Sensory Processes3270

Lecture 4

KEYWORDS from Lecture 3Psychophysics

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) Webers law (1834)the just noticeable increment is a constant fraction of the stimulusWeber FractionsTaste0.08 8% Brightness0.088% Loudness0.055% Vibration0.044% Line length0.033% Heaviness0.022% Electric shock0.011% Fechners law (1860)sensation magnitude proportional to logarithm (stimulus intensity)assumption: all jnds are the samestood for 100 years! Stevens law (1961)(To honour Fechner and repeal his law)sensation magnitude proportional to (stimulus intensity) raised to a power

Ernst Weber (1795-1878)Increase in intensityIntensity= constant

Gustav Fechner (1801-1887)Perceived magnitudeLog (intensity)

S.S. Stevens (1906-1973)Perceived magnitude(intensity) h

Consequences of Stevens Law

response compression response expansion linear on a log scale

Somatosensory System

section 3

Why?Perception--- body parts (proprioception)--- touch--- special --vibrissaeantennaepainbrailletemperatureProtectionTemperature regulationLimb arrangement and controlHead orientation (vestibular system)

How?ReceptorsNeural pathwaysNeural codes(remember those common features)

Coding in the somatosensory system detection

identify modality (Mller'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) SKINMEISSNERSCORPUSCLE(RA)MERKELSDISK (SA)RUFFINICORPUSCLE(SA)PACINICORPUSCLE(very RA)

MERKELSDISK (SA)Free nerveendingPACINICORPUSCLE(very RA)Nerve endingaround hair(RA)HAIRYSKINMEISSNERSCORPUSCLE(RA)RUFFINIENDING(SA)

SARARASA

RA SA very RA SA

stretchingvibrationfine detailhand grip control

SPATIAL EVENT PLOTSSA (Merkel)

RA (Meissner)

RA (Pacinian)

MERKEL (SA)PACINIAN (vRA)

SomatosensorypathwayDORSAL COLUMNSCROSS OVERIN BRAIN STEMVENTRAL POSTERIOR LATERALNucleus of the thalamusSOMATOSENSORY CORTEX

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

Demonstrates: 1 plasticity, 2 Mllers law of specific nerve energies

Area of somatosensory cortex representing finger tipstimulate finger tip over many daysLarger area now devoted to this finger tip

DEMONSTRATESPLASTICITY

PRESSURETHRESHOLDSDont vary much

POINT LOCALIZATIONTHRESHOLDS

RECEPTIVE FIELDS ON THE ARM

Afferent fibresSARAPCCortical cells in area 3b (SA)

Lateral inhibition improves 2-point discrimination

Somatosensorypathways3a3b1254DORSAL COLUMNSCROSS OVER

3a3b1254Multiple representations

3a -- muscle spindles3b -- SA (cutaneous)1 ---- RA (cutaneous)2 ---- joints

LIMB SENSING ORGANSMuscle spindles, cutaneous mechanoreceptors and joint receptorscutaneous mechanoreceptorsMuscle spindlesJoint receptors

3a3b1254Multiple representations

3a -- muscle spindles3b -- SA (cutaneous)1 ---- RA (cutaneous)2 ---- joints

Secondary Somatosensory cortexSecondary Somatosensory cortexMultiple representations

3a -- muscle spindles3b -- SA (cutaneous)1 ---- RA (cutaneous)2 ---- joints

superior colliculus

SuperiorColliculus

SuperiorColliculus

Active vs passive touch

active objectpassive sensation

identifying cookies cuttersactive 95% correctpassive 49% correct

judged as samecould distinguishJUDGING TEXTURE

MeissnersRAPacinianvRAMeissnersRAPacinianvRAMeissnersRAPacinianvRASlow freqnoneHigh freqADAPT

chanceDEMONSTRATES THAT VIBRATION NEEDED FOR TEXTUREPOST-ADAPT

explore surface texture with tool

demonstrates use of vibration

haptic perception

Stereognosis: 3d object perception by haptic exploration

SARARASABARE NERVE ENDINGS

TEMPERATURE

Normal = 34Cold 5-40Warm 30-45Ratio (channel) codingParadoxical cold at high temps

PAIN

pain insensitivity = badreferred pain (eg. Angina to chest wall)sharp 1st followed by dull 2ndGATE theory (why rubbing helps)

To brainSlow pain fibresFast mechano-receptor fibres Closed by rubbing So pain stopped from going to brain... Normally held closed Opened by pain fibres

phantom limb painAcupunctureHypnosisExpectation (cognitive factors)endorphins and enkephalins (natural opiates)Naloxone (antagonist) makes pain worsealso reverses acupunctureendorphins up with stress..PAIN

pain insensitivity = badreferred pain (eg. Angina to chest wall)sharp 1st followed by dull 2ndGATE theory (why rubbing helps)

Sensation and Perception II3270

RevisionFor 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 propagationKEYWORDS from NEURAL BASIS

KEYWORDS from NEURAL BASIS modality (Mller'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 BASISreceptive 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 PSYCHOPHYSICSFechner, 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 cortexKeywords 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 weeks examThere 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.