a tracking unit configured to determine a location of the one or more peripherals in dependence upon images captured by a camera associated with an HMD worn by the user;

a generation unit configured to generate, in response to a determination by the tracking unit that one or more of the peripherals is not visible in the images, an array of home points behind the user, the home points being locations defined in dependence upon constraints upon the user's motion;

an estimation unit configured to estimate the respective locations of non-visible peripherals in dependence upon the output of one or more inertial measurement units associated with each peripheral; and

a selection unit configured to select a home point, from amongst the array of home points, for each of the non-visible peripherals,

wherein the tracking unit is configured to generate a location for each non-visible peripheral such that the location converges towards the selected home point.