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Post No.: 0773illusions


Furrywisepuppy says:


I find illusions incredibly fascinating. They reveal so much about the inner workings of the brain. Illusions and hallucinations can affect every one of our five main senses – namely sight or vision, hearing or audition, smell or olfaction, taste or gustation, and touch or tactition.


Smelling and tasting are chemical senses, or about sensing chemical elements and compounds. Hearing and touching are mechanical senses, or about sensing pressures and vibrations; although touching also involves sensing for temperatures or thermoception (whether or not there is a separate sense for cold is contested), skin-stretch, and pain or nociception. Seeing is about sensing photons and/or wavelengths of light.


These five main senses are to sense the external world around us. But most of our senses are about sensing our internal states, like body awareness or proprioception, balance or equilibrioception, hunger, thirst, and mental senses like of the self. Experts disagree about the total number of senses that humans, or dogs, possess.


Visual or optical illusions can arise from our physical, physiological and cognitive processes or tendencies, and can manifest as ambiguities, distortions, paradoxes and fictions. We might perceive impossible objects, bistable images, illusory contours, motion after-effects, and many more kinds of optical illusions – several of which have been covered before in this blog, like the Ames room mentioned in Post No.: 0622. Pareidolia can result in seeing clear patterns or objects within random stimuli – quite often faces, like on some wood grain or clothing stains. The Dunstanburgh Castle illusion can trick us into temporarily seeing colour on a black and white image.


We intuitively tend to think that ‘seeing is believing’, yet there are numerous visual perception effects and illusions that demonstrate how we do not visually see things objectively but via the interpretations, assumptions and expectations, or heuristics and biases, present in our minds – despite so much brain power being dedicated to visual processing; or perhaps precisely because of it.


For humans at least, the visual system tends to override all the other senses, even though this can result in errors of perception. There’s for example the rubber hand illusion (or more generally body transfer illusions), which can also be achieved via virtual reality – this is where people can feel like they inhabit a body part or even entire body other than their own. Freaky! If you feed the view from someone of another sex in VR, while mirroring their bodily movements as closely as possible, as if you’re inhabiting their body – you can start to feel a little bit more like being the other sex. I would presume this malleability works when we appear to inhabit the bodies of people with different skin colours or heights too? Our cognition is, after all, embodied.


After you’ve been driving fast on the motorway/freeway for a long time then you suddenly enter an urban area and stop at the first traffic light, it can temporarily appear like the world is moving slowly backwards since our perceptions have adapted to moving forwards rapidly. Other examples of illusions of self-motion include when the train one is in stops at a station and then an adjacent train immediately moves off forwards, which can give the illusion that one’s own train has suddenly moved in the opposite direction.


We shouldn’t always believe what we see; and this includes touched-up photographs and manipulated videos. And we shouldn’t always disbelieve what we cannot see, like invisible-to-the-naked-eye atmospheric greenhouse gases or microscopic viruses.


There are many auditory illusions too, including the octave illusion, scale illusion, Shepard-Risset glissando, tritone paradox and Franssen effect, to name just a few.


We often hear clocks alternating between ‘tick’ then ‘tock’ when they’re not actually alternating in sound at all i.e. they only go ‘tick’, or only go ‘tock’. The McGurk effect – where we hear ‘fa’ or ‘da’ instead of ‘ba’ depending on how we see a person’s mouth moving – shows us that when sight and sound are incongruent, the brain will interpret the world as if it is congruent, with usually the visual signal overriding the auditory signal.


And even when we know that we’re perceiving illusions that don’t match the true objective reality, our brains cannot help but still rely heavily on our prior beliefs and expectations, and so we cannot help but still hear ‘fa’ or ‘da’ instead of ‘ba’, or see a parallel-walled room, for instance.


Not an auditory illusion but there is an infrasound ‘frequency of fear’ that cannot be heard yet can be felt as unsettling or supernatural for humans.


Auditory hallucinations are the most common kind of hallucination. These can be first-person or hearing your own thoughts as if spoken by someone else; second-person or as if hearing a separate voice talking to you; or third-person or as if hearing voice(s) talking about you (like what Senua hears in the videogame Hellblade: Senua’s Sacrifice). If those third-person voices are critical and persistent then they’re considered derogatory hallucinations, and it’s a reliable sign of schizophrenia.


It stems from a problem with distinguishing between internally generated versus externally generated activity i.e. voices from one’s internal monologue versus voices from the external environment. A test for psychosis (although not a totally reliable one) is seeing if you can tickle yourself – most people can’t because they can recognise it as self-generated.


When it comes to smell, anyone’s nose can be fooled by olfactory illusions according to how something is labelled. For example, a particular odour could be considered pleasant if labelled as ‘Christmas tree’. Nice. Yet the exact same odour could be considered unpleasant if labelled as ‘toilet cleaner’. Yuck.


Olfactory hallucinations, or phantosmia, most often relate to smelling ‘burnt’ smells like smoke or burnt toast.


The five basic tastes are sweet, sour, salty, bitter, and umami. There are others though, and these include spicy hotness or pungency, astringency, metallicness, coolness, numbness, fat taste, calcium, and heartiness or kokumi.


And the perception of flavour depends on taste, as well as smell, sight, and one’s expectations and prior experiences – with a stuffed nose and a blindfold on, apples, onions and potatoes will be hard to distinguish, which could count as a taste illusion. The sense of taste can be easily overridden by other information. Well humans have a weak sense of taste full stop (and I mean that in multiple ways! Woof!)


The cutaneous rabbit illusion is an example of a touch or tactile illusion. Or you could try the Aristotle illusion by crossing your fingers and touching a small spherical object, like a dried pea or ball bearing, with the inside part of your crossed fingers. It should feel like you’re touching two peas; although this doesn’t work on everybody. Close your eyes to maximise the effect.


One can feel warmer after drinking alcohol even though, because the overall reaction is exothermic, one is actually losing heat rather than gaining it.


…For some technical definitions, an ‘illusion’ is a misinterpretation of sensing that generally anyone can experience.


A ‘hallucination’, meanwhile, would stem from what would be considered a malfunction somewhere in the brain. Rather than a misinterpretation of something out there, one would sense something that seems very real from completely nothing out there. Hallucinations are a main symptom of psychosis.


A ‘delusion’ is when one unquestionably believes in something that demonstrably isn’t true. Delusions are another main symptom of psychosis. They similarly signify a compromised ability to distinguish between what’s real or not.


Delusions come in various forms, including the belief that one is being persecuted (e.g. that everyone is part of a fuzzy shadowy plot to kidnap oneself), the pomposity of grandiose feelings (e.g. believing that one is a world-renowned business genius when one is not), believing that one’s loved ones have been replaced by impostors (Capgras delusion), that different people are the same person but in disguise (Fregoli delusion), or one is a walking corpse (Cotard’s delusion)! Even after being presented proof that one is mistaken, delusions are quite stubborn to shift – more so compared to something like hearing voices.


So much – from stress, sleep deprivation, psychoactive drugs like cannabis, Lyme disease, brain tumours, dementia, bipolar disorder, and more – can trigger either hallucinations or delusions.


The brain expects something to happen, something different appears to happen, and therefore an explanation needs to be found to resolve the dissonance. And it starts to become problematic if those solutions rely on preposterous or improbable conclusions.


A delusion may suggest the nature of the problem producing it. For instance, if you interpret harmless background mutterings as about you, it could indicate a problem with your brain’s threat-detection system. If you are depressed, you may interpret innocent gestures of people moving away from you just as you go near them as due to you being repulsive or unlovable. However, mental illness isn’t the only explanation for delusions because we get those who believe in a flat Earth, those who claim to sense their deceased relatives around them, or those who believe in karma and a ‘just world’, for instance. What’s considered ‘culturally normal enough’ is thus a factor and, psychopathologically, they’ll only be classed as delusions if one’s unrealistic beliefs are inconsistent with the rest of one’s belief system – hence why religious people who believe they can hear the voice of their god(s) aren’t considered delusional. This highlights that what’s considered ‘normal’ or ‘abnormal’ has less to do with fundamental facts than whatever is the general consensus or common-enough belief or practice of a particular time and place.


We could also possibly include, as illusions or delusions of the mind, the many cognitive or logical fallacies that we all frequently fall for, like reading too much into coincidences, or how hindsight makes it appear like we knew for certain in the past what we really only knew for certain now. Indeed a lot of the above delusions fall into this category, like the paranoia that certain people are out to get or spite us when they’re not.


Time or temporal illusions include the feeling that time goes fast when we’re having fun but drags on when it’s meh. The oddball effect happens whenever salient stimuli are perceived to accompany longer time durations. The flash-lag effect occurs when a moving object and a flashing non-moving object that are aligned with each other are perceived to be displaced from one another. The kappa effect arises when we judge the elapsed time between a sequence of consecutive sensory stimuli coming from different locations – we tend to overestimate the elapsed time between two successive stimuli when the distance between them is large enough, and vice-versa.


There’s also saccadic masking or saccadic suppression, which occurs when we move our eyes from looking at one object to another object, and the brain fills in the blurred transition by assuming that the destination view was occurring during the transition. This can be seen in the stopped-clock illusion, where the second hand on a ticking clock appears to hang for a moment when you first look at it, or, when flipping between looking at your left eye then right eye in front of a mirror, you won’t be able to see your eyes move at all. This chronostasis effect can possibly work with auditory and tactile information too.


All in all, if one’s senses appear to be telling the brain something, the brain will find it difficult to override that sensory information, even though the brain is considered to have the ultimate responsibility and final say for all of one’s decisions and behaviours. It’s metaphorically like the master of a gigantic vessel attempting to override his/her pilot, who is assumed to know better about his/her specialty – the master just ends up trusting the pilot.


And only then do you realise you were just having a dream…




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