Table 4.

Eye-movement features (22 features).

Saccade amplitude (mean and s.d.): The mean and standard deviation of the amplitude of the saccades, averaged over all saccades in a trial (2 features).

Saccade distance (mean and s.d.): The mean and standard deviation of the number of words covered in a saccade, averaged over all saccades in a trial (2 features).

Regression amplitude (mean and s.d.): The mean and standard deviation of the amplitude of the regressions (saccades ending on an AOI that precedes the AOI on which they started), averaged over all regressions in a trial (2 features).

Regression distance (mean and s.d.): The mean and standard deviation of the number of words covered in a regression, averaged over all regressions in a trial (2 features).

Max regression amplitude: Maximum amplitude of a regressive saccade (1 feature).

Max regression distance: Maximum number of words covered in a regressive saccade (1 feature).

Fixation count: The total number of fixations in a trial (1 feature).

First-pass first fixation count: The total number of first fixations occurring in the first pass of a trial. That is, a first-pass first fixation occurs when it is the first fixation on the given word, and there have been no fixations on any words occurring later in the text (1 feature).

Later-pass first fixation count: The total number of first fixations occurring outside the first-pass of a trial. That is, a later-pass first fixation occurs when it is the first fixation on the given word, but there have already been fixations on words occurring later in the text (1 feature).

Multi-fixation count: The total number of fixations on a word in the first-pass, excluding the first fixation. That is, a multi-fixation occurs when a word is fixated on multiple times in the run which starts with a first-pass first fixation (1 feature).

Re-fixation count: The total number of fixations on a word outside the first pass, excluding the first fixation (1 feature).

Reading fixation count: Number of fixations occurring before the first visit to the last AOI in the text (1 feature).

Re-reading fixation count: Number of fixations occurring after the last AOI has been visited at least once (1 feature).

First-pass first fixation duration (mean and s.d.): The mean and standard deviation of the duration of the first-pass first fixations (2 features).

Wrap-up gaze duration (mean and s.d.): The mean and standard deviation of the gaze time on the last word in a sentence, which is typically longer than normal gaze time, to allow extra time for semantic processing and integration (Payne and Stine-Morrow, 2014) (2 features).

Wrap-up ratio: Ratio of mean wrap-up gaze time to mean sentence-internal gaze time (1 feature).