Taking a running leap off of the diving board set up here, I will attempt to swan dive into a useful conclusion. (Or a water death).
What I’m wondering is, going with the previous assumption that grapheme synesthesia (GS) can be understood as the product of an interaction between the shape of a printed character and the position of a sort of internally perceived light, if GS is not so much an abstract connection between two entirely unrelated stimuli, but rather a concrete associated between light and space.
Given the previous examples, I’ll use O (black) and I (white) again. The shape of ‘O’ creates a large space that all light becomes trapped inside, creating black. ‘I’ reflects this light. This is not so abstract as it may seem, given the properties of light and space. An object that holds all light and does not reflect any back will appear black in colour. An object that reflects light will appear white. This is why it’s cooler to wear white in the hot sun than it is to wear black.
This is where we dive, get ready.
If each letter takes up a certain amount of space and creates a semi-unique area in which light is either absorbed or reflected according to where the light is, then logically, there is a semi-unique amount of light that pertains to each as well. Examine the room that you are sitting in. It has certain qualities lent to it by the positioning of the objects within it, the proximity of the walls and ceiling, and the colours that are present. Now imagine if the ceiling were higher or lower, the walls farther from you, if it were brighter, dimmer. Does it same the same, or does the room have at least a slightly different ambiance and tone? I hope that it’s the latter or else all my time spent in art courses was useless.
The letters could, in essence, carve away the space where the light can be in a similar fashion for the synesthete. If so, then all the synesthete has done is applied a basic human recognition of the designs that he or she is in has on them to the microcostic space created by the letters. The letters allow or prohibit a certain amount of light to enter into the space provided and are assigned a colour based upon how the light interacts.
A documentary on synesthesia, Derek Tastes of Earwax, considers the possibility that synesthesia might be a beneficial evolutionary trait, which is exciting.