Author: Denis Avetisyan
New research reveals how the intrinsic dimensionality of language can offer a deeper understanding of text complexity, going beyond traditional predictive metrics.

This review explores intrinsic dimension as a geometric property of text, analyzing its applications in representation learning and distinguishing characteristics across diverse genres.
While large language models excel at predicting text, understanding the geometric complexity underlying different writing styles remains a challenge. This is addressed in ‘Unveiling Intrinsic Dimension of Texts: from Academic Abstract to Creative Story’, a study demonstrating that intrinsic dimension (ID)-a measure of representational freedom-complements traditional prediction-based metrics and reveals distinct characteristics across genres. Specifically, the research shows scientific prose exhibits lower ID than creative writing, suggesting contemporary models find representing factual content comparatively simpler. Could these findings inform strategies for optimizing model architectures and improving the nuanced understanding of diverse textual data?
Beyond Word Count: The Futility of Simple Text Complexity Measures
The long-held practice of gauging textual complexity through simple word counts or sentence lengths proves remarkably inadequate when confronting the subtleties of language. While easily quantifiable, these metrics fail to discern the cognitive demands a text truly places on a reader; a short sentence employing rare vocabulary and complex syntactic structures can be far more challenging than a lengthy, grammatically simple passage. Indeed, texts of equivalent word counts can vary drastically in their conceptual density and the inferences required for comprehension. This limitation stems from an inability to account for the diversity of linguistic features – such as the frequency of uncommon words, the depth of syntactic embedding, and the use of figurative language – all of which contribute significantly to a text’s overall difficulty and, crucially, remain invisible to basic statistical analyses. Consequently, relying solely on these traditional metrics provides a misleadingly simplistic view of textual complexity, hindering accurate comparisons and potentially misrepresenting a text’s true cognitive load.
Truly gauging how challenging a text is demands more than simply counting words; it necessitates a detailed examination of its linguistic characteristics. A comprehensive analysis moves beyond lexical features-like word frequency and rarity-to include syntactic complexity, encompassing sentence length, grammatical structures, and the use of passive voice. Furthermore, textual structure plays a vital role, considering elements such as cohesion, transitions between ideas, and the overall organization of information. Assessing this diversity of features – vocabulary, syntax, and structure – allows for a more nuanced understanding of textual complexity, moving beyond superficial measures to capture the cognitive demands placed upon a reader and ultimately providing a more accurate benchmark for readability and comprehension.
The prevailing methods for gauging textual complexity often fall short due to an inability to effectively quantify the multifaceted linguistic features that truly define it. While tools might assess surface-level characteristics like sentence length or word frequency, they struggle to capture the subtle interplay of syntax, the richness of vocabulary beyond simple counts, and the structural organization that contributes to a text’s difficulty. This limitation poses a significant challenge for researchers aiming to compare texts accurately, particularly when evaluating materials for educational purposes or assessing reading comprehension levels. Consequently, interpretations of textual difficulty can be subjective and inconsistent, hindering reliable analysis and potentially misrepresenting a text’s cognitive demands. Developing more nuanced quantification methods remains a crucial area of study, requiring computational linguistics to move beyond easily measured variables and embrace the intricate dimensions of language itself.

Intrinsic Dimension: A Geometric View of Textual Complexity
Intrinsic Dimension (ID) offers a geometric approach to quantifying text complexity by representing text as points in a high-dimensional embedding space. This space is created through the use of large language models, and the ID corresponds to the number of independent directions needed to represent the data within that space. Essentially, ID measures the degrees of freedom required to capture the underlying structure of a text; a higher ID suggests the text occupies a more complex region of the embedding space, requiring more dimensions to accurately represent it, while a lower ID indicates a more constrained and simpler structure. This geometric perspective allows for a quantifiable assessment of complexity beyond traditional metrics like word count or sentence length.
Intrinsic Dimension (ID) is computed by first generating text embeddings using large language models, specifically Gemma, Qwen, and RoBERTa. These models transform text into high-dimensional vector representations, where each dimension captures a semantic or syntactic feature of the text. The resulting embedding space allows for the quantification of text complexity; the ID reflects the number of dimensions necessary to represent the text without significant information loss. These embeddings effectively capture the underlying structure of the text by mapping similar texts to nearby points in the vector space, and dissimilar texts to more distant points. The ID is then estimated from these embeddings using techniques such as Principal Neighborhoods, Maximum Likelihood Estimation, and Two Nearest Neighbors.
Higher intrinsic dimension (ID) values correlate with increased textual complexity, as evidenced by richer vocabulary, more varied syntactic structures, and a more nuanced expression of concepts. Analysis demonstrates a strong consistency in ID measurement across different estimators; specifically, pairwise correlation coefficients (r) exceeded 0.45 when comparing PHD, MLE, TLE, and TwoNN methods. This consistency suggests that ID provides a reliable geometric measure of text complexity regardless of the specific estimator employed, indicating the underlying dimension accurately reflects the structural properties of the text.
Intrinsic Dimension (ID) measurements exhibit increased reliability in texts exceeding 150 tokens. Below this length, the variance of ID calculations is demonstrably higher, indicating less stable and potentially inaccurate results. This phenomenon is attributed to the need for sufficient data points to accurately estimate the dimensionality of the text’s embedding space; shorter texts provide insufficient information for a stable geometric representation. Consequently, ID is most effectively utilized as a metric for assessing text complexity when applied to documents or passages containing at least 150 tokens, ensuring a more consistent and dependable measurement of underlying linguistic structure.

Correlation Does Not Equal Causation: ID and Linguistic Diversity Measures
Analysis reveals a statistically significant correlation between Intrinsic Dimension (ID) and established metrics of textual diversity, namely Type-Token Ratio (TTR) and Lexical Diversity. TTR, calculated as the number of unique words (types) divided by the total number of words (tokens), provides a measure of lexical richness. Similarly, Lexical Diversity, often assessed using metrics like Moving Average Type-Token Ratio (MATTR), quantifies the range of vocabulary employed in a text. Empirical results demonstrate that as ID increases, both TTR and Lexical Diversity scores also tend to increase, indicating that higher-dimensional representations correspond to texts with greater vocabulary variation. This suggests ID effectively captures aspects of textual complexity directly related to the breadth of vocabulary utilized.
Linear regression analysis was performed to quantify the relationship between Intrinsic Dimension (ID) and established metrics of lexical diversity-Type-Token Ratio (TTR) and Lexical Diversity. The resulting models demonstrate statistically significant predictive power, with ID accounting for a substantial proportion of the variance in both TTR ($R^2$ values exceeding 0.7 for both metrics in the tested corpora) and Lexical Diversity. This confirms that ID is not merely correlated with lexical diversity but actively captures and explains the variance within these measures, offering empirical validation for its use as a proxy for textual complexity and providing support for its theoretical basis. The models’ coefficients were also assessed for significance using standard t-tests, further reinforcing the reliability of the observed relationships.
Intrinsic Dimension (ID) demonstrates an ability to differentiate between texts exhibiting comparable lexical diversity, as measured by metrics like Type-Token Ratio, but possessing varying degrees of underlying linguistic complexity. This sensitivity stems from ID’s capacity to capture nuanced patterns in textual data beyond simple vocabulary counts; it effectively resolves ambiguity where traditional diversity scores fail to capture differences in semantic richness or the distribution of word usage. Analysis indicates ID can distinguish between texts with identical TTR values, revealing distinctions in how information is conveyed and the cognitive load associated with processing those texts, indicating its value as a more granular measure of textual characteristics.
Analysis reveals that Intrinsic Dimension (ID) demonstrates a notable correlation with lexical diversity metrics, but a significantly weaker correlation with measures of syntactic diversity. This suggests that ID primarily captures variations in vocabulary richness and semantic content, rather than the structural complexity of sentence construction. Specifically, texts differing primarily in word choice and the range of concepts expressed exhibit greater differentiation in ID scores than texts with similar vocabularies but differing sentence structures. This indicates that ID is a more sensitive indicator of lexical and semantic variation than of syntactic complexity.

Beyond Analysis: ID and the Detection of Sophisticated Deception
Intrinsic Dimension (ID), a measure of a text’s complexity, demonstrates a surprising sensitivity to the presence of homoglyphs – visually identical characters with differing underlying code. This characteristic opens new avenues for detecting sophisticated deception tactics employed in phishing schemes and disinformation campaigns. Subtle character substitutions, imperceptible to the human eye, create deviations in a text’s ID, signaling potential malicious intent. By analyzing these shifts in dimensionality, systems can flag compromised texts with greater precision than traditional methods relying on surface-level character comparison. This capability offers a powerful tool for bolstering cybersecurity, verifying content authenticity, and ultimately, reinforcing trust in digital communications by uncovering hidden manipulations within seemingly legitimate text.
The nuanced capability of Intrinsic Dimension (ID) extends beyond simple textual analysis to reveal even the most cleverly disguised manipulations. Subtle character substitutions – employing homoglyphs that visually mimic legitimate characters but utilize different underlying code – often evade traditional detection methods. However, these minute alterations induce measurable deviations in a text’s ID, providing a telltale signature of compromise. By quantifying these shifts, systems can proactively flag potentially malicious content – such as phishing attempts or disinformation – with significantly improved accuracy. This approach doesn’t rely on known bad patterns, but rather on the inherent structural integrity of language itself, offering a robust defense against evolving deceptive tactics and bolstering trust in digital communications.
The ability to detect subtle textual anomalies through Intrinsic Dimension (ID) analysis extends far beyond simple error correction, offering a powerful new tool in the ongoing battle against digital deception. This capability holds significant promise for bolstering cybersecurity protocols by identifying phishing attempts and malicious code hidden within seemingly legitimate text. Furthermore, content verification processes benefit from this technology, allowing for a more robust assessment of information authenticity and reducing the spread of disinformation. By establishing a greater degree of confidence in the integrity of digital communication, ID analysis ultimately serves to enhance trust in online interactions and safeguard against manipulation, fostering a more reliable information ecosystem.
Investigations into the behavior of large language models reveal a nuanced relationship between sampling temperature and Perplexity of Hidden Diffusion (PHD), a metric indicating the model’s sensitivity to subtle textual alterations. Specifically, the study demonstrates that different model architectures respond distinctively to temperature adjustments; Qwen-3-8B-base exhibited a sharp escalation in PHD values as the temperature increased from 0.2 to 0.8, suggesting heightened sensitivity to even minor input variations at warmer settings. In contrast, Qwen-3-8B-instruct displayed a more tempered response, with PHD increasing at a slower rate over the same temperature range. This discrepancy highlights the importance of considering model-specific characteristics when interpreting PHD results and tailoring security protocols to optimize deception detection capabilities.

The pursuit of quantifying text complexity, as this paper outlines with its exploration of intrinsic dimension, feels…familiar. It’s another layer of abstraction built atop layers of abstraction. They measure the ‘geometric measure’ of text, striving for elegance, but one suspects production data will happily ignore all these carefully calculated dimensions. As Grace Hopper observed, “It’s easier to ask forgiveness than it is to get permission.” This rings true; someone will inevitably shoehorn a complex model into a simple use case, ignore the warning signs of high intrinsic dimension, and then complain when it fails. The documentation will lie again, promising scalability and robustness. It used to be a simple bag-of-words model, and now it’s…this. They’ll call it AI and raise funding.
The Road Ahead
The exploration of intrinsic dimension as a proxy for text complexity offers a neatly defined metric, but one suspects the elegance will prove… fragile. It’s a common pattern: a beautiful geometric interpretation, followed by the inevitable discovery that real-world data rarely conforms to ideal manifolds. The current work demonstrates correlation, a promising start, yet production systems will undoubtedly reveal edge cases – texts that score deceptively low or high, and quickly expose the limits of any purely geometric assessment. It recalls earlier attempts at ‘universal sentence embeddings’; the theory was compelling, the initial results promising, and the practical implementation… complicated.
Future research will likely focus on hybrid approaches, combining intrinsic dimension with prediction-based metrics. This feels less like progress and more like acknowledging the inherent messiness of language. The question isn’t whether intrinsic dimension can capture complexity, but whether it can do so in a way that meaningfully improves performance over existing, simpler measures. It’s a good bet that any gains will be marginal, and quickly consumed by the ever-increasing demands of scale.
Ultimately, the true test will be whether this framework illuminates something fundamentally new about language, or simply offers a different way to quantify what was already known. One anticipates the latter. The pursuit of ‘intrinsic’ properties is often a search for a simpler truth, a search that frequently ends in rediscovering the original complexity, just with a new set of parameters.
Original article: https://arxiv.org/pdf/2511.15210.pdf
Contact the author: https://www.linkedin.com/in/avetisyan/
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2025-11-24 20:59