Principles of Neural Organization Lecture 3

1. Principles of Neural Organization Lecture 3

2. KEYWORDS from Lecture 2 • ACTION POTENTIALS • 1 -- electrical stimulation (artificial depolarization) • 2 -- spatial and temporal integration of EPSPs and IPSPs… Generator potential • 3 -- 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)

3. 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)

8. BRAIN STEM FRONTAL PARIETAL INFEROTEMPORAL CEREBELLUM

9. 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 patterns • Population coding • only codes one thing • 2 stimuli --> smaller ignored • integration of activity means all neurones involved • Good for coding a single parameter such as direction • Specificity coding • can code more than one thing • 2 stimuli always coded as separate • each neurone acts alone (therefore vulnerable) • Good for coding patterns • Channel 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.

10. Psychophysics section 2

11. PSYCHOPHYSICS DETECTION THRESHOLDS Section 1 method of limits method of constant stimuli method of adjustment Section 2 signal detection theory DISCRIMINATION THRESHOLDS Section 3 Weber’s Law Fechner’s Law Steven’s Power Law

12. PRECISION vs ACCURACY Method of limits bias of expectation bias of habituation staircase Method of constant stimuli 2AFC; 4AFC Method of adjustment rather variable “quick and dirty” 1. Multiple presentations 2. Staircase METHOD OF LIMITS

13. PRECISION vs ACCURACY Method of limits bias of expectation bias of habituation staircase Method of constant stimuli 2AFC; 4AFC Method of adjustment rather variable “quick and dirty” perfect performance half way between chance performance METHOD OF CONSTANT STIMULI

14. SIGNAL DETECTION THEORY

15. probability low firing rate high SPONTANEOUS ACTIVITY time

16. time probability low firing rate high GENTLE STIMULUS

17. “yes” “no” SIGNAL + NOISE NOISE Probability low firing rate high CRITERION

18. “yes” “no” Probability low firing rate high

19. gentle stimulus medium stimulus stronger stimulus

20. SIGNAL DETECTION THEORY • sensory noise • criterion • stimulus magnitude • outcome matrix (hit/miss/false alarm/correct rejection)

21. RESPONSE “yes” “no” present 100% CORRECT HITS MISS STIMULUS FALSE ALARM CORRECT 100% absent

22. RESPONSE “yes” “no” present 100% CORRECT MISS 25% 75% STIMULUS FALSE ALARM CORRECT 100% absent 10% 90%

23. SIGNAL DETECTION THEORY • sensory noise • criterion • stimulus magnitude • outcome matrix (hit/miss/false alarm/correct rejection) • receiver operator characteristic curve (ROC)

24. RECEIVER OPERATOR CHARACTERISTIC (ROC) 75% percentage of hits percentage of false alarms 10%

25. RECEIVER OPERATOR CHARACTERISTIC (ROC) more liberal percentage of hits more conservative percentage of false alarms

26. 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

27. RECEIVER OPERATOR CHARACTERISTIC (ROC) your sensitivity percentage of hits percentage of false alarms

28. PSYCHOPHYSICS DETECTION THRESHOLDS Section 1 method of limits method of constant stimuli method of adjustment Section 2 signal detection theory DISCRIMINATION THRESHOLDS Section 3 Weber’s Law Fechner’s Law Steven’s Power Law

29. DIFFERENCE THRESHOLDS change in stimulus magnitude ΔI is constant WEBER’S LAW I stimulus magnitude

30. 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 same • stood for 100 years! • Weber Fractions • Taste 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%

31. 6 jnd 5 jnd 4 jnd perceived magnitude 3 jnd 2 jnd 1 jnd stimulus intensity Perceived magnitude  log (intensity)

32. 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 same • stood for 100 years! • Steven’s law (1961) • (“To honour Fechner and repeal his law”) • sensation magnitude proportional to • (stimulus intensity) raised to a power

33. so this is the Weber-Fechner law… …but Stevens noticed that not everything went like that! Stevens introduced the idea of “magnitude estimation”

34. Stevens’ Power Law Perceived magnitude  (intensity) h

35. Response compression Response expansion

36. power equal to 1 power more than 1 power less than 1 Perceived magnitude (intensity) h  Perceived magnitude  (intensity) h

37. Increase in intensity Intensity = constant Ernst Weber (1795-1878)

38. Perceived magnitude  log (intensity) Gustav Fechner (1801-1887)

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

40. Somatosensory System section 3

41. somatosensory • Why? • Perception --- body parts • --- touch • --- special -- vibrissae • antennae • pain • braille • temperature • Protection • Temperature regulation • signals (flushing/muscle arrangement)

42. somatosensory • How? • Receptors • Neural pathways • Neural codes • (remember those ‘common features’…)

43. 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

44. MEISSNER’S CORPUSCLE (RA) MERKEL’S DISK (SA) RUFFINI CORPUSCLE (SA) PACINI CORPUSCLE (very RA) GLABROUS (non-hairy) SKIN

45. MEISSNER’S CORPUSCLE (RA) MERKEL’S DISK (SA) Free nerve ending HAIRY SKIN RUFFINI ENDING (SA) PACINI CORPUSCLE (very RA) Nerve ending around hair (RA)

46. SA RA SA RA

47. RA SA very RA SA