Running head: INFANT EYE-TRACKER DATA QUALITY
Supplementary Methods
Data shown in Figure S1 is pilot data recorded from typically developing 12-month-old infants
viewing videos and still images. All stimuli were presented on a Tobii TX300 integrated with a 23inch monitor. Infants were seated on their caregiver’s lap at circa 60cm viewing distance from the
monitor. Stimuli were presented using Matlab, Psychtoolbox and the Matlab SDK. The infant
illumination mode was used.
Data shown in Figure S2 is taken from Analysis 1.
Data shown in Figure S3 is taken from Analysis 4.
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Running head: INFANT EYE-TRACKER DATA QUALITY
Supplementary Results
Figure S1: Further raw data samples. These data were recorded from typically developing 12month-old infants on a Tobii TX300, running via Matlab and the SDK.
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Running head: INFANT EYE-TRACKER DATA QUALITY
Figure S2: Supplementary analyses for our robustness measures. The data reported are taken from Analysis
1. a) A scatterplot showing the relationship of average fragment duration (our principal robustness measure
that we report on throughout the text) to proportion available data. A high average fragment duration and
high proportion available data indicate almost complete data; low fragment duration and high proportion
available data indicate unbroken looking but interspersed with occasional short periods of missing data;
high fragment duration and low proportion available data indicate periods of unbroken looking interspersed
with periods of completely missing data, which may be attributable to cases in which the tracking quality
was high but the participant looked away from the screen during tracking. b) A histrogram showing the
distribution of the proportion of available data segments. Data from infants has been drawn in black and
from adults in grey. The maximum possible fragment duration is 8 seconds in this data sample as the video
clips used were 8 seconds long.
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Running head: INFANT EYE-TRACKER DATA QUALITY
Figure S3: An identical analysis to that shown in Figure 7, but examining the number of samples
recorded to eyes and nose/mouth instead of the proportion of available samples. Identical analyses
were conducted on these data as on the data in the main ms. The Pearson’s product moment
correlation identified a significant relationship between precision and number of samples recorded
to eyes: r(64)=-.37, p=.003. Spearman’s ϱ was calculated to assess the relationship between
precision and number of samples recorded to nose and mouth. This was found not to be significant :
ϱ (64)=.20, p=.11, although a similar directional effect was observed to the relationship
documented in the main text.
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