The Index of Intrusion Control (IIC): A guide to capturing individual variability in intentional intrusion control in the laboratory

Abstract

Intrusive memories can be downregulated using intentional memory control, as measured via the ‘Think/No-Think’ paradigm. In this task, participants retrieve or suppress memories in response to an associated reminder cue. After each suppression trial, participants rate whether the association had intruded into awareness. Using linear modelling, previous research has found that repeatedly exerting intentional control over memory intrusions reduces their frequency. This paper discusses the differences in methodology and analytical approaches used by studies in the past 10 years investigating intrusion control via the T/NT paradigm. In addition, by reanalysing published datasets, we demonstrate large individual variability within studies in the number of intrusions reported within each block of the T/NT task. Results revealed that the change in intrusion frequencies across time is not linear, but quadratic. We propose the Index of Intrusion Control (IIC) to measure the change in intrusion frequencies across time. Furthermore, we demonstrate how this metric has superior predictive value for subsequent forgetting effects, when compared to approaches used in previous studies. We conclude with recommendations for improving the validity of the design and results of future studies and streamlining methodology and analyses between studies investigating intrusion control in the laboratory.

A mindful approach to controlling intrusive thoughts

“…Using the IQR, as specified in the preregistered report, all participants with scores less than 100% were identified as outliers (No-Think recall range: 60-100%; Baseline recall range: 81.82-100%). These ceiling effects for the final recall are in line with several previous studies 49,51,52 and render the IQR as an ineffective approach. Therefore, we do not identify these cases as outliers and their data is included in the analysis.…”

“…One method could be to have the participant freely press a button if and when a target word intrudes during the presentation of a cue, rather than ask the question directly at the end. It would be of interest see if an alternative method of intrusion ratings produces comparable SIF effects to the traditional method employed in the current study (see 49 for methodological considerations in measuring intrusions in T/NT tasks).…”

“…(multiple regression model using 3 predictors: f 2 = 0.15, α = 0.025, 1 − β = 0.95) 48 indicated a sample size of N = 136 to detect the effects of MT on intrusion control and its moderation by executive functioning. The alpha level was adjusted via the Bonferroni correction to account for multiple testing on the two dependent variables to measure intrusions (total number of intrusions and Index of Intrusion control (IIC) 49 ; cf. analysis: pre-processing steps).…”

“…removing missing responses; M = 0.41%). From these responses, we calculated 2 measures of intrusions: (1) the total frequency of intrusions across the 10 blocks of the T/NT task and (2) Index of Intrusion Control (IIC) reflecting the change in the frequency of intrusions across the 10 blocks 49 . Increasingly negative values indicate a larger decrease in intrusions over time.…”