Neuroadaptive technology (NAT) is a closed-loop neurotechnology designed to enhance human–computer interaction. NAT works by collecting neurophysiological data, which are analysed via autonomous algorithms to create actions and adaptations at the user interface. This paper concerns how interaction with NAT can mediate self-related processing (SRP), such as self-awareness, self-knowledge, and agency. We begin with a postphenomenological analysis of the NAT closed loop to highlight the built-in selectivities of machine hermeneutics, i.e., autonomous chains of algorithms that convert data into an assessment (...) of psychological states/intentions. We argue that these algorithms produce an assessment of lived experience that is quantitative, reductive, and highly simplistic. This reductive assessment of lived experience is presented to the user via feedback at the NAT interface and subsequently mediates SRP. It is argued that congruence between system feedback and SRP determines the precise character of the alterity relation between human user and system. If feedback confirms SRP, the technology is regarded as a quasi-self. If there is a disagreement between SRP and feedback from the system, NAT is perceived to be a quasi-other. We argue that the design of the user interface shapes the precise ways in which NAT can mediate SRP. (shrink)