United States

The rise of online platforms has facilitated covert forms of explicit content, which pose significant challenges for detection and regulation. Often using coded language to bypass moderation, this content erodes user trust and may be associated with scam-related risks, posing direct financial and personal risks. In this study, we map the landscape of online explicit content posts, focusing on their categorization, linguistic strategies, and temporal and behavioral patterns as they appear within mainstream platform reddit. We investigated five distinct content categories including Virtual Services (VS), Physical Services (PS), Exhibitionism (Ex), Couples and Group Interactions (CGI), and Content Creation and Sales (CCS) and performedmed large-scale experimentation using state-of-the-art large language models (LLMs) such as GPT-4, LLaMA 3.3-70B-Instruct, Gemini 1.5 Flash, Mistral 8×7B, Qwen 2.5 Turbo, and Claude 3.5 Haiku. Our work demonstrates that a nuanced classification of these services requires moving beyond simple keywords, and we establish that expressive signals such as sentiment, emotion, and tone are critical features for accurate detection. Our analysis reveals the distinct behavioral and psychosocial expression patterns that characterize each service category, providing a robust framework for future moderation.

ACL 2026

Mapping the Landscape of Unregulated eXplicit Contents on Reddit

llm analysis

nsfw

data mining

reddit

computational social science

It is my great pleasure and honor to welcome you to the 64th Annual Meeting of the Association for Computational Linguistics (ACL 2026), held in San Diego, California, USA, July 2–7, 2026. ACL 2026 continues our fields tradition of excellence in scholarship, innovation, and inclusivity, and I am deeply grateful to the many volunteers who have worked tirelessly to bring this event to life.

It is exciting to see the many developments in the field reflected at our conference, such as the advancement of large language models (born out of our community) into many application directions. This is not without challenges, partly due to unsolved problems, and partly due to misuse of the technology. All this is reflected well at ACL 2026. The conference also reflects that the field is not only about advancing technology, but also the science of fundamentally understanding language and how it is use by many different speaker communities. <br>
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The 64th Annual Meeting of the Association for Computational Linguistics (ACL 2026) will take place in San Diego, California, from July 2 - 7, 2026.

workshop paper

This paper offers a new perspective on the computational complexity of reduplication. Since one-way deterministic transducers cannot model reduplication in a straightforward way, the phenomenon has long been considered the outlier of morphology from a complexity perspective. Drawing on algebraic methods, I show that the vast majority of reduplicative processes belong to a few remarkably simple
classes of subregular functions. A detailed study of the RedTyp database (Dolatian and Heinz, 2019) reveals that 100% of the
surveyed reduplicative processes correspond to string-to-string functions in the class DA, while over 98% are locally testable (LJ1 ) and over
87% are locally trivial (L1). These results indicate a new upper bound on the complexity of reduplication that is comparable to that of morphological processes in general.

Algebraic Classification of Reduplicative Processes

Cue-based interference theory predicts that distractors similar in syntax or semantics can disrupt retrieval. Predictors derived from attention weights in selective heads or aggregated across layers remain opaque to support clear mechanistic interpretations. We propose a transparent, factorized alternative that models retrieval as an asymmetric linear transformation from a cue space to a target space along syntactic and semantic dimensions. On the materials manipulating syntactic similarity and semantic plausibility, the two submodels yield independent interference signals. The results demonstrate that a simple linear combination of these signals reproduces the graded interference pattern in the experimental design while providing a clearer and more mechanistically interpretable account of cue-based retrieval than attention-based predictors from large neural models.

A Transparent Model of Syntactic and Semantic Cue-based Retrieval

Naturalistic language comprehension often involves interpretations that go beyond literal meaning. In continuous narratives, literal and non-literal meanings are tightly intertwined, making them difficult to distinguish computationally. Here, we introduce a framework that separates literal sentence representations from human-annotated non-literal interpretations for model-brain alignment. Using fMRI data recorded during passive listening to the Chinese version of The Little Prince, we annotated sentences containing non-literal meaning with human-written interpretations of their implied meaning. We derived sentence representations from LLaMA3.1-8B and evaluated their correspondence with neural activity using whole-brain encoding models. Literal representations aligned strongly with left-lateralized frontotemporal regions, whereas non-literal interpretations showed broader right-hemisphere involvement. Combining the two further improved the performance of the encoding in the bilateral temporal and dorsal frontal cortices, suggesting that naturalistic comprehension engages complementary levels of meaning.

Non-literal Meaning Representation in the Brain during Naturalistic Listening

This paper investigates whether tonotactic learning differs across representations and learning models. We conduct an experiment using the same dataset encoded in three representations: segments, features, and autosegmental representations (ARs). To the extent possible, two learning models are evaluated, the Maximum Entropy (MaxEnt) model and the Bottom-Up Factor Inference Algorithm (BUFIA), to examine how learning outcomes interact with both model type and representations. A follow-up experiment further explores the roles of frequency and complexity thresholds. The results show that (1) AR-based learning gives the strongest overall performance; (2) there is no consistent advantage between segmental and featural representations across learning models; (3) MaxEnt performance improves substantially when frequency information is introduced and lastly (4) the effects of complexity bounds interact with representation type and frequency information. These findings suggest that tonotactic learning benefits from structurally explicit representations. Overall this work highlights the importance of using linguistically meaningful representations into learning.

What Matters in Tonotactic Learning

Korean stem-final conjugations illustrate the interaction between lexical exceptionality and heterogeneous phonological processes. When /p/-, /t/-, and /s/-final stems occur before vowel-initial suffixes, the irregular classes in these paradigms undergo intervocalic lenition, each adopting a distinct alternation strategy. This study explores how learners acquire lexically-specific phonological patterns given multiple possible solutions. Specifically, it employs a lexically scaled MaxEnt model \citep{hughto2019learning,linzen2013lexical} to learn these paradigm-specific alternations. We run simulations under two learning scenarios: (1) when repair strategies occur at equal frequencies and (2) when one strategy significantly outnumbers the others. Results show that the model favors a \emph{least-cost} solution by treating statistically dominant classes of morphemes as the general pattern. We conclude by discussing the model's sensitivity to lexical statistics, predictions for empirical testing, as well as its implications and challenges for language acquisition.

Lexical exceptionality in paradigm-specific learning: modeling stem-final obstruent alternations in Korean verbs and adjectives

A question for computational linguistics has been to what degree do language models encode case information. However, the majority of the work has focused on structural cases (cases which change when the syntactic configuration changes). On the other hand, inherent cases (which are assigned by specific lexical items and do not change if the syntactic configuration changes) have not been investigated. This paper sets out to investigate if German language models distinctly encode inherent dative from structural accusative and nominative. We conducted a linguistic probing investigation where probes are trained on contextual word embeddings of active nominative, accusative, and dative arguments to predict if passivised datives are analysed as a structural nominative. We provide a cased and caseless version of the experiment. Our results suggest that when case information is removed language models can distinguish between inherent dative and structural accusative, regardless of argument position, due to verb information. However, language models cannot distinguish between structural nominative and inherent dative when the dative appears in a position where there is an expected nominative, due to over-relying on surface patterns.

An LLM Investigation into Inherent and Structural Case Representation: a German Case Study

Context-dependent morphophonological rules -- consonant gradation, vowel harmony, possessive suffix assimilation -- lack a compositional formalization: cascades of finite-state transducers (FSTs) require multiplicative state explosion to encode rule interactions, and neural models provide no formal account of the underlying processes. We formalize these rules as coKleisli arrows of the Writer comonad (DeletionSet x Zipper), where extend lifts a local rule to a global transformation and coKleisli composition chains rules with strict associativity. This resolves length-changing operations -- notably consonant deletion -- algebraically, restoring compositionality that FST cascades sacrifice. Thirteen coKleisli arrows replace 874 FST continuation classes at the morphophonological rule level (67:1 reduction via orthogonal composition), and the same abstraction unifies character-level, morpheme-level, and sentence-level processing. Evaluated on Universal Dependencies (UD) Finnish-TDT, the system achieves 83.92% universal part-of-speech (UPOS) accuracy with rule-only disambiguation (94.66% with a lightweight suffix tagger), and the coKleisli pipeline enables bidirectional morphology -- a MorphGenerator reuses the same arrows for generation.

Comonadic Morphophonology: A Compositional Framework for Context-Dependent Morphological Rules in Finnish

Models of morphophonological learning have focused primarily on concatenative processes, leaving the challenges of non-concatenative morphology largely unaddressed. Reduplication, the systematic copying operation (e.g., Ilokano pluralization [kal-kald\'IN}] `goats'), is particularly revealing because successful learning requires the joint inference of prosodic templates that govern copying, underlying representations (URs) of stems and other affixes, and the phonological grammar. In this paper, we present a learner that tackles this challenge by allowing reduplication to be learned alongside general morphophonemic alternations, a combination that, to our knowledge, has not been directly modeled in prior computational work. We show that the learner successfully captures the attested typology of reduplication–phonology interaction.

Learning reduplicative templates as hidden structures: the case of reduplication-phonology interactions

This paper investigates the learnability of interacting phonological processes by restricting the hypothesis space to a subregular class of functions. Interacting processes can be modeled as function composition, where the output of one function serves as the input to another. We focus specifically on interactions between two simplex Input Strictly Local (ISL$_2$) functions, a proper subclass of the ISL function class. We propose a decomposition algorithm that reconstructs both the individual component processes and their relative ordering by exploiting structural properties of simplex ISL$_2$ transducers and their compositions. This work provides an initial step toward understanding how learners can infer not only single phonological processes, but structured interactions between processes.

Learning Process Interaction Through Simplex ISL Transducers

Few studies have examined how large language models (LLMs) handle negative polarity items (NPIs) in languages other than English. This study investigates NPI licensing in Korean, an under-explored language that is subject to a well established syntactic constraint. Compared to human judgments, Korean-trained models exhibit clear difficulties in detecting this requirement, underscoring a persistent gap between human and model performance on syntax-sensitive phenomena. The consistently poor performance of all three GPT language models examined suggests that the syntactic properties of NPI licensing are not adequately captured. This study thus contributes to the growing literature on linguistic dependencies in language models, while extending evaluation to underrepresented languages. (We will be able to present our work in person.)

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