FDBeye: Functions to Ease Work with Eyetracker Data

##' @title Data: Eye movements (fixations) over text.
##'
##' @description Nine different readers reading the same three stories. Some included data is
##'     poor quality.
##'
##' @details Data were collected using an SR Research Eyelink 1000+ eye tracker with remote camera
##'     configuration and head stabilization. Data were extracted from EDF files as
##'     "fixation reports" using the SRR Data Viewer software.
##'
##' @format A data.frame with 6676 rows and 8 variables:
##' \describe{
##'     \item{subj}{Subject identifier.}
##'     \item{eye}{The eye being tracked. Always "RIGHT".}
##'     \item{xpos}{Screen coordinates of the fixation; its (average) x position in pixels.}
##'     \item{ypos}{Screen coordinates of the fixation; its (average) y position in pixels. Note that the origin is in the upper left hand corner.}
##'     \item{stime}{Start time of fixation, in milliseconds from the beginning of the trial.}
##'     \item{etime}{End time of fixation, in milliseconds from the beginning of the trial.}
##'     \item{label}{Hand assigned labels corresponding to the nominal line of text for each fixation (line 1, 2, 3, etc).
##'                  Assignment was done by first identifying the "retrace" (return from the end of line n to the beginning
##'                  of line n+1) after each line of text. Then, fixations
##'                  before the first retrace were assigned to line 1; those between the first and second retrace were
##'                  assigned to line 2, etc. Labels with values like "x.5" indicate fixations that occur within a retrace.}
##'     \item{story}{Identifier for the text being read (1,2, or 3). Bit map images for each text can be found as
##'                     system.file("extdata/story01.png", package="FDBeye"), for example. Coordinate values for fixations
##'                     correspond to pixel locations in the bitmaps.}
##' }
##'
##' @source Data collected as part of U.S. National Institutes of Health grant R01 HD071988 to
##'     Haskins Laboratories.
##'
"EToralreading"