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Using Custom Methods

You can pass a custom function to the extract_saccades() alongside the internally implemented method. The function must be declared as follows:

custom_saccade_voting_method <- function(x,
                                         y,
                                         vel,
                                         acc,
                                         sample_rate,
                                         trial,
                                         options) {
                                         
  # implement you method that computes a 0/1 vote per sample
  
  sample_votes
}

Arguments that are passed to the function (all vectors/tables have the same length/number of rows):

Your function must return a vector of the same length as x with votes (\(1\) if sample is a potential saccade, \(0\) otherwise, you can also use logical values).

Example implementation

Here is an example implementation of an overly simple custom method that labels a sample as a saccade if its velocity exceeds a predefined threshold. It expects the threshold parameter as "st_velocity_threshold" member of the list and uses a default threshold of \(50 \deg / s\) (an arbitrary number!) if no threshold was provided.

simple_threshold_method <- function(x,
                                    y,
                                    vel,
                                    acc,
                                    sample_rate,
                                    trial,
                                    options) {

  # obtain method parameters or use defaults
  velocity_threshold <- saccadr::option_or_default(options, "st_velocity_threshold", 50)

  # vote on each sample  
  sample_vote <- vel[['amp']] > velocity_threshold
  
  # return votes
  sample_vote
}

Once you implemented your method, you can pass it alongside internally implemented methods:

data("single_trial")
saccades <- saccadr::extract_saccades(x = single_trial$x,
                                      y = single_trial$y,
                                      sample_rate = 500,
                                      methods = list("ek", "om", "nh", simple_threshold_method),
                                      options = list("st_velocity_threshold" = 70))

These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.