Why Your Native Language Makes Certain English Sounds So Hard

By the time you were twelve months old, your brain had already made some important decisions about sound. It had figured out which acoustic differences matter in your language and which ones don’t. It had built a sorting system for speech sounds, a set of categories that would let you process your native language efficiently for the rest of your life.

The problem is that English uses a different set of categories. And your brain is still using the old ones.

How do infants learn to filter speech sounds?

Patricia Kuhl, a developmental psychologist at the University of Washington, discovered something remarkable about how infants learn language. In the first six months of life, babies can discriminate virtually any speech sound contrast from any language in the world. They’re universal listeners.

But between six and twelve months, something changes. As infants hear more and more of their native language, their brains start to specialize. The sounds they hear frequently become category prototypes, and these prototypes start acting as what Kuhl calls “perceptual magnets.” Sounds that are acoustically similar get pulled toward the prototype. The baby stops noticing differences that don’t matter in their language.

This is brilliant engineering for a baby learning one language. It’s a problem for an adult learning a second one.

You might think completely foreign sounds would be hardest to learn. The research says otherwise.

Why are “similar” sounds harder than completely new ones?

James Flege spent decades studying how adults learn second language pronunciation. His Speech Learning Model makes a counterintuitive prediction: the hardest sounds to learn aren’t the ones that are completely new. The hardest sounds are the ones that are similar to something in your native language, but not quite the same.

If a sound is totally novel, your brain recognizes it as new and tries to create a new category for it. But if it’s close to something you already know, your brain just maps it onto the existing category. You literally can’t hear the difference, because your perceptual system is treating both sounds as “the same thing.”

This explains a lot. The English “th” sounds don’t exist in most languages, so learners know they need to learn something new. But the English vowel distinction between “ship” and “sheep”? Spanish has a vowel that’s close to one of them. So Spanish speakers’ brains map both English sounds onto that single Spanish category, and the distinction disappears.

This pattern plays out differently depending on which language you grew up speaking.

Which sounds are hardest for speakers of different languages?

Different native languages create different blind spots.

Spanish speakers typically struggle with the /ɪ/ vs /iː/ distinction (ship vs sheep), because Spanish has only one high front vowel. They also conflate /b/ and /v/, struggle with word-final consonant clusters, and often add a vowel before words starting with /s/ clusters (“espeak” for “speak”).

Japanese speakers famously can’t distinguish English /r/ from /l/, because Japanese has a single sound that’s articulated somewhere between the two. They also struggle with the “th” sounds, consonant clusters, vowel length distinctions that don’t pattern like Japanese.

Mandarin speakers tend to drop word-final consonants entirely, because Mandarin syllables almost never end in consonants other than /n/ or /ŋ/. They struggle with “th” sounds, voiced/voiceless distinctions, the reduced vowels that are everywhere in unstressed English syllables.

German speakers like me often confuse /w/ and /v/ (“vine” for “wine”), struggle with “th” sounds, and devoice final consonants (“dok” for “dog”) because German has a rule that does exactly that.

Arabic speakers often substitute /b/ for /p/, because Arabic has /b/ but not /p/. They struggle with vowel distinctions that don’t exist in Arabic and have difficulty with certain consonant clusters.

These aren’t random difficulties. They’re predictable from the phoneme inventory of your native language. But predictable doesn’t mean permanent.

Can adults form new phoneme categories?

Here’s what the research also shows: adults can form new phoneme categories. It takes work, but it’s not impossible.

Ann Bradlow and colleagues showed that Japanese speakers could learn to distinguish English /r/ from /l/ after just a few weeks of perceptual training. The training involved listening to many different speakers producing minimal pairs and getting immediate feedback on which sound they’d heard. Crucially, this perceptual learning transferred to production, the listeners started pronouncing the sounds more distinctly too.

What makes category formation work? High-variability training, for one you need to hear the target sounds from many different speakers in many different contexts, so your brain can separate what’s essential about the sound from what’s just individual speaker variation. Unlike infants, adults also benefit from being told what they’re listening for. Knowing that a distinction exists helps you attend to the right acoustic cues. Immediate feedback matters because without it you can’t update your categories, you need to know whether you correctly identified or produced the sound. And new categories need reinforcement over time through spaced repetition, because a single training session isn’t enough to make them stick.

What does this mean for practice?

The fact that certain sounds are hard for you isn’t a personal failing. It’s a predictable consequence of which language you grew up speaking not a sign that your accent is permanently “fossilized”. Your brain optimized for that language, and now you’re asking it to do something different.

But “predictable” also means “addressable.” If you know which specific sounds are likely to give you trouble based on your L1, you can focus your practice there. There’s no point drilling sounds you already produce correctly. Target the ones where your native language is working against you.

And be patient with sounds that your brain is literally learning to distinguish for the first time. When a Spanish speaker works on /ɪ/ vs /iː/, they’re not just learning to move their mouth differently. They’re building a new perceptual category, carving out a distinction in acoustic space that didn’t exist for them before.

That’s harder than it sounds. It’s also entirely possible.

This is why we built SpeechLoop. The app knows which sounds are typically hard for speakers of your native language. The /w/ vs /v/ confusion for German speakers like me. The /ɪ/ vs /iː/ collapse for Spanish speakers. The /r/ and /l/ merger for Japanese speakers. It doesn’t waste your time on sounds you already produce correctly. It goes after the phonemes where your L1 is actively working against you. Your first language spent a decade wiring your perception. Rewiring it won’t happen by accident.

---

References

Kuhl, P. K. (1991). Human adults and human infants show a “perceptual magnet effect” for the prototypes of speech categories, monkeys do not. Perception & Psychophysics, 50(2), 93–107.

Kuhl, P. K. (2004). Early language acquisition: Cracking the speech code. Nature Reviews Neuroscience, 5(11), 831–843.

Flege, J. E. (1995). Second language speech learning: Theory, findings, and problems. In W. Strange (Ed.), Speech Perception and Linguistic Experience (pp. 233–277). York Press.

Flege, J. E., & Bohn, O.-S. (2021). The revised Speech Learning Model (SLM-r). In R. Wayland (Ed.), Second Language Speech Learning: Theoretical and Empirical Progress (pp. 3–83). Cambridge University Press.

Bradlow, A. R., Pisoni, D. B., Akahane-Yamada, R., & Tohkura, Y. (1997). Training Japanese listeners to identify English /r/ and /l/: IV. Some effects of perceptual learning on speech production. Journal of the Acoustical Society of America, 101(4), 2299–2310.