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We consider a network of interacting individuals, whose actions or transitions are determined by the states (behavior) of their neighbors as well as their own personal decisions. Specifically, we develop a model according to two simple decision-making rules that can describe the growth of the user population of a newly launched product or service. We analyze 22 sets of real-world historical growth data of a variety of products and services, and show that they all follow the growth equation. The numerical procedure for finding the model parameters allows the market size, and the relative effectiveness of customer service and promotional efforts to be estimated from the available historical growth data. We study the growth profiles of products and find that for a product or service to reach a mature stage within a reasonably short time in its user growth profile, the user growth rate corresponding to influenced transitions must exceed a certain threshold. Furthermore, results show that individuals in the group of celebrities having numerous friends become users of a new product or service at a much faster rate than those connected to ordinary individuals having fewer friends.

In the last decade, reading research has seen a paradigmatic shift. A new wave of computational models of orthographic processing that offer various forms of noisy position or context-sensitive coding have revolutionized the field of visual word recognition. The influx of such models stems mainly from consistent findings, coming mostly from European languages, regarding an apparent insensitivity of skilled readers to letter order. Underlying the current revolution is the theoretical assumption that the insensitivity of readers to letter order reflects the special way in which the human brain encodes the position of letters in printed words. The present article discusses the theoretical shortcomings and misconceptions of this approach to visual word recognition. A systematic review of data obtained from a variety of languages demonstrates that letter-order insensitivity isneithera general property of the cognitive systemnora property of the brain in encoding letters. Rather, it is avariantand idiosyncratic characteristic of some languages, mostly European, reflecting a strategy of optimizing encoding resources, given the specific structure of words. Since the main goal of reading research is to develop theories that describe thefundamental and invariantphenomena of reading across orthographies, an alternative approach to model visual word recognition is offered. The dimensions of a possible universal model of reading, which outlines the common cognitive operations involved in orthographic processing in all writing systems, are discussed.

We agree with many of the principles proposed by Frost but highlight crucial caveats and report research findings that challenge several assertions made in the target article. We discuss the roles that visual processing, development, and bilingualism play in visual word recognition and reading. These are overlooked in all current models, but are fundamental to any universal model of reading.

A universal property of visual word identification is position-invariant letter identification, such that the letter “A” is coded in the same way in CAT and ACT. This should provide a fundamental constraint on theories of word identification, and, indeed, it inspired some of the theories that Frost has criticized. I show how the spatial coding scheme of Colin Davis (2010) can, in principle, account for contrasting transposed letter (TL) priming effects, and at the same time, position-invariant letter identification.

I argue, contra Frost, that when prime lexicality and target density are considered, it is not clear that there are fundamental differences between form priming effects in Semitic and European languages. Furthermore, identifying and naming printed words in these languages raises common theoretical problems. Solving these problems and developing a universal model of reading necessitates “cracking” the orthographic input code.

We suggest that the linguistic characteristics of letters also need to be considered to fully understand how a reader processes printed words. For example, studies in Korean showed that unambiguity in the assignment of letters to their appropriate onset, vowel, or coda slot is one of the main sources of the letter-transposition effect. Indeed, the cognitive system that processes Korean is tuned to the structure of the Korean writing system.

There are universals of language; but is it also true, as the target article claims, that there are universals of reading? We believe there are no such universals, and invite others to refute our claim by providing a list of some universals of reading. If there are no universals of reading, there cannot be a universal model of reading.

The principles for universal reading models proposed by Frost correspond to developmental theories, in which neurocognitive constraints and cultural experiences shape development. We question his contention that Hebrew word identification is fundamentally about roots, excluding verbal and nominal word-pattern morphemes; and we propose that readers use all information available in stimuli, adjusting for volume and usefulness.

We qualify Frost's proposals regarding letter-position coding in visual word recognition and the universal model of reading. First, we show that perceptual uncertainty regarding letter position is not tied to European languages – instead it is a general property of the cognitive system. Second, we argue that a universal model of reading should incorporate a developmental view of the reading process.

Frost has given us good reason to question the universality of existing computational models of reading. Yet, he has not provided arguments showing that all languages share fundamental and invariant reading universals. His goal of outlining the blueprint principles for a universal model of reading is premature. Further, it is questionable whether natural evolution can provide the optimal solutions that Frost invokes.

Reading development is integral to a universal model of reading. Developmental research can tell us which factors drive reading acquisition and which are the product of reading. Like adult research, developmental research needs to be contextualised within the language and writing system and it needs to include key cross-linguistic evaluations. This will create a universal model of reading development.