Conceived and designed the experiments: DBT PB. Performed the experiments: DBT. Analyzed the data: DBT. Contributed reagents/materials/analysis tools: DBT PB. Wrote the paper: DBT PB.
The authors have declared that no competing interests exist.
Although forgetting is often regarded as a deficit that we need to control to optimize cognitive functioning, it can have beneficial effects in a number of contexts. We examined whether disrupting memory for previous numerical responses would attenuate repetition avoidance (the tendency to avoid repeating the same number) during random number generation and thereby improve the randomness of responses. Low suggestible and low dissociative and high dissociative highly suggestible individuals completed a random number generation task in a control condition, following a posthypnotic amnesia suggestion to forget previous numerical responses, and in a second control condition following the cancellation of the suggestion. High dissociative highly suggestible participants displayed a selective increase in repetitions during posthypnotic amnesia, with equivalent repetition frequency to a random system, whereas the other two groups exhibited repetition avoidance across conditions. Our results demonstrate that temporarily disrupting memory for previous numerical responses improves random number generation.
Although forgetting is often regarded as a deficit that we need to control to optimize cognitive functioning, it can have beneficial effects in a number of contexts
Posthypnotic amnesia involves a suggestion to forget some type of information following hypnosis and can be strikingly effective at disrupting recognition and recall of both semantic and episodic information in highly suggestible (HS) individuals
All participants provided informed written consent and all procedures were performed in accordance with the approval of the Swedish Federal Human Subjects Agency (Etikprövningsnämden).
Eight low suggestible (LS) and twelve HS individuals, drawn from a sample of over 600 individuals
We measured RNG by having participants verbally respond to 50 ms 1 Hz auditory tones with 5000 ms interstimulus intervals with a random number from the range of 1 to 6
In a few moments I will dehypnotize you by counting backwards from 10 to 1. At 1, you will open your eyes and be wide-awake. Shortly afterwards, I'm going to ask you to complete the same number task that you did before. However, when you perform the task this time, you will find that whenever you hear one of the auditory tones you will immediately forget the last number that you stated and all of the numbers that came before it. Forgetting your previous responses will not affect your ability to state numbers when you hear the auditory tones. You will remain this way until I say “Okay, you can remember previous numbers now” [post-cancellation cue]. When I say those words you will again be able to remember what happened during hypnosis as well as the numbers you stated prior to each auditory tone.
The experimenter then administered a hypnotic de-induction and participants completed the task a second time (posthypnotic amnesia condition) and once more after the cancellation of the suggestion (post-cancellation control condition). Upon completion of the latter condition, participants provided self-reports regarding the magnitude of forgetting of previous responses in the RNG task during the posthypnotic amnesia condition relative to the post-cancellation control condition (1 = no forgetting to 4 = complete forgetting); this score was used as a measure of self-perceived magnitude of response to the posthypnotic amnesia suggestion.
RNG performance was evaluated by the analysis of first-order differences (FODs) computed from sequential responses. The analyses were focused on repetitions (FOD = 0) and descending and ascending counting (FOD = −1 or +1, respectively). In order to evaluate whether participants' responses deviated from random responding, we also contrasted participants' FODs with FODs computed from a single set of 1000 simulated vectors of 66 random numbers from the range 1 to 6 (
Self-reports of the perceived magnitude of forgetting of previous responses during the completion of the RNG task in the posthypnotic amnesia condition were analyzed with a Kruskal-Wallis test because the data violated the assumption of homogeneity of variance. This analysis revealed a main effect of Group,
Repetition avoidance (reduced FOD 0 counts relative to the simulated data) can be seen in
The data (
A mixed-model ANOVA on FOD −1 counts (descending counting bias) revealed a main effect of Condition,
A mixed-model ANOVA on FOD +1 counts (ascending counting bias) revealed a main effect of Condition,
Our results show that, in a subset of HS individuals, temporarily disrupting memory for previously generated numbers reduces repetition avoidance during RNG, thereby increasing the randomness of responses. In particular, we show that during posthypnotic amnesia HDHS, but neither LDHS nor LS, participants exhibited a selective increase in repetitions, resulting in equivalent performance to a purely random system. These results provide evidence that repetition avoidance during RNG stems from the retention of previous responses in working memory (see also
The observed variability in responding among HS individuals is consistent with previous research. That the improvement in RNG during posthypnotic amnesia was only present in HDHS individuals fits with previous studies showing greater responsiveness to posthypnotic suggestions in this subgroup
Notably, the posthypnotic amnesia suggestion did not reduce counting biases, probably because counting was not a prominent bias in the present sample at baseline. Alternatively, repetition avoidance may be a function of one's