PSYC 367: Sensory Systems - Quiz 1

what are the steps of the sensory process?

what are the steps of the sensory process?

physical stimulus → physiological response → sensory experience

• easiest to study physical stimulus to sensory experience, skipping physiological response (just ask participant what they are sensing)

sensation

ability to detect stimulus and turn detection into a private experience

perception

giving meaning to a detected sensation

studying physical stimulus to physiological response

• Animal single-unit recording

• Human brain imaging (magnetoencephalography, positron emission tomography, functional magnetic resonance imaging, event-related potentials

  difficult to study, expensive, specialized

studying physiological response to sensory experience

• animal lesion studies

• Human clinical studies, human brain imaging

methods for studying sensation (textbook)

1. thresholds

2. scaling (measuring private experience

3. signal detection theory (measuring difficult decisions)

4. sensory neuroscience

5. neuroimaging

6. computational models

Gustav Fechner (1801-1887)

pioneer of psychophysics, true founder of experimental psychology - preliminary work relating changes in physical world to changes in psychological experiences

• invested in relationship between mind and matter - believed consciousness to be present in all nature (panpsychism)

His methods are still used today:

• absolute threshold

• psychometric function

• method of limits

• method of adjustment

• method of constant stimuli

psychophysics

formally describing relationship between sensation and energy that gives rise to sensation - proposed by Fechner (inspired by Weber)

absolute threshold for detection

minimal amount of stimulation necessary to just detect presence of a stimulus 50% of the time

• lower = higher sensitivity

psychometric function

graph of stimulus value (intensity) on horizontal axis versus subject’s responses (proportion of yes or no) on vertical axis

• vary depending on the person and the moment

• Ogive = typical S shape of the functions

method of constant stimuli

select stimulus intensities above and below expected threshold - present many trials of each intensity in random order to identify average smallest intensity that can be detected

• standard (fixed value) and comparison (value changes) stimuli presented together

• identify point of psychometric function where stimulus is identified 50% of the time (absolute threshold)

• interested in upper and lower limits - 0.75 point is upper limit, 0.25 point is lower limit read from graph

• JND = (upper limit - lower limit)/2

• 0.50 point is point of subjective equality

difference threshold

size/level of stimulus difference for participant to notice a change between two instalments

advantages of method of constant limits

accurate and repeatable threshold values

disadvantages of method of constant stimuli

• 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)

method of limits

alternate between descending intensity (until participant says they can’t hear) and ascending intensity during trials (until participant can hear) and determine cross-over point between each series (average)

• not necessary to obtain a psychometric function, saves time

• standard and comparison stimuli presented together

• upper limit: crossover point stronger and equal on each series

• lower limit: crossover point between equal and weaker on each series

• JND = (average upper limit - average lower limit)/2

• PSE = (average upper limit + average lower limit)/2

advantages of method of limits

saves time - don’t have to trace out whole psychometric function

disadvantages of method of limits

• error of habituation (make same response too many times)

  • Reduce by alternating the series takes more time

• Error of anticipation (change response after fixed number of trials)

  • Reduce by varying start point on each series — requires extra stimulus levels so becomes less efficient

method of adjustment

observer adjust stimulus intensity using a potentiometer until just detectable - calculate average of threshold adjustments

• adjustment also varies between descending and ascending

• JND = standard deviation of the matches x 0.6745

• PSE = average of matches

method of adjustment advantages

• quick

• participants like it

method of adjustment disadvantages

• not very accurate or repeatable

scaling methods

measuring how strong experiences are

• magnitude estimation

• Steven’s power law

• cross-modality matching

detection experiments

measure absolute thresholds

suprathreshold stimulus

above absolute threshold, always detectable

just noticeable difference (JND)

smallest difference between stimuli or change in a stimulus that observer notices 50% of the time

modern improvements to Fechner’s methods

• staircase method

• 2-alternative forced-choice paradigm

• psychophysical scaling

staircase method

stimulus intensity decreased (or increased) in equal steps until stimulus can’t (or can) be detected, then increased (or decreased) until stimulus can be detected

• keeps going instead of stopping after ability to detect or not detect

• stimuli kept hovering around threhold by adapting test sequence to participant’s response

• response reversal = whenever response changed from yes to no

• ends after fixed # of trials

• absolute threshold = average of cross-over points at response reversal

staircase method advantages

• efficient, most data collected around threshold

• can be used to track threshold changes over time - wouldn’t level off

staircase method disadvantages

• error of anticipation and habituation

  • randomly interleaved descending and ascending staircases can be used to prevent this (2 staircases)

2-alternative forced-choice paradigm

• additive to experimental methods discussed above

• participant has to choose one or the other - prove they can detect (where/when was this)/discriminate (what is different) stimulus

2-alternative forced-choice paradigm advantages

• more accurate threshold

• reduces non-sensory differences between participants (bias or criterion towards saying we detect saying something)

• can be used with method of constant stimuli, method of limits, staircase method, but not method of adjustment

psychophysical scaling

difference thresholds are larger for larger stimuli - identified by Weber

• Weber’s law: ∆I = k I

  • ∆I = difference threshold (JND)

  • I = physical magnitude of stimulus

  • k = constant that depends on sensory system

  • The difference threshold is a constant proportion of physical magnitude of stimulus

• Fechner suggested using JNDs to describe perceived intensity (produce equal steps in sensation)

• In reality, sensory steps at upper end of scale require larger increases in stimulus intensity to get equal sensation increasing steps

Fechner’s Law

principle describing 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 (also = I)

Weber’s Law

∆I = k I

• ∆I = just detectable difference

• k = constant

• I = stimulus intensity

• JND is a constant fraction of the comparison stimulus

numerical example of Weber’s law (ΔI = k I)

• 150 watts is just noticeable different from 100 watts (JND = 50, have to increase by at least 50 to notice a change)

• 450 watts is just noticeable different from 300 watts (JND = 150, have to increase by at least 150 to notice a change)

• k = 0.5 (JND/initial watts value [I])

numerical example of Fechner’s Law

• 150 watts (S = 1.1) looks 0.1 brighter than 100 watts (S = 1.0); ΔS = 0.1

  • k = 0.5

• 450 watts (S = 1.3) looks 0.1 brighter than 300 (S = 1.2); ΔS = 0.1

  • k = 0.5

magnitude estimation

participant assigns number to describe stimulus intensity

• ex. whiteness of standard dot pattern is 100

• sensory magnitude of a stimulus increases with its physical magnitude, within limits, but rate of increase varies with different sensations - curves are different but can be describe with a power law

Steven’s power law

magnitude of subjective sensation is proportional to stimulus magnitude raised to an exponent (power)

• S = aI^b

  • S = sensation

  • a = constant

  • I = stimulus intensity

  • b = exponent (determines shape of curve)

• Exponent value curves line

• identifies sensory modalities that do not follow Fechner’s laws

• Predicts same scaling result as Fechner’s law

• If exponent is less than one, it means sensation grows less rapidly than stimulus

cross-modality matching

scaling method in which intensities of sensations that come from different sensory modalities are matched

signal detection method

quantifies response of an observer to presentation of signal in presence of noise - 2-alternative forced-choice paradigm reduces perceiver bias, bias free estimate of sensitivity

• recognized perceptual measurements are influenced by motivational state/sensory capacities by perceiver (other methods don’t do this) - how we make decisions under uncertainty

• catch trials

• outcome matrix: when stimulus is present 50% of the time

• sensitivity (d’: d prime)

catch trials

trials in a signal detection experiment on which stimulus/signal is absent

outcome matrix (signal detection)

response rate has to add up to 1 (know percentage of Yes, you also know percentage of No)

• no dependent relationship between present and absent scores

• Hit rate and false alarm rate together provide sensitivity measure

sensitivity (d’) (signal detection)

ease with which perceiver can tell difference between presence and absence of a stimulus

• insensitive = hit rate and false alarm rate are equal

• manipulated by changing intensity of the stimuli - ex. lightening/darkening the colour

• depend on overlap of signal absent and signal present distributions

  • distance between means of N and S+N distributions (doesn’t change with changes in criterion

why do people make false alarms? (signal detection)

• endogenous noise: spontaneous neural activity - affects measurement of threshold and sensitivity (sensory reason)

• criterion (𝞫): response bias within a perceiver - depends on expectations and motivation (non-sensory)

  • Manipulating motivation/expectations can change it

  • Bigger the criterion, the stricter it is

  • manipulated by changing the probability of a stimulus appearing (reducing it increases criterion strictness)

signal detection and endogenous noise

when signal is present, it adds to noise (S + N (sensory activity during catch trials))

• sensory activity for signal + noise is on average, more intense than noise alone

• noise can produce sensation as strong as that produced by signal

• criterion is the level above attribution to signal and not to noise

correct rejection

correctly identify signal as absent (activity to left of criterion)

hit

correctly identify signal as present (activity to right of criterion)

miss

incorrectly identify signal as absent (activity to left of criterion)

false alarm

incorrectly identify signal as present (activity to right of criterion)

size of criterion

small = high hits and high false alarms

large = low hits and low false alarms

strong motivation = small beta

receiver operating characteristic (ROC) curves

used to compare performance of two+ tests - curves show a different level of decline/sensitivity - different levels of criterion indicated

• d’ is lower with lighter stimulus

biology of sensation

physiological response to stimulus

• ignored by psychophysics

• transduction

• information processing

• sensory coding

• doctrine of specific nerve energies

• cranial nerves

• synapse

• neurotransmitters

transduction

how energy in environment gets transformed into electrical energy by the nervous system

• different for each energy system

information processing

what happens to electrical signals as they travel

• different routes for each sensory system

sensory coding

how brain understands what electrical signals reaching it mean

doctrine of specific nerve energies (Muller, 1801-1858)

nature of a sensation depends on which nerves are stimulated, not on how nerves are stimulated

• neural signals are identical across sensory modalities and we have specific nerves for each sensory system

cranial nerves

12 pairs of nerves that originate in brain stem or thalamus and reach periphery through opening in the skull

nerve pairs carrying sensory info (7)

• sensory only

  • olfactory (I)

  • optic (II)

  • vestibulocochlear (VIII) - auditory + vestibular nerves

• sensory and motor

  • trigeminal (V)

  • facial (VII)

  • glossopharynegal (IX)

  • vagus (X)

synapse

junction between neurons that permits information transfer

• occurs between axon terminal and dendrites of post-synaptic neuron

neuron electrochemical responses

1. Na⁺ rushes in

2. Inflow of Na⁺ depolarizes adjacent membrane to let more Na⁺ in down the line

3. Neuron recovers by quickly sending K⁺ out of the cell to get back to resting potential

neurotansmitter

chemical substance used in neuronal communication at synapses

action potential

rapid depolarization of membrane potential during neuron activity

animal single-unit recording

can look at individual neurons this way - only can with animal studies

electroencephalography (EEG)

electrodes on subject’s scale and they perform perceptual tasks, measuring voltage changes

• map signal strength over time across scale through many neurons

• good temporal resolution (looking at changes over time)

• poor spatial resolution (looking at specific point of occurrence)

• most similar to animal single-unit

• voltage change averages = event related potentials

magnetoencephalography (MEG)

measures magnetic fields created by flow of ion currents between neuron with magnetometers (superconducting quantum interference devices (SQUID))

• see where activity is occurring in the brain

• not good at seeing activity deep in the brain

positron emission tomography (PET)

radioactive tracer injected into participant and as tracker 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 (cancer) or brain chemicals

• poor spatial resolution (used with MRI to improve)

• invasive

structural MRI

large magnet obtains high res images of body based on differences in water content

• gets a good picture of the brain

• can’t look at brain function

functional MRI (fMRI)

same scanner as MRI, but images blood-oxygen levels instead

• neural activity → increase in blood flow/volume → increase in oxygen consumption → increase in oxygen in venous blood (gets redder) → stronger MRI signal

• display as activation map - 2 conditions

• non-invasive procedure

• best spatial resolution, but response changes very slowly

• See where something is happening

studying physiological response to sensory experience

• animal lesion studies

• human clinical lesion studies

animal lesion studies

• MT lesion disrupts motion perception

• V4 lesion disrupts colour perception

human clinical lesion studies

ex. damage to Broca’s area = problems with speech production, damage to Wernicke’s area = problems with understanding speech

sense of hearing

physical stimulus = sound → physiological response = pattern of electrical activity in sensory receptors, nerves, brain → sensory experience = hear something

components of physical stimulus

sound produced by physical vibrations

• compression

• refraction

• frequency

• phase

• amplitude

compression and rarefaction

• compression: air molecules bunch together

• rarefaction: air molecules spread apart

frequency

rate of fluctuations of sound pressure per second

• measured in cycles/second or hertz (Hz)

• perceived as pitch

phase

part of cycle sound pressure wave has reached at given point in time

• measured in degrees (∘)

amplitude

max pressure change of wave above normal atmospheric pressure, difference between highest and lowest pressure of the wave - several different units

• sound pressure: force against eardrum - dynes/cm² or pascals (newtons/m²)

  • absolute threshold of 1000 Hz tone = 0.0002 dynes/cm²

  • painful 1000 Hz tone = 2000 dynes/cm²

  • sound intensity is proportional to pressure²

• sound pressure level (amplitude or intensity): ratio of sound pressures converted to log scale - decibels (dB)

  • dB = 20*log (P/Po) - P is sound pressure of tone, Po (”P not”) is reference pressure of 0.0002 dynes/cm^2 or 0.00002 pascal)

  • Measuring intensity = dB = 10 * log (P^2/Po^2)

human hearing range

20-20000 Hz

• lose highest frequency sounds first

pure tones

Made by tuning forks - represented by single sine waves (only they achieve this)

• sound frequency corresponds to perceived pitch

• sound pressure level corresponds to perceived loudness

• frequency and amplitude are independent from each other

complex tones

most sounds we hear - set of sine waves (according to Fourier’s theorem)

fourier theorem

mathematical procedure for separating a complex pattern into component sine waves that vary over time (hearing) or space (vision)

amplitude spectra (from Fourier analysis)

extracts sine wave components from complex sounds - shows frequency of sine wave, complexity of sound wave, amplitude, phase

fundamental frequency

lowest sine-wave frequency in a complex sound - usually determines perceived pitch

harmonic frequency

higher frequency sine-wave components - integer multiples of fundamental frequency

• differences determine psychological attribute of quality or timbre (why different musical instruments sound different)

• Instruments can have same pitch but differ in timbre

outer ear

gathers sound energy and funnels it to the tympanic membrane (eardrum)

• ear canal

• pinna

pinna

external ear shape - helps with sound localization

ear canal

outer ear to middle ear - length/shape enhances sounds between 2000 and 6000 Hz

middle ear

amplifies sound energy and protects inner ear from harmful loud sounds

• ossicles

• impedance matching

• tympanic membrane

• acoustic reflex

• eustachian tube

• tensor tympani

ossicles

malleus, incus, stapes - small bones in middles ear that transmit air vibrations from outer ear to inner to be processed as sound

• act like levers - even out the weight from tupanic membrane (factor of 1.3)

impedance matching

middle ear amplifies sound energy to reduce loss due to reflection at oval window - middle ear is filled with air and inner with fluid

• middle ear contains low-impedance sounds, inner ear has high-impedance fluid

tympanic membrane

aka eardrum, separates outer ear from middle ear - larger than neighbouring stapes footplate and increases pressure change at oval window by ~17x

• sound waves at it cause it to vibrate, transfer vibrations to ossicles who transfer the signals to inner ear

• pressure = force/unit area

• like a high heel stepping on your foot

tensor tympani

muscle that contracts and pulls the malleus to tense the tympanic membrane and dampen vibration in the ear ossicles, reducing perceived amplitude of sounds

• stapes do the same thing

acoustic reflex

in response to prolonged loud sounds, tensor tympani and stapedius muscles contract to reduce magnitude of auditory signal transmitted to inner ear

• reduce sound pressure level by 30 dB

eustachian tube

equalizes air pressure between middle and outer ear

• pressure needs to be the same on both sides or it is painful for the ear (like plugged ears on an airplane)

• every time we swallow, air flows into middle ear to equalize pressure

inner ear

helps hearing, balance, detecting and transferring auditory signals to brain

• vestibular, tympanic canals (perilymph fluid)

• cochlear duct (endolymph fluid)

• organ/tunnel of corti

• basilar membrane

• cochlea

• hair cells (stereocilia)

• auditory nerve fibres

tympanic and vestibular canals

transduce movement of air that cause tympanic membrane and ossicles to vibrate to movement of liquid and basilar membrane

• filled with perilymph fluid to assist

reissner’s membrane

aka vestibular membrane - separates cochlear duct from vestibular duct and helps transmit vibrations

basilar membrane

separates the cochlea from the tympanic and vestibular canals

cochlear duct

houses organ of corti, filled with endolymph fluid, between the tympanic and vestibular duct - self-contained