Principles of Neural Organization Lecture 3
Dec 30, 2015
Principles of Neural Organization
Lecture 3
KEYWORDS from Lecture 2
ACTION POTENTIALS 1 -- electrical stimulation (artificial depolarization)2 -- spatial and temporal integration of EPSPs and
IPSPs… Generator potential3 -- sensory stimulation (transduction), mechanical (cytoskeleton), chemical (receptors, second messengers), light (hyperpolarization)
• 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)
KEYWORDS from Lecture 2 (cont’d)
Pacinian corpuscle, adequate stimulus, 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(olfactory, somatosensory, visual, auditory), motor cortex, association cortices (parietal, inferotemporal, frontal)
BRAIN STEM
PARIETALFRONTAL
INFEROTEMPORAL
CEREBELLUM
Across pattern coding• can code more than one thing at the same time• can code ‘similarity’• 2 stimuli coded as two stimuli (if sufficiently different)• Good for coding patternsPopulation coding• only codes one thing• 2 stimuli --> smaller ignored • integration of activity means all neurones involved• Good for coding a single parameter such as directionSpecificity coding• can code more than one thing• 2 stimuli always coded as separate• each neurone acts alone (therefore vulnerable)• Good for coding patternsChannel coding• only codes one thing• 2 stimuli perceived as 1 (different from either alone - metamer)• Good for extracting a single parameter in the presence of
other potentially confusing factors.
Psychophysics
section 2
DETECTION THRESHOLDS
Section 1 method of limitsmethod of constant stimulimethod of adjustment
Section 2 signal detection theory
DISCRIMINATION THRESHOLDS
Section 3 Weber’s LawFechner’s LawSteven’s Power Law
PSYCHOPHYSICS
PRECISION vs ACCURACY
Method of limitsbias of expectationbias of habituationstaircase
Method of constant stimuli2AFC; 4AFC
Method of adjustmentrather variable“quick and dirty”
1. Multiple presentations
METHOD OF LIMITS
2. Staircase
PRECISION vs ACCURACY
Method of limitsbias of expectationbias of habituationstaircase
Method of constant stimuli2AFC; 4AFC
Method of adjustmentrather variable“quick and dirty”
perfect performance
chance performance
half way between
METHOD OF CONSTANT STIMULI
SIGNAL DETECTION THEORY
time
low firing rate high
pro
bab
ility
SPONTANEOUS ACTIVITY
low firing rate high
pro
bab
ility
GENTLE STIMULUS
time
low firing rate high
P
rob
abili
ty
SIGNAL+
NOISENOISE
“yes”“no”
CRITERION
low firing rate high
P
rob
abili
ty
“yes”“no”
medium stimulus
gentle stimulus
stronger stimulus
SIGNAL DETECTION THEORY
• sensory noise• criterion• stimulus magnitude• outcome matrix (hit/miss/false alarm/correct rejection)
RESPONSE
STIMULUS
“yes” “no”
present
absent
CORRECTHITS
CORRECT
MISS
FALSEALARM
100%
100%
RESPONSE
STIMULUS
“yes” “no”
present
absent
CORRECT
CORRECT
MISS
FALSEALARM
100%
100%
75% 25%
90%10%
SIGNAL DETECTION THEORY
• sensory noise• criterion• stimulus magnitude• outcome matrix (hit/miss/false alarm/correct rejection)• receiver operator characteristic curve (ROC)
percentage of false alarms
per
cen
tag
e o
f h
its
10%
75%
RECEIVER OPERATOR CHARACTERISTIC (ROC)
percentage of false alarms
per
cen
tag
e o
f h
its
more liberal
more conservative
RECEIVER OPERATOR CHARACTERISTIC (ROC)
SIGNAL DETECTION THEORY
• sensory noise• criterion• stimulus magnitude• outcome matrix (hit/miss/false alarm/correct rejection)• receiver operator characteristic curve (ROC)• from which we can measure your sensitivity
percentage of false alarms
per
cen
tag
e o
f h
its your sensitivity
RECEIVER OPERATOR CHARACTERISTIC (ROC)
DETECTION THRESHOLDS
Section 1 method of limitsmethod of constant stimulimethod of adjustment
Section 2 signal detection theory
DISCRIMINATION THRESHOLDS
Section 3 Weber’s LawFechner’s LawSteven’s Power Law
PSYCHOPHYSICS
DIFFERENCETHRESHOLDS
WEBER’S LAWΔI
Iis constant
change in stimulus magnitude
stimulus magnitude
The difference threshold
• just noticeable difference (jnd)• Weber’s law (1834)
the just noticeable increment is a constant fraction of the stimulus
Weber FractionsTaste 0.08 8%
Brightness 0.08 8% Loudness 0.05 5% Vibration 0.04 4% Line length 0.03 3% Heaviness 0.02 2% Electric shock 0.01 1%
• Fechner’s law (1860)sensation magnitude proportional to
logarithm (stimulus intensity)assumption: all jnd’s are the samestood for 100 years!
stimulus intensity
per
ceiv
ed m
agn
itu
de
1 jnd
2 jnd
4 jnd
5 jnd
6 jnd
3 jnd
Perceived magnitude
log (intensity)
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)sensation magnitude proportional to
logarithm (stimulus intensity)assumption: all jnd’s are the samestood for 100 years!
• Steven’s law (1961)(“To honour Fechner and repeal his law”)
sensation magnitude proportional to (stimulus intensity) raised to a power
…but Stevens noticed that not everything went like that!
Stevens introduced the idea of “magnitude estimation”
so this is the Weber-Fechner law…
Perceived magnitude
(intensity) h
Stevens’ Power Law
Response compression
Response expansion
power less than 1
power more than 1power equal to 1
Perceived magnitude (intensity) h
Perceived magnitude (intensity) h
Ernst Weber (1795-1878)
Increase in intensityIntensity = constant
Gustav Fechner (1801-1887)
Perceived magnitude
log (intensity)
S.S. Stevens (1906-1973)
Perceived magnitude
(intensity) h
Somatosensory System
section 3
Why?• Perception --- body parts
--- touch--- special -- vibrissae
antennaepainbrailletemperature
• Protection• Temperature regulation• signals (flushing/muscle arrangement)
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’SCORPUSCLE(RA)
MERKEL’SDISK (SA)
RUFFINICORPUSCLE(SA)
PACINICORPUSCLE(very RA)
MERKEL’SDISK (SA)
Free nerveending
PACINICORPUSCLE(very RA)
Nerve endingaround hair(RA)
HAIRYSKIN
MEISSNER’SCORPUSCLE(RA)
RUFFINIENDING(SA)
SA
RA
RA
SA
RA SA very RA SA
Somatosensorypathway
Trigeminalsystem fromface
DORSAL COLUMNS
1st2nd
3rd
4th
CROSS OVER
Somatosensory Cortex
Afferent fibres
SA
RA
PC
Cortical cells in area 3b (SA)
Effect ofLateralinhibition
Lateral inhibition improves 2-point discrimination
POINT LOCALIZATIONTHRESHOLDS
PRESSURETHRESHOLDS