The AI Perception Stimuli Source Component gives the owning Actor a way to automatically register itself as a stimuli source for the designated Sense(s) within the Perception System. An example use case would be to have an AI character with an AI Perception Component set up to perceive stimuli based on Sight. You could then use the Stimuli Source Component in an Actor (such as an item pickup Actor) and register it as a stimuli for Sight (which would enable the AI to "see" the Actor in the Level).