Sebastian & Hernandez, 2012

The researchers used Spanish participants, which has some relevance for the findings, and the study was about how digit span develops from children to adolescence and looked at older people as well. Their study is part of Baddeley's working memory model, the phonological loop.

Their aim was to analyse the developmental pattern of the phonological loop in children aged 5-17 years olds. This involved looking at the age at which digit span stopped increasing in adulthood/adolescence. They also wanted to look at the decline of digit span in older people, including those with two types of dementia: Alzheimer's and fronto-temporal dementia. 

There were two parts to this study.

The first part gathered primary data and used 5-17 year olds from the Spanish population. There were 570 volunteers from various schools in Madrid, all born in Spain. None of the participants had difficulties such as in reading, writing or hearing. This was to control for education and cognitive differences.

The second part of the study used data from the researchers' previous study in 2012 where data was gathered about digit span of elderly people without impairment, those with Alzheimer's and those with fronto-temporal dementia. Thus the secondary part of the study used secondary data. The second part used 25 healthy older people as the control group, 25 with Alzheimer's and 9 with fronto-temporal dementia. 

The hypothesis was that there is a difference in digit span which increases with age, from 5-17 years. The independent variable was the age of the participant and the dependent variable was the digit span. The digit span was measured by reading allowed sequences of digits one per second. Each time a participant got the sequence right, another digit was added to increase the span and the particpant tried again. They required that they recalled the correct number in the correct order. Participants were tested individually in their break time. 

Age                                         Digit Span                                 Development Period 

5 years                                         3.76                                            3.76 (5 years)

7 yeras                                         4.26                                            4.34 (6-8 years)

10 years                                       5.13                                            5.13 (9-11 years)

13 years                                       5.89                                            5.46 (12-14 years) 

16 years                                       5.75                                            5.83 (15-17 years)

Aged 5 years had a very low digit span and showed significant difference from the other age groups. From 6-8 years, the children had a very similar digit span. The increase in one digit, from four to five occured at nine years old and rose to 11 years. Older children aged 12-14 had a similar digit span to one another but differed from the age groups 'above' them. A similar digit span was found for 15-17 year olds. 

The researchers compared their data to data from the previous experiment, which showed that digit span increases with age. 

The second part compared the results of this study with another study from 2010. The participants were healthy older people, people with Alzheimer's demantia and people with fronto-temporal dementia. The digit span task was the same as the first part. 

Group                           Mean digit span

AD                                         4.20

FTD                                       4.22

Healthy (control)                      4.44          

The performance of the elderly participants was compared with the youngest in the first part of the study and showed a higher digit span than both the five year olds. The performance of the elderly participants did not differ from the other year groups.  

A main conclusion is that digit span increases with age from 5-17 years.

A conclusion around older people  showed that the digit span of a healthy older person was similar to a seven year old, which does show an age effect in that there is a decine in digit span in age. 

The digit span of those with AD and FTD is not that much different from that of a healthy older personand similar to a six year olds digit span, so dementia did not seem to affect digit span in itself. The capacity of the phonological loop seems to be affected by age not by dementia. 

Strengths

• A strength is the careful controls used in the study. The digit span task is a standard one and then same procedure was used in the 2012 study as in the 2012 study. 
• They analyse not only for actual age using school years, but also for age groups so that they have individual digit span scores for each year and age group, which means they have more informatopn from whcih to draw conclusions. 

Weaknesses

• The task is artificial, as we do not generally recall lists of digits, so there might be a lack of validity.