Do my eyes deceive me? Sight and it's role in the Sensory Evaluation of food.

As many of you know, sight is one of the 5 human senses along with, taste, touch, smell and hearing. What many people underestimate is how critical sight is in food choice and acceptance.

Sight is usually the first sense activated in relation to food, in other words we usually see something before we smell or taste it. There are some exceptions; take that stinky cheese you have been treasuring in the fridge which shares a little bit of its aroma each time the door is opened!

Sight is often referred to as a primal sense in that it protects us from harm. If we see something that is mouldy, rotting, physically contaminated or even just an unusual colour it triggers us to think twice about eating it. For example, a green tinge in potatoes indicates the presence of a harmful toxin – most people know not to eat green potatoes but don’t necessarily know why. The green is actually chlorophyll which indicates that the potato has been exposed to sunlight, and it is in this area that the toxin ‘solanine’ becomes concentrated to harmful levels. Solanine is a natural defense mechanism of the potato to ward off fungus and pests and although fairly harmless to humans at low concentrations, if we were to eat lots of green potatoes we might detect a more bitter taste to the potato and experience nausea, vomiting and digestive problems.

Vision works by a stimulus activating receptor cells in the eye, namely rods that detect light and dark, and cones that detect colour. These receptors send a message to the brain which trawls through our bank of memories to identify what we are seeing and what our reaction to it should be; to eat or not eat for example.

Our eyes can however deceive us, or more to the point our brains can. When the brain trawls through our bank of memories it looks for traces of items that are similar rather than necessarily identical to what we are seeing. The brain can actually think it is seeing something that it is not which is referred to as an optical illusion. There are many well know illusions that you can try for yourself – here are some simple ones.

Rabbit-Duck Illusion

What do you see? Can you see both the rabbit and the duck?

You will only see either the duck or the rabbit at a time as your visual attention flips back and forth between the animals.

"Duck-Rabbit illusion". Licensed under Public Domain via Commons -

Kanizsa Triangle

In this illusion people will see a white triangle. This triangle doesn’t really exist; it is not physically drawn in with lines however the brain has essentially filled in the lines for so that we see the shape. The brain essentially likes to see whole or complete shapes.

"Kanizsa triangle" by Fibonacci - Own work. Licensed under CC BY-SA 3.0 via Commons -

Simultaneous Contrast Illusion

The grey bar in the centre is the same shade all the way across, however the changing shade of the background makes it appear to differ. If you cover up the background around the bar with your hands you will see that this is so.

"Gradient-optical-illusion" by Dodek - Own work. Licensed under CC BY-SA 3.0 via Commons -

Why is all of this important in the sensory perception of food?

When we explore appearance of food from a sensory perspective we look at a number of different things; colour, shape, size, visual texture. All of these characteristics can give us cues as to how a food will taste or feel when we eat it. e.g. if we see that something is overbrowned or burnt we tend to expect that it will be drier or more bitter to taste than normal.

One sensory study presented a plated meal to people and asked them to rate its visual acceptability. The meal was then put into a blender in its entirety and presented back to people. The visual acceptability ratings dropped massively as might have been expected but so too did the taste, aroma and texture acceptability levels. This highlights how vision is important not only in its own right but also has an effect on acceptability of food by the other senses.

Grocery retailers need to use packaging designs that are attractive to customers to lure them in. When food is unpackaged, such as loose fruit and vegetables, retailers need to be aware of people’s natural avoidance of blemished or misshapen produce and usually set specifications on the amount of blemishes in the produce they will accept from farmers.

Restaurants use plating techniques to present food to customers in a way that shows it off and is attractive to customers. It is well known that white plates help to highlight the food and draw focus to it, whereas patterned plates can distract from the food. Chefs will often arrange items in a certain order on the plate, or create different heights on the plate to drawn people’s attention to different parts of the dish.

Interestingly, when it comes to food consumption, people tend to serve themselves more food, and therefore eat more food when they use dishes that are a similar colour to the food. Dishes that contrast with the colour of the food tend to cause people to serve themselves less.

One of the most unique dining experiences you can have to see what effect vision has on your perception of taste and other sensory characteristics is to go to one of the restaurants where people dine in the dark. Suddenly your other senses start to work in overdrive; the food smells so much stronger than normal, that rare steak suddenly feels somewhat gelatinous and slimy in the mouth, and the people talking around you seem so much louder than normal.

And its not just the food that we are assessing with our eyes. If you walk into a dirty grocery store with flies on the produce it will likely put you off purchasing the items there. Similarly, if you walk into a restaurant and the table is dirty you may be inclined to leave. These are all impacting food choice for the purchaser or consumer.

Sensory analysis techniques and sensory panels are often employed by the food industry to help developers, chefs and packaging designers to name a few, to understand the effects that the different appearance of products, and indeed the surrounding environment, on the perception of quality and ‘attractiveness’ to the end user. If sales can be maximised by optimising visuals for foods, then elements such as customer loyalty and profits follow leading to success in the market.

To learn more about Sensory Science and how it can help to grow your business contact Sarah Cowen or John Hale or visit us at

To view the post on the Food Starter website, please click here.

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