The dynamical response of a soft X ray emission profile to different external perturbations - gas feed, impurity injection, RF power, surface loop voltage - has been studied on the TCA tokamak and analysed using a single technique. The frequency dependence of the response has been exploited to distinguish between the dominant transport processes. Remarkably similar phase response profiles were obtained with different stimuli; they show a link with sawtooth activity. The model that most plausibly explains these experimental observations requires diffusive transport with a diffusive coefficient locally modulated by the perturbation.