Tag Archives: perception

Zapping Brains, Seeing Scenes

May 1, 2014 By in Brains, Science Tags: , , , 3 Comments

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More than fifteen years ago, neuroimagers found a region of the brain that seemed to be all about place. The region lies on the bottom surface of the temporal lobe near a fold called the parahippocampal gyrus, so it was called the parahippocampal place area, or PPA. You have two PPAs: one on the left side of your brain and one on the right. If you look at a picture of a house, an outdoor or indoor scene, or even an empty room, your PPAs will take notice. Since its discovery, hundreds of experiments have probed the place predilections of the PPA. Each time, the region demonstrated its dogged devotion to place. Less clear was exactly what type of scene information the PPA was representing and what it was doing with that information. A recent scientific paper now gives us a rare, direct glimpse at the inner workings of the PPA through the experience of a young man whose right PPA was stimulated with electrodes.

The young man in question wasn’t an overzealous grad student. He was a patient with severe epilepsy who was at the hospital to undergo brain surgery. When medications can’t bring a person’s seizures under control, surgery is one of few remaining option. The surgery involves removing the portion of the brain in which that patient’s seizures begin. Of course, removing brain tissue is not something one does lightly. Before a surgery, doctors use various techniques to determine in each patient where the seizures originate and also where crucial regions involved in language and movement are located. They do this so they will know which part of the brain to remove and which parts they must be sure not to remove. One of the ways of mapping these areas before surgery is to open the patient’s skull, plant electrodes into his or her brain, and monitor brain activity at the various electrode sites. This technique, called electrocorticography, allows doctors to both record brain activity and electrically stimulate the brain to map key areas. It is also the most powerful and direct look scientists can get into the human brain.

A group of researchers in New York headed by Ashesh Mehta and Pierre Mégevand documented the responses of the young man as they stimulated electrodes that were planted in and around his right PPA. During one stimulation, he described seeing a train station from the neighborhood where he lives. During another, he reported seeing a staircase and a closet stuffed with something blue. When they repeated the stimulation, he saw the same random indoor scene again. So stimulating the PPA can cause hallucinations of scenes that are both indoor and outdoor, familiar or unfamiliar. This suggests that specific scene representations in the brain may be both highly localized and complex. It is also just incredibly cool.

The doctor also stimulated an area involved in face processing and found that this made the patient see distortions in a face. Another study published in 2012 showed a similar effect in a different patient. While the patient looked at his doctor, the doctor stimulated the face area. As the patient reported, “You just turned into somebody else. Your face metamorphosed.” Here’s a link to a great video of that patient’s entire reaction and description.

The authors of the new study also stimulated a nearby region that had shown a complex response to both faces and scenes is previous testing. When they zapped this area, the patient saw something that made him chuckle. “I’m sorry. . . You all looked Italian. . . Like you were working in a pizza shop. That’s what I saw, aprons and whatnot. Yeah, almost like you were working in a pizzeria.”

Now wouldn’t we all love to know what that area does?

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Photo credit: thisisbossi on Flickr, used via Creative Commons license

*In case you’re wondering, the patient underwent surgery and no longer suffers from seizures (although he still experiences auras).

Mégevand P, Groppe DM, Goldfinger MS, Hwang ST, Kingsley PB, Davidesco I, & Mehta AD (2014). Seeing scenes: topographic visual hallucinations evoked by direct electrical stimulation of the parahippocampal place area. The Journal of neuroscience : the official journal of the Society for Neuroscience, 34 (16), 5399-405 PMID: 24741031

Can You Name That Scent?

January 27, 2014 By in Minds, Science Tags: , , , , 3 Comments

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We are great at identifying a color as blue versus yellow or a surface as scratchy, soft, or bumpy. But how do we do with a scent? Not so well, it turns out. If I presented you with several everyday scents, ranging from chocolate to sawdust to tea, you would probably name fewer than half of them correctly.

This sort of dismal performance is often chalked up to idiosyncrasies of the human brain. Compared to many mammals, we have paltry neural smelling machinery. To smell something, the smell receptors in your upper nasal cavity must detect a molecule and pass this information on to twin nubs that stick out of the brain. These nubs are called olfactory bulbs and they carry out the earliest steps of scent processing in the brain. While the size of the human brain is impressive with respect to our bodies, the human olfactory bulbs are nothing to brag about. Below, take a look at the honking olfactory bulbs (relative to overall brain size) on the dog. Compared to theirs, our bulbs look like a practical joke.

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Human (upper) and dog (lower) brain photos indicating the olfactory bulb and tract. From International Journal of Morphology (Kavoi & Jameela, 2011).

It’s easy to blame our bulbs for our smelling deficiencies. Indeed, many scientists have offered brain-based explanations for our shortcomings in the smell department. But could there be more to the story? What if we are hamstrung by a lackluster odor vocabulary? After all, we use abstract, categorical words to identify colors (e.g., blue), shapes (round), and textures (rough), but we generally identify odors by their specific sources. You might say: “This smells like coffee,” or “I detect a hint of cinnamon,” or offer up a subjective judgment like, “That smells gross.” We lack a descriptive, abstract vocabulary for scents. Could this fact account for some of our smell shortcomings?

Linguists Asifa Majid and Niclas Burenhult tackled this question by studying a group of people with a smell vocabulary quite unlike our own. The Jahai are a relatively small group of hunter-gatherers who live in Malaysia and Thailand. They use their sense of smell often in everyday life and their native language (also called Jahai) includes many abstract words for odors. Check out the first two columns in the table below for several examples of abstract odor words in Jahai.

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Table from Majid & Burenhult (2014) in Cognition providing Jahai odor and color words, as well as their rough translations into English.

Majid and Burenhult tested whether Jahai speakers and speakers of American English could effectively and consistently name scents in their respective native languages. They stacked the deck in favor of the Americans by using odors that are all commonplace for Americans, while many are unfamiliar to the Jahai. The scents were: cinnamon, turpentine, lemon, smoke, chocolate, rose, paint thinner, banana, pineapple, gasoline, soap, and onion. For a comparison, they also asked both groups to name a range of color swatches.

The researchers published their findings in a recent issue of Cognition. As expected, English speakers used abstract descriptions for colors but largely source-based descriptions for scents. Their responses  differed substantially from one person to the next on the odor task, while they were relatively consistent on the color task. Their answers were also nearly five times longer for the odor task than for the color task. That’s because English speakers struggled and tried to describe individual scents in more than one way. For example, here’s how one English speaker struggled to describe the cinnamon scent:

“I don’t know how to say that, sweet, yeah; I have tasted that gum like Big Red or something tastes like, what do I want to say? I can’t get the word. Jesus it’s like that gum smell like something like Big Red. Can I say that? Ok. Big Red. Big Red gum.”

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Figure from Majid & Burenhult (2014) comparing the “codability” (consistency) and abstract versus source-based responses from Americans and Jahai.

Now compare that with Jahai speakers, who gave slightly shorter responses to name odors than to name colors and used abstract descriptors 99% of the time for both tasks. They were equally consistent at naming both colors and scents. And, if anything, this study probably underestimated the odor-naming consistency of the Jahai because many of the scents used in the test were unfamiliar to them.

The performance of the Jahai proves that odors are not inherently inexpressible, either by virtue of their diversity or the human brain’s inability to do them justice. As the authors state in the paper’s abstract and title, odors are expressible in language, as long as you speak the right language.

Yet this discovery is not the final word either. The differences between Americans and Jahai don’t end with their vocabularies. The Jahai participants in the study use their sense of smell every day for foraging (their primary source of income). Presumably, their language contains a wealth of odor words because of the integral role this sense plays in their lives. While Americans and other westerners are surrounded by smells, few of us rely on them for our livelihood, safety, or well-being. Thanks to the adaptive nature of brain organization, there may be major differences in how Americans and Jahai represent odors in the brain. In fact, I’d wager that there are. Neuroscience studies have shown time and again that training and experience have very real effects on how the brain represents information from the senses.

As with all scientific discoveries, answers raise new questions. Is it the Jahai vocabulary that allows the Jahai to consistently identify and categorize odors? Or is it their lifelong experience and expertise that gave rise to their vocabulary and, separately, trained their brains in ways that alter their experience of odor? If someone magically endowed English speakers with the power to speak Jahai, would they have the smelling abilities to put its abstract odor words to use?

Would a rose by any other name smell as Itpit? The answer awaits the linguist, neuroscientist, or psychologist who is brave and clever enough to sniff it out.

Asifa Majid, Niclas Burenhult (2014). Odors are expressible in language, as long as you speak the right language Cognition, 130 (2), 266-270 DOI: 10.1016/j.cognition.2013.11.004

Photograph by Dennis Wong, used via Creative Commons license

Sight Unseen

August 1, 2013 By in Brains, Science Tags: , , , 1 Comment

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Eyelids. They come in handy for sandstorms, eye shadow, and poolside naps. You don’t see much when they’re closed, but when they’re open you have an all-access pass to the visible world around you. Right? Well, not exactly. Here at Garden of the Mind, the next two posts are dedicated to the ways that you are blind – every day – and with your eyes wide open.

One of the ways you experience everyday blindness has to do with the movements of your eyes. If you stuck a camera in your retina and recorded the images that fall on your eye, the footage would be nauseating. Think The Blair Witch Project, only worse. That’s because you move your eyes about once every half a second – more often than your heart beats. You make these eye movements constantly, without intention or even awareness. Why? Because, thanks to inequalities in the eye and visual areas of the brain, your peripheral vision is abysmal. It’s true even if you have 20/20 vision. You don’t sense that you are legally blind in your peripheral vision because you compensate by moving your eyes from place to place. Like snapping a series of overlapping photographs to create a panoramic picture, you move your eyes to catch different parts of a scene and your brain stitches these ‘shots’ together.

As it turns out, the brain is a wonderful seamstress. All this glancing and stitching leaves us with a visual experience that feels cohesive and smooth – nothing like the Frankenstein creation it actually is. One reason this beautiful self-deception works is that we turn off much of our visual system every time we move our eyes. You can test this out by facing a mirror and moving your eyes quickly back and forth (as if you are looking at your right and left ears). Try as you might, you won’t be able to catch your eyes moving. It’s not because they’re moving too little for you to see; a friend looking over your shoulder would clearly see them darting back and forth. You can feel them moving yourself if you gently rest your fingers below your lower lashes.

It would be an overstatement to say that you are completely blind every time you move your eyes. While some aspects of visual processing (like that of motion) are switched off, others (like that of image contrast) seem to stay on. Still, this means that twice per second, or 7,200 times each hour, your brain shuts you out of your own sense of sight.  In these moments you are denied access to full visual awareness. You are left, so to speak, in the dark.

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Photo credit: Pete Georgiev on Flickr under Creative Commons license

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