  This paper considers the lexicographical challenge of defining actions a
person takes while eating. The goal is to establish objective and repeatable
gesture definitions based on discernible intent. Such a standard would support
the sharing of data and results between researchers working on the problem of
automatic monitoring of dietary intake. We define five gestures: taking a bite
of food (bite), sipping a drink of liquid (drink), manipulating food for
preparation of intake (utensiling), not moving (rest) and a non-eating category
(other). To test this lexicography, we used our definitions to label a large
data set and tested for inter-rater reliability. The data set consists of a
total of 276 participants eating a single meal while wearing a watch-like
device to track wrist motion. Video was simultaneously recorded and
subsequently reviewed to label gestures. A total of 18 raters manually labeled
51,614 gestures. Every meal was labeled by at least 1 rater, with 95 meals
labeled by 2 raters. Inter-rater reliability was calculated in terms of
agreement, boundary ambiguity, and mistakes. Results were 92.5% agreement (75%
exact agreement, 17.5% boundary ambiguity). Mistakes of intake gestures (0.6%
bite and 1.9% drink) occur much less frequently than non-intake gestures (16.5%
utensiling and 8.7% rest). Similar rates were found across all 18 raters.
Finally, a comparison of gesture segments against single index labels of bites
and drinks from a previous effort showed an agreement of 95.8% with 0.6%
ambiguity and 3.6% mistakes. Overall, these findings take a step towards
developing a consensus lexicography of eating gestures for the research
community.
