We Got the Beat


It is both amusing and enlightening to hear my 21-month-old daughter sing the alphabet song. The song is her favorite, though she is years from grasping how symbols represent sound, not to mention the concept of alphabetical order. Still, if you start singing the song she will chime in. Before you think that’s impressive, keep in mind that her version of the song is more or less this: “CD . . . G . . . I . . . No P . . . S . . . V . . . Dub X . . . Z.”

Her alphabet song adds up to little more than a Scrabble hand, yet it is a surprising feat of memory all the same. My daughter doesn’t know her last name, can’t read or write, and has been known to mistake stickers for food. It turns out that her memory for the alphabet has far less to do with letters than lyrics. From Wheels on the Bus to Don’t Stop Believin’, she sings along to all of her favorite songs, piping up with every word and vowel she remembers. Her performance has nothing to do with comprehension; she has never seen or heard about a locker, yet she sings the word at just the right time in her rendition of the Glee song Loser like Me. (Go ahead and judge me. I judge myself.)

My daughter’s knack for learning lyrics is not unique to her or to toddlers in general. Adults are also far better at remembering words set to song than other strings of verbal material. That’s why college students have used music to memorize subjects from human anatomy to U.S. presidents. It’s why advertisers inundate you with catchy snippets of song. Who can forget a good jingle? To this day, I remember the phone number for a carpet company I saw advertised decades ago.

But what is it about music that helps us remember? And how does it work?

It turns out that rhythm, rather than melody, is the crucial component to remembering lyrics. In a 2008 study, subjects remembered unfamiliar lyrics far better if they heard them sung to a familiar melody (Scarborough Fair) than if they heard them sung to an unfamiliar song or merely spoken without music. But they remembered the lyrics better still if they heard the lines spoken to a rhythmic drummed arrangement of Scarborough Fair. Even an unfamiliar drummed rhythm boosted later memory for the words. By why should any of these conditions improve memory? According to the prevailing theory, lyrics have a structural framework that helps you learn and recall them. They are set to a particular melody through a process called textsetting that matches the natural beat and meter of the music and words. Composers, lyricists, and musicians do this by aligning the stressed syllables of words with strong beats in the music as much as possible. Music is also comprised of musical phrases; lyrics naturally break down into lines, or “chunks,” based on these phrase boundaries. And just in case you missed those boundaries, lyricists often emphasize the ends of these lines with a rhyming scheme.

Rhythm, along with rhyme and chunking, may be enough to explain the human knack for learning lyrics. Let’s say you begin singing that old classic, Twinkle, Twinkle, Little Star. You make it to “How I wonder,” but what’s next? Since the meter of the song is BUM bah BUM bah and you ended on bah, you know that the next words must have the stress pattern BUM bah. This helps limit your mental search for these words. (Oh yeah: WHAT you!) The final word in the line is a breeze, as it has to rhyme with “star.” And there you have it. Rhythm, along with rhyme and chunking, provide a sturdy scaffold for your memory of words.

For a more personal example of rhythm and memory, consider your own experience when you remember the alphabet. It’s worth noting that the alphabet song is set to a familiar melody (the same as Twinkle, Twinkle, Little Star and Baa, Baa, Black Sheep), a fact that surely helped you learn the alphabet lyrics in the first place. Now that you know them, ask yourself this: which comes first, the letter O or L? If you’re like me, you have to mentally run through the first half of the song to figure it out. Yet this mental rendition lacks a melody. Instead, you list the letters according to the song’s rhythm. Your list probably pauses after G and again after P and V, which each mark the end of a line in the song. The letters L, M, N, and O each last half as long as the average letter, while S sprawls out across twice the average. Centuries ago, a musician managed to squeeze the letters of the alphabet into the rhythm of an old French folk song. Today, the idiosyncratic pairing he devised remains alive – not just in kindergarten classrooms, but in the recesses of your brain. Its longevity, across generations and across the lifespan, illustrates how word and beat can be entwined in human memory.

While a rhythm-and-rhyme framework could explain the human aptitude for learning lyrics, there may be more to the story. As a 2011 study published in the Journal of Neuroscience shows, beat and meter have special representations in the brain. Participants in the study listened to a pure tone with brief beats at a rate of 144 per minute, or 2.4 Hz. Some of the participants were told to imagine one of two meters on top of the beat: either a binary meter (a march: BUM bah BUM bah BUM) or a ternary meter (a waltz: BUM bah bah BUM bah bah BUM). These meters divided the interval between beats into two or three evenly spaced intervals, respectively. A third group performed a control task that ensured subjects were paying attention to the sound without imagining a meter. All the while, the scientists recorded traces of neural activity that could be detected at the scalp with EEG.

The results were remarkable. Brain waves synchronized with the audible beat and with the imagined meters. This figure from the paper shows the combined and averaged data from the three experimental groups. The subjects in the control group (blue) heard the beat without imagining a meter; their EEGs showed strong brain waves at the frequency of the beat, 2.4 Hz. Both the march (red) and waltz (green) groups showed this 2.4 Hz rhythm plus increased brain waves at the frequency of their imagined meters (1.2 Hz and 0.8 Hz, respectively). The waltz group also showed another small peak of waves at 1.6 Hz, or twice the frequency of their imagined meter, a curiosity that may have as much to do with the mechanics of brain waves as the perception of meter and beat.

Screen Shot 2013-08-21 at 1.15.47 PMIn essence, these results show that beat and meter have a profound effect on the brain. They alter the waves of activity that are constantly circulating through your brain, but more remarkably, they do so in a way that syncs activity with sound (be it real or imagined). This phenomenon, called neural entrainment, may help you perceive rhythm by making you more receptive to sounds at the very moment when the next beat is due. It can also be a powerful tool for learning and memory. So far, only one group has tried to link brain waves to the benefits of learning words with music. Their papers have been flawed and inconclusive. Hopefully some intrepid scientist will forge ahead with this line of research. Until then, stay tuned. (Or should I say metered?)

Whatever the ultimate explanation, the cozy relationship between rhythm and memory may have left its mark on our cultural inheritance. Poetry predated the written word and once served the purpose of conveying epic tales across distances and generations. Singer-poets had to memorize a harrowing amount of verbal material. (Just imagine: the Iliad and Odyssey began as oral recitations and were only written down centuries later.) Scholars think poetic conventions like meter and rhyme arose out of necessity; how else could a person remember hours of text? The conventions persisted in poetry, song, and theater even after the written word became more widespread. No one can say why. But whatever the reason, Shakespeare’s actors would have learned their lines more quickly because of his clever rhymes and iambic pentameter. Mozart’s opera stars would have learned their libretti more easily because of his remarkable music. And centuries later you can sing along to Cyndi Lauper or locate Fifty Shades of Grey in the library stacks – all thanks to the rhythms of music and speech.


Photo credits: David Martyn Hunt on Flickr and Nozaradan, Peretz, Missal & Mouraux via The Journal of Neuroscience

Nozaradan, S., Peretz, I., Missal, M., & Mouraux, A. (2011). Tagging the Neuronal Entrainment to Beat and Meter The Journal of Neuroscience DOI: 10.1523/JNEUROSCI.0411-11.2011

Genetics Post on DoubleXscience

I recently contributed a post to DoubleXScience, a site dedicated to all things women and science. The piece is called Armchair Genetics from Jamestown to Scott Brown and can be found here. It touches on children and race, assumptions, celebrities, a Cheerios ad, and the history of anti-miscegenation laws in the US (particularly relevant in light of the recent rulings on gay marriage). Please feel free to comment and share your own experiences or just let me know what you think!

Flipping the Baby Switch

img_2348-1Rewind to last night. It was bedtime. My infant daughter was screaming and struggling in my lap while I tried to rock her to sleep. She pulled and twisted the skin on my face. She sunk her tiny teeth into my shoulder and chest. Exasperated, I rose from the rocker and started pacing around the nursery. Her tense little body instantly relaxed. Within ten seconds she was quiet and still. Within two minutes she was asleep.

The scene was not unusual for our household. Even as a newborn, my daughter was easy to upset and hard to soothe. When nothing else worked and I was about to lose my mind I’d get up and walk with her. Often the results were nothing short of miraculous. Imagine going from 100 miles per hour to zero in a snap. For those who recall the child android Vicki on the ‘80s TV show Small Wonder, think of the times someone flipped the off-switch on her back. That’s what it’s like when I walk with my daughter. Our aimless walking flips a switch somewhere inside of her. But how does the switch work? And why does she have one in the first place? A study published in Current Biology last month helps to explain this curious facet of infant behavior.

The head scientist behind the study was Dr. Kumi Kuroda at the RIKEN Brain Science Institute in Japan. As she described in an interview with ScienceNOW, she became interested in the topic when she noticed that she could calm her own newborn son by carrying him. She later tested 12 other newborns with their mothers and found that they behaved like her son. Overall, the effect was rapid and dramatic. Some babies stopped crying as soon as their mothers began to walk with them. The rest cried less and were less shrill when they did cry. The babies also moved less and had lower heart rates while they were being carried.

To study the biological mechanisms behind this remarkable calming response, Dr. Kuroda and her colleagues turned to mice. They showed that mouse pups have a similar response when carried by their mothers. Mouse moms carry their pups by the scruff of their necks. When carried, mouse pups less than 20 days old stop wriggling. Their heart rate slows and they stop crying out. (Like most mouse vocalizations, baby mouse cries are ultrasonic). They also draw their legs in when carried, making their bodies more compact for toting around.

Kuroda and colleagues investigated several physiological aspects of the calming response in mice. Only a few of these experiments are probably relevant for infants, since human babies don’t assume a compact position like carried mouse pups do. One looked for the triggers that make carried pups stop squirming. The scientists anesthetized the neck skin of baby mice and found that these animals wriggled more than untreated mouse pups when carried. They got the same result when they overdosed pups with vitamin B6 before testing. (Vitamin B6 overdose causes animals and humans to lose the sense of their body position and movement.) The upshot? For a mouse pup to stop wriggling when carried it must 1) sense that it’s being lifted and 2) sense that something is pulling on its neck skin. Take either sense away and the calming response disappears. My daughter may draw on similar senses to trigger her miraculous stillness while carried. (Only if you replace neck pulling with the pressure of my arms around her, of course. I don’t carry her by her neck skin, I swear.)

The scientists also wondered why a baby’s heart rate drops when it’s picked up and carried. To test this in mice, they gave pups a drug that turns down the parasympathetic nervous system (the set of nerves that return the body to a calm state after arousal). Pups treated with the drug still stopped wriggling when lifted, but their heart rates didn’t drop as they do in untreated pups. So while the parasympathetic nervous system slows down the carried pup’s (and possibly infant’s) heartbeat, it can’t take credit for other features of the calming response.

Clearly this calming response is more complicated than it seems. Many of my daughter’s brain areas, neural pathways, and sensory mechanisms were working in concert to soothe her last night as I walked her in circles. But why does she have this complex reaction to carrying in the first place? Grateful parents might imagine that the calming response evolved to keep us from going crazy, but unless going crazy involves committing infanticide, this explanation doesn’t hold water. Evolution doesn’t care whether parents are happy or well rested or have time to watch Game of Thrones. It only cares whether our offspring survive.

Dr. Kuroda and her colleagues propose that the calming response helped parents escape dangerous situations while protecting their young. According to this logic, calmer carried babies meant faster escapes and higher rates of survival. Certainly if you were running from a wild beast or a member of a rival village, holding a struggling infant might slow you down. Of course holding any infant would slow you down and it’s not clear that sprinting with a struggling newborn is much harder than lugging one that’s asleep.  The paper’s authors present little evidence to support their proposal, particularly in the context of human evolution. They point to a minor result with their mice that doesn’t easily translate to human behavior. In effect, the jury’s still out.

There are other possible explanations for the calming response, ones that don’t involve predators outrunning parents. Shushing can calm crying babies too, probably because it simulates an aspect of their environment in the womb (in this case,  physiological noise). The same could be true of walking with infants. The mothers in the Kuroda study held their babies against their chest and abdomen, which is also how I hold my daughter when I walk to soothe her. The type of movement she feels in that position is probably similar to the rocking and jostling she felt as a fetus in utero whenever I walked. If so, the calming response might be a result of early learning and comfort by association – a nice thought when you consider the gory alternative.

Each year at the end of May we find ourselves as far as possible from Thanksgiving Day. It can be something of a thankfulness drought. This May I am thankful for women in science and maternity leaves, computer-generated dragons and ’80s sitcom androids. And like Vicki’s parents, I am profoundly thankful that my daughter came furnished with an off-switch. Whatever the reason why.


Photo credit: Sabin Dang

Esposito G, Yoshida S, Ohnishi R, Tsuneoka Y, Rostagno Mdel C, Yokota S, Okabe S, Kamiya K, Hoshino M, Shimizu M, Venuti P, Kikusui T, Kato T, & Kuroda KO (2013). Infant Calming Responses during Maternal Carrying in Humans and Mice. Current biology : CB, 23 (9), 739-45 PMID: 23602481

Pb on the Brain


I’ve got lead on my mind. Lead the element, not the verb; the toxic metal that used to grace every gas tank and paint can in this grand country of ours. For the most part we’ve stopped spewing lead into our environment, but the lead of prior generations doesn’t go away. It lingers on the walls and windows of older buildings, on floors as dust, and in the soil. These days it lingers in my thoughts as well.

I started worrying about lead when my daughter became a toddler and began putting everything in her mouth. I fretted more when I learned that lead is far more damaging to young children than was previously thought. Even a tiny amount of it can irreversibly harm a child’s developing brain, leading to lower IQs, attention problems and behavioral disorders. You may never even see the culprit; lead can sit around as microscopic dust, waiting to be inhaled or sucked off of an infant’s fingers.

Public health programs use blood lead levels (BLLs) to evaluate the amount of lead in a child’s system and decide whether to take preventative or medical action. In the 1960s, only BLLs above 60 μg/dL were considered toxic in children. That number has been creeping downward ever since. In 1985 the CDC’s stated blood lead level of concern became 25 μg/dL and in 1991 it went down to 10. But last year the CDC moved the cutoff down to 5 μg/dL and got rid of the term “level of concern.” That’s because scientists now believe that any amount of lead is toxic. In fact, it seems as if lead’s neurotoxic effects are most potent at BLLs below 5 μg/dL. In other words, a disproportionately large amount of the brain damage occurs at the lowest doses. Recent studies have shown subtle intellectual impairments in kids with BLLs as low as 2 μg/dL (which is roughly the mean BLL of American preschoolers today). All great reasons for parents to worry about even tiny exposures to lead, no?

Yes. Absolutely. Parents never want to handicap their children, even if only by an IQ point or two. But here’s what’s crazy: nearly every American in their fifties, forties, or late-thirties today would have clocked in well over the current CDC’s cutoff when they were little. The average BLL of American preschoolers in the late ‘70s was 15 μg/dL – and 88% had BLLs greater than 10 μg/dL.

These stats made me wonder if whole generations of Americans are cognitively and behaviorally impaired from lead poisoning as children. Have we been blaming our intellectually underwhelming workforce on a mismanaged education system, cultural complacency, or the rise of television and video games when we should have been blaming a toxic metal element?

I was sure I wasn’t the first person to wonder about the upshot of poisoning generations of Americans. And lo and behold, a quick Google search led me to this brilliant article on Mother Jones from January. The piece chronicles a rise in urban crime that began in the ‘60s and fell off precipitously in the early-to-mid ‘90s nationwide. The author, Kevin Drum, walks readers through very real evidence that lead fumes from leaded gasoline were a major cause of the rise in crime (and that increased regulation restricting lead in gasoline could be credited for the sudden drop off.)

The idea certainly sounds far-fetched: generations of city-dwellers were more prone to violence as adults because they breathed high levels of lead fumes when they were kids. It doesn’t seem possible. But when you put the pieces together it’s hard to imagine any other outcome. We know that children of the ‘50s, ‘60s, and ‘70s had BLLs high enough to cause irreversible IQ deficits and behavioral problems (of which aggression and impulse control are particularly common). Why is it so hard to imagine that more of these children behaved violently when they became adults?

In the end, this terrible human experiment in mass poisoning has left me pondering two particular questions. First, what does it mean for generations of children to be, in a sense, retroactively damaged by lead? At the time, our levels were considered harmless, but now we know better. Does knowing now, at this point, explain anything about recent history and current events? Does it explain the remarkable intransigence of certain politicians or the bellicosity of certain talk show hosts, athletes, or drivers with a road rage problem? Aside from the crime wave, what other sweeping societal trends might be credited to the poisoning of children past? How might history have played out differently if we had all been in our right minds?

Finally, I’ve been thinking a lot about the leads and asbestoses and thalidomides of today. Pesticides? Bisphenol A? Flame retardants? What is my daughter licking off of those toys of hers and how is it going to harm her twenty years down the line? This is not just a question for parents. Think crime waves. Think lost productivity and innovation. Today’s children grow up to be tomorrow’s adults. Someday when we are old and convalescing they’ll take the reigns of our society and drive it heaven-knows-where. That makes child health and safety an issue for us all. We may never even know how much we stand to lose.


Photo credit: Zara Evens

At the Gates of Sleep

497736998_45c09a136e_oNow that my daughter is about to reach her first birthday, I’m in the mood to reflect on the year that just passed. Unfortunately, my recollections of it are a little fuzzy, probably because I can count on one hand the number of times I’ve enjoyed a good night’s sleep over the past year. Some people have babies who regularly sleep through the night and I am happy for them. Truly, I am. But clearly I was not meant to be in their ranks.

Still, the never-ending parade of nighttime awakenings has taught me something about my own brain. It is precisely tuned to hear my baby. Although I sleep blithely through my husband’s thunderous snoring and the loud buzz of his alarm clock – multiple times a day, thanks to the snooze button – I awaken at the faintest sound of my daughter’s sighs, coos, or grumbles. When she cries, I am immediately awake while my husband sleeps on beside me, undisturbed.

People are generally able to sleep through minor sounds and sensations thanks to a subcortical structure in the brain called the thalamus. This structure receives incoming signals from our senses and relays them to cortical areas devoted to processing sensory information like sounds or tactile sensations. When we’re awake, the thalamus faithfully relays nearly every sensory signal on to the cortex. But when we’re asleep, neurons in the thalamus participate in strong, synchronized waves of activity that squelch incoming signals. As a result, about 70% of these signals never make it to the cortex. This process, known as sensory-gating, is how we manage to sleep through the roar of rainstorms or the brush of the sheets against our skin each time we turn in bed. It is also how we sleep through our husband’s room-rattling snores.

Yet some sensory information does get through to the rest of the brain during sleep. These signals do get processed and can even wake us up if they are either intense (like a loud noise) or personally relevant. A clever study illustrated the importance of personal relevance by exposing sleeping subjects to a loud presentation (via tape recorder) of their own name spoken aloud. The scientists played the recording either normally or backwards and found that subjects awoke in less than half the time when they heard their names presented in the recognizable form.

So did my daughter, in effect, sleep train me by training my brain to recognize her sounds as personally relevant? It’s a plausible explanation, but one that is ultimately lacking. It cannot explain that first night when I slept beside my baby at the hospital nearly one year ago. Although I had labored through the entire night before and had not slept in the ensuing day, I awoke constantly to every little sound my mewing newborn made, not to mention the cries that told me she wanted to nurse. She’d had no time to train me; I had come pre-trained. Just as my breasts were primed to make milk for her, my brain was primed to wake for her. We seemed to be engineered for one other, mother and child, body and brain. And we spent that first long night discovering how clever a designer Nature can be, while my husband slept peacefully on the couch.


Photo credit: planetchopstick

Tooling Around

tools1There was a time when my daughter used her hands exclusively to shovel things into her mouth. Not so anymore. For the last few months, she has been hard at work banging objects together. This simple action is setting the stage for some pretty cool neural development. She is learning to use tools.

Of course it doesn’t look too impressive right now. She might bang a ball with a block and then switch and strike the block with the ball. In one recent playtime she tore a cardboard flap out of her board book and examined it, trying different grips and holding it from different angles as she watched how it cut the air. Then, brandishing her precious flap, she went to work. She wielded it with a scooping motion to lift other flaps in the book, and later, to turn the book pages themselves. After that, she descended on her toy box with the flap. She used it to wipe her blanket, poke her stuffed animal, and finally scrape its face like she was giving it a close shave.

Although my daughter’s fun with flaps may seem aimless, it had an important purpose. Through experimentation and observation, she was learning how two objects can interact and how such interactions are affected by object shape, configuration, and pliability. Such details are so well known to adults that we forget there was anything to learn. But consider how often we use objects against one another. We hammer nails, rake leaves, and staple pages. When using scissors, we must apply different levels of force to cut through paper versus cardboard or fabric. When lifting a pan with a potholder, we must adjust our grip depending on the weight of the pan and whether we are lifting it by the base, side, or handle. We must know the subtle differences between holding a sponge to wash a glass and using a towel to dry it, and we must do each deftly enough that our glassware comes out clean and intact at the end.

There are also countless tools we create on the fly every day. When you use a magazine to nudge your cell phone within reach or flip a light switch with a book because your hands are full, you are devising novel tools to fit your momentary needs. To do this, our brains must store extensive knowledge about the properties of household objects. Through experimentation, like the kind my daughter is doing, we learned to predict how objects will interact and to capitalize on those predictions.

So far I’ve described the value of tools in terms of what they can do: push, pull, gather, polish, lift, etc. But there is another side to tool use that may play a role in my daughter’s little experiments: sensory information gleaned through the tool. As I watched her probe one object with another, I was reminded of research described in Sandra and Matthew Blakeslee’s book The Body Has a Mind of Its Own. The book discussed neurons in the parietal cortex that are tuned to the sight or feel of objects near a particular body part. For example, cells representing your right hand would fire if something touched your right hand, if you saw an object near your right hand, or both. Neuroscientists have discovered that experience using a tool can change the properties of these cells in monkeys (and therefore likely in us as well). They found that if monkeys used a rake to gather goodies otherwise beyond their reach, the parietal neurons that had responded to objects around the hand now fired for items located anywhere along both the hand and the rake it held. In a sense, object manipulation can temporarily extend certain neural body representations to include the tools we wield. The Blakeslees suggest that this may be how a blind person learns to perceive the contour of items encountered at the tip of his cane. In effect, the cane and the hand are one.

For now, our house is filled with smashing, scraping, banging and bending as our baby descends on toys and her parents’ belongings alike. In the midst of such havoc, it’s good to know that the destruction is part of a crucial learning process. And someday, once it slows down, I can buy her a new board book with all the flaps intact.


Photo credit: zzpza

It’s a Zoo Out There!


Our house is filled with animals. We’ve got animal rattles, animal teethers, stuffed animals and all manner of animal-patterned clothing, towels, and bedding. Then of course there are the board books; those that don’t name animals and list their moos and oinks star bipedal animals that brush their teeth, wear pajamas, and often suffer crushing insecurities. And we’re not talking about your standard cat, dog or hamster. They are usually elephants. Giraffes. Hippopotami. Animals you don’t see cruising down the street on an ordinary day. They are animals you’d probably never see in person if not for your local zoo.

The exotic menagerie that has descended on our house has got me wondering: why do we surround our children with animals that will have no discernible role in their future lives? Why aren’t there more infant toys based on tax returns or grocery lists? Where are the books with titles like The Grumpy Morning Commute or Fruit Salad Makes a Friend? I imagine the reason we supply young children with all-things-animal is because that’s what they like. That’s what fascinates them. And who can blame them? From the elephant’s trunk to the lightning bug’s glow, the odd, diverse traits of other species are just about the neatest show on this planet of ours. It’s a fact we lose sight of as we get older. Giraffes are old news to us now. They’ve got super long necks. So what? Big deal.

This past week, however, I noticed my husband checking his iPhone with unusual glee. Had I heard? The new Mars rover landed without a hitch. Against all odds! And now it’s looking for signs of past or present life on Mars. How cool is that? As a scientist, I have to admit it’s pretty cool. But I can’t get as excited as my husband. It seems odd that we are investing so much to seek out microscopic life on another planet while there are still species here on Earth we have yet to discover. And while our own actions drive other species to extinction.

Clearly, we’ve forgotten how beautiful and strange and remarkable animals are. Perhaps we should re-brand them for adults. Maybe market them as aliens. If we found a cell on Mars (not to mention a roach or a mouse) we would go wild with excitement. Just imagine if the Curiosity rover found something as elegant as a jellyfish, as colorful as a peacock, or as chatty as a wise old humpback. Imagine how cool that would be.

I will have a chance to try this idea out sometime soon, as my new house in Michigan is near a big zoo. My husband and I have been meaning to go there ever since our move, not to see the animals ourselves but to witness our daughter’s reaction to them. Now I have a second reason to go. When we’re there, I’ll try to view the creatures as they might look to my daughter, who will be seeing them for the very first time. I’ll try to think of them as new and fantastic aliens that just so happen to live here on earth.


Photo credit: Doug Kukurudza

%d bloggers like this: