We may not have total control of what we will think of next, according to a new study which found that thoughts are influenced by the outside environment, sometimes even against our will.
The research, by San Francisco State University, found that the stream of consciousness is more susceptible to external stimuli than had previously been proven.
The study is the first demonstration of two thoughts in the stream of consciousness being controlled externally and against participants' will, researchers said.
"Our conscious thoughts seem protected from our surroundings, but we found that they are much more tightly linked to the external environment than we might realise, and that we have less control of what we will think of next," said Ezequiel Morsella, associate professor of psychology and co-author of the study.
Morsella and his team showed the study's participants 52 black-and-white images corresponding to familiar words of varying lengths - basic drawings including a fox, heart and bicycle.
Participants were instructed not to subvocalise (speak in the mind) each word or how many letters the word had. On average, 73 per cent subvocalised a word, and 33 per cent counted its letters.
"We triggered with our experiment not one but two different kinds of unintentional thoughts, and each thought required a substantial amount of processing," Morsella said.
"We think that this effect reflects the machinery of the brain that gives rise to conscious thoughts. When you activate the machinery - and it can be activated even by being told not to do something - the machinery cannot help but deliver a certain output into consciousness," Morsella added.
The study found that people were much more likely to experience counting subvocalisations of shorter words. For words with three letters, 50 per cent of participants reported counting. At six or more letters, the rate dropped to just over 10 per cent.
"It shows you the limits of the unconscious machinery that generates conscious thoughts - it seems that it can't count above four or five," Morsella said.
He added that the limits to the automatic triggers are not clear, nor is it understood why they exist.
Morsella said that the research has important implications for the study of psychopathological disorders that afflict people with uncontrollable repetitive thoughts or, more commonly, the inability to stifle an obsession.
"When people have a thought they can't control, this machinery may be at work," Morsella said.
"We're learning not only that the brain does work this way, but that unfortunately, under most circumstances, the brain should work like this," Morsella added.
The study was published in the journal Consciousness and Cognition.
