PEST Procedure

This script allows users to implement the PEST procedure (Macmillan and Creelman, 2005, p282-283) to determine the appropriate stimulus intensity per trial.

Parameters

This table lists the parameters associated with this plugin. Parameters can be left unspecified if the default value is acceptable.

Parameter	Type	Default Value	Descripton
starting_intensity	numeric	0.7	The starting intensity of the stimulus.
down_threshold	numeric	3	The number of trials in a row the participant gets correct before a step down is taken. (E.g., If this is set to 3, then 3 correct responses in a row causes the stimulus intensity to take a step down.)
up_threshold	numeric	1	The number of trials in a row the participant gets incorrect before a step up is taken. (E.g., If this is set to 1, then every incorrect response causes the stimulus intensity take a step up.)
upper_intensity_limit	numeric	1	The highest intensity of the stimulus for this PEST procedure. Any intensity level that is supposed to be higher than this limit is set to this limit.
lower_intensity_limit	numeric	0	The lowest intensity of the stimulus for this PEST procedure. Any intensity level that is supposed to be lower than this limit is set to this limit.
starting_step_size	numeric	0.32	The starting step size for this PEST procedure.
min_step_size	numeric	0.01	The smallest step size for this PEST procedure. Any step size that is supposed to be smaller than this step size is set to this step size.
max_step_size	numeric	0.32	The largest step size for this PEST procedure. Any step size that is supposed to be larger than this step size is set to this step size.

Example

Setting up the parameters of the PEST procedure (i.e., the staircase):

//Create a JS Object to hold the parameters
var myParameters = {
	starting_intensity: 3,
	upper_intensity_limit: 5,
	lower_intensity_limit: 0.2,
	starting_step_size: 1,
	min_step_size: 0.0625,
	max_step_size: 2
};

Create the staircase object:

//Create and initialize a new pest object with the parameter object passed in as an argument
var myPest =  new pest(myParameters);

//Parameters of myPest are now initialized, and you can use its staircase() method

Use the staircase:

//In every trial, call the staircase() method of the pest object with the correctness of the previous trial (boolean) passed in as an argument.

var intensity_for_this_trial = myPest.staircase(correctness_of_previous_trial);

// ^ The argument for the first trial will be ignored, so it is safe to use the same function to determine the correctness_of_previous_trial for all your trials.