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Sensory Processes 3270 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

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Sensory Processes 3270 Lecture 4

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  1. Sensory Processes 3270 Lecture 4

  2. 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

  3. 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% • Steven’s law (1961) • (“To honour Fechner and repeal his law”) • sensation magnitude proportional to • (stimulus intensity) raised to a power

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

  5. Response compression Response expansion

  6. Perceived magnitude  Log (intensity) Gustav Fechner (1801-1887)

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

  8. Consequences of Steven’s Law • response compression • response expansion • linear on a log scale

  9. Somatosensory System section 3

  10. somatosensory • Why? • Perception --- body parts (proprioception) • --- touch • --- special -- vibrissae • antennae • pain • braille • temperature • Protection • Temperature regulation • Limb arrangement and control • Head orientation (vestibular system)

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

  12. 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

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

  14. 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)

  15. SA RA SA RA

  16. RA SA very RA SA

  17. fine detail hand grip control stretching vibration

  18. SPATIAL EVENT PLOTS SA (Merkel) RA (Meissner) RA (Pacinian)

  19. PACINIAN (vRA) MERKEL (SA)

  20. 4th 3rd Trigeminal system from face 2nd 1st SOMATOSENSORY CORTEX VENTRAL POSTERIOR LATERAL Nucleus of the thalamus CROSS OVER IN BRAIN STEM DORSAL COLUMNS Somatosensory pathway

  21. After a limb has been amputated, “phantom” sensations can sometimes be created by stroking other areas of skin.

  22. Demonstrates: 1 plasticity, 2 Müller’s law of specific nerve energies

  23. Area of somatosensory cortex representing finger tip stimulate finger tip over many days Larger area now devoted to this finger tip DEMONSTRATES PLASTICITY

  24. PRESSURE THRESHOLDS Don’t vary much

  25. POINT LOCALIZATION THRESHOLDS

  26. RECEPTIVE FIELDS ON THE ARM

  27. Afferent fibres SA RA PC Cortical cells in area 3b (SA)

  28. Lateral inhibition improves 2-point discrimination

  29. Trigeminal system from face 1 2 3b 4 5 CROSS OVER 3a DORSAL COLUMNS Somatosensory pathways

  30. Multiple representations 3a -- muscle spindles 3b -- SA (cutaneous) 1 ---- RA (cutaneous) 2 ---- joints 1 2 3b 4 5 3a

  31. cutaneous mechanoreceptors Muscle spindles Joint receptors LIMB SENSING ORGANS Muscle spindles, cutaneous mechanoreceptors and joint receptors

  32. Multiple representations 3a -- muscle spindles 3b -- SA (cutaneous) 1 ---- RA (cutaneous) 2 ---- joints 1 2 3b 4 5 3a

  33. Secondary Somatosensory cortex Multiple representations 3a -- muscle spindles 3b -- SA (cutaneous) 1 ---- RA (cutaneous) 2 ---- joints Secondary Somatosensory cortex

  34. superior colliculus

  35. Superior Colliculus

  36. Superior Colliculus

  37. Active vs passive touch active  “object” passive  “sensation” identifying cookies cutters active  95% correct passive  49% correct

  38. could distinguish judged as same JUDGING TEXTURE

  39. ADAPT none Slow freq High freq Meissner’s RA Pacinian vRA Meissner’s RA Pacinian vRA Meissner’s RA Pacinian vRA

  40. POST-ADAPT chance DEMONSTRATES THAT VIBRATION NEEDED FOR TEXTURE

  41. explore surface texture with tool demonstrates use of vibration

  42. haptic perception Stereognosis: 3d object perception by haptic exploration

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