Download 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