How Do English Speakers Differentiate a “Th” Sound From an “F” Sound?

The best answer to any question.
May 16 2014 8:17 AM

How Do English Speakers Differentiate a “Th” Sound From an “F” Sound?

This question originally appeared on Quora.

Answer by Marc Ettlinger, Ph.D., linguistics, U.C. Berkeley:

Advertisement

English speakers don't actually differentiate "th" and "f" all that well. Indeed, in certain speech perception tests, native English speakers can perform as poorly as random guessing in distinguishing "th" and "f" because it's one of the most difficult contrasts in English.

That should be clear when you look at the spectrograms:

quora_140516_language

Courtesy of Marc Ettlinger

While "s" and "sh" have pretty clear differences in the amount of energy in the mid- to upper part of the spectrum, "th" and "f" are barely distinguishable, corroborating what we find in perception tests. The nature of some of these tests gives us insight into how this contrast is perceived.

First of all, people have done tests juxtaposing purely auditory stimulus with auditory plus visual. You'll notice that although this is one of the most difficult perceptual distinctions in language, it is also among the easiest visual distinctions. They're made with the lips (as noted in this great Quora answer), which we can see, but in different positions. Indeed, seeing the lips accounts for about a 20-30 percent difference in performance, all other things being equal.

Second, people are particularly bad at this contrast when any noises are present or when they have any hearing loss. This is because the acoustic differences are primarily in the upper part of the speech spectrum (see figure above), and the upper part of the spectrum is where noise and hearing loss are particularly problematic. So, your typical elderly person with mild hearing loss will perform around guessing level for out-of-context "th" and "f," too.

Given those perceptual challenges, we English speakers clearly use an appreciable amount of context in differentiating these sounds.

Luckily (but not coincidentally), the English language facilitates that. The functional load for this contrast is relatively low compared to other contrasts, meaning, aside from thin and fin there aren't too many words that critically rely on differentiating these sounds.

So, the answer to your question of how? Not all that well. And when we do, it's often due to context or visual cues. Otherwise, it's that small difference in the upper part of the speech spectrum, around 8 kHz, that serves as the differentiator.

More questions on Quora:

TODAY IN SLATE

Foreigners

More Than Scottish Pride

Scotland’s referendum isn’t about nationalism. It’s about a system that failed, and a new generation looking to take a chance on itself. 

What Charles Barkley Gets Wrong About Corporal Punishment and Black Culture

Why Greenland’s “Dark Snow” Should Worry You

Three Talented Actresses in Three Terrible New Shows

Why Do Some People See the Virgin Mary in Grilled Cheese?

The science that explains the human need to find meaning in coincidences.

Jurisprudence

Happy Constitution Day!

Too bad it’s almost certainly unconstitutional.

Is It Worth Paying Full Price for the iPhone 6 to Keep Your Unlimited Data Plan? We Crunch the Numbers.

What to Do if You Literally Get a Bug in Your Ear

  News & Politics
Weigel
Sept. 16 2014 7:03 PM Kansas Secretary of State Loses Battle to Protect Senator From Tough Race
  Business
Moneybox
Sept. 16 2014 4:16 PM The iPhone 6 Marks a Fresh Chance for Wireless Carriers to Kill Your Unlimited Data
  Life
The Eye
Sept. 16 2014 12:20 PM These Outdoor Cat Shelters Have More Style Than the Average Home
  Double X
The XX Factor
Sept. 15 2014 3:31 PM My Year As an Abortion Doula
  Slate Plus
Slate Plus Video
Sept. 16 2014 2:06 PM A Farewell From Emily Bazelon The former senior editor talks about her very first Slate pitch and says goodbye to the magazine.
  Arts
Brow Beat
Sept. 16 2014 8:43 PM This 17-Minute Tribute to David Fincher Is the Perfect Preparation for Gone Girl
  Technology
Future Tense
Sept. 16 2014 6:40 PM This iPhone 6 Feature Will Change Weather Forecasting
  Health & Science
Medical Examiner
Sept. 16 2014 11:46 PM The Scariest Campfire Story More horrifying than bears, snakes, or hook-handed killers.
  Sports
Sports Nut
Sept. 15 2014 9:05 PM Giving Up on Goodell How the NFL lost the trust of its most loyal reporters.