1. A vehicle including a passenger compartment, comprising: a frame defining the passenger compartment and at least one seating location in each of which an occupant may be seated; and an arrangement for determining the location of the eyes of an occupant in a vehicle, said arrangement comprising: at least one wave-receiving transducer arranged to receive waves from the passenger compartment generated or modified by the occupant, each of said at least one transducer being arranged in front of at least one seating location and configured to receive waves from a front of the occupant when the occupant is situated in that seating location, and a processor coupled to said at least one transducer for analyzing the waves received by said at least one transducer and determining the location of the head of the occupant relative to the passenger compartment based on the analysis of the received waves and then determining the location of the eyes from the determined location of the head of the occupant, said processor comprising a trained pattern recognition algorithm which has been trained using data about known locations of the heads of occupants in different positions and waves received from the passenger compartment when the occupants in the different positions are present.