The study is well-planned and well-conducted. It addresses an important issue: clinical psychological treatments that either suppress or accept negative thoughts. 

Thought suppression is a specific psychological technique ('thought stopping') that has been practised since the 1970s on the basis of behaviour modification - not of Freudian theories. It is still effective, but only with certain non-intrusive and non-self-applied thoughts. The technique is based on the application of verbal punishment immediately after the person thinks it, or says they are thinking it. However, when these are self-intrusive, intrusive and intense thoughts, it is more difficult to make them go away.  

From an analysis of habitual behaviour, avoidance maintains the behaviour it follows, so also negative (emotionally aversive) thoughts, if avoided or tried to be eliminated - with distraction, thinking about something else, repetitive motor activity or counting - tend to increase. Several systematic reviews point to this effect [Abramowitz et al., 2001; Wand et al., 2020]. 

Later on, contextual therapies - especially Acceptance and Commitment Therapy (ACT) [Hayes et al., 2011] - have applied the opposite technique since the 1990s: eliminating the emotional effect of negative, repetitive, self-applied and intrusive thoughts. It consists, precisely, in accepting those thoughts, observing them, not rejecting them, not trying to remove them; just letting them pass, letting them flow, but at the same time getting on with our life and keeping on doing what we have to do, without paying any more attention to these thoughts. Together with other thought change techniques, this 'acceptance' has been shown to be very effective in decreasing discomfort, so that it eventually disappears or becomes unimportant to the individual. However, there is a wide range of techniques for suppressing negative thoughts.

Methodologically, several criticisms can be levelled at Mammat and Anderson's study. It presents a study of 120 people across 16 countries, and it is conducted online. There are less than 10 people per country; the variability and poor control of the experimental setup itself give little reliability to the results. This variability is evident in Figures 2 and 3, where individual data are plotted. In addition, the design is divided into four groups, so there are even fewer participants [per group]. Using participants from multiple countries does not, in this case, mean the results can be generalised, but rather the opposite, because of the poor representativeness and cultural variability it can introduce into the data. 

It is difficult for the experimenter to control whether the person is 'imagining/not imagining' a certain scene, as described by the authors. You can say participants are 'imagining' because they are given the stimulus immediately beforehand, but when they are 'not imagining', what are they doing - are they thinking about something else, are they distracted, are they looking away from the screen, doing an arithmetic problem, or recalling a poem? You cannot 'keep your mind blank', as the authors claim. Simply stating to a person "don't imagine the hospital", as the authors say in their example, already gives a stimulus to automatically think of a hospital, even if they don't want to. 

The scale for measuring 'emotional intensity' is a numerical scale, but it is qualitative and not continuous homogeneous. Midpoint 5 would indicate 'neutral' emotionality, but 1 as very 'aversive', and 7 as very 'pleasurable'. The scale should be from 0 to 10 points. Being from 1 to 7, with a midpoint of 5, the scale overestimates the changes in the lower range. 

In figure C, which represents the possible correlation between changes in affect and changes in vividness of the suppressed images, there should be homogeneous scales on both axes. In addition, using percentage change post-pre, rather than direct data, in all measures maximises the small changes that are present. 

An important difference from other similar studies is that here the authors use 'negative' words associated with pictures and are asked to rate the emotionality or vividness of the pictures and their recall, not the words. Typically, studies on suppression or acceptance of negative thoughts ask people to recall words or phrases, and to perform a task of suppressing the recall of those words. In their clinical application, the words are usually self-applied (e.g. "I am stupid", "I am worthless", "I am a coward") and here they are general words and images. 

The study is robust in terms of quality and data. The researchers have used rigorous methods to reach their conclusions. 

This study challenges a widely accepted consensus in the therapeutic community that suppressing negative thoughts is harmful. While the idea that suppression is counterproductive has been dogma, this research suggests that the reality may be more nuanced, highlighting that it does not always lead to negative outcomes. This seems to be partly related to the approach taken by third-generation therapies, such as Acceptance and Commitment Therapy (ACT), Mindfulness-Based Therapy (MBCT) and Dialectical Behaviour Therapy (DBT), which have particular approaches to thought suppression. 

However, it is important to note some limitations. The study may not address all situations and nuances, and its findings may not apply uniformly to all individuals or therapeutic contexts. In addition, more research is needed to fully understand the implications of these results. 

In terms of the impact on individuals undergoing psychotherapy, this study could provide therapists with a more balanced understanding of negative-thought suppression. It could offer additional tools to help people deal with their thoughts effectively, always taking into account the circumstances and context. However, it is essential that therapists continue to assess each situation individually and consider the limitations and complexity of this issue in their clinical practice.