Consciousness can be divided into access consciousness (A-C), which involves reasoning and memory and is measurable, and phenomenal consciousness (P-C), the subjective experience of 'what it's like,' which is harder to test directly. Researchers previously developed indirect measures of P-C using subjective questions informed by objective dimensions of A-C. To bridge the gap before clinical validation, they adapted a thought experiment from quantum physics—'Schrödinger's cat and mouse'—to test the principles underlying their operationalization of P-C. This thought experiment suggests their theories on consciousness, particularly P-C, resonate with disorders of consciousness such as delirium.
A set of candidate measures for assessing phenomenal consciousness in delirium has been developed and validated. Delirium is traditionally considered a disorder of consciousness, but clinical assessments of alertness and arousal are insufficient for a dimensional evaluation. A narrative review of 814 articles identified 14 existing tools across three domains of phenomenal consciousness—prereflective consciousness, phenomenal-sensed experience, and reflective thought—but only one met eligibility criteria for delirium assessment. Fifty-seven new tests were generated using the silent generation technique, later reduced to 26 and then 22 after content validity evaluation. The scale average content validity index was 0.89, inter-rater agreement ranged from 80% to 97%, and face validity was 100% positive. The Flesch Reading Ease Score was 91.6, indicating very easy readability. Early validation results are promising.