Mental representations, as internal cognitive symbols that represent abstract core properties of sensory signals, are a fundamental building block of human cognition (Thagard, 2005). Mental representations permit us to learn from prior experience and to infer meaning from novel sensory signals (G. A. Miller, 1990), thus enabling intricate cognitive capacities such as learning, memory, and communication (Fodor & Pylyshyn, 1988; Jackendoff, 1995; Perszyk & Waxman, 2018). Speech sounds, as an essential type of sensory input for hearing individuals, are no exception. Decades of linguistic research have focused on theorizing the architecture of mental representations of speech sounds, i.e., phonological representations (J. Anderson & Jones, 1974; Jones, 1957; Pierrehumbert, 2016). Based on theories on the abstract symbolic systems of how speech sounds and their systematic variations are represented as phonological representations in memory (i.e., the lexicon) (McQueen et al., 2006), linguists were able to advance our understanding of speech and language as a hallmark of human communication. They do so by examining how phonological representations guide the perception of invariant meaning from highly variable acoustic signals (Kuhl, 1991; Pierrehumbert, 2016), the generation of novel but patterned sound sequences in language production (Chomsky & Halle, 1968; Prince & Smolensky, 2004), and the acquisition of language in infancy (Kuhl et al., 2008). The present study aims to advance current understandings of the architecture of phonological representations, by examining how neural speech processing is modulated by structures of phonological representations that vary cross-linguistically.

Ever since the earliest theories of the phoneme (Trubetzkoy, 1939), phonological representations have been conceptualized not only as a shorthand for formal analysis, but also as neurocognitively real computational primitives that are actively involved in speech and language processing and production. In cognitive neuroscience, ever since the first demonstration of abstract properties of phonological representations in neural speech processing in Näätänen’s pioneer mismatch negativity study (Näätänen et al., 1997), an abundance of neurolinguistic research has demonstrated the neurocognitive reality of phonological representations from phonological features (e.g., Eulitz & Lahiri, 2004; Mesgarani et al., 2014), segments (e.g., Domahs et al., 2009; Ulbrich et al., 2016; White & Chiu, 2017; Wiese et al., 2017), and prosody (e.g., Domahs et al., 2008, 2013; Honbolygó & Csépe, 2013).

However, one of the most important notions in phonological theories (Archangeli & Pulleyblank, 2014; Chomsky & Halle, 1968; Lahiri & Reetz, 2010; Pierrehumbert, 2001), i.e., the level of abstractness that speech sounds are represented in the mind and the brain, has received less attention in neurolinguistic work. Traditional generative theories (e.g., Chomsky & Halle, 1968; Prince & Smolensky, 2004) including underspecification theories (Archangeli, 1988; Lahiri & Reetz, 2010) postulate that phonological representations are abstract, distinct from the phonetic realization of sounds known as surface representation. On the other hand, exemplar-based theories suggest that speech sounds are represented by traces of the concrete phonetic forms stored in memory (Bybee, 2002; Johnson, 2007; Pierrehumbert, 2001).

A core issue in this quest to understand the nature of phonological representations in phonological theory is the phenomenon of phonological alternation (Anttila, 2002). Phonological alternation refers to the realization of morphemes into perceptually distinct speech sounds as conditioned by the interaction among phonological, morphological, and lexical surroundings (Anttila, 2002). Phonological alternation is a core issue in the study of phonology not only because the architecture of phonological representations (e.g., the level of representational abstractedness) is postulated differently across phonological theories, but also as the theorized architecture of phonological representations changes, such changes entail a different understanding of how phonological alternation is realized in the phonetic form, e.g., the nature of the phonological grammar.

Earlier generative phonological theories (Archangeli, 1988; Chomsky & Halle, 1968) suggest that there exist abstract representational primitives known as the underlying representation (UR) that can be distant from their corresponding concrete phonetic forms known as surface representations (or SR) which may alternate in different morphophonological contexts. The theorized roles of the grammar are to transform and specify features of the abstract UR into concrete pronounceable forms (i.e., the SR) according to the morphophonological context. The more recent emergent phonological theory (Archangeli & Pulleyblank, 2014) posits that different allomorphs of a morpheme are listed in parallel and linked with each other in the mental lexicon; derivation of listed allomorphs into SR involves domain-general cognitive combinatorial processes that combine each allomorph with the morphophonological context as candidate SRs, which are then evaluated for their phonological well-formedness. Without positing a distinction between UR and SR, exemplar-based phonological models (Bybee, 2002; Johnson, 2007; Pierrehumbert, 2001) postulate that instead of morphemes represented in isolation, multimorpheme sequences are directly stored in memory, such that alternation as a phenomenon represents the manifestation of frequency effects of the multimorpheme sequences (i.e., which forms of morphemes appear more with each other) and articulatory mechanisms that modify the quality of speech sounds in morphological combinations.

While the long-standing debate on these theoretical models also pertains to issues beyond phonological alternation, the present study focuses on phonological alternation with an aim to advance the current understanding of the architecture of phonological representations. Specifically, we seek to examine the extent to which the abstract phonological representations are more than formal entities, but are in fact neurocognitive primitives that impact speech processing and lexical access. Specifically, we examine the extent to which neural speech processing of phonological alternations is modulated by structures of phonological representations that vary cross-linguistically. Following the spirit of modern phonological frameworks (Mascaró, 2007; Pierrehumbert, 2016), we hypothesized that phonological representations are multiform in nature, i.e., that phonological representations may take abstract and concrete forms, which are determined by the grammar based on factors including lexical distributional properties of the phonological alternation. We predicted that the processing of surface-similar phonological alternation patterns subserved by different phonological representational structures are neurocognitively distinct.

In this study, we examined the processing of a tone alternation pattern that is similar in surface, but with distinct lexical distributions across Mandarin and Cantonese, using a cross-modal priming paradigm. Behavioral and ERP responses in priming paradigms reflect abstract properties of mental representations (Jakimik et al., 1985; Seidenberg & Tanenhaus, 1979; Ventura et al., 2004), including phonological representations (Bohn et al., 2013; Domahs et al., 2008, 2013, 2014; Henrich et al., 2014; Molczanow et al., 2013). Results of Experiments 1 and 2, ERP responses in particular, suggest cross-linguistic differences in the processing of a surface-similar lexical tone alternation pattern.

At the behavioral level, Experiments 1 and 2 exhibited largely similar response patterns in the phonological judgment task embedded in the cross-modal priming paradigm. A main effect of Violation Type in both experiments 1 and 2 suggests that rejections of underapplication and overapplications of tone alternation (mT3 sandhi in Experiment 1; pinjam in Experiment 2) were both slower (in terms of RT) than plain violations. This similarity is striking, suggesting that despite their well-established lexical distributional differences and productivity of the alternation phenomenon, Mandarin tone sandhi and Cantonese pinjam appear to be subserved by the same type of phonological representation.

According to our prediction, both tone alternation patterns are subserved by Listed UR, converging with previous behavioral studies using visual-to-visual priming (Nixon et al., 2015) and auditory-to-auditory priming (Chien et al., 2016) to confirm the presence of priming effects among surface variants in a lexical tone alternation. Specifically, these results suggest that the elicitation of surface variants of lexical tone may facilitate behavioral responses involving its alternating surface variants relative to a contrastive tone category. However, the significant Violation Type × Context interaction identified only in Experiment 1 was not consistent with any of our predictions. Specifically, rejection of tone sandhi overapplications was faster than underapplications, but was different (i.e., slower) than plain violations. Although the behavioral RT results do not align exactly with any set of our predictions, the presence of the Violation Type × Context interaction for Mandarin sandhi in Experiment 1, and its lack thereof for pinjam in Experiment 2, suggest that for Mandarin sandhi, the underlying mTL is more relevant during the priming process, or that for pinjam, the surface cTR is more relevant.2

ERP results yielded specific patterns consistent with our competing hypotheses, providing a clearer picture. Crucially, notably different ERP patterns were found across Experiments 1 and 2. Experiment 1 found that the processing of both tone sandhi underapplications and overapplications both elicited an earlier N400 response and an additional LPC response compared to plain violations. The N400 and LPC responses in the underapplication and overapplication conditions were comparable (no difference in amplitude or latency). In contrast, it was found in Experiment 2 that both pinjam underapplications and overapplications only elicited N400 but not LPC responses. The amplitude and latency of the N400 responses across all conditions (underapplication, overapplication, and plain violations) were not different. While not fully compatible with the behavioral results (i.e., the lack of ERP differences despite behavioral differences in Experiment 2), these ERP patterns from Experiments 1 and 2 reflected that the processing of similarly surface-patterned violations in tone alternation involved different neurocognitive underpinnings across Mandarin and Cantonese. We interpret such neurocognitive differences to reflect differences in underlying phonological presentations that subserve the tone alternation patterns across the two languages.

In the cross-modal priming paradigm, a mismatch between representations elicited by the prime and the target is known to elicit the N400 and the Late Positive Complex (LPC) ERP responses, relative to a baseline where the prime and target match with each other (J. E. Anderson & Holcomb, 1995; Holcomb, 1993; Holcomb et al., 2005; Kiyonaga et al., 2007). The N400 is an ERP component identified as a neural-marker for lexico-semantic integration in language processing, most commonly elicited by lexico-semantic violations (Kutas & Federmeier, 2000). The N400 is generated by a cortical semantic processing network involving mid temporal inferior frontal brain areas (Kutas & Federmeier, 2000; E. F. Lau et al., 2008), and peaks negatively at around 300–500 ms post-stimulus. The N400 component is often accompanied by the LPC (Curran et al., 1993; Karayanidis et al., 1991; Woodward et al., 1993), a posterior-distributed ERP component that peaks at a later 400–800 ms post-stimulus time window (Friedman & Johnson, 2000). LPC, generated in the lateral parietal cortex (Rugg & Curran, 2007), reflects the levels of effort or confidence in lexico-semantic judgment (Domahs et al., 2009; Finnigan et al., 2002), lexical “patching’’ in erroneous contexts (Daltrozzo et al., 2012), and memory recollection (Friedman & Johnson, 2000). In the context of phonological cross-modal priming, a collection of neurolinguistic studies found that given orthographic primes, violations of phonological properties of the auditory target affect lexical integration (as reflected in N400) and restructuring (“patching’’) of such phonological violations (as reflected in LPC) (Bohn et al., 2013; Domahs et al., 2008, 2013, 2014; Friedrich et al., 2008; Henrich et al., 2014; Molczanow et al., 2013). Specifically, phonologically ill-formed violations in the target which are semantically recoverable, but require mental phonological restructuring to match with the prime, will elicit the LPC (Domahs et al., 2008). Meanwhile, violations of the phonological form which hinder lexical access, but are otherwise phonologically well-formed, will only elicit the N400 (Domahs et al., 2013).

In Experiment 1, the underapplication condition, as compared to the plain violation control, elicited a robust LPC response that followed an earlier N400 response. This suggests that although the violation form is phonologically ill-formed, hindering lexical access initially, the violation was deemed recoverable phonologically. This prompted a subsequent phonological restructuring process that recovered the correct phonological form to facilitate lexical access, as reflected by the LPC (Domahs et al., 2008). This violation was deemed recoverable phonologically potentially because the underapplication violation contains a low tone, which either matches 1) Single UR form, or 2) one of the listed allomorphs in the Listed UR.

Results of the overapplication condition provide deeper insight on which of the three forms subserve the alternating mT3 in the phonological representation. A priori, it was predicted that if the tone alternation pattern is subserved by a single phonological representation, overapplication violations would only elicit an N400 response comparable to plain violations because the auditory target would not match the form of phonological representation elicited by the prime (i.e., a Low tone). While an N400 was indeed elicited in the overapplication condition in Experiment 1, this N400 was accompanied by a robust LPC, consistent with the predictions of the Listed UR account, and with previous behavioral and ERP experiments (Y. Chen et al., 2011; Li & Chen, 2015; Nixon et al., 2015). In cross-modal priming studies embedding a phonological judgment task, the LPC is interpreted as an index to the level of effort required to restructure violations in the auditory target to match with the primed lexical item to achieve behavioral judgment (Domahs et al., 2008, 2009, 2013, 2014). In addition, the literature on the bilingual lexicon suggested that the LPC may reflect the amount of cognitive resources required to inhibit coactivated mental representations in language judgment tasks (P. Chen et al., 2017). Therefore, the LPC in the overapplication condition may reflect that all alternation forms listed in the phonological representation were coactivated by the visual prime, regardless of its surface phonological context. Specifically, since mTR and mTD/mTL were all coactivated by the visual prime, the mTR in the overapplication violation can be traced back to its mT3 lexical representation, and was therefore deemed recoverable. Excess mental effort was then needed to restructure the violation into the corrected listed phonological form (i.e., mTL), while inhibiting the wrong alternation form perceived from the auditory prime (i.e., the mTR). The combination of both processes manifested into the LPC.

Importantly, the comparably robust LPC responses in underapplication and overapplication conditions suggest that the LPC was not solely elicited due to the ill-formed mTL+mTL tone sequence in the underapplication condition; LPC was elicited despite the fact that the mTR+mT1 overapplication violation was phonologically acceptable. This implies that the coactivation of all listed forms is not contingent upon its neighboring phonological contexts, such that the mTR can be recovered to match with the mT3 lexical representation even in a mTR+mT1 sequence which is not a phonological context triggering tone sandhi.

While the presence of N400 components was expected in all conditions, their lower latency in the underapplication and overapplication conditions was not expected. Such lower latency of N400 response as compared to the N400 in the plain violation conditions may further speak to the differential source of the N400 components elicited in the cross-modal priming paradigm and the influence of Listed UR on lexical access.

One potential source of the earlier N400 component is a phonotactic violation detection mechanism (henceforth, phonological N400) (Zhang et al., 2022), potentially distinct from the conventional N400 component indexing lexical access mechanisms (lexical N400). The presence of this putative phonological N400 is supported by a body of ERP studies which identified an N400-like component in the processing of phonotactically illegal sequences, both segmental (Domahs et al., 2009; Ulbrich et al., 2016; White & Chiu, 2017; Wiese et al., 2017) and suprasegmental (Zhang et al., 2022) in nature.

Therefore, the N400 components that differ in latency in Experiment 1 may reflect distinct components: the early N400 component elicited in the overapplication condition (which contained a phonotactically illegal tone sequence [*mTL+mTD]) is phonological in nature, whereas the later N400 component elicited in the plain violation conditions with phonotactically well-formed tone sequences is lexical in nature. Interestingly, the early N400 in the overapplication condition of Experiment 1 was present despite a phonotactically well-formed tone sequence (mTR+mT1). Such results may reflect that this putative phonological N400 component not only reflects the detection of phonotactic violations on the surface, but also the detection of ill-derived grammatical transformation from the UR to the SR (i.e., the selection of the [mTR] allomorph in a /mT3+mT1/ sequence despite the lack of the sandhi-trigger phonological context).

Another possibility is that the earlier N400 may indicate more efficient detection of lexical violations. The more efficient detection of lexical violation in the underapplication and overapplication conditions is not contradictory to the LPC responses, which index a higher load of cognitive resources. In the psycholinguistics literature on the lexicon, it is known that coactivated representations exhibit both facilitative and inhibitory effects on language processing: weak coactivation leads to facilitative effects, whereas strong coactivation leads to inhibitory effects (Q. Chen & Mirman, 2012). Hence, it is likely that weak coactivation in earlier stages of processing (i.e., initial lexical access) facilitates the detection of tone alternation violation in the auditory target per se. Yet, later task-relevant stages of processing, which require an explicit and attentive mapping between the primed representation and the auditory target, may have led to stronger coactivation, which requires more cognitive resources to inhibit and restructure.

In contrast, Experiment 2 demonstrated a distinct set of the ERP patterns in the processing of Cantonese pinjam. In both underapplication and overapplication conditions, violations elicited an N400 response were comparable to the plain violation control. This N400 effect is consistent with the Single SR account, suggesting both overapplications and underapplications of pinjam were processed no differently than across-tone category plain violations.

The N400-only results suggest that the ill-formed *cTL+cT1 sequence in the overapplication condition was deemed the same as across-tone category plain violations; what seems surprising is that the N400 in the underapplication condition indicates lexical mismatch even though the citation cTL form appears in the underapplication violation (i.e., *cTL+cTL).

Traditionally, pinjam has indeed been analyzed in the theoretical literature as a morpho-phonological process that attaches a high tone target to the low tone citation form cT4 (Kam, 1977; M. Yip, 2002). The analysis was believed to reflect an ongoing sound change that involves the morphologization of a fossilized tone sandhi process in Cantonese (Yu, 2007). However, as mentioned in the introduction, lexical items that undergo pinjam are limited. Beyond those lexical items, Low+Low tone sequences are not phonologically ill-formed. Importantly, the productivity of pinjam is questionable, while the relationship between the pinjam form and its alleged base is not always apparent to native speakers (Kam, 1977; Yu, 2007), casting doubt on the analysis of pinjam as an active morphological process that is grammatical in nature. Therefore, one possibility is that, at least for the specific surname+honorific compounds tested in the current study, the disyllabic pinjam forms are lexicalized as cTR+cTL disyllabic sequences and directly stored in the lexicon without further abstracting from the SR. Lexicalization refers to a process of language change that fossilizes alternation patterns originally derived by phonological processes directly into the lexical representations (Brinton & Traugott, 2005). In the process of sound change, morphologization and lexicalization reflect different stages of “dephonologization” of phonological alternations that cause morphophonological processes to cease to be part of the productive phonological system (Bostoen, 2008). Perhaps with the limited lexical distribution of pinjam, through time, certain pinjam lexical items once morphological in nature further undergo lexicalization where the whole pinjam process is degrammaticalized. Specifically, instead of a /cTL/+/cTL/ disyllabic sequence, our lexical items that seemingly undergo pinjam from their “citation forms” are in fact lexicalized, such that the mental representation takes the form of [cTR+cTL], without undergoing any phonological processes that alter the surface tone. Therefore, any violations to this lexicalized form (e.g., the cTL+cTL sequence in the underapplication condition) are processed no differently than plain violations in terms of lexical access as indexed by N400. Meanwhile, the lexical base forms of the surnames are stored in separate phonological representations as cTL, hence a comparable N400 effect in the overapplication condition in a non-pinjam cT4+cT4 sequence.

Whereas the current study only focuses on a very specific class of lexical items with pinjam for cross-linguistic matching of surface tone patterns, future studies can utilize a similar experimental approach to examine the neural processing of different lexical classes of pinjam. For example, a cross-sectional investigation across different age groups may provide an insightful model to assess the potential diffusion of lexicalization of pinjam in contemporary Cantonese, and how such potential degrammaticalization of pinjam may be tied to productivity of pinjam as an active grammatical process.

To further understand how other patterns of phonological alternation in the typology are represented, and how specific structures of phonological representations may reflect stages of sound change, further studies can also examine the neural processing of tone alternation in languages like Southern Min where the connection between the alternating tones is clear and recognized by speakers (unlike pinjam), but the alternation itself is not productive (unlike Mandarin tone sandhi) (e.g., Chien et al., 2017; Zhang et al., 2011).3 Another question is how alternations of sounds of different nature (e.g., segments and tones) dynamically interact to shape the phonological representation neurocognitively.

While the current study on the neural processing of phonological alternation invites various further topics of inquiry, the current cross-linguistic results provide strong support for the notion that phonological representations postulated in linguistic theory are not only formal entities for linguistic analysis, but are neurocognitive in nature, active in modulating phonological processing, speech production, and lexical access. Specifically, our distinct cross-linguistic ERP patterns identified in a set of surface-similar, but distributionally distinct phonological alternation phenomena highlight that phonological representations with different structures and levels of abstractedness (listed allomorphy versus lexicalized SR) may manifest into distinct neurocognitive processes during speech processing.

Several potential limitations should be considered and addressed in future work. To maintain maximal experimental control at the phonological level, our stimuli carried surname+honorific combination which carry little semantic meaning. It is unclear how the form of phonological representations may interact with lexical factors such as meaning and lexical frequency. Future experiments utilizing a larger variety of stimuli in different languages discourses may strengthen the understanding of the multiform nature of phonological representations.

Another potential limitation lies in the specificity of the cross-modal priming paradigm in specifically tapping abstract phonological representations (e.g., the UR) versus more concrete surface representations and acoustic factors. Prior studies (Friedrich et al., 2008; Lahiri & Reetz, 2010) have suggested that an abstract level of representation corresponding to the UR is tapped in priming paradigms, especially considering the later timescale of processing (>400 ms) where higher-level lexical-access is hypothesized to take place (E. F. Lau et al., 2008), while the extraction of lower-level phonological features takes place as early as 100 ms as reflected in the N100 component (Meng, Kotzor, et al., 2021; Obleser et al., 2004). However, it remains unclear the extent to which SR-level representations are tapped in the N400 time range in addition to the more abstract UR level, considering recent evidence suggesting both UR and SR are encoded at different stages of tone sandhi word production (X. Chen et al., 2022). Indeed, the experimental results of both of our studies implicate that both types of tone alternation are subserved by different organizations of concrete representations (listed allomorphy and lexicalization), but not the most abstract Single UR account (although importantly, results suggest that listed URs in Mandarin T3 Sandhi are more abstract than Single SRs in Cantonese pinjam). Future studies where more stringent acoustic control can be implemented (e.g., with synthesized stimuli) and with alternation patterns that may be represented by very abstract Single URs (e.g., Turkish final devoicing (Inkelas, 1995; Kager, 2008)) may better tease these factors apart.

The behavioral responses were also puzzling, with specific patterns not predicted from any of the competing hypotheses. The behavioral results were also incompatible with the ERP results, considering there was a lack of ERP differences across conditions in Experiment 2 despite behavioral differences. One potential explanation was that compared to ERP, the abstract phonological representations were tapped to a lesser extent in behavioral manifestations of priming, reflecting levels of downstream processing that were not tapped by the N400 and LPC components. As such, as compared to ERP components which are more specifically tied to lexical and phonological processes, behavioral responses are interlaced with factors beyond phonological representations, e.g., meaning and lexical frequency. Alternatively, this may reflect the two types of tone alternation patterns being processed differentially at the neural level to arrive at a similar behavioral pattern (i.e., priming effect) cross-linguistically.

Another possibility is that the ERP differences in Experiment 2 may be potentially minute, and therefore not detectable statistically given our sample size. Indeed, our ERP analysis was implemented with a jackknife approach to reduce potential Type I and II errors, which may have limited the sensitivity of our statistical approach. Future, larger-scale studies with a more comprehensive set of stimuli, a larger number of trials, and a larger participant sample may be able to better tease apart the relationship between behavioral and ERP responses in the cross-modal priming paradigm more conclusively.

From a methodological perspective, the inconsistent results may further suggest that different experimental methods and paradigms may tap into different levels of phonological representations. Indeed, laboratory phonology studies examining the UR structure of Mandarin tone sandhi comprise a large variety of methodologies across modalities, targeting speech perception (Chien et al., 2016; J. C. Lau et al., 2019; Li & Chen, 2015; Politzer-Ahles et al., 2016; Zeng et al., 2021) versus production (X. Chen et al., 2022; Zhang & Lai, 2010; Zhang et al., 2022), at neural (X. Chen et al., 2022; J. C. Lau et al., 2019; Li & Chen, 2015; Politzer-Ahles et al., 2016; Zeng et al., 2021; Zhang et al., 2022) versus behavioral levels (Y. Chen et al., 2011; Chien et al., 2016; Meng, Wynne, & Lahiri, 2021; Zhang & Lai, 2010), and at single-syllables (J. C. Lau et al., 2019; Li & Chen, 2015; Politzer-Ahles et al., 2016) versus larger linguistic constituents (X. Chen et al., 2022; Y. Chen et al., 2011; Chien et al., 2016; Meng, Wynne, & Lahiri, 2021; Nixon et al., 2015; Zeng et al., 2021; Zhang et al., 2022). Therefore, experimental methods, especially to the extent that they provide time-sensitive information on lexical access and production processing, may determine what level of representations are relevant. Indeed, phonological representations modulate speech and language processing tasks widely across system levels of the brain (Hickok & Poeppel, 2007). Phonological representations are tapped into by neurophysiological pathways that subserve speech and language functions across modalities (Hickok, 2012). For example, phonological representations impact speech processing as fundamentally as by actively modulating sensory encoding of auditory signals at the subcortical auditory system (J. C. Lau et al., 2019), through interactive effects between neuronal adaptation mechanisms and top-down predictive tuning through the corticofugal pathway (J. C. Lau et al., 2017). One possibility is that neural pathways across system levels and modalities may invoke different levels of the multiform phonological representations (Pierrehumbert, 2016) during speech- and language-related processing. Future experiments should consider employing a multimethod approach performed on the same cohort of participants and the same set of stimuli, not only to unify the mixed results in lexical tone alternation, but also to provide methodological insight into how different levels of the phonological representation can be more precisely tapped in laboratory phonology inquiries.

Another limitation is this study’s assumption that the phonologies of individuals speaking the same language are uniform. However, an abundance of experimental evidence on individual differences in speech sound processing (e.g., Bones & Wong, 2017; Deng et al., 2018; Maggu et al., 2021; Maggu et al., 2018) implies that phonological representations and grammars may differ even among individuals speaking the same language. Although the current study employs a within-subject design where individual differences are not a confounder, the extent to which individual differences at processing, representational, and grammatical levels may have impacted our experimental results are not clear. Individual differences in speech sound representations and processing are critical as metrics of learning (Antoniou & Wong, 2015; Ingvalson et al., 2013; Wong et al., 2017) and indices of clinical phenotypes (J. C. Lau et al., 2021, 2022; Liu et al., 2014), with implications to the genetic bases of language (Wong et al., 2012, 2017, 2020). The issue of individual differences in phonological representations and grammars in formal phonological theory should therefore be more directly addressed in future studies.

In summary, the present study identified different ERP patterns in the neural processing of a lexical tone alternation similar on the surface in two languages, but with crucial differences in lexico-phonological distribution across languages. We interpret the cross-linguistic patterns as indicative of the multiform nature of phonological representations that can be shaped with different levels of abstractedness, by taking into account factors including lexical and phonological distributions. By showing neurocognitive evidence for a multiform architecture of phonological representations, the results invite further theoretical and empirical investigations to further advance the current understandings of the role of phonological derivation in language production, and the acquisition of the multiform nature of phonological representations.