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Visual Contrast Response Function Program
vb.net program: attachment:VisualResponseContrast
Participants view 10 levels of contrast in sine wave gratings presented as dynamic moving images surrounding a central fixation target spotting task (spot the target 'x' in a continuous stream of letters).
attachment:disc.PNG BR
Stimulus is displayed for 12 secs with a 6 sec blank screen rest period (target spotting task continues throughout rest and null trials)
Parameters
A block design is used to allow for maximal HRF values and return to baseline. Alternate runs of the constant stimulus and adaptive procedure.
4 epis (2 constant and 2 adaptive runs at 2.5 and 6.5 each) Measurements: 780BR TR 1 (64x64 matrix, 3x3x3.75mm voxels)BR 16 slices BR V1 ROI BR
Scanning Protocol: BR Gre_Field mappong sequence, EPIS (4 blocks, 12 minutes, 40 trials per block), standard CBU MPRAGE sequence
Example of Real-Time Output
attachment:graph.png BR
Bold Guided Adaptive procedure
A neurometric model is fitted to the data using a Bayesian procedure. The adpative procedure presents the stimuli around the contrast level of the model best describing the threshold at that point (see figure below). BR The constant stimulus procedure presents stimuli in a randomised order, irrespective of threshold estimates.
attachment:graphs2.png