jspsych-vsl-animate-occlusion plugin

The VSL (visual statistical learning) animate occlusion plugin displays an animated sequence of shapes that disappear behind an occluding rectangle while they change from one shape to another. This plugin can be used to replicate the experiments described in:

Fiser, J., & Aslin, R. N. (2002). Statistical learning of higher-order temporal structure from visual shape sequences. Journal of Experimental Psychology: Learning, Memory, and Cognition, 28(3), 458.

Dependency

This plugin requires the Snap.svg library, available at http://www.snapsvg.io. You must include the library in the <head> section of your experiment page.

Parameters

Parameters with a default value of undefined must be specified. Other parameters can be left unspecified if the default value is acceptable.

Parameter	Type	Default Value	Description
stimuli	array	undefined	Each element of the array is a stimulus. A stimulus is a path to an image file. The order of stimuli in the array determines the order of the animation sequence.
canvas_size	array	`[400, 400]`	Array specifying the width and height of the area that the animation will display in. Stimuli will move to the edges of this area, so increasing the width without increasing the `timing_cycle` parameter will speed up the images.
image_size	array	`[100, 100]`	Array specifying the width and height of the images to show. The occluding rectangle will have a width equal to the width of image_size.
initial_direction	string	"left"	Which direction the stimulus should move first (subsequent directions will alternate). Choices are "left" or "right".
occlude_center	boolean	true	If true, display a rectangle in the center of the screen that is just wide enough to occlude the image completely as it passes behind.
choices	array of keycodes	`jsPsych.ALL_KEYS`	This array contains the keys that the subject is allowed to press in order to respond to the stimulus. Keys can be specified as their numeric key code or as characters (e.g., `'a'`, `'q'`). The default value of `jsPsych.ALL_KEYS` means that all keys will be accepted as valid responses. Specifying `jsPsych.NO_KEYS` will mean that no responses are allowed.
cycle_duration	numeric	1000	How long it takes for a stimulus in the sequence to make a complete cycle (move to the edge and back to the center) in milliseconds.
pre_movement_duration	numeric	500	How long to wait before the stimuli starts moving from behind the center rectangle.

Data Generated

In addition to the default data collected by all plugins, this plugin collects the following data for each trial.

Name	Type	Value
stimulus	JSON string	A JSON encoded array where each element of the array is a stimulus from the sequence, in the order that they were shown.
responses	JSON string	A JSON encoded array containing all response information. The encoded object is an array containing one element for each valid response. Each response item has three properties: `key` the key code of the response key, `stimulus` the index of the stimulus that was displayed when the response was made, and `rt` the response time measured since the start of the sequence.

Examples

Displaying a simple sequence.

var trial = {
  type: 'vsl-animate-occlusion',
  stimuli: [
    "img/1.gif",
    "img/2.gif",
    "img/3.gif",
    "img/4.gif",
    "img/5.gif",
    "img/6.gif",
    "img/7.gif",
    "img/8.gif",
    "img/9.gif",
    "img/10.gif"
  ]
}

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