Synaesthesia

1. Hearing colours, seeing tones and unusual associative perceptions such as sensing colours as an aspect of numbers.

2. Types of synaesthesia may be called photisms (visual), phonisms (aural), tactile, olfactory and gustatory, or they may be multisensory.

3. Synaesthesia may relate to clairvoyance, clairaudience, etc., and other extrasensory psychological phenomena most of which are unexplained and lack any prudent, modern theoretical formulation. Older theories spoke of a common sense or sixth sense as the one that united the other five(see also: synaesthesis).