In my first post in this series, I described the differences between seeing and hearing. I noted that what characterizes sounds is that they are not persistent. One may say that sounds are “events”, as opposed to “objects”. I avoided this term because it is implied that an event has a definite start and end. Although this sometimes true (for example speech), many sounds actually do not have a definite end. For example, the sound produced when striking an object has a definite start (the impact) but not a definite end (energy decays exponentially). This is not to say that we hear these sounds as lasting forever, but simply that it is somewhat arbitrary to define a clear ending time. Worse, a number of sounds also have no start and no end. For example, the sound made by a river, or by wind. So what characterizes sounds is not exactly that they have a clear start and end, but rather that they are not persistent, they change through time. So, it could be said that sounds are events, but in the sense that they “happen”. When the sound is heard, the acoustical wave responsible for it is actually not here anymore (this is related to Husserl’s phenomenological description of time).

Now it could be argued that, if one could repeat the sound (with a recording for example, or less accurately by physically producing the sound several times), then perhaps it could qualify as an object. The notion of “repeatable object” is discussed by Jérôme Dokic (“Two ontologies of sound”), where there is an interesting remark about the notion of depiction. When seeing a painting, one sees both the content in the painting and the painting itself. But at first sight, it seems that sounds are not like this: the reproduction of a sound is like the original sound – possibly altered, but not a representation of the sound. But in fact there is an interesting auditory example: when a loud voice is heard through a phone and the volume is low, you actually hear a loud sound (the voice) inside a soft sound (the sound coming out of the phone).

Nevertheless, I think even in this case, describing the sound as a sort of “object” is misleading. An object is something that can be manipulated. For example, if you are looking at a box on the table, you can change your perspective on it, turn around it, see a face disappear behind an edge, etc. You can do this exploration because the object is persistent. In the same way, you could touch it, hold it, turn it, etc. So it makes sense to say that visual or tactile experience is about objects. But the same does not hold for sounds because they are transient, you cannot explore them. If you read my post on spatial hearing, you could oppose that you actually can: some of the properties of sound change when you move around the source. It is true, but precisely you do not hear these changes as changes in the sound, but in the localization of the sound. You feel the same sound, coming from some other direction. How about being able to repeat the sound with a recording? The point is that repeating is not manipulating. To manipulate, you need to change the perspective on the object, and this change of perspective tells you something about the object that you could not know before the manipulation (for example looking behind) – to be more precise, it can be said that visual shape is isomorphic to the relationship between viewing angle and visual field. If you repeat a recording exactly as in the original production, there is no manipulation at all. If you repeat it but, say, filter it in some way, you change it but it does not reveal anything about the sound, so it is not a change in perspective. You just produce a different sound, or possibly a depiction of the sound as in the phone example. The right visual analogy would be to insert a colored filter in front of your eyes, and this does not reveal anything about visual shape. Finally, it could be opposed that a sound could be repeatedly produced, for example by hitting the box several times, and the sound could be manipulated by hitting it with different strengths. But this is in fact not accurate: when the box is hit with a different strength, a different sound is produced, not a new perspective on the same sound. Here the object, what is persistent and can be manipulated, is not the sound: it is the material that produces the sound.

In fact, there is a well-known example in which the environment is probed using acoustical waves: the ultrasound hearing of bats. Bats produce loud ultrasound clicks or chirps and use the echoes to navigate in caves or localize small insects. In this case, acoustical waves are used to construct some sort of objects (the detailed shape of the cave), but I think this is really not what we usually mean by “hearing”, it seems rather closer to what we mean by seeing. I can of course only speculate about the phenomenological experience of bats, but I would guess that their experience is that of seeing, not of hearing.

To summarize: sounds are not like objects, which you can physically manipulate, i.e., have some control over the sensory inputs, in a way that is specific of the object. One possibility, perhaps, is to consider sounds as mental objects: things that you can manipulate in your mind, using your memory – but this is quite different from the notion of visual or tactile object.