5.1 Spatial Perception as Orientation Structure
If frequency organizes tonal expectation and time organizes anticipation, space organizes orientation. Auditory space is not a background container in which sound occurs; it is a dimension of perceptual structuring. The auditory system continuously estimates direction, distance, depth, and environmental boundaries, and these estimations contribute to the separation of a sound source from its surrounding environment. This contribution should not be overstated: Bregman (1990) treats spatial cues as comparatively weak and easily overridden contributors to the sequential grouping of sounds over time, compared to cues like frequency proximity and timbral similarity, even though they remain informative for the simultaneous integration of concurrent sound energy into a single perceived source. The spatial axis discussed in this section concerns that second role, environmental construction and figure to ground salience within a moment, rather than a claim that space is the primary cue by which listeners track a source across time.
In everyday listening, spatial precision reinforces causal clarity: a sound is localized, it has an origin, it occupies a position relative to the listener. Predictive processing frameworks treat spatial cues as contributing to the stabilization of environmental models, with localization supporting certainty about source identity and environmental structure. When spatial cues become diffuse, predictive anchoring shifts accordingly.
5.2 Reverberation as Environmental Construction
Reverberation does not simply simulate room acoustics; it constructs an acoustic environment. At moderate levels, reverberation enhances realism by embedding a sound source within a perceivable space. At more extensive or dense levels, it alters the listener’s relationship to the source itself.
The auditory system’s actual response to reverberation, however, works in the opposite direction from what an immersive listening intuition might suggest, and stating this plainly is important for the rest of this section. Working with ferret auditory cortex and simulated rooms ranging from a small tunnel to a larger one, Ivanov, King, Willmore, Walker, and Harper (2022) showed that cortical neurons adapt their spectrotemporal receptive fields to extend the inhibitory component of their filters in more reverberant conditions, in a frequency-dependent way consistent with a normative dereverberation model. The function of this adaptation, in their account, is to recover the anechoic structure of the source by filtering the reverberation out, not to represent or track the reverberant field as such. Traer and McDermott (2016), working with a large survey of real-world impulse responses, found a complementary result at the level of the whole auditory system: human listeners can separate the statistical contribution of a source from that of its environment because natural reverberation follows lawful statistical regularities, and listeners appear to use exactly those regularities to undo the environment’s contribution and recover source identity. Both lines of evidence point the same way: the auditory system’s default operation in a reverberant environment is source-environment separation, not source-environment fusion.
This is a constraint on the spatial axis of PAF, not evidence for it, and it should be treated as one. Deep or sustained reverberation extends the decay of sonic gestures, blurs transient boundaries, and diffuses directional precision; the open empirical question, left unresolved by Ivanov et al. (2022) and Traer and McDermott (2016), is at what point, if any, these active separation mechanisms are overwhelmed or saturated, so that the listener stops recovering a clean source-plus-room percept and instead experiences the reverberant field as the primary perceptual object. Ivanov et al.’s simulated rooms were considerably smaller and less densely reverberant than the sustained, dense reverberation this practice uses, so their finding constrains but does not by itself establish the claim that PAF makes about very dense or very long reverberation; it is stated here as the boundary condition any account of that claim needs to address, not as its support.
5.3 From Localization to Diffusion
Clear localization supports figure to ground hierarchy: the source stands out against the acoustic background, and attention orients toward it. The auditory system’s default strategy for achieving this in reverberant space is the precedence effect, the strong perceptual weighting of the first-arriving wavefront of a sound over its later, reflected copies, which allows accurate localization despite the presence of echoes, and which is classically understood to arise at the level of the brainstem and inferior colliculus (Litovsky, Colburn, Yost, & Guzman, 1999). A recent rat study using electrocorticography suggests that consistent, robust onset weighting may also require integration at the level of cortical population responses rather than being fully explained by earlier stages alone (Li, Auksztulewicz, Chan, Mishra, & Schnupp, 2022); this is one animal study using click trains rather than reverberant room acoustics, and it is offered here as a suggestive data point about where onset weighting is completed, not as an established fact about human spatial hearing in naturalistic reverberant environments.
When reverberation diffuses spatial boundaries beyond what onset weighting can resolve, through very long decay times, dense early reflections, or continuous overlapping sources, figure and ground become less sharply differentiated. The source remains perceptible, but its edges soften, its position becomes less precisely defined, and its separation from the surrounding field decreases. This spatial diffusion does not imply confusion; it represents a reconfiguration of spatial salience. In predictive terms, localization precision contributes to environmental certainty, and when spatial cues become less distinct the system shifts from pinpoint orientation toward field-level integration.
This shift is gradual and depends on degree and structure: excessive or chaotic reverberation produces perceptual overload, while structured and coherent reverberation maintains stability while altering emphasis.
5.4 Immersive Depth and Decentering
When reverberation creates the impression of extended or near-infinite depth, spatial boundaries recede and the environment feels less bounded. Within such environments, the perceptual center, the implied position of the listener relative to discrete sources, becomes less rigidly defined. This does not imply loss of self or cognitive alteration; it refers to perceptual decentering, a reduced dominance of sharply localized acoustic anchors. The sound field becomes immersive rather than object-focused.
In immersive conditions, prediction operates at the level of maintaining environmental coherence rather than tracking discrete spatial changes. The listener’s orientation shifts from identifying where a sound originates to inhabiting a continuous acoustic space.
5.5 Spatial Continuity and Predictive Redistribution
Just as microtonality redistributes predictive density in the frequency domain, and delay redistributes it across time, reverberation redistributes predictive emphasis across space. In highly localized sound environments, prediction focuses on tracking source movement and position. In diffuse environments, prediction shifts toward maintaining overall spatial continuity.
This does not eliminate spatial prediction; it alters its granularity. Where reverberation stays within the range that active dereverberation and source-environment separation mechanisms can resolve (Ivanov et al., 2022; Traer & McDermott, 2016), the predictive system continues to recover a source and a room as separate estimates, just at a computational cost. What changes, as reverberation becomes denser or more sustained, is a hypothesis this paper makes rather than a finding either study reports: that the system shifts from attempting fine-grained source-environment separation toward tracking coarser, field-level statistical regularities of the whole acoustic scene. From an experiential standpoint, were this shift to occur, it would correspond to reduced spatial sharpness, increased immersion, and decreased emphasis on discrete boundaries; this remains this paper’s extrapolation from the cited mechanisms, not a result either cited study demonstrates.
5.6 Field Formation Across Frequency, Time, and Space
With frequency, tonal anchoring softens. With delay, temporal linearity loosens. With reverberation, spatial localization diffuses. Individually, each axis modulates a dimension of perceptual organization; together, they generate a coherent acoustic field.
This field is not empty. It is internally complex, containing frequency relationships, temporal extensions, and spatial depth, yet it reduces external perceptual competition by minimizing abrupt segmentation across all three axes. The Perceptual Attenuation Field, formally defined in the following section, depends on this triadic integration. It is not the absence of structure that matters; it is the reorganization of structure into continuity. When frequency, time, and space converge toward field-like coherence, prediction operates less around discrete resolution points and more around sustaining global stability.
5.7 Spatial Modulation and PAF Neutrality
As with microtonality, reverberation is not intrinsically transformative; its effects depend on context and listener conditioning. The PAF is not defined by a specific reverb algorithm, acoustic simulation, or spatial technology. It is defined by relational modulation: how spatial diffusion interacts with the frequency and temporal axes relative to the listener’s internalized predictive framework.
PAF thus remains structurally relational rather than technologically prescriptive. The next section integrates the three axes into a formal conceptualization of the Perceptual Attenuation Field, followed by an explicit articulation of its theoretical boundaries.