Abstract
Purpose: Visually mediated action is an area of contemporary interest. At one extreme is the attempt at inaction represented by the goal of postural stability, for which vision plays an important role. We wanted to develop an inexpensive and reliable means of quantifying postural stability so as to study the role of vision. Method: An electro-optical mouse (Microsoft's Intellimouse) was coupled to a snug-fitting hat and faced upwards. A mouse pad was suspended just over the mouse. Software (Matlab code will be made available) was used to process the resulting signal. Quantitative expressions of instability are readily obtained from the relative movement of mouse and pad. Total path length in a defined time interval, and maximum deviation from the starting point during that interval, were calculated in tests of the technique. A trajectory plot was readily obtained. Results: We recorded postural instability in real time for two subjects. Total path length increased in a 10 second interval with eyes closed compared to eyes open replicating the classic finding in this area. Average total travel for two subjects was 3.94 CM with eyes open vs. 11.19 CM with eyes closed. Maximum deviations were 1.28 and 4.33 CM respectively. Discussion: These recordings demonstrate proof of concept — an Intellimouse is sensitive enough to transduce movement in the range of physiological action. Coupling the mouse to the head leaves the technique open to a head movement artifact. This can be minimized (but not eliminated) by coupling to the trunk, an improvement presently under study.