Fleming and Michel propose a compelling framework that conscious vision evolved to support model-based planning in organisms with extended sensory horizons. They link the development of conscious vision to the water-to-land transition. According to their view, the spatial and temporal reach of visual perception on land allows organisms to simulate and evaluate possible future states, thereby allowing for planning and adaptive decision-making. This framework is persuasive within the visual modality. However, and as pointed out by the authors, it is unclear whether this framework can be generalized across sensory modalities. More specifically, the water-to-land transition may have exerted a more profound influence on visual than on olfactory processing. In part due to an abundance of unscattered light, terrestrial environments present a richer and more complex array of visual stimuli, which can be integrated into spatially organized and predictive models. In contrast, olfactory stimuli may have undergone comparatively moderate changes. This disparity suggests that consciousness may play a more central role in vision-related processes, whereas olfaction could operate effectively with minimal involvement of consciousness. Olfaction is a very developed, although often underrated and mistrusted sensory modality in humans (e.g., McGann, Reference McGann2017), and operates under fundamentally different principles than vision.

First, neuroanatomically, olfactory information bypasses the thalamus, which is traditionally considered a central relay station for sensory processing and attentional modulation (Merrick et al., Reference Merrick, Godwin, Geisler and Morsella2014). In most sensory systems, the thalamus acts not only as a relay but also as a gatekeeper that regulates which sensory signals gain access to higher cortical processing and thus to conscious awareness. This neuroanatomical pathway could consequently predispose olfaction to influence behavior implicitly, without giving rise to conscious experience. Second, functionally, olfaction has been characterized by “change blindness” (Sela & Sobel, Reference Sela and Sobel2010): unlike vision, olfactory changes frequently go unnoticed unless they are intense or emotionally salient. This is true for both odor quality and odor intensity changes. One own olfactory abilities often operate beyond conscious recognition. This supports the idea that olfactory processing is largely implicit and that conscious olfactory perception may be the exception rather than the rule.

Third, another key difference between olfaction and vision lies in their temporal dynamics. Vision is a “fast” sense because photons travel at the speed of light and retinal transduction is rapid, enabling near-instantaneous environmental updates. By contrast, olfaction would be slower, due to the relatively slow speed of olfactory molecule transmission and processing, especially in comparison to photons (Keller, Reference Keller2011). Although olfaction may be slower in terms of initial detection, it can still provide temporally extended information. For example, the lingering presence of a smoke scent or the gradual decay of a food odor can inform decisions about safety and resource availability (Finnerty et al., Reference Finnerty, McArthur, Banks, Price and Shrader2022). This directly related to olfaction’s three main functions (see Stevenson, Reference Stevenson2010): ingestion (e.g., detecting food), avoidance of environmental hazards (e.g., avoiding smoke or gas leak), and social communication (e.g., communication of stress, de Groot & Smeets, Reference de Groot and Smeets2017, or other emotional states, Calvi et al., Reference Calvi, Quassolo, Massaia, Scandurra, D’Aniello and D’Amelio2020, through body odors or chemosignals). For none of these functions, and although the extent to which they require planning could be debated, consciousness would be necessary or sufficient (Bratman et al., Reference Bratman, Bembibre, Daily, Doty, Hummel, Jacobs, Kahn, Lashus, Majid, Miller, Oleszkiewicz, Olvera-Alvarez, Parma, Riederer, Sieber, Williams, Xiao, Yu and Spengler2024). For instance, olfactory landmarks could be used for navigation if they are differentiable but would not need to be identifiable or explicitly labeled (Hamburger & Knauff, Reference Hamburger and Knauff2019; Schwarz & Hamburger, Reference Schwarz and Hamburger2023). This observation challenges the notion that consciousness plays a similar role for navigation across all sensory modalities.

Fourth, besides olfactory inputs benefiting from a direct pathway to limbic and cortical areas, another neuroanatomical characteristic of olfaction is that olfactory and emotional circuits overlap to a great extent (Soudry et al., Reference Soudry, Lemogne, Malinvaud, Consoli and Bonfils2011). Olfaction is intimately linked with emotion and memory in a way that vision is not (Delplanque, Coppin, & Sander, Reference Delplanque, Coppin, Sander and Buettner2017). Odor-evoked memories tend to be more emotional, vivid, less often recalled and older than memories evoked by other sensory cues (Herz, Reference Herz2016; Rey et al., Reference Rey, Désoche, Saive, Thévenet, Garcia, Tillmann and Plailly2023). Such properties could serve long-term adaptive purposes, such as reinforcing avoidance of harmful foods or locations, without requiring continuous conscious access as observed in vision.

Fifth, the conceptualization of olfactory objects is more elusive than visual ones (Gotffried, Reference Gottfried2010). Olfactory imagery capacity varies greatly across individuals but would be less acute than visual imagery in most individuals (e.g., Arshamian & Larsson, Reference Arshamian and Larsson2014). This could reduce the need for constant monitoring between internal vs. external origins, which is the core of reality monitoring.

Methodologically, olfaction presents unique challenges for consciousness research (e.g., Coppin, Reference Coppin2020). For instance, it is difficult to control the presentation of olfactory stimuli with the same precision as visual ones. These technical hurdles may have contributed to the underrepresentation of olfaction in many psychological theories, including theories of consciousness (Stevenson, Reference Stevenson2009). However, exploring the question of when conscious olfaction arises would not only challenge the often visual-centric view of consciousness (Young, Reference Young2012) but also offers a valuable test case for the generalizability of frameworks such as the one proposed by the authors.

A possible extension of the authors’ argument would be to explore how “sensory horizons” apply to modalities like olfaction, which may rely more on temporal integration and emotional tagging than spatial mapping. For example, in species heavily reliant on olfaction (e.g., rodents), the “horizon” might be defined not in terms of visual distance but in terms of certain odors reach and persistence. These horizons might still enable some forms of planning, such as tracking food, avoiding environmental hazards, or locating mates, albeit through different computational architectures, temporal strategies and reliance on consciousness than vision.

In sum, the authors’ framework makes a strong case for the role of conscious vision in extended-horizon planning, but the olfactory system shows that different sensory modalities may achieve adaptive outcomes without the same reliance on consciousness. Incorporating cross-modal perspectives could strengthen the theoretical reach of their proposal, shifting it from a vision-specific account to a broader theory of how consciousness arises when sensory systems, in their ecological and neurobiological context, can most usefully guide flexible, future-oriented behaviors.