Using multidimensional scaling to determine distances in the perceptual space of rolling sounds

We recorded sounds generated by a ball rolling over a wooden plate. Ball diameter, rolling speed, and plate thickness were varied. In a difference-scaling experiment, the important dimensions of the space spanned by these sounds were determined. All sounds were combined in pairs and subjects were asked to quantify the difference they heard in each pair. In this way all possible perceptual differences could play a role in the difference scalings without a need to interpret these differences in terms of underlying object properties such as size or speed. Using multidimensional scaling, a good fit for the scaled differences was obtained with a minimum of three dimensions. None of the dimensions corresponded directly with one of the three mechanical parameters varied in the rolling sounds. Differences in speed lead to a smaller distance in the thus-obtained perceptual space than differences in size, for the ranges we used. This corresponds to results from experiments where the subjects were directly asked to judge size and speed differences using the same sounds. Remarkably, the plate thickness resulted in large distances in perceptual space, while this mechanical property is poorly recognized when participants are directly asked for it.