Study shows people overestimate hill steepness based on their eye level

People’s perceptions of the world are easily impacted by the angle at which they view objects in it, suggests a new study.

This finding, made by researchers from The Ohio State University, was revealed by testing people’s ability to estimate the steepness of a hill. The study, recently published in the journal Perception, showed that most people, regardless of their visual orientation — or line of sight — will consistently overestimate its steepness.

Dennis Shaffer, lead author of the study and a professor of psychology at The Ohio State University’s Mansfield campus, said his team’s research aimed to understand why this may be, as well as how manipulating a person’s gaze might result in notable differences in their perception.

“If you’re driving toward a hill that you see in the distance, it typically looks a lot steeper from far away than when you get right on it,” he said. “Part of that is because of the way you’re looking at it, you’re changing your gaze relative to the object.”

In one study, testing this phenomenon involved having 36 participants determine the slant of a wooden ramp while either lying down or sitting on a yoga mat. Participants estimated the orientation of four slopes from about 7 feet away.

In a second experiment, researchers further tested how eye height would impact participants’ perception by having them stand on the third rung of a step ladder or sitting cross-legged on the yoga mat while estimating the slope of the ramp.

“In general, people overestimate the slopes of surfaces by a factor of 1.5, so most people would estimate a 30 degree hill to be 45 degrees,” said Shaffer.

In both scenarios, results show that people overestimated the slopes even more when the distance between their eye height and the surface of the slope was lessened. This phenomenon occurred when they were seated compared to standing on the step ladder, and even more so when they were lying on the yoga mat.

According to Shaffer, this verifies long-held theories about how people tend to judge slope.

“One of our lab’s superpowers is finding interesting methodologies to get at the questions we’re interested in,” he said. “In doing so in this study, we saw a lot of our and others’ predictions pan out.”

Whereas previous work failed to find a solid connection between slope perception and a person’s eye height, this study tested a wider range of slopes and observer eye heights than other researchers had. These differences, said Brooke Hill, co-author of the study and an undergraduate student in psychology at Ohio State Mansfield, are what led this team to discover a significant negative correlation between eye height and slant estimates, meaning that shorter individuals tended to predict ramp orientations to be steeper than taller individuals would.

This helps to explain why the world might be perceived much differently by someone seated in a car versus higher up in a truck or a bus, or why a hill may look to be an even more insurmountable challenge to a small child than to a fully grown adult.

“We don’t realize that as humans, perception is everything,” she said. Furthermore, gaining better insight into how our gaze changes our worldview is also a step toward improving systems used for road safety, GPS navigation, vehicle design and other assistive technologies.

In the future, Shaffer and his team plan to continue demonstrating how the angle of an individual’s gaze can be influenced by various vantage points and methods, in part to discover how even unique perspectives of the environment shape our collective society.

“Humans are really good pattern-seekers,” said Shaffer. “But by teaching people about head orientation and what it does for their perception of different things, we can help them keep a steadier version of what the world looks like.”

People’s perceptions of the world are easily impacted by the angle at which they view objects in it, suggests a new study.

This finding, made by researchers from The Ohio State University, was revealed by testing people’s ability to estimate the steepness of a hill. The study, recently published in the journal Perception, showed that most people, regardless of their visual orientation — or line of sight — will consistently overestimate its steepness.

Dennis Shaffer, lead author of the study and a professor of psychology at The Ohio State University’s Mansfield campus, said his team’s research aimed to understand why this may be, as well as how manipulating a person’s gaze might result in notable differences in their perception.

“If you’re driving toward a hill that you see in the distance, it typically looks a lot steeper from far away than when you get right on it,” he said. “Part of that is because of the way you’re looking at it, you’re changing your gaze relative to the object.”

In one study, testing this phenomenon involved having 36 participants determine the slant of a wooden ramp while either lying down or sitting on a yoga mat. Participants estimated the orientation of four slopes from about 7 feet away.

In a second experiment, researchers further tested how eye height would impact participants’ perception by having them stand on the third rung of a step ladder or sitting cross-legged on the yoga mat while estimating the slope of the ramp.

“In general, people overestimate the slopes of surfaces by a factor of 1.5, so most people would estimate a 30 degree hill to be 45 degrees,” said Shaffer.

In both scenarios, results show that people overestimated the slopes even more when the distance between their eye height and the surface of the slope was lessened. This phenomenon occurred when they were seated compared to standing on the step ladder, and even more so when they were lying on the yoga mat.

According to Shaffer, this verifies long-held theories about how people tend to judge slope.

“One of our lab’s superpowers is finding interesting methodologies to get at the questions we’re interested in,” he said. “In doing so in this study, we saw a lot of our and others’ predictions pan out.”

Whereas previous work failed to find a solid connection between slope perception and a person’s eye height, this study tested a wider range of slopes and observer eye heights than other researchers had. These differences, said Brooke Hill, co-author of the study and an undergraduate student in psychology at Ohio State Mansfield, are what led this team to discover a significant negative correlation between eye height and slant estimates, meaning that shorter individuals tended to predict ramp orientations to be steeper than taller individuals would.

This helps to explain why the world might be perceived much differently by someone seated in a car versus higher up in a truck or a bus, or why a hill may look to be an even more insurmountable challenge to a small child than to a fully grown adult.

“We don’t realize that as humans, perception is everything,” she said. Furthermore, gaining better insight into how our gaze changes our worldview is also a step toward improving systems used for road safety, GPS navigation, vehicle design and other assistive technologies.

In the future, Shaffer and his team plan to continue demonstrating how the angle of an individual’s gaze can be influenced by various vantage points and methods, in part to discover how even unique perspectives of the environment shape our collective society.

“Humans are really good pattern-seekers,” said Shaffer. “But by teaching people about head orientation and what it does for their perception of different things, we can help them keep a steadier version of what the world looks like.”