Visual illusions

Visual Illusions Perception Psychology

Visual perception is a critical aspect of our survival. It allows us to explore and react to our environment. Visual illusions can confuse our brains into missing visual information or thinking we are seeing something that is not necessarily there, but what exactly do we mean by visual illusions?

Perception can be explored from a psychological perspective using visual illusions by examining what kind of misinterpretations in stimuli affects the majority of people and why. This can help to understand why humans have evolved particular cognitive and visionary abilities and can contribute to creating design features that people find easy and enjoyable to view.

Types of Visual Illusions

Visual illusions can vary in how and why they affect our perception. Some can be quite subtle and difficult to distinguish between the real and perceived image. In contrast, others are overwhelmingly tough to look at, where identifying a certain image or pattern is almost impossible.

A few types of visual illusions include:

• Cognitive visual illusions - are the most common type of visual illusions. They rely on tricking the subconscious mind based on how you usually infer and relate what you see to what you already know about the world. This causes your brain to think there is a certain image present, even though it is not there or it is something else entirely.
• Physiological visual illusions - these geometric images contain so many visual cues that the brain sees different depths and lines of travel. They often look different every time, and some can appear to be moving.
• Literal visual illusions - these are made up of two images that are present at the same time. People can perceive them differently initially and often need the other image in the illusion pointing out to them to distinguish between the first image noticed.

Visual Illusions Examples

Several kinds of visual illusions have been created and used by psychologists in perception research over the years. Fantastical images that test the brain's ability to make sense of illogical or ambiguous content have been created to explore perception. Visual illusion examples include:

• The Ponzo Illusion
• The Müller-Lyer illusion
• Rubin's Vase
• The Ames Room
• The Kanizsa Triangle
• The Necker Cube

The Ponzo Illusion

Can you guess the visual trick in this illusion from the Italian psychologist Mario Ponzo?

In the Ponzo visual illusion, the horizontal lines are the same length. Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0)

Both of the parallel horizontal lines in the Ponzo illusion are the same length! The top horizontal line appears to be longer due to its placement converging at the top of the narrower part of the vertical lines.

The Müller-Lyer illusion

Do you notice anything particular about the three lines in the illusion below?

An example of the Müller- Lyer illusion, all of the parallel lines are the same length, Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0)

The three long parallel lines are all the same length, as shown in the bottom image, with the lines highlighted in red. Many believe certain lines are longer due to the direction of the arrows at the end - outward arrows are often said to contain longer lines, although this is not the case.

Rubin's Vase

Look at the image below. Can you see a vase or two faces?

Rubin's Vase visual illusion, can you spot a vase or two faces? Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0)

The yellow part of the image shows a vase, but the black parts of the image make up a silhouette of two faces, one on the left and one on the right.

The Ames Room

Can you spot the differences between the three circles below? Where do you think the visual illusion here is?

The Ames Room visual illusion, Attribution - Alex valavanis, Public domain, via Wikimedia Commons

The illusion comes from the pink circle (the apparent position of person A) appearing directly opposite and smaller from the viewing point than the green circle (person B). The actual position of person A is further behind the apparent position. Because of the room shape and viewing angle, the distance is perceived to be shorter and, therefore, smaller.

The Kanizsa Triangle

Look at the image below. How many triangles can you see?

In the Kanizsa Triangle illusion, how many triangles can you see? Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0)

There aren't any triangles in this image! Your brain fills in the gaps to create a large white triangle in between the gaps of the black circles. People often fill in gaps as well, to say there are three smaller black-lined triangles or one big triangle with a black outline too.

The Necker Cube

Which side of the cube below do you notice first?

The Necker Cube, which side do you perceive the cube from? Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0)

People can perceive the cube to be angled towards the left and right.

Visual Illusions and Explanations

There are several explanations for why we can misinterpret information seen in visual illusions like the ones above. Some of the common explanations include:

• Ambiguity - the image of a visual illusion can be perceived in several different ways, all of which make sense. Like Rubin's Vase illusion, there is no clear, correct answer, and both images can be seen if looked at for long enough.
• Depth cues - our visual system uses depth perception to judge how far away or big an object is. Visual illusions cause misinterpretations of visual information by tricking the brain into thinking a part of the image is further away or bigger than it is. For instance, with the Ponzo illusion, the horizontal lines appear to be different sizes because the angle of the two vertical lines makes the top section of converging lines appear further away.
• Fictions - when we perceive something as part of an image that is not really there, like the white triangle in the Kanizsa triangle illusion.
• Visual constancy - an object's size, colour and shape can appear to be different due to environmental conditions, but in reality, the object has not altered. For example, in the Ames room illusion, Person A appears smaller, even though they have not shrunk in any way. They are just perceived at an angle that makes it appear that way.
• Distortions - occur when the aspects of an object appear to be different than what they are. For example, the lines in the Müller-Lyer illusion appear to be of different lengths.

Possible Causes of Visual Illusions

There are two main theories of perception that we will briefly explore that can explain some possible causes for why visual illusions work:

• Gibson's (1966) The Direct Theory of Perception suggests that we perceive the world through our eyes using the information we see directly. Nature influences our perception of the world. Gibson referred to how this direct information about the world is sent to our brain from our eyes as bottom-up processing.
• Gregory's (1970) The Constructivist Theory of Perception suggests that we use information stored in our brains from previous experiences to perceive the world around us. How we perceive the world is influenced by nurture and external factors from our environment. Gregory referred to this stored information being brought down to our visual senses for interpretation as top-down processing.

Both of these theories can explain why we fall for visual illusions because the image we see either does not match up with information that we already have stored. So it isn't easy to interpret and understand because we automatically trust what we see in front of us as the truth.

Either way, our visual system gets easily overwhelmed and misinterprets the image.