Mask Stimulus¶
Description¶
Masks are useful only in conjuction with layers.
A mask can truncate, obscure, or erase stimuli in its layer that lie below it. The “masked out” regions become transparent or semi-transparent “windows”, through which any stimuli below the layer are visible. If the mask is inverted, it will make a “hole” through the stimuli under it, allowing the stimuli beneath the layer to show through.
For example, the following layer will produce a red ring with inner radius 5 and outer radius 10:
layer the_layer {
circle (
color = 1,0,0
x_size = 20
)
mask (
mask = ellipse
inverted = true
x_size = 10
)
}
Signature¶
stimulus/mask
Optional Parameters¶
inverted¶
- Default
NO
If YES
, the effect of the mask is inverted: Areas of the display that normally would be visible through the mask are hidden, and areas that normally would be hidden are visible.
std_dev¶
- Default
1.0
Standard deviation of Gaussian mask.
The Gaussian mask is computed on a 2x2 square, centered at the origin, using the equation:
exp(-1.0 * (dist - mean) * (dist - mean) / (2.0 * std_dev * std_dev))
where dist
is distance from the center. The mask is then stretched
to cover a rectangle of x_size by y_size degrees. If the x and y
sizes are equal, then the mask is scaled by size/2 in both directions,
so std_dev has units of size/2 degrees.
mean¶
- Default
0.0
Mean of Gaussian mask.
This value determines the radial offset of the Gaussian peak from the center of the mask. If non-zero, the peak will be a circle, rather than a point, and luminance will decrease both inside and outside the circle, producing a toroidal mask.
normalized¶
- Default
NO
If YES
, the Gaussian mask includes a multiplicative normalization term (1/(std_dev*sqrt(2*pi))
). If NO
, this term is omitted.
edge_width¶
- Default
0.125
Edge width of raised cosine mask.
This value specifies the width of the sinusoidal edge as a fraction of the total width (i.e. diameter) of the mask. It should be greater than zero and less than or equal to 0.5.
x_size¶
- Example
5.0
Horizontal size (degrees).
If omitted, the value of y_size is used. It is an error to omit both
x_size and y_size (unless fullscreen is YES
).
y_size¶
- Example
5.0
Vertical size (degrees).
If omitted, the value of x_size is used. It is an error to omit both
x_size and y_size (unless fullscreen is YES
).
fullscreen¶
- Default
NO
If YES
, the stimulus is sized to fill the display. In this mode, x_size, y_size, x_position, y_position, and rotation are ignored.
deferred¶
- Options
no
yes
explicit
- Default
no
Controls when the stimulus is loaded. If no
, the stimulus is loaded at experiment load time. If yes
, the stimulus is loaded the first time it is queued. If explicit
, the stimulus must be loaded explictly with Load Stimulus.
Placement¶
Allowed at top level: |
Yes |
---|---|
Allowed parent: |
Folder, Frame List Stimulus, Layer Stimulus, List Replicator, Movie Stimulus, Range Replicator, Stimulus Group |