Sound design dimensions to evaluate

While our interactions with Jake will not be controlled experiments, we should nonetheless think about what design choices we will need to make in soundscape design, and try where practical to create alternative versions that vary along that dimension for evaluation and feedback.  Here are some dimensions that come to mind so far:

• Natural (mimetic) sounds vs symbolic (non-mimetic) sounds:  I conjecture that natural sounds (like water flowing for a water feature) may be easier to initially learn, but we can make symbolic music sounds that are faster to distinguish (allowing a faster scan of a map display) with practice.  Also I think it will be easier to design systematic variations among musical sounds (e.g., different piano intervals are all recognizably piano and not marimba, but can be distinguished from each other).  I would like in an initial prototype to include a soundscape that uses only natural sounds, one that uses only musical sounds, and one that layers an initial very short musical sound over a mimetic natural sound. 
• Fewer or more classes of sounds.  For example, we have three classes of water feature for Yellowstone (stream, river, and lake, as I recall).  Should they be distinguished in sound representation?  I am not sure whether we want to create variations along this dimension right away ... but perhaps it would not be too hard.  
• Sound groupings.  If we do want larger sets of sounds with finer distinctions (e.g., stream vs river), then we should consider ways of thematically grouping sounds.  For example, different classes of water feature could all be represented by piano, with pitch (or interval) distinguishing the particular feature class. 
• Sound duration.  How long does a clip need to be to be recognizable?  This is surely tangled up with the kinds of sounds we use, and how distinct they are.  As mentioned above, my initial thought is that a percussive musical instrument that is identifiable by timbre (e.g., piano, xylophone, tympani, glockenspiel, plucked violin string, etc.) will allow scans that are quick relative to either musical sounds with a less rapid attack and decay (e.g., oboe, flute, bowed violin) or non-percussive natural sounds (water, car horn, phone touch-tone).   Levitin's book "This is Your Brain on Music" notes that our near-instantaneous recognition of familiar recorded music depends primarily on timbre (as versus the sound dimensions pitch, tempo, rhythm, loudness).  If mimetic natural sounds are indeed more learnable, we may need to consider both the required duration of an initial symbolic sound and a longer mimetic sound. 

These are initial thoughts.  What are some other design parameters we should be considering?