Grating Component¶

The Grating stimulus allows a texture to be wrapped/cycled in 2 dimensions, optionally in conjunction with a mask (e.g. Gaussian window). The texture can be a bitmap image from a variety of standard file formats, or a synthetic texture such as a sinusoidal grating. The mask can also be derived from either an image, or mathematical form such as a Gaussian.

When using gratings, if you want to use the spatial frequency setting then create just a single cycle of your texture and allow PsychoPy^® to handle the repetition of that texture (do not create the cycles you’re expecting within the texture).

Gratings can have their position, orientation, size and other settings manipulated on a frame-by-frame basis. There is a performance advantage (in terms of milliseconds) to using images which are square and powers of two (32, 64, 128, etc.), however this is slight and would not be noticed in the majority of experiments.

Categories:: Stimuli
Works in:: PsychoPy, PsychoJS

Parameters¶

Basic¶

The required attributes of the stimulus, controlling its basic function and behaviour

Name: Everything in a PsychoPy^® experiment needs a unique name. The name should contain only letters, numbers and underscores (no punctuation marks or spaces).

Start: When the Grating Component should start, see Defining the onset/duration of components.

Expected start (s): If you are using frames to control timing of your stimuli, you can add an expected start time to display the component timeline in the routine.

Start type

How do you want to define your start point?

Options:

time (s)
frame N
condition

Stop: When the Grating Component should stop, see Defining the onset/duration of components.

Expected duration (s): If you are using frames to control timing of your stimuli, you can add an expected duration to display the component timeline in the routine.

Stop type

How do you want to define your end point?

Options:

duration (s)
duration (frames)
time (s)
frame N
condition

Layout¶

How should the stimulus be laid out on screen? Padding, margins, size, position, etc.

Size [w,h]: Size of this stimulus (either a single value or x,y pair, e.g. 2.5, [1,2] ). If the mask is a Gaussian then the size refers to width at 3 standard deviations on either side of the mean (i.e. sd=size/6)

Position [x,y]: Position of this stimulus (e.g. [1,2] )

Spatial units

Spatial units for this stimulus (e.g. for its position and size), see Units for the window and stimuli for more info.

Options:

from exp settings
deg
cm
pix
norm
height
degFlatPos
degFlat

Anchor

Which point in this stimulus should be anchored to the point specified by Position [x,y]?

Options:

center
top-center
bottom-center
center-left
center-right
top-left
top-right
bottom-left
bottom-right

Orientation: The orientation of the entire patch (texture and mask) in degrees.

Draggable?: Should this stimulus be moveble by clicking and dragging?

Appearance¶

How should the stimulus look? Colors, borders, styles, etc.

Foreground color: Foreground color of this stimulus (e.g. $[1,1,0], red )

Color space

In what format (color space) have you specified the colors? See Color spaces for more info.

Options:

Opacity: Vary the transparency, from 0.0 (invisible) to 1.0 (opaque)

Contrast: Contrast of the stimulus (1.0=unchanged contrast, 0.5=decrease contrast, 0.0=uniform/no contrast, -0.5=slightly inverted, -1.0=totally inverted)

OpenGL blend mode

OpenGL Blendmode: avg gives traditional transparency, add is important to combine gratings)]

Options:

Texture¶

Texture: A filename, a standard name (sin, sqr) or a variable giving a numpy array specifying the image that will be used as the texture for the visual patch. The image can be repeated on the patch (in either x or y or both) by setting the spatial frequency to be high (or can be stretched so that only a subset of the image appears by setting the spatial frequency to be low). Filenames can be relative or absolute paths and can refer to most image formats (e.g. tif, jpg, bmp, png, etc.). If this is set to none, the patch will be a flat colour.

Mask

The mask can define the shape (e.g. circle will make the patch circular) or something which overlays the patch e.g. noise.

Options:

gauss
circle

Phase (in cycles): The position of the texture within the mask, in both X and Y. If a single value is given it will be applied to both dimensions. The phase has units of cycles (rather than degrees or radians), wrapping at 1. As a result, setting the phase to 0,1,2… is equivalent, causing the texture to be centered on the mask. A phase of 0.25 will cause the image to shift by half a cycle (equivalent to pi radians). The advantage of this is that is if you set the phase according to time it is automatically in Hz.

Spatial frequency: The spatial frequency of the texture on the patch. The units are dependent on the specified units for the stimulus/window; if the units are deg then the SF units will be cycles/deg, if units are norm then the SF units will be cycles per stimulus. If this is set to none then only one cycle will be displayed.

Texture resolution

Defines the size of the resolution of the texture for standard textures such as sin, sqr etc. For most cases a value of 256 pixels will suffice, but if stimuli are going to be very small then a lower resolution will use less memory.

Options:

Interpolate

If linear is selected then linear interpolation will be applied when the image is rescaled to the appropriate size for the screen. Nearest will use a nearest-neighbour rule.

Options:

linear
nearest

Data¶

What information about this Component should be saved?

Save onset/offset times: Store the onset/offset times in the data file (as well as in the log file).

Sync timing with screen refresh: Synchronize times with screen refresh (good for visual stimuli and responses based on them)

Testing¶

Tools for testing, debugging and checking the performance of this Component.

Disable Component: Disable this Component

Validate with…: Name of the Validator Routine to use to check the timing of this stimulus. Options are generated live, so will vary according to your setup.