Sebastian & Hernandez-Gil (2012)

to investigate development of the phonological loop

- 575 children from pre-, primary and secondary schools in Madrid
- all were born in Spain
- aged 5-17 years
- none presented with impairments

- field setting - schools
- IV was year of schooling
- DV was mean verbal digit span
- tested individually
- sequences of random digits that gradually increased by one digit in length each time
- read aloud to each ppt at one per second
- began with 3 sequences of 3 digits, then 3 of 4 and so on
- ppts listened to each sequence and then were asked to repeat them in order
- each child completed practice sequence at start
- digit span was recorded as longest sequence the child could recall 2/3 times presented in order without error

- clear increase in digit span with age
- 5rs = mean digit span of 3.76
- 17yrs = mean of 5.91

- digit span increases with age up to adolescence
- Spanish children age increases to 17 but levels out at 15 for English children
- average digit span lower for Spanish children than English
- however Spanish names for numbers are longer

A strength is that the researchers used several standardised procedures
For example, the digits were read aloud at a constant rate of one per
second for every participant.
These procedures ensured that the
experience of the study did not vary greatly from one participant to
enother.
This means the outcomes could not be attributed to differences
in how the procedure was conducted
The use of standardised procedures helped to control potentially
confounding variables and therefore contributed to a reasonable degree of internal validity.

However, the procedure lacked control in some areas. For instance, the researchers report that the children 'did not present impairments'
This means the children were not directly tested and the researchers relied upon the children or their parents to divulge any hearing, reading or other cognitive impairments.
Given that any such impairments could influence performance on the digit span task, this may have seriously undermined the validity of the study.