Synesthesia
This derangement has little to do with logic and more with sensory interpretation. The afflicted vampire's sensory input is somewhat "scrambled"; although he's still capable of receiving sensory information, the information each sense provides is processed in terms of a different sense. In short, the synesthetic "hears" colors, "smells" textures, "tastes" sounds and the like, and is hard-pressed to think of such stimuli in any other fashion.
Although the synesthetic is presumably accustomed to the unusual sensory input, his real problem lies in communicating what he senses to others. A character so afflicted has difficulty expressing concepts as simple as "cut the red wire" - he's much more likely to say "cut the sandpapery wire" or something similar - and even has similar difficulties comprehending speech from others. Since the associations vary from individual to individual, there's not even any guarantee that another synesthetic would be able to understand the vampire.
Apart from the aforementioned difficulties in daily communication, the synesthetic receives +2 difficulty to any Expression and Performance rolls that don't involve creatign purely surreal art, poetry or the like. The synesthetic may spend a Willpower point to correlate her sensory input in a "normal" fashion for a turn - or rather, at least to be able to communicate "normally" in terms of colors, textures, smells, tastes, temperature or sound. The character would still hear a ringing noise and think of it as a spicy smell, for instance - he's just able to focus enough to associate that spicy smell he hears with what other people call "ringing."
