Consonant and Dissonant Sounds

T has gotten really into music in the last month or so. Lately, when he hears music he likes, he’ll start dancing. We went out to eat a few weeks ago, and the restaurant had music playing in the background, and T was dancing up a storm in his high chair – it was adorable! And, I especially love when T dances when I play the piano!

T’s evident love of music made me start thinking about babies and qualities of music that they may innately appreciate. A little reading led me to a few studies (for example, this one by Trainor and Heinmiller) that have shown that even infants that are just a few months old prefer pairs of musical notes played together (a musical interval) that are consonant (pleasant sounding) rather than dissonant (harsh or unpleasant). What’s interesting to me about these studies is that babies seem to recognize and prefer musical intervals widely recognized by adults (both musicians and non-musicians) as being consonant, even without much music-listening experience. Here’s a YouTube video that gives examples of consonant (for example, an octave, a perfect fourth, a perfect fifth, etc.) and dissonant intervals (a minor second, a major second, etc.) – the difference between consonant and dissonant intervals is really striking, even if you don’t know the names of the intervals!

The study I linked to above showed that infants prefer listening to consonant intervals rather than dissonant intervals. And, this study (by Sugimoto et al.) showed than even an infant chimpanzee preferred listening to consonant intervals rather than dissonant intervals. So this seems to suggest that there’s something hard-wired in our brains that makes us prefer consonant musical intervals, even if we haven’t heard much music or had any musical training.

So, I decided to test T to see if he has a preference for consonant musical intervals over dissonant intervals! I played different examples of consonant and dissonant sounds for T, both on an iPad and on the piano to see if he had different reactions (this was not the protocol used in any research study, but it was the best I could do at home :)). When I played consonant and dissonant intervals on the piano, I got no noticeably different reaction from T, although, this may have been because he was preoccupied with trying to lick the fan. I then played consonant and dissonant sounds three different times on the iPad. Two of the times, he started smiling when he heard the consonant sounds and reaching for the iPad, and when he heard the dissonant sounds, he turned away from the iPad and even seemed a little visibly distressed (although this may have been because my experiment was running into snack time; I’m beginning to understand why research studies with babies often have a high attrition rate). The third time got no difference in reaction. So, it seem possible that T has a preference for consonant sounds over dissonant ones, but I can’t really be sure based on this.

One thing that piqued my curiosity is that these studies were done in normal hearing babies (and a normal hearing chimpanzee), so I wondered whether people with hearing loss hear consonant and dissonant intervals different than normally-hearing people. I found this study (Tufts, et al.) which showed that people with hearing loss do hear consonant and dissonant intervals differently, and their explanation of why was so interesting to me!

Before I talk about what Tufts et al. found, here’s a quick explanation of why different intervals are heard as consonant or dissonant. The big difference between different intervals is how far apart the two notes are – for example, a minor third is 3 semitones apart (an example is C and E-flat) and an octave is 12 semitones apart. I think that the accepted theory for why an interval sounds consonant is that the component notes of the interval are far enough apart to be easily resolved by the cochlea – one technical way to say this is that the two notes fall into different auditory filters. Here’s a picture I made to go along with an analogy:

intervals.jpg

Imagine you’re rolling balls down a hill into different buckets (I have no idea why you’d be doing this, but just go along with it!). How far apart two balls are at the top of the hill represents a musical interval, and each bucket at the bottom of the hill represents an auditory filter. If two balls fall into the same bucket, the interval composed of those two “balls” (notes) will sound dissonant, whereas if they fall into different buckets, they’ll sound consonant. People with hearing loss are known to have broader auditory filters – that is, the buckets at the bottom of the hill are a lot bigger, so more balls would fall into them. So, based on this theory, you’d predict that people with hearing loss would find closely spaced intervals dissonant that people with normal hearing would find more consonant.

And, to some extent, this is what Tufts et al. found – here are two cool plots (FIGS. 3 and 4):

tufts.jpg

From Tufts, et al. – Top – FIG. 3 of Tufts, et al – Consonance/Dissonance scores for Normal Hearing adults. Bottom – FIG. 4 of Tufts, et al. – Consonance/Dissonance scores for Hearing Impaired adults.

FIGS. 3 and 4 of Tufts show people’s consonance/dissonance ratings for different musical intervals (indicated by the ratio of the frequencies) – as you can see from FIG. 3 – people with normal hearing say that notes with a ratio of 1 (this is the “unison interval,” or the same note!) is very consonant, and then there’s a steep drop where very closely spaced notes (a frequency ratio between 1.0 and 1.1) sounds VERY dissonant (from the analogy above, where balls are landing in the same bucket), and then as the notes get farther apart, the intervals become more and more consonant (analogy – balls more likely to land in different buckets) as the interval approaches an octave (a frequency ratio of 2.0). While the pattern is similar for people with hearing loss (the bottom figure), the curves look slightly different – if you look at the solid line on the bottom figure, the curve is flatter and has a negative peak later, which shows that people with hearing loss generally rated all intervals as sounding less consonant (because the curve is flatter overall), and that the most dissonant intervals to people with hearing loss were ones that were already “recovering” in consonance for people with normal hearing.

This may explain why people with hearing loss often say that music doesn’t “sound right” to them, even if they wear hearing aids or cochlear implants – the musical intervals that people with normal hearing find pleasant and that are therefore used heavily in music may sound harsh and unpleasant to people with hearing loss.

(By the way, the Tufts, et al. study was done with adults with mild-moderate hearing loss; I have no idea what you would find for babies with hearing loss, which I think is a really interesting question!)

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Singing to Babies

(Note: a lot of the research with infants I’ve been writing about has been done with normally-hearing infants. Although there’s a lot of great research on children with Cochlear Implants, I’m finding that there’s less research on children with mild hearing losses, especially for infants and in interesting areas like music. So, I end up writing about studies that have been done with normally-hearing infants, and I’m really not sure how they translate!)

It’s been clear since T was just a few weeks old that he loved hearing me sing (this was a surprise to me, since pretty much no one else enjoys hearing me sing :)). Since then, I’ve sang to him A LOT – I sing when I play with him, when he’s cranky in the stroller or carrier, lullabies at bedtime, etc. I started wondering what research has been done on singing to babies, so I did a little searching.

One interesting question is whether/how we change how we sing when we sing to a baby compared to singing to an adult or to no one. It’s pretty obvious that people talk to babies differently than they talk to adults – the typical “baby-speak” is called “infant-directed speech” and it has a lot of potential benefits for babies to acquire language. Infant-directed speech is usually characterized by slower speech, repetitiveness (e.g., “look at the doggie! the doggie says woof! hi, doggie!”), higher pitch, and more pitch variation (i.e., MUCH less monotone than when talking to adults). This probably helps babies learn new words and understand the structure of language (e.g., the concept of phrases and sentences) by helping them focus their attention on particular words or groups of words by repeating and emphasizing them.

But do adults sing differently to babies than they do in their absence (even when singing the same song)? This is an especially interesting question, because many of the ways we change our speaking when it’s directed to a baby aren’t easily done in singing – for example, a particular song has constraints on pitch (based on the tune of the song) and rhythm, so it’s harder to vary pitch and rhythm when we sing and still maintain the song. But,it turns out that, similar to infant-directed speech, adults sing differently when the singing is directed to a baby! Studies ([1] and [2]) have shown that when we sing to babies (rather than singing the same song in their absence), we sing with a higher pitch (just like in infant-directed speech) and with a slower tempo (also like in infant-directed speech). And, even though mothers tend to sing more to their babies than fathers, fathers show the same pattern of singing in a higher pitch and with a slower tempo, so there may be something intrinsic about the characteristics of infant-directed singing. (See [2])

And, it turns out that the way we change our singing when it’s directed to a real, live baby and not just an empty room is pretty robust – adults listeners are really good at identifying instances in which another adult was singing to a baby rather than to an empty room – that is, which songs were “infant-directed.” (See [1]).  The adult listeners tended to say that the “infant-directed songs” were sung with a “more loving tone of voice.” ([1]).

I tried to think of whether I sing differently when I’m singing to T than when I’m singing by myself, and it’s hard to say, mostly because I rarely sing if it’s not to T 🙂 But, I wouldn’t be surprised if I sound more loving when I’m singing to T than when I’m singing by myself!

 

On a totally unrelated topic, another interesting study that I came across looked at the effects of moms singing on their babies’ arousal levels as measured with cortisol in saliva ([3]).  They found that babies (averaging 6 months in age) who had relatively low cortisol levels initially (for example, if they weren’t paying attention to anything in particular and were sort of just chilling) had an increase in cortisol after their mom sang to them for 10 minutes – that is, they were more aroused after hearing their mom sing and more in a “playtime” state. Conversely, babies who had higher initial cortisol levels had a decrease in cortisol after their mom sang to them for 10 minutes – that is, they went from a more aroused state to a more chilled out state after their mom sang to them.

This was interesting to read, because I’ve definitely found that my singing to T can have totally different effects on him, even singing the same song! Sometimes, he’ll get really excited and wound up and ready to play, and other times, he’ll totally relax and often, will get kind of drowsy.

References

[1] Trainor, L.J., “Infant Preferences for Infant-Directed Versus Noninfant-Directed Playsongs and Lullabies.” Infant Behavior and Development. (19) 83-92 (1996). (full text here)

[2] Trehub, S.E. et al. “Mothers’ and Fathers’ Singing to Infants.” Developmental Psychology. Vol. 33, No. 3. 500-507 (1997). (full text here)

[3] Shenfield, T. et al. “Maternal Singing Modulates Infant Arousal.” Psychology of Music. Vol. 31, No. 4. 365-375. (2003). (full text here)