During the process of food consumption, humans recognize food by sight and olfaction and judge the properties of food based on previous dietary experiences and memories. This cognition is important for the transport of food to the mouth by the upper limbs, head motion towards the food, mouth opening and closing motion, mastication, swallowing, and the coordination of these motions. For example, Daet et al. (1995) suggest that the degree of mouth opening during food intake increases with increasing food size and that sight may play a major role in determining the degree of mouth opening required, especially for large foods.

Appropriate coordinated motions contribute to stable feeding behavior the acquisition of appropriate feeding function skills in childhood, and the maintenance and improvement of feeding function skills in old age (Matsuo and Palmer, 2008, Matsuo and Palmer, 2009). For this reason, there have been various studies on coordinated motions during feeding motions. Shinya et al. (2013) measured head motions during mastication and reported that in the early stages of mastication, when the food in the mouth is larger and requires greater mouth opening and closing motions, the head flexes forward to stabilize the head motions. Matsubara et al. (2002) reported differences for foods with different properties; for example, the head moves downwards in coordination with mandibular motions when chewing more elastic foods. Häggman-Henrikson and Eriksson (2004) reported that mastication involves both mandibular and head extension and flexion motions and that the degree of head motion depends on the bolus in the mouth. Although food feeding involves a series of motions from food intake to swallowing, many studies have focused on the coordinated motions of the head during mastication. However, few studies have focused on coordinated motions of the head and mouth opening and closing with food intake.

Various methods have been used in the past to assess feeding function. Ogawa et al. (2012) videotaped the feeding motions of children with pervasive developmental disorder during spoon-feeding and assessed them using the Enjoji Scale of Infant Analytical Development Test. This measurement method is simple and can be used for participants who cannot cooperate; however, the evaluation depends on the subjectivity of the surgeon and this makes objective assessment difficult. Kitte et al. (2017) used two digital cameras, jaw markers, and three-dimensional imaging software to obtain three-dimensional motion data to assess masticatory behavior from food intake to swallowing. Pinheiro et al. (2008) used video cameras and computer programs to measure reflective markers fixed to the mandible to quantify the opening, closing, protruding, and lateral projecting motions of the mandible. Kuroda et al. (2011) used six degrees of freedom to analyze adults and children concerning the coordinated motions of the mandible and head during jaw motions. However, these studies involved expensive machines and complicated procedures, such as the need to place measurement markers on the body surface, making it difficult to measure natural feeding behavior.

In this study, a motion capture system that can measure more natural motions was developed to measure and analyze head motions during food intake. The measurement results were then used to verify the hypothesis that “during food intake, the head motions change according to the properties of the food.”