To unify,or not to unify,that is the question: A commentary on Taha et al. (2025)

Abstract

Advances in science are often achieved by bringing together seemingly disparate phenomena or observations within a single explanatory theoretical framework. Hence, it is laudable that Taha et al. venture to propose that a collection of seemingly disparate observations on dyslexia can be explained by a single factor: a deficiency in anticipatory planning. Their effort, as they themselves state, is intended to advance the science of dyslexia by inspiring new questions and new empirical approaches to address these. The question we ask here is if their argumentation is sufficiently robust to fulfil this promise.

A concise summary of Taha et al.’s (2025) proposal runs as follows: (oral) reading, spoken language production, language processing (comprehension) and handwriting all demand a type of anticipatory planning. The (neuro)cognitive processes involved control the apprehension or production of sequences of stimuli or actions. Anticipatory planning in this context entails that the cognitive system, while engaged with processing a percept or action at time t needs to (simultaneously) “look forward” to, and prepare for, what comes (or may come) at time t + x. Sequences of stimuli or actions (that unfold in time) have a rhythm, which is to say that their constituting elements, each of which have a particular duration, are grouped, just like musical notes (with different durations) are perceptually grouped into rhythmic phrases. The rhythmic structure of a sequence facilitates anticipation on elements that are yet to be produced or perceived. People with dyslexia have been shown to have deficient rhythmic ability, as indicated, for instance, by limitations in perceiving and reproducing musical rhythms. As a corollary, people with dyslexia have difficulty with anticipatory planning, which, in its turn, explains their atypical behavioral profiles with regard to reading, language production and comprehension, and handwriting.

Clearly, the notion “anticipation,” or “anticipatory planning” (also referred to as “being in anticipatory mode”) is critical in Taha et al.’s (2025) framework. Given its central role in their argument, one would expect to see it clearly defined. However, the definition provided in the glossary is rather vague: “the ability to process information in advance to prepare for future actions . . . a specific form of prediction . . . .” The article does not specify what exactly it is that is shared by the various phenomena that are discussed: co-articulation in speaking, its analogue in handwriting, the prediction of upcoming words in (spoken or written) language comprehension, and look ahead in reading. Yes, each of these have to do with being engaged with something that comes next, but other than that, there is no explicit statement about the nature or functioning of the neurocognitive mechanism these phenomena are purported to have in common. This is regrettable, as there appear to be important differences between, on the one hand, programming/-planning processes in producing articulatory movements or handwriting and, on the other, predicting upcoming information in language comprehension. By the same token, it is not clarified how such a mechanism may control anticipation during reading (i.e., parafoveal processing in the service of planning a saccade to an “information-rich” next point in the text).

Rhythm is also a core element of Taha et al.’s (2025) framework. The proposition is that rhythm supports (facilitates) anticipation: “ (Incidentally, the authors seem to be suggesting here that it is specifically metric rhythmicity that supports anticipation, while elsewhere they stress that non-metric rhythm can do the same.) We acknowledge that activities such as speaking, speech recognition and various non-speech motor actions (all of which have been argued to be affected in dyslexia) involve the creation or apprehension of rhythmic structures. Also, it appears reasonable (and there is some evidence) that rhythmic structures may assist in predicting or anticipating beyond the current percept or action. However, in other activities, notably processing written language (reading), the authors’ case for rhythmic structure as a facilitatory factor is tenuous. It seems that the authors are somewhat conflicted here, as they first state that “(i)n reading, words are grouped together, such as pairing a determiner with its noun and inserting pauses, with grouping being the main feature of rhythm.” (p. 19) and then, in the same paragraph note that “Reading does not have a clear rhythmic structure.”

In our view, only the latter statement is correct. There is no such thing as the temporal organisation of a written sentence. The authors allude to the hierarchical (grammatical) structure of sentences, but grammatical structure does not have an obvious temporal reflection. Phonological structure does, but there is no consistent one-to-one mapping between grammatical structure and phonological structure, and consequently this is not the mechanism by which the “temporal organisation” suggested by the grammar can be made explicit. Moreover, such a grammar to phonology mapping would require that a reader (always) generates an “implicit” phonological representation of the written input, and that is a contentious question.

We are not implying here that there is no anticipatory (predictive) processing in (written) language processing, on the contrary. The syntactic structure of a sentence fragment, as inferred by a reader or listener, contributes to creating predictions regarding potential upcoming words or structures. For example, if the initial words of a string are construed as a (potential) subject, the parser will be able to predict that a verbal predicate with certain morphological properties (e.g. agreeing features) will follow. However, it is principally impossible to predict at what point in the upcoming string this element will occur, unlike in the case of musicians in an orchestra who can predict where they have to start playing a phrase on the basis of the rhythmic (and melodic) structure of a preceding phrase played by other instruments.

Along the same lines, the study on predictive language processing by Altmann and Kamide (1999), which the authors cite, shows that semantic features of a sentence’s main (transitive) verb helps in predicting that a particular noun (of a certain semantic class) will fill the object position. This, we would say, is completely detached from the (putative) rhythmic structure of the sentence. Even if the rhythmic structure of a spoken sentence is somehow equated with the syntactic structure, it cannot account for the observed differences between the experimental conditions in Altman and Kamide’s experiment (exemplified by “take” vs. “eat” in combination with “cake”). The authors also refer to the predictive processing study by Huettig and Brouwer (2015), which shows that people with dyslexia are less efficient in exploiting the gender of a (Dutch) definite article to predict the upcoming noun. The authors argue that this is due to inefficient anticipatory planning, and they suggest that this inefficiency, in its turn, is caused by a failure to apprehend the combination of determiner and noun as a “rhythmic unit.” It should be noted, however, that if there is a role for such a rhythmic unit it would also apply to determiner-noun combinations in which the grammatical genders of the determiner and the noun do not match. In other words, we would say, rhythm is irrelevant here.

The question that we don’t see answered in Taha et al.’s (2025) study is how the inefficient anticipatory planning hypothesis may contribute to a better understanding of (developmental) dyslexia. The authors acknowledge that dyslexia is a heterogeneous and multifactorial condition, in line with the current consensus. They nonetheless maintain that inefficient anticipation is a “primary deficit” in dyslexia, which we read as a core (explanatory) mechanism. In the past decades, a variety of hypotheses on dyslexia have seen the light that all claim to identify one specific neurophysiological or neurocognitive mechanism as the core feature of dyslexia; most of these are cited by the authors. A shared pitfall of such single-factor hypotheses is that it is virtually never the case that all individuals with dyslexia show all the phenotypical characteristics that the hypothesis predicts. This is what the “heterogeneity” that Taha et al. (2025) refer to entails. Any proposal that aspires to contribute to the explanation of dyslexia should account for this heterogeneity; the present proposal does not seem to do this.

A proposal that is meant to contribute to explaining dyslexia should also be explicit on how a hypothesised underlying deficit – in this case: inefficient anticipation – may help in understanding the defining phenotypical characteristics of the condition. What is defining for (developmental) dyslexia is that it is a specific learning disorder. Children with dyslexia struggle with learning the associations between the speech sounds (phonemes) of their native language and the written characters (graphemes) that represent them, much more so than unaffected children do. This struggle results in an extended and effortful learning trajectory, and in most cases the difficulty in decoding written words, and its corollary, spelling, persist into adulthood. The evidence accumulated over the past five decades or so strongly indicates that these reading and spelling difficulties have their roots in atypical or disordered phonological processing and representation, although the exact nature of the deficiency is still under debate. We fail to see how the inefficient anticipatory planning hypothesis can cast a new light on this matter.

Our criticisms notwithstanding, we appreciate Taha et al.’s (2025) attempt to identify a unifying principle for a set of seemingly unrelated but co-occurring phenotypical characteristics of dyslexia. However, the unification needs to go beyond stating what these characteristics have in common: (some form of) anticipation. To make the inefficient anticipatory planning hypothesis effective as an instrument to inspire new questions and new empirical approaches, we think it is necessary to provide a precise specification of the mechanism underlying anticipatory planning in each of the domains covered, and of the nature of its inefficiency in people with dyslexia. In doing this, the authors may also want to reconsider the role of rhythm. This is not to say that rhythm is irrelevant. Clearly, as the synchronisation experiments and other studies indicate, people with dyslexia underperform on tasks in which detecting and utilising (metrical) rhythmic structure is critical. However, the inference that the authors make – that since rhythmic anticipation in individuals with dyslexia is impaired, it must be the case that (inability to utilise) rhythm is at stake in other tasks that involve anticipation or prediction – is unwarranted. By contrast, stating that anticipation is impaired in people with dyslexia, and that this affects tasks and processes that either do or don’t involve a rhythmic structure, has merit.