In the study of working memory, Baddeley and Hitch used an experimental procedure known as a dual task technique. This is when a participant is asked to perform two tasks simultaneously to see how doing so affects one's overall performance.  In the Working Memory model, there are two key modalities - the phonological loop, which is where auditory processing takes place and the visuospatial sketchpad, where visual and spatial processing takes place.  When we use both of these STM stores, there is little interference.  When we try to do two tasks that use the same STM store, then it becomes very difficult, if not impossible, for us to do either task well. For example, it is possible to have a conversation (phonological loop) while driving your car (visuospatial sketchpad).  However, if you try to have a conversation while trying to read the study below, you would find that you were only able to do one of those tasks successfully - and not that well.

The following study wanted to see what happens when asked to carry out a dual task technique which focuses on the phonological loop.

Landry and Bartling (2011) conducted an experiment using articulatory suppression to test the Working Memory Model. The aim was to investigate if articulatory suppression would influence recall of a written list of phonologically dissimilar letters in serial recall.

The participants consisted of thirty-four undergraduate psychology students. The researchers used an independent samples design. The participants were tested individually. In the experimental group, participants first saw a list of letters that they had to recall while saying the numbers '1' and '2' at a rate of two numbers per second (an articulatory suppression task). The control group saw the list of letters but did not carry out the articulatory suppression task.

There were ten lists each consisting of a series of 7 letters randomly constructed from the letters F, K, L, M, R, X and Q. These letters were chosen because they don't sound similar. The experimenter presented one letter series at a time. The participants received an answer sheet with seven blanks in each row. Before the experiment started, each participant viewed one practice list in order to become acquainted with the procedure.

In the control group, the experimenter showed participants a printed list for five seconds, instructed them to wait for another five seconds, and then instructed them to write the correct order of the letters on the answer sheet as accurately as possible. This was repeated ten times. In the experimental group, participants received instructions to repeatedly say the numbers '1' and '2' at a rate of two numbers per second from the time of presentation of the list until the time they filled the answer sheet. This was also repeated ten times. Each trial was scored for the accuracy of recall. The trial was scored as correct if the letters were in the correct position. The experimenter then calculated the average per cent correct recall for both groups.

The results showed that the scores from the experimental group were much lower than the scores from the control group. The mean per cent of accurate recall in the control group was 76% compared to a mean of 45% in the experimental group. Although the difference in the means was large, the standard deviations were nearly identical with SD = 0.13 for the control group and SD = 0.14 for the experimental group. A T-test was calculated and found a significant difference of p ≤ 0.01.

The results supported the experimental hypothesis as the mean per cent of accurate recall in the control group was higher than the mean percent of accurate recall in the experimental group. In line with the Working Memory Model, articulatory suppression is preventing rehearsal in the phonological loop because of overload. This resulted in difficulty in memorizing the letter strings for participants in the experimental conditions whereas the participants in the control condition did not experience such overload.

The study is a well-controlled study with a high level of internal validity. A cause and effect relationship can be determined.

However, the nature of the study is rather artificial and thus lacks ecological validity.

The study supports the Working Memory Model and is easily replicable.  The findings are, therefore, reliable.