Article Review – “Infants’ listening in multitalker environments: Effect of the number of background talkers”

This week, I’m going to talk about this study (full text available!) looking at infants’ ability to listen in noise.  (Newman, R.S. “Infants’ listening in multitalker environments: Effect of the number of background talkers.” Attention, Perception, & Psychophysics. 71(4), 822-836, 2009).

Background

As anyone who has tried to have a conversation in a noisy bar or restaurant can tell you, understanding speech in noisy environments, particularly when the noise is other people talking, is REALLY difficult.

Adults tend to do better at listening to a target talker when the competing noise is just one other talker compared to when the competing noise is several talkers all at once (like the din of a crowded restaurant). This difference could be for a couple of reasons. First, when the competing noise is just a single talker, adults may be able to recognize words or a topic of the competing talker, and use that context to selectively switch their attention away from the competing talker and toward the target talker. Secondly, speech naturally has pauses (like between syllables, phrases, or sentences), and adults may use pauses in a competing talker’s stream of speech to hone in on what a target talker is saying – with multiple talkers, the pauses tend to all average out so that there aren’t really any pauses (just a steady “roar”), which might make listening in the presence of multiple talkers more challenging for adults.

In this study, the researchers wanted to see if this is true for infants, as well. Note that the infants in this study were normally-hearing, and I’m not sure how the results would translate to infants with hearing loss.

The Study

The researchers had infants (an average age of about 5 months old) listen to a target stream of speech in the presence of competing speech. The target stream of speech consisted of a person saying a name, which could either be the infant’s name, a name other than the infant’s name that was similar (a “stress-matched foil”), or a name other than the infant’s name that wasn’t particularly similar (a “non-stress-matched foil”). The competing speech was either a single voice, or a composite of 9 voices all talking at the same time.

The researchers measured how long the infants listened to each name in the presence of the competing speech, the idea being that infants would listen for a longer duration of time to someone saying their own name if they recognized it. So, the researchers wanted to see if the infants listened longer during trials in which their name was said in the single-voice noise condition compared to the multi-voice noise condition to see whether infants were better able to recognize their own name in one condition versus the other.

And now, on to the results! FIG. 1 shows how long infants listened to their name compared to the other names in both a multi-voice competing speech condition (left-most panel) and a single-voice competing speech condition (middle panel).

fig1_newman.jpg

Interestingly, the infants listened significantly longer to their own name compared to other names in the nine-voice noise condition but there was no difference  in the single-voice noise condition. This suggests that infants had more trouble understanding speech (in this case, recognizing their name) in the single-voice noise condition, which is the opposite of adults!

The researchers hypothesized that the infants might have had more trouble in the single-voice noise condition because they might have recognized the single-voice as speech and found it interesting, or possibly, because they recognized some of the words in the single-voice competing speech and therefore, focused on it. This is different than what an adult might do in the same situation – if an adult is trying to focus on one talker, but there is a single competing talker nearby, they might recognize words from each conversation and realize that the topics of each conversation are different. For example, the first talker might be saying words like “breakfast,” “pancakes,” and “eggs,” and the second talker might be saying words like “rain,” “umbrella,” and “soaked” – an adult listener might be able to use these words to identify topics of each conversation and they could then target their attention on the conversation they’re interested in (this all happens subconsciously, of course!). On the other hand, a baby might recognize a few words in each conversation, but might not have the vocabulary to group recognized words into topics, making the two conversations harder to disentangle. In the case of a multi-talker competing background noise, neither the adult nor the baby would recognize individual words in the background noise – this might be detrimental to the adult (who can’t segregate the noise from the target speech based on conversation topic or gaps in the noise), but might be helpful to the baby (who isn’t distracted by a competing talker that seems like they might be saying something interesting).

To try and address the issue of why the single-talker competing speech condition was so difficult for the infants, the researchers repeated this task, but using single-talker speech played BACKWARDS! In this case, the competing speech would have some acoustic properties similar to single-talker speech played forwards (e.g., gaps in the speech, changes in loudness, changes in pitch, etc.), but would be different in that the infants wouldn’t be able to recognize any words.

The results of this experiment are shown in FIG. 1 (above) in the right-most panel – as you can see, there was no difference in how long the infants listened to their own names versus other names in the single-talker speech played backwards condition. This indicates that the infants had a hard time recognizing speech in the presence of the single-talker backwards noise. This in turn suggests that the infants’ difficulty with understanding speech in the presence of a single competing talker is not due to recognizing some words in the competing speech and finding that distracting, but rather due to other characteristics of competing single-talker speech.

My Reflections

I thought it was so interesting that adults find a multi-talker background noise (like a restaurant) to be more difficult than a single competing talker but that infants are the opposite. I often extrapolate my experiences to T – if we are in a crowded restaurant, I assume he must have a harder time understanding what we’re saying than if there’s just one or two people talking nearby, because *I* find the crowded restaurant more difficult to listen in. It never occurred to me that it might be exactly the opposite for T!

This article also highlighted to me how much cognitive development is required for babies to mature to the point where they can listen to speech in noisy environments the way adults do. For example, they need to learn enough vocabulary to be able to group words in a conversation into topics, learn how to listen in the gaps of competing speech (like between sentences or phrases) to focus in on the target speech, and all sorts of other things – and all of this takes time and experience! I think this is especially important to remember because infants often spend a lot of their waking hours in environments that are very noisy – like daycare!

Additionally, this is yet another study that made me think about the importance of hearing aids for children with hearing loss – this study was done with normally-hearing infants, and they had a hard time understanding speech in noise – this difficulty must be so much worse for infants with hearing loss!

 

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