Alternative Facts and Realities: How the Brain Anticipates Perception

The Russian physiologist Ivan Pavlov is best known for his studies on classical conditioning showing that dogs repeatedly presented with a combination of food and a sound would subsequently salivate upon hearing the sound alone, in anticipation of the meal. The combination of the two stimuli – food and sound – over time “conditioned” the dogs’ brains to link these two stimuli. A variation of this experiment was performed on human subjects by Ellson and published in the Journal of Experimental Psychology in 1941. In Ellson’s study, 40 subjects were “conditioned” over time by hearing a sound and seeing a light. Ellson later on exposed the subjects to only the light, yet 32 of 40 subjects claimed to have also heard the sound. Ellson concluded that such conditioning could lead to hallucinations – the hearing of sounds which, objectively speaking, are not present.

Recently, the Yale University psychiatrist Philip Corlett and his colleagues conducted a very interesting variation on this earlier study by asking whether some people are especially vulnerable to having auditory hallucinations induced by conditioning. The researchers recruited four groups of study subjects: 1) Fifteen patients with severe mental illnesses who also regularly heard voices (an auditory hallucination), 2) fifteen patients with severe mental illnesses who did not hear voices, 3) fifteen individuals without any evidence of mental illnesses who also claimed to hear voices and 4) fourteen healthy individuals who did not hear voices. Group 3 consisted of voice-hearing psychics (“clairaudient psychics”) who identified themselves as such via their own websites, at psychic meetings, or referrals from other psychics. Another important innovation in Corlett’s study was the inclusion of brain imaging studies on all subjects, thus allowing the researchers to study functional brain responses when exposing them to auditory and visual stimuli. The researchers then repeatedly exposed the study subjects to a checkerboard image and 1 kHz tone while they were lying in the brain scanner. The subjects were asked to press one button to indicate that they heard the tone, and a second button if they did not. They were also instructed to press down the button longer, the more confident they were in having heard the tone.

After conditioning the subjects, the researchers then intermittently began to show them images of the checkerboard without playing the tone. As expected, many subjects indicated having heard the tone even when it had not been played. However, patients with severe mental illness and a history of hearing voices (group 1) as well as healthy psychics with a history of hearing voices (group 3) were significantly more likely to wrongly indicate that they had heard the non-existing tone. Members of these two groups were also more confident that their hallucination was actually real, since they pressed down the button for longer. Healthy subjects and patients with mental illness who did not have a history of hearing voices were comparatively more correct in identifying whether or not the tone was present. Importantly, when the researchers repeatedly showed the image without the tone, voice-hearing, mentally ill patients were unable to “update” their beliefs when compared to the other groups, whereas the psychics gradually recognized that the tone was non-existent.

Brain imaging showed that the brain regions which respond to sounds were activated by the auditory hallucinations, meaning the brain perceived the non-existent tone as being real! The researchers also found that the subjects who continued to perceive the non-existent tones and did not update their beliefs – even after repeatedly being exposed to the image without the tone – had reduced activation in the brain areas which help integrate and coordinate predictions and perceptions. This could suggest that suppressed activity in these brain regions may contribute to persistent voice-hearing or other hallucinations.

The study has some important limitations: 1) The sample sizes are quite small and the some of the finds – especially those related to the brain imaging – are often only borderline statistically significant; 2) as is the case in many behavioral brain imaging studies, it is difficult to establish cause and effect – was the reduced activity in the parts of the brain which coordinate and integrate perceptions the cause of the inability to update beliefs or merely a correlation; 3) tones are well-suited for conditioning experiments in the laboratory but in the real world, conditioning may occur via specific words or phrases and this could have greater bearing on understanding voice-hearing.

Future studies could therefore address these issues by increasing the sample size, introducing more complex stimuli such as phrases or words, and perhaps also ask other inter-connected questions. Are individuals who are prone to voice-hearing also more likely to have visual hallucinations and hallucinations of smell? Can magnetic stimulation of selected brain areas perhaps improve the ability to update false beliefs? Does conditioning by political, religious or cultural education also affect us in a way that we perceive our hallucinations? For example, would adherents of an extreme political ideology mis-perceive words uttered by political opponents because their brains are conditioned to expect a narrow spectrum of answers and they are unable to update their beliefs? The study by Corlett and colleagues provides some very interesting insights into how our brain anticipates reality due to conditioning which could have important implications for understanding the nature of hallucinations in mental illness and develop new targeted therapies. However, it raises even more fascinating questions which – if addressed in future studies – could have an even broader impact on understanding our perception.


AR Powers, C Mathys, PR Corlett. (2017). Pavlovian conditioning–induced hallucinations result from overweighting of perceptual priors Science, 357 (6351):596-600; DOI: 10.1126/science.aan3458


Note: An earlier version of this article was first published on the 3Quarksdaily blog.

Male Contraception

My recent essay for Aeon Magazine discusses the development of newer male contraceptives which may offer a degree of reliability and reversibility similar to that of female contraceptives. Male hormonal contraceptives have been tested in small clinical trials since the 1970s, but none of them have been approved for general use. Research funding agencies and pharmaceutical companies need to make the necessary investments and forge partnerships so that the stalled research in male contraception can be revitalized.

It is a fascinating area of research and I hope you enjoy reading  the Aeon Magazine essay.


I also encourage you to also read some of the original references to learn more about the research. Here is a list of key references and a couple of informative websites:


CONRAD (2011). “Male Hormonal Contraceptive Trial Ending Early

Gifford, B. (2011). “The Revolutionary New Birth Control Method for Men.” WIRED

Glasier, A. F., R. Anakwe, et al. (2000). “Would women trust their partners to use a male pill?Human Reproduction 15(3): 646-649.

Heinemann, K., F. Saad, et al. (2005). “Attitudes toward male fertility control: results of a multinational survey on four continentsHuman Reproduction 20(2): 549-556.

Lidegaard, O., E. Lokkegaard, et al. (2012). “Thrombotic stroke and myocardial infarction with hormonal contraceptionNew England Journal of Medicine 366(24): 2257-2266.

Matzuk, M. M., M. R. McKeown, et al. (2012). “Small-molecule inhibition of BRDT for male contraceptionCell 150(4): 673-684.

Mruk, D. D., C. H. Wong, et al. (2006). “A male contraceptive targeting germ cell adhesionNature Medicine 12(11): 1323-1328.

Nieschlag, E. (2010). “Clinical trials in male hormonal contraceptionContraception 82(5): 457-470.

Nieschlag, E. (2013). “Hormonal male contraception: end of a dream or start of a new era?Endocrine 43(3): 535-538.

Trussell, J. (2011). “Contraceptive failure in the United StatesContraception 83(5): 397-404.

Youssef, H. (1993). “The history of the condomJournal of the Royal Society of Medicine 86(4): 226-228. (PDF)



Parsemus Foundation:

Male Contraception Information Project:

Resisting Valentine’s Day

To celebrate Valentine’s Day (as a geeky scientist), I decided to search the “Web of Science” database for published articles with the phrase “Valentine’s Day” in the title. The article with the most citations was “Market-resistance and Valentine’s Day events” published in the Journal of Business Research in 2009, by the authors Angeline Close and George Zinkhan. I had never heard of the journal before, but the title sounded rather interesting so I decided to read it.

The authors reported the results of a survey of college students and consumers conducted in 2003-2005 regarding their thoughts about gift-giving on Valentine’s Day:

1) Most males (63%) and some females (31%) feel obligated to give a gift to their partner for this holiday

2) Males in a new relationship (i.e. less than six months) feel most obligated (81%), females in a new relationship are the second most obligated group (50%)

3) Less than half of males (44%) in a more established relationship feel obligated, and this number is even lower for females in more established relationships (13%)


The authors also conducted interviews using open-ended questions and reviewed diaries and E-diaries to investigate whether people indicated a “resistance” to giving gifts. They found that people expressed three different types of resistance, either opposing or severely limiting the giving of gifts (gift resistance), resisting the purchase of gifts (retail resistance) or broadly opposing the Valentine’s Day business in general (market resistance). All of these forms of “resistance” appeared to be connected to an anti-consumption attitude, the desire to not be drawn into a culture of excessive consumerism.

Here are a couple of quotes from the participants:

Valentine’s Day is a marketing strategy by the flower and candy companies. It’s a cheesy, overblown, stupid “holiday” to force you to spend money on each other.

Valentine’s Day is a way for retailers to get you to spend money in their stores. People get caught up in the B.S. and I should not have to spend extra to show I care, and my girlfriend agrees. But we both still spent plenty!

The survey results indicating differences between men and women are interesting but the paper also shows that even though the majority of people in the US might feel obligated to give each other gifts on Valentine’s Day, there is a strong anti-consumption attitude. People are not willing to succumb to the pressure to spend a lot of money that ultimately benefits retailers. They are instead expressing their affection for each other in ways that do not involve purchasing expensive gifts.

If you forgot to get a Valentine’s Day gift for your partner or spouse, just print out a copy of this paper and give it to them instead, saying that your lack of gift-giving is your expression of anti-consumption resistance. If that person is just as geeky as you are, you might be able to pull it off.

There is one caveat: The Journal of Business Research is not open access, so you may hit a paywall asking for $31.50 to read the article, which is more than a typical box of chocolates. Don’t panic, fortunately, you can read it for free here.


Image credit: Early 20th century Valentine’s Day card, showing woman holding heart shaped decoration and flowers, ca. 1910 – via Wikimedia Commons – Public Domain

Close, A., & Zinkhan, G. (2009). Market-resistance and Valentine’s Day events Journal of Business Research, 62 (2), 200-207 DOI: 10.1016/j.jbusres.2008.01.027