The Cochlear Chiasm: Trapezoid Body Geometry and Field-Based Auditory Routing

This paper, authored by Ghassan Ahmed Mubasher Mohamedsalih, introduces the Cochlear Chiasm Analogy — a novel, geometry-based reinterpretation of auditory brainstem routing that parallels the optic chiasm in vision. Building on the Visual-Origin Theory of Neural Decussation (VOD), Mohamedsalih proposes that auditory decussation via the trapezoid body, MSO, LSO, and MNTB is not primarily for binaural comparison, but for preserving field-to-hemisphere alignment and ensuring spatially coherent motor reflexes. The manuscript challenges traditional symmetry-based models by demonstrating that auditory input is spatially sorted based on wavefront geometry, onset slope, and directional asymmetry. The paper introduces the Field-Coherent Cochlear Output Hypothesis, the Monauron Model for unilateral hearing reflex preservation, and the Bent Field concept linking Doppler compression to reflex biasing. These findings are extended into a unified sensory-motor framework integrating auditory and visual decussation strategies under a shared architectural logic. Clinical correlates—such as auditory neglect, asymmetric startle reflex, and perceptual-motor dissociations—are reinterpreted through this lens. The final sections explore philosophical and design-based implications, arguing that decussation is not a developmental quirk but a functional solution embedded in the nervous system’s geometry. This work offers a high-resolution, anatomically grounded alternative to the current evolutionary explanations of contralateral control and redefines auditory routing as a reflex-first, geometry-aligned system, with relevance to neuroscience and cognitive science.