1. Artifact can make everything upside down and meaningless

2. Remove artifact to find reliable answers

3. VHS Zimbardo #3, ~15 min, E Roy John’s work

4. Recording Montages

5. Montages We measure different electrical potential between sensors Bipolar montage = two active channels Monopolar or referential montage = one active, one “inactive” such as ear –Linked Ears –Linked Mastoids –Nose Average reference montage Mathematical sharpening techniques (e.g., Laplacian)

6. Dis/Advantages

7. Disadvantage with Monopolar –No such thing as inactive reference (including ear, neck, nose – cortical signal bleeds through – see scallop shaped topometric) Disadvantage with Bipolar –Source of signal not localizable directly, but only through inference and comparison with other channels

8. Effect of monopolar reference (linked ears) (temporal lobe activity attenuated)

10. 98% of EEG energy is between 0.1 & 30 Hz

12. Artifact Equipment-related Physiological (non-cerebral signals) Computational Functional (unstable background/state transitions; transients, sleep!)

13. Impedence <5-10K Ohm

14. Impedence artifact?

15. Eye movement & blinks

19. Muscles: Heart, jaw, and neck

23. Non-biological artifacts 60 Hz, electrode pops

26. Equipment or gross movement artifacts

27. Eye blinks in 19 channel NeuroNavigator

28. Muscle, forehead and jaw

29. Sleep “artifact”

30. The Problems with Artifact

31. Computational Artifact: Undersampling Heart beat of 60 sec –60 samples/min = DC –90 samples/min = 15 bpm

32. Spectral Leakage

33. See ShowDFT.xls

34. Data Windows eliminate leakage significantly

35. But they come with two artifacts of their own: 1. Smearing (spectral broadening), & 2. Sampling bias

39. Sampling bias makes analysis sensitive to epoch positions

41. Arbitrary segmentation (epoching) of signal can produce different spectral means

44. Artifact Management

48. Seaming

50. Power vs Magnitude (the square root of power)

51. Ln Magn (or Ln Power) Ln = Natural log (base e, not base 10) e = 1 + 1/1! + 1/2! + 1/3! +... or ~= 2.718…

52. Skewed distribution of power

53. Greek Astronomer Hipparchus (190-120BC) 6 brightness classification for stars Each 2.5x as bright as next classification Logarithmic relationship

54. Subjective Brightness ( S ) jnd units Light energy ( I ) Psychophysical Function Fechner’s Law: S = (1/k) log (I)

55. Mean magnitude estimations ( S ) Stimulus intensity ( I ) Psychophysical Function Stevens’ Power Law: S = aI m Electric shock (m > 1) Brightness (m < 1) Apparent length (m = 1)

56. Basic law of psychophysics (correspondence between physical energies and mental experiences) appears linear

58. Untailored Dominant Frequency IAF – individual’s alpha frequency

59. State Transitions

60. State transitions

62. Sources of artifact by frequency