A low cost stereophotogrammetric system for the evaluation of tridimensional head translations during visual tasks.

A simple, low cost and easy-to-operate 3D stereophotogrammetry system was developed to measure the kinematic pattern of head stabilisation during visual tasks. The system differs from commercially available ones since it: (a) takes into account the gaze motor coordination characteristics and measures the head translations quantified at the point that best represents the translations caused by the eyes' movement during visual tasks, that is, the midpoint between the eyes; (b) offers minimum restriction to the head movement and minimum interference with it; (c) innovates when using the position coordinates produced by a free-online tracker software. The system was effective in recording the head movements and its RMS total error was 0.705 mm with ±0.808 mm standard deviation. This represents an RMS total error of 3.5%, considered satisfactory because it provided results with a confidence level higher than 95%. The system was effective to record differences in head movements of 11 individuals in open and closed eyes conditions and revealed the direction-specific feature of the head displacements size. The results showed that the system is a cost-effective and accurate alternative for studies needing to accurately measure head movements during visual tasks.