Measuring Behavior, Cognition and Perception Techniques for learning how the brain works Lesion...
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Transcript of Measuring Behavior, Cognition and Perception Techniques for learning how the brain works Lesion...
Techniques for learning how the brain works
• Lesion• Clinical case studies• Electrical brain stimulation• Transcranial magnetic stimulation• Recording gross electrical activity (ERP)• Single cell recording• Neuropharmacology• Brain imaging• Experimental psychology
Techniques for learning how the brain works
• Lesion• Clinical case studies• Electrical brain stimulation• Transcranial magnetic stimulation• Recording gross electrical activity (ERP)• Single cell recording• Neuropharmacology• Brain imaging• Experimental psychology
Classical and operant conditioning
Psychophysics
Reaction time
Epistemology - the origins of knowledge
• nativism - the order we perceive in nature is the order our minds impose on nature
Epistemology - the origins of knowledge
“Imagine a man born blind and taught by his touch to distinguish between a cube and a sphere. If the blind man were made to see,
would he be able to distinguish the two shapes based on sight alone?”
“The blind man would not be able to say which was the globe and which the cube
whilst he only saw them.”
Naïve Realism - the world is as the world appears to the mind;
all ideas and perceptual experiences are creations of the
mind“All the choir of heaven and furniture of the earth … have not any subsistence
without a mind, that their being is to be perceived or known.” (
recall Whitehead’s quote)
“ [objects] are perceived as with qualities that in reality do not belong to them, qualities which are
in fact purely the offspring of the mind. Thus nature gets credit which should in truth be
reserved for ourselves: the rose for its scent; the nightingale for his song; and the sun for its
radiance. The poets are entirely mistaken. They should address their lyrics to themselves and
should turn them into odes of self-congratulations on the excellency of the human
mind. Nature is a dull affair, soundless, scentless, colourless; merely the hurrying of
material, endlessly, meaninglessly.”
Science and Medicine
Johannes Muller (1801-1858)
Law of Specific Nerve Energies
• one is directly aware of nerve impulses, not external world (recall Mountecastle’s quote)
• different nerves/brain areas create different sensations
• same stimulus applied to different nerves elicits different sensations
• different stimuli applied to same nerve elicit same sensation
Science and Medicine
Gustav Fechner (1801-1887)
Elements of Psychophysics
• consumed with relation of mind to brain
• variations in mental intensity is proportional to variations in physical intensity (∆I/I) = constant
• formulated psychophysical techniques
Experimental Psychology
Wilhelm Wundt (1832-1920)
Structuralism
• established first laboratory for experimental study of psychology (1879)
• study of consciousness and perception
Experimental Psychology
Ivan Pavlov (1849-1936)
Classical conditioning
• established technique for behaviorally studying non-human species
• study of stimulus discrimination
Strategies for Studying Perception
• What do things look like? (phenomenology)• What are the limits to perception? (thresholds)• What are the scaling properties of perception (ME &
MDS)• When does perception produce mistakes (study of
illusions)• Where in the brain does perception occur? (fMRI)• When does perception fail? (clinical neurology)• How does perception vary among individuals and
among species?
Phenomenology
Colors appear more saturated toward dusk
Moon looks larger when on the horizon
High frequency sounds are more difficult to localize
Food tastes bland when your nose is stopped up
Object size influences perceived weight
Viewing real motion subsequently produces experience of illusory motion
QuickTime™ and aAnimation decompressorare needed to see this picture.
PsychophysicsInvented by Gustav Fechner in 1860
Three measures of importance:
• absolute threshold - the lower limit of perception; weakest stimulus that can just barely be detected• difference threshold - smallest reliably discriminable difference between two stimuli
• point of subjective equality - magnitude of one stimulus at which it is perceived as equivalent in magnitude to another
• absolute threshold - the lower limit of perception; weakest stimulus that can just barely be detected
• point of subjective equality - magnitude of one stimulus at which it is perceived as equivalent in magnitude to another
Techniques for Measuring Thresholds and PSEs
method of adjustment - person adjusts stimulus to value where it is barely detectable (absolute threshold) or adjusts one stimulus until it matches another (difference threshold/PSE)
method of limits - experimenter changes stimulus by small amounts to find point where person’s judgment of stimulus first changes
method of constant stimuli - present stimuli (or pairs of stimuli) one at a time; person responds “yes” or “no” following each presentation, generating a psychometric function
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100001000100
Frequency (Hz)
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Stimulus intensity
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Stimulus intensity
A psychophysical function from a set of psychometric functions
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864200.00
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Stimulus intensity
Problem of criterion
“.. we must never take a person’s testimony, however sincere, that he has felt nothing, as proof positive that
no feeling has been there.” W. James, 1890
Problem of criterion
• perceptual decisions are influenced not only by person’s sensory abilities but by the individual’s motivations and expectations• willingness to say “yes” or “no” in threshold experiments depends on the consequences of those responses (rewards and costs)• willingness to say “yes” or “no” depends on likelihood (i.e., the probability) of an event• performance differences among people (or among groups of people) could be attributable, in part, to criterion differences
• Set of assumptions and procedures for measuring perceptual performance (decision making) under conditions of uncertainty, the goal being to distinguish performance changes/differences attributable to sensitivity vs criterion
• Applies to any situation where a binary decision must be made under conditions of uncertainty or doubt - make an observation and draw a conclusion
Signal Detection Theory (SDT)
- detecting faint sounds (e.g., murmur heard through stethoscope)
- diagnosing X-ray images (e.g., “is it a tumor?”)
- interpreting “blips” on a radar screen (“plane vs flock of birds”- stock market transactions (“buy or sell?”)
- jury decision (“innocent vs guilty”)
- deciding whether or not two lines are identical in length
Accused is guilty
Accused isinnocent
Jury decision
correctverdict Error
guiltyinnocent
correctverdictError
• Discrete observations occasioned by presence of “noise” only or “signal plus noise”
- “noise” is anything that complicates detection of “signal” by introducing uncertainty about whether or not the signal is present
distracting background noise in a hearing task
misleading evidence in a legal trial
flock of birds on a radar screen
scar tissue on a mammogram
- Strength of signal relative to background level of noise- Person’s sensitivity to the signal- Relative frequency of occurrence of the signal- Person’s level of motivation- Costs associated with hits and false alarms
Signal detection theory measures sensitivity independent of criterion - Assume each observation produces given amount of information - Amount of information varies from observation to observation - Person “measures” the amount of information on each trial and decides whether signal was present or notFour possible outcomes:
- Signal was present and person says “yes” - HIT- Signal was present and person says “no” - MISS- Signal was not present and person says “no” - CORRECT REJECTION- Signal was not present and person says “yes” - FALSE ALARM
Factors that influence person’s willingness to say “signal present”
“noise” “signal + noise”
Magnitude of sensory response
Strong response -- signal highly likely
Weak response -- signal highly unlikely
Magnitude of sensory response
criterion
“false alarm”
“correct rejection”
“Signal absent”
“no” “yes”
Magnitude of sensory response
criterion
"no"
stimulus event
person'sresponse
hit falsealarm
miss correctrejection
present absent
"yes"
criterioncriterion
Magnitude of sensory response
criterion
"no"
stimulus event
person'sresponse
hit falsealarm
miss correctrejection
present absent
"yes"
Psychophysical Scaling Techniques
Scaling - establishment of a quantitative metric expressing the relation among a sequence of stimuli. Scaling involves the assignment of numbers (scale values) to psychological attributes
Nominal scales - arbitrary assignment of numbers to objects, with no order implied; nominal scale values simply identify or categorizeOrdinal scales - objects arranged according to the order of their magnitudes (e.g., smallest to largest ), but with no reference to the spacing between stimuli; ordinal scale items obey the principle of transitivity: if a<b and b<c, then a<c
Interval scales - ordered stimuli in which the magnitude of the differences among various stimuli is meaningful
Ratio scales - ordered stimuli in which magnitude and ratio of values is meaningful
Just noticeable differences and psychological scales
Perceived size measured using the method of paired comparisons
Ratio Scaling of Sensory Experience: Magnitude Estimation
Magnitude estimation is a procedure where people directly assign numbers to stimuli in proportion to the perceived intensity of those stimuli. The procedure allows us to study the way in which perceived intensity grows with physical intensity. People are assumed to be “instruments” that can directly measure themagnitude of a sensory event.
Magnitude Estimation: Loudness
Assign a number proportional to the loudness of the following
sound bursts
.
Physical unit of measurement
painsize
loudness
• works for psychological variables where there exists one underlying dimension that can be scaled in physical units
Learning about Perception From Studies of Nonhuman Subjects
• reflex reactions (e.g., alarm calls)
Altered alarm whistle (blank)
Normal alarm whistle
Altered alarm whistle (noise)
Learning about Perception From Studies of Nonhuman Subjects
• reflex reactions (e.g., curiosity)
QuickTime™ and aSorenson Video decompressorare needed to see this picture.
Learning about Perception From Studies of Nonhuman Subjects
• reflex reactions (e.g., alarm calls)
• operant conditioning (discrimination training)
Learning about Perception From Studies of Nonhuman Subjects
• reflex reactions (e.g., alarm calls)
• operant conditioning (discrimination training)
Learning about Perception From Studies of Nonhuman Subjects
• reflex reactions (e.g., alarm calls)
• operant conditioning (discrimination training)
Reaction time: A Behavioral Index of Mental Events
Hermann von Helmholtz (1821-1894)
Treatise on Physiological Optics
• measured the speed of neural impulses (27 m/sec)
• developed trichromatic color theory
• developed pitch theory of hearing
• proposed that perception involves unconscious inference
Reaction time as an index of cognitive processing
Same/Different judgments: reaction time on speeded decisions reflects stages of processing
Mental Rotation: Use of reaction time to study mental imagery
.
deviation from upright (degrees)
0 9090180 180CCW CW
Use of RT together with error rate data to draw inferences about mental processing. Try
this simple color naming test:xx xx xx xx xx xx
The Stroop Effect: A Demonstration of Attentional Interference
Discovered by John Ridley Stroop, PhD Peabody College 1933 (his
dissertation)
Using RT to study attention: See if you notice anything strange happening in the scene I’m about to show
you?
You will be shown list of words divided into two columns. Do your best to memorize these words; your ability to remember them will be tested in a
moment
Learning from Mistakes: Patterns of Errors Reveal Properties of the Structure of Memory
• Bed• Rest• Awake• Tired• Dream• Wake• Snooze• Blanket• Slumber• Snore• Nap• Yawn• Drowsy
• Hot• Snow• Warm• Winter• Ice• Wet• Frigid• Chilly• Heat• Weather• Freeze• Air• Shiver
Now the test! As I call off the words in the next slide, say out loud “yes” or “no” to indicate
whether or not the word was among the ones you memorized.
• Snore• Heat• Dance• Tired• Dream• Balloon• Snooze• Blanket• Breakfast• Slumber• Fever• Sleep• Lawn• Frigid• Shiver
• Frost• Guide• Snow• Warm• Winter• Flower• Wet• Belt• Chilly• Family• Cold• Freeze• Air• Shave• Awake
• Snore• Heat• Dance• Tired• Dream• Balloon• Snooze• Blanket• Breakfast• Slumber• Fever• Sleep• Lawn• Frigid• Shiver
• Frost• Guide• Snow• Warm• Winter• Flower• Wet• Belt• Chilly• Family• Cold• Freeze• Air• Shave• Awake
False memories created by context
The more mental effort required by a task, the longer it takes to complete the task but the more long lasting the effects:"Depth of Processing" Demonstration
You will be shown a list of words. Read through the list quickly and for each word silently name a synonym
for that word.
apple = fruitsimple = easy
You will be shown a list of words. Read through the list quickly and for each word silently name the
font in which the word is printed.
apple = "Courier"simple = "Chicago"
Now you're going to see a longer list of words. As I call off the
word, you yell out whether it's an "old" word (one that
appeared on the previous list) or a "new" one.
Which of these were on the previous list?
_ flower_ chalk_ leaves_ derivative_ alley_ smart_ garage_ orange_ delicate_ easy
_ children_ damage_ trumpet_ victory_ duck_ glamour_ jingle_ butter_ snow_ nurse
“deep” processiing promotes retention