The condition under which the nervous system receives physically consistent inputs from a simulation environment.
Sensory fidelity is the first step in the Human Outcomes Layer. It determines what the nervous system has to work with. All downstream outcomes — neurological processing, adaptation, and training transfer — depend on the quality of the inputs received at this stage. This document defines sensory fidelity as a framework concept and establishes its relationship to simulation tier.
Sensory fidelity is the degree to which a simulation environment delivers inputs to the vestibular, proprioceptive, and visual systems that are physically consistent with one another and with the motion state being represented.
A simulation environment with high sensory fidelity presents each channel with information that agrees with every other channel. The vestibular system receives acceleration data. The proprioceptive system receives loading and positional data consistent with that acceleration. The visual system receives scene motion that corresponds to the same event. The three channels form a coherent description of a single physical event.
A simulation environment with low sensory fidelity presents channels with information that disagrees. Each channel may receive a signal — there may be motion, there may be visual information, there may be gravitational loading — but the signals do not form a coherent description of the same physical event. One channel may describe an event that another channel contradicts or does not confirm.
Sensory fidelity is not a subjective quality. It is not determined by visual richness, perceived immersiveness, or participant rating. It is a structural property of how the simulation system delivers sensory data relative to the physics model it is intended to represent.
The nervous system's model of physical state during motion is constructed from three primary input sources. Sensory fidelity requires that all three channels deliver consistent information about the same physical event.
The vestibular system detects linear and rotational acceleration through the otolith organs and semicircular canals of the inner ear. In real-world motion, vestibular input arrives before visual confirmation of the motion event. This temporal priority gives vestibular information a dominant role in the nervous system's initial motion state estimate and in anticipatory motor control.
The proprioceptive system receives signals from mechanoreceptors in muscles, tendons, joints, and skin. In a vehicle environment, these signals include gravitational loading, seat and harness pressure, control surface resistance, and body position relative to the cabin structure. These signals are continuous and simultaneous with the motion event, providing ongoing positional and loading data throughout the maneuver.
The visual system provides motion-correlated scene information. In real-world vehicle operation, visual input confirms and refines the motion state estimate already formed from vestibular and proprioceptive input. Visual information arrives slightly after the onset of the physical motion event and plays a secondary role in the nervous system's initial response to the event, with its influence increasing as the event progresses.
Sensory coherence requires that all three channels form a consistent description of the same physical event. When they do not — when one channel describes motion that another channel contradicts or does not support — the nervous system must allocate processing resources to identifying and resolving the conflict. Those resources are not then available for productive task processing.
Sensory coherence is the condition in which vestibular, proprioceptive, and visual inputs delivered by a simulation environment are physically consistent with one another and with the motion state being simulated. Sensory coherence exists when no channel delivers information that contradicts another channel. It is a necessary condition for In-the-Loop classification and a prerequisite for the neurological processing conditions that support training transfer.
Sensory coherence is a structural property. It is either present or it is not. A simulation environment that delivers motion through a physics-derived, center-of-mass-referenced, temporally synchronized system may produce sensory coherence. A simulation environment that delivers motion as a post-physics approximation, or that resolves motion at a geometric point other than the center of mass, may not.
The following conditions may break sensory coherence between channels:
Sensory coherence is distinct from sensory accuracy. A system may deliver mutually consistent inputs that are nonetheless inaccurate representations of the intended physics state. Coherence requires internal consistency; accuracy requires correspondence to real-world physics. In-the-Loop classification requires both. For the purposes of the Human Outcomes Layer, sensory coherence is the more directly relevant condition: it is the property that determines whether the nervous system can process inputs without generating compensatory demand.
The SFR classification system assigns simulation systems to one of three tiers. The tier of a system determines the structural conditions under which sensory fidelity can and cannot be achieved.
This table describes structural conditions, not performance claims for any specific system. The determination of which tier a system occupies is made through the evaluation process defined in the Reference Test Methodology, Evaluation Inputs, and Evaluation Process documents.
Sensory fidelity is the first step in the Human Outcomes Layer because it determines the quality of inputs available to all subsequent processes. The nervous system cannot produce outcomes better than the inputs it receives. The downstream steps — neurological processing, neurological adaptation, and training transfer — operate on the sensory data delivered at this stage.
When sensory fidelity is high — when inputs are coherent and the three channels describe the same physical event consistently — neurological processing can direct its full capacity toward task-relevant integration. When sensory fidelity is low — when channels disagree — a portion of neurological processing capacity may be consumed by conflict resolution rather than productive task processing.
Sensory fidelity is not a claim about outcomes for any individual participant or any specific session. It is a structural characterization of the input conditions that a simulation environment provides. The framework proposes that these input conditions have implications for what kinds of neurological outcomes are achievable. The strength of that relationship, and the conditions under which it applies, are appropriate subjects for research using the framework's terminology and classification system.
The Human Outcomes Layer is the third layer of the SFR framework. It is downstream of the Foundation Layer, which defines what correct simulation is physically, and the Control Layer, which defines what incorrect simulation produces structurally. The Human Outcomes Layer addresses what simulation architecture does to the person in the system.
Sensory fidelity is the point at which the framework transitions from describing the machine to describing the person. The Foundation and Control Layers are about the physics system. The Human Outcomes Layer begins with the interface between that physics system and the nervous system that operates within it.
See Human Outcomes Framework for the full Layer 3 overview. See Canonical Definitions for the normative definition of Sensory Coherence and all related terms.