What is speech intelligibility?
To begin, let’s discuss what ‘intelligibility’ means. The classic definition of intelligibility is “the proportion of a speaker's output that a listener can readily understand.” So, simply put, intelligibility = understandability. Intelligibility is typically measured in a percentage (the number of utterances understood divided by total utterances spoken). Because it is relatively easy to measure, intelligibility does not require a ‘trained ear’ to gauge. Anyone (parents, teachers, friends, etc.) can assess a child’s or person’s intelligibility by simply making note of the number of times they understood the message.
However, the caveat is that there is some variability in who is measuring intelligibility. Oftentimes, a parent/caregiver will rate their child’s intelligibility much higher than the general community will. This is due to the fact that parents and caregivers (familiar listeners) typically understand the various nuances and patterns within their child’s speech, better than unfamiliar listeners (such as teachers, doctors, or extended family). A parent/caregiver may not consciously be aware of the fact that their child substitutes velar sounds /k/ and /g/, but the brain is truly phenomenal - it will subconsciously notice patterns within their child’s speech and correct for it.
For example, that same young child who cannot produce velar sounds may say “I see a deen tar,” and the parent will likely understand the message (correctly) as “I see a green car,” while unfamiliar listeners may not understand it at all. In addition, parents and familiar caregivers also have the advantage of understanding their child’s usual behaviors and gestures, thus increasing the chances of understanding the overall message. Young children who are neurotypical often utilize hand gestures and exaggerated facial expressions to get their meaning across, especially when not understood through speech alone. This is why phone conversations are oftentimes difficult with toddlers - there are limited context clues, no gestures, and no facial expressions to gauge the overall message. Video chatting helps by allowing for use of gestures and facial expressions, although the audio quality is oftentimes poorer than via phone.
What is normal speech intelligibility for my toddler?
Okay, so we’ve established that you can probably understand your child better than anyone else and now you know why. You are probably wondering “What is normal speech intelligibility for my toddler?” To answer this, we have to review some basics of early speech development. Let’s begin with babbling. Babbling is basically a baby exploring their own vocal and oral motor (lips, tongue, cheeks) mechanisms through practice. There are many types and stages of babbling (that can get very technical), so for simplicity’s sake, let’s review three basic stages :
Age birth - 3 months: Expect cooing (soft, throaty sounds with many open vowels).
Age 4 - 6 months: Baby continues cooing and true babbling begins with the introduction of early consonant sounds (/p, m, b, d, t, w, n, h/), either in isolation or with vowels within simple consonant-vowel combinations. Examples: “mmm”, “pa”, or “wee.”
Ages 7 - 12 months: Baby first begins to babble longer strings of repeated sounds, typically in consonant-vowel-consonant-vowel syllable shapes, such as “mimi”, “upup” “babababa.” As babbling progresses, the syllable shapes may become more complex, involving a variety of vowels and early consonant sounds within the same utterance, such as “de-da-de-da” or “ba-gu-ba-gu.” or Parents and caregivers will often mistake some of these babbles as first words, although they are usually spoken without true intent.
After 12 months of age, neurotypical young children will begin to use true words containing a variety of vowels and early consonant sounds in a variety of syllable shapes. Because many of these sounds and sound combinations are new to them, we certainly do not expect them to be fully intelligible right away. In fact, the latest research from Husted, et al, 2021 breaks down intelligibility by specific age ranges and differentiates single-word intelligibility (words spoken alone) from multi-word intelligibility (words spoken within a short phrase or sentence):
50% understood by 31 months old (2;7). Children in the 5th percentile (significantly delayed) were not 50% understood until 47 months old (3;11).
75% understood by 49 months old (4;1). Children in the 5th percentile (significantly delayed) were not 75% understood until 87 months old (7;3).
90% understood by 83 months old (6;11). Children in the 5th percentile (significantly delayed) were not 90% understood until 120+ months (10;10).
50% understood by 34 months old (2;10). Children in the 5th percentile (significantly delayed) were not 50% understood until 46 months old (3;10).
75% understood by 46 months old (3;10). Children in the 5th percentile (significantly delayed) were not 75% understood until 61 months old (5;1).
90% understood by 62 months old (5;2). Children in the 5th percentile (significantly delayed) were not 90% understood until 87 months old (7;3).
The researchers noted a wide range of variability and conclude that children should be at least 50% intelligible by 48 months old (4 years). In other words, if your child is at least 4 years old and you or others are not understanding at least 50% of what they are saying, that is a strong indicator of a speech sound impairment. To properly diagnose and treat a speech sound impairment, seek out a licensed Speech-Language Pathologist in your area.
What is a phonological process disorder?
Speech delays and disorders can come in a variety of forms, but typically they involve the use of phonological processes. These are habitual error patterns within a child’s speech, which are expected until about 3 years of age. Phonological processes are caused by an underlying weakness in the child’s phonological system (mental organization of sounds). The phonological system starts to develop around 9 months of age, and we currently do not know why some children develop a stronger or weaker phonological system than others. Here are the most commonly seen phonological processes in children with delayed speech:
Final Consonant Deletion: leaving out the final consonant sound of a word. For example, “bu” for bus.
Syllable Reduction/Weak Syllable Deletion: When the unstressed or weakest syllable within a word is deleted. For example “puter” for computer.
Cluster Reduction: When a consonant cluster is simplified into a single consonant. For example, “pider” for spider. This can occur anywhere within a word.
Stopping: When a fricative and/or affricate is replaced with a stop sound. Fricatives and affricates are sounds that require adequate airflow. For example, “tee” for see and “chop” for shop.
Fronting: When a sound made in the back of the mouth (velar) is replaced with a sound made in the front of the mouth. For example, “do” for go and “tat” for cat.
Gliding: When a liquid sound (/r/ or /l/) is replaced with a glide (/w/ or “y”). For example, “wing” for ring or “lello” for yellow.
There are many more phonological processes and it will require a trained Speech-Language Pathologist to identify the exact ones your child is using, in order to properly correct it. Oftentimes, children with significantly delayed speech will use multiple phonological processes at the same time, even within the same word!
How can I help my toddler speak?
Although speech sound errors are the most common cause of low/poor intelligibility, there could be other reasons why your child is not being understood. Are they speaking with a low volume? Are they exhibiting any fluency issues (stuttering)? Are they using a lot of jargon (nonsense words) due to a weak vocabulary? These are other areas that a qualified Speech-Language Pathologist will take into consideration when evaluating. For those parents/caregivers waiting for an evaluation (or those already involved with speech-language therapy services), here are some general tips for increasing your child’s speech intelligibility:
Model all words correctly. Do not give items nicknames or imitate incorrect productions, no matter how cute it may be. For example, use the correct pronunciation of blanket each time your child says “bankie”. IMPORTANT: Do not reprimand or correct your child during their errors, but instead model with emphasis on the correct form. For example, if they say “weaf” you say “Yes, a pretty LEAF.”
Hold desired items and toys up near your face when you talk about them, so that your child can see and hear what you are saying. Bringing attention to your lips and mouth/tongue moving can help your toddler start to make attempts at new sounds. You can also look into a mirror while saying words and sounds with your child, so they can see their own mouth, lips, and tongue move.
Slow down your speech, enunciate the sounds, or break down words into their individual sounds or syllables. Such as “SSSss-pi-der” for spider or “BA-na-na” for banana. Many kids think it’s hilarious when you do that and really it engages their listening, which they need in order to imitate new speech sounds.
Encourage your child to slow their rate of speech by modeling a slower rate yourself. Ask them to repeat themselves if not understood and use terminology like “tell me with turtle words” to have them slow down.
Encourage the use of simple gestures to aid in their communication. Show them simple hand gestures that they can use with others.
Play silly sound games or sing silly sound songs with your child, working on building in different consonant-vowel combinations, such as starting with easier sounds such as “mamama”, changing it to “moo-moo-moo” and “my-my-my” and then trying more difficult sounds, such as “ga-ga-ga”, “goo-goo-goo” or “ya-ya-ya”, “yee-yee-yee”, “yo-yo-yo” etc. This will engage them and enhance their phonological system. See if your child will imitate you.
Keep it fun and low-pressure! For more specific ideas relative to your child, ask your Speech-Language Pathologist for strategies or activities that you can use to carry over skills at home. Children who have difficulty communicating may develop negative behaviors and other social-emotional difficulties. Keep this in mind when interacting with your child and help to support them in any way possible!