Noise, neural codes and cortical organization - Redwood Center for
Principles of Neural Organization Lecture 3
-
Upload
barrett-edwards -
Category
Documents
-
view
38 -
download
2
description
Transcript of Principles of Neural Organization Lecture 3
![Page 1: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/1.jpg)
Principles of Neural Organization
Lecture 3
![Page 2: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/2.jpg)
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)
![Page 3: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/3.jpg)
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)
![Page 4: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/4.jpg)
![Page 5: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/5.jpg)
![Page 6: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/6.jpg)
![Page 7: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/7.jpg)
![Page 8: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/8.jpg)
BRAIN STEM
PARIETALFRONTAL
INFEROTEMPORAL
CEREBELLUM
![Page 9: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/9.jpg)
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.
![Page 10: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/10.jpg)
Psychophysics
section 2
![Page 11: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/11.jpg)
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
![Page 12: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/12.jpg)
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
![Page 13: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/13.jpg)
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
![Page 14: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/14.jpg)
SIGNAL DETECTION THEORY
![Page 15: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/15.jpg)
time
low firing rate high
pro
bab
ility
SPONTANEOUS ACTIVITY
![Page 16: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/16.jpg)
low firing rate high
pro
bab
ility
GENTLE STIMULUS
time
![Page 17: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/17.jpg)
low firing rate high
P
rob
abili
ty
SIGNAL+
NOISENOISE
“yes”“no”
CRITERION
![Page 18: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/18.jpg)
low firing rate high
P
rob
abili
ty
“yes”“no”
![Page 19: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/19.jpg)
medium stimulus
gentle stimulus
stronger stimulus
![Page 20: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/20.jpg)
SIGNAL DETECTION THEORY
• sensory noise• criterion• stimulus magnitude• outcome matrix (hit/miss/false alarm/correct rejection)
![Page 21: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/21.jpg)
RESPONSE
STIMULUS
“yes” “no”
present
absent
CORRECTHITS
CORRECT
MISS
FALSEALARM
100%
100%
![Page 22: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/22.jpg)
RESPONSE
STIMULUS
“yes” “no”
present
absent
CORRECT
CORRECT
MISS
FALSEALARM
100%
100%
75% 25%
90%10%
![Page 23: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/23.jpg)
SIGNAL DETECTION THEORY
• sensory noise• criterion• stimulus magnitude• outcome matrix (hit/miss/false alarm/correct rejection)• receiver operator characteristic curve (ROC)
![Page 24: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/24.jpg)
percentage of false alarms
per
cen
tag
e o
f h
its
10%
75%
RECEIVER OPERATOR CHARACTERISTIC (ROC)
![Page 25: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/25.jpg)
percentage of false alarms
per
cen
tag
e o
f h
its
more liberal
more conservative
RECEIVER OPERATOR CHARACTERISTIC (ROC)
![Page 26: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/26.jpg)
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
![Page 27: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/27.jpg)
percentage of false alarms
per
cen
tag
e o
f h
its your sensitivity
RECEIVER OPERATOR CHARACTERISTIC (ROC)
![Page 28: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/28.jpg)
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
![Page 29: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/29.jpg)
DIFFERENCETHRESHOLDS
WEBER’S LAWΔI
Iis constant
change in stimulus magnitude
stimulus magnitude
![Page 30: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/30.jpg)
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!
![Page 31: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/31.jpg)
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)
![Page 32: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/32.jpg)
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
![Page 33: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/33.jpg)
…but Stevens noticed that not everything went like that!
Stevens introduced the idea of “magnitude estimation”
so this is the Weber-Fechner law…
![Page 34: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/34.jpg)
Perceived magnitude
(intensity) h
Stevens’ Power Law
![Page 35: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/35.jpg)
Response compression
Response expansion
![Page 36: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/36.jpg)
power less than 1
power more than 1power equal to 1
Perceived magnitude (intensity) h
Perceived magnitude (intensity) h
![Page 37: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/37.jpg)
Ernst Weber (1795-1878)
Increase in intensityIntensity = constant
![Page 38: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/38.jpg)
Gustav Fechner (1801-1887)
Perceived magnitude
log (intensity)
![Page 39: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/39.jpg)
S.S. Stevens (1906-1973)
Perceived magnitude
(intensity) h
![Page 40: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/40.jpg)
Somatosensory System
section 3
![Page 41: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/41.jpg)
Why?• Perception --- body parts
--- touch--- special -- vibrissae
antennaepainbrailletemperature
• Protection• Temperature regulation• signals (flushing/muscle arrangement)
somatosensory
![Page 42: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/42.jpg)
How?• Receptors• Neural pathways• Neural codes(remember those ‘common features’…)
somatosensory
![Page 43: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/43.jpg)
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
![Page 44: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/44.jpg)
GLABROUS (non-hairy) SKIN
MEISSNER’SCORPUSCLE(RA)
MERKEL’SDISK (SA)
RUFFINICORPUSCLE(SA)
PACINICORPUSCLE(very RA)
![Page 45: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/45.jpg)
MERKEL’SDISK (SA)
Free nerveending
PACINICORPUSCLE(very RA)
Nerve endingaround hair(RA)
HAIRYSKIN
MEISSNER’SCORPUSCLE(RA)
RUFFINIENDING(SA)
![Page 46: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/46.jpg)
SA
RA
RA
SA
![Page 47: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/47.jpg)
RA SA very RA SA
![Page 48: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/48.jpg)
![Page 49: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/49.jpg)
![Page 50: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/50.jpg)
![Page 51: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/51.jpg)
Somatosensorypathway
Trigeminalsystem fromface
DORSAL COLUMNS
1st2nd
3rd
4th
CROSS OVER
![Page 52: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/52.jpg)
Somatosensory Cortex
![Page 53: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/53.jpg)
Afferent fibres
SA
RA
PC
Cortical cells in area 3b (SA)
![Page 54: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/54.jpg)
Effect ofLateralinhibition
![Page 55: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/55.jpg)
Lateral inhibition improves 2-point discrimination
![Page 56: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/56.jpg)
POINT LOCALIZATIONTHRESHOLDS
![Page 57: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/57.jpg)
![Page 58: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/58.jpg)
PRESSURETHRESHOLDS
![Page 59: Principles of Neural Organization Lecture 3](https://reader030.fdocuments.in/reader030/viewer/2022032708/56812a57550346895d8dafa5/html5/thumbnails/59.jpg)