A circular checkerboard pattern. Properties set options for size, pattern, scaling of radial check sizes (e.g. for cortical scaling), amplitude/contrast, and color. This element type includes three animation options commonly used in retinotopy tasks:

(1) flicker: switch dark and light checks at a specified frequency.
(2) wedges: show a repeating sequence of isolated wedges, moving angularly around the dartboard in steps.
(3) rings: show a repeating sequence of isolated rings, moving radially through the dartboard in steps.

You can also show solid concentric rings if you set number of angular checks = 1.

For just a static dartboard or with flicker only, see also element type dartboard. For fixation see element types dots, cross, fixationGrid, etc.

No—runs until any condition you set in property end.

diameter          
centerDiameter

Default: diameter = 10 deg
Default: centerDiameter = 0.2 deg

diameter is diameter of the dartboard (deg).

centerDiameter is diameter of the center area, which is transparent (deg).

numAngularChecks
numRadialChecks

Default: numAngularChecks = 20
Default: numRadialChecks = 8

numAngularChecks is integer number of segments (light or dark) around the dartboard at any radius.

numRadialChecks is integer number of segments in any radial line, from edge of the transparent center area to outer edge of the dartboard.

e.g. numAngularChecks = 4, numRadialChecks = 1 → a dartboard consisting of four segments in quadrants.

radialScale

Default: equal radial check sizes

You can use this property to apply cortical (or other) scale factors to check sizes in the radial direction. This is a vector of numbers > 0 that are radial check sizes, from innermost to outermost. Number of sizes must = numRadialChecks above. The absolute magnitudes of the sizes don't matter, only their magnitudes relative to each other. Actual radial sizes are automatically scaled to fit numRadialChecks into the radius from edge of the transparent center area to outer edge of the dartboard.

phase

Default: first check right and below center is light

0/1 setting the initial pattern: 0 = first check right and below display center is dark, 1 = light. Note currently the dartboard is always centered at element position, with a boundary between checks along the right horizontal bisector. Element position can be set in property position.

meanIntensity
amplitude
contrast

Defaults: mean intensity = 0.5, amplitude = 0.5 → black & maximum intensity

meanIntensity is a number between 0–1 (black–maximum) setting the mean pixel intensity of dark and light checks.

Also set one of:

amplitude is max intensity − mean intensity.

OR

contrast is Michelson contrast, amplitude / mean intensity. If you set contrast, meanIntensity must be > 0.

It's possible to set a combination of these properties that causes the dartboard to clip at intensity 0 or 1. See record properties maxAmplitude and maxContrast below.

color

Default: white

A 1×3 RGB vector with numbers between 0–1. This defines color at pixel intensity = 1. Color at intensity = 0 is <cd>[0 0 0]<cd> (black).

flickerFrequency

Default: no flicker

Frequency of switching between dark–light (cycles/sec). 0 = no flicker.

wedgeVelocity
ringVelocity

Default: show whole dartboard

You can set one of these properties:

wedgeVelocity lets you show a repeating sequence of isolated wedges, moving angularly around the dartboard in steps. Each wedge is an integer number of angular checks wide (apertureSize below). Velocity is rate and direction (angular checks/sec, + = clockwise, − = counterclockwise).

ringVelocity is similar but for isolated rings moving radially through the dartboard in steps. Each ring is an integer number of radial checks wide. Velocity is rate and direction (radial checks/sec, + = outward, − = inward).

apertureSize
apertureStepSize
aperturePhase

Default: apertureSize = 2 checks
Default: apertureStepSize = 1 check
Default: aperturePhase = 0 → see below

If you set wedgeVelocity or ringVelocity:

apertureSize is integer wedge or ring width as number of checks.

apertureStepSize is integer number of checks the wedge or ring moves by each time. Rate is set by the respective velocity above.

aperturePhase is for wedges only. It sets the initial wedge shown. It is an integer number of angular checks clockwise. The zero point depends on wedgeVelocity: 0 = first wedge below the right horizontal bisector if wedgeVelocity > 0, or first wedge above if wedgeVelocity < 0.

For rings, initial ring is always the ring starting with the innermost radial checks if ringVelocity > 0, or the outermost checks if ringVelocity < 0.

position
nn_eyes
rotation
colorMask
alpha
intensity
contrastMult
drawCodeVars

maxAmplitude
maxContrast

Values for input properties amplitude and contrast that would cause intensity to clip at 0 or 1 given the current value of meanIntensity.