Auditory-visual synaesthesia: investigations using dynamic sounds and spontaneous reports between sleep and wakefulness

Visual images induced by music or other sounds represent a relatively common type of synaesthesia that is fairly well documented in the synaesthesia literature. It sometimes occurs in certain altered states of consciousness and in individuals with (visual) sensory loss in addition to healthy synaesthetes. Furthermore, it has been suggested that there are some common trends between synaesthetes and non-synaesthetes when it comes to matching sounds with colours. Specifically, brighter colours tend to matched with high pitched sounds. Here we report a novel study looking at colours matched to dynamic auditory stimuli. We used stimuli with high/low base pitch, rising/falling pitch and increasing/decreasing spectral brightness. We replicated the finding that brighter colours are chosen for higher pitch sounds. We also found that rising pitch tends to be associated with brighter colours (regardless of average pitch), however, changes in spectral brightness did not affect colour choices. The same pattern of results was obtained for synaesthetes and non-synaesthetes, indicating further similarities between the two groups than previously documented. A second novel observation we have noted concerning auditory-visual synaesthesia is that it may be experienced by non-synaesthetes between sleep and wakefulness, adding to the list of altered states of consciousness in which synaesthetic perception may be encountered.