Most synesthetes become aware of their distinctive mode of perception in their childhood.
Some have learned how to apply their ability in daily life and work.
In spatial-sequence, or number form synesthesia, numbers, months of the year, or days of the week elicit precise locations in space (for example, 1980 may be "farther away" than 1990), or may appear as a three-dimensional map (clockwise or counterclockwise).
This hypothesis – referred to as semantic vacuum hypothesis – explains why the most common forms of synesthesia are grapheme-color, spatial sequence and number form.
In one common form of synesthesia, known as grapheme-color synesthesia or color-graphemic synesthesia, letters or numbers are perceived as inherently colored.Types of synesthesia are indicated by using the notation x → y, where x is the "inducer" or trigger experience, and y is the "concurrent" or additional experience.For example, perceiving letters and numbers (collectively called graphemes) as colored would be indicated as grapheme → color synesthesia.This variability was first noticed early in synesthesia research.Self reports, interviews, and autobiographical notes by synesthetes demonstrate a great degree of variety in types of synesthesia, intensity of synesthetic perceptions, awareness of the perceptual discrepancies between synesthetes and non-synesthetes, and the ways synesthesia is used in work, creative processes, and daily life.For example, in the common form chromesthesia (sound to color) a projector may hear a trumpet and see an orange triangle in space while an associator might hear a trumpet and think very strongly that it sounds "orange".