Terminology and Concepts

The QExE tool is built around concepts that will be familiar to researchers with a background in sensory evaluation or perceptual quality assessment. However, virtual reality introduces some distinctions worth clarifying. The following definitions describe how these terms are used throughout the QExE documentation and configuration.

Terms

Concept	Description
Method	A test method is the means by which dependent variable data is collected. The QExE tool currently includes five methods, and specifying a method is a mandatory entry in the configuration file. The chosen method determines how AudioVSTConditions and Scenes are combined to calculate the number of unique test items.
Questionnaire	A questionnaire is a research instrument comprising a set of phrases, statements, or questions to which subjects provide responses. In the QExE tool, questionnaires are a supplementary component that can be used alongside the primary method to capture additional attitudinal or cognitive dimensions.
Modality	Modality refers to the audio, visual, or audiovisual sensory streams under evaluation. By setting the modalityRatio entry to "A", "V", or "AV", the tool determines which elements of the configuration file are used to construct test items.
Scene	A scene represents a collection of uni- or multimodal stimuli presented within a 3D environment. Analogous to audio sample files or video clips in conventional evaluation, scenes in QExE are the raw stimuli that are combined with rendering conditions to form the items under test. In VR, scenes are audiovisual and can use 360° video or CGI visuals together with Ambisonics or object-based audio.
Audio Condition	In traditional quality evaluation, conditions typically refer to offline processing applied to stimuli. In interactive VR, conditions are rendered in real time. An audio condition in QExE corresponds to an AudioVSTCondition — a VST plug-in loaded to render spatial audio dynamically. Depending on the method, one or more conditions may be presented simultaneously, with subjects switching between them using buttons A, B, C, etc.
Test Item	A test item is the fundamental unit of a subjective experiment. Subjects progress through evaluation items sequentially until the test is complete. In the QExE tool, test items are calculated automatically from the combination of method, modality, scenes, and audio conditions.