Sebastián & Hernández-Gill (2012) Digit Span (Edexcel A-Level Psychology): Revision Notes

Sebastián & Hernández-Gil (2012) Digit Span

Theorist, title, year

Sebastián and Hernández-Gil (2012) conducted research at the University of Madrid examining the developmental pattern of digit span in the Spanish population. The study tested the phonological loop component of working memory, as proposed by Baddeley and Hitch (1974).

Participants

• 570 volunteer participants were recruited from schools in Madrid
• All participants were native Spanish speakers
• Participants were divided into five age groups: preschool (5 years), primary school (6-8 years), primary school (9-11 years), secondary school (12-14 years), and secondary school (15-17 years)
• Participants with impairments in hearing, reading, or writing ability were excluded from the study
• The sample was representative of the general Spanish population within these age ranges

Aim

The study had two main aims:

1. To investigate the development of the phonological loop in children between the ages of 5 and 17 years, using digit span as a measure of phonological capacity
2. To compare these findings with previous research conducted on adult, aged, and dementia patients

The researchers wanted to establish whether digit span would show similar developmental patterns in a Spanish population as had been found in Anglo-Saxon research, and whether the capacity would differ across different ages.

Procedure

Participants were tested individually using a digit span task. The procedure involved:

• Participants were read increasing sequences of digits at a rate of one digit per second
• The digit sequences increased by one digit per sequence (e.g., 2-5-9-4-5, then 3-7-8-1-6-9)
• Participants were required to recall the digits in the correct sequential order immediately after hearing them
• Digit span was recorded as the maximum number of digits recalled in correct order without error
• The average digit span was calculated for each age group

Findings

The study produced clear evidence of a developmental trend in digit span capacity:

Age group	Mean digit span (SD)
Preschool (5 years)	3.76 (.52)
Primary school (6-8 years)	4.34 (.58)
Primary school (9-11 years)	5.13 (.81)
Secondary school (12-14 years)	5.46 (.85)
Secondary school (15-17 years)	5.83 (.84)

Key patterns observed:

• Children aged 5 years demonstrated a very low digit span (mean 3.76)
• Digit span increased steadily through childhood
• The most rapid increase occurred between ages 5 and 11 years
• After age 11, the rate of increase slowed considerably
• Between ages 15 and 17, digit span remained fairly stable

Cross-cultural comparison

When comparing the Spanish data to previous Anglo-Saxon research, the study found:

• The developmental trend of increasing digit span with age was consistent with Anglo-Saxon research
• However, the overall capacity of digit span was lower in the Spanish population compared to Anglo-Saxon studies (Spanish participants recalled approximately one digit fewer on average)

Word length effect

The word length effect explains why digit span differs across languages:

• Spanish digits tend to be two or more syllables (e.g., uno, cuatro, cinco, ocho)
• Anglo-Saxon digits are predominantly monosyllabic (e.g., one, two, three, four)
• Longer words take more time to sub-vocally repeat and rehearse in the phonological loop
• This occupies more space in the phonological loop, resulting in lower digit span capacity

Timing of word length effect

The researchers examined when the word length effect begins to influence digit span:

• Before age 7-8 years: No difference in digit span between Spanish and Anglo-Saxon children (sub-vocal rehearsal has not yet developed)
• From age 9 years onwards: A noticeable difference emerges, suggesting the word length effect occurs once sub-vocalisation appears in phonological development
• The study speculates that digit span in Spanish children continues to increase beyond age 15, unlike previous research suggested

Comparison to dementia patients

Sebastián and Hernández-Gil compared their findings to previous research on elderly and dementia patients:

• Elderly participants (without dementia) showed higher digit span than younger children in this study
• Patients with advanced dementia (AD) demonstrated a similar digit span profile (mean 4.2) to elderly participants without dementia
• Patients with frontal variant frontotemporal dementia (fvFTD) had digit spans that were similar to younger age groups in this study

Key definitions:

• Frontal variant frontotemporal dementia (fvFTD): a degenerative neurological disease affecting the frontal lobes of the brain
• Advanced dementia (AD): the later stages of dementia where symptoms are more profound

Conclusions

The study drew several important conclusions:

1. Digit span increases with age, with the starting point of development occurring when children become able to sub-vocalise at around 7 years of age

2. Digit span in the Spanish population is shorter than in Anglo-Saxon populations, likely due to the word length effect associated with Spanish digit words being longer

3. When comparing findings to research on degenerative neurological disease and the aged population, the study suggests that poor digit span is a result of ageing rather than dementia itself

4. The research supports the existence of a relationship between language structure and the phonological loop, demonstrating how linguistic characteristics can influence working memory capacity

Evaluation: Strengths

1. Large sample size: The study tested 570 participants, which provides reliable and generalisable findings for the Spanish population as a whole

2. Cross-cultural validity: The research was conducted in a different culture (Spanish rather than Anglo-Saxon), allowing comparisons to be made across populations and testing whether previous findings could be replicated

3. Controlled participant selection: The study excluded participants with any hearing, reading, or language impairments, which are known to diminish digit span. This control measure ensured that results were not affected by confounding variables

4. Wide age range: By examining participants from ages 5 to 17 years, the study captured the full developmental trajectory of digit span in childhood and adolescence

5. Practical methodology: The digit span task is relatively simple to administer, making it a practical tool for assessing phonological loop capacity

Evaluation: Weaknesses

1. Ecological validity concerns: Digit span experiments measure the phonological loop, but we rarely use verbal memory to memorise lists of digits in everyday life (except when trying to remember telephone numbers). Everyday verbal memory is typically used to comprehend sentences, learn new languages, or process complex information. Therefore, it is questionable whether digit span experiments reflect everyday use of verbal memory

2. Correlation with other abilities: Research has shown that digit span has been reliably linked to performance in reading ability and intelligence, suggesting digit span may be a general measure of verbal memory rather than a pure test of the phonological loop. This raises questions about what the task is actually measuring

3. Cultural factors: Despite claims that digits are a culture-free and meaning-free way of measuring pure verbal memory, the cultural differences found in this study suggest digits may not be the best culture-free determinant of verbal memory capacity

4. Cross-cultural digit span differences: Other research has reported cultural differences in digit span:

   • Ellis and Hennelley (1980) found poorer digit span in Welsh-speaking children compared to English children, because Welsh words for digits take longer to pronounce
   • Stigler et al. (1986) reported longer digit spans in Chinese because the words for digits are very short
   • These findings support that language and the phonological loop are interrelated, but complicate cross-cultural comparisons

5. Individual differences: There are individual differences that can be detected by digit span testing. Dyslexia, which is associated with problems learning to recognise words at an age-appropriate level, is linked to poor digit span (Helland and Asbjørnsen, 2004). This suggests the task may be measuring reading-related abilities as well as pure phonological capacity

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