By Jordan Raine

Have you ever heard of the Baader-Meinhof phenomenon? If you haven’t, you’ve definitely experienced it at some time in your life. It’s the term given for when you learn, notice or experience something for the first time, and then you start noticing it everywhere.

Most PhD students will tell you that this phenomenon ramps up into overdrive for the particular subject matter that they have decided to dedicate a vast proportion of their foreseeable future to. For me, that something is every noise that comes out of any person’s mouth that isn’t speech. The cacophony of grunts, moans, shouts, roars, whines and screams that pepper the interactions of human society play an almost invisible role in most people’s experience, but to me they stick out like a sore thumb.

Animals, lacking sufficient vocal control and cognitive complexity, don’t have the luxury of communicating by combining sets of words with culturally agreed meanings. The systems controlling their vocal apparatus are intimately tied to their internal states, and their vocalisations communicate simple but information relevant to survival.

Before humans developed the ability to control their voice and detach it from underlying feelings – which colleagues and I argue in a recent review was vital in the gradual evolution of speech – we most probably communicated in the same way. Even though this arbitrary system for conveying meaning now predominates, nonverbal vocalisations still retain their more ancient communicative function. Yet, aside from laughter, nonverbal vocalisations have remained almost untouched by the scientific community. So, my research aims to discover what is communicated in such vocalisations, and what influence they have on listeners.

One area in particular that I am investigating is tennis grunts. Their legitimacy has been widely debated in the tennis community amid accusations they are distracting, but my research aims to show that they may provide cues to each player’s mental state.

We know from previous research that higher pitch is associated with higher levels of arousal and distress, and lower pitch with dominance, in both humans and other mammals, and that listeners perceive these associations. I have performed acoustic analysis on hundreds of grunts from TV footage of professional matches, and am currently running experiments to determine whether listeners can predict the winner of a match just from a set of grunts. If they can, it is likely that when a player grunts, they are broadcasting signals that may provide their opponent with a mental advantage.

I am also interested in the expression of strength in aggressive roars (see below) and fear screams. In evolutionary terms, strength is a useful attribute to be able to perceive, as it would allow the listener to make good decisions about whether to enter into conflict with fellow competing males or not.

I’m asking people to imagine themselves in a situation where they need to convey aggression, and one where they should express fear, and recording the upper-body strength of each individual. Given that the process of evolution would favour strength-tracking capabilities, we are predicting that listeners will be able to track strength from these vocalisations, and that the acoustic structure of aggressive roars may be designed to increase perceptions of strength. We are also investigating whether males might engage in behavioural strategies to exaggerate their strength, in the similar way to some species of deer.

We produce vocalisations in many more contexts than the two examples mentioned here – this is just the tip of the iceberg. In many nonverbal interactions, seemingly meaningless noises may actually contain a wealth of information and substantially influence our perceptions and behaviour. I’m only halfway through my PhD but already I see human vocal behaviour in a new, broader light. Maybe after reading this you’ll have some vocalisation-related Baader-Meinhof experiences of your own…!

Jordan is doing a PhD on human non-verbal vocalisations with Dr David Reby. He has recently published an article in The Conversation about the evolutionary origins of laughter.

Find out more about our research on Cognitive Psychology.