Identifying content-invariant neural signatures of phenomenal magnitude

Some experiences are stronger than others: they have greater phenomenal magnitude. Although the phenomenal magnitude of experience is a familiar component of human consciousness, the computational scheme underpinning its encoding in the brain is unknown. In particular, it is unknown whether phenomenal magnitude is encoded in a “rich” manner, via the strengthening or broadcast of content-specific perceptual representations, or a “sparse” scheme, in which a content-invariant signal monitors the reliability or precision of first-order contents. In a reanalysis of existing MEG and fMRI data from two distinct studies, we operationalise phenomenal magnitude as subjective ratings of awareness and visibility to address this question. We find that phenomenal magnitude is associated with content-invariant neural signatures distributed across visual, parietal, and frontal cortices. Moreover, we show that these neural signatures exhibit similarities with other analogue magnitude codes such as number, with each rating being represented as being more similar to its neighbours, and less similar to more distant ratings. Our findings suggest a role for a content-invariant analogue magnitude code in determining the strength of perceptual experience.