
the stimulus is presented to a participant
a concept in signal detection theory
What is classical psychophysics?
study the relationship between physical qualities and the experience of them
can be used to understand detection, discrimination, and scaling of physical stimuli
What is the absolute threshold?
minimal limit of sense modality
also called limen
point at which physical stimulation enters into consciousness (threshold theory)
minimum stimulus energy (or chemicals) required to be detected 50% of the time
What is the method of constant stimuli?
stimulus values chosen at random from a predetermined (“constant”) set
- select intensity range: 0 to 100 lumens
- determine set of values: 8, 97, 42, 8, 67, 4, 35, 51, …
- observer says “yes” when stimulus is perceived
- records observations (“trials”)
- plot results
at threshold, the probabilities of saying “yes” and “no” are equal
What is the pro of the method of constant stimuli?
gives good estimate of threshold
What is are the cons of the method of constant stimuli?
time-consuming (must know proper range)
cannot measure threshold changes over time (e.g., in dark adaptation)
What is the method of limits?
change stimuli intensity monotonically
ascending series: stimulus values increased until perceived
descending series: stimulus values reduced until not perceived
What is the pro of the method of limits?
can track threshold changes over time
What are the cons of the method of limits?
induces errors of habituation
induces errors of anticipation
What is adaptive testing?
stimuli presented in a continuous series
“staircase” method: changes from ascending to descending when “yes” encountered; vice versa for “no”
change start point for a series from trial to trial
threshold may vary between trials; take the mean
What is the method of adjustment?
observer directly controls stimulus values until threshold reached
What is the pro of the method of adjustment?
fast
What is the con of the method of adjustment?
least accurate method
What is the difference threshold?
minimum difference needed to discriminate between two stimuli, 50% of the time
judgment made between standard and comparison stimuli (both are well above absolute threshold)
a.k.a. “just noticeable difference” or JND
e.g., 100 g standard vs comparison stimuli; is comparison heavier
What is the point of subjective equality (PSE)?
stimulus that is apparently most like the standard
e.g., could think 99g is the same as 100g
PSE may differ from standard stimulus
What is Weber’s Law?
is the difference threshold the same for all standard stimuli, or does it vary somehow?
e.g., for a 100g weight, JND = 3g (difference = 3%)
for a 1,000g weight, JND = 30g (difference = 3%)
Weber fraction = 3/100 = 0.03
What are the problems with Weber’s Law?
“law” does not extend to extremes
cannot be applied to stimuli close to absolute threshold
also breaks down at higher stimulus intensities
What is scaling?
what is the magnitude of the stimulus?
e.g., are two 60 W lights twice as bright as one 60 W light?
What is indirect scaling?
magnitude derived from multiple difference judgements
What is Fechner’s Law?
derived a scale based on two assumptions:
Weber’s law is valid
basic perceptual unit is the JND
e.g., what if intensity is doubled? let k = 1
if I = 100, S = 4.61
if I = 200, S = 5.30 (not double 4.61)
doubling intensity does not make stimulus seem twice as big
What are the problems with Fechner’s Law?
Webber’s law breaks down at extremes
research showed Fechner’s formulation was insufficient
What is direct scaling?
observers assign values to stimulus intensities
What is magnitude estimation?
- observer presented with a reference stimulus (modulus); and a certain value (say, 10)
- other stimuli are presented; observer assigns values to them (if half as bright, give it a 5; if twice as bright, 20, etc.)
values of stimulus magnitude provided directly by observer
results conflicted with Fechner’s Law
What is Steven’s Law?
P = KS^n
What do the variables in P = KS^n mean?
P = perceived magnitude
S = stimulus intensity
K = constant
n = exponent
How does the exponent in Steven’s law express the nature of the relation?
n > 1: response expansion (e.g. doubling voltage more than doubles sensation of electric shock)
n = 1: linear relation: magnitude of response matches changes in physical quantity (e.g. estimates of line length, distance)
n < 1: response compression (e.g. doubling intensity of light produces only a small change in perceived brightness)
What were the criticisms of Steven’s Law and their solutions?
criticism: the lines describing Steven’s law look very different
solution: plot a log-log graph
criticism: why does the system operate this way?
answer: evolution (pain very quickly becomes aversive, estimating distances is very accurate, allow is to handle a large range of light intensities)
criticism: magnitude estimation may tell us how people “use numbers” instead of how they judge stimuli
solution: cross-modality matching
What is cross-modality matching?
one sense is used to provide a measure of intensity in another sense
typically uses a hand dynamometer
grip squeezed to indicate magnitude of stimulus
kinanesthesia used to estimate quantity in other modality
results match magnitude estimation
How was the problem of observers saying “yes” a lot in signal detection experiments solved?
“response bias” confounds attempts to measure sensitivity
solution: “catch trails” where no stimulus is presented in half the trials
help determine whether observer has a tendency to response “yes” (or “no”) more frequently
What is the receiver operating characteristic (ROC) curve?
each point represents a different payoff
note: stimulus value has remained constant
“bowing” of curve affected by: observer’s sensitivity and intensity of the stimulus
What is subliminal stimuli?
a stimulus that is below threshold may be consciously detected up to 49% of the time
however, a subliminal stimulus is below threshold, and does not enter awareness
can we (unconsciously) sense subliminal stimuli?
will this information affect us without our awareness?
What was the Murphy & Zajonc (1993) study asking if we can process information without awareness?
had observers rate liking of Chinese characters out of 5
each character preceded by a priming stimulus: positive affective (happy face photo), negative affective (scowling face photo), irrelevant (geometric shape), no prime
results: no liking differences in optimal prime condition, facial expression affected liking in subliminal condition, stimuli can affect us outside of our awareness, but they create a feeling, not awareness or action
What was the Vokey & Read (1985) study on if backward messages can be perceived?
played Lewis Carroll’s (1871) “Jabberwocky” and Psalm 23 backwards
observers were equally likely to identify reverse-played psalms as pornography and vice versa
listeners had no idea what was being said, or what it was about
backward messages are not perceivable
What was the Cheesman & Merikle (1984) study?
- presented congruent or incongruent “prime”; colour-name word
- presented visual “mask” of random letters
- presented color patch “target”
task: name target colour: 1 of 4 colour patches
suprathreshold prime: congruent named 95 ms faster than incongruent (100% correct; chance = 25%)
subliminal prime: congruent named 40 ms faster (66% correct)
subjectively imperceptible (but objectively detectable) stimuli may affect responses
What was the Spangenberg, Obermiller, & Greenwald (1992) study?
double-blind study assessed subliminal message self-help audiotapes (e.g. self-esteem, weight loss, memory ability)
subliminal messages ineffective at inducing any change: “illusory placebo effect”
however, labels on the tape (not correlated with the content) influenced perceived effectiveness
