Non-verbal communication may include any type of change expressed within a pattern that can be related to other information.
(The following is a quick brainstorm. You may want to categorize and group these; e.g. graphical, facial expressions, sound, etc)
Here are some other examples of non-verbal communication variables for us to consider:
touch, pressure, expanse of contact, vibration, motion sequence, direction of motion
smell, intensity or thickness, temperature changes, sequence of smell, eye contact (gaze), sequence of gaze, duration of gaze, motion of gaze, body and gaze combinations
volume, variation of volume, duration of one volume contrasted with duration of another volume, context of volume variation etc
vocal nuance, intonation proximity, duration, environmental context during proximity, gestures, “size” or “expansion of gesture”, speed of gesture, duration of gesture, motion of gesture, sequence of gesture
facial expression? pause (silence)
dress, meaning of color, size, objects within cultural lexicon, physical variables (e.g. size, etc)
posture, sequence, duration, context of posture..
motion, color, shape, size, thickness, width,
texture, opacity, distortion, number of occurrences
Line thickness (think barcode)
Space between any elements (eg. Space between sound elements (think music)
Space between contact of elements (think telegraph’s morse code)
Saturation, brightness, reaction to other elements, weight, maleability, heat, durability of gesture, quantity, connection, angle, location, etc.
Update: May 3, 2012: Someone has done a good job at documenting non-verbal communication in Wikipedia