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My Walk in the Woods

Last weekend I went for a walk in the woods. It’s not something I do often, but I was with friends who wanted to do it, so alright. We hiked for about four miles. It was not strenuous. It was warm, but not too warm, with a light breeze. The trees protected us from the sun. The canopy was intensely green, and the sky, peeking through, was cornflower blue.

While my friends walked along merrily, ostensibly enjoying their surroundings, I spent much of the hike wondering why anybody would bother with this kind of activity. I find hikes repetitious and boring. My mind goes idle (other than its constant scanning for beetles, ticks, rocks, and face-slapping branches). I look at my feet more the trees, and when I do look up, everything looks the same, a wash of brown and green. I try to think of it as good exercise, but the inefficiency! The same 90 minutes at the gym would be far more helpful.

It’s odd, when you think about it: My friends and I were all absorbing the same sights, sounds, smells and touches. We’re all about the same age and live in big cities. But they seemed to like it very much and I didn’t like it much at all.

Wilhelm Wundt, known by some as the father of psychology, pondered this very conundrum more than a century ago. In his 1896 book, Outlines of Psychology, Wundt wrote that our experiences can be broken into two elements: objective sensations and subjective affect. For instance, if you put your hand under hot water, you’ll feel a sensation of the heat. That’s the objective part. It’s hot, not cold. But then there’s the affect, the way the sensation affects you. For some people, the hot water will be excruciating, for others it will be rapturous. The sensation and the affect are inseparable, and both are crucial to perception, Wundt wrote: “The actual contents of psychical experience always consist of various combinations of sensational and affective elements.” Our experience, he added, “depends for the most part not on the nature of these elements so much as on their union.”

Wundt’s ideas have been difficult to prove empirically, but new evidence comes from a paper published Sunday in Nature Neuroscience. Adam Anderson, a cognitive psychologist at Cornell University, and his colleagues used brain scanners to show that our brains use different codes to represent these objective and subjective aspects of an experience.

Chikazoe et al, Nature Neuroscience 2014

In the first part of the experiment, the researchers showed 16 volunteers 128 pictures portraying a wide range of scenes—a girl checking a man’s pulse, a bloody surgery, an igloo, tree bark, three adorable puppies. The volunteers rated how positively or negatively they felt about each picture and the researchers compared these responses to volunteers’ brain activity while looking at each picture.

The researchers found that brain activity in the visual cortex, at the back of the head, tends to correspond with basic visual properties of a picture, such as its luminosity. Meanwhile, activity in a region called the ventral temporal cortex (VTC), above the ears, codes whether a picture contains inanimate or animate objects. And activity in the orbitofrontal cortices (OFC), just above the eyes, predicts how a participant rated a given picture — the affect code, you might say.

Intriguingly, the OFC seems to deal with both positive and negative ratings. That makes some sense, the researchers note, because monkey studies have pinpointed individual neurons in this region that respond to rewarding stimuli, aversive stimuli, or both. All three types of neurons are likely conflated in this human imaging study because a voxel represents the combined activity of hundreds of thousands of neurons.

The second part of the experiment investigated whether the brain uses the same affect code for different types of sensory experiences. “It is presently unknown,” the researchers explain,”whether the displeasure evoked by the sight of a rotting carcass and the taste of spoiled wine are at some level supported by a common neural code.”

So they put the same participants back in the scanner, but instead of showing them pictures they fed them liquids of different flavors: sour, sweet, bitter, salty, and no taste. Just as before, the volunteers rated each taste and the researchers had a look at how their brains responded.

It turns out that the brain has certain affect codes that are specific to the sensory experience. Brain activity in the VTC, for example, corresponded to the volunteers’ ratings of taste, but not their ratings of the pictures. However, their brains used other affect codes, in parts of the OFC as well as other regions, for both taste and sight ratings.

It’s not clear why the brain would have so many different affect codes, but it makes intuitive sense. If an experience had pleasant smells but frightening sounds, say, you’d want to be able to assess each one separately before making an overall judgment.

In the last part of the study, the researchers looked at these patterns across the 16 volunteers. They found that the volunteers gave different ratings for the same pictures and tastes — just as I realized in the woods, some people like things more than others do. But the way their brains coded positive ratings (and negative ratings) was similar for everybody, regardless of which stimuli were considered positive or negative.

Other researchers have used the same brain-imaging methods* to do “mind-reading” of other kinds — using brain scans to predict, for example, what pictures a person is looking at. The predictive accuracy is somewhat crude, for now, but good enough to be creepy. This new study adds another layer of creepiness, showing that even our most subjective personal experiences could be decoded by a machine.

To put it another way: If these researchers had appeared in the woods last weekend with a brain scanner, and convinced me to crawl into it and cogitate on my forest experience, their algorithms may have been able to predict how I was feeling about the hike. Of course, they could have just asked me. And what these algorithms can’t answer, not yet, is the most interesting question of all: What determines affect? Why oh why do people like the woods?

*A bit about the imaging methods, for the curious. Traditional brain imaging, as I blogged about a couple of weeks ago, looks at brain activity voxel by voxel. (A voxel is a three-dimensional pixel, or a cube.) Researchers ask whether the activity in a given voxel differs between two experimental conditions, and then average across all of the voxels that do show significant differences. One downside of this technique is that it won’t pick up voxels that show a weak response to a given stimulus because it will be impossible to tell whether the response was due to chance alone. This study, in contrast, used a method called multi-voxel pattern analysis, which analyzes brain activity across many voxels. It’s basically a way to pick up more fine-grained patterns of activity. The trade-off with this approach is that it’s more difficult to compare activity across individuals.

17 thoughts on “My Walk in the Woods

  1. Well, for one thing, many people (mentally) possess abstractions and other associations with the woods (or other environments), due to life experience, culture, and maybe even genetic programming, any of which might produce emotional effects. For instance, I have mystical ideas about plants, especially trees, having minds, as well as all the non-human animals running about through the woods, so when I am out in the woods I am surrounded by minds, some of them rather alien. In a real wilderness, the aggregate feeling can be one of combined exhilaration and terror: anything could happen. But also, as a famous politician and philosopher said — and in a sense this is unquestionably true — ‘When you’ve seen one tree, you’ve seen them all.’ And that could be quite tedious if it’s the only or strongly dominant dimension of your perceptions.

    It’s not merely a matter of the brain but all the stuff in the brain and the way it’s hooked up. That’s going to vary a lot from person to person in incomputable ways.

  2. I’m hardly qualified to speak with any confidence on this subject, so I’m just spit balling and may be way off base. However I wonder if the affect comes first, then we rationalize what we feel after the fact without realizing it to make sense of it. I certainly enjoy hiking, but do the reasons I enjoy it actually explain why I enjoy it or is it just how I make sense of that enjoyment?

  3. I find walking anywhere, especially on a beautiful day,just so invigorating getting off on the beauty of nature. I cannot fathom anyone not enjoying it.

  4. I thought Wild Brazil and Wild Amazon were super, the best. They were the newest shows I have seen on this channel thanks alot

  5. ‘The beauty of nature’ is a convention. People in some places and times have often thought nature (that is, the world before human intervention) forbidding, boring, dangerous, or even demonic.

  6. Fundamentally human built environments lack the staggering variety of texture, color, sounds and smell of natural environments. This is why I leave the streets and sidewalks or gyms of urban or suburban areas, to actually fill the senses that we, as a species, have evolved. How can you be bored when you are in natural setting that actually engages your senses as you indicate the hike did? How is it inefficient to be exercising, engaging senses, discovering, and allowing time for self-reflection all at once? Wonder about natural process from flowers blooming and insects crawling to streams carving and mountains building has shaped our drive for discovery and enabled our dominance, regardless of value judgment, of this planet. I find it difficult to believe that a science writer working for National Geographic can’t find the joy and benefit of natural environments. I would actually be surprised if your issue with the hike could be boiled down to simple like vs dislike that could be predicted by brain-imaging. There is way more going on than simple reaction to an image or taste.

    1. Don’t know how to respond to this other than to say: believe it. Walking in the woods does nothing for my senses or aesthetics. I would probably get much more of that stuff from reading Emerson in my office (if I liked Emerson, which I don’t, but that’s another story). Thanks for reading…

  7. Virginia, I love your column as I love those of all the other Phenoms. Some of the best science writing out there, if you ask me.

    I’m going to make a frivolous comment now: Have you read Bill Bryson’s “A Walk in the Woods”? I wonder how your brain’s affect would respond to an often sardonic, wryly bemused account of two unfit guys attempting the Appalachian Trail, each never fully sure he’s enjoying himself. Would you relate to the ambivalence, and by relating derive some sense of satisfaction from the experience?

  8. Hi Virginia,
    First time on your blog; caught my eye through digg, and enjoyed this post. I hope you’ll enjoy hiking more some day, but it may be that we’re all wired differently. When I walk through the woods, I enjoy the immense variety. It’s not just a green canopy, it’s white cedars, ash, maples. Every leaf and every sounds is unique. The sky will never be the same again, the stream will never contain the same water. When I walk in a city, I experience cacophony, a variety that nevertheless results in sameness, but at an ear-offending noise-level. I know there is an endless variety in the human condition, and art in much of what we as humans create, but I see the sameness more than the diversity. It tires me more than stimulates me and assaults me more than gives me peace. For me, the natural world is the opposite. It stimulates me and causes my mind to relieve itself of busy-life stresses, often bringing novel ideas to the fore; it gives me peace and tranquility, and a time for quiet reflection which is hard to get elsewhere. Very best!

    PS, I work in IT, and can walk directly into a wooded area from our backyard (Southern Ontario, Canada). So I appreciate the forest during all four seasons, and pretty much on a daily basis.

  9. Well, Virginia, I have to agree with you. I find rambling, interminable bike rides and this type of outdoor pursuit completely boring too. I always hate them and probably always will.
    I get far more pleasure from sitting in my postage stamp of a back garden with a good book and a morning cup of tea or with a glass of vino and friends on a summer evening. Still outdoors but at home.
    Really enjoyed your article, I must say. Very interesting.

  10. Thanks for your honest and insightful article. I find that my mood determines whether I’ll enjoy a walk in the woods. Some days it helps me to meditate on problems in my life, and some days it’s a waste of time because I have more urgent things to do. The other variables in our life can change our perceptions.
    Thanks again for your interesting article.

  11. Interesting article. I appreciate your honesty in your dislike of such a commonly presumed pleasure-it’s refreshing! The comments section reminds me that as much as we pay lip service to respecting other peoples’ opinions, it is difficult to truly imagine the same stimulus having a completely opposite affect for someone else. It seems as if this opposition is interpreted as an invalidation of one’s own experience, the validity of which one is compelled to defend and uphold. I wonder how we can better practice inhabiting each others’ perspectives? (i.e. yes, I like this, and yes, you don’t, and I can imagine that even if it’s not what I experience.) Otherwise, how can we have constructive dialogue about disagreements when we are all having our own subjective experiences, each in a separate world?

  12. Hiking and neuroscience, two of my favorite things! I actually take hikes in the woods to process recently read neuroscientific theories and blogs such as yours 🙂 I think it isn’t hiking that I really like though, it’s the meditative aspect of it. It’s letting my brain be free, somewhere quiet. Modern times are so overwhelming to the senses, it’s important to find a way to quiet it down – the method for this being different for every individual.


  13. It used to be that I was bored during a hike until I got to a vista or panorama where I could take in the view.

    Since I’ve been practicing mindfulness, however, I find an ordinary patch of woods without a “view” to be quite stimulating. When the inner chatter is quiet, I experience sensory amplification and am particularly aware of the three-dimensionality of the scene before me.

    I believe this amplification has to do with what Daniel Siegel has described in terms of shifting to more of a bottom-up rather than top-down flow in the cortex.

  14. Is your response the same, I wonder, to any and all natural landscapes and/or experiences? A tropical beach, or rocky tide pools, or mountain meadows, or snowy alpine skiing? What natural setting or activity does engage your interest, your curiosity, your need to investigate your surroundings?

  15. Virginia, phenomena (hey, the name of this set of blogs), their interpretations and the emotions they evoke are all subjective – they are all collective representations constructed by our brains after sensation, processing and individual and social learning. The collective representations of a 21st century person are quite different from those of a 17th century person, and almost unimaginably different from those of a 4th millennium B.C. animist. Of course the raw sensations are probably more similar between different people, even in different ages, than the conscious interpretations and emotional reactions, but how would we really know?

    You may come to enjoy walks in the woods more as you get older. I always enjoyed them, but as you get old it’s easier to enjoy something that comes at a slower pace and isn’t so hard on your joints. I ran a lot when I was young (until I realized my allergies were always going to get me,) but now it’s pleasant to slow down and look for the critters (I walk at night – cooler down here in Texas.) Anyway, I hope it comes to be something you can enjoy. If you’re ever in Fort Worth, give me a call and we’ll can give it a try. 🙂

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