You have probably been told, at some point, to eliminate your filler words. "Um" and "uh" are verbal clutter, the thinking goes. They make you sound uncertain, unprepared, and unprofessional. Speech coaches build entire practices around helping people purge these sounds from their vocabulary.
There is just one problem: the science says they are wrong. Your "ums" and "uhs" are not verbal garbage. They are communication tools that help your audience understand you.
The Research
In 2001, psycholinguist Jean E. Fox Tree at UC Santa Cruz published a study in Memory & Cognition that challenged everything we thought we knew about filler words. She ran a clever experiment using recordings of spontaneous speech and did something unusual: she digitally edited them. In one version, she left the natural "uhs" intact. In the other, she surgically removed them, leaving the rest of the audio perfectly unchanged.
Then she had participants listen to both versions and measured how quickly they could recognize words in each one. This was not a subjective rating. It was a precise measurement of word recognition speed.
The results contradicted decades of speaking advice. When "uh" was present in the recording, listeners recognized the following words faster than when the filler had been removed. The filler was not slowing comprehension. It was speeding it up.
Interestingly, the study found different effects for "um" versus "uh." While "uh" significantly improved word recognition, "um" showed no effect either way. Fox Tree suggests this may be because "uh" signals a brief pause while "um" signals a longer delay, and the two fillers serve different communicative functions.
Fox Tree replicated the "uh" finding in a second experiment with Dutch speakers, confirming the effect was not limited to English. Across both studies (N=34 plus the Dutch replication), the pattern held: natural "uh" fillers improved, not impaired, listener comprehension.
Why Fillers Help Your Audience
The key insight from this research is that "um" and "uh" are not meaningless noise. They are signals that carry information.
When you say "uh," you are telling your listener: "I am about to pause briefly, but keep listening." When you say "um," you are signaling a longer delay is coming. These sounds function like verbal yellow lights, preparing your audience for what is about to happen in your speech.
Without these signals, listeners have to work harder. They cannot predict when you will resume speaking or how long a pause might last. The cognitive load increases, and comprehension suffers. Your brain has to do extra work parsing speech that lacks these natural markers.
Written language needed hundreds of years to develop punctuation marks. Spoken language already has them built in. We call them filler words.
Practical Applications
1. Stop Aiming for Zero Fillers
The goal is not elimination. A speaker with no fillers at all can sound robotic, rehearsed, or even untrustworthy. Some research suggests overly polished speech triggers skepticism in listeners. Natural speech includes pauses and fillers. Embrace that reality.
2. Distinguish Signals from Tics
There is a difference between a natural "uh" while gathering your thoughts and a nervous "um-um-um" repeated rapidly without pause. The former helps comprehension. The latter can distract. Focus on reducing the tics, not the signals. Track your filler patterns to understand which ones serve communication and which ones stem from nervousness.
3. Trust Your Natural Speech Patterns
Your brain developed these filler sounds for a reason. They evolved as part of human communication. Rather than fighting your biology, work with it. Use your fillers intentionally when you need a moment to think. A well-placed "um" gives you time to formulate a better response while keeping your listener engaged.
The Bottom Line
The advice to eliminate all filler words was never backed by evidence. It was an assumption that sounded logical but failed the test of scientific investigation. Fox Tree's research, along with subsequent studies, shows that natural fillers actually help your audience process and understand your message.
The perfectly fluent speaker is not the ideal. The authentic, naturally paced speaker is. Your "ums" are not your enemy. They are part of what makes you sound human.
Put This Into Practice
Understanding that filler words help does not mean you should ignore them entirely. Awareness is still valuable. The goal is finding your natural balance between helpful signals and nervous tics.