Synaesthetic interactions across vision and audition

In everyday life our senses are exposed to a constant influx of sensory signals. The brain binds signals into a coherent percept based on temporal, spatial or semantic correspondences. In addition, synaesthetic correspondences may form important cues for multisensory binding. This study focussed on the synaesthetic correspondences between auditory pitch and visual size. While high pitch has been associated with small objects in static contexts, recent research has surprisingly found that increasing size is linked with rising pitch. The current study presented participants with small/large visual circles/discs together with high/low pitched pure tones in an intersensory selective attention paradigm. Whilst fixating a central cross participants discriminated between small and large visual size in the visual modality or between high and low pitch in the auditory modality. Across a series of five experiments, we observed convergent evidence that participants associated small visual size with low pitch and large visual size with high pitch. In other words, we observed the pitch-size mapping that has previously been observed only for dynamic contexts. We suggest that these contradictory findings may emerge because participants can interpret visual size as an index of permanent object size or distance (e.g. in motion) from the observer. Moreover, the pitch-size mapping may depend not only on relative but also on the absolute levels of pitch and size of the presented stimuli.