Drifting Grating Stimulus

Description

A drifting grating stimulus

Signature

stimulus/drifting_grating

Required Parameters

spatial_frequency

Example:1

Spatial frequency (cycles per degree)

speed

Example:1

Drift speed (degrees per second)

grating_type

Options:
sinusoid
square
triangle
sawtooth

Grating type

Optional Parameters

direction

Default:0.0

Direction of drift (degrees)

starting_phase

Default:0.0

Starting phase (degrees)

compute_phase_incrementally

Default:NO

If NO, the current phase of the grating is computed from starting_phase, spatial_frequency, speed, and the total time elapsed since the stimulus started playing.

If YES, the current phase is computed from the previous phase (i.e. the phase when the stimulus was last drawn), spatial_frequency, speed, and the time elapsed since the previous phase was computed.

This parameter is relevant only when the stimulus is live queued and the values of starting_phase, spatial_frequency, and/or speed are changed while the stimulus is playing. Most notably, if the parameter’s value is NO, then changes to speed will cause a discontinuous jump in phase. If the value is YES, then changes to speed will be smooth, with no phase jump.

mask

Default:NO

If YES, the grating will function as a mask (similar to a Mask Stimulus). When used as part of a layer, “high” regions of the grating (where the value is close to one) will allow stimuli beneath it in the layer to show through, while “low” regions (where the value is near zero) will partially or fully erase such stimuli, exposing any stimuli beneath the layer.

When the value of this parameter is YES, color and alpha_multiplier are ignored.

Note: For compatibility with existing experiments, the value of this parameter can also be one of rectangle, ellipse, or gaussian, in which case it specifies the type of mask to apply to the grating. However, this usage is deprecated, and new experiments should use a Mask Stimulus instead.

inverted

Default:NO

If YES, all grating values are inverted, e.g. high values become low, and low values become high

color

Default:1.0,1.0,1.0

The color of the stimulus, expressed as a comma-separated list of red, green, and blue components. Each component may be described by any valid expression, but the expression must result in a value between 0 and 1 (inclusive).

alpha_multiplier

Default:1.0

Controls the transparency of the stimulus. 1.0 is fully opaque, while 0.0 is fully tranparent.

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).

x_position

Default:0.0

Horizontal center position (degrees)

y_position

Default:0.0

Vertical center position (degrees)

rotation

Default:0.0

Rotation (degrees)

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.

autoplay

Default:NO

If YES, the stimulus will start playing automatically (as if by an implicit Play Dynamic Stimulus action) after it has been queued and Update Stimulus Display has been invoked. It will also stop playing automatically (as if by an implicit Stop Dynamic Stimulus action) after it has been dequeued and Update Stimulus Display is invoked.

Deprecated Parameters

std_dev

Default:1.0

Standard deviation of Gaussian mask

mean

Default:0.0

Mean of Gaussian mask.

This value determines the radial offset of the Gaussian peak from the center of the grating. 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 stimulus.

normalized

Default:YES

If YES, the Gaussian mask includes a multiplicative normalization term (1/(std_dev*sqrt(2*pi))). If NO, this term is omitted.