A new study led by Professor of Psychology Frank Durgin, which appears in the journal I-Perception, finds that older adults are better at interpreting the correct slope of a hill than young adults, which he believes is because of greater life experience.

In the study, Durgin and his team – which includes Assistant Professor of Psychology Cat Norris, Psychology Department research manager Abigail Dean, Jeahyun Oh ' 15, and Chris Thomson '15 – asked about 50 college students and 50 adults from the surrounding community ranging from age 18 to 72 to properly gauge the slope of the hill from Sharples Dining Hall to Parrish Hall. They discovered that among participants with no knowledge of slope, older participants gave significantly more accurate estimates of the Sharples Hill than younger adults. 

Below, Durgin answers a few questions about the study.

Why study the perception of hill slant?

Hills look very steep to humans compared to their true slant. A sloped path that looks like it is 20 degrees is probably no more than about 5 degrees. There is a very steep path from the Sharples Dining Hall up toward Parrish Hall. Students who walk it everyday typically judge it to be about 20-25 degrees. Measured with an inclinometer, it is less than six degrees. Our lab has proposed that hills look steep because it is useful for perception to exaggerate differences. Gravity is so strong that very few surfaces that we encounter are steeper than 35 degrees. Most on this campus,are less than 10 degrees, but they certainly look much steeper to us. Understanding how hill slant can be distorted may tell us something more about how perception works.

What was the purpose of your particular study and how did you carry it out?

There is a lot of folklore suggesting that hills might look even steeper if you are an older adult or you are fatigued. But we were somewhat skeptical of these ideas. Indeed, most of the data that has been published on how aging affects the perception of hill slant has been more consistent with the idea that older adults give lower, more accurate estimates than younger adults, but a subset of data collected many years ago where older adults gave higher estimates has continued to be used to argue that older adults really do see hills as steeper.

We were concerned that the instructions used in that study may have biased the older adults they tested to think the experimenters wanted them to give high estimates, and people tend to try to be helpful. In our study, we sought to sample a wide range of ages and personalities by recruiting not only college students, but also about 50 adults from the surrounding community ranging in age from 18 to 72. We didn't want people to feel like we were selecting them for their age.

We asked each participant in our study to give estimates of a few hills on campus (while standing near the base of the hill) using a variety of measures - verbal estimates, adjustment of a 2-D angle to represent the hill slant, and holding their unseen hand out parallel to the hill - to assess their perception of hill slant. We also assessed their knowledge about slant. For example, people who participate in downhill skiing have often had opportunity to learn the true slants of hills and thus to learn about the discrepancy between perception and reality. We gave them personality measures as well to measure things like conscientiousness and agreeableness.

And you found that older adults didn't give higher estimates than younger adults?

Our overall sample of just over 100 people was not particularly large, but the data gave us a very clear picture of two main effects.  First, there was a clear effect of having experiential knowledge.  Although they still gave overestimates, people who reported having some experiential knowledge about hill slants gave lower, more accurate estimates than those who reported no knowledge. Similarly, we observed that our older participants gave estimates that were about the same as our knowledgable participants -- even if the older participants did not report having any specific knowledge, it still seemed like their life experience had made them better estimators.

In support of the idea that people were intentionally applying their knowledge (rather than actually seeing the hills as less steep), we found that more conscientious people were more likely to use their knowledge (show an effect of knowledge) than less conscientious people.  

Were you surprised by what you found and how can your findings be applied in the future?

Our findings are probably surprising to many because of the widespread belief that things like aging can make the world look different. But the perception of the geometry of the world, in itself, doesn't seem to be affected by aging, apart from possible effects of lost acuity. This fits the idea that the overestimation of perceived hill slant is an adaption to the environment (the predominance of shallow slants) rather than a measure of individual strength or ability.

It is not possible to measure perception directly because perception is subjective, but there are lots of reasons to believe that people share a common perceptual experience, such as the impression that hills are much steeper than they are. Our research helps to provide new ways to try to dissociate differences in judgment from genuine differences in perception. And whereas much research on aging emphasizes perceptual decline, when it comes to space perception for navigation, older adults do well. And they also seem to have acquired wisdom with their years about the difference between how thing seem and how things are. This is a point well worth making.