A system for determining a direction of gaze of a user, comprising: an audio end-point including a pair of earpieces, each earpiece intended to be worn adjacent to a respective one of the user's ears, a set of electrodes (10, 10a, 10b) arranged on each earpiece, such that they, in use, are placed in contact with the user's skin, each electrode comprising a patch of compressible and electrically conducting foam material, configured to provide a reliable electrical connection with the skin, and circuitry connected to the electrodes and configured to: receive a set of voltage signals from a set of electrodes arranged on an audio endpoint worn by a user, multiplex said voltage signals into an input signal, remove a predicted central voltage, representing a forward gaze direction, from said input signal, to provide a detrended signal, and determine said gaze direction based on said detrended signal; wherein said predicted central voltage is a current predicted central voltage and wherein said determined gaze direction is a current gaze direction, and wherein said circuitry is further configured to determine a subsequent predicted central voltage by: calculating (28, 29) a central voltage as a difference between the input signal and a voltage representing the current gaze direction, providing a first estimate as a linear weighting of the calculated central voltage and the current predicted central voltage, providing (32, 33, 35) a second estimate as a mean of the calculated central voltage and a prediction based on a set of preceding predicted central voltages, and determining the subsequent predicted central voltage as an average of the first and second estimates; wherein said circuitry is configured to determine a subsequent gaze direction based on the subsequent predicted central voltage. an audio end-point including a pair of earpieces, each earpiece intended to be worn adjacent to a respective one of the user's ears, a set of electrodes (10, 10a, 10b) arranged on each earpiece, such that they, in use, are placed in contact with the user's skin, each electrode comprising a patch of compressible and electrically conducting foam material, configured to provide a reliable electrical connection with the skin, and circuitry connected to the electrodes and configured to: receive a set of voltage signals from a set of electrodes arranged on an audio endpoint worn by a user, multiplex said voltage signals into an input signal, remove a predicted central voltage, representing a forward gaze direction, from said input signal, to provide a detrended signal, and determine said gaze direction based on said detrended signal; receive a set of voltage signals from a set of electrodes arranged on an audio endpoint worn by a user, multiplex said voltage signals into an input signal, remove a predicted central voltage, representing a forward gaze direction, from said input signal, to provide a detrended signal, and determine said gaze direction based on said detrended signal; wherein said predicted central voltage is a current predicted central voltage and wherein said determined gaze direction is a current gaze direction, and wherein said circuitry is further configured to determine a subsequent predicted central voltage by: calculating (28, 29) a central voltage as a difference between the input signal and a voltage representing the current gaze direction, providing a first estimate as a linear weighting of the calculated central voltage and the current predicted central voltage, providing (32, 33, 35) a second estimate as a mean of the calculated central voltage and a prediction based on a set of preceding predicted central voltages, and determining the subsequent predicted central voltage as an average of the first and second estimates; calculating (28, 29) a central voltage as a difference between the input signal and a voltage representing the current gaze direction, providing a first estimate as a linear weighting of the calculated central voltage and the current predicted central voltage, providing (32, 33, 35) a second estimate as a mean of the calculated central voltage and a prediction based on a set of preceding predicted central voltages, and determining the subsequent predicted central voltage as an average of the first and second estimates; wherein said circuitry is configured to determine a subsequent gaze direction based on the subsequent predicted central voltage.