Phenomenal consciousness in the split brain: A layered unity model

Split-brain subjects, whose corpus callosum has been severed, can consciously perceive two different stimuli presented simultaneously in opposite visual fields but cannot compare them, suggesting a breakdown in the unity of conscious experience. This poses challenges for philosophical and scientific theories about consciousness. Existing models preserve the subject's unity as an agent but admit that their right- and left-side experiences are not phenomenally unified. A new model proposes that conscious experience has layers: local layers may be disunified, but global layers remain unified. This is supported by preserved attentional capacities in split-brain subjects, which connect phenomenal unity to attention and explain how right- and left-side experiences can be integrated at a higher level.

Study at a glance

Abstract

Split-brain subjects can consciously perceive and identify two stimuli presented simultaneously but separately in opposite hemifields. Yet, they seem to lack a conscious experience of the two stimuli together, as they cannot judge whether these are the same or different. Such breakdowns in experiential or phenomenal unity would carry important implications for philosophical reflection on the essential properties of conscious experience, as well as for scientific theorising about consciousness’ neural and functional bases. Extant models support the preserved unity of split-brain subjects as subjects or agents but nonetheless admit that their right- and left-side conscious experiences are not unified in the problem cases. Here, I offer a new model that supplies the missing phenomenal unity. Based on the construct of layers of conscious experience, my model acknowledges breakdowns in local experiential layers but warrants preserved unity in global ones. A supporting argument draws on the preserved attentional capacities of split-brain subjects. My proposal goes beyond extant research in that it focuses on the conjoint phenomenology of simultaneous right- and left-side experiences, highlights the conceptual connections of phenomenal unity to attention, and discusses the impact of specific split-brain attentional capacities on the unity of right- and left-side experiences.