Sensory Processes 3270 Lecture 4

KEYWORDS from Lecture 3 Psychophysics Fechner, Weber, Threshold, Method of limits, staircase, Method of constant stimuli, two alternative forced choice, method of adjustment Signal detection theory, threshold as probability, sensitivity versus response bias, criterion, outcome matrix, hit/miss/false alarm or false positives/correct rejection, receiver operating characteristic curves (ROC curves), sensitivity, d-prime (d') Just noticeable difference, Weber fraction/law/constant, Fechner's law, Stevens' power law, magnitude estimation, standard stimulus, response compression, response expansion

The difference threshold just noticeable difference (jnd) Weber’s law (1834) the just noticeable increment is a constant fraction of the stimulus Weber Fractions Taste0.08 8% Brightness0.088% Loudness0.055% Vibration0.044% Line length0.033% Heaviness0.022% Electric shock0.011% Fechner’s law (1860) sensation magnitude proportional to logarithm (stimulus intensity) assumption: all jnd’s are the same stood for 100 years! Steven’s law (1961) (“To honour Fechner and repeal his law”) sensation magnitude proportional to (stimulus intensity) raised to a power

Ernst Weber ( ) Increase in intensity Intensity = constant

Response compression Response expansion

Gustav Fechner ( ) Perceived magnitude  Log (intensity)

S.S. Stevens ( ) Perceived magnitude  (intensity) h

Consequences of Steven’s Law response compression response expansion linear on a log scale

Somatosensory System section 3

Why? Perception--- body parts (proprioception) --- touch --- special --vibrissae antennae pain braille temperature Protection Temperature regulation Limb arrangement and control Head orientation (vestibular system) somatosensory

How? Receptors Neural pathways Neural codes (remember those ‘common features’…) somatosensory

Coding in the somatosensory system detection identify modality (Müller's doctrine of specific nerve energies 1826; labelled lines); identify properties and spatial form magnitude intensity (APs/sec; frequency coding; population coding; thresholds); location (absolute, two-point discrimination, topographical coding) movement

GLABROUS (non-hairy) SKIN MEISSNER’S CORPUSCLE (RA) MERKEL’S DISK (SA) RUFFINI CORPUSCLE (SA) PACINI CORPUSCLE (very RA)

MERKEL’S DISK (SA) Free nerve ending PACINI CORPUSCLE (very RA) Nerve ending around hair (RA) HAIRY SKIN MEISSNER’S CORPUSCLE (RA) RUFFINI ENDING (SA)

SA RA SA

RA SA very RA SA

stretching vibration fine detail hand grip control

SPATIAL EVENT PLOTS SA (Merkel) RA (Meissner) RA (Pacinian)

MERKEL (SA) PACINIAN (vRA)

Somatosensory pathway Trigeminal system from face DORSAL COLUMNS 1st 2nd 3rd 4th CROSS OVER IN BRAIN STEM VENTRAL POSTERIOR LATERAL Nucleus of the thalamus SOMATOSENSORY CORTEX

After a limb has been amputated, “phantom” sensations can sometimes be created by stroking other areas of skin.

Demonstrates: 1 plasticity, 2 Müller’s law of specific nerve energies

Area of somatosensory cortex representing finger tip stimulate finger tip over many days Larger area now devoted to this finger tip DEMONSTRATES PLASTICITY

PRESSURE THRESHOLDS Don’t vary much

POINT LOCALIZATION THRESHOLDS

RECEPTIVE FIELDS ON THE ARM

Afferent fibres SA RA PC Cortical cells in area 3b (SA)

Lateral inhibition improves 2-point discrimination

Somatosensory pathways 3a 3b Trigeminal system from face DORSAL COLUMNS CROSS OVER

3a 3b Multiple representations 3a -- muscle spindles 3b -- SA (cutaneous) RA (cutaneous) joints

LIMB SENSING ORGANS Muscle spindles, cutaneous mechanoreceptors and joint receptors cutaneous mechanoreceptors Muscle spindles Joint receptors

3a 3b Multiple representations 3a -- muscle spindles 3b -- SA (cutaneous) RA (cutaneous) joints

Secondary Somatosensory cortex Secondary Somatosensory cortex Multiple representations 3a -- muscle spindles 3b -- SA (cutaneous) RA (cutaneous) joints

superior colliculus

Superior Colliculus

Superior Colliculus

Active vs passive touch active  “object” passive  “sensation” identifying cookies cutters active  95% correct passive  49% correct

judged as same could distinguish JUDGING TEXTURE

Meissner’s RA Pacinian vRA Meissner’s RA Pacinian vRA Meissner’s RA Pacinian vRA Slow freqnoneHigh freq ADAPT

chance DEMONSTRATES THAT VIBRATION NEEDED FOR TEXTURE POST-ADAPT

explore surface texture with tool demonstrates use of vibration

haptic perception Stereognosis: 3d object perception by haptic exploration

SA RA SA BARE NERVE ENDINGS

TEMPERATURE Normal = 34 Cold 5-40 Warm Ratio (channel) coding Paradoxical cold at high temps cold fibres warm fibresbody temp skin temp response

PAIN pain insensitivity = bad referred pain (eg. Angina to chest wall) sharp 1st followed by dull 2nd GATE theory (why rubbing helps)

To brainThe Gate -ve+ve -ve +ve Slow pain fibres Fast mechano-receptor fibres Closed by ‘rubbing’ So pain stopped from going to brain... Normally held closed Opened by ‘pain fibres’ -ve

phantom limb pain Acupuncture Hypnosis Expectation (cognitive factors) endorphins and enkephalins (natural opiates) Naloxone (antagonist) makes pain worse also reverses acupuncture endorphins up with stress.. PAIN pain insensitivity = bad referred pain (eg. Angina to chest wall) sharp 1st followed by dull 2nd GATE theory (why rubbing helps)

Sensation and Perception II 3270 Revision For first midterm

Electrode, Microelectrode, Micron (1/1000th mm), membrane, nucleus, cytoplasm, Neuron, axon, dendrite, Schwann cell/glial cell, myelin sheath, node of Ranvier, Synapse, synaptic cleft, vesicle, neurotransmitter, receptors, ions, permeability, ion channels, voltage-dependent sodium channels, neural threshold, positive feedback, sodium (Na+), potassium (K+), sodium-potassium pump, electrochemical equilibrium potentials, sodium (Na+) +55mv, potassium (K+) -75mv, resting potential -70mv, polarization/ depolarization/ hyperpolarization, inhibitory post-synaptic potential (IPSP), Excitatory post-synaptic potential (EPSP), integration, axon hillock, action potential (AP), all-or- none, neuron threshold -55mv, saltatory propagation, AP propagation KEYWORDS from NEURAL BASIS

modality (Müller's doctrine of specific nerve energies 1826; labelled line); intensity (APs/sec; frequency coding; population coding; thresholds); duration (rapidly and slowly adapting neurones) location (absolute, two-point discrimination, topographical coding) Pacinian corpuscle

KEYWORDS from NEURAL BASIS receptive fields, thalamus, cortex, sulcus, gyrus, brainstem, topographic (maps) representation, superior colliculus, inferior colliculus (those are the names of the bumps on the brain stem that deal with vision and hearing respectively), Brodmann, phrenology, areas of cortex: primary sensory areas (chemical, somatosensory, visual, auditory), motor cortex, association cortices (parietal, inferotemporal, frontal)

KEYWORDS from PSYCHOPHYSICS Fechner, Weber, Threshold, Method of limits, staircase, Method of constant stimuli, two alternative forced choice, method of adjustment Signal detection theory, threshold as probability, sensitivity versus response bias, criterion, outcome matrix, hit/miss/false alarm or false positives/correct rejection, receiver operating characteristic curves (ROC curves), sensitivity Just noticeable difference, Weber fraction/law/constant, Fechner's law, Stevens' power law, magnitude estimation, standard stimulus, response compression.

Receptors, hairy/glabrous skin, rapidly/slowly adapting (RA/SA), transduction, Meissner's corpuscles (RA), Merkel's discs (SA), Nerve ending around hair (RA), Pacinian corpuscle (RA), Ruffini Ending (SA), free nerve endings, receptive fields, dorsal root, dorsal columns, dorsal column nuclei, trigeminal nerve, thalamus, somatosensory cortex, homunculus, somatotopic representation/map spatial event plots, lateral inhibition, sharpening of receptive fields cortex, Brodmann areas 3a, 3b, 1, 2. Joint detectors, muscle spindles, RAs, SAs, convergence Secondary somatosensory cortex Keywords for SOMATOSENSORY SYSTEM

KEYWORDS from SOMATOSENSORY 1 detection 2 identify (modality) 3 identify (properties, spatial form) 4 magnitude 5 location 6 movement which fibre?, mapping of location, identifying modality/ sub- modality what pattern? frequency coding of magnitude

somatosensory psychophysics, detection thresholds, point threshold, two-point discrimination (larger than point thresholds because of need for unstimulated receptive field in between stimuli), texture perception: vibration and active motion important stereognosis, Haptic perception, variations over body surface, active touch/exploration, stereognosis, Aristotle's illusion, Temperature Pain (perception),

As promised.. The following is a question that will appear on the midterm next week… (no, I did not promise to ANSWER it too….! GOOD LUCK!

A question from next week’s exam There will be 35 multiple choices: 1 point each = 91% There will be one ‘label the diagram’: 3.5 points= 9% Total = 38.5 points = 100% Counts for 30% or 40% if it is your best.