L1-L3 Flashcards
Perceptual illusion
a difference between what is perceived and what is physically present in the world
Optical illusion
a difference between what is in the retinal image and what is physically present in the world
Sensation
the ability to detect a stimulus and turn that detection into a private experience
Perception
the act of giving meaning/purpose to those detected sensations
3 stages of the sensation process
physical stimulus, physiological response, sensory experience
Examples of techniques for studying the physiological response from a physical stimulus
animal single-unit recording, human brain imaging (e.g. MEG, PET, fMRI, ERPs)
Examples of techniques for studying the sensory experience from a physiological response
animal lesion studies, human clinical studies, human brain imaging
What is Fechner’s contribution to psychology?
invented psychophysics and believed to be the true founder of experimental psychology
Psychophysics
the science of quantifying the relationship between physical and psychological experiences
Just noticeable difference (JND)
i.e. difference threshold
the smallest change in a stimulus or difference between stimuli that can be detected 50% of the time
bigger JND needed for heavier standard weights relative to comparison
Absolute threshold
minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time
Psychometric function
a graph of stimulus value (e.g. intensity) on the horizontal axis versus the subject’s responses (e.g. proportion of “yes”) on the vertical axis
ogive or typical S shape
Weber’s law
the size of the JND or the difference threshold (△I) is a constant proportion (K) of the physical magnitude of the stimulus (I)
△I = KI
Fechner’s law
a principle describing the relationship between stimulus magnitude and the resulting sensation magnitude (i.e. scaling)
S = KlogR
What does Fechner’s law predict?
stimulus intensity increases more rapidly than sensation intensity (i.e. a larger change is needed to produce a JND in sensation as stimulus intensity increases)
Magnitude estimation
easier method for psychophysical scaling, wherein a participant assigns a number to describe stimulus intensity
What do magnitude estimation experiments show?
once detected, the sensory magnitude of a stimulus increases with its physical magnitude, within limits
Steven’s power law
the magnitude of subjective sensation (i.e. perceived intensity) is proportional to stimulus magnitude raised to an exponent (or power)
S = aI^b
2 possible reasons for the discrepancy between Fechner’s law and Steven’s law
assumption that all JNDs are perceptually equal (Fechner’s) is violated for some sensory modalities; magnitude estimation is more subjective than determining JNDs
3 classical psychophysical methods
method of constant stimuli, method of limits, method of adjustment
Discrimination
the ability to tell the difference between two stimuli or if a stimulus has changed
Suprathreshold stimulus
above the absolute threshold so always detectable
Method of constant stimuli
standard and comparison stimuli presented together; magnitude of comparison (above and below standard) varies randomly from trial to trial
Formula for JND
(upper limit - lower limit)/2
Method of limits
standard and comparison stimuli are presented together, and you alternate between descending and ascending series while varying the starting point in each
Method of adjustment
observer adjusts the comparison stimulus until it matches the standard stimulus while the experimenter randomly varies the starting point
Advantages of method of constant stimuli
accurate and repeatable threshold values
Disadvantages of method of constant stimuli
time-consuming; not good for children or clinical patients; not good for tracking thresholds over time; lots of data collected far from threshold
Advantages of method of limits
saves time and not necessary to trace out the entire psychometric function
Disadvantages of method of limits
habituation error (making the same response repeatedly) and anticipation error (changing response after a fixed number of trials)
How to reduce habituation and anticipation errors in the method of limits?
alternate the series (requires extra series) and vary the starting point in each (requires extra stimulus levels)
Advantages of method of adjustment
quick and participants like it
Disadvantages of method of adjustment
not very accurate or repeatable
2 modern improvements to the classic psychophysical methods
staircase method and 2-alternative forced-choice paradigm
Staircase method
increase (or decrease) intensity of stimulus in equal steps until it can (or can’t) be detected
Absolute threshold in the staircase method
the average of the cross-over points at response reversals
Adaptive function of the staircase method
stimuli intensity keeps hovering around the absolute threshold by adapting the test sequence to the participant’s responses
Advantages of using the staircase method
efficient, most data collected around the threshold (adaptive!), can be used to track threshold changes over time
How do you reduce habituation and anticipation errors in the staircase method?
use randomly interleaved descending (strongest to weakest stimulus intensity) and ascending staircases
What is the difference between a yes/no paradigm and the 2-alternative forced-choice paradigm?
former is subjective and the participant has to report whether they can detect or discriminate a stimulus; latter is more objective and the participant must prove that they can detect or discriminate the stimulus
e.g. Was the tone in the first or second interval? (detection) or in which interval are the 2 tones different? (discrimination)
Advantages of using a 2-alternative forced-choice paradigm
accurate thresholds and reduces non-sensory differences among participants (bias or criterion differences)
Cross-modality matching
scaling method in which the intensities of sensations that come from different sensory modalities are matched (e.g. brightness and loudness)
How does the signal detection method provide a bias-free estimate of sensitivity?
the use of a 2-alternative forced-choice paradigm reduces perceiver bias/criterion because bias is measured directly
2 factors affecting perceptual measurements in signal detection method
motivational state and sensory capacities of the perceiver
Catch trials
trials in a signal detection experiment wherein the stimulus/signal is absent
Sensitivity
the ease with which a perceiver can tell the difference between the presence and absence of a stimulus
d’
the statistic that reflects a perceiver’s sensitivity
What happens to the response outcome as you reduce stimulus intensity in a signal detection experiment?
reducing stimulus intensity decreases sensitivity (d’), so you make less hits and more false alarms
2 reasons why people make false alarms
endogenous noise and criterion (β)
Endogenous noise (sensory)
spontaneous neural activity that affects the measurement of thresholds and sensitivity
Criterion (β)
response bias within a perceiver that depends on expectations and motivation
level above which sensation is attributed to the signal and not the noise
How can you manipulate criterion in a signal detection experiment?
varying the stimulus probability or expectations
What happens to the response outcome as you reduce stimulus probability
reducing stimulus probability increases criterion strictness or β (e.g. say “no” more so low hits and false alarms) but doesn’t affect sensitivity (d’)
