Methodological differences between Glenberg et al (1998) and Rae (2011)

In summary, Glenberg et al. (1998) found a distraction effect on word-list recall but Rae (2011) did not. There may be multiple reasons why findings from the two studies do not agree but two key differences in methodology stand out and thus are discussed in detail below.

2.1.7.1 Visual distractor

Glenberg et al. (1998) and Rae (2011) both asked their participants to recall word-lists under static and dynamic distraction, but whilst Glenberg et al. used a semantic-rich distractor, Rae did not. It is not possible to tell whether an idiosyncratic semantic aspect of Glenberg et al.’s movie-clips was responsible for the resulting

84 distraction effect. That is, Glenberg et al.’s reported effect may be specific to

recalling words whilst watching a silent Charlie Chaplin movie versus looking at a sunset picture rather than a more generalisable explanation that visual distraction disrupts memory. Participants were asked to watch a 30s silent movie clip during recall of one word list. Recall of the next word list was accompanied by a different 30s clip from the same movie. It is therefore feasible that this continuation of movie clip created a distraction rich with semantic content but specific to the movie. This is because a series of 30s movie clips, from the same movie, are perhaps semantically associated to each other in a way that, for example, a series of moving coloured boxes are not. The Charlie Chaplin movie clips have rich visual scenes, each consisting of numerous visual details that can be semantically linked back to (by a participant) from the next movie clip presented in the next distraction condition. In contrast to Glenberg et al.’s semantic-rich distractor, Rae presented Dynamic Visual Noise (DVN) which is a semantically-neutral visual distractor developed by Quinn and McConnell (1996). Based on optimal parameters determined through memory tests run by the developers, Rae’s DVN consisted of a 700 x 700 pixel field of black and white squares (10 x 10 pixels per square) which changed from black to white to black at a rate of 291 per second. The black and white colour change gives an effect similar to white noise on a television screen. Recall under DVN can be contrasted to

85 that under Static Visual Noise (SVN). SVN is a freeze frame of DVN, Figure 1

provides an example SVN image.

DVN has been widely tested and shown to have negative effects on cognitive processes, including memory. For example, Anderson et al. (2017) investigated the role of visual imagery and executive processes on recall of autobiographical

memories. Participants were presented with an on-screen cue word surrounded by a field of DVN, or not, and asked to describe an autobiographical memory associated with the word. The DVN screen remained throughout the retrieval and reporting period. Participants in the control condition were presented with the cue word on a blank white screen. Reponses to the cue words were recorded and coded (a random sub-sample showed high inter-rater reliability). Memories were coded as ‘specific’ (a single specific event), ‘erroneous’ (for example, non-specific repeated events) or ‘omitted’ (no memory was recalled). DVN, compared to blank screen, significantly decreased the number of specific memories, significantly increased the number of erroneous memories and, had no effect on omissions. This pattern of distraction effect is similar to that discussed in Chapter 1 (for example, as reported by Perfect et al. 2012 when distraction was in the form of moving coloured boxes). DVN has been reported to disrupt a range of cognitive processes including recognition memory

86 (Santana et al., 2013), food cravings (Kemps & Tiggemann, 2013), digit-sequence recall (St Clair-Thompson & Allen, 2013), memory of a peg-word mnemonic

(Andrade et al., 2002), identifying visual changes in patterns (Dean et al., 2008), high imagery words (Parker & Dagnall, 2009) and when comparing performance under DVN to SVN (McConnell & Quinn, 2000; Quinn & McConnell, 2006). Throughout the thesis, the term DVN is used specifically as a reference to Quinn and McConnell’s (1996) black and white flickering squares.

In summary, there is clear evidence that DVN compared to blank screen or to SVN interferes with retrieval processes. In contrast and not surprisingly, distraction effects based on Glenberg et al.’s (1997) unique dynamic and static material have not been reported elsewhere in the literature.

2.1.7.2 Multiple word-lists and list order

Glenberg et al. presented participants with multiple word-lists (10 15-word word-lists) whereas Rae presented one single list (36 word-pairs). Participants studying and recalling multiple lists may be more vulnerable to proactive interference (PI, for a review, see Anderson and Neely, 1996). Proactive interference describes a phenomenon whereby previously studied information can interfere with the recall of recently studied information. For example, participants studying and recalling words from the 10th _{list in Glenberg et al.’s study had previously studied 9 other lists}

consisting of a total of 135 words. Speculatively, it would be surprising if those 135 words had not in some way interfered with recall of words from the 10th _{list. In}

contrast, recall of their 2nd _{presented list would have had interference from only one}

87 One theory as to why PI builds up across multiple lists is that participants become unable to distinguish whether a recalled word came from the most recent target list or, from an earlier list (for example, Bennett, 1975; Wixted & Rohrer, 1993). This is at most a minimal possibility with Rae’s single list study because during the half-hour experimental slot, participants were not asked to study any other material prior to studying the single list. Whilst Glenberg et al. briefly note that there was no list effect or interaction with list and distraction, it is not clear how they analysed these data. If analysis was based on mid-list recall alone they may have missed a PI effect because they did not take recall of the full lists in to account. If PI causes memory to be vulnerable to distraction, a distraction effect would be more likely for the last lists than the first lists. However, Glenberg et al.’s method of

presenting the distraction conditions was to randomly assort them across the 10 lists (within the boundary of 5 lists per condition), thus the first list under one condition is not necessarily the very first list presented to participants. At best, it can be

concluded that the first two lists recalled under the static control condition will have had fewer preceding lists than the last two lists recalled under the same condition.

Furthermore, Glenberg et al.’s study included 33 participants but the number of permutations of fully randomising the presentation of 10 lists under two conditions is 252. The authors provide no details of the randomisation of lists thus there is no way of knowing whether this was successful.