Chapter 13

Chapter summary

Multi-sensory information aids processing in several ways. Orienting to novel stimuli is faster and more reliable with multi-modal stimulation. The different senses combine to alter perception of objects and their properties, for example: Visual and vestibular responses contribute jointly to estimates of body motion; information from olfaction and gustation is combined to mediate perception of food edibility and flavor.

Some neurons in the sensory cortex respond to multiple modalities, provided that the stimulation is coincident in space and time. The established view is that multi-sensory neurons are present only in high-level convergence zones in the temporal and parietal cortex, but recent research has found multi-modal responses in other brain areas including superior colliculus, primary sensory cortex, and secondary association cortex.

Synaesthesia is a merging of modalities in sensory experience, and is accepted as a genuine sensory phenomenon. For example, spoken words can evoke stable and idiosyncratic colour experiences. Brain imaging studies find differences between the brains of synaesthetic and control subjects, while family and population studies indicate a genetic contribution to synaesthesia.

Synaesthesia is probably due to direct neural connections between uni-modal cortical areas. Synaesthesia may have survived during evolution because it is accompanied by enhanced memory for words and colours.