Internal function to detrend pupil data

This function detrends pupil data by fitting a model of pupil_data ~ time and returning the fitted values (the estimated trend) together with the residuals (pupil_data - fitted_values).

When method = "linear" (the default) the trend is a straight line fit with lm(pupil ~ time). When method = "spline" the trend is a natural cubic spline of time fit with lm(pupil ~ splines::ns(time, df = spline_df)), allowing a smooth nonlinear drift to be removed.

This function is called by the exposed wrapper detrend().

Usage

detrend_pupil(x, prev_op, method = "linear", spline_df = 5)

Arguments

x

A data frame containing pupil data with columns time_secs and the previous operation's pupil column

prev_op

The name of the previous operation's pupil column

method

A string indicating the detrending model to fit, either "linear" (the default) or "spline"

spline_df

The degrees of freedom for the natural cubic spline basis used when method = "spline". Defaults to 5

Value

A list containing the fitted values, coefficients, and residuals