Directing attention toward the body's internal signals (interoception) versus external sounds (exteroception) produces distinct brain activity patterns. Exteroceptive attention flattened overall brain wave power, while interoceptive attention reduced brain signal complexity, increased frontal connectivity and theta oscillations, and modulated the heartbeat-evoked potential (HEP). Classifiers using HEP features correctly identified the attentional state in 17 of 20 healthy participants; power spectral density features classified all 20. In five brain-injured patients, one with unresponsive wakefulness syndrome and one with locked-in syndrome showed willful modulation of the HEP, suggesting they could follow commands. These findings highlight how attention shapes sensory processing and may aid diagnosis in disorders of consciousness.
Pupil dilation is a reliable marker of conscious mental effort. In healthy volunteers, consciously detected violations of global auditory patterns triggered pupil dilation, whether participants actively counted or passively listened. This effect appeared at both group and individual levels. Unreported violations of global patterns, and local violations that do not require conscious awareness, produced no pupil dilation. The results were replicated with phonemes. Pupil dilation appears to be a somatic marker of conscious access in the auditory modality, offering a way to probe conscious processing without interrupting a person's stream of thought.