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Lecture 1 – Introduction to Psychophysics & Neuroimaging Ilan Dinstein

Lecture 1 – Introduction to Psychophysics & Neuroimaging Ilan Dinstein. “The scientific study of the relation between stimulus and sensation” Behavioral studies of perceptual abilities. How sensitive are we to different stimuli? What affects our ability to detect a stimulus?

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Lecture 1 – Introduction to Psychophysics & Neuroimaging Ilan Dinstein

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  1. Lecture 1 – Introduction to Psychophysics & NeuroimagingIlan Dinstein

  2. “The scientific study of the relation between stimulus and sensation” • Behavioral studies of perceptual abilities. • How sensitive are we to different stimuli? • What affects our ability to detect a stimulus? • Perceptual learning – improving sensitivity with practice. Psychophysics

  3. What is the smallest difference in the stimulus that we can detect. Weber’s law: Just noticeable difference Where I is the “reference” and ∆I is the additional amount of stimulus needed to detect a difference. K is surprisingly consistent across multiple amplitudes and sensory domains.

  4. Contrast sensitivity Contrast Spatial frequency

  5. Contrast sensitivity & threshold

  6. Visual search

  7. Accuracy & Reaction time Can the subject detect something at above-chance levels? How quickly does the subject perform the task? Things to worry about Is the subject cooperative? Motivation? Arousal level? Stress? What is creating the difference? Slow motor responses? Behavioral measures

  8. Magnetic resonance imaging (MRI)

  9. Anatomy - Separating tissues 1T 2T

  10. Anatomy – Cortical thickness

  11. Anatomy – Cortical folding

  12. Brain function Neurovascular coupling

  13. Vasculature

  14. Changes in oxygenated blood זמן Heeger et. al. 2002

  15. fMRI experiment

  16. In fMRI we always compare measures over time Experimental results

  17. Mirror system areas in autism Observingfacial expression Control > Autism Dapretto, Nat. Neurosci. 2006

  18. Electroencephalogram Control > ASD

  19. Signal = Potential Difference

  20. What causes potential changes between the electrodes? • Muscle contractions anywhere in the head. • Heart beat (ECG). • Electromagnetic noise – AC, Cell phones, etc… • Synchronized cortical neural activity over large areas (>1cm) – Sources and Sinks. Source of EEG signals

  21. Source of EEG signals • The larger the synchronicity, the stronger the signal (potential difference). • Topography of the brain – Sulci and Gyri. • Changing conductance in the brain – CSF, dura, skull (strong resistor). • Inverse problem – almost infinite combinations of dipoles can create the same potentials on the scalp.

  22. Differentiating responses to illusory contours… Show many trials of each stimulus and average across presentations. See how and where the brain response differs. Example of Event Related Potential experiment

  23. You need many trials!

  24. Spatial selectivity of response Control > ASD

  25. ERPs

  26. EEG Frequencies

  27. EEG coherence Similarity of activity across electrodes. Control > ASD

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