The objective of the subjective preference theory founded by the Japanese acoustician Yoichi Ando is to examine the emergence of a satisfying aural experience in a space that supports learning and creative processes.
At a moment of utter discouragement, I found myself between mute walls, thinking what if those walls could speak to me in a tone that is both comforting and encouraging. What needed to be spoken could only be voiced in that muteness, and no human word could have vocalised what I needed to hear. This confession, no doubt, is human and possibly known to many others.
For a long time, architectural acoustics revolved around subsequent reverberation time. The fact that rooms with identical reverberation time could in fact sound very different led to further studies, bifurcating towards the United States on the one hand, and Japan on the other. The American school is mainly concerned with the physical properties of a sound field, while the Japanese school has integrated studies on perception into the underlying physics. The subjective preference theory was formulated by the Japanese acoustician Yoichi Ando who, in collaboration with colleagues and architects, has designed several concert halls and auditoria in Japan based on the theory.
Peter Cariani, a neuroscientist and expert on temporal coding, writes in the Guest Editor’s Preface to Ando’s pioneering book “Auditory and Visual Sensations” (2009), that linking room properties to human subjective preference and the underlying brain activity has come to fruition through the correlation functions1. The ability of these mathematical mechanisms to describe neural activity onset by different stimuli is related to the architecture of the inner ear. Different frequencies are picked up by different length hair cells positioned along the hearing organ (cochlea), creating spikes in the fibers of the hearing nerve. The temporal pattern of these spikes strongly correlates to the temporal structure of the stimuli at the location corresponding to the frequency in the cochlea. Intervals between spikes inform us of stimuli periodicities, starting from several kilohertz to oscillations related to infrasound, room reverberation, rhythms and longer acoustic events. The spikes are directly linked with the waveform of the stimuli, and when we amass all statistical spikes from each of the 30,000 nerve fibers that make up the hearing nerve, it is possible to retrieve an analog representation of the acoustic signal’s auto-correlation.
The complicated body of information incited a subtle discernment that I was entering a world of quantified abstraction, a place where the materiality of our tissue meets the mathematical spirit, opening the processes occurring in our bodies and linking them to the surrounding environment.
At closer inspection it began to unfold that the above function contains several factors, effective duration among others, which expresses how long a period faithfully repeats itself. From previous practice, I was familiar with the role of the alpha-rhythm2 in regulating the resting cycles of our consciousness. Ando’s research is also centered around the alpha-rhythm because, according to him, subjective preference cannot be determined from other cerebral rhythms. Studying subjective perceptions is naturally based on averaging data stacked from human individuals in a group. The pleasant nature of a sound field gives a cue to the brain that it is now time to relax and the brain signs this off with a pattern that can be measured with electroencephalography, for example. EEG activity is then analysed using the autocorrelation function where the effective duration represents the time during which the brain repeats the alpha-rhythm. A remarkable discovery by Ando and co. was that the longer the effective duration, the stronger the preference for a stimuli, whereas the amplitude of the rhythm is not significant in formation of preference. Studies also indicated that in a preferred sound field, alpha-brainwaves propagated from the right cerebral hemisphere to the left (the international 10–20 system of electrode placement was used here). Studies with magnetoencephalography (MEG) showed that when listeners were stimulated with speech stimuli in a preferred sound field, the alpha-rhythm endured over a larger area of the cortex and that there was higher alpha-coherence between these regions. These important results led to the conclusion that most of the brain is relaxed under preferred conditions. We are currently discussing the sound field and its parameters.
The alpha-rhythm is universally associated with feelings of relaxation and well-being, creativity and a heightened capacity to acquire knowledge. The same could be paraphrased by saying that in many a way, the brain interprets these subjective expressions indivisibly. This may seem a trifling rumination but such mirror images between the self and information are recurrent and significant on a journey of discovering what it means to be human. Subjective experience is an abstraction hovering above and between so-called hard science and the elasticity and sensitivity of our tissue. Merging these two seeming extremities reminds me of how the interdependency in M.C. Escher’s stairways makes us consider possible realities outside our daily thought. In Ando’s engagingly pure and wise words, the theory is for the purpose of creating spaces where the passage of time could be enjoyed.
Humans can distinguish a sound source in the proximity of 1–2 degrees in azimuth, which corresponds to a 20 microsecond interaural time difference. The interaural mechanism for identifying a sound source is considered more precise than our visual sense; our sense of hearing has also been assumed evolutionarily older than our sense of sight.
IACC (interaural cross-correlation coefficient) is provably the most powerful factor for predicting subjective preference in Ando and co’s research into the correlations between sound field factors and neurological evidence. No other parameter of the sound field has as strong an influence on the brain in the formation of subjective preference. It describes the difference of the signal when it reaches the two ears. Humans (while listening) prefer minimal correlation, that is, as diffuse a sound field as possible where the location of the source and its apparent width are maintained. These moments matter because it is important to know what is being “said” and where – more often than not, contact from the outer world does not arrive in the form of any human language, but instead as a mild swishing of tree leaves, a glacier singing to its own cracking, or a threatening horsefly in summer heat. Evolutionarily speaking, this factor of the sound field is a meeting point for our sense of danger and security – without knowing the first it would have been challenging to reach the latter. Speech intelligibility is closely related to IACC, making it a significant factor in public space (transport hubs, streets, etc) where clarity of transmitted information may be tied to safety issues.
Upon entering private space, I imagine an architect to first consider functionality and soft values, not the elimination of life-threatening hazards. This harder function should be served by outer walls, the roof, fence and gate. What if, however, the so-called enemy is hiding in between the ears and the architect has the power to keep it abay? The interaural crosscorrelation coefficient and effective duration, that is, the time span over which the brain devotes itself to enjoying a vitally agreeable conjuncture, could be of help here. The longer the cerebral cortex is subject to the alpha-rhythm, the clearer the sensation of subjective preference. Preferences mirror the fundamental bond between our neuro-biological survival instinct and aesthetics. What the brain perceives as pleasant is known to us linguistically as “beautiful”. Beauty lies not only in the eyes of the beholder, but also the ears, touch, scents, temperature – all of which supports our wellbeing through our senses and relaxes us, sometimes by shaking us only to release us. The antithesis of preference is stress. To a degree, every impulse causes the body to undergo a certain stress level as our senses are conditioned to react to changes in signal pattern. Complex signals in an environment create entire fields with which the physiology of our brain relates, and we are able to design and shape these fields so that the organism in them would not remain in a stressed state but could move forward (or back) to a healing sense of peace. The correlation functions named herewith can be applied to study the preferences of most sensory modalities. In addition to the sound field, Ando has investigated visual material in the form of pulsating light and monochromatic textures and patterns in tree leaves. Ultimately, aesthetic preference and our survival instinct, two sensations that might seem quite distant from one another at first, share many traits if we look at a human being with all their feelings and movements as an embodiment of electrical impulses. A similar tendency to converge toward a common neurological signature occurs with creativity, feelings of well-being and a state of restful awareness. It seems that such is our deeper essence in measure to sustainability and life.
I would like to bring a modest example from my work process on the installation “Interaural Contour I” which was discussed in the previous issue of Maja. I say modest because every creative individual who invests themselves into their work entirely has surely recognised similar moments. Aside from acoustic measurements there are numerous alternative approaches to creating more sustainable environments. In a context where a large portion of the process of designing rooms is entrusted to various software solutions, the work process seemed worthy of mentioning namely from the perspective of self-analysis – how an intellectual effort driven to extremes modulated into a soft, enjoyable act of creation. Learning is like the inevitable scorching of a space probe upon its return from quests in the space of ideas and entering the native atmosphere of consciousness, which is completed by a fall into a familiar cooling waterbody, where, yet, nothing is the same anymore.
Being in the so-called mind field of the subjective preference theory, studying the various experiments and results, led to understanding the objective criteria on how an optimal sound field was achieved in different concert halls and auditoria. For example, Ando and Suzumura (2002) found that the IACC decreased at almost every seat in the investigated concert hall when the rear wall of the stage took on a “convex” shape. The horizontal tilt was increased to +10° while the vertical tilt was at 80°. Previous studies have shown that the rear wall of the hall should be diffusive as well. In another hall, sound field measurements performed in mixed and bamboo forests were utilised and 52 pillars or “tree trunks” were installed around the audience area, which adjusted the sound field in the concert hall. Imagining these interventions applied to the source form (usually a simple rectangular volume with case-specific dimensions) was mostly challenged by how to unite the spatial adjustments with what is simultaneously occurring in the brain. Each change made toward the optimal geometry of a chosen form would immediately change the neuronal activity in the listener, which could be followed on the auto- and crosscorrelation functions. Relying on the above description by Cariani, it took tens of times of re-reading and background study to be able to comprehend these occurrences both intellectually and imagine them in my own physiology; but, on each round new links were produced, the information cloud gradually unified and became perceptible as a bodily experience. While in this cloud of experience, I consciously drafted the source form. Acoustic optimisation, that is, adjusting the tilts and angles of the shape using designated software was planned as the next step in the design process. Calculations3 revealed that adjustments were not necessary because the sound field created in the space met the required criteria. The novelty of the theory is in inciting alpha-activity with the help of room geometry, which supports feelings of pleasantness, creativity and the ability to acquire new knowledge. Bearing this in mind, it would seem that all the studies and results that the theory builds on are driven toward this rhythm by default, and directed by it once the mind-body integration has taken effect. While this might seem an arbitrary denouement (or on the contrary, self-evident), it is noteworthy in a time where, in addition to co-operation between artificial intelligence and the capacity of human consciousness, competition is also feasible.
Mathematics is the communication channel between the branches of science. The world of particles unveils in conjunction with the tendency of science to converge toward one point in perspective – the unified field that permeates and unites all. Disclosure of matter to our consciousness occurs based on the presumption that there is one fundamental law of nature. Evolution toward higher and higher frequencies and accuracy goes hand-in-hand with accidents, symmetry and approximate self-similarity across scales: each following layer of the world can be described by mathematic formulae that resemble the descriptions of the previous layer. Newton called this tendency the self-similarity of Nature. Murray Gell-Mann, particle physicist, winner of the Nobel Prize in Physics and author of the book “The Quark and the Jaguar”, explains this evolution as movement carried by the principle of beauty, as simplicity, elegance of formula. To get more, you do not have to add more, he says.
Application of the subjective preference theory goes beyond acoustics of interior spaces. Just like any other branch of science, it aims at a deeper and deeper understanding of the nature of phenomena – in this case a perception, so as to find the causes behind the connection between our preferences and the properties of the surroundings. Noticing natural rhythms is a major factor in Ando’s philosophy of science. Sunlight, or moonlight, reflecting back from the rippling water surface excites the left cerebral hemisphere where temporal patterns are processed. This hemisphere activates when we study and use language, math or music. We can observe twinkling starlight, knowing that humans feel most comfortable around pulsating light with about a 1 second period. It seems there might be a connection to a peaceful heart rate here. Landscape forms that invite the gaze into the depth of space activate our right cerebral hemisphere, involved in processing spatial information. Ando encourages us to notice the big in the small and the small in the big, and to recognise the links between different rhythms that might even seem incompatible at first sight. These links exist because we perceive them through our bodies and they all mark us with their seal for a shorter or longer period of time. The role of the architect, the artist or any creator would be to separate a space out of the infinite that would enable these recognitions, while at the same time supporting the human being based on the best knowledge available.
Our personality creates the space that we carry with us, even when we are in the public. In that sense, humans are indeed like snails with their shells. Our mood, mental establishment or, on the contrary, restlessness, is primarily conditioned on the object of our awareness, that is, where our attention is drawn. We may perceive our shell as a state with a specific neurological pattern. How this pattern materialises into physical form is shaped by the person and the public space which is just one sphere among many. Public space as an architectural term resembles the shell of humanity in nature’s space. Nature’s space, in turn, is the ecological structure’s private space in the public space of the solar system. And so forth. The farther the consideration for the force that organises public space, the easier it is to see that it is all governed by forces of natural law. We direct immense resources into studying them. This knowledge is a promise of a relationship with the unknown. A wish to communicate with the unseen has inspired nearly every ancient civilisation to personify these forces. And human-like features they must possess. However, noone, has ever succeeded in creating a new solar system. On a daily level we can, therefore, rely on closer means to create environments that would foster our highest natural gifts: creativity, peacefulness, and alertness. This is the foundation of beauty. Living beauty.
MARIANNE JÕGI has graduated from Georg Ots Music School where she majored in music theory. She holds an MA in sculpture and installation from the Estonian Academy of Arts. Her postgraduate research and practice involves investigations at the intersection of architectural acoustics and art, with the aim of integrating sensory environmental technologies with spatial form.
1 In Ando’s theory, the autocorrelation function and interaural crosscorrelation function are based on temporal patterns observed in nerve impulses. The first mechanism expresses temporal sensations such as pitch, timbre, duration, loudness and longer delays associated with sound reflections. The second mechanism expresses the perception of the spatial relations of sound vis-á-vis the listener, such as sound direction, apparent size of sound source and diffuseness. Subjective diffuseness is related to the listener’s sense of envelopment by the sound. (Ando, Y. , Guest Ed. Peter Cariani. Auditory and Visual Sensations. Springer, 2009)
2 Normal neural oscillations occurring in the frequency range 8–13 Hz. Blocked upon mental effort and fatigue.
3 I would like express my deep gratitude to Gerda Kaasik from Akukon Estonian Branch who performed the calculations.
Published in Maja’s summer/autumne edition (No 94)
Photo above: Michael Heilgemeir (Eesti Kaasaegse Kunsti Arenduskeskus)