A model of head movement contribution for gaze transitions.

Head posture has been associated with work-related neck symptoms and discomfort, but its relationship with visual tasks has received much less attention. Head movement amplitude is normally a fraction of the angular distance to a visual target, as gaze transition is usually achieved through the combination of both head and eye movement. In this study, the proportion of head orientation vs. target orientation, named head movement contribution ratio (HMCR), was quantified and modelled as a function of target location. Head movements were measured on subjects orienting and maintaining gaze for 2 s at randomly presented visual targets distributed along an arc placed horizontally or vertically. Bootstrap regression models showed that the horizontal HMCR was approximately 69% of target azimuth. The vertical HMCR was bilinear and corresponded to 52% and 8% and of target elevation for targets above and below the horizontal plane, respectively. The data also demonstrated that head orientation is affected by the kinematic coupling between horizontal and vertical components of head movement. STATEMENT OF RELEVANCE: Awkward head and neck posture is a risk factor for work-related musculoskeletal disorders. This study investigated the influence of visual target location on head orientation over a large range of target eccentricity, as an attempt to predict the head and neck posture required for visual target detection and identification.