Through the work of Darwin and subsequent related studies, evidence supports that the emotional state of humans can be recognized through the characteristics of their vocalizations. While adults may have more control over how they react, babies tend to show their emotional cards in their cries. For these little humans, who are in the process of learning communication from scratch, these limbic proclamations and the responses they evoke from the rest of us are a survival mechanism, even if they give mom and dad a killer headache. Read on to find out why a baby crying forces everyone, not just the parents, to pay attention.
Baby cries containing frequencies in our sensitive range are sure to be noticed, which is the evolutionary intent. Humans are most sensitive to sounds that have spectral content in the 1,000-5,000 Hz range, with peak sensitivity occurring between 3,500-4,000 Hz. This is due to ear canal resonance, which is related to the canal’s length, volume and curvature leading to the ear drum. Sounds in this sensitive range are perceived louder to humans than other frequencies that we hear. This is reflected in the A-weighting network, which accounts for how humans hear across the audible spectrum. As shown in the figure below, low and very high frequencies are not perceived as being as loud to us as frequencies in the 1,000-5,000 Hz range.
The way babies vocalize and how loud they wail is important in separating discomfort from just being chatty. When a baby is experiencing pain or discomfort, the frequency of the cry is higher in pitch with more modulation and longer duration. Additionally, babies’ cries are louder than typical chatter. The combination of these two factors alert adult ears that something is amiss and that the infant is likely in need of something.
The choice of spectral content is not limited to infants. Scary movie season is upon us, and these films are bound to have a scream or shriek in them. These fear reactions tend to be shrill, loud, and sustained. This tends to elicit our own ‘fight-or-flight’ response and alerts us that something is very wrong, when compared to a loud laugh or excitable conversation. It is not just the content of the vocalization, it is how it is expressed that signifies the intent.
Whether it is hunger, need for a diaper change, fatigue, gas, or just plain loneliness, the specific intent of a discomfort cry is a riddle that varies from baby to baby. Over time, it is possible for parents to learn and distinguish the difference between these cries; for most, they will be able to pick out their little one’s voice over some other tot. To all the recent parents out there, congratulations and know that all the noise is just part of your baby’s survival biology!