Seeing isn’t always believing. The Müller-Lyer illusion is such an example. This optical trick highlights how our brains can be shaped by the spaces we grow up in. But some people aren’t fooled at all, raising questions about how culture, environment, and early life experiences change the way we see the world. Will you fall for it?
the full story
Where do you see the midpoint of this line? Most people see the center of the line left of the actual midpoint. While those who get tricked, wonder how much they can trust their own eyes, it is those who don’t see the optical illusion, that is science’s real mystery. But first things first.
The Müller-Lyer illusion
The Müller-Lyer illusion, in its most famous form, features two lines, each flanked by a set of opposing arrows which tricks you into thinking that one line looks shorter because the other appears further away—when in fact they are exactly the same.
3D Perception and illusions
The effect is the result of our perception of three-dimensional space where the inward-pointing arrows are perceived as further away while outward-pointing ones seem closer—and shorter.
And because you probably grew up in three-dimensional spaces full of right angles, your brain, in an attempt to make sense of these cues, can get fooled by a two-dimensional illustration. But what about people who don’t see it?
Culture and visual perception
Like most social science, the research was mostly conducted with people who are WEIRD: Western, Educated, Industrialized, Rich, and from a Democratic country—that is. And so some scientists wondered whether it would work on people who were raised in environments with no rectangular architecture. The question: Would the illusion also trick them?
And so, in the 1960s two researchers and one of their students began investigating the illusions’ effect on people from all over the world—seventeen different cultures in total. This is what they found.
How childhood shapes sight
People who grew up in spaces with clear corners were fooled most of the time, whereas bushmen from southern Africa, tribespeople from Angola, and Kalahari hunter-gatherers almost always perceived the lines as identical. The researchers concluded that our perception is not a reflection of reality, but a construction shaped by minds who experienced growing up in a particular culture.
This makes sense, since it’s during the early years of life, that our brains are highly receptive to environmental stimuli and capable of forming new neural connections at a rapid pace. This part of our life is known as the critical period because the most relevant cognitive functions develop right then.
Neural development and perception
If we look, for example, at a child’s rate of synaptic formation over the first 11 months and the following years, we can see that the speed at which each new connection for vision and hearing is created peaks at around 3 to 4 months of age. For language that’s around month 8 and higher cognitive functions, like decision making, at age 2 to 3.
In other words, the experiences children have during the first years of life can significantly impact the construction of their brains—all up to the point that they literally see the world differently. But some questions remain.
share your thought
What explains the Ebbinghaus Illusion? And what’s behind the Checker Shadow Trick, where two squares appear to be different shades of gray, but are exactly the same? Or don’t you see that? And if not, is that because you aren’t WEIRD? Tell us your thoughts and experiences in the comments below.
Sources
- Davis, C.M., & Carlson, J. A. (1970). A Cross-cultural Study on The Strength of The Müller-Lyer Illusion As a Function of Attentional Factors. Journal of personality and social psychology, 16(3), 403-410.
- Müller-Lyer illusion – Wikipedia.org
- Critical period – Wikipedia.org
Dig deeper!
- Learn about the development of the visual cortex of kittens
- Read about temperamental components of the Mueller-Lyer Illusion
- Read about how perception drives illusions
- Read about the critical period
Classroom activity
Objective:
Students will examine how culture, environment, and early-life experiences shape perception by exploring the Müller-Lyer illusion (and related optical illusions). They will discuss the implications of cross-cultural research, the brain’s developmental “critical periods,” and what it all reveals about the nature of seeing.
Materials Needed:
- Sprouts Video on Optical Illusions
- Excerpts from the script highlighting cross-cultural studies and the illusion’s historical background
- Brief case studies or articles on perception in different cultures
- Whiteboard or large post-it notes for group brainstorming
Duration: 60 minutes
Steps:
1. Introduction and Video Viewing (10 minutes):
- Explain that today’s focus is on optical illusions and how they can reveal the influence of culture and environment on our perception.
- Show Sprouts Video on Optical Illusions
- Ask students:
- What was surprising about these illusions?
- Was anyone not fooled in class? Why do they think that is?
2. Analysis of Illusions (15 minutes):
- Divide into Four Groups, assign each group one of the following themes:
- Theme 1: The role of cultural background (e.g., “WEIRD” societies) and how this might affect seeing illusions.
- Theme 2: The significance of early childhood (critical periods) and brain development in perception.
- Theme 3: How three-dimensional spaces and architectural environments can shape our visual interpretation.
- Theme 4: Cross-cultural studies’ key findings (e.g., bushmen from southern Africa vs. Western urban populations).
- Script & Case Studies, Provide each group with relevant excerpts from the script or short articles illustrating how different environments or cultural practices affect perception.
- Group Discussion, in their groups, students discuss:
- Key Challenges or Observations related to their theme
- Potential Explanations for why some illusions fool certain people more than others
- Implications for understanding human perception and development
3. Group Presentations and Connections (15 minutes)
- Each group briefly presents:
- Main Points: Summarize their theme and findings
- Notable Insights: Any surprising or thought-provoking details
- Class Discussion, after each presentation, invite questions from the class.
- Encourage students to make connections across themes (e.g., how cultural background ties in with the brain’s plasticity).
4. Class Debate: Nature vs. Culture in Perception (15 minutes)
- Divide Students into two Sides, and pose the questions:
- Question 1: Are optical illusions mainly a byproduct of universal brain processes, or are they largely shaped by culture and environment?
- Question 2: Should researchers rely on illusions to gauge cross-cultural differences in cognition, or do illusions oversimplify complex brain processes?
- Debate Preparation, give each side a few minutes to gather arguments. Encourage them to use examples from the video, group discussions, and personal experiences.
- Debate, allow each side to present opening arguments, then facilitate a back-and-forth discussion. Aim to help students see the complexity of perception’s nature vs. nurture aspects.
5. Reflection and Sharing (5 minutes)
- Individual Reflection: Ask students to write down a brief response:
- What was the most surprising discovery you made today about perception?
- How might understanding illusions improve our awareness of cultural biases and brain development?
- Share Out: Invite a few students to share their reflections with the class.
Assessment
- Engagement: Observe students’ participation during group discussions, presentations, and the debate.
- Critical Thinking: Evaluate their ability to connect the information from the script and video with broader real-world contexts.
- Argumentation: Assess how well they use evidence from the illusions, script excerpts, and class materials to support their points.
- Respectful Discourse: Encourage students to listen actively, ask constructive questions, and consider multiple perspectives.
This activity helps students understand that perception isn’t merely about eyesight—it’s deeply intertwined with culture, environment, and the developmental processes that shape our brains from an early age.
Collaborators
- Script: Jonas Koblin and Ludovico Saint Amour di Chanaz, PhD
- Cartoon artist: Pascal Gaggelli
- Producer: Selina Bador
- Voice artist: Matt Abbott
- Coloring: Nalin
- Editing: Peera Lertsukittipongsa
- Sound Design: Miguel Ojeda
- Publishing: Vijyada Songrienchai
