2. Research methods Flashcards
classical psychophysics (CLPH)
the study of the relationship between physical quantities and the experience of them
can be used to understand detection, discrimination, and scaling of physical stimuli
detection CLPH
detecting stimuli
did you see that animal? yes
discrimination CLPH
being able to tell the difference between stimuli
cats and dogs
Scaling CLPH
being able to tell how two stimuli
dogs tend to be bigger, louder, and have more district snouts and variation in shape/size
cats all tend to have a more consistent shape with small snouts and paws.
Absolute threshold
minimal limit of a sense modality, what is the smallest stimuli you can become aware of?
the smallest amount of a stimulus necessary to allow an observer to detect its presence
minimum stimulus energy or chemicals required to be detected 50% of the time
the point at which physical stimuli enters consciousness (threshold theory)-present a stimulus to an observer and ask if they can detect it
also called a limen
Method of constant stimuli
stimulus intensity chosen at random from a predetermined (“constant”) set on each trial (observation)
Constant meaning predetermined
- select intensity range: 0 to 100 lumens
- determine set of values: 8, 97, 42, 8, 67, 4, 35, 51,…
- observer says “yes” when stimulus perceived
- record observations
- plot results:
Pros and cons of the method of constant stimuli
☑ gives good estimate of threshold
☒ time-consuming(must know proper range because it could be between 1-100 or 0-1 for example)
☒ cannot measure threshold changes over time (e.g., in dark adaptation)
Method of Limits
change stimulus intensity monotonically(increasing or decreasing)
- increase stimulus intensity until it is perceived (ascending series) or reduce stimulus intensity until it is not perceived (descending series)
pros and cons of the method of limits
Pros & Cons:
☑ can track threshold changes over time
☒ induces errors of habituation-participants giving the same answers: yes,yes,yes, no (repeat)
☒ induces errors of anticipation-saying yes forever
Adaptive testing variant
stimulus intensity changed over a continuous series
▸ e.g., staircase method: changes intensity from ascending to descending when “yes” encountered; vice-versa for “no” (not just continuously going up or down, but also switching directions)
▸ the point at which perception changes is called the turnaround
▸ choose different starting point for each series from trial to trial
▸ threshold may vary between trials: take the mean of the turnarounds
Method of adjustment
observer directly controls stimulus values until threshold reached
Pros & Cons:
☑ fast
☒ least accurate method
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., present 100 g standard vs. multiple comparison stimuli; ask whether there is a difference (yes/no)
- 0.75 → upper difference threshold
- 0.25 → lower difference threshold
- difference threshold = (upper - lower) ÷ 2
0.50 → Point of subjective equality (PSE)
Point of subjective equality (PSE)
stimulus that is apparently most like the standard
(PSE may differ from standard stimulus)
Weber’s Law (1834):
Is the difference threshold the same for all standard stimuli, or does it vary somehow?
k = JND / S
k = constant (“Weber fraction”)
S = standard stimulus intensity
e.g., for a 100 g weight, JND = 3 g (difference = 3%)
for a 1,000 g weight, JND = 30 g (difference = 3%)
Weber fraction = 3/100 = 0.03
What is the problem with Weber’s Law?
“law” does not extend to extremes. not a law because a law is supposed to hold under all conditions
☒ cannot be applied to stimuli close to absolute threshold-such as 0,000001 grams of salt
☒ also breaks down at higher stimulus intensities-like a million pounds
Scaling
- what is the subjective magnitude of a stimulus?
- e.g., are two 60 W lights twice as bright as one 60 W light? (no)
only concerned with if there is a difference or not, not with the degree/amount of difference
Indirect scaling
magnitude derived from multiple difference judgments
Fechner’s Law (1860)
derived a scale based on two assumptions:
* Weber’s Law is valid
* basic perceptual unit is the JND (there is no half JND)
S = (1/k) loge (I )
k = Weber fraction
I = stimulus intensity(physical magnitude)
S = sensory experience(perceived magnitude)
e.g., what if intensity is doubled? Let k = 1
if I = 100, S = 4.61
if I = 200, S = 5.30
- doubling intensity does NOT make stimulus seem twice as big
e.g., a light 20 JNDs above threshold is twice as bright as a light 10 JNDs above threshold
Problems with Fechner’s Law
☒ Weber’s Law breaks down at extremes
☒ research showed Fechner’s formulation was insufficient
Direct Scaling
observers assign values to stimulus intensities
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; instead, a “power law” held (power function)
Steven’s Law 1957 (SL)
P = K S^n
P = perceived magnitude
K = constant
S = stimulus intensity
n = exponent
response expansion SL
n > 1
e.g., doubling voltage more than doubles sensation of electric shock
linear relation SL
n = 1
magnitude of response matches changes in physical quantity
e.g., estimates of line length, distance
response compression SL
n < 1
e.g., doubling intensity of light produces only a small change in perceived brightness
Criticism of Steven’s Law
all the line describing it all look very different, the solution was to draw a line graph
perceived magnitude in descending order of stimulus is: electric shock, apparent length, brightness
Why are electric shocks perceived higher than apparent length and brightness?
Answer: evolution, aka, internal nervous system thinks pain is bad, distance gauge good, seeing in different light conditions good
- pain very quickly becomes very aversive
- estimating distances is very accurate-being able to tell how far prey or predators were compared to yourself
- allows us to handle a large range of light intensities, and not be blinded either in a dim room or by sunlight
Criticism: magnitude estimation may tell us how people “use numbers,” instead of how they judge stimuli
e.g., Which is the “bigger” difference: 1-2? or 2-3?
what are some problems and solutions?
Problem: How to estimate magnitude without using verbal reports of numbers?
Solution: cross-modality matching: one sense used to provide a measure of intensity in another sense
- typically uses a hand dynamometer
- grip squeezed to indicate magnitude of stimulus-squeeze harder if the light is brighter
- Kinesthesia (sense of movement of the parts of the body) used to estimate quantity in other modality
- results match magnitude estimation-bro finally got the numbers to prove his shit
Theory of Signal Detection (TSD)
(Tanner & Swets, 1954)-were developing radar in WWII
Problem: observer says “yes” a lot
- response bias confounds attempts to measure sensitivity-people just wanted to be helpful but instead muddied results
Solution: catch trials: no stimulus presented in half the trials-so they could reliably detect if the radar wasn’t detecting a plane
- help determine whether observer has a tendency to respond “yes” (or “no”) more frequently, aka if the person has a response bias
How can the probabilities for people’s responses be changed?
by adding payoffs for certain conditions
eg: by making hits pay $10, correct rejections +$1, and misses or false alarms -$1, you increase the rates of people responding with hits and false alarms
same can be done for any desired response
what is an ROC curve?
receiver operating characteristic curve?
-everyone’s will look different
-each point on the curve represents a different payoff
-the “bowing” of the curve is affected by:
1. the oberverst sensitivity
2. the intensity of the stimulus
Why do people respond when there is no stimulus present?
because background “noise” exists in the sensory system
the optic nerve in our eyes has a base level of activity, even with our eyes closed, this applies to all of our senses
sensitivity or discriminability, d’ (the difference in the means of the 2 distributions)
- is the distance between the means of the noise and signal + noise distributions
*is independent of response criterion (β) - the concept of threshold is not used in TSD
TSD and discriminating between stimuli:
- measured as discriminability (d’ ) between two signal + noise distributions (S1+N vs. S2+N)
- both must be detectable
Subliminal Stimuli
- a stimulus that is below threshold may be consciously detected up to 99% of the time
- however, a subliminal stimulus is below threshold, and does not enter awareness
Can we process information without awareness?
Murphy & Zajonc (1993)
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
- two priming presentations: subliminal (4 ms) or optimal prime (1,000 ms, aka 1 second)
- no liking differences in optimal prime condition
- facial expression affected liking in subliminal condition
- stimuli can affect us outside of our awareness–but they creates a FEELING, NOT awareness or action
Can backward messages be perceived?
Vokey & Read (1985)
- 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
Cheesman & Merikle (1984)
- presented congruent or incongruent prime: colour-name word
- presented visual mask of random letters
- presented colour patch target
- task: name target colour: 1 of 4 colour patches
- suprathreshold prime: congruent named 25ms faster than incongruent (100% correct; chance=25%)
- subliminal prime: congruent named 40ms faster (66% correct)
- subjectively imperceptible (but objectively detectable) stimuli may affect responses even if people can’t recall what they saw
Illusory placebo effect
despite the lack of an “active ingredient”, people believed there was a change–but there was no actual difference
Spangenberg, Obermiller, & Greenwald (1992):
- double-blind study assessed subliminal message self-help audiotapes
e.g., self-esteem, weight loss, memory ability
- labels on the tape (not correlated with the content) influenced perceived effectiveness
- however, the subliminal messages were ineffective at inducing any objective change
Can subliminal ads be detected?
subliminal ads will not affect your behaviour
CBC’s Close-Up (1958):
- they flashed a message 352 times; asked viewers to identify it
- 500 people wrote in–all were wrong
- message was: TELEPHONE NOW
- no increase in phone usage (but almost half of respondents claimed to be hungry or thirsty during the show)
“EAT POPCORN” story?
- concocted by James Vicary, unemployed marketing researcher
1957: movie audiences in New Jersey reportedly induced to buy snacks by subliminal messages (“EAT POPCORN”)
- made big money, then…disappeared
What are some methods of measuring brain activity?
EEG, MEG, PET, TMS, and fMRI
electroencephalography (EEG)
records electrical activity in the brain-like trying to understand a soccer game based off of the cheers of the crowd
Measures electrical activity in the brain through electrodes placed on the scalp. It has high temporal resolution (milliseconds), allowing tracking of fast brain processes, but low spatial resolution (difficult to pinpoint exact brain areas).
amplifies evoked (electrical) potentials produced by large numbers of neurons when a stimulus is presented
- intra/extracellular recording: measures activity of a single neuron, using a microelectrode
MEG (magnetoencephalography)
brain imaging
It also has high temporal resolution and slightly better spatial resolution than EEG.
▸ similar to EEG, but detects magnetic fields
▸ uses arrays of SQUIDs (superconducting quantum interference devices) to detect weak signals
▸ shows neural activity
- PET (positron emission tomography):
brain imaging
Uses radioactive tracers to measure brain metabolism. It has lower spatial and temporal resolution but can map chemical activity in the brain.
▸ take radioactive form of glucose
▸ X-rays cause positron to be emitted
▸ shows metabolic activity
- fMRI (functional magnetic resonance imaging):
brain imaging
Measures brain activity by detecting changes in blood flow. It has high spatial resolution (detailed images of where activity occurs) but low temporal resolution (delayed by a few seconds).
▸ hemoglobin (which carries oxygen in the blood) contains an iron atom that has magnetic properties
▸ strong magnetic field aligns magnetic molecules
▸ radio wave pulse disorients them
▸ upon realignment, protons emit radio waves like an echo which can be measured quickly
▸ shows metabolic activity
ascending series
a series in which a stimulus gets increasingly larger along a physical dimension
capsaicin
the active ingredient in chili peppers that provides the experience of hotness, piquancy, or spiciness
catch trial
a trial in which the stimulus is not presented
correct rejection
in signal detection analysis, a correct rejection occurs when a nonsignal is dismissed as not present
criterion
is an internal cut-off determined by the observer, above which the observer makes one response and below which the observer makes another response
crossover point
the point at which a person changes from detecting to not detecting a stimulus or vice versa
d′ (d-prime)
a mathematical measure of sensitivity
descending series
a series in which a stimulus gets increasingly smaller along a physical dimension
difference threshold (JND)
the smallest difference between two stimuli that can be reliably detected
false alarm
in signal detection analysis, a false alarm is an error that occurs when a nonsignal is mistaken for a target signal
forced-choice method
The forced-choice method is a psychophysical technique in which participants are presented with multiple options (typically two or more) and must choose the one that they believe contains the target stimulus. This method minimizes guesswork by requiring a decision, even if the participant is uncertain. It is commonly used to measure sensory thresholds or perceptual accuracy.
hit
in signal detection analysis, a hit occurs when a signal is detected when the signal is present
Magnitude estimation
a psychophysical method in which participants judge and assign numerical estimates to the perceived strength of a stimulus
masking
the difficulty in seeing one stimulus when it is quickly replaced by a second stimulus that occupies the same or adjacent spatial locations
Method of Adjustment
a method whereby the observer controls the level of the stimulus and “adjusts” it to be at the perceptual threshold
method of constant stimuli
a method whereby the threshold is determined by presenting the observer with a set of stimuli, some above threshold and some below it, in a random order
method of limits
stimuli are presented in a graduated scale, and participants must judge the stimuli along a certain property that goes up or down
miss
in signal detection analysis, a miss is an error that occurs when an incoming signal is not detected
Point of subjective equality (PSE):
the settings of two stimuli at which the observer experiences them as identical
psychophysical scale
a scale on which people rate their psychological experiences as a function of the level of a physical stimulus
Receiver-operating characteristic (ROC) curve:
in signal detection theory, a plot of false alarms versus hits for any given sensitivity, indicating all possible outcomes for a given sensitivity
response compression
as the strength of a stimulus increases, so does the perceptual response, but the perceptual response does not increase by as much as the stimulus increases
response expansion
as the strength of a stimulus increases, the perceptual response increases even more
scoville scale
a measure of our detection of the amount of an ingredient called capsaicin in chili peppers
sensitivity
the ability to perceive a particular stimulus; it is inversely related to threshold
Sensitivity (signal detection theory):
the ease or difficulty with which an observer can distinguish signal from noise
signal detection theory
the theory that in every sensory detection or discrimination, there is both sensory sensitivity to the stimulus and a criterion used to make a cognitive decision
Stevens’s power law:
a mathematical formula that describes the relationship between stimulus intensity and our perception; it allows for both response compression and response expansion
Transmagnetic stimulation TMS
a procedure in which a magnetic coil is used to stimulate electrically a specific region of the brain
Uses magnetic fields to temporarily disrupt brain activity in specific regions, allowing for causal inference about brain function.
two-point touch threshold
the minimum distance at which two touches are perceived as two touches and not one
What does the Scoville scale measure? Why is it considered to be a psychophysical scale?
The Scoville scale measures the spiciness or heat of chili peppers and other spicy foods, in terms of the concentration of capsaicin, the chemical responsible for the burning sensation. It was created by Wilbur Scoville in 1912, who developed a sensory-based method where capsaicin was diluted in sugar water until the heat was no longer detectable.
The Scoville scale is considered psychophysical because it links a physical property (the concentration of capsaicin) with a subjective sensory experience (the perception of heat). In psychophysics, scales like this connect physical stimuli to human perception.
What is the method of limits? How is it used to determine absolute thresholds?
The method of limits is a technique in psychophysics to determine an individual’s absolute threshold, or the smallest level of stimulus intensity that can be detected. Stimuli are presented in increasing or decreasing intensities, and the participant indicates when they can (or can no longer) detect the stimulus.
Use in Absolute Threshold: For example, to find the threshold for hearing, tones are played at progressively lower volumes until the person can no longer hear them, and then increased again. The point where detection is reliably reported marks the absolute threshold.
What is the method of adjustment? How is it used to determine the point of subjective equality?
The method of adjustment involves the participant directly controlling the intensity of a stimulus, adjusting it until it matches a reference or until they perceive it as equal in intensity to another stimulus.
Use in Point of Subjective Equality: This method is used to determine the point of subjective equality (PSE), which is the point at which two stimuli are perceived as equal. For instance, a participant may adjust the brightness of a light until it appears to match the brightness of a reference light.
What is the two-point touch threshold? How does it illustrate the concept of a JND? How do two-point touch thresholds differ across the human body?
The two-point touch threshold is the smallest distance at which a person can perceive two separate points of contact on the skin, rather than a single touch. It demonstrates the JND in tactile sensitivity, showing the smallest difference in spatial separation that can be detected.
Illustration of JND: The threshold illustrates the just noticeable difference in spatial touch perception, as it measures the minimal detectable distance between two touch stimuli.
Differences Across the Body: The two-point threshold varies across different body parts. Areas like the fingertips and lips have low thresholds (high sensitivity), meaning they can detect very small separations, while areas like the back or thighs have higher thresholds (low sensitivity).
What is the difference between response expansion and response compression? How do both relate to Stevens’s power law?
Response Expansion: This occurs when an increase in stimulus intensity leads to a disproportionately larger increase in perceived intensity. For example, a small increase in electric shock intensity might feel much stronger.
Response Compression: This happens when an increase in stimulus intensity leads to a smaller increase in perceived intensity. For instance, doubling the brightness of a light might not make it seem twice as bright.
Relation to Stevens’s Power Law: Stevens’s power law describes the relationship between stimulus intensity and perceived magnitude, and it accounts for both response expansion and compression. The law suggests that perception grows as a power function of stimulus intensity, and the exponent in this function determines whether the response is expanding or compressing.
What is signal detection theory? How is it used to predict performance on perception tests?
Signal Detection Theory (SDT) is a framework used to understand how people detect weak signals amidst noise. It focuses on the decision-making process under conditions of uncertainty, recognizing that perception is not a straightforward result of stimuli, but also involves subjective factors like attention, motivation, and expectations.
Use in Perception Tests: SDT predicts how well a person can detect a signal, distinguishing between true detections (hits) and false alarms (mistakes due to noise). It also explains how external factors (e.g., incentives or penalties) can influence performance.
Define the terms criterion and sensitivity. How do they interact in signal detection theory?
Criterion: This refers to the decision threshold a person sets for deciding whether a stimulus is present or not. A conservative criterion means the person will only say the signal is present if they are very sure, resulting in fewer hits but also fewer false alarms. A liberal criterion will lead to more hits but also more false alarms.
Sensitivity: This reflects the person’s ability to distinguish the signal from noise. High sensitivity means that the person can accurately detect the signal, while low sensitivity means that the signal and noise are difficult to differentiate.
Interaction: Sensitivity measures actual perceptual ability, while the criterion reflects the decision strategy. Both interact to determine how often the signal is detected and how often errors (misses or false alarms) occur.
What is visual masking? How is it affected by consistent and inconsistent odors?
Visual masking occurs when the visibility of one visual stimulus (the “target”) is reduced by the presentation of another stimulus (the “mask”), either before or after the target.
Effect of Odors: Research has shown that consistent odors (i.e., odors that match the context or stimulus) can enhance the perception of a target, while inconsistent odors can weaken or disrupt perception, altering the effectiveness of visual masking.
Effect of odors
An example of the effect of odors can be found in how ambient scents influence consumer behavior in retail environments.
Imagine you walk into a bakery that uses a consistent, pleasant vanilla scent in the air. The vanilla scent is congruent with the type of products being sold (cakes, cookies, pastries). Studies have shown that such congruent scents can enhance the perception of the products’ freshness and sweetness, increase sales, and even make the overall environment more enjoyable, leading to longer browsing times and a greater likelihood of making a purchase.
On the other hand, if the bakery used an inconsistent odor, like the scent of cleaning chemicals or something unrelated like pine, it could negatively affect the experience. The incongruent scent might distract from the perception of the baked goods and reduce the likelihood of purchases, even if the quality of the products remains the same.
How is an audiogram used to assess hearing loss? How might an audiogram help an audiologist program a hearing aid?
An audiogram is a graph that represents an individual’s hearing ability across different frequencies. It shows the softest sounds that can be heard at various pitches, which helps assess the degree and type of hearing loss.
Use for Programming Hearing Aids: An audiogram helps audiologists fine-tune hearing aids by identifying the specific frequencies where hearing is diminished. The hearing aid can then be adjusted to amplify sounds more effectively at those frequencies, improving hearing for the individual in everyday environments.
