Circular Fixation Point Stimulus

Description

An elliptical fixation point stimulus

Signature

stimulus/circular_fixation_point

Required Parameters

trigger_width

Width of the (circular) fixation window, which shares its center with the visible stimulus ellipse

trigger_watch_x

Variable containing the horizontal eye position

trigger_watch_y

Variable containing the vertical eye position

trigger_flag

Variable to which fixation status is written. When the subject’s gaze (as reported by trigger_watch_x and trigger_watch_y) enters the fixation window, the variable is set to true. When the subject’s gaze leaves the fixation window, the variable is set to false.

Optional Parameters

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

By default, the alpha multiplier controls the transparency of the stimulus. 1.0 is fully opaque, while 0.0 is fully tranparent.

Changes to the parameters source_blend_factor and dest_blend_factor can alter how (or if) the alpha multiplier is used.

source_blend_factor

Options
zero
one
source_color
one_minus_source_color
dest_color
one_minus_dest_color
source_alpha
one_minus_source_alpha
dest_alpha
one_minus_dest_alpha
Default

source_alpha

Source blending factor.

The parameters source_blend_factor, dest_blend_factor, source_alpha_blend_factor, and dest_alpha_blend_factor provide detailed control over how the color components and alpha multiplier of each fragment of the stimulus (the “source”) are combined with the color and alpha values already present in the framebuffer (the “destination”), which in turn result from blending the stimulus display background with any stimuli drawn beneath the source stimulus. These parameters correspond directly to the four arguments of the OpenGL function glBlendFuncSeparate. Please refer to that function’s reference page for explanations of the different blend factor options.

Note: Irrespective of the blend factors used, the blend equation is always GL_FUNC_ADD.

dest_blend_factor

Default

one_minus_source_alpha

Destination blending factor. Accepts the same values as source_blend_factor.

source_alpha_blend_factor

Source alpha blending factor. Accepts the same values as source_blend_factor.

If omitted, the value of source_blend_factor is used.

dest_alpha_blend_factor

Destination alpha blending factor. Accepts the same values as source_blend_factor.

If omitted, the value of dest_blend_factor is used.

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.