Although the term "user experience" (UX) has been used extensively in recent years, it has been associated with a wide range of meanings [10]. Commonly, however, the definition of UX goes beyond the traditional instrumental conception of usability common in the HCI literature [2, 3]. Unlike usability, UX tends to include wider human experience dimensions (such as pleasure, fun, and other emotions) and also may have a temporal or longitudinal component. While usability tends to be focused on task efficiency and effectiveness measures, UX includes emotional and perceptual components across time. UX involves a constant feedback loop repeated throughout the usage lifecycle including from initial discovery through purchase, out-of-box, usage, maintenance, upgrades, and disposal.

At a minimum, there are at least four components of UX. The components and a simplified relationship between these components are shown in Figure 1. The UX consists of perceptions that shape emotions, thoughts, and attitudes. The UX directly influences behavior that then continues the loop.

Components of UX

Figure 1: Components of User Experience
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The following definitions are based on a literature review within psychology and HCI and have been developed to be relevant across different perspectives. The goal is to provide distinctions between key terms associated with UX. These distinctions are also relevant to potential UX goal setting and measurement.

• User Experience (UX): Emotions, attitudes, thoughts, and perceptions felt by users across the usage lifecycle.
• User Experience Quality (UXQ): (1) degree to which a system meets the target user's tacit and explicit expectations for experience or (2) the measured level of quality of a particular UX when compared to a specific target, using a specified metric and method or tool.
• Perceptions: The process of acquiring and interpreting sensory information. Focus is on the intake of information. Psycho-visual and psycho-acoustics studies assess human perceptual variables that can provide data to drive requirements and assess human perceptual aspects of interaction with technology such as video quality, audio quality, acoustical, and thermal performance.
• Emotions: Subjective states of consciousness that evoke positive or negative feelings. Emotions, both positive and negative, are critical to learning, trust, and assessment of what's desirable [7, 8, 11]. These, in turn, affect purchasing behavior, how much the technology is used, and what consumers say about their experiences. Despite the widely held impression that people make decisions logically, in fact, research shows that decisions are highly dependent on the emotional states of end users [12, 13].
• Attitudes: Judgments about a target, usually expressed as good or bad, helpful or harmful. Attitudes are a function of experience or anticipated experience with the target and include value judgments.
• Thoughts: Mental and cognitive processes that allow humans to model what they experience and plan behavior.
• Behaviors: Observable overt movement that includes verbal behavior as well as physical. Actions in response to our environment or experience.

Measurement of UX can be explicitly targeted to measure certain aspects of these constructs depending upon the product goals.