Method

2.3.1.1 Power calculation

2.3.1.1.1 Power throughout the thesis

Various effect sizes for both the effect of eye-closure and visual distraction on memory have been reported (please see Chapter 3 section 3.2 for an in-depth review). As classified by Cohen (1992), the magnitude of these sizes range from medium to very large (d’s for example between 0.50 and 1.20). Power calculations for Experiments 1 through to 8 were therefore based on detecting medium to large main effects of distraction (d = 0.80 or, f = 0.40) with a minimum power of .80. At times, a lower power value of .80, rather than a higher value of .95, was used as a practicality. This was to encompass periods of time throughout the year when it is notoriously challenging to recruit participants but when it remains crucial in the time- limited scheme of the thesis work to continue to collect data (such as end of term and academic holiday periods).

A priori power calculations were carried out using G*Power version 3.1.9.4 (Faul, Erdfelder, Lang, & Buchner, 2007) and are reported separately for each experiment throughout the thesis.

3 _{A third recall condition of eye-closure was also included however, post-test inspection revealed a}

coding error in the program: the condition had not been randomised. As eye-closure was not used elsewhere in the thesis, these data were therefore dropped from analysis.

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2.3.1.1.2 Experiment 1 power

Experiment 1 explored the main effect on recall of DVN compared to SVN. The distraction condition was presented as a within variable. Power analysis to examine the difference between two dependent means with an effect size of d = 0.8 and power 0.95 indicated the need for 23 participants in the total sample.

2.3.1.2 Participants

Thirty-nine participants (24 females), average age 25.9 years (SD= 9.33) took part for course credit or as a paid volunteer. All participants had normal or corrected to normal vision and were fluent English speakers. All participants were made aware that the study involved being exposed to onscreen flickering; anyone concerned about this effect or with a history of seizures or migraines was asked not to sign-up. One participant’s data (male, aged 28 years) was excluded from analysis due to failure to comply with procedural instructions (consistently looking away from the visual distractor when prompted) and another (female, aged 20 years) was

incomplete due to being interrupted by a fire-alarm. Therefore, data were analysed from thirty-seven participants.

2.3.1.3 Design and Materials

The central design of Experiment 1 followed 2 (Distraction: DVN, SVN) repeated measures structure. Extended analysis, including all additional variables, followed a 2 (Distraction: DVN, SVN) X 3 (list order: first, mid, last list) X 3 (Word Position: recall of first 5, mid 5, last 5 words in each list) repeated measures structure.

2.3.1.4 Word-lists

The same material source as Glenberg et al. was used and 150 words were randomly selected from the 1,080-word Toronto Word Pool (Friendly et al., 1982).

92 This selection was used to randomly generate (without replacement) a unique set of 10 lists of 15 words for each participant. The order in which words were randomly presented for each list was digitally recorded so that post-test, each correctly recalled word could be coded as having originally been presented in the first 5, middle 5 or last 5 position of the list.

2.3.1.5 Filler task

To address recency effects in a similar way to Glenberg et al.’s design, a pool of 100 two-addend addition sums (e.g. 24 + 3 =) was created from which 10 sets of ten sums were randomly selected without replacement, for each participant.

2.3.1.6 Distraction conditions

Static (SVN) and dynamic visual noise (DVN) were presented on a computer screen using parameters set out by Quinn and McConnell (2006): each field

measured 700 x 700 pixels and consisted of a random pattern of ten x ten pixel blocks of black and white squares. This field was static during the SVN condition but appeared to flicker during the DVN condition as random pixel blocks changed colour from black to white to black at a rate of 291 per second. The surrounding

background screen was white. The order in which SVN and DVN were presented was randomised across the 10 word-lists.

2.3.1.7 Procedure

Participants were told they would be shown several lists of words, one list at a time and one word at a time and later be asked to recall the words one list at a time. To comply with the school of Psychology’s ethics committee’s approval for this series of experiments, participants were also reassured that the study had been designed

93 to make it difficult to recall all of the words on the lists so not to worry if they could not remember many.

Participants studied 10 lists of individual words, each word presented visually for 2s, with an inter-stimulus blank screen interval of 150ms. Words were centred in the middle of the screen and appeared in black capital Arial-font, size 18. A filler task of a series of 10 sums immediately followed the presentation of each word-list; each sum was shown centre screen for 2s at a time with a 200ms inter-stimulus interval between sums. Participants were asked to call out the solution to each sum as it appeared on the screen: all participants answered all sums. Participants were also told that their answers to the sums were not being recorded so not to worry if their answers were incorrect. Following the last sum an onscreen instruction reminded participants to keep looking at the screen. This was followed by a fixed 30-second recall period. During the fixed recall period, participants verbally recalled words from the word-list they had just seen whilst looking at a screen which displayed SVN or DVN for the entire 30 seconds. Each participant recalled five word lists under DVN and five under SVN, the order of DVN and SVN was randomised within the

boundaries of there being 10 lists and participants were not aware which recall condition would be presented with each list. The experimenter was seated adjacent to participants such that participants were unable to make eye-contact (without moving their head) with the experimenter during encoding or retrieval phases. This also enabled the experimenter to make sure participants were watching the screen throughout the retrieval phase.

Word-lists were randomised and because the experimenter could not clearly see the experiment screen, the experimenter was not aware of which words had been presented in which list. The experimenter wrote down words as the participant

94 called them out; there was no issue with matching speed of writing with calling out because although participants typically called out the first few words quickly, subsequent words were slow to follow.

The coding of participants’ word-recall took place after the experiment was completed. The experiment’s programme automatically recorded which words were presented in which serial order for each list and for each participant. Distraction condition of each list was also recorded. Words were coded as correct if they had been presented in the target list and incorrect if they had not.

Across all participants, four words were recalled outside the 30-second recall period and these were therefore excluded from analysis.