Tall and needle-like from one angle, short and squat from another. Auckland’s Sky Tower has been playing tricks on people’s eyes since it opened in 1997. How can the same 328-metre-tall structure look so different depending on where you stand? NZASE chats with Dr Sam Schwarzkopf, Associate Head (Research), Optometry and Vision Science at the University of Auckland, who investigated what the Sky Tower illusion reveals about how brains process visual information.
When vision scientist Sam Schwarzkopf arrived from London in 2017 to take up a position at the University of Auckland, he noticed something peculiar about the Sky Tower. As he and his wife explored the city while house-hunting, the landmark seemed to change shape depending on where they stood: “in ways that didn’t seem to really make sense,” recalls Sam.
Friends and colleagues saw it too, particularly newcomers to Auckland. Sam suspected long-time residents had simply grown accustomed to the illusion. But what was causing the weird phenomenon? He embarked on a city tour, viewing the tower from 36 locations, and concluded, based on this anecdotal evidence, that it looked tall and thin from a distance but shorter and wider up close.
Four optometry honours students joined his research, asking 23 volunteers to judge 62 geotagged camera phone photographs of the Sky Tower taken around Auckland. The results echoed Sam’s observations: tall and thin from afar, short and wide up close. A subtle altitude effect also appeared, with the tower looking taller from elevated viewpoints, such as Rangitoto Island.
Because Auckland is quite hilly, Sam suspects topography might boost the illusion, and that the surrounding architecture may also influence it. “For example, if you look from the sea, either from the ferry to Waiheke or from Devonport, you have a sort of spread-out skyline, and actually it sort of sticks out there. But from other angles, and especially if you’re in a ditch somewhere between hills, it might be much more bunched together with the surrounding skyscrapers, which are much shorter.”
Is this phenomenon unique to Auckland’s Sky Tower? Possibly. Sam hasn’t heard of similar experiences with other famous landmarks, such as Seattle’s Space Needle or the Eiffel Tower. However, while living in London, he noticed Big Ben looked tall and thin from across the Thames, but shorter and wider up close. “I think it might capture the same effect, but clearly not to the same extent.”
Ultimately, his research suggested the tower’s proportions change with viewing distance. But why? Sam points to the moon illusion, where the moon appears larger near the horizon than high in the sky. This is thought to occur because our brains misjudge how far away the moon truly is. Yet he acknowledges this doesn’t fully explain what’s happening with the Sky Tower—so what could be happening inside our brains?
How the brain builds the world we see
We don’t actually see what our eyes detect; we see what our brains make of it, Sam says. “Perception is a generation of the brain. This is not true only about vision; it’s pretty much about everything, including your higher thoughts and political opinions.”
Eyes follow optical principles similar to cameras, he says, but then our brains do far more than just record incoming light. The brain processes input to understand what’s out there: recognising objects, interacting with the world, and giving humans a sense of where they are—essentially, allowing us to survive.
Perceiving depth is also interpretive. Each eye receives a two-dimensional image, but the brain combines information from both eyes with other visual clues to construct our perception of depth. “Even that step alone…already comes with a lot of interpretation,” he says. “Then working out how far away an object is [uses] a lot of information. Our brain is actually very good at this. [It] knows that something further away is usually smaller, and therefore we don’t see it as a small thing, but we see it as further away.”
But this critical processing has consequences: “Visual illusions are a perfect example of the ways that our perception is really manufactured by the brain,” says Sam. “It’s an interpretation, and it doesn’t necessarily reflect the physicality of the world.”
Capturing these visual experiences in photographs presents another challenge. During his research, phone cameras flattened the perspective of the Sky Tower images shown to volunteers. Beyond 10 kilometres, the tower appeared tiny, so researchers used closer photographs.
Even so, the illusion wasn’t entirely lost—but nothing beats seeing things firsthand, says Sam. “If you’re standing up on the peak in Queenstown looking down on Lake Wakatipu and the Remarkables, this will give you a rather different sense of awe than looking at a photograph, even one taken by a professional with a proper camera—although they can do a lot better to approximate the real feeling than a mobile phone can.” This helps explain why the Sky Tower illusion may be more striking in person than in photographs.
In another example, anthropologist Colin Turnbull described taking Kenge, a BaMbuti man accustomed to the dense forests of Central Africa, onto an open plain in his 1961 book The Forest People. Seeing buffalo grazing in the distance, Kenge mistook them for insects. As they approached and the animals appeared to grow, he was astonished. The incident illustrates how size constancy can be influenced by experience and environment.
Does everyone see illusions the same way?
If our brains construct what we see, does everyone experience the same illusions? Not necessarily, says Sam. Figuring out whether illusions are perceived universally is an active area of research. “There’s just a normal variation across the population. Some people experience certain illusions as stronger and other illusions as weaker. Just in the way that we have different fingerprints and different faces.”
He says our experience of the world is unique, citing the 2015 viral phenomenon ‘The Dress,’ which had millions disagreeing on whether it was blue and black or white and gold, as an extreme example. “What is fascinating about The Dress is how people differ so much in the assumptions they bring in,” Sam says. “And most people simply cannot shift their assumptions to see it the other way—although a handful of people apparently can. Merely telling people to assume they see it in cool/warm lighting isn’t enough.”
Despite a few theories about why people have these different assumptions, none has satisfactorily explained how extreme these differences are, Sam says. “And if you cannot convince your brain to see some blurry photo in another colour, imagine how hard it might be to convince people to change other assumptions or beliefs they have…”
The next steps
While Sam has no immediate plans for further experiments, he hopes virtual reality could help unravel the illusion in the future. A controlled VR environment would allow him to test how surrounding buildings and changes in land elevation affect what people see. His findings could even have implications for urban design, helping architects create imposing landmarks that look tall and slender rather than “squat and fat”—potentially avoiding costly design mistakes.
Sam hasn’t spoken to the tower’s original architects, so doesn’t know whether they anticipated the illusion. Either way, he considers the landmark a success. “It makes people think about it and talk about it,” he says. “It has become an iconic feature of Auckland.”
At the start of his research, Sam wondered whether only he and a few others noticed the tower’s shape-shifting appearance. “Is it just us who feel this?” Discovering that others see it too has only deepened his curiosity about how our brains interpret the world—and sometimes play tricks on us.
About Sam
Sam completed a PhD at Cardiff University before undertaking research at the University of Birmingham and University College London. In 2017, he moved to Auckland’s School of Optometry and Vision Science, where he investigates how we see and interpret the world around us, and how this might differ in neurological and psychiatric conditions.
More information: read Sam’s research study and explore his lab website.
Ngā kupu
Tirohanga: view, sight, aspect
Karu: eye
Wairoro: brain
Pohewa: imagination, illusion, vision, apparition
Kitenga: seeing, sighting, finding, observation, perception, view.
Classroom activity: Testing peripheral vision
Explore how eyes detect movement, colour and shapes across our field of vision. Using a simple semicircular cardboard device, students test when objects become visible and when they can identify their colour and shape. This hands-on experiment demonstrates the differences between central and peripheral vision and provides a starting point for discussing how the eyes and brain process visual information. View activity online
How does the Sky Tower stand?
Interested in how the Sky Tower was built? Here’s a video about its engineering. [6:23]