3 Bussemakers, M. P. de Haan, A. 1998 Brewster, S. Proceedings of the 5th International Conference on Auditory Display (ICAD98) University of Glasgow, U.K. British Computer Society In this study, the modality appropriateness hypothesis that originated from experiments in perception is tested for human computer interaction situations. In multimodal information processing users need to integrate the data coming from various sources into one message. In a visual and auditory categorisation task with accessory stimuli in the other modality, containing a mood, it was shown that in tasks where choices need to be made based on the meaning of the stimuli, the visual modality seems more appropriate. From the results can be concluded that users do not always benefit from having information in more than one modality. Proceedings/1998/BussemakersdeHaan1998.pdf