Fine Structure Project. This project investigates how amplitude modulation (AM) of very soft sounds (near the hearing threshold) is processed by the ear. The question is whether we use the periodic level changes of the signal in order to detect AM, or whether we use spectral cues given by the sidebands in the spectrum of an amplitude modulated signal instead. For this purpose use is made of an (often periodic) fine structure which is present in many normal hearing subjects' hearing thresholds. A fast method for screening this fine structure has been developed.
Complex Modulations Project. This project examines how higher order AMs are processed (e.g. a 2nd order AM is an amplitude modulation whose amplitude is modulated, i.e. whose depth changes over time). First experiments have shown that 2nd order AM may interfere with 1st order AM. The goal is to find a model which can predict this processing correctly.