"Feedback to the user comes in many forms. The user interface responds to actions. The system reacts and produces output. Feedback is used to engage and explain, and can improve user satisfaction. Feedback can change a confusing experience to a pleasant experience that teaches you how the system works."
"All systems require feedback to monitor and change behavior. Feedback usually compares current behavior with predetermined goals and gives back information describing the gap between actual and intended performance."
"Feedback communicates the results of any interaction, making it both visible and understandable. Its job is to give the user a signal that they (or the product) have succeeded or failed at performing a task."
"In this paper, we briefly covered current work on the topics of subliminal perception and affective computing. We then presented an approach for enriching human-computer interaction with analog communication channels. Instead of predefined mappings, this approach is based on an evolutionary feedback loop."