A sensory event differs from a sensory emanation in that an emanation is ongoing and passive, while an event is isolated in time and actively notifies observers.
SensoryEvent : object
'source' is the source object - this is the physical object in the simulation that is causing the event. For example, if the event is the sound of a phone ringing, the phone would probably be the source object. The source is used to determine which observers are capable of detecting the event: an observer must be able to sense the source object in the appropriate sense to be notified of the event.