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Alongside a classic study, the Edexcel Cognitive topic requires a contemporary study — a more recent piece of research that extends, updates or contrasts with the classic. This lesson examines Sebastián and Hernández-Gil (2012), "The developmental pattern of digit span" (published in the journal Psicothema), which measured the digit span of children and adolescents in Madrid to chart how the capacity of the phonological loop develops with age. It is an ideal contemporary partner to Baddeley's (1966) classic: where Baddeley used adults to establish that short-term memory codes acoustically, Sebastián and Hernández-Gil use a developmental sample to show how the acoustically-coded phonological loop grows through childhood — moving from what the store is to how it develops, and from a Cambridge volunteer panel to a large real-world sample of schoolchildren. This lesson gives the study in full — aim, method, results and conclusion — then evaluates it and shows precisely how it updates and contrasts with the classic study.
Key Definition: A contemporary study in the Edexcel topic is a more recent piece of research (here, 2012) that develops, tests or challenges the ideas established by the classic study — allowing students to see how a research question has moved on.
This lesson addresses the Edexcel 9PS0 — Paper 1, Topic 2: Cognitive Psychology requirement to know a contemporary study in depth: Sebastián and Hernández-Gil (2012) on the developmental pattern of digit span. You must be able to state its aim, method/procedure, results and conclusion, evaluate it (methodology, validity, generalisability, ethics), and explain how it relates to the classic study (Baddeley, 1966) and to the working memory model. In assessment-objective terms, you should be able to describe the study accurately (AO1), apply its findings to the development of the phonological loop (AO2), and evaluate its methodology and its relationship to the classic study (AO3).
Connects to…
By 2012, it was long established (from Jacobs, 1887, onwards) that adult digit span is around seven items, and that span increases through childhood. The working memory model located verbal short-term memory in the phonological loop, whose capacity depends on how much can be sub-vocally rehearsed before the trace decays — roughly what can be said in about two seconds (the basis of the word-length effect, Baddeley, Thomson & Buchanan, 1975). Sebastián and Hernández-Gil set out to describe, in a large modern Spanish-speaking sample, exactly how digit span develops with age across childhood and adolescence, and to relate this to the development of the phonological loop.
Key Aim: To investigate the developmental pattern of digit span — how the capacity of verbal short-term memory (the phonological loop) changes with age across childhood and adolescence — in a Spanish-speaking population.
A further motivation was cross-linguistic. Because digit span depends on how quickly the digit words can be rehearsed, and Spanish number words differ in length and syllable structure from English ones, the researchers were interested in the developmental trajectory of span in Spanish specifically — allowing later comparison with English-language norms and testing whether the phonological-loop account (span limited by rehearsal time) holds across languages.
There is a clear theoretical reason to expect development to be tied to the phonological loop rather than to a fixed number of "memory slots". If short-term capacity were simply a fixed number of items, span should not depend on how long the items take to say — yet the word-length effect shows it does, and the effect vanishes under articulatory suppression, implicating sub-vocal rehearsal. A developmental study of span is therefore an indirect test of this mechanism: if span tracks the maturation of articulation speed (which is known to increase through childhood), that is strong evidence that the growing capacity reflects a faster rehearsal loop rather than more slots. This is why Sebastián and Hernández-Gil frame their developmental question explicitly in terms of the phonological loop, and why the shape of the developmental curve (rapid rise, then plateau) matters as much as the fact of an increase.
The study was a quasi-experiment using a cross-sectional developmental design: children of different ages were tested at one time and their digit spans compared, so that the "independent variable" (age group) was a naturally-occurring participant characteristic, not something the researchers manipulated.
A large sample of around 570 children and adolescents aged approximately 5 to 17 years, drawn from schools in Madrid, Spain. Participants were grouped into age bands (for example 5–6, 7–8, 9–10, 11–13, 14–15 and older), giving a broad developmental range from the start of formal schooling to late adolescence. Participants with conditions that might affect memory or language were excluded, so the sample represented typically-developing children.
Digit span was measured using a standard forward digit-span procedure (a component of widely-used standardised memory scales). The procedure follows the classic Jacobs logic:
The study focused on forward digit span (simple storage and reproduction, a relatively pure measure of the phonological loop) rather than backward digit span (which additionally requires the central executive to manipulate the sequence). This is an important design point: forward span isolates the storage capacity of the phonological loop, which is exactly the developmental question of interest.
flowchart TD
SAMPLE["~570 children, ages ~5–17<br/>Madrid schools (typically developing)"] --> BANDS["Grouped into age bands"]
BANDS --> TASK["Forward digit-span task<br/>(hear sequence → repeat in order)"]
TASK --> MEASURE["Span = longest sequence<br/>reliably recalled in order"]
MEASURE --> COMPARE["Compare mean span across age bands<br/>= developmental pattern"]
Key Definition: Forward digit span measures the number of digits a person can hear and immediately repeat in order — a relatively pure index of the storage capacity of the phonological loop. Backward digit span requires reversing the sequence and so additionally taxes the central executive.
The central finding was clear and orderly: digit span increased steadily with age across childhood and adolescence, but the increase was not uniform — it was steeper in the younger years and flattened out approaching adulthood.
| Approximate age | Approximate forward digit span | Developmental picture |
|---|---|---|
| ~5 years | ~3–4 digits | Shortest span; loop capacity low |
| ~7–8 years | rising | Rapid growth phase |
| ~9–10 years | substantially higher | Growth continuing, still steep |
| ~11–13 years | approaching adult level | Growth slowing |
| ~14–17 years | ~6–7 digits (near adult) | Plateauing near the adult ceiling |
The researchers interpreted the developmental increase in terms of the maturation of the phonological loop. As children get older, their speed of articulation (how fast they can rehearse sub-vocally) increases, so more digits can be refreshed before the phonological store's trace decays — expanding the effective span. The slowing of the increase in adolescence reflects articulation rate (and hence loop capacity) approaching its adult limit. This directly links the behavioural finding (span grows then plateaus) to the mechanism proposed by the working memory model (a time-limited rehearsal loop whose speed matures with age).
The authors also noted the cross-linguistic dimension: because Spanish number words tend to be somewhat longer / more syllabically complex than English ones, and span is limited by rehearsal time, digit spans in Spanish samples can be slightly lower than in English samples at equivalent ages — a difference that itself supports the phonological-loop account, since it is exactly what a time-limited-rehearsal model predicts (longer words → fewer rehearsable per two seconds → shorter span).
Sebastián and Hernández-Gil concluded that digit span develops systematically with age, increasing rapidly in childhood and approaching the adult level by adolescence, and that this developmental pattern reflects the maturation of the phonological loop — specifically, the age-related increase in the speed of sub-vocal rehearsal that allows more items to be maintained. The plateau in adolescence corresponds to articulation rate reaching its adult ceiling.
The study therefore confirms, in a large modern sample and a different language, that verbal short-term memory capacity is not fixed but develops, and that its development is well explained by the working memory model's account of a time-limited phonological loop. The cross-linguistic sensitivity of span (shorter for longer number words) further supports the claim that span is governed by rehearsal time rather than a fixed number of "slots".
A central skill in this topic is explaining how the contemporary study relates to the classic study. Baddeley (1966) and Sebastián and Hernández-Gil (2012) are a well-matched pair — same broad theme (verbal short-term memory / the phonological store), very different in emphasis.
| Dimension | Classic: Baddeley (1966) | Contemporary: Sebastián & Hernández-Gil (2012) |
|---|---|---|
| Core question | What code does STM (vs LTM) use? | How does verbal STM (the phonological loop) develop with age? |
| Focus | Coding (acoustic vs semantic) | Capacity and its developmental trajectory |
| Participants | Adults (Cambridge volunteer panel) | ~570 children/adolescents (Madrid schools) |
| Design | Laboratory experiment, independent groups | Quasi-experiment, cross-sectional developmental |
| Model supported | Multi-store model (separate stores) → seeds the phonological loop | Working memory model (maturation of the phonological loop) |
| Language / era | English, 1960s | Spanish, 2010s (cross-linguistic dimension) |
How it updates the classic. Baddeley established that STM codes acoustically — that is, that there is a phonological (sound-based) short-term store. The contemporary study takes that store as given and asks the next question: how does it develop? In doing so it moves the research programme forward in time (from the store's existence and code to its maturation), forward in theory (from the multi-store model to the working memory model's phonological loop), and forward in method (from a small adult lab sample to a large developmental sample in a different language). It also modernises the evidence base: a 2012 study in Spanish shows that the phonological-loop account is not a 1960s English-language artefact but generalises across time and language.
How it contrasts with the classic. The two differ in what they measure (coding vs capacity/development), who they study (adults vs children), and which model they principally support (MSM vs WMM). They also illustrate a methodological contrast: Baddeley manipulated an independent variable (list similarity) in a true experiment allowing causal inference, whereas Sebastián and Hernández-Gil compared naturally-occurring age groups in a quasi-experiment, which describes a developmental pattern but cannot experimentally manipulate age and so is more limited in causal terms.
Where they agree. Both point to the same underlying system — a sound-based, time-limited verbal short-term store. Baddeley shows it is acoustic; Sebastián and Hernández-Gil show its capacity is set by rehearsal time (hence sensitive to word length and to the maturing speed of articulation). Together they give a fuller picture of the phonological loop than either alone: its code (classic) and its development (contemporary).
A major strength is the study's large sample of around 570 children spanning a wide age range. This matters because a big, broad sample makes the developmental pattern — the steady rise and adolescent plateau — statistically reliable and less vulnerable to the influence of a few atypical individuals, and it allows the trajectory to be charted across many age bands rather than inferred from a couple of points. The implication is that the study provides a robust description of how digit span develops, with better generalisability across childhood than a small study could achieve — a clear methodological advantage over the narrow adult panel of the classic study.
A second strength is the use of a standardised digit-span procedure taken from established memory scales. Because the task is administered the same way every time (steady presentation rate, sequences of increasing length, span as the reliable maximum), it has high reliability — the measurement is consistent and replicable. This matters because a standardised, well-established measure means differences in span can be attributed to age rather than to inconsistencies in how the task was given. The implication is that the study's internal consistency is high, and its findings can be readily compared with digit-span data from other studies and languages — which is precisely what enables the informative cross-linguistic comparison with English norms.
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