The Human Truth Foundation

Perception is Influenced By Expectation
You Can't Always Trust Your Senses

By Vexen Crabtree 2016

#epistemology #expectation #experiences #memories #perception #psychology #thinking_errors

Our expectations and our interpretation of sensory input form part of how we perceive the world. We don't just passively accept sensory information, we construct a synthesis between that and what we think we should be seeing1,2. The very things we see and hear, clear as daylight and right in front of our eyes, can be falsehoods caused by expectation3. We trust our senses far too much; we will fly into defensive and heated arguments at the mere suggestion that we saw something wrongly, and yet our Human faculties are unreliable and very prone to such invention. They say "few things are more dangerous to critical thinking than to take perception and memory at face value"4. One fascinating aspect of this is our enjoyment of drinks. For example studies have shown consistently that when people don't know which wine they are drinking they tend to enjoy the cheapest ones most, as judged by their taste, texture and smell. But if you add packaging then they rate the wines that are most expensive to be the best5. The effects of expectation are not always trivial however, and police psychologists such as Elizabeth Loftus have spent their lives educating investigators on the power of expectation over our senses. You simply cannot blindly trust what you see.

1. Top-Down Influences


Top-down processing describes conscious and subconscious thought that is driven by our higher faculties. Our desires, wishes, previously experiences and expectations are all facets of top-down processing. The unexpected role of top-down effects on perception became a hot-topic in cognitive research from the 1970s. According to two cognitive psychologists, Eysenck and Keane:

Towards the end of the 1970s, theorists argued that virtually all cognitive activity consists of interactive bottom-up and top-down processes occurring at the same time. Perception... might seem to be [an exception because it] depends heavily on the precise stimuli presented (and thus on bottom-up processing) [...] however perception is also much affected by the perceiver's expectations about to-be-presented stimuli.

"Cognitive Psychology" by Michael Eysenck and Mark Keane (1995)3

Psychiatric studies have shown consistently that expectation and active interpretation are a key and unstoppable part of our perception of the world. We don't just passively accept information from the outside world, not via any of our senses; we construct a synthesis between pure sensory input and what we think we should be seeing. That's why it is so essential to construct proper scientific studies, where human biases are controlled as much as possible. Areas where our brains get easily confused are often used by artists in their work, and sometimes knowingly abused by peddlers of paranormal misinformation. More frequently, it becomes an accidental part of the support for otherwise nonsensical notions about the world.1

An experiment had a mangled and unclear word played to subjects in three different contexts. In each round, the sound played to the subjects was exactly the same. The subjects all heard a different word depending on the words preceding and immediately following the mangled word. They didn't report "I think the word must have been..." - they reported "the word was...". Their brains filled in the expected word from its context, with the people themselves being unaware that this pre-processing took place. Context and expectation caused them to hear detail, where in reality there was none.2

It is not just random events, confusing correlations or data processing where our expectations cause us to have certain experiences in place of others. Our mental thoughts can influence the very objects that we see before us, overriding what is real or merging reality with fantasy. Donald D. Hoffman, cognitive psychologist, affirms that "vision is not merely a matter of passive perception, it is an intelligent process of active construction"6. After citing some more experiments and examples, Eysenck and Keane report on a particularly colourful demonstration of it:

Another illustration [...] comes in a classic study by Bruner, Postman, and Rodrigues (1951). Their subjects expected to see conventional playing cards, but some of the cards used were incongruous (e.g. black hearts). When these incongruous cards were presented briefly, subjects sometimes reported seeing brown or purple hearts. Here we have an almost literal blending of stimulus information (bottom-up processing) and stored information (top-down processing).

"Cognitive Psychology" by Michael Eysenck and Mark Keane (1995)7

Visual illusions betray the fact that what we think we perceive in the world is actually a result of subjective construction. We are given a representation of the world that looks to us to be coherent, but is in reality a hodge-podge of bits of evidence and guesswork. The real problem is that we trust what we think we see, without realizing that most of it is assumption intermingled with reality.

The brain seems to make a 'best guess' of a plausible filler and normally we notice nothing unusual. [...] There are numerous other illusions which suggest that what we are conscious of can be a distortion of what is actually there. [...] Some important parts of our conscious experience may be underpinned by the brain 'jumping to conclusions' or applying rules of thumb.

Saroj Datta (2004) in Toates, Romero & Datta (2004)8

In general the effect of expectation appears linked to psychosomatic effects such as the placebo and nocebo effect.

2. Expectation and Pain: The Placebo Effect

#expectation #nocebo #pain #placebo #psychology #UK

The association between the expectation of pain and the experience of it is well-established9. Ružic, Ivanec & Modic Stanke (2016) experimented with the experience of pain with four groups of patients, administering painful electrical stimulus and asking the patients to rate the pain. Before this, each group was told how powerful the stimuli would be. In all cases their experience of pain was correlated strongly with what they expected to receive rather than the pain they actually received. This mind-over-matter is very typical of a placebo or nocebo effect. The effect of expectation on pain has been studied for decades. The UK's National Health Service introduces the concept of the placebo effect with a description of a very typical experiment conducted in 1996:

Trivaricaine was a brown lotion to be painted on the skin, and that smelled like a medicine. But the students were not told that, in fact, trivaricaine contained only water, iodine and thyme oil - none of which are painkilling medicines. It was a fake - or placebo - painkiller. With each student, the trivaricaine was painted on one index finger, and the other left untreated. In turn, each index finger was squeezed in a vice. The students reported significantly less pain in the treated finger, even though trivaricaine was a fake. In this example, expectation and belief produced real results. The students expected the "medicine" to kill pain; and, sure enough, they experienced less pain. This is the placebo effect.


Many similar experiments have found that the placebo effect is effective in reducing pain simply due to psychological effects - the power of the mind to control our experiences. In a study of neural pathways, patients were told to lay in a scanner whilst being delivered painful electric shocks to their hand:

Book CoverHalf of the people were then supplied with a fake pain-relieving cream. Even though the cream had no analgesic properties - it was just a hand moisturizer - people given the pretend cream said the shocks were significantly less painful. The placebo effect eased their suffering. Wager then imaged the specific parts of the brain that controlled this psychological process. He discovered that the placebo effect depended entirely on the prefrontal cortex, the center of rational thought. When people were told that they'd just received pain-relieving cream, their frontal lobes responded by inhibiting the activity of their emotional brain areas (like the insula) that normally respond to pain. Because people expected to experience less pain, they ended up experiencing less pain. Their predictions became self-fulfilling prophecies.

"The Decisive Moment: How the Brain Makes Up Its Mind" by Jonah Lehrer (2009)11

Although the case above was controlled and safe, sometimes the placebo effect manifests itself in ways which has serious effects upon medical understanding. In the 1950s doctors operated on patients suffering from angina (which often leads to heart attacks) by bundling some blood vessels together that were near the heart, expecting to stimulate growth. The patients then suffered less pain and required fewer drugs, and could walk further without pain. It was discovered quite a while later in 1959 that the surgery wasn't actually making any difference to the blood vessels. The success was due to the effect of the patient's minds on their bodies. This was tested by telling people they were undergoing surgery for their heart and putting them to sleep for it, but, not actually doing it. These patients also showed progress as a result of the non-surgery. This was an early realisation of the power of expectation and psychology in medicine.12,13

For more, see:

3. Marketing Relies Upon the Effect of Expectation on Taste

The effects of expectation on the senses are now well-known by neurologists, critical thinkers and academics. It is also well-known in the food and drink industry, who spend a lot of money on marketing in order to raise your expectations about how well their products taste.

Take the examples reported on by a neurologist in "The Decisive Moment: How the Brain Makes Up Its Mind" by Jonah Lehrer (2009)5: Blind trials are those in which the subjects do not know which brand they are tasting. When it comes to wines, blind trials consistently show that the cheapest ones are rated highest according to smell, taste and texture. If you add the packaging so that it is clear which wines are the most expensive, then, those ones are rated as the favourites. The effect of branding is strong and genuinely improves the enjoyment of the product, because of people's expectations of those products. If you put a Coca Cola sticker on cheap coke, everyone rates that coke much better from its taste.

Our experiences are tied to our rational brain. Our sensory inputs are not driven purely by the outside world. Lehrer notes that we can often make better decisions (more realistic ones) when we have less information about brands! This is because our rational brain tricks us with a distorted awareness of the world which stems from clever marketing campaigns.

4. Subjectivism and Phenomenology: Is Objective Truth Obtainable?

#epistemology #perception #philosophy #solipsism #subjectivism

The problems with our perception of the world feeds into the overall problem of subjectivism:

Subjectivism is a problem of epistemology (theory of knowledge). The word describes the fact that we can only understand the world through our own senses and our own rational deliberations, in conjunction with our own limited experience in life. Our brains are imperfect organic machines, not a mystical repository of truth. Our senses are imperfect, our point of view limited, and the reality we experience is never the total picture. Our divergent contexts result in each of us interpreting, understanding and perceiving the world differently to one another even when looking at the same stimulus. Human thought is infused with systematic thinking errors. Our knowledge of absolute reality is hampered by our limited insights and imperfect brains, and we can never truly escape from the shackles of our own minds. Our total take on reality is a mix of guesses and patchwork. These problems have been debated by the most ancient philosophers, thousands of years ago, and no practical answers have yet been forthcoming.14.

"Subjectivism and Phenomenology: Is Objective Truth Obtainable?" by Vexen Crabtree (2017)