Visual memories and sensory experiences

It seems people who lose vision use information that transfers between the senses to retrieve visual memories. And that their visual memories decay when they have reached a certain level of experience in the other senses. (See our blog for the scientific approach, the crossmodal correspondences between the senses, and Decay and maintenance of sensory memories). But what happens when people who are born blind gain vision and then lose it again?


I have invited P.B. to share his experiences of visual memories and sensory information when going from blind to partially sighted and back to being blind again. P.B. was born blind with some light perception in one eye. After surgery and other medical treatments, he had gained about 7% vision in the other eye at three and a half years old. P.B. does not remember this shift from being blind to being partially sighted. Then, in his early twenties, P.B. had an accident that rendered him totally blind in both eyes. P.B. thinks of himself as a sighted person who happens not to see. He visualises when making plans. And his dreams are always visual. P.B. approved this text before we posted it on our blog.


P.B. has several visual memories from when he was little. From the house he grew up in, for example, he remembers the light from a chandelier hanging over the coffee table in the living room, the patterned wallpaper in his room, and the countries on the world map hanging on the wall. And he remembers the colours on the outside walls, the doors, and the window frames.


Today, when he has no new visual input, P.B. creates visual images based on his memories and knowledge. For example, that of a White Swiss Shepherd Dog working as a guide dog from his memories of both the white colour and the German Shepherd Dog. As well as his knowledge of guide dogs.


His visual memories are typically triggered by somebody describing how something looks, like a bright red sunset – not by information from the other senses.


P.B.’s visual memories “flash up almost like the flavour when eating or drinking”.


He has to decide not to focus on visual memories and images when talking to people: the memories are now 20 years old and people have changed. And his created visual images of what new people look like may be very wrong.


P.B. has to actively suppress his urge to retrieve visual memories or create visual images of people based on their voices.


He describes not having visual memories and images of spatial relations and distances. P.B. rather remembers them through his body. He walks around in the city centre with no vision, a podcast or some music in his ears, and shoes with a thick curved sole (which makes it difficult to feel the surfaces on pavements, streets, steps, floors, etc.). He does not count steps or any of that and pauses the podcast or music in his ears only when he feels he might get lost.


For P.B., sensory experiences include a variety of simultaneous sensations as well as visual memories and created images – they are multisensory. The forest, for example, is the sound of wind and trees, the texture of surfaces under his feet, scents, and the memories of colours. He zooms in on whatever attracts his attention: indeed, not on one piece of sensory information after the other in a certain order. For example, zooming in on a sudden shift from soft to hard texture under his feet.


An interesting sensory experience, according to P.B., is that of new flavours, the texture of the food, and the sound of crunch when chewing, He describes a cloudberry cream dessert as “not very sweet, but also not sour, light orange colour, and creamy texture”. But a redcurrant jelly only as “something wobbling on the plate”. He does not describe the flavour, scent, and/or feel in his mouth – merely how the jelly looks on the plate.


Was he not able to suppress his visual memories of jelly – did they take over?


When P.B. is sensory tired, he relaxes his senses by listening to “concentration music, like opera or prog rock where I can immerse myself and get absorbed by a different universe”.


It seems P.B. can maintain his visual memories and ability to create visual images through people’s descriptions of what something looks like. But, at the same time, these memories and images are distracting him from focusing on sensory information that is more relevant to him today with no vision, for example, people’s voices and the feel of wobbling jelly in his mouth, So is this, in fact, a negative spiral – that maintaining visual memories prevents experiences in the other senses, which in turn helps nurture the visual memories?


See our blog for Activities; especially 49-51.

Food for thought: taste, smell and flavour

Eating and drinking are a truly multisensory experience – flavour occurs when input from all senses is combined. Not just from two or three senses; like when admiring the sea or the botanical garden; when skiing on a cold winter day; or when playing with a kitten or a puppy. (See our blog for Multisensory processing.)


In this blog post, I have invited Dr Xinni Xua,b and Professor Thomas Hummela to explain the relationship between smell and taste (known as chemical senses), and the other senses too. Dr Xinni Xu specialises in ear, nose, and throat conditions, both as a clinician and a researcher. Professor Thomas Hummel’s research focuses on the diagnostics and treatment of olfactory / gustatory loss, the mechanisms involved in irritation of the upper airways, the olfaction in neurodegenerative disorders, and the interactions between the olfactory, trigeminal, and gustatory systems. Between them, they have published over 800 articles, books, book chapters, and abstracts. And received several awards for their work (e.g., the Young Surgeon Award and the European Chemoreception Research Organization (ECRO) for “Excellence in Chemosensory Research”).


aSmell & Taste Clinic, Department of Otorhinolaryngology, Universitätsklinik Dresden. bDepartment of Otolaryngology – Head & Neck Surgery, National University Hospital, Singapore.


Let’s start with a simple exercise. Think about one of your favourite foods. Why is it your favourite?


Perhaps some of the immediate things that came to mind were that you like the way it tastes, or that its flavour appeals to you. But are taste and flavour the same thing? These terms are often used interchangeably in common language. Biologically speaking, they mean different things.


Not just a matter of taste

Humans can recognise five fundamental tastes: sweet, sour, salty, bitter and umami (savoury). In the last decade, the taste of fat (oleogustus)1 and even water2 have been added to this list. The taste buds containing taste receptor cells that are responsible for detecting these tastes are located mainly on the tongue, but they can also be found in other areas such as the soft palate, epiglottis and upper esophagus.


The scientific meaning of taste, of gustatory function, is therefore rather narrow. Food is much more than just these few categories. For example, vanilla and chocolate ice cream both taste sweet, but at the same time, you would not say that they “taste” the same. Your ability to smell is what distinguishes between the two flavours.


The nose knows

Diagram of how flavour is synthesised by the brain, mouth, nose and ears
Figure 1: The senses in flavour (Xu & Hummel)

There are two ways that odour molecules reach the olfactory receptors high up in the nose. The first is by sniffing through the nose, which is called orthonasal olfaction. The second way is from the back of the mouth and through the back of the nose. This is termed retronasal olfaction. Retronasal olfaction plays a bigger role in flavour perception than orthonasal olfaction3 . The next time you eat, for example something fruity, try chewing first with your nose pinched and focus on the taste. Then, after some 15-20 seconds, release your nose. With the first part of the experiment, the experience may have come across as somewhat flat. In the second part of the experiment, the added dimension of smell from retronasal olfaction creates the perception of flavour. One reason why the sense of smell adds body to flavour is because humans can detect thousands of distinct odours, if not more, compared to our ability to detect only a few types of taste4. We have about 400 different receptor types for smell5. In addition, combinatorial encoding occurs in olfaction, in which each odourant is recognised by varying combinations of olfactory receptors6. This makes our olfactory sense significantly more intricate than the gustatory sense.


Another aspect of smell is that it is directly linked with emotions – neurologically speaking. The olfactory bulb, a structure at the base of the brain, receives olfactory signals from the nasal olfactory receptors. The olfactory bulb projects neurons directly to the limbic system, including the amygdala and hippocampus, which are responsible for regulating emotions, memory and behaviour. This is why odours can involuntarily evoke memories of events past and feelings associated with them. This experience has a name: the Proustian effect, coined after the French author Marcel Proust. In his tome “À la recherche du temps perdu (Remembrance of things past)”, he famously reflected on how a morsel of madeleine soaked in tea brought forth a heady rush of vivid memories from the past and whimsical nostalgia.


“Mouth-feel”

A big part of food experience is how food feels in the mouth. This is known as somato-sensation. Receptors from the trigeminal nerve in the oral cavity are responsible for this, and they include mechanoreceptors to detect texture and tactile stimulation, thermoreceptors to detect temperature and nociceptors detect noxious stimuli. Mouth-feel is what allows us to savour the creaminess of a pudding, the crunch of crisps, the prickle of carbonated drinks and the spiciness of curries. These sensations can influence our preference or rejection for foods of certain temperatures or textures. Somato-sensation becomes even more important in improving the hedonic quality of a meal for people who have lost their sense of smell or taste.


In short, flavour is the synthesis of individual tastes, smells and feels into an overall perception, modified by mastication sounds during eating, the appearance of the food and numerous environmental factors7. Yet at the same time, flavour is more than the sum of its parts, because it is shaped by our individual experiences, cultures and preferences. Hence the reason why the flavour of your favourite food appeals to you is really a matter of personal taste.


See our blog for Activities; especially 40-42.


Some suggestions for further listening, reading, and watching:

Losing the sense of taste

Madeleines and memories – the Proust Effect

Overview of Smell and Taste Disorders

This is What it’s Like to Live in a World Without Smell

Taste Test

What is life like without smells

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1Running, C. A., Craig, B. A., & Mattes, R. D. (2015). Oleogustus: The Unique Taste of Fat. Chemical Senses, 40(7), 507-516. DOI: 10.1093/chemse/bjv036

2Zocchi, D., Wennemuth, G., & Oka, Y. (2017). The cellular mechanism for water detection in the mammalian taste system. Nature Neuroscience, 20(7), 927-933. DOI: 10.1038/nn.4575

3Hummel, T., & Seok, H. S. (2016). Orthonasal and retronasal perception. In: E. Guichard, C., Salles, M. Morzel, and A.-M. Le Bon (eds). Flavour: From food to perception [pp 310-318]. Oxford: Wiley Blackwell. DOI: 10.1002/9781118929384.ch13

4Dunkel, A., Steinhaus, M., Kotthoff, M., Nowak, B., Krautwurst, D., Schieberle, P., & Hofmann, T. (2014). Nature’s Chemical Signatures in Human Olfaction: A Foodborne Perspective for Future Biotechnology. Angewante Chemie International Edition, 53(28), 7124-7143. DOI: 10.1002/anie.201309508

5Mainland, J. D., Keller, A., Li, Y. R., Zhou, T., Trimmer, C., Snyder, L. L., Moberly, A. H., Adipietro, K. A., Liu, W. L. L., Zhuang, H., Zhan, S., Lee. S. S., Lin, A., & Matsunami, H. (2014). The missense of smell: functional variability in the human odorant receptor repertoire. Nature Neuroscience, 17(1), 114-20. DOI: 10.1038/nn.3598

6Firestein, S. (2001). How the olfactory system makes sense of scents. Nature, 413(6852), 211-218. DOI: 10.1038/35093026

7Spence, C. (2020). Multisensory Flavour Perception: Blending, Mixing, Fusion, and Pairing Within and Between the Senses. Foods, 9(4), 407. DOI: 10.3390/foods9040407