Transcript lecture 4
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 • Fechner’s law (1860) Weber Fractions sensation magnitude Taste proportional to 0.08 logarithm (stimulusBrightness intensity) 0.08 assumption: all jnd’s are the same Loudness 0.05 stood for 100 years! Vibration 0.04 • Steven’s law (1961) Line length 0.03 (“To honour Fechner and Heaviness repeal his law”) 0.02 sensation magnitude proportional Electric shock to 0.01 (stimulus intensity) raised to a power 8% 8% 5% 4% 3% 2% 1% Increase in intensity = constant Intensity Ernst Weber (1795-1878) Response compression Response expansion Perceived magnitude Gustav Fechner (1801-1887) Log (intensity) Perceived magnitude S.S. Stevens (1906-1973) (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 MEISSNER’S CORPUSCLE (RA) MERKEL’S DISK (SA) RUFFINI CORPUSCLE (SA) PACINI CORPUSCLE (very RA) GLABROUS (non-hairy) SKIN MEISSNER’S CORPUSCLE (RA) MERKEL’S DISK (SA) Free nerve ending HAIRY SKIN Nerve ending around hair (RA) PACINI CORPUSCLE (very RA) RUFFINI ENDING (SA) SA RA SA RA RA SA very RA SA fine detail stretching hand grip control vibration SPATIAL EVENT PLOTS SA (Merkel) RA (Meissner) RA (Pacinian) MERKEL (SA) PACINIAN (vRA) SOMATOSENSORY CORTEX 4th Trigeminal system from face CROSS OVER IN BRAIN STEM DORSAL COLUMNS 1st 3rd VENTRAL POSTERIOR LATERAL Nucleus of the thalamus 2nd Somatosensory pathway 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 Trigeminal system from face CROSS OVER 1 4 3b 2 5 3a DORSAL COLUMNS Somatosensory pathways Multiple representations 1 4 3b 3a 2 5 3a -- muscle spindles 3b -- SA (cutaneous) 1 ---- RA (cutaneous) 2 ---- joints cutaneous mechanoreceptors Muscle spindles Joint receptors LIMB SENSING ORGANS Muscle spindles, cutaneous mechanoreceptors and joint receptors Multiple representations 1 4 3b 3a 2 5 3a -- muscle spindles 3b -- SA (cutaneous) 1 ---- RA (cutaneous) 2 ---- joints Secondary Somatosensory cortex Multiple representations 3a -- muscle spindles 3b -- SA (cutaneous) 1 ---- RA (cutaneous) 2 ---- joints Secondary Somatosensory cortex superior colliculus Superior Colliculus Superior Colliculus Active vs passive touch active “object” passive “sensation” identifying cookies cutters active 95% correct passive 49% correct could distinguish judged as same JUDGING TEXTURE ADAPT none Meissner’s RA Pacinian vRA Slow freq Meissner’s RA Pacinian vRA High freq Meissner’s RA Pacinian vRA POST-ADAPT chance DEMONSTRATES THAT VIBRATION NEEDED FOR TEXTURE explore surface texture with tool demonstrates use of vibration haptic perception Stereognosis: 3d object perception by haptic exploration SA RA SA RA BARE NERVE ENDINGS TEMPERATURE response •Normal = 34 •Cold 5-40 •Warm 30-45 •Ratio (channel) coding •Paradoxical cold at high temps body temp cold fibres skin temp warm fibres PAIN •pain insensitivity = bad •referred pain (eg. Angina to chest wall) •sharp 1st followed by dull 2nd •GATE theory (why rubbing helps) Slow pain fibres The Gate -ve +ve To brain -ve +ve Fast mechano-receptor fibres +ve • Normally held closed • Opened by ‘pain fibres • Closed by ‘rubbing’ • So pain stopped from going to brain... PAIN •pain insensitivity = bad •referred pain (eg. Angina to chest wall) •sharp 1st followed by dull 2nd •GATE theory (why rubbing helps) •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.. Sensation and Perception II 3270 Revision For first midterm KEYWORDS from NEURAL BASIS 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-ornone, 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. Keywords for SOMATOSENSORY SYSTEM 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 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/ submodality 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….! 12. IPSPs are a. Inhibitory pre-synaptic potentials b. Inhibitory post-synaptic potentials c. Inhibitory pre-spike potentials d. Inhibitory post-spike potentials e. none of the above. GOOD LUCK! 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. A question from next week’s exam 2. A target neurone receives inputs from many other neurones. An action potential is evoked in that target neurone: a. if enough excitatory input neurones fire at the right time b. if any one of the input neurones fires c. if any excitatory input neurone fires d. a and c e. none of the above