The distinction between phenomenal consciousness (raw subjective experience) and access consciousness (information available for reasoning and reporting) is conceptually clear but empirically difficult to separate. Existing evidence has not resolved whether they can actually occur apart. A major methodological obstacle is that researchers typically rely on verbal reports, which already involve access consciousness. This paper proposes studying phenomenal consciousness as a natural kind, analogous to how water was identified before its chemical structure was known. By treating phenomenal consciousness as a natural kind with an underlying nature to be discovered, researchers can identify instances of it independently of access consciousness, just as non-liquid samples of water are still water. This framework provides a systematic way to move beyond the reliance on verbal report.
The quality space hypothesis holds that conscious sensory states, such as colors, are experienced in relation to one another—red feels more like orange than like green or blue. Recent evidence indicates that subjective similarity among experiences can be explained by similarities in neural activation patterns. This review examines how localist, workspace, and higher-order theories of consciousness can account for the qualitative character of experience and functionally support a quality space. Existing empirical evidence for each theoretical position is assessed, and novel experimental methods—including altering local activation spaces through brain stimulation or behavioral training—are highlighted as ways to distinguish among these accounts.