Channel-Dependent Discriminability: How a Difference Becomes Detectable Only Through a Channel and a Detector

Two states can differ without producing distinguishable readings. This paper develops Channel-Dependent Discriminability, the mechanism by which the detectability of a difference depends on the channel carrying information about it and the detector registering that information. Changing either can reveal a source distinction, suppress it, or introduce an apparent distinction that is absent from the source. The paper separates a structural limit from empirical questions about measurement. When two source states produce the same channel output, a detector receiving only that output cannot distinguish them. Whether a particular instrument detects a particular difference, across which conditions, and with what error requires investigation. The discussion relates this account to signal detection theory and examines research on pulse oximetry and skin pigmentation as a documented case of readings shaped by both the target and the measuring arrangement. Part of the Relational Conditions and Dynamics series within On Human Modeling, the paper distinguishes detection from awareness, understanding, and significance. It sets out practical questions for evaluating a reading: what carried the source information, what registered it, and which reference measurements and uncertainties support its interpretation.