The research, conducted by Assistant Professor Shingo Nahatame of the Institute of Human Sciences at the University of Tsukuba and Associate Professor Tomoko Ogiso of the Faculty of Education at the University of Toyama, was published in the journal Reading & Writing. The study set out to address a central concern in English language education: how to evaluate the difficulty of the texts used in educational materials and language assessments. Traditionally, researchers have relied on objective measures of text difficulty grounded in linguistic features, including characteristics of words and sentences. Yet learners can differ substantially in how difficult they perceive the very same text to be, and understanding that gap matters for anyone who selects, writes, or assesses reading material.

To examine the relationship between objective and subjective text difficulty, the researchers designed a study with two complementary strands. First, they evaluated the objective difficulty of 30 English reading passages spanning a broad range of difficulty levels. Objective difficulty was assessed in two ways: using established readability measures based on linguistic characteristics, and using an evaluation method based on a large language model, reflecting the growing role of artificial intelligence tools in text analysis. This dual approach allowed the team to compare how well both traditional formula-based indices and modern computational methods captured the demands each passage placed on readers.

The second strand of the study turned to the readers themselves. Forty-one undergraduate and graduate students whose first language was Japanese read the same 30 passages and rated the difficulty of each one on a nine-point scale. These ratings provided a direct window into subjective difficulty—the felt experience of struggling with, or sailing through, a text. Because all participants read all passages, the design made it possible to compare, passage by passage and reader by reader, how objective estimates lined up with personal perceptions.

The analyses revealed a strong relationship between objective and subjective difficulty. Passages rated as more difficult by objective measures were also perceived as more difficult by readers. In other words, the traditional intuition behind readability formulas holds up: texts with longer sentences, rarer words, and more complex linguistic characteristics genuinely do feel harder to read, at least on average. The large language model–based evaluation method, likewise, produced difficulty estimates that corresponded with readers’ perceptions, suggesting that computational approaches can serve as viable complements to conventional readability indices.

But the study did not stop at ratings. The researchers also recorded participants’ eye movements as they read, adding a process-level measure of reading behavior to the product-level measures of text features and subjective judgments. Eye-tracking has long been used in reading research because the eyes provide a moment-by-moment record of cognitive effort: fixations lengthen when processing is demanding, and readers skip words that are easy to identify. In this study, objective and subjective difficulty measures were both associated with eye-movement patterns during reading. More difficult texts tended to be read more slowly, and readers skipped fewer words when reading them. The convergence is striking: three independent sources of evidence—linguistic formulas, learner judgments, and real-time gaze behavior—all pointed in the same direction.

The most novel finding, however, concerned the discrepancy between the two kinds of difficulty. The researchers found that the extent to which an individual reader’s rating differed from the group’s average rating for the same passage provided additional information for explaining eye-movement behavior beyond what could be accounted for by text-level difficulty measures alone. In practical terms, if a particular student found a passage harder than their peers did, that deviation was reflected in the way their eyes moved through the text, even after the general difficulty of the passage had been taken into account. Subjective difficulty, in other words, is not simply a noisy version of objective difficulty—it carries unique, reader-specific signal.

These findings indicate that objective measures of text difficulty and subjective perceptions of learners generally correspond closely but are not identical. Objective measures are useful for characterizing the general difficulty of a text, and they remain an efficient tool for grading passages, leveling curricula, and calibrating assessments across large populations. But subjective evaluations provide additional insight into how individual learners experience and process the same text. A readability score describes the passage; a learner’s rating describes the encounter between the passage and a particular mind. The study suggests that both perspectives are needed to build a complete picture of reading difficulty.

The implications reach into several corners of language education. For teachers and materials developers, the results support a two-step approach: objective measures can be used to shortlist texts at an appropriate general level, while learner feedback can then be used to fine-tune selections for specific students or classes. For researchers, the demonstration that rating deviations predict eye-movement behavior opens the door to more personalized models of second-language reading, in which individual differences in perception are treated as meaningful data rather than measurement error. The work also speaks to the growing interest in using large language models for text evaluation, showing that such tools can align with human perceptions while still leaving room for individual variability.

More broadly, the study is a reminder that difficulty is not a property of a text alone, nor of a reader alone, but of the interaction between them. The 30 passages, 41 readers, nine-point ratings, and recorded eye movements together paint a technically grounded picture of that interaction: strong average correspondence between formulas and feelings, reliable links between both and the microstructure of gaze, and a persistent, informative residue of individual difference. As English language education moves toward more personalized approaches to reading support, the message from Tsukuba and Toyama is clear—measure the text, but also listen to the reader, because the two are related, yet not the same.

Subject of Research: The relationship between objective and subjective text difficulty in second-language English reading and its link to eye-movement behavior

Article Title: Subjective and objective difficulty of English texts are related—but not the same

Article References: Subjective and objective difficulty of English texts are related—but not the same. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: text difficulty, readability, second-language reading, eye-tracking, English language education, large language models, reading assessment, subjective perception, University of Tsukuba, Reading & Writing, L2 learners, reading materials

MROH1, also known as HEATR7A, first drew attention from work on the humble roundworm Caenorhabditis elegans. Researchers had identified the worm protein HPO-27, a HEAT repeat protein, as a critical mediator of lysosomal membrane scission. When HPO-27 is lost, the worm’s tissues fill up with aberrant tubular lysosomal networks instead of the usual discrete vesicles. The mammalian homologue MROH1 was subsequently shown to interact with the WASH–actin machinery to regulate lysosomal fission, positioning it as a gatekeeper of lysosomal integrity. What remained entirely unknown was whether this housekeeping role had any physiological relevance for hormone-producing tissues, and no prior study had ever connected MROH1 to thyroid biology.

A crucial clue came from human gene expression databases. Transcriptomic profiling across the GTEx portal and the Human Protein Atlas classifies MROH1 as markedly tissue-enhanced in the thyroid gland relative to other organs—striking preferential expression for a core component of the lysosomal fission machinery. That observation prompted the Tsukuba team, led by Nami Ohuchi and Yoshinori Osaki under the supervision of Hitoshi Shimano, to generate a global MROH1 knockout mouse line. Sperm carrying the Mroh1(tm1a(KOMP)Wtsi) allele were obtained from the European Mouse Mutant Archive, floxed mice were created by Flpe-mediated excision of the gene trap cassette, and ubiquitous deletion of exons 5 through 7 was achieved by crossing with Ayu1-Cre transgenic mice. Cre-negative floxed littermates served as wild-type controls throughout.

The knockout strategy worked as designed: quantitative RT-PCR confirmed the complete absence of Mroh1 transcripts in the thyroids of the deficient animals. To address possible genetic compensation, the team also measured Mroh2a, a close paralog of Mroh1, and found only a non-significant upward trend in its expression. Metabolic phenotyping then produced a subtle but revealing picture. Food intake and body length were unchanged between genotypes, but the knockout mice gained weight gradually, reaching a statistically significant difference by 24 weeks of age. The weight gain occurred independently of altered skeletal growth, suggesting systemic metabolic adaptations rather than a primary effect on development.

The endocrine phenotype emerged clearly when the researchers measured serum hormones. Free thyroxine (FT4) was significantly reduced in knockout mice at both 3 and 6 months of age, while free triiodothyronine (FT3) was significantly lower by 6 months. Serum TSH showed only a non-significant increasing trend—a puzzling feature the authors openly acknowledge, since standard rodent thyroid economy would predict a compensatory TSH rise when circulating hormones fall. Whether the discrepancy reflects altered central feedback, differences in hormone metabolism, or transport effects remains unresolved and will require functional assessment of the hypothalamic–pituitary axis in future work.

Consistent with the well-known clinical association between hypothyroidism and dyslipidemia, total serum cholesterol was comparable at 3 months but significantly elevated in the knockout animals by 6 months, while triglycerides remained unchanged. Importantly, markers of liver and kidney function, blood glucose, and creatine kinase levels were all unremarkable, and histological examination of the lung, brain, liver, and skeletal muscle revealed no overt abnormalities. The thyroid, in other words, stood out as the principal site of pathological consequence—an outcome that mirrors MROH1’s preferential expression in that gland and strengthens the causal narrative.

To understand the structural basis of the hormone deficit, the team turned to histology. At 3 months of age, thyroid morphology in the knockout mice looked essentially normal. By 6 months, however, the gland showed clear architectural remodelling: follicular area was reduced, and follicles were progressively replaced by interstitial cells and adipocyte-like structures. Quantification of the follicle area ratio showed a downward trend that narrowly missed statistical significance, but a more sensitive analysis of individual follicles—over 1,700 follicles measured across both groups—revealed a statistically significant shift towards smaller follicle sizes in the knockout mice (p = 0.0095, Kolmogorov–Smirnov test). The gland, in effect, was quietly remodelling itself at the cellular level long before gross pathology would appear.

Molecular profiling pointed to the transcriptional roots of the defect. Expression of Nkx2-1 and Foxe1, the master regulators of thyroid differentiation, was significantly reduced in the knockout thyroids, with Pax8 and Hhex trending in the same direction. Concurrently, thyroglobulin—the essential precursor of thyroid hormone synthesis—was significantly downregulated, as was Slc16a2 (Mct8), the thyroid hormone transporter. Other genes involved in hormone production, including Tshr, Slc5a5 (Nis), and Slc26a7, showed decreasing trends. This coordinated loss of lineage-defining transcription factors and their functional target genes suggests that MROH1 is required for the long-term maintenance of follicular cell identity and differentiated function, not merely for organelle housekeeping.

What the study did not find is equally telling. Given MROH1’s established role in lysosomal fission and the dependence of hormone release on lysosomal proteolysis, the team fully expected to find impaired lysosomal function. Instead, immunoblotting showed that protein levels of LAMP2, cathepsin L, and cathepsin D were unchanged, and two independent assays—a live-cell fluorogenic substrate assay in primary thyroid cells and an enzymatic activity assay in whole-tissue lysates—revealed no significant difference in cathepsin L activity. The fundamental capacity for lysosomal degradation appeared intact. The authors caution that bulk assays may simply be too blunt to detect localized defects in lysosomal membrane trafficking, and that subtle, progressive endo-lysosomal trafficking failures could still accumulate over time, as seen in the delayed thyroid pathology of lysosomal storage disease models such as cystinosis.

The broader significance is twofold. First, the work establishes MROH1 as a genetic factor for thyroid hormone homeostasis in vivo, with a phenotype distinct from the profound hypothyroidism and goitre seen in complete MCT8 or thyroglobulin knockouts—the partial downregulation of thyroid genes produces a milder, late-onset endocrine defect without gland enlargement. Second, it extends the emerging view that lysosomal membrane dynamics are not merely cellular plumbing but active participants in tissue-level physiology, with the caveat that the precise mechanistic bridge from MROH1 deficiency to transcriptional downregulation remains to be charted. Because the mice carry a congenital deletion yet show a late-onset phenotype, extrathyroidal contributions cannot be excluded. Tissue-specific knockout models, currently the next step for the Tsukuba group, should disentangle the global versus thyroid-specific roles of MROH1—and may ultimately clarify whether subtle lysosomal trafficking defects in humans contribute to mild hypothyroidism, thyroid remodelling, and the cardiovascular risk that follows from unexplained hypercholesterolemia.

Subject of Research: The role of the HEAT repeat protein MROH1 in lysosomal fission and thyroid hormone homeostasis in mice

Article Title: The HEAT Repeat Protein MROH1 Deficiency Leads to Reduced Circulating Thyroid Hormone Levels in Mice

Article References: Ohuchi, N., Osaki, Y., Nakagawa, Y., Miyamoto, T., Araki, M., Mizunoe, Y., Matsuda, T., Murayama, Y., Sugano, Y., Iwasaki, H., Matsuzaka, T., Sekiya, M., & Shimano, H. (2026). The HEAT Repeat Protein MROH1 Deficiency Leads to Reduced Circulating Thyroid Hormone Levels in Mice. Endocrinology, Diabetes & Metabolism, 9(5), Article e70348. https://doi.org/10.1002/edm2.70348

Image Credits: AI Generated

DOI: 10.1002/edm2.70348

Keywords: MROH1, thyroid hormone, lysosomal fission, hypothyroidism, hypercholesterolemia, knockout mice, Nkx2-1, Foxe1, thyroglobulin, cathepsin L, endocrine physiology, University of Tsukuba