Measuring emotions to understand ancient communities

23 March, 2020

By José Valenzuela, Doctoral Researcher. 

How can we understand the psychological response to sound in a prehistoric rock art landscape? The Artsoundscapes project seeks to analyse soundscapes to understand the role of sound and emotion in the engagement with the sacred in the rock art landscapes of premodern Holocene societies. This basically means trying to grasp how human minds worked several thousand years ago. The limitation is obvious: prehistoric people cannot come to a laboratory and participate in our experiments. This is a huge methodological challenge, but one that a multidisciplinary team is willing to face.

We, modern humans, belong to the Homo sapiens specie. This includes you, me, everybody from one hundred years ago, as well as communities from the Holocene period. The differences between someone living in those Holocene hunter-gatherer societies and someone in the Western world today are more than obvious, but anatomically speaking, we all belong to the same species. And this includes having the same brain morphology. So, can we measure today any kind of human response to sound or music? Can we understand how these people thought or felt in the past?

This is certainly not an easy task. From a psychological point of view, subjective impressions of listeners are influenced by many cognitive factors: interpretation, emotions and any social component could easily affect the results. The psychology of sound, also known as psychoacoustics, is an interdisciplinary field between physical acoustics and psychology with the remit of studying how humans perceive and interpret sound. The distinction between perception and interpretation of sound is relevant in soundscape studies. Sound sensation is cognitively neutral but auditory perception and interpretation reflects the listener’s subjective level of appreciation. The former depends on the physiological mechanism of hearing by which many perceptual properties of sound are extracted from the spectral contents, the temporal patterns, and the spatial distribution of acoustic signals reaching the ears. This is the biological part. In contrast, sound interpretation also relies on higher-level functions of the auditory system that are influenced by several factors, such as attitudes, beliefs, judgments, habits and familiarity with sounds. This is the cultural part. If we want to obtain conclusive results, we will have to focus in our experiments on sound sensations as they can then be extrapolated to any human from any period.

From theory to practice: after having decided what to measure, the next challenge is to decide where to do the listening evaluations of a natural soundscape. A large variety of tests and human response evaluations have been developed over the years to study concert hall acoustics. These tests can be divided into field and laboratory-based studies. The first method exposes participants undertaken the experiment to the complete sound field, something that can only be obtained in a concert hall.  In contrast, the laboratory-based approach allows a stricter experimental control of the sounds participants are subjected. The same dichotomy can be found in the evaluation of soundscape: they can be carried out in open field experiments or in a sound laboratory. From the point of view of acoustics, undertaking experiments in a specific shelter or cave is a very complex problem as carrying there all the technical equipment needed could be daunting task. Moreover, measuring the sound field in such settings is more complicated than in more controlled and delimited spaces (i.e., in an enclosed space). On the one hand, natural soundscapes tend to be open, non-regular and include elements (plants, trees, rocks, water) that add complexity to the behaviour of sound. On the other hand, in laboratory-based studies it is important to rate parameters that correlate the real sound field with its reproduction. For example, ‘naturalness’ appears to arise in subjective data in relation to spatial sound reproduction. It relates to the subject’s perception of the degree of ‘realism’ or ‘resemblance to nature’ of spatial experience. It is mainly an evaluative or emotive judgement of the ecological validity of the experiment, something that doesn’t happen when doing ‘live experiments’ in the field.

In the Artsoundscapes Project, our experiments will be carried out in the Faculty of Psychology of the University of Barcelona, using a technique called ‘auralization’ developed some years ago. Architects and interior designers often use visual rendering to see their designs and constructions even before they are actually built. Virtual reality systems have also improved the illusion of being in these potential places and even allow us to choose materials, colours and distributions. Auralization acts in a similar way but in the field of acoustics. It allows us to close our eyes and experience the simulated acoustics of a specific place as if we were there.

We can hear how an old cathedral sounded several hundred years ago if we model it with the appropriate tools, or we can also observe how the shape of a rock art shelter influences reverberations and echoes. This is the technique we are planning to use in our experiments. We will place the participants in our experiments in an immersive acoustics laboratory where we will reproduce sound through headphones and recreate an acoustic simulation of the real places (rock art shelters) through a complex setup of sixteen loudspeakers.

Well. Even if at this point we have decided how to take measurements to unveil the minds of the past, and we have figured out where to measure them, the question now arises: how can we measure emotions in participants? Emotions can be measured in three different ways depending on emotion-related subjective, behavioural or physiological changes. In the case of sound or sound fields’ subjective evaluation, participants rate their consciously felt emotional experience. This is generally obtained through self-reports that can be divided into verbal and visual tests. Emotional categorization is an important aspect in assessing how people categorize sounds and sound fields. Verbal self-reports are constructed by means of descriptions of feelings or attitudes; responses can be given by answering different kinds of rating scales, open-ended questions and interviews. It may seem very simple, but many aspects are involved in our subjective rating, as shown in the scheme below:

Cognitive aspects that affect subjective rating during a test in a listening room (from Acoustics of Small Rooms, Kleiner & Tichy 2014)

Cognitive aspects that affect subjective rating during a test in a listening room (from Acoustics of Small Rooms, Kleiner & Tichy 2014)

A second approach to study emotions focuses on behavioural measures. They assess variations on performance or behaviour in tasks that are emotion-sensitive (i.e., information processing tasks, identification tasks, motor performance tasks). Behavioural experiments are based on the fact that emotional stimuli are faster to identify than non-emotional stimuli.

The third approach consists on measuring physiological responses to sound. Physiological measurements involve registering changes in biological systems that are caused by emotional processes. Two commonly used non-invasive techniques are the measurement of both the electrodermal activity (EDA) and the heart rate (HR). Skin conductance or electrodermal activity measurements detect changes in the skin’s electrical conductivity. Variations in skin resistance relate to sweating, a process controlled by our sympathetic nervous system, and they are an indication of psychological or physiological arousal. For example, an increase of skin conductance means a change in participants’ emotional response. This can be used to study aspects such as attention, cognition and affect, and it is associated with emotional arousal and stressful states. A physiological arousal can appear with the presence of a novel stimulus but also with the omission of something expected. The high sensitivity of this technique allows researchers to use it when measuring low arousal ranges in emotional responses. Heart rate (HR) measurements relate to changes in heart activity caused by emotional reactions. The beating speed of a heart can be an indicator of attention, arousal, and cognitive or physical effort.

The post-processing of the data obtained in the experiment is the logical step that follows in our experiment and will consist in analysing the data and formulating conclusions. These will be both challenging and exciting moments, when we will get closer to obtaining knowledge on what past people felt in those landscapes in which rock art was produced. If they were indeed ritual places, as the archaeologists tell us, we may get closer to understanding their spiritual nature and the role that sound may have had in order to engage with the sacred. If you are interested in knowing the results… please stay tuned to the Artsoundscapes Project!