Epistemic Parallax: A Theory of Structural Cognitive Misalignment and Its Implications for AI in Neurodivergent Mental Health

The Flatland thought experiment, drawn from Abbott's 1884 novella and developed by Carl Sagan, has been increasingly applied to neurodiversity discourse and artificial intelligence ethics as a metaphor for constrained perception. The standard reading positions neurotypical cognition as the three-dimensional Sphere — the more complete, higher-dimensional observer — and neurodivergent cognition as the two-dimensional Square, generating a cross-section interpreted as disorder rather than difference. This article argues that this reading encodes the deficit model it was designed to challenge and introduces Epistemic Parallax as a novel theoretical construct to correct it. Epistemic Parallax is defined as the systematic displacement in meaning, classification, and judgment that arises when a cognitive system, institutional framework, or artificial intelligence observes neurodivergent experience from a non-parallel normative frame — producing distortions that are a geometric property of the observational relationship rather than a feature of the observed. The construct is distinguished from the Double Empathy Problem, institutional ableism, and algorithmic bias by its specification of mechanism over outcome and its applicability to non-adaptive systems that cannot self-correct through reciprocal interaction. Grounded in the Double Empathy Problem's empirical record, the full dimensional progression from point to tesseract, Intense World Theory, monotropism, and multidimensional sensory processing research, Epistemic Parallax is applied to AI in digital mental health to identify the deployment of neurotypically-trained systems as clinical arbiters of neurodivergent experience as a form of structural hermeneutical injustice in Fricker's precise sense. The Dimensional Parity Standard is proposed as the operational correction, comprising six criteria — bidirectional validation, cross-plane transparency, co-authorship of ground truth, relational deployment, dimensional humility, and a sixth principle extending the Feynman honesty framework developed in the companion article. Implications for regulatory policy, system design, and a three-priority research agenda are identified.