 One feature of these environmental interactions is that they suppress interference between states from some preferred set (‘eigenstates of the decohering variable’). This can be a discrete set of states, e.g. the upper and lower component of the wave function in our simple example of the two-slit experiment, or left- and right-handed states in models of chiral molecules; when an atom interacts with the electromagnetic field, the preferred states will be the stationary states (which are the states we observe in spectroscopy). Or it could be some continuous set, e.g. the ‘coherent states’ of a harmonic oscillator (in which case the terminology of ‘eigenstates’ or ‘eigenbasis’ of a preferred observable is not quite accurate). The intuitive picture is one in which the environment monitors the system of interest by spontanesouly and continuously ‘measuring’ some quantity characterised by the set of preferred states (i.e. the environment interacts with the system in such a way that it could in principle be used as a measuring apparatus).