1. A self-developing device comprising: input means for determining the value of a set of one or more sensory-motor variables (S(t)) representative of the status of the environment; control means ( 10 ) for outputting a set of one or more control signals (M(t)) adapted to control action of a sensory-motor apparatus with which the self-developing device is associated in use; a motivation module ( 11 ) for calculating a reward (R(v,t)) associated with a candidate value that can be taken by said set of control signals (M(t)); and selection means ( 10 ) for deciding, based on reward values calculated by the motivation module ( 11 ), which value should be taken by said set of control signals (M(t)), the selection means controlling the control means to output the selected value; wherein the motivation module ( 11 ) is adapted to evaluate rewards by calculating a function (R(v,t)) of at least one motivational variable (v) whose value is derived from at least one of the sensory-motor variables of said set (SM(t)); characterized in that the motivation module ( 11 ) uses a computation device ( 15 ) adapted to perform a history-dependent calculation to calculate the value of said at least one motivational variable (v), said history-dependent calculation being dependent upon at least one of: a) one or more time-varying internal parameters of the computation device ( 15 ) or of a device cooperating with the computation device in the computation of the at least one motivational variable (v), and, b) values (SM(t),SM(t−1)) taken at different times by said at least one sensory-motor variable of said set.