2.15 - Contemporary Study: Sebastián & Hernández-Gil (2012)
Introduction to digit span and the phonological loop
Digit span refers to an individual's ability to remember and recall a sequence of digits or numbers held in short-term memory. This capacity is closely linked to the phonological loop, which is a component of working memory responsible for temporarily storing and manipulating verbal information, such as sounds or words.
Aims of the study
Sebastián and Hernández-Gil (2012) conducted this research to explore how digit span evolves from childhood to adolescence, providing evidence about the growth of phonological loop capacity.
Primary aims
- To measure changes in digit span among children and adolescents aged 5 to 17 years, using it as an indicator of phonological loop development.
- To compare digit span in Spanish speakers with previous findings in English speakers, where development typically plateaus at age 15.
- To examine whether digit span declines in older adults with dementia.
Participants in the study
The study was divided into two parts, each with distinct groups to ensure a broad examination of digit span across ages and conditions.
Participants in the first part
- 585 volunteers from schools in Madrid, Spain, all native Spanish speakers.
- Ages ranged from 5 to 17 years, divided into five 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).
- Controls were applied for hearing, reading, and writing impairments to minimise variations due to educational or cognitive differences.
Participants in the second part
- Secondary data from a 2010 study by the same researchers, including 28 healthy older adults (as a control group), 27 individuals with Alzheimer's disease, and 11 with frontotemporal dementia.
- Gender distribution: Alzheimer's group (8 males, 19 females), frontotemporal dementia group (6 males, 5 females), healthy older group (7 males, 21 females).
Method and procedure
The research used a structured approach to measure digit span, with age as the independent variable and digit span as the dependent variable.
Procedure for the first part
- Participants were tested individually in a controlled school setting.
- A researcher read sequences of digits aloud at a rate of one per second.
- Sequences started short and increased by one digit each time the participant recalled them correctly in the exact order.
- The longest correct sequence determined the digit span score.
- Average scores were calculated for each age group.
Method for the second part
This relied on secondary data from the 2010 study, where similar digit span tests were administered to older adults. The procedure mirrored the first part, focusing on recall of digit sequences to measure short-term memory capacity.
Results of the study
The findings highlighted patterns in digit span development and decline, with comparisons to previous research.
Results from children and adolescents
Digit span increased steadily with age from 5 to 17 years. Spanish speakers showed lower overall digit spans compared to English speakers in prior studies, attributed to longer Spanish number words leading to slower sub-vocal rehearsal and more decay.
Average digit span by age group:
| Age group | Mean digit span |
|---|---|
| Preschool (5 years) | 3.85 |
| Primary school (6–8 years) | 4.40 |
| Primary school (9–11 years) | 5.20 |
| Secondary school (12–14 years) | 5.55 |
| Secondary school (15–17 years) | 5.90 |
Results from older adults
Healthy older adults had a mean digit span of 4.50, which was higher than 5-year-olds but similar to other young groups. No significant differences were found between healthy older adults and those with dementia.
Average digit span by adult group:
| Group | Gender | Mean digit span |
|---|---|---|
| Alzheimer's | 8 males/19 females | 4.25 |
| Frontotemporal dementia | 6 males/5 females | 4.30 |
| Healthy older people | 7 males/21 females | 4.50 |
These results suggest that digit span in Spanish speakers may continue developing beyond age 15, unlike in English speakers.
Conclusions and evaluation
The study drew key insights about memory development and ageing, while also identifying areas for further research.
Conclusions
- Digit span grows with age from 5 to 17 years in Spanish speakers, potentially continuing past 15 years, contrasting with English-language studies where it peaks earlier.
- Healthy older adults exhibit a digit span similar to that of 7-year-olds, indicating a decline with age, though the exact onset of this decline remains unclear.
- Digit span in individuals with Alzheimer's or frontotemporal dementia matches that of healthy older adults and typical 6-year-olds, implying that reduced capacity results from ageing rather than dementia specifically.
- Language differences affect digit span: Spanish speakers have spans about one digit lower than English speakers due to longer word processing times, which increase decay in the phonological loop.
Evaluation
- Strengths: Large sample size in the first part (585 participants) enhances reliability; controls for impairments reduce confounding variables; use of secondary data allows efficient comparison with dementia groups.
- Limitations: Reliance on secondary data for the second part may introduce inconsistencies; the study speculates on continued development beyond 15 without testing adults in their 20s or older; cultural and language factors were noted but not fully explored across diverse populations.
- Implications: These findings support the idea that phonological loop capacity matures gradually and is influenced by linguistic factors, informing educational strategies for memory development in children.