lecture 1 – introduction to psychophysics & neuroimaging ilan dinstein
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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? - PowerPoint PPT PresentationTRANSCRIPT
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Lecture 1 – Introduction to Psychophysics & Neuroimaging
Ilan Dinstein
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Psychophysics
“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.
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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.
Just noticeable difference
What is the smallest difference in the stimulus that we can detect. Weber’s law:
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Contrast sensitivity
Spatial frequency
Con
trast
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Contrast sensitivity & threshold
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Visual search
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Behavioral measures
Accuracy & Reaction time
Can the subject detect something at above-chance levels?How quickly does the subject perform the task?
Things to worry aboutIs the subject cooperative? Motivation? Arousal level? Stress?
What is creating the difference? Slow motor responses?
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Magnetic resonance imaging (MRI)
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Anatomy - Separating tissues
1T 2T
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Anatomy – Cortical thickness
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Anatomy – Cortical folding
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Brain function
Neurovascular coupling
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Vasculature
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Changes in oxygenated blood
Heeger et. al. 2002
זמן
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fMRI experiment
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Experimental results
In fMRI we always compare measures over time
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Observing facial expression
Mirror system areas in autism
Dapretto, Nat. Neurosci. 2006
Control > Autism
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Electroencephalogram
Control > ASD
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Signal = Potential Difference
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Source of EEG signals
1. Muscle contractions anywhere in the head.2. Heart beat (ECG).3. Electromagnetic noise – AC, Cell phones, etc…4. Synchronized cortical neural activity over large areas (>1cm) –
Sources and Sinks.
What causes potential changes between the electrodes?
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Source of EEG signals
1. The larger the synchronicity, the stronger the signal (potential difference).
2. Topography of the brain – Sulci and Gyri.3. Changing conductance in the brain – CSF, dura, skull (strong
resistor).4. Inverse problem – almost infinite combinations of dipoles can create
the same potentials on the scalp.
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Example of Event Related Potential experiment
Differentiating responses to illusory contours…
Show many trials of each stimulus and average across presentations.
See how and where the brain response differs.
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You need many trials!
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Spatial selectivity of response
Control > ASD
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ERPs
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EEG Frequencies
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EEG coherence
Control > ASD
Similarity of activity across electrodes.