The magnitude of variation in the gaze position signals recorded by an eye tracker, also known as its precision, is an important aspect of an eye tracker’s data quality. However, data quality of eye-tracking signals is still poorly understood. In this paper, we therefore investigate the following: (1) How do the various available measures characterizing eye-tracking data during fixation relate to each other? (2) How are they influenced by signal type? (3) What type of noise should be used to augment eye-tracking data when evaluating eye-movement analysis methods? To support our analysis, this paper presents new measures to characterize signal type and signal magnitude based on RMS-S2S and STD, two established measures of precision. Simulations are performed to investigate how each of these measures depends on the number of gaze position samples over which they are calculated, and to reveal how RMS-S2S and STD relate to each other and to measures characterizing the temporal spectrum composition of the recorded gaze position signal. Further empirical investigations were performed using gaze position data recorded with five eye trackers from human and artificial eyes. We found that although the examined eye trackers produce gaze position signals with different characteristics, the relations between precision measures derived from simulations are borne out by the data. We furthermore conclude that data with a range of signal type values should be used to assess the robustness of eye-movement analysis methods. We present a method for generating artificial eye-tracker noise of any signal type and magnitude.

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Syntax highlighting or syntax colouring, plays a vital role in programming development environments by colour-coding various code elements differently. The supposition is that this syntax highlighting assists programmers when reading and analysing code. However, academic text books are largely only available in black-and-white which could influence the comprehension of novice and beginner programmers. This study investigated whether student programmers experience more difficulty in reading and comprehending source code when it is presented without syntax highlighting. Number of fixations, fixation durations and regressions were all higher for black-and-white code than for colour code but not significantly so. Subjectively students indicated that the colour code snippets were easier to read and more aesthetically pleasing. Based on the analysis it could be concluded that students do not experience significantly more difficulty when reading code in black-and-white as printed in text books.

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