Perceptual Organization in EA Music IGNACIO PECINO Novars Research Centre, University of Manchester, UK E-mail: ignaciopecino@hotmail.com This essay is an attempt to explore and formalize the hidden/actual mechanisms of perceptual organization in EA music. This is achieved by taking in consideration the findings and principles of several related disciplines such as “Structural Information Theory” (SIT), “Gestalt Psychology” or “Complexity Theory”. Therefore, we will need to set the existence conditions of sound objects from a perceptual point of view and focus on how our brain organizes auditory information in order to “shape” possible sources and meanings. Relationship between simultaneous stimuli are also discussed with an emphasis in the “emergence” phenomenon and its structural and semantic consequences for music composition. INTRODUCTION The study of the mechanisms of our perception or, in other words, the study of “reality” as a construct of our mind through our senses, has been widely discussed from the very early stages of human thought (e.g. Aristotle's Methaphysics). But it wasn't until the early twentieth century when Gestalt (German for “shape” or “form”) psychologists such as Wertheimer, Koffka or Köhler, approached this issue from a modern scientific outlook. The fundamental principle of this “Berlin School of Psychology” is known as the Law of Prägnanz (German for pithiness) or Simplicity Principle which states that ““the perceptual system will try to find the simplest perceptual organization consistent with the sensory input”. This is done through a number of grouping principles: symmetry, similarity, proximity and good continuation, thus connecting with the idea of a holistic perceptual system in which “the whole is different from the sum of its parts ” (emergence). A different approach to perceptual organization was given in 1909 by german physiologist and physicist Hermann Ludwig Ferdinand von Helmholtz. He stated that “sensory input will be organized into the most probable distal object or event consistent with that input (proximal stimulus)” or, in other words, “perception is modelled as selecting, for a given proximal stimulus, the interpretation with the highest probability of being correct”. This statement is commonly known as the Likelihood Principle and its most direct consequence is that our cultural background, our previous experience, everything we have perceived before, has a massive influence over what we might perceive in the future. A distal stimulus is the stimulus of an object as it actually exists in the real world. By contrast, a proximal stimulus is the sensory transduction of the physical (distal) stimulus, so it might differ from the distal stimulus, depending on the accuracy of the particular perceptual sense. We know, for instance, that not all animal species perceive the same proximal stimulus for a given common distal stimulus (e.g. a sound). So we could first talk about a “physiological limit” to the amount of information that a particular perceptual system is able to apprehend from the actual distal stimulus, and secondly, a limit in the amount of information coming from ours senses (proximal stimulus) that our mind is able to “understand”. The Likelihood Principle is of great significance in the context of acousmatic music, where sound sources are frequently open to diverse interpretation depending on our previous listening experiences. However, these two perceptual principles, sometimes considered as conflicting each other, were unified under a common framework, thanks to advances in Coding Theory or Structural Information Theory (SIT) (Leeuwenberg, 1971). Therefore, SIT suggests that “ given a stimulus, the preferred interpretation is that with the simplest code”, namely, that with the “minimum information load” that enables a reconstruction of the stimulus using a minimum number of descriptive parameters. Such a code is obtained by capturing a maximum amount of regularity (repetition, symmetry) and it specifies a hierarchical organization of the stimulus in terms of wholes and parts (van der Helm, P. A., & Leeuwenberg, E. L. J. ,1991).