A Psychometric Evaluation of the Body Image Questionnaire Child and Adolescent Version.

Two observers presented with the exact same visual stimulus may experience a qualitatively very different percept (e.g., ‘the dress’; ). While intuitively this may seem puzzling, theories on consciousness and vision explain such phenomena by noting that human perception, rather than a direct reflection of the external (shared) world, emerges in a constructive process of adjusting incoming sensory signals against our idiosyncratic expectations, knowledge, and experiences (; ; ; ; ). This constructed understanding becomes especially apparent in color perception; even though color space is clearly defined in its physical and perceptual dimensions (), it still fails to capture the aspect of an individual's color experience (; ). Not surprisingly, being able to measure, understand, and eventually describe the emergence of these subjective qualia is therefore one of the most hotly debated questions in the neurosciences, philosophy, and beyond (; ; ; ). Here, we present a natural experiment of subjective color phenomenology; a condition called grapheme-color synesthesia (; ; ; ). For grapheme-color synesthetes, certain linguistic inducers (e.g., grapheme 4) automatically and consistently trigger additional and idiosyncratic conscious color percepts (e.g., a bright-blue color) alongside the veridical sensory input. The different synesthesia types all share the defining characteristics of an additional conscious and consistent experience. Synesthetes can verbally report their additional experience, and synesthetic sensations can be measured in behavioral paradigms such as the synesthetic Stroop effect, or brain activation patterns in sensory cortex (). Furthermore, test–retest paradigms show how synesthetic, but not non-synesthetic associations are highly specific and consistent (; ; ). Thus, over the past decades, research has established synesthesia as a real condition that can reliably be identified using behavior, neurophysiology, and neuroimaging (; ; ; ; ; ; ). The most remarkable aspect of synesthesia is the subjective perceptual phenomenology of the induced additional sensation, that is, color in grapheme-color synesthesia. This sets synesthetic sensations apart from (color) memory, thought, or amodal association. Synesthesia can thus offer an interesting doorway into examining qualia, the subjective perceptual phenomenology or first person (whats-it-like) perspective. Furthermore, much like ordinary perception, the synesthetic experience is described as ‘automatic’ in the sense that it comes effortlessly (; ; ; albeit not pre-attentive, see ; ); the concurrent synesthetic color is ‘just there’, even if incongruent with the task at hand (; ; ). Because each synesthete has a stable set of grapheme-color pairings, the color phenomenology can be examined independently of the physical properties of the inducing stimuli. Therefore, synesthesia might provide a unique window into how the brain's constructive processes can generate additional, conscious content, cross-over experiences, often across modalities, going all the way down to the level of sensory phenomenology. The measurement of such sensory phenomenology primarily relies on subjective reports and introspection, methods often criticized for potential unreliability and susceptibility to biases or expectancy effects (e.g., ; ; ). These concerns extend to synesthesia research, where objective measurements are called for to corroborate subjective reports (; ; ). Instead, current paradigms capturing synesthesia employ objective measures, but fail to capture its phenomenology (; ; ; ). Behavioral and neurophysiological findings suggesting synesthetic colors behave like printed colors in turn have been questioned regarding replicability and interpretability (; ; ; ). In short, the lack of agreed-upon objective methodology is a critical roadblock obstructing scientific examination of the extraordinary synesthetic phenomenology. By extension, this locks the conditions potential to inform our understanding of the constructive top-down cross-over processes that can generate additional conscious percepts.