Dots Component¶

The Dots Component allows you to present a Random Dot Kinematogram (RDK) to the participant of your study. Note that this component is not yet supported for online use (see status of online options) but users have contributed work arounds for use online. These are fields of dots that drift in different directions and subjects are typically required to identify the ‘global motion’ of the field.

There are many ways to define the motion of the signal and noise dots. In PsychoPy^® the way the dots are configured follows Scase, Braddick & Raymond (1996). Although Scase et al (1996) show that the choice of algorithm for your dots actually makes relatively little difference there are some potential gotchas. Think carefully about whether each of these will affect your particular case:

limited dot lifetimes: as your dots drift in one direction they go off the edge of the stimulus and are replaced randomly in the stimulus field. This could lead to a higher density of dots in the direction of motion providing subjects with an alternative cue to direction. Keeping dot lives relatively short prevents this.
noiseDots=’direction’: some groups have used noise dots that appear in a random location on each frame (noiseDots=’location’). This has the disadvantage that the noise dots not only have a random direction but also a random speed (whereas signal dots have a constant speed and constant direction)
signalDots=’same’: on each frame the dots constituting the signal could be the same as on the previous frame or different. If ‘different’, participants could follow a single dot for a long time and calculate its average direction of motion to get the ‘global’ direction, because the dots would sometimes take a random direction and sometimes take the signal direction.

As a result of these, the defaults for PsychoPy^® are to have signalDots that are from a ‘different’ population, noise dots that have random ‘direction’ and a dot life of 3 frames.

Categories:: Stimuli
Works in:: PsychoPy

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 Dots 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 Dots 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.

Dot size: Size of the dots in pixel units.

Field size: A single value, specifying the diameter of the field (in the specified Spatial Units). Sizes can be negative and can extend beyond the window.

Field position: Where is the field centred (in the specified units)?

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

Field anchor

Which point in this field should be anchored to the point specified by dotscomponent-pos?

Options:

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

Field shape

Defines the shape of the field in which the dots appear.

Options:

circle
square

Appearance¶

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

Dot color: Color of the dots.

Dot 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)

Dots¶

Number of dots: Number of dots in the field (for circular fields this will be average number of dots)

Direction: Direction of motion for the signal dots (degrees)

Speed: Speed of the dots (displacement per frame in the specified units)

Coherence: Coherence of the dots (fraction moving in the signal direction on any one frame)

Dot life-time: Number of frames before each dot is killed and randomly assigned a new position

Signal dots

If ‘same’ then the signal and noise dots are constant. If different then the choice of which is signal and which is noise gets randomised on each frame. This corresponds to Scase et al’s (1996) categories of RDK.

Options:

same
different

Dot refresh rule

When should the whole sample of dots be refreshed

Options:

none
repeat

Noise dots

Determines the behaviour of the noise dots, taken directly from Scase et al’s (1996) categories. For ‘position’, noise dots take a random position every frame. For ‘direction’ noise dots follow a random, but constant direction. For ‘walk’ noise dots vary their direction every frame, but keep a constant speed.

Options:

direction
position
walk

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.