MT 1 Flashcards
perceptual illusion
a discrepancy between what is perceived and what is physically present in the real world
optical illusion
a discrepancy between what is in the retinal image and what is
present in the real world
e.g., rainbow
you are viewing what is on your retina accurately
what’s the difference between perception and sensation
- sensation: ability to detect a stimulus, and perhaps to turn that detection into a private experience
- perception: giving meaning to a detected sensation
psychophysics
- the science of defining quantitative relationships between physical and psychological (subjective) events
- Psychophysics is interested in what the brain is doing, not how it does it… so it ignores the physiological response stage
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 “yes”) on the vertical axis
ogive
the typical s-shape of a psychometric function
list the techniques available to study each step of the sensory
process
-
physical stimulus –> physiological response
- mostly animal single-unit recording
- magnetoencephalography
- positron emission tomography
- functional magnetic resonance
- imaging event-related potentials -
physiological process –> sensory experience
- animal lesion studies
- human clinical studies
- human brain imaging -
physical stimulus –> sensory experience
- behavioural techniques
difference threshold
the smallest difference between stimuli or change in a stimulus that the observer noticed 50% of the time (also called a just noticeable difference [JND])
suprathreshold stimulus
for sensory discrimination, this is above the absolute threshold and is always detectable
what are the main differences between measuring DETECTION thresholds with the method of constant stimuli, the method of limits, and the method of adjustment
how to use the method of constant stimuli to measure detection thresholds
- select stimulus intensities above and below expected threshold
- present many trials of each intensity in random order
- plot psychometric function; read 0.50 (or 50%) detected point from graph
- what is the weakest stimuli you can detect?
- the lower the absolute threshold, the higher the person’s sensitivity
how to use the method of limits to measure detection thresholds
- starts with the descending series: stimulus intensity decreased in equal steps until response changes to “no”
- after, it changes into an ascending series: stimulus intensity increased in equal steps until response changes to “yes”
- alternate between ascending & descending series; vary start point
- crossover point calculated for each series
- when the yes changes to no, or vice versa
- absolute threshold is the average of all crossover points
how to use the method of adjustment to measure detection thresholds
- observer adjusts stimulus intensity, using a potentiometer, until it is just detectable
- potentiometers you can encounter everyday… eg, volume dial
- experimenter randomly adjusts starting point (position of potentiometer)
- calculate average (mean) of these threshold adjustments
who was Fechner and what did he do
- Fechner’s use of Weber’s findings to describe sensation
- Fechner’s Law: a principle describing the relationship between stimulus magnitude and
resulting sensation magnitude (scaling)
what are the classical methods of psychophysics
What is Fechner’s Law? What is it’s equation?
Fechner’s Law: a principle describing the relationship between stimulus magnitude and resulting sensation magnitude (scaling)
as stimulus intensity increases, sensation intensity increases rapidly at first, but then more slowly
S = k log R
S = sensation intensity
k = Weber fraction
R = stimulus level
what is magnitude estimation
participant assigns a number to describe stimulus intensity
- demonstration: whiteness of standard dot pattern is 100
- An easier technique!
* assign number to perceived whiteness of each comparison dot pattern
* more white should be >100; less white <100
What is Stevens’ power law
the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent (or power)
- all of these can be described using stevens’ power law
- S = aIb
- S = sensation
- a= constant
- I = stimulus intensity
- b = exponent (determines the shape of the curve) … this is what changes between different stimuli
what is cross-modality matching
a scaling method in which the intensities of sensations that come from different sensory modalities are matched
where are catch trials, and what does hit or miss mean in this context
trials in a signal detection experiment on which the stimulus/signal is absent
- hit: signal present; sensory activity to the right of criterion
- miss: signal present; activity to the left of criterion
what is sensitivity in the context of detecting signals
- ease with which a perceiver can tell the difference between the presence and absence of a stimulus
- depends on overlap of signal absent and signal present distributions
- doesn’t depend on motivation!
what is the difference between a false alarm and a correct rejection, and how does this relate to a hit or miss
both are when the signal is absent
false alarm: response yes
correct rejection: response no
what is the statistic d’
- the statistic that reflects a perceiver’s sensitivity (not usually calculated by hand)
- hits and false alarms should be equal if the participant cannot tell the difference between stimuli
what is endogenous noise
- spontaneous neural activity; affects measurement of thresholds & sensitivity
what is criterion
- Beta
- response bias within a perceiver; depends on expectations & motivation
- can manipulate this within an individual person by messing with their expectations and motivation
What is Beta and what does it relate to?
beta is criterion
relates to degree of response bias within a perceiver
the bigger the beta, the more strict the criterion
How does Fechner’s law relate to Weber’s law? give a definition of both laws
Fechner’s Law: a principle describing the relationship between stimulus magnitude and resulting sensation magnitude (scaling)
what is a magnitude estimation experiment? How does this relate to Stevens’ power law?
- participant assigns a number to describe stimulus intensity
- magnitude estimation experiments showed that once detected, the sensory magnitude of a stimulus increases with its physical magnitude, within limits but rate of increase varies with different sensations
- different for different sensory modalities
explain the discrepancy between Stevens’ and Fechner’s scaling results
Stevens’ law and Fechner’s law predict the same scaling result for sensory modalities in which b < 1, but not for other sensory modalities
- they match up only for some sensory modalities
possible reasons for the discrepancy:
* Fechner’s law assumes that all JNDs are perceptually equal, but this law is violated for some sensory modalities
* magnitude estimation is more subjective than determining JNDs
what are the 4 classes of responses in a signal detection experiment
- hit
-miss - false alarm
- correct rejection
State the difference between sensitivity (d’) and criterion (ß), and describe the effect of stimulus probability on each
- sensitivity is the ease with which a perceiver can tell the difference between the presence and absence of a stimulus
- criterion is like alpha–it’s the point at which the perceiver decides that X is a real sound and not them hallucinating
Describe signal detection theory in terms of the hypothetical distributions underlying performance. Show how d’, criterion, hits, false alarms, misses and correct rejections are represented on these distributions
- assumes that endogenous noise (N) has a normal (bell-shape) distribution
- N represents sensory activity during catch trials
- when signal is present, it adds to the noise (S+N)
- sensory activity for signal + noise is, on average, more intense than noise alone
- but noise can produce sensation as strong as that produced by the signal (could be endogenous + external noise)
- it can change due to fatigue or external noise
receiver operating characteristic (ROC) curve
raphical plot of hit rate as a function of false
alarm rate for different criterion values in a signal detection experiment; d’ is constant and
criterion is changing along each curve
transduction
how energy in the environment gets transformed into electrical energy by the nervous system
information processing
what happens to the electrical signals as they travel through the nervous system to the brain
sensory coding
how the brain understands what the electrical signals reaching it mean
doctrine of specific nerve energies
- the nature of a sensation depends on which nerves are stimulated, not on how the nerves are stimulated
- seems logical because neural signals are identical across sensory modalities
synapse
junction between neurons that permits information transfer
neurotransmitter
chemical substance used in neuronal communication at synapses
action potential
rapid depolarization of membrane potential
lesion
compression
air molecules bunch together (high air pressure)
rarefaction
air molecules spread apart (low air pressure)
phase
part of cycle the sound pressure wave has reached at a given point in time; measured in degrees ̊
amplitude
maximum pressure change of wave above normal
frequency
rate of fluctuation of sound pressure; measured in cycles/second or Hertz (Hz)
sound pressure
sound pressure level
sound pressure level (amplitude or intensity)
- relative measure
- ratio of sound pressures converted to log scale–decibels (dB)
dB = 20 * log (P/Po) or dB = 10 * log (P2/Po2)
(P is sound pressure of tone; Po is reference pressure of 0.0002 dynes/cm2 or 0.00002 pascal)
Define receiver operating characteristic (ROC) curve, and describe how sensitivity and
criterion are represented
List the 7 sensory cranial nerves and show how they illustrate the doctrine of specific nerve
energies
7 pairs of cranial nerves carry sensory information
sensory only
- Olfactory (I)
- Optic (II)
- Vestibulocochlear (VIII) - auditory + vestibular nerves
sensory & motor
- Trigeminal (V)
- Facial (VII)
- Glossopharyngeal (IX)
- Vagus (X)
doctrine of specific nerve energies: e.g. stimulation of optic nerve, by light or a finger, produces the sense of vision
Define synapse, neurotransmitter and action potential, and describe how neurons communicate
with each other
- presynaptic neuron sends electrical impulse to the postsynaptic neuron
Compare and contrast the 4 neuroimaging techniques for studying human brain function.
- event-related potentials
- eegs
- good temporal resolution, bad spatial resolution
- magnetoencephalography
- similar to EEGs but uses magnets
- good temporal resolution, even better than EEG
- good spatial resolution if used with MRI
- positron emission tomography
- functional magnetic resonance imaging
- bad temporal resolution
- good spatial resoltuion
Indicate frequency, amplitude and phase on a diagram of a simple sine wave, and define sound
pressure level. List the units of measurement for each feature
- frequency: rate of fluctuation of sound pressure; measured in cycles/second or Hertz (Hz)
- phase: part of cycle the sound pressure wave has reached at a given point in time; measured in degrees ( ̊ )
- amplitude: maximum pressure change of wave above normal
- atmospheric pressure; several different units (see slide 27)
Describe 4 types of computational models that have been applied to the study of sensation and
perception
Fourier’s theorem
most sounds are complex and can be described as a set of sine waves
Fourier analysis
mathematical procedure for separating a complex pattern into component sine waves that vary over
fundamental frequency
lowest sine-wave frequency in a complex sound; usually determines perceived pitch
harmonics
higher frequency sine-wave components; integer multiples of fundamental frequency
timbre
differences in frequency & amplitude of harmonics determines psychological attribute of quality
impedance matching
middle ear amplifies sound energy to reduce loss due to reflection at oval window (air/fluid boundary)
acoustic reflex
in response to prolonged loud sounds, tensor tympani & stapedius muscles contract to reduce magnitude of auditory signal transmitted to inner ear
afferent fibres
- afferent fibres carry sensory information to central nervous system
- 90% connected to inner hair cells (Type I)
- 10% connected to outer hair cells (Type II)
efferent fibres
- carry information from central nervous system to inner ear
- comprise most neurons synapsing with outer hair cells
graded potential
slow change in membrane voltage that varies in size (not all-or-nothing); occurs in hair cells
List the normal human range for sound frequency. Name the psychological properties corresponding to sound frequency and to sound pressure level, respectively.
- Humans: 20-20,000 hz
Define Fourier’s theorem and Fourier analysis, and relate these concepts to complex sounds and timbre.
- Fourier said that all sound waves are a set of mixed sine waves.
- pure sounds is just one sine wave, but complex sounds are multiple
- timbre is due to differences in frequency and amplitude
Describe 2 ways in which the middle ear functions to amplify the sound pressure reaching the inner ear.
- impedance matching: middle ear amplifies sound energy to reduce loss due to reflection at oval window (air/fluid boundary)
- ossicles act like levers, increases force at stapes by a factor of 1.3 (like a teeter totter)
Define the acoustic reflex and name the 2 muscles involved.
in response to prolonged loud sounds, tensor tympani & stapedius muscles contract to reduce magnitude of auditory signal transmitted to inner ear
Compare and contrast the anatomical arrangement and innervation of the inner and outer hair cells.
Describe the transduction of mechanical energy into action potentials in the cochlea.
- hair cells have no axons, but release neurotransmitter at synapse with dendrites of auditory nerve fibres
- axons of auditory nerve fibres form auditory (cochlear) nerve [part of 8th cranial vestibulocochlear nerve]
- transduction occurs when stereocilia are bent
- when basilar membrane moves up & down, hair cell stereocilia bend back & forth against tectorial membrane
Describe the response of the basilar membrane to sounds of different frequencies.
what is the process of sensation
physical stimulus –> physiological response –> sensory experience
what is the difference between difference thresholds and absolute thresholds
both are trying to find the minimal stimulus where the participant can detect the stimulus 50% of the time….
but the absolute threshold is purely about detection
whereas the difference threshold is about when the participant can detect the difference between 2 stimuli
what is the benefit of using the method of limits to study sensory detection
Saves time because you don’t need to find the psychometric function! Here, you can just narrow in on the absolute threshold
how to use the method of constant stimuli to study sensory DISCRIMINATION
- standard (fixed value) and comparison (value changes) stimuli presented together
- magnitude of comparison (values above & below standard ) varied in random order with many trials of each value
- plot proportion “bigger” responses versus comparison magnitude
pros and cons of using the method of constant stimuli to study sensory DISCRIMINATION
advantages
- accurate & repeatable threshold values
disadvantages
- time consuming
- not good for tracking thresholds that change over time
- not good for children or clinical patients
- lots of data collected far from threshold (inefficient)
how to use method of limits to study sensory discrimination
- standard and comparison stimuli presented together
- descending series: comparison decreased in equal steps until response
- changes from “stronger” to “equal” to “weaker”
- 2 stimuli, but this trial order is not random
- ascending series: comparison increased in equal steps until response
- changes from “weaker” to “equal” to “stronger”
- alternate between descending & ascending series; vary starting point
- upper limit is crossover point between “stronger” & “equal” on each series
- lower limit is crossover point between “equal” & “weaker” on each series
what is subjective equality
measure of accuracy
pros and cons of the method of limits for sensory discrimination
Advantages
* Saves time(efficient);
* don’t have to trace out whole psychometric function
disadvantages
* error of habituation
* make same response too many times
* (alternate the series to reduce; requires extra series)
* Error of anticipation
* change response after fixed number of trials
* (vary starting point to reduce; requires extra stimulus levels)
what is the method of adjustment for sensory discrimination
- observer adjusts comparison stimulus until it matches the standard stimulus
- experimenter randomly varies starting point
- Main difference is that the participant is now in charge
pros and cons of the method of adjustment
advantages
* quick
* participants like it
disadvantages
* not very accurate or repeatable
* used to get initial idea of where a threshold is… and then the experimenters use another method
* not used as much due to inaccuracy
how is JND and PSE calculated for the 3 types of experiments
pros and cons of the method of adjustment
advantages
* quick
* participants like it
disadvantages
* not very accurate or repeatable
* used to get initial idea of where a threshold is… and then the experimenters use another method
* not used as much due to inaccuracy
describe the staircase method and its problem
- starts out like method of limits
- stimulus intensity decreased (or increased) in equal steps until stimulus can’t be detected
- then, stimulus intensity increased (decreased) until stimulus can be detected, etc.
- adaptive method - stimuli kept hovering around threshold by adapting test sequence to participant’s responses
- change what’s given to the participant based on what they say that they can see
what is a response reversal?
point where a response changes
run ends after fixed # of reversals or fixed # of trials
what is an absolute threshold in the context of the staircase method
is the average of the cross-over points at response reversals (eg. 63.5, 63.5, 61.5, 61.5)
advantages and disadvantages of the staircase method
advantages
* efficient;
* most data collected around threshold
* other methods have you collect data far from thresholds
* can be used to track threshold changes over time
disadvantages
* errors of anticipation and habituation… the same as the method of limits
what are some modern improvements to the staircase method
to avoid anticipation and habituation errors, randomly interleaved descending and ascending staircases can be used
yes/no paradigm
everything you’ve seen so far
- participant reports presence or absence of stimulus (detection) or stimulus difference (discrimination)
- very subjective
- experimenter can’t verify or dispute participant’s response
2-alternative forced-choice paradigm
- more objective
- participant must prove they can detect or discriminate the stimulus
- detection - “is the circle on the left or the right?”; “was the tone in the first or second interval?”
- discrimination – “in which interval are the 2 stimuli different?”
advantages of the 2-alternative forced-choice paradigm
- more accurate thresholds
- reduces non-sensory differences between participants (bias or criterion differences)
what is Weber’s law
Weber’s law: the difference threshold is a constant proportion of the physical magnitude of the stimulus
DI = k I
DI is the difference threshold (JND)
I is the physical magnitude of the stimulus
k is a constant that depends on the sensory system
what does a small beta produce?
- lax criterion
- high hits and low false alarms
what does a large beta produce?
- strict criterion
- low hits and low false alarms
how does motivation affect signal detection theory
- affects criterion, not sensitivity
- strong motivation = small beta
describe EEG
- electrodes on scalp;
- subject performs perceptual task
- non-evasive
- measures populations of neurons
- when EEG action and it’s related to a task, it’s called an event-related potential
describe an MEG
- is also about electronic energy around neurons
- contains magnetometers
o arrays of superconducting quantum interference devices (SQUID) - measures magnetic fields created by the flow of ion currents between neurons
- high temporal resolution; use with MRI for good spatial resolution
o better temporal resolution compared to EEG! - difficult to measure signals deep in brain
positron emission tomography (PET)
- as tracer decays, positrons are emitted and picked up by scanner
- areas of high radioactivity are associated with neural activity (based on blood flow)
- good for studying disease or brain chemicals
- poor spatial resolution, but can be improved if used with MRI
- invasive procedure
functional magnetic resonance imaging (fMRI)
- non-invasive procedure;
- best spatial resolution;
- response changes very slowly
- neural activity -> blood flow and volume -> oxygen consumption -> oxygen in venous blood (gets redder) -> stronger MRI signal
what is phase often used for
to compare the timing of 2 sound waves
