Simulation Modes¶

Added in 7.1

Simulation mode allows you run your experiment automatically and generate artificial data.

Getting Started¶

To use simulation mode, replace jsPsych.run() with jsPsych.simulate().

jsPsych.simulate(timeline);

This will run jsPsych in the default data-only simulation mode. To use the visual simulation mode you can specify the second parameter.

jsPsych.simulate(timeline, "data-only");
jsPsych.simulate(timeline, "visual");

What happens in simulation mode¶

In simulation mode, plugins call their simulate() method instead of calling their trial() method. If a plugin doesn't implement a simulate() method, then the trial will run as usual (using the trial() method) and any interaction that is needed to advance to the next trial will be required. If a plugin doesn't support visual mode, then it will run in data-only mode.

`data-only` mode¶

In data-only mode plugins typically generate resonable artificial data given the parameters specified for the trial. For example, if the trial_duration parameter is set to 2,000 ms, then any response times generated will be capped at this value. Generally the default data generated by the plugin randomly selects any available options (e.g., buttons to click) with equal probability. Response times are usually generated by sampling from an exponentially-modified Gaussian distribution truncated to positive values using jsPsych.randomization.sampleExGaussian().

In data-only mode, the plugin's trial() method usually does not run. The data are simply calculated based on trial parameters and the finishTrial() method is called immediately with the simulated data.

`visual` mode¶

In visual mode a plugin will typically generate simulated data for the trial and then use that data to mimic the kinds of actions that a participant would do. The plugin's trial() method is called by the simulation, and you'll see the experiment progress in real time. Mouse, keyboard, and touch events are simulated to control the experiment.

In visual mode each plugin will generate simulated data in the same manner as data-only mode, but this data will instead be used to generate actions in the experiment and the plugin's trial() method will ultimately be responsible for generating the data. This can create some subtle differences in data between the two modes. For example, if the simulated data generates a response time of 500 ms, the data.rt value will be exactly 500 in data-only mode, but may be 501 or another slightly larger value in visual mode. This is because the simulated response is triggered at 500 ms and small delays due to JavaScript's event loop might add a few ms to the measure.

Controlling simulation mode with `simulation_options`¶

The parameters for simulation mode can be set using the simulation_options parameter in both jsPsych.simulate() and at the level of individual trials.

Trial-level options¶

You can specify simulation options for an individual trial by setting the simulation_options parameter.

const trial = {
  type: jsPsychHtmlKeyboardResponse,
  stimulus: '<p>Hello!</p>',
  simulation_options: {
    data: {
      rt: 500
    }
  }
}

Currently the three options that are available are data, mode, and simulate.

`data`¶

Setting the data option will replace the default data generated by the plugin with whatever data you specify. You can specify some or all of the data parameters. Any parameters you do not specify will be generated by the plugin.

In most cases plugins will try to ensure that the data generated is consistent with the trial parameters. For example, if a trial has a trial_duration parameter of 2000 but the simulation_options specify a rt of 2500, this creates an impossible situation because the trial would have ended before the response at 2,500ms. In most cases, the plugin will act as if a response was attempted at 2500, which will mean that no response is generated for the trial. As you might imagine, there are a lot of parameter combinations that can generate peculiar cases where data may be inconsistent with trial parameters. We recommend double checking the simulation output, and please alert us if you discover a situation where the simulation produces inconsistent data.

`mode`¶

You can override the simulation mode specified in jsPsych.simulate() for any trial. Setting mode: 'data-only' will run the trial in data-only mode and setting mode: 'visual' will run the trial in visual mode.

`simulate`¶

If you want to turn off simulation mode for a trial, set simulate: false.

Functions and timeline variables¶

The simulation_options parameter is compatible with both dynamic parameters and timeline variables. Dynamic parameters can be especially useful if you want to randomize the data for each run of the simulation. For example, you can specify the rt as a sample from an ExGaussian distribution.

const trial = {
  type: jsPsychHtmlKeyboardResponse,
  stimulus: '<p>Hello!</p>',
  simulation_options: {
    data: {
      rt: ()=>{
        return jsPsych.randomization.sampleExGaussian(500, 50, 1/100, true)
      }
    }
  }
}

Experiment-level options¶

You can also control the parameters for simulation by passing in an object to the simulation_options argument of jsPsych.simulate().

const simulation_options = {
  default: {
    data: {
      rt: 200
    }
  }
}

jsPsych.simulate(timeline, "visual", simulation_options)

The above example will set the rt for any trial that doesn't have its own simulation_options specified to 200. This could be useful, for example, to create a very fast preview of the experiment to verify that everything is displaying correctly without having to wait through longer trials.

You can also specify sets of parameters by name using the experiment-level simulation options.

const simulation_options = {
  default: {
    data: {
      rt: 200
    }
  },
  long_response: {
    data: {
      rt: () => {
        return jsPsych.randomization.sampleExGaussian(5000, 500, 1/500, true)
      }
    }
  }
}

const trial = {
  type: jsPsychHtmlKeyboardResponse,
  stimulus: '<p>This is gonna take a bit.</p>',
  simulation_options: 'long_response'
}
timeline.push(trial);

jsPsych.simulate(timeline, "visual", simulation_options)

In the example above, we specified the simulation_options for trial using a string ('long_response'). This will look up the corresponding set of options in the experiment-level simulation_options.

We had a few use cases in mind with this approach:

You could group together trials with similar behavior without needing to specify unique options for each trial.
You could easily swap out different simulation options to test different kinds of behavior. For example, if you want to test that a timeline with a conditional_function is working as expected, you could have one set of simulation options where the data will cause the conditional_function to evaluate to true and another to false. By using string-based identifiers, you don't need to change the timeline code at all. You can just change the object being passed to jsPsych.simulate().
In an extreme case of the previous example, every trial on the timeline could have its own unique identifier and you could have multiple sets of simulation options to have very precise control over the data output.

Current Limitations¶

Simulation mode is not yet as comprehensively tested as the rest of jsPsych. While we are confident that the simulation is accurate enough for many use cases, it's very likely that there are circumstances where the simulated behavior will be inconsistent with what is actually possible in the experiment. If you come across any such circumstances, please let us know!

Currently extensions are not supported in simulation mode. Some plugins are also not supported. This will be noted on their documentation page.

Simulation Modes¶

Getting Started¶

What happens in simulation mode¶

data-only mode¶

visual mode¶

Controlling simulation mode with simulation_options¶