# Mental space as an innate foundational structure for cognition: from quantities to events

Vittoria Volpi, Maria Dolores de Hevia

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Vittoria Volpi, Maria Dolores de Hevia. Mental space as an innate foundational structure for cognition: from quantities to events. Developmental Review, 2026, 79, pp.101246. 10.1016/j.dr.2026.101246. hal-05497801

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Review

# Mental space as an innate foundational structure for cognition: from quantities to events

Vittoria Volpi<fnref n="1" />,*, Maria Dolores de Hevia<fnref n="1" />

Université Paris Cité, INCC UMR 8002, CNRS, F-75006, Paris, France

## ARTICLE INFO

**Keywords:**

- Spatial cognition
- Spatial mappings
- Newborns
- Infancy
- Development
- Number
- Order

## ABSTRACT

Humans appear to rely on spatial mental structures across a wide range of cognitive domains—from reasoning about quantity and serial order to recalling events in episodic memory. While individual domains such as number, language, or memory have been associated with spatial representations, we propose a broader hypothesis: that humans possess an innate predisposition to use *mental space* as a foundational structuring format. We argue that this spatial scaffolding supports the organization of both concrete and abstract information, including continua (e.g., magnitude), ordered sequences (e.g., rules), and event order (e.g., what happened when). Drawing on findings from developmental and cognitive psychology, we suggest that this capacity emerges early, extends across domains, and reflects a fundamental constraint of human cognition. Understanding the origins, developmental trajectory, and functional role of this spatial predisposition can shed light on how abstract knowledge is learned, represented and reasoned about, and how space supports learning across development.

## 1. Spatial foundations of human cognition

Humans spontaneously use spatial structures to organize diverse kinds of knowledge, from quantities and time to memories and concepts. This pervasive use of space in thought suggests that spatial representation constitutes a fundamental organizing principle of cognition—one that may have evolved from neural systems originally dedicated to navigating the physical world. We propose that the capacity to map abstract information onto spatial formats emerges early in development as a flexible scaffold, supporting the growth of increasingly complex and abstract forms of thought.

### 1.1. A predisposition for spatial structure

Humans organize different kinds of knowledge—e.g., quantities, sequences, memories—using spatial structures in the mind. Spatial thinking forms a foundation for abstract thought, allowing us to structure time, number, causality, and other non-spatial domains using spatial metaphors and mental models (Tversky, 2014; Starr & Brannon, 2016). It has been put forward that spatial thinking underlies not only how we navigate the physical world, but also how we make sense of abstract domains: diagrams, mental

<footnote>* Corresponding author at: Université Paris Cité, CNRS UMR 8002, Integrative Neuroscience and Cognition Center, 45 rue des Saint Pères, 75006 Paris, France.</footnote>

<footnote>E-mail addresses: volpivittoria@gmail.com, volpi.vittoria@u-paris.fr (V. Volpi), dehevialola@gmail.com, maria-dolores.de-hevia-abuin@cnrs.fr (M.D. de Hevia).</footnote>

<footnote n="1">¹ All authors contributed equally to this work.</footnote>
maps and event structures are spatial formats that serve as cognitive tools that externalize, simplify, and support complex reasoning (Kosslyn, 1980; Tversky, 1993). This scaffolding appears to be deeply rooted in human cognition, helping us represent relationships, structure time, and guide learning from early in development. Using a mental spatial structure is therefore a powerful and versatile tool of organizing thought across domains.

The capacity to represent and navigate space is among the most ancient cognitive abilities in vertebrates. As Llinás (2001) argued, spatial representation may constitute a foundational principle of vertebrate cognition, from which higher-order processes such as planning, reasoning, and even the construction of the self have evolved. Thus, the human tendency to map abstract concepts onto spatial formats might reflect the reutilization of an ancient neural architecture originally dedicated to navigating the physical environment. Comparative neuroscience has shown that the hippocampal formation and associated parietal and cortical networks—critical for spatial navigation and memory—have maintained their fundamental organization throughout vertebrate evolution (Murray et al., 2018).

Much research has been devoted to disclosing the existence of mental number lines, mental timelines, and spatial metaphors. These mental structures represent abstract concepts, such as quantity (Dohaene et al., 1993), time (Boroditsky, 2000), causality (Maass & Russo, 2003), or even social relationships (Son et al., 2021) along spatial dimensions, allowing us to organize and process information in a way that is both intuitive and efficient. Despite these advances, studies have mostly focused on isolated domains—such as number or time—leaving open the question of whether spatial structuring reflects a more general cognitive predisposition. More importantly, the field has not fully explored the breadth or possible innateness of this spatial organization system: to our knowledge, these spatial structures for organizing thought have primarily been studied in educated adults.

Here we entertain the idea that spatial scaffolding is fundamental, and initially unlearned, with growing evidence supporting the hypothesis that it emerges early in development. We therefore propose that humans are predisposed to use a mental space as a structuring tool across domains, providing a flexible scaffold for organizing both concrete and abstract information from early in development. In line with this, recent developmental research has begun to reveal a growing body of empirical findings suggesting that this spatial predisposition emerges and becomes functionally relevant shortly after birth. This evidence supports the view that spatial cognition may serve as an early-developing foundation for organizing experience. Building on foundational accounts, here we argue that spatial representation is a core organizing principle in human cognition, and discuss evidence from newborns and infants, as well as cross-species studies, which highlight the predisposed nature of these representations and point to an innate tendency to use space to organize abstract knowledge. We also examine evidence from adults, where cultural experience shapes representations such as numerical and letter sequences. Importantly, we view cultural learning as building on pre-existing spatial biases, providing a scaffold for the development of more complex and abstract cognitive representations.

## 1.2. Conceptual mapping within mental space

By “mental space”, we refer to an internal representational medium in which humans and non-human animals organize and relate information along structured dimensions. These dimensions can mirror the geometry of external space (e.g., left-right, up-down, near-far) but need not be limited to the three dimensions of physical space, and can also extend to more abstract, multidimensional formats that preserve relational and metric properties. Crucially, such spaces are characterized by their geometric structure (e.g., distances, similarity relations, and neighborhood structure), rather than by their direct embeddability in the external world. In other words, mental space provides a structured, often Euclidean or Euclidean-like framework that supports the representation, comparison, and manipulation of both concrete and abstract information, including high-dimensional representational spaces, without implying that all such representations are directly tied to the physical environment. This definition builds on Tolman's early proposal that organisms construct cognitive maps to guide flexible behavior, suggesting that spatial representations may serve as a general format for organizing both physical and abstract knowledge (Tolman, 1948). These mental structures serve as scaffolds for mapping abstract content—such as numbers, time, events or rules—onto spatial dimensions, enabling more efficient reasoning, memory, and learning. The idea that spatial structure serves as a foundational format for cognition resonates with classical proposals across psychology, linguistics, and neuroscience, which have long argued that mental representations preserve the geometric relationships found in the physical world, enabling the flexible use of spatial knowledge (O'Keefe & Nadel, 1978; Shepard, 1984; Tolman, 1948), and it aligns with early theories of spatial cognition, which suggest that the human mind represents both abstract and perceptual information within a common spatial format supported by evolutionarily conserved neural systems (Kosslyn, 1980; Kosslyn, 1994; Kosslyn et al., 2001). For instance, adult participants mentally rotate objects as if manipulating them in real space: response times increase linearly with the angular disparity between objects (Shepard & Metzler, 1971). This classic finding suggests that even abstract cognitive tasks engage spatial transformations, implying that internal representations preserve the geometric relations found in the physical world. By drawing an isomorphism between physical reality and cognitive representations, this work supports the idea that the mind operates within a structured “mental space”, where proximity implies similarity or relatedness. Along these lines, concepts are suggested to be
<figure><img src="image_5.png" /><figcaption>**Fig. 1.** Schematic illustration of the developmental progression of visuo-spatial processing and, in parallel, the emergence of increasingly complex spatial mappings from birth to adulthood. Within a given age range, identical symbols in the *Visuo-spatial processing* and *Spatial mapping* columns denote potential correspondences between the two domains.</figcaption></figure>

represented within structured conceptual spaces—geometric structures where each dimension reflects a meaningful quality—allowing similarity and categorization to be understood in terms of spatial distance (Gärdenfors, 2000).

This view has found renewed support in recent neuroscience. Grid and place cells—spatially-tuned neurons that provide a coordinate system for measuring distance and direction during navigation (Bicanski & Burgess, 2020; Hafting et al., 2005)—may offer a universal scaffolding mechanism not only for physical navigation but also for abstract cognitive mapping (Doeller et al., 2010; Moser et al., 2008). For example, Doeller and colleagues (2010) found grid-cell-like representations in the human entorhinal cortex during memory tasks, suggesting the presence of a domain-general spatial coding system. These same cells are also recruited during tasks involving internally-generated spatial content, such as imagined navigation (Bellmund et al., 2016; Horner et al., 2016), and visual scene exploration (Nau et al., 2018). Other work has extended these findings to abstract spaces—demonstrating that the human brain may organize semantic and conceptual information using a grid-like code (Constantinescu et al., 2016). In this view, dimensional spaces serve as a framework for organizing conceptual knowledge in the brain: knowledge is structured atop the spatial scaffolding provided by sensorimotor experience and attentional mechanisms, allowing us to navigate conceptual or working memory space much like we navigate the physical world (Bottini & Doeller, 2020). This supports the idea that the neurocognitive structures and algorithms originally evolved to map and structure the physical world may have been recycled to support the internal representation and organization of non-spatial conceptual knowledge (Buzsáki & Moser, 2013).

Building on this view, Representational Similarity Analysis (RSA) offers a complementary framework for examining how mental content is organized within structured representational spaces (Kriegeskorte et al., 2008). By revealing the relational geometry of neural and behavioral responses, RSA captures how the mind organizes perceptual, semantic, and categorical information within abstract similarity spaces. Initially developed for adult neuroimaging (Kriegeskorte & Kievit, 2013), RSA is now increasingly applied in developmental research, revealing emerging categorical organization in infants' neural and visual responses (Spriet et al., 2022; Xie et al., 2022; Yan et al., 2024). Together, these findings suggest that even early in development (Ellis, 2024), mental representations are structured according to spatial principles, providing a spatially inspired framework for conceptual organization across domains. While these spaces may not correspond to physical or perceptual dimensions in the classical sense (Shepard & Metzler, 1971; Tolman, 1948), they nonetheless provide a spatially-inspired framework for conceptual organization across development.

In what follows, we review evidence from developmental and cognitive research to illustrate how space is used across cognitive domains. We highlight recent findings suggesting that spatial scaffolding may reflect a deeper, more primitive constraint on cognition—an idea foreshadowed by classic theoretical work (Shepard, 1984, 2001), which emphasized that these spatial structures might
be universal and innate, stemming from the regularities of the physical world and their imprint on our cognitive systems. We believe this pervasive spatial organization may reflect a functional property of working memory (WM), which relies on spatial structuring to encode, maintain, and manipulate information efficiently.

## 2. Spatial representations as scaffolds for early thought

Across the lifespan, human cognition reveals consistent visuo-spatial signatures that might shape how abstract information is mentally organized. Evidence from adults, neuropsychological patients, children and even infants and newborns, suggests that spatial attention and orientation biases extend beyond perception and action, influencing how we represent and manipulate non-spatial dimensions such as number, time, and order.

The visuo-spatial processing signatures observed at specific points in development—including biases in spatial axes and orientations—likely shape and are mirrored in the way humans mentally organize abstract content using spatial structures (Fig. 1). For instance, in adults, the mental representation of number reflects spatial biases also observed in physical space: when bisecting numerical intervals, adults tend to err toward the smaller number (Loftus et al., 2009)—echoing the leftward bias seen when bisecting physical lines, a phenomenon known as pseudoneglect (Jewell & McCourt, 2000; Longo & Lourenco, 2007). Similarly, patients with unilateral spatial neglect show consistent rightward biases in both tasks, neglecting the smaller (leftward) portion of the number line just as they do the left side of physical space (Zorzi et al., 2002).

We propose a continuity between spatial processing and abstract thought, examined in the current and following sections through the ways visuo-spatial biases emerge, develop, and shape higher cognitive representations. Importantly, we believe this convergence does not emerge abruptly in adulthood but builds gradually on early perceptual and attentional asymmetries that refine with experience. From birth through the first year of life, infants show a remarkable progression in their ability to perceive, represent, and use space (for a review, see Hospodar & Adolph, 2024), establishing the foundations for increasingly complex mental organization. We propose that these early spatial structures not only enhance cognitive processing when aligned with task demands, but may also be essential for certain kinds of knowledge to form at all. Early cognitive limitations may thus reflect the absence of a sufficiently organized spatial framework, rather than a lack of conceptual understanding. In this view, early-emerging spatial distinctions—such as near versus far, left versus right, or up versus down—provide the scaffolding for the development of higher-order reasoning about time, number, sequence, and other abstract domains.

### 2.1. *From perceptual asymmetries to spatialization of abstract information*

Asymmetries in perceptual processing across development appear to parallel how humans organize abstract information in space. For instance, visual sensitivity is higher along the horizontal than the vertical meridian, with particularly reduced sensitivity in the upper visual field (Carrasco et al., 2022). Consistently, horizontal spatial mappings tend to dominate over vertical ones in spatial-numerical tasks (Holmes & Lourenco, 2012), and effects of motion-numerical compatibility also emerge primarily along the horizontal axis (Volpi et al., in press).

Parallel perceptual and spatial asymmetries seem to emerge early in development, as evidenced by the presence of both spatial pseudoneglect and numerical pseudoneglect in children from 7 years (Göksun et al., 2013). In newborns, studies have shown an upper visual field advantage, as newborns preferentially attend to upward space (Simion et al., 2002; Turati et al., 2002). This resonates with findings that newborns associate numerical and pitch increases with upward spaces, but fail to map decreases to downward space, showing a vertical asymmetry in magnitude mapping (de Hevia et al., 2025). This asymmetry is not observed in the horizontal axis, along which newborns seem to map both smaller and larger numerosities symmetrically to the left and right (de Hevia, Veggiotti, et al., 2017; Di Giorgio et al., 2019). However, under certain conditions, newborns treat the horizontal axis asymmetrically, showing a left hemifield preference for numerical processing (McCrink et al., 2020), which mirrors the leftward bias in spatial bisection tasks at 4 months of age (Nava et al., 2022).

Altogether, these findings suggest that spatial processing is available from birth and develops rapidly in the first year, potentially shaping how infants come to represent and organize abstract content. The directionality and asymmetries observed—such as the leftward bias in spatial and numerical tasks, or the vertical asymmetry in mapping magnitude—may reflect deeper constraints in how space is encoded and used to structure experience. These spatial asymmetries appear to extend to the processing of ordered sequences: at 4 months, infants reliably detect increasing sequences of numerical or physical magnitudes but fail to discriminate their decreasing counterparts—a bias that disappears by 7 to 8 months (de Hevia, Addabbo, et al., 2017; de Hevia & Spelke, 2010; Macchi Cassia et al., 2012; Picozzi et al., 2010). More recently, the same result was found for newborns that can successfully extract and represent ordinal relations for increasing sequences but not for decreasing ones (Arioli et al., 2025).

These biases reflect not only ontogenetic but also phylogenetic continuity, as evidenced by findings from monkeys, who can generalize previously learned increasing ordered sequences but fail to do so with decreasing ones (Brannon, Cantlon, et al., 2006; Brannon, Lutz, et al., 2006; Brannon & Terrace 1998; Cantlon & Brannon 2006; Judge et al., 2005). This ontogenetically preserved and
phylogenetically shared advantage for increasing ordered sequences has been linked to the well-studied looming vs. zooming advantage (de Hevia, Addabbo, et al., 2017): objects that appear to be approaching are perceived as more salient than those that are receding (Van der Weel et al., 2009). Interestingly, infants show clear behavioral reactions to approaching objects—such as blinking or moving their head in response to looming stimuli—but do not react to zooming ones (Arioli et al., 2025; Ball & Tronick, 1971; Náñez, 1998). This likely reflects an adaptation mechanism to approaching stimuli, which are potentially threatening. What is particularly intriguing is that this sensitivity to approaching stimuli in the physical domain might translate into a cognitive bias for increasing order, even in the absence of actual motion in depth. These patterns raise the possibility that early spatial biases do more than reflect perception—they may actively scaffold the detection of structure in non-spatial domains (McCrink & de Hevia, 2018).

## 2.2. Early spatial biases and mappings in newborns

Behavioral and developmental findings support the idea that infants use spatial frameworks from the very start, even before acquiring locomotor experience or language. At birth, newborns can direct their gaze toward the spatial source of a sound (Butterworth & Castillo, 1976; Wertheimer, 1961), revealing early cross-modal spatial integration. They also show sensitivity to spatial contingencies, such as reacting to tactile stimuli modulated by sound intensity in ways that resemble adult patterns (Orioli et al., 2019), suggesting early peripersonal space encoding (Orioli et al., 2018). Newborns show a preference for horizontally oriented stimuli over vertically oriented ones (e.g., gratings of different spatial frequencies, Slater et al., 1985; or sets made of discrete elements, Farroni et al., 2000), and newborns' as well as infants' eye movements reveal an advantage for visual scanning along the horizontal rather than the vertical axis (Van Renswoude et al., 2016). They also categorize spatial relations based on left and right positions (Gava et al., 2009). Moreover, newborns can use these spatial representations to structure abstract domains, in which their perceptual biases and spatial processing characteristics are mirrored. For instance, they map numerical magnitude and duration onto spatial extent (de Hevia, Izard, et al., 2014), spontaneously associate larger numerical quantities with the right and top sides of space and smaller ones with the left side, their horizontal mapping being privileged relative to the vertical one (de Hevia, Veggiotti, et al., 2017; de Hevia et al., 2025; Di Giorgio et al., 2019) (see Fig. 2), show a preference for the left spatial hemifield in numerical discrimination (McCrink et al., 2020), and are able to map numerical magnitude onto the amplitude of a hand opening (de Hevia et al., 2026).

Newborns' ability to map smaller numerosities to the left and larger ones to the right does not appear to be limited to the Approximate Number System (ANS), the evolutionarily ancient and widely shared cognitive system that enables humans and other animals to extract and manipulate numerosities (Brannon & Merritt, 2011; Feigenson et al., 2004), supporting approximate and imprecise representations of quantity and enabling basic numerical estimation in the absence of language (Dela Haiene, 2011). Rather, the same mapping also extends to precise, subitizable quantities such as 1 and 2 items. This suggests that spatialization of magnitude is not confined to approximate numerical representations, but also applies to small, exact sets (Volpi & de Hevia, under revision). These findings point to the presence of a primitive yet functional spatial framework available from birth, one that supports the mapping of both physical and abstract dimensions in space.

<figure><img src="image_6.png" /><figcaption>**Fig. 2.** Depiction of stimuli and procedure used in de Hevia, Veggiotti, et al. (2017). Newborns were familiarized (60 s) with auditory sequences of either 6 or 18 syllables, each paired with a central image of a colored rectangle (short or long, respectively). At test, infants were presented with the opposite numerosity (18 or 6 syllables) paired with the corresponding rectangle (long or short), displayed once on the left and once on the right side of the screen. The order of test trials was counterbalanced across participants. Newborns experiencing an increase in number from familiarization to test (from 6 to 18) looked significantly longer to the test trial depicting the long rectangle on the right side of the screen; those experiencing a decrease in number from familiarization to test (from 18 to 6) looked significantly longer to the test trial depicting the short rectangle on the left side of the screen. These findings provide evidence for a few-left/many-right mapping at the start of postnatal life.</figcaption></figure>
## 2.3. Developmental trajectory and increasing complexity

During the first year, we observe a development of these abilities toward more complex forms of spatial cognition: Infants as young as 3 to 4 months spontaneously bisect visual areas (Quinn, 2012), and by 8 months, they can transfer the ordinal properties of numerosities to line lengths (de Hevia & Spelke, 2010). They demonstrate leftward biases (akin to adult, pseudoneglect) in line bisection by 4 to 5 months of age (Nava et al., 2022), show sensitivity to spatial constancy at 4.5 months (Kaufman & Needham, 2011), and from 3 months even exhibit behavior consistent with emerging mental rotation capacities (Johnson & Moore, 2020). At 6 months of age, infants seem to possess complex geometric intuitions: when watching streams of visual images, they are able to detect changes that violate Euclidean geometry principles such as identity, scale and affinity (e.g., changes in distances and angles) in 2D visual representations (Lefer et al., 2024). By 7 months, they distinguish within- vs. beyond-reach auditory space (Clifton et al., 1991) and use object size to infer distance (Yonas et al., 1979). These findings highlight a developmental trajectory toward increasingly refined spatial representations: As infants gain postural and motor control, agency, and active exploratory abilities, their spatial representations become more complex and refined (Adolph & Hoch, 2019) and so does the information they structure. We propose that this growing sophistication in spatial coding enables the organization of increasingly abstract and complex content.

This idea is gaining increasing empirical support. Infants as young as 3 months, who normally fail to learn abstract rules, can instead succeed when the sequences are structured in space (Ferguson et al., 2018). At 7 months of age, infants' ability to extract ordinal information from numerical sequences presented spatially depends on the specific directionality (de Hevia, Girelli, et al., 2014). Similarly, spatial orientation critically determines whether or not infants are able to learn ordered information embedded in abstract rules for visual sequences more generally (Bulf et al., 2017) (see Fig. 3), and their abilities to transfer rules from a sequence of numerosities to a sequence of shapes (Bulf et al., 2022). Further evidence of the tight link between space and number, and of the idea that space acts as a scaffold for the organization of numerical thought, comes from findings showing that 8- to 9-month-old infants spontaneously direct their eye movements toward the portion of space that is congruent with a number's relative position: left for smaller magnitudes and right for larger ones (Bulf et al., 2016). Nonetheless, evidence suggests that, particularly in contexts with multiple and diverse cues, the ability to learn probabilistic event sequences and extract purely location-based associations might depend on the maturation of dedicated spatial representation systems. Indeed, only by 11 months of age, infants can respond based solely on location statistics, exhibiting a post-habituation novelty preference when the positions of stimulus elements are randomly rearranged (Kirkham et al., 2007).

<figure><img src="image_7.png" /><figcaption>**Fig. 3.** Schematic representation of Bulf et al. (2017). Seven-month-old infants were habituated to a visual abstract rule (e.g., ABB), in which three-element sequences were presented. All infants were exposed to sequences within a spatio-temporal organization; however, in contrast to Ferguson et al. (2018), half of the infants received a left-to-right spatial layout and the other half a right-to-left spatial layout. Moreover, each element of the sequence appeared in isolation at its corresponding spatial location, such that infants did not have the opportunity to perceive the complete three-element sequence at once. Critically, at test, only infants who received information presented from left to right showed a preference for the novel abstract sequence (e.g., ABA) compared to the habituated one, while infants exposed to the opposite, right-to-left spatial layout failed to dis-habituate to the novel rule. These findings provide evidence for a privileged left-to-right spatial mapping in abstract rule learning.</figcaption></figure>
# 3. Spatial mappings across cognitive domains and development

An emerging body of evidence suggests that humans—and in some cases other animals—use spatial representations to structure abstract domains such as quantities, sequences, and memories. While this phenomenon has been well documented in adults, it is now increasingly being traced back to infancy, and even to the newborn period. These recent findings are especially promising from a developmental perspective: they suggest that the tendency to spatialize conceptual knowledge is not merely a product of learning or cultural convention, but reflects early-emerging—and possibly predisposed—modes of organizing experience. By reviewing evidence across age groups and domains, we aim to shed light on the continuity and developmental refinement of these spatial frameworks.

## 3.1. Spatial mappings of quantity

Since the early observations of Francis Galton (1880), who noted that many individuals intuitively “saw” numbers unfolding in space—along curves, lines, or other idiosyncratic configurations—cognitive psychology has accumulated compelling evidence that numerical magnitude and ordinal information is mentally organized along spatial dimensions. This phenomenon is most notably captured in the concept of the mental number line (MNL), where, in Western cultures, numbers are represented from left to right, with smaller magnitudes on the left and larger ones on the right (Restle, 1970). Empirical evidence for this hypothesis came from the so-called SNARC effect (Spatial-Numerical Association of Response Codes), whereby adults tend to respond faster to smaller numbers with their left hand and to larger numbers with their right hand (Dehaene et al., 1993; Fias, 1996), suggesting an implicit left-to-right spatial mapping of numerical magnitude.

While the MNL is typically conceived as a one-dimensional horizontal line, it nonetheless reflects a form of spatial organization. Furthermore, SNARC-like effects have also been reported along other spatial axes, such as top-bottom and near-far configurations (Aleotti et al., 2020; Bourgaux et al., 2023; Schwarz & Keus, 2004), suggesting that our mental representation of magnitude may be better characterized as a three-dimensional mental space, defined by Cartesian coordinates, rather than a strictly one-dimensional number line. The association between numbers and space might be universal, as it is systematically observed across cultures (Eccher et al., 2025), although its directionality is influenced by culture. For example, Canadian participants, who read and write from left to right, exhibit a left-to-right MNL, whereas Palestinian participants, accustomed to reading and writing from right to left, display an MNL oriented in the opposite direction. These findings suggest that the link between space and number is predisposed, but its directional expression is shaped by cultural experience (Shaki et al., 2009). However, certain populations, such as preschoolers and illiterate adults, do not seem to exhibit a systematic spatial directionality in their mappings (e.g., Guida et al., 2018, 2020; Pitt et al., 2021; for a discussion, see Section 3.7).

Remarkably, spatial-numerical associations have also been investigated in infants, newborns, and non-human animals; while these populations do not possess organized, culturally shaped, and symbolic numerical knowledge, they still show basic numerical abilities, such as estimation and comparison, supported by the ANS. Indeed, spatial-numerical associations appear to emerge very early: 0- to 3-day-old newborns (de Hevia, Veggiotti, et al., 2017; Di Giorgio et al., 2019) and 8-month-old infants (Bulf et al., 2016) already exhibit a lateralized mapping of numerical magnitude onto horizontal space, associating smaller numbers with the left and larger ones with the right. Intriguingly, this spatial structuring of quantity is not unique to humans—young chicks not only spontaneously align smaller numerosities with the left and larger ones with the right (Rugani et al., 2015), but also exhibit left-to-right biases in learning ordered sequences (Rugani & Regolin, 2020). Even invertebrates such as honeybees show this dichotomous, lateralized spatial mapping of number (Giurfa et al., 2022). These studies in preverbal and nonverbal populations have primarily revealed dichotomous spatial mappings (e.g., left vs. right), whereas the mental number line (MNL) conveys a sense of directionality and continuity. Directional number-space mappings (i.e., within a spatial layout of at least three positions) are reliably observed by 7 months of age, with a preference for increasing, left-to-right oriented numerical sequences de Hevia, Girelli, et al., 2014). Together, these findings point to a widespread, possibly evolutionarily conserved tendency to use spatial frameworks to encode abstract information.

Beyond the use of spatial positions to organize numerical magnitude and order, another way in which space is recruited to represent number involves mapping numerical magnitude onto spatial extent. This distinction highlights different ways in which spatial information can serve numerical representation. In the first case, space functions as a positional dimension, providing discrete locations (e.g., left vs. right, or left-to-right orientation) to categorize smaller and larger numbers and order them in space (Bulf et al., 2016; de Hevia, Girelli, et al., 2014; de Hevia, Veggiotti, et al., 2017). In the second, space is treated as a quantitative dimension, where numerical magnitude is expressed through continuous spatial metrics, such as length or area. While the former reflects a discrete organization of numbers in space, the latter captures a graded, analog correspondence between quantity and spatial extent. These mapping types might appear at different developmental stages and rely on distinct cognitive processes (de Hevia, 2021).

The magnitude-based mapping (where space is treated as a quantitative dimension) reflects a broader cognitive tendency—particularly in adults—to align different continuous dimensions and even translate one form of magnitude into another, as described in work on psychophysical scaling (Stevens, 1957). In this sense, spatial extent is not merely a layout for ordering numbers but another analogical, continuous dimension that shares structural properties with number. In the case of number-spatial extent mappings, numerical values correspond to varying spatial lengths or sizes, increasing parametrically with numerical magnitude (Restle, 1970). This mapping is evident in robust interactions between number and physical size or length, such as interference effects between numerical and spatial magnitude (Girelli et al., 2000; Henik & Tzelgov, 1982; Hurewitz et al., 2006), biases in line bisection toward the side flanked by a larger number (de Hevia et al., 2006; de Hevia & Spelke, 2009), and distortions in spatial extent estimation depending on whether it is bounded by smaller or larger numbers (de Hevia et al., 2008; Viarouge & de Hevia, 2013). This number-spatial extent mapping appears early in development: it has been observed not only in preschool children (de Hevia et al.,
2012; de Hevia & Spelke, 2009), but also in infants (de Hevia & Spelke, 2010; Lourenco & Longo, 2010) and even in newborns (de Hevia, Izard, et al., 2014), suggesting that this particular cross-dimensional link may be developmentally privileged.

## 3.2. Spatial mappings of action

Another way in which number and space are linked is through action-related dimensions, which are inherently spatial—such as finger movements, hand aperture, and grasping size. This link is supported by evidence, in adults, of interference effects between numerical values and actions such as finger movements or grasping gestures (Andres et al., 2004; Badets et al., 2007), as well as by the motion-numerical compatibility effect, i.e., small numbers are more easily associated with leftward movements, while large numbers are associated with rightward movements (Cheng et al., 2015; Volpi et al., in press). Similar effects are already present in children from the age of 6, explicitly linking numerical quantities to magnitude-congruent actions (de Hevia & Nava, 2024). Even in preverbal infants, hand openings and numerical arrays can be mapped only when both magnitudes vary congruently (Decarli, Veggiotti, et al., 2022; see also Decarli, Veggiotti, et al., 2025), with complementary neural evidence showing modulation by the congruency—or lack thereof—of number-action pairs (Decarli, Rämä, et al., 2022). Interestingly, adapting the same methods that successfully disclosed a number-spatial extent mapping at birth (de Hevia, Izard, et al., 2014), newborns have been shown to map the size of a hand aperture to numerical magnitude (de Hevia et al., 2026). This study shows, in newborns, a spontaneous association of action-related magnitude and number, with smaller apertures linked to smaller magnitudes, and wider apertures to larger magnitudes—an effect that has been shown to be specific to biological stimuli. Action-related biological information may constitute an additional early-emerging dimension of magnitude, which is mapping onto quantity in a manner analogous to number, duration, or spatial extent. However, no evidence has yet been gathered as to whether action-related biological information (e.g., a series of different hand apertures) is directionally spatialized along a mental continuum at any point during development.

## 3.3. Spatial mappings of temporal dimensions

Not only are numbers spatially organized, but other abstract domains—such as time—also appear to rely on spatial representations. Adults spontaneously rely on spatial schemas when thinking about time (Boroditsky, 2000), as reflected in everyday language—for example, expressions like “a short break” or “a long time ago” encode temporal concepts using spatial metaphors. This type of mapping is structurally analogous to the magnitude-based mapping discussed earlier (3.1.), particularly in instances where space serves as a metaphor for spatial extent rather than for positional or directional information, as in the examples above. Although such mappings do not correspond to spatial layout representations or cognitive maps in the Tolmanian sense, they nonetheless reflect the use of spatial extent to encode magnitude, as in cases where an object is represented by an area proportional to its real-world size.

These mappings are consistent with the theoretical tradition of spatial metaphors proposed by Lakoff and Johnson (1980). Children (3- to 5-year-olds) show a better ability to learn a new adjective when this is presented in the domain of space, and then extend it to new associations, showing that spatial metaphors may be so common partly because they provide a scaffold for the acquisition of new word meanings (Starr et al., 2021). Interestingly, an asymmetry characterizes the relationship between space and time: spatial information systematically biases temporal judgments, whereas temporal information scarcely affects spatial ones, suggesting that it is the dimension of space that used to represent more abstract concepts (Boroditsky, 2000). Starr and Brannon (2016) showed that this asymmetry depends on visuospatial working memory, suggesting that abstract dimensions such as time are grounded in spatial representational systems. Moreover, spatial representations influence time judgments even when they are task-irrelevant: Adults are unable to ignore spatial information when estimating durations (Casasanto & Boroditsky, 2008).

This non-directional, magnitude-based mapping appears to emerge very early in development. At 9 months, infants bind representations of temporal durations and spatial lengths more successfully when these are positively correlated (Srinivasan & Carey, 2010). Similarly, 9-month-old infants are able to transfer associative learning between object size to temporal durations, mapping smaller and larger objects onto, respectively, shorter and longer durations, suggesting a shared representational format between time and space (Lourenco & Longo, 2010). Remarkably, even newborns (0–3 days old) respond to simultaneous increases (or decreases) in spatial extent and temporal or numerical magnitude, but only when these changes are congruent, further supporting an innate sensitivity to cross-dimensional regularities (de Hevia, Izard, et al., 2014).

Much like numbers are mapped along a mental number line, time appears to be arranged along a mental timeline, with the past on the left and the future on the right (Santiago et al., 2007; for a review, see Bonato et al., 2012). This spatially oriented grounding of time is also observed in children, and further supported by neuropsychological evidence. For instance, patients with hemispatial neglect—who fail to attend to the left side of space—are also slower to respond to events that occur before a temporal reference point, suggesting that the concept of “before” is mentally mapped to the left side of a mental space (Bonato et al., 2016). Nonetheless, culture appears to play a significant role in how people map time onto space. Evidence indicates that speakers of different languages organize time in ways that align with the typical spatial metaphors of their language (for a review, see Boroditsky, 2018). For example, Mandarin frequently relies on vertical terms, and Mandarin speakers tend to create vertical spatial associations for time more often than English speakers (Boroditsky, 2010; see also Vallesi et al., 2014). Importantly—similarly to the SNARC effect with numbers—although languages differ in the specific mappings of time onto space, the use of spatial language to describe temporal concepts is widespread across cultures, suggesting a potential predisposition to associate time and space.

Further evidence in favour of such a predisposition comes from the study of children, in which the directional mental timeline begins to emerge around 5 years of age (Sener & Starr, 2025). Critically, children who spontaneously arrange events along a linear mental timeline also show a better memory for the temporal order of those events compared to children who use a non-linear
arrangement, suggesting that the development of a spatial representation of temporal order supports the encoding and/or retrieval of temporal information (Sener & Starr, 2025). Furthermore, only 6-month-old infants who are habituated to a linear left-to-right sequence (opposite to a non-linear one) show evidence of discriminating the temporal order with which three figures appeared (i.e., what happened when), suggesting that a linear, spatial structure facilitates temporal memory (Pathman et al., 2018; Sener et al., 2024). This work is currently being extended to newborns to examine whether such effects emerge prior to extensive experience.

## 3.4. Spatial mappings of pitch

The auditory continuum of musical pitch has received considerable attention, partly because pitch is externally represented along a vertical axis—as reflected, for example, in musical notation where higher pitches are placed higher on the staff. This spatialization of pitch is further supported by behavioral evidence: in classification tasks involving pitch variation, adults tend to respond faster when higher pitches are associated with an upward-located button and lower pitches with a downward-located button, a phenomenon known as the SMARC (Spatial–Musical Association of Response Codes) effect (Rusconi et al., 2006). In the same work it was shown that among musicians, this spatial mapping extends to the horizontal plane as well, with lower pitches associated with the left and higher pitches with the right. Developmental research suggests that sensitivity to such pitch-space associations emerges early. Newborns, as well as infants at 3–4 and 7–8 months, show increased attention to stimuli where pitch height is congruent with vertical movement direction, such as rising pitch paired with upward motion (Chow et al., 2024; Dolscheid et al., 2014; Walker et al., 2010, 2018; see also de Hevia et al., 2025). Interestingly, when newborns are tested in their ability to map auditory low vs. high pitches onto static, dichotomous spatial positions (up versus down), they appear to associate higher pitch with the upper position; however, they do not extend this vertical mapping to the horizontal axis, left vs. right (de Hevia et al., 2025).

## 3.5. From early selectivity to cross-dimensional flexibility in spatial mappings

The transition from selective to flexible spatial mappings reveals how early-evolving biases may serve as a foundation for the later emergence of domain-general spatial organization. Developmental evidence suggests that the adult capacity to translate across magnitudes emerges gradually. While adults can flexibly relate number to space, brightness, force, or loudness (Stevens & Marks, 1965, 1980), children, infants, and newborns show selective patterns: preschoolers readily create number–spatial extent mappings but fail to relate number to brightness (de Hevia et al., 2012); preverbal infants map number to spatial extent (de Hevia & Spelke, 2010) but not number to brightness (de Hevia & Spelke, 2013), and they map duration to space but not loudness to space (Srinivasan & Carey, 2010). Newborns, too, prefer congruent over incongruent magnitude changes for both number and spatial extent, and for temporal duration and spatial extent (de Hevia, Izard, et al., 2014), but accept both congruent and incongruent magnitude changes for number and brightness (Bonn et al., 2019). Furthermore, at birth, evidence for spatial mappings has been found primarily for number, and only

<figure><img src="image_8.png" /><figcaption>**Fig. 4.** Schematic illustration of one of the tasks used by Previtali et al., 2010, in which participants learned a nine-word list and then classified the items using left- and right-located buttons in explicit order tasks. Participants judged whether a word or its image came before or after a reference word (the fifth in the list). The response mapping (“before”/“after”) was counterbalanced across blocks, with the assignment of responses to the left or right buttons alternating between blocks.</figcaption></figure>
in dichotomous spatial terms (e.g., left vs. right or up vs. down) (de Hevia, Veggiotti, et al., 2017; de Hevia et al., 2025; Di Giorgio et al., 2019). Over the first months, however, infants show the ability to process and spatially structure ordered sequences, revealing a broader—but still selective—sensitivity to ordinal information (Bulf et al., 2017, 2022; de Hevia, Girelli, et al., 2014; Ferguson et al., 2018). This developmental progression suggests that although the ability to organize conceptual domains spatially becomes increasingly flexible and domain-general, it is initially grounded in a narrower set of evolutionarily salient associations.

Remarkably, numerosity, duration and spatial extent reliably co-vary in the environment, and this ecological consistency may have, through evolutionary mechanisms, led certain dimensions to become preferentially and consistently associated with spatial representations. The ability to detect and exploit regularities among quantitative dimensions such as number, time, and space would have conferred clear adaptive advantages, enabling more precise navigation, timing, and prediction of environmental events. For example, the quantity of items often correlates with their spatial dispersion or temporal frequency—regularities that can guide action and decision-making. Over evolutionary time, such statistical co-variation may have favored the development of overlapping neural codes for magnitude information. These findings suggest that although adults exhibit a generalized ability to map across quantitative dimensions, the number-spatial extent mapping, along with the temporal duration-spatial extent one, may hold a special status early in development, forming a core cross-dimensional correspondence that scaffolds later generalizations (de Hevia, 2021).

This pattern of results raises the possibility that, over development, all continuous dimensions—whether numerical, spatial, temporal, or sensory (such as brightness, weight, or loudness)—may come to be represented along mental lines. Adults readily describe non-spatial experiences using spatial metaphors (“a long day,” “a high-pitched sound,” “feeling low”), suggesting that the mind spontaneously spatializes a wide range of continua. In line with this possibility, adults are faster to respond to typically small objects and animals with a left-located response button, and bigger ones with a right-located button, suggesting that the conceptual size of objects is also spatially arranged along a left-to-right axis (Ren et al., 2011; Sellaro et al., 2015). Also, participants arrange emotional intensity along a mental line, associating less emotional faces with the left side and more emotional ones with the right (Holmes et al., 2019; Holmes & Lourenco, 2011). Similarly, shorter durations are typically matched with left-located responses and longer durations with right-located ones (Vallesi et al., 2008). This left-to-right mapping also extends to risk assessment, with low-risk scenarios linked to the left and high-risk ones to the right (Macnamara et al., 2019). Luminance follows the same pattern, with darker stimuli mapped to the left and brighter ones to the right (Fumarola et al., 2014), as does loudness, with softer sounds linked to the left and louder ones to the right (Hartmann & Mast, 2017). Weight also appears to be represented along a left-to-right spatial orientation, as it can implicitly interfere with the SNARC effect: placing a heavier weight on the left and a lighter one on the right hand disrupts the mapping of small numbers to the left and large numbers to the right (Holmes & Lourenco, 2013).

## 3.6. *Spatial organization of sequential and ordered information*

The spatial organization of ordered information extends beyond numerical cognition, shaping how humans represent, remember, and learn sequences across development. From adults' spatial mapping of ordinal series to infants' reliance on spatial structure for rule learning, evidence suggests that spatial frameworks provide a foundational scaffold for encoding order and supporting memory.

When asked to categorize months of the year, days of the week or letters of the alphabet, adults are faster to respond when the left response is associated with months, days and letters that come first in the sequence, and when the right response is associated with those that come last (Gevers et al., 2003, 2004). This finding points to the existence of a left-to-right oriented spatial mental representation that becomes automatically activated when ordered sequences in long term memory are retrieved. Notably, this effect does not only appear in over-learned sequences, with which participants have extensive experience, but also in newly learned sequences. For instance, *Previtali and colleagues* (2010) asked participants to first memorize a sequence of 9 words presented in a specific order, and then to classify whether a target word or its image appeared before or after the 5th word (middle one) from the learned list, using spatially lateralized responses (e.g., left vs. right key presses) (see Fig. 4). Critically, participants tend to respond faster with the left hand to items appearing earlier in the sequence and with the right hand to items appearing later, extending the spatial alignment to WM and demonstrating a spatial mapping of serial order. Even non-verbal sequences follow this pattern: in an ordinal task emphasizing spatial reasoning, with participants required to mentally rotate and reposition a sequence of visual elements, children from 4 years of age show a tendency to associate the start of the sequence with the left and the end with the right. This spatial bias strengthens by age 7, likely reflecting increased exposure to cultural conventions such as reading and writing (Vivion et al., 2025).

The observation that SNARC-like effects extend beyond numbers to familiar, well-learned ordinal sequences challenges the notion that spatial associations arise exclusively from numerical magnitude. Instead, this broader applicability points to ordinal structure itself as a key driver of spatial mapping.

Moreover, the finding that even ad-hoc, recently learned ordinal sequences—thus not stored in long-term memory like numbers or letters—can elicit spatially oriented response patterns (*Previtali et al., 2010*) has inspired the idea that spatial frameworks may serve as a general scaffold for organizing information in working and episodic memory. This suggests that spatial coding is not limited to well-established sequences, but may reflect a more fundamental cognitive strategy for structuring sequential information. More generally, it has been suggested that the position of items in WM is linked to spatial positions, as reflected in response tendencies: elements at the beginning of a sequence are typically responded to faster and more accurately with the left hand, while elements at the end of a sequence are associated with the right hand (*Guida & Lavielle-Guida, 2011; Previtali et al., 2010; Van Dijck & Fias, 2011*). Notably, retrieval from WM seems to suggest a spatial arrangement of knowledge: task-irrelevant cues can modulate performance, with left/right targets facilitating retrieval of items earlier/later in a sequence, respectively (*De Belder et al., 2015*).

When asked to recall pairings that involve ordinal information, adult participants perform better when the pairing was learned in a spatially structured way (from left-to-right for English speakers and right-to-left for Hebrew speakers) (McCrink & Shaki, 2016). When
a simple three-letter sequence is shown in a spatial way, participants are better at recalling temporal information (e.g. the order in which the letters appeared) of the sequence when this is presented from left to right rather than from right to left (Fischer-Baum & Benjamin, 2014). This phenomenon appears early in development. Not only adults but also 7-, 9- and 11-year-old children successfully recall the individual elements of a three-object sequence; however, they fail to remember the correct temporal order—unless the sequence has been learned in a spatially congruent, left-to-right layout (Pathman et al., 2018). This striking result highlights how even with just three items, temporal order information is easily lost in memory unless it is supported by a spatial structure, reinforcing the idea that spatial alignment plays a critical role in encoding and retrieving sequential events.

The strength of spatial structure may be most critical when a memory trace is first being formed. Although adults' tendency to spatialize information from left to right decreases with repetition—likely because participants begin to rely more on familiarity or recognition-based processes rather than spatial scaffolding (Ftaita et al., 2024)—spatial frameworks appear to play a foundational role in the initial encoding of episodic content. This pattern highlights that spatialization operates at multiple levels: transient spatial scaffolds can guide the organization of new information early in learning, while long-term, experience-dependent maps support enduring semantic and conceptual representations. Indeed, episodic memory itself seems to be organized spatially: participants are faster to associate past events with the left and future ones with the right (Santiago et al., 2007). When judging whether life events occurred before or after a reference point, responses are also faster when past events are aligned to the left and future ones to the right, suggesting that autobiographical memory is structured along a spatial, left-to-right mental timeline (Santiago et al., 2010).

Crucially, the reliance on spatial structure to support the encoding of order is not limited to individuals with access to cultural tools such as reading and writing; a growing body of research shows that even during the first year of life, before exposure to formal education or symbolic systems, infants also benefit from spatially structured input. Although it was previously reported that infants could successfully abstract rules only from auditory sequences early in life—and that this ability generalized to other types of stimuli, such as visual shapes, only later (Dawson & Gerken, 2009; Gervain et al., 2008; Johnson et al., 2009)—more recent findings show that infants as young as 3 months can extract rules in the visual modality, following ABB or ABA patterns, but only when sequences are spatio-temporally organized (see Fig. 5; Ferguson et al., 2018). This suggests that spatial structure serves as a powerful scaffold for early rule learning, allowing infants to detect regularities in visual input that might otherwise remain inaccessible. Moreover, by 7 months of age, infants show a directional bias for learning ordered information, succeeding only when sequences are presented from left to right, but not from right to left (Bulf et al., 2017, 2022; de Hevia, Girelli, et al., 2014). This asymmetry suggests not only that the left-to-right orientation facilitates consolidation of regularities, but also that a right-to-left direction is hindering the formation of a stable internal representation, thus disrupting the effect. These findings may reflect a deeper, potentially automatic and necessary reliance on spatial structure. That is, rather than space being merely facilitative, it may in some cases be essential for processing, retrieving, and organizing abstract thought.

Similarly, 14-month-old infants—who typically fail to track more than three hidden objects at once—can overcome this limitation when spatial cues are provided. In particular, when individual objects are bound into spatiotemporally-defined sets, for instance 2 sets of two objects or 3 sets of two objects, then infants can internally represent a total of 4 and 6 items, respectively, while in absence of these spatial chunking cues, infants would be limited to three objects (Feigenson & Halberda, 2004, 2008). These findings demonstrate that visuo-spatial organization can substantially expand infants’ representational capacity, allowing them to overcome apparently rigid limits in perception and internal representation simply by exploiting basic spatial structures.

## 3.7. *Variability and flexibility in spatialization*

Although SNARC and SNARC-like, ordinal effects in adults are robust at the group level, their expression varies considerably across and within individuals. A few studies have shown that in adults, only a subset of participants often drives the overall group effect, and even within individuals, the strength of the association can fluctuate depending on contextual or strategic factors (Cipora et al., 2024,

<figure><img src="image_9.png" /><figcaption>**Fig. 5.** Schematic representation of Ferguson et al. (2018). Three-month-old infants were habituated to a visual abstract rule (e.g., ABB), in which three-element sequences were presented within a spatio-temporal organization (the first element appeared on the left, the second in the center, and the third on the right side of the screen). At test, infants showed a preference for a novel abstract sequence (e.g., ABA) compared to the habituated one, even though the individual elements forming the sequences differed in both shape and color, providing evidence that they had learned and applied the abstract rule.</figcaption></figure>
preprint; Roth et al., 2024). This variability does not necessarily contradict the idea of a widespread spatial bias but rather suggests that spatial-numerical mappings may be modulated by differences in cognitive style, strategy, or experience. At the same time, studies with newborns and infants typically reveal that a majority of participants display spatial mappings, supporting the view that this bias is widespread early in development.

Evidence from individuals with aphantasia—who lack voluntary visual imagery yet can still perform spatial transformation tasks such as mental rotation (e.g., Zhao et al., 2022)—suggests that spatial processing can operate independently of visual imagery, further supporting the notion that these mappings rely on abstract, amodal mechanisms. Moreover, evidence from adult blind participants demonstrates that spatial-numerical mappings can emerge independently of visual imagery or experience, relying instead on shared parietal mechanisms in both blind and sighted individuals (Castronovo & Seron, 2007; Kanjlia et al., 2016). However, little is known about the presence of non-numerical ordinal mappings in such populations, or about whether these associations arise in blind infants and newborns who lack cultural exposure to spatial conventions. It is also an open question whether spatialization across different conceptual domains (e.g., numbers, months, letters) correlates within individuals—suggesting a core, abstract propensity for spatial mappings—or whether these mappings are domain-specific, reflecting multiple developmental trajectories. Together, these considerations underscore that while the tendency to spatialize abstract information may reflect a fundamental cognitive bias, it is also shaped by individual experience and contextual constraints.

It is important to note that some studies have reported an absence of spatialization or consistent directionality in certain populations, such as preschool children and illiterate adults (Guida et al., 2018, 2020; Pitt et al., 2021; Tillman et al., 2018; van Dijck et al., 2020). This raises the question of how to reconcile these findings with the evidence supporting early-emerging, possibly innate, spatialization observed at birth and in infancy, as well as with the presence of similar spatial mappings in non-human species. A plausible interpretation is that the relationship between number/order and space is not fixed but dynamically shaped throughout development by multiple interacting factors. As proposed by McCrink and de Hevia (2018), spatial mappings may “wax and wane” during infancy and early childhood as children gradually shift from relying on innate spatial biases to being influenced by the cultural conventions that organize space. The toddler and preschool years may therefore constitute a transient, highly flexible stage in which orientation preferences for spatialization are not yet consolidated, resulting in the apparent absence or inconsistency of spatial mappings (Guida et al., 2020; Tillman et al., 2018; van Dijck et al., 2020). Similarly, in illiterate adult participants the lack of systematic spatial-numerical mappings and spatialization of ordinal information may reflect the coexistence of unreinforced biological biases and the influence of cultural spatial habits that remain only partially internalized. For instance, in contexts where right-to-left cultural orientations oppose a putative left-to-right innate bias, the two tendencies could effectively cancel each other out (Guida et al., 2018). Thus, the apparent absence of spatialization in these groups does not contradict the idea of an early and biologically grounded origin of spatialization, but rather highlights how its expression depends on the interaction between innate predispositions, experimental reinforcement, and task demands.

# 4. Mechanisms of spatial scaffolding

The behavioral and developmental evidence reviewed above raises the question of what neural mechanisms might support the emergence of spatial mappings across domains. A growing body of developmental cognitive neuroscience suggests that the neural systems originally evolved for spatial navigation and perception may also provide a representational structure for more abstract cognitive functions.

The spatial mappings described from birth and during the first year of life—such as the association of larger numerosities with the right and top sides of space (de Hevia, Veggiotti, et al., 2017; de Hevia et al., 2025)—might be accounted for by the early availability of a dedicated neural system for Euclidean-like spatial representation (Tolman, 1948). According to the cognitive map theory, the hippocampal-entorhinal system constructs internal representations of space along metric axes, supporting allocentric navigation (O'Keefe & Nadel, 1978). In fact, O'Keefe and Nadel explicitly entertained the possibility that the hippocampus might provide organisms with “an a priori Euclidean spatial framework” (p. 6), suggesting that such a structure may exist independently of extensive learning or experience. While originally described in adult rodents, evidence suggests that key components of this system, including place cells and grid cells, emerge early in development (Langston et al., 2010; Wills et al., 2010). Spatially organized representations are a widespread principle of cortical organization, observable in retinotopic maps in visual cortex (coding spatial position in the visual field), tonotopic maps in auditory cortex (coding sound frequency along spatial gradients), and somatotopic maps in somatosensory cortex (coding body surface location) (e.g., Harvey et al., 2015; Saenz & Langers, 2014; Sereno & Huang, 2014; Tsouli et al., 2022). Also, examples of retinotopic, somatotopic and tonotopic maps have been found early in the development of infants' perceptual systems (Ellis et al., 2021; Saby et al., 2015; Graven & Browne, 2008). This early emergence indicates that spatial organization is a foundational property of at least some perceptual representations, rather than a format that must always be constructed via later-developing spatial brain systems or associative mechanisms. Importantly, these maps arise within domain-specific perceptual systems and do not depend on a single centralized spatial module. The ubiquity of spatially organized representations supports the view that spatial coding may serve as a general organizing principle of neural computation, extending beyond navigation and perception to diverse cognitive domains, while allowing for multiple neural implementations depending on task demands and representational content.

Recent developmental neuroimaging work further supports the early availability of spatial-coding systems. Longitudinal resting-state studies show that hippocampal functional connectivity networks emerge within the first two years of life and predict later working-memory outcomes (Liu et al., 2021). Awake-infant fMRI reveals hippocampal encoding of individual memories even before age two (Yates et al., 2025). Moreover, network-level analyses demonstrate rapid maturation of spatially organized brain networks
from birth to 6 months of age (Seraji et al., 2025). These findings suggest that the neural infrastructure for spatial coding is present early and may provide the scaffold upon which infants begin to structure experience, including the representation of abstract, non-spatial domains.

This developmentally early neural system may reflect, at a cognitive level, an innate core system for representing geometric properties of the environment, as proposed in core knowledge theory (Spelke & Kinzler, 2007). According to this view, humans are endowed with a dedicated, domain-specific system for Euclidean geometry, which allows infants to perceive and reason about distances, directions, and layout. The hippocampal-entorhinal system—by providing an a priori, metric spatial framework—could thus instantiate the neural basis of this core geometric system. Importantly, such a system may not be limited to physical space: it could serve as a scaffold for organizing non-spatial dimensions of experience, including number, time, and conceptual relations, in spatial format.

We do not argue that domains such as number, time, ordered or semantic information are inherently spatial in nature. The format of representation remains abstract—humans can perceive and reason about them without necessarily relying on spatial representations. We propose that space provides a powerful medium that imposes structure on these abstract dimensions, in some cases enabling them to be conveyed, organized, and manipulated. Spatial organization offers a framework for structuring information—such as temporal order or position within a sequence—and may, even, serve as a scaffold that allows computations or relational operations that would otherwise be difficult or impossible to achieve. In this context, the use of spatial structures to represent abstract content may be understood as a case of neural recycling—a process by which evolutionarily older neural systems are co-opted to support culturally acquired functions such as reading, mathematics, or symbolic reasoning (Dehaene & Cohen, 2007). Here, we adopt the term in a broader, evolutionary sense: rather than referring to the cultural reuse of circuits for skills such as reading, we propose that neural systems originally devoted to processing physical space have been redeployed to represent non-spatial domains like number or time. The spatial coding of abstract sequences may thus reflect an adaptive reuse of ancient spatial mechanisms supporting the emergence of abstract thought.

While we argue that spatial frameworks originally devoted to processing physical space are recruited to structure conceptual representations, caution is needed before assuming a perfect correspondence between spatial biases in the physical domain and those in the representational domain. Our position is that it is the availability of these spatial structures—developed for navigating the physical world—that enables the representation of conceptual content. Similar underlying mechanisms may be engaged across domains, but their expression can diverge depending on task demands and representational context. General spatial biases are more likely to be observed across both domains, yet these do not imply a strict one-to-one mapping. It is important to distinguish these cognitive maps from early forms of spatialization. The former represent stable, long-term spatial frameworks that support navigation and semantic organization, whereas early or transient spatial associations likely function as flexible scaffolds that structure new information. These two processes may thus operate at different timescales—predisposed, short-term spatialization mechanisms facilitating initial encoding, and experience-dependent maps supporting enduring representations.

In parallel, this spatial scaffolding may operate in concert with attentional mechanisms that support learning and memory. Research in developmental cognitive neuroscience suggests that structured spatial layouts enhance attention allocation and stability, acting as attentional scaffolds that guide processing toward relevant dimensions of experience (Amso & Scerif, 2015). During infancy, regularities in spatial structure—such as consistent left-to-right orientations—may increase the salience of certain elements within a sequence, thus facilitating the detection of patterns, the abstraction of rules, and the encoding of order (Bulf et al., 2017, 2022; de Hevia, Girelli, et al., 2014; Ferguson et al., 2018). Emerging evidence also indicates that the way infants explore space from the earliest months of life likely shapes how they attend to and process information, influencing the dimensions they prioritize and the strategies they use to extract structure from the environment (Leehey et al., 1975; McCrink et al., 2020; Nava et al., 2022; Petroff et al., 2025). For instance, infants with stronger inhibitory control in visuo-spatial tasks show reduced sensitivity to spatial biases in numerical tasks—known as Operational Momentum (Macchi Cassia et al., 2016, 2017; McCrink & Wynn, 2009)—suggesting that during infancy early inhibitory mechanisms in visuo-spatial processing contribute to and modulate tasks that are not inherently spatial but likely engage spatial attention processes (Decarli, Illikoud, et al., 2025). Further evidence from neurodevelopmental studies of attentional and orienting systems (Ross-Sheehy et al., 2015) and memory-related structural maturation (Bevandić et al., 2024) underscores the interconnected nature of spatial, attentional, and mnemonic mechanisms in early life. Taken together, evidence from neuroscientific and developmental studies converges on the idea that spatial coding constitutes a domain-general representational format, instantiated through distributed cortical maps and available early in life to scaffold both spatial and abstract forms of cognition.

While the hippocampal-entorhinal system offers one influential model of spatial coding (e.g., O'Keefe & Nadel, 1978), we do not assume that spatial scaffolding for abstract cognition depends exclusively on this circuit. Rather, converging evidence suggests that a broader fronto-parietal network—including the intraparietal sulcus and posterior superior parietal lobule, which encode spatial relations, and the supplementary motor area (SMA), which supports temporal and sequential organization—contributes to representing numerical and temporal magnitudes, order, and other forms of relational structure (Protopapa et al., 2019; Van Opstal et al., 2008; Xu et al., 2024). Moreover, some forms of spatial mappings such as retinotopy, tonotopy or somatotopy, are revealed within the cortical structures of the perceptual system involved in the processing of the information and do not rely on frontal nor hippocampal involvement (e.g., the visual cortex; Engel et al., 1997). These mappings provide spatially organized representational formats that are intrinsic to perceptual processing itself, and can therefore support certain spatially structured cognitive effects without invoking additional, domain-general spatial coding mechanisms in other brain regions (e.g., parietal, frontal, sensorimotor, or distributed cortical networks). Within this broader framework, the hippocampal-entorhinal system can be viewed as one component of a distributed spatial coding architecture that interacts with perceptual, parietal, and premotor regions to support certain forms of abstract cognition. Moreover, while the hippocampal system is involved in serial order working memory processing (Cristoforetti et al.,
2022), this system cannot account for the directional biases—such as the left-to-right mapping of number—observed in infants and non-human animals. These asymmetries have instead been attributed to hemispheric specialization, whereby the dominant role of the right hemisphere in visuospatial and numerical processing biases attention leftward, favoring left-to-right increasing sequences (de Hevia, Girelli, et al., 2014; de Hevia et al., 2012; Rugani et al., 2015; Rugani & de Hevia, 2017). Other accounts point to hemispheric differences in spatial-frequency tuning (Felisatti et al., 2020) or to valence-related lateralization (Vallortigara, 2018).

The proposed view does not suggest that evolution directly predisposed humans to develop a "mental space" for abstract thought. Rather, this capacity likely emerged as a by-product of general organizational mechanisms that originally evolved to efficiently encode, store, and navigate information about the external world. Because these spatial functions require flexible relational mapping, the neural systems that support them—particularly hippocampal and parietal networks—are well suited to be co-opted for organizing non-spatial, abstract information along analogous relational dimensions. Once in place, these spatial organizational principles may have provided a flexible scaffold upon which experience, explicit learning, or maturation could progressively build increasingly complex and abstract forms of thought.

## 5. Conclusions

In the present paper, we put forward the idea that humans are innately predisposed to use spatial mental structures (e.g., left-right, near-far, up-down) to organize experience and abstract knowledge (quantities, sequences, events, etc.). We reviewed evidence supporting this idea, highlighting the findings that humans, since birth, rely on spatial mappings to organize abstract thought.

Importantly, we hypothesize that, it is not only that congruent spatial cues boost processing, but also, in some cases, the absence of a congruent spatial framework may prevent knowledge from emerging altogether. We speculate that some cognitive limitations observed early in development may result not from conceptual unavailability, but from the absence of an adequate mental space for organizing such knowledge. We argue that innate or early-developing spatial structures (like understanding left vs. right, near vs. far, up vs. down) provide a mental framework that scaffolds the development of more complex cognitive abilities over time—such as reasoning about quantity, time, sequence, or even abstract concepts.

Evidence across populations and methods supports this hypothesis. In infants, spatial incongruency impairs the learning of ordered structures or the expression of ordinal knowledge. For example, while 7-month-old infants can extract numerical order from centrally presented stimuli (Picozzi et al., 2010), this ability is disrupted whenever spatial directionality is incongruent or non-canonical (de Hevia, Girelli, et al., 2014). Conversely, using congruent and preferred spatial frameworks can support the earlier emergence of such abilities or enhance them (Bulf et al., 2017; Feigenson & Halberda, 2008; Ferguson et al., 2018). Children and adults who use stable, canonical spatial mappings perform better in numerical processing, episodic memory, and ordinal tasks (Gunderson et al., 2012, 2019; McCrink et al., 2014; McCrink & Shaki, 2016; Opfer et al., 2010; Opfer & Furlong, 2011; Pathman et al., 2018; Sener & Starr, 2025). Additional evidence comes from neuropsychological patients, whose impairments in spatial processing (e.g., neglect syndrome) disrupt not only the representation of physical space but also mental number lines and abstract reasoning (Bisiach & Luzzatti, 1978; Bonato et al., 2016; Zorzi et al., 2002). We also briefly discussed how this may reflect a process of neuronal recycling: humans repurpose pre-existing neural structures devoted to processing physical space—a fundamental dimension of experience—for organizing higher-order cognition. Neural evidence supports this view, as spatially tuned cells such as grid cells extend their function beyond physical navigation to the representation of abstract information (Bellmund et al., 2018; Constantinescu et al., 2016).

A substantial body of experimental and neuroimaging research has provided important insights into how spatial organization contributes to the representation of non-spatial information—such as numbers, time, and other abstract domains (e.g., Fias, Lau-wereyns, & Lammertyn, 2001; Holmes & Lourenco, 2013; Pathman et al., 2018). These studies have typically interpreted congruency, interference, and facilitation effects as evidence that spatial structure can enhance or hinder cognitive performance across domains. However, rather than merely being the cause of these effects, spatial cognition may play a more fundamental role in abstract reasoning than previously assumed. This view is compatible with the idea that early, possibly innate, spatial frameworks—such as a Euclidean reference system—serve as scaffolds for structuring increasingly abstract knowledge across development, and echoes classical theories that have long emphasized the centrality of spatial structure in thought, converging on the idea that spatial frameworks are not merely useful, but foundational for abstract cognition (Johnson-Laird, 1983; Kant, 1781; Piaget et al., 1957; Shepard, 1984; Tolman, 1948; Tversky, 2005). As infants' spatial representations grow in resolution and flexibility, so does the complexity of the knowledge they can organize. In this view, spatial cognition is not only supportive—it may be essential to the emergence of structured abstract thought.

## Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgement

The preparation of this article was supported by a grant from the Agence Nationale de la Recherche (SPACEODC-ANR-24-CE28-0969) to MDdH (https://anr.fr/) and a PhD fellowship from Université Paris Citè - ED3C to VV.
## Data availability

No data was used for the research described in the article.

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