Digit Span: memory span and capacity of STM without rehearsal: it can be tested by reading a sequence of numbers to someone which increases each time
Aims
- To study the developmental pattern of working memory over time, including changes from ageing or dementia
- To analyse the developmental pattern of the phonological loop in children aged 5-17 – this involved looking at the age the digit span stopped increasing in adulthood/adolescence
- To look at the decline of the digit span in older people, including those with two types of dementia – Alzheimer’s and fronto-temporal dementia
- To see if Anglo-Saxon data, which found 15 years to be the age at which digit span stops developing further, were replicated or whether digit span would be higher for Spanish speakers, as word length may affect digit span
Procedure
Part 1
- Primary data gathering to test the hypothesis
- Sample: 570 volunteers, from various schools in Madrid. Extraneous variables ruled out as no ppt had repeated a school year/had learning difficulties
- Separated into 5 groups: ages 5, 6-8, 9-11, 12-14 and 15-17 years.
- IV: age of the participants DV: digit span
- Task: Sequences of digits were read aloud, one per second. Each correct sequence meant the sequence increased by 1 digit. Began with 3 sequences of 3 digits. The digit span measure was the number of digits in the sequence where they recalled at least two of the three sequences correctly.
Part 2
- Secondary data from their previous study in 2010
- Sample: 25 healthy older people (control group), 25 Alzheimer patients, 9 dementia
- Data was gathered for the three groups with the same task as above
Results Part 1 – mean number of digits recall by year group and developmental period
| Age Group | Mean Digit Span |
| Preschool (5 years) | 3.76 |
| Primary school (6-8 years) | 4.34 |
| Primary school (9-11 years) | 5.13 |
| Secondary school (12-14 years) | 5.46 |
| Secondary school (15-17 years) | 5.83 |
Shows that digit span increased with age
Part 2 – digit span from the previous study
| Group | Gender | Mean Digit Span |
| Alzheimer’s dementia | 7m/18f | 4.20 |
| Fronto-temporal dementia | 5m/4f | 4.22 |
| Healthy older people | 6m/19f | 4.44 |
- Older ppts had a higher digit span than 5 year olds (sig level 0.0001) and 6 year olds (0.03) however lower digit spans than ages 9+
Conclusion
- Study proved that digit span increases ages 5-17; this contrasts with Anglo-Saxon data as that showed digit span to stop increasing at 15
- Highlighted the difference in word length between Spanish and English words
- Baddeley found that memory span is affected by lists using long words vs short words
- Sub-vocal rehearsal: the longer the digit takes to say, the more the trace would decay
- Sub-vocal rehearsal doesn’t start until the age of 7 so there should be little difference between English and Spanish children under the age of 7
- Digit span is one digit lower for Spanish children over the age of 7
- Dementia did not significantly impact the digit span, therefore the capacity of the phonological loop is affected by age, not dementia