In the preceding chapters, I focused on the psychopathology of perception or of sensation. These pathologies often, if not invariably, are recognized as indicating underlying disorders or diseases. I now turn to synaesthesia, a condition that is not usually thought of as a disorder or disease but rather as a variant of normal experience. Put simply, it is the merging of the senses, in which a stimulus in one sensory modality both evokes a normal perception, as expected, in the same modality and an anomalous perception in another modality. In other words, there is cross-modal perception.