The Contrast Window
The Contrasts Window shows a list of all defined contrasts. Contrasts are typically defined automatically, based on either triggers or a protocol file (.prt). The Contrast column lists the names of available contrasts. A contrast can be enabled by clicking in the “+/-” column of the respective contrast. Squares with a cross in this column indicate that the positive contrast (+1) is enabled, while squares with a “-” indicate that the negative (-1) contrast is enabled. Empty squares indicate that the contrast is disabled. These squares act as toggles, i.e. they can be clicked repeatedly to flip between the positive enabled, negative enabled, and disabled state. Contrasts are always enabled in a two-sided fashion. This means that a “+” will highlight all channels exceeding the selected minimal t-Threshold in both directions, positive (red color coding) and negative (blue color coding). The resulting statistical map of each enabled contrast is superimposed on channel names and in the layout view. It is also possible to specify a conjunction of contrasts by turning on the Conjunction of contrasts option. If this option is checked, the minimum of t values of all active contrasts for channels is determined and used as the channels threshold for the resulting conjunction map. Note that the conjunction applies to different contrasts defined on the separate contrast pages (see page contrast page number at the bottom right of the dialog).
If a defined contrast is enabled, all channels passing the current significance criteria (t-threshold) are shown in the Contrasts Overlay Window.
In case that multiple conditions are used, the “Select All conds.” and “Change All Values” buttons allow to toggle selection options for all conditions at the same time. The “Select All conds.” button will toggle the check mark in front of the condition. This either hides or shows the modeled HRF and the event related average plot of this specific condition. The “Change All Values” button will change the contrasts of all conditions.
The contrast page spin box (bottom right) can be used to switch between different contrast pages, which are also the basis for the conjunction analysis, if selected.
Note: The contrast does only apply to the t-Statistics and Beta values and does not affect the Ch.-Corr. and Anti-Corr. option. Instead of creating an implicit contrast for Beta values, the average of the Betas per contrast are calculated. A “+” is treated as positive contribute and a “-” will invert the beta sign (multiple by -1) before averaging.
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