An interesting concept has come from the Retro Remakes 2006 competition, via "Rogue", for making games more accessible to deaf gamers.
"ActionCaptions would be based on their original auditory counterparts. So a dripping sound in the background would be visualised (symbolized!) by a small blue-ish watery text balloon. Depending on the location of the sound, the balloons would be placed on those spots. A boulder crashing down from the ceiling would invoke a much greater balloon with stylized lettering (e.g. grey, cracked stoney characters). The louder the sound, the bigger and more obvious the balloon. Timing & placement is very important in this regard as well. A blowing wind would linger longer on-screen than a slap in the face, or a gunshot."