Synesthesia

#1 Synesthesia: it is a condition where one sense such as seeing is leads to the occurring impression of another sense like taste. Synesthesia can involve any of the senses however it is rare that it involves three or more senses. Although the true reason behind however scientists believe that it happens because some neurons are "crossed-wired" and the neurons that are suppose to be connected to one sense are connected to another. 

There is no establish method to diagnosis it however some characteristic of synesthesia are: it is involuntary, projected( ex. you see the color rather than imagine it), consistent (it happens every time)and memorable ( ex. it is always color brown to the number 4). [Neuroscience for Kids]

#2 Grapheme-color Synesthesia: It is a form of synesthesia where a particular color is seen when seeing a letter, word or number(referred to as grapheme).[Pubmd.gov]

#3 Ordinal-Linguistic Personification: when people link animate qualities like personality and gender to linguistic units like letters, numerals, days and months.[MITpress]

#4 Number-Form Synesthesia:in this form of synesthesia a persons imagines diagrams when they see numbers. The diagrams vary from person to person but are sometimes similar. 

The people that have this type of condition can go to be math geniuses, but only if they understand it. Because of this ability they are able to do very complex mental arithmetic. However, it would be impossible for them to explain the process.[babycentre]

#5 Sound-Color Synesthesia: In this type of synesthesia that when they hear something the person sees color shapes (called photisms).[Elizabethtown College]

#6 Lexical-Gustatory Synesthesia: is a form of synesthesia that the person relates a word's meaning to a certain taste. The curious thing is that the word's meaning not the sound or spelling that triggers the taste , studies shown.[Live Science]

http://faculty.washington.edu/chudler/syne.html

http://www.ncbi.nlm.nih.gov/pubmed/19302164

http://www.mitpressjournals.org/doi/abs/10.1162/jocn.2007.19.4.694?journalCode=jocn

http://community.babycentre.co.uk/post/a11638125/number-form_synesthesia

http://www.etown.edu/CETL.aspx?topic=An+fMRI+Study+of+Sound-Color+Synesthesia

http://www.livescience.com/1141-insight-people-taste-words.html