Those who suffer from a stutter get hung up on individual sounds or syllables, making everyday interactions like placing calls or asking for directions difficult. The disorder cannot be cured, but therapy can help.
"I always compare it with someone who's listening to a car radio with bad reception. There's some static, but it's enough to understand the news. But when an additional disruption comes into the mix, like a bridge or a very narrow street, then the signal breaks off," says neurologist Martin Sommer about stuttering. Sommer suffers from the speech disorder himself, but also researches stuttering at the University of Göttingen's clinic.
There are around 800,000 people in Germany - one percent of the total population - who stutter. A similar proportion is found in other countries around the world, Sommer says.
The phenomenon usually first manifests in children aged three to six. At that age, the prognosis is still good. Between 60 and 80 percent of these children are able to move past their stutters. Others have to learn how to cope with the disorder, which cannot be cured.
Men face the problem much more often than women, who account for just 20 percent of stutterers.
The standard symptom of stuttering is the frequent repetition of individual sounds, syllables or entire words. Along with repeated sounds, stutterers often also prolong sounds within words. In extreme instances, nothing at all comes out when they try to speak. Their speech organs may be exerted to their fullest, but no sound follows. The words simply will not come out even though the stutterer knows exactly what he wants to say.
Many of those afflicted also deal with related psychological problems. They may isolate themselves socially, or they may try to avoid saying certain words and speaking in certain situations - including mundane things like buying a train ticket, telephoning others at work or asking for directions. Social interactions that represent no difficulty at all for most can become insurmountable for those who stammer.
Plethora of studies and theories
How stuttering comes about - which disruptions and tiny mechanisms are at work - remains a tough question for researchers. Visualization techniques have been used for around 15 years to examine the phenomenon. One key tool is the use of magnetic resonance imaging (MRI), which can generate pictures of how a person's brain is structured.
Many studies on adult stutterers have been undertaken, Sommer said. "They show what seem to be subtle disruptions of the brain - of its hardware, in a sense - in the left, frontal part of the brain."
The researcher adds that this part of the brain is responsible for speech and that the problem also affects the fiber tracts, which connect relevant brain regions with one another. The grey cells are indeed present there, but their connections have either been disrupted or are more prone to disruption than in non-stutterers. In turn, the precise cooperation needed among many muscles for fluid speech can get interrupted.
Genes play a key role
Stuttering could have its basis in the brain's hardwiring, but there can clearly be a psychological component as well. Under pressure, stammering tends to get worse.
Genetics also play a key role in the disorder's emergence, and studies make genes responsible for up to two-thirds of all cases of stuttering. That is true of Reiner Nonnenberg, a tax accountant in Cologne, Germany. His grandfather suffered from stuttering, as did his father, and now Nonnenberg as well as his 18-year-old son. While speaking, he makes arbitrarily long pauses during which he struggles to arrive at words and repeats individual sounds. It can last several seconds before he is able to speak the word.
Nonnenberg says he never received speech therapy, which was not common in Germany when the 71-year-old was growing up.
"The fact that I am still in a self-help organization shows that I still constantly work on getting to a point where I'm content. I have phases in which I speak very fluently but then very badly again," Nonnenberg said.
He and other stutterers are in good company as there are a number of well-known fellow sufferers. They include British writer George Bernard Shaw, actor Bruce Willis and even Aristotle. The stuttering problem of King George VI was the main plot in the 2010 Oscar-winning movie "The King's Speech."
Ways of coping
Reiner Nonnenberg takes part regularly in meetings held by the Cologne Self-Help Group for Stutterers, which offers training for telephone conversations, group reading sessions and video training modules in which the group's members are confronted with problematic situations from everyday life. Peter Czolbe helps organize the group's activities and notes that one method members use to cope is to practice limiting their vocabularies to words that they know present few or no problems in speech.
Neurologist Martin Sommer explains another therapy method called fluency shaping, in which speakers attempt to shift to a gentler manner of speaking in an effort to bypass stuttering altogether.
"The price, however, is that I have to speak rather strangely the whole time," the doctor says of the method, which renders speech somewhat choppy and robotic.
"The other school of thought involves stuttering modification. I speak just like I normally would, but at the junctures where I get stuck, I try to move past the speech blockade slowly and with control," Sommer said.
Singing rather than speaking?
In stutterers' brains, one half of the organ tries to compensate for the deficits in the other half.
"We know that singing is primarily activated in the right side of the brain, and almost all stutterers are able to sing without complication. But in speaking, which lies overwhelmingly in the left part of the brain, disruptions emerge in these same people," Sommer says.
Singing is no problem, then, which Peter Czolbe is happy to demonstrate. He sings a line from an old song by pop group Genesis: "Was it summer when the river ran dry, or was it just another dam?"
He doesn't just hit the notes - the words flow out uninterrupted and without the faintest trace of stammering.
Ever wanted to peek inside a black hole, even if just in theory? Kip Thorne, the physicist behind "Interstellar" and "Contact," takes us on a headlong dive into space-time exotica.
A train expert tells DW that Germany's rail system is highly automated and dependable - but occasionally requires manual signals. Though newer technologies exist, most Germans won't see them any time soon.
Once upon a time, it was Bolivia's second-largest lake. Today, it has all but vanished. New satellite images have confirmed this. The disappearance of Lake Poopó has dramatic consequences for wildlife - and people.
Reputed to be home to the greatest range of biodiversity of any country in the world, Costa Rica is a natural paradise. Artist Manuel E Gonzalez aims to transport these riches onto canvas.