There has been little work on Comodulation Detection Differences (CDD) compared to the related paradigm of Comodulation Masking Release (CMR). In a CMR experiment, a sinusoidal signal is masked by a modulated band of noise that has energy at the signal frequency. Adding noise with the same envelope (comodulated) at other frequencies in either ear has been shown to reduce the signal threshold. In a CDD experiment, a modulated noise signal is masked by another modulated noise presented to the same ear. If the signal and masker bands are comodulated, the threshold for detection is higher. The peripheral auditory system is widely assumed to contain an array of overlapping bandpass filters (the auditory filters). The classical power spectrum model of detection makes the assumption that the output of only one filter (channel) is monitored during signal detection. A detection process in such a situation is described as being within-channel. However, CMR shows that energy in an independent channel (which could even be in the other ear, so that it can be certain there is no interaction) can affect signal threshold. This means that a number of channels must be being monitored; such a detection process is described as being across-channel.
There is considerable evidence to show that both within- and across-channel processes contribute to detection in CMR experiments. There has often been the tacit assumption that what is true for CMR is true for CDD due to the similarity in the experimental paradigms. This thesis presents work designed to assess the relative contributions of within- and across channel processes in CDD. A number of experiments manipulating factors known to affect within-channel processes, but not across-channel processes (or vice versa) were performed (such as altering masker level and signal-masker onset asynchrony). A model based on a within-channel process only was presented and the predictions that it made were tested experimentally. The model successfully predicted the outcomes of a number of CDD experiments. The experiments, in general, gave no evidence for an across-channel process; the results can be explained satisfactorily by a within-channel mechanism.