Chapter 5

Perception is the process by which sensations are assembled into a mental representation of the external world. From the cacophony of auditory, visual, tactile and other sensory inputs, our perceptual systems attempt to construct a coherent mental picture of the objects, actors, events and their relations in our immediate surroundings.

It is often thought that perceptual systems (such as audition) are organized to create as accurate a mental representation of the world as possible, but this is not quite correct. Perceptual systems create mental representations of the external world only to the extent that these representations enhance survival and facilitate propagation of the individual's genes. Usually this evolutionary goal is indeed best served by assembling an accurate mental representation of the world. However, perception is often most adaptive when systematic biases are introduced. For example, it is better for an organism to see danger in a thousand circumstances where there is no danger, than to see no danger in one circumstance where danger is present. The startle response is meant to be adaptive rather than accurate, so we are far more easily startled by unexpected sounds than is warranted by the actual danger. As we will see later, the biases generated by the human auditory system have concrete repercussions for the experiencing of music.

Reality and Appearance

One of the oldest and most venerable philosophical concepts is the distinction between reality and appearance. We know from optical illusions that things are not always as they appear. In fact, optical illusions are only special cases of a more general phenomenon: our senses never provide us with an unbiased picture of the world. Our senses are oblivious to certain kinds of information (such as our inability to hear ultrasonic frequencies), and our senses also add interpretations that go beyond the information present in the environment.

One philosophical school (known as idealism) suggests that there is no such thing as a reality external to our senses. According to idealism, the world is literally a figment of our imaginations or a sort of collective mental illusion. For the philosophical idealist, you only think you are holding a physical book; the book is simply an illusion created by your mind.

Most people do not subscribe to philosophical idealism. People typically find their senses just too compelling, and so accept at face value the impression that there really is a world "out there" independent of our minds. This latter belief is called philosophical realism or sometimes naive realism. Most researchers who study human sensation are philosophical realists; they consider the physical world and our mental experience of that world to be two different things. As a consequence, a recurrent distinction in psychology is made between objective reality and subjective experience.

The study of perception traditionally begins with the task of mapping the objective world of physical phenomena to the subjective world of inner experience. Consider, for example, the color yellow. Yellow is not simply a light of a certain wavelength near the middle of the visible spectrum. It turns out that "yellow" can be evoked by a wide variety of very different visual stimuli and that the perception of yellow depends also on the context. "Yellow" is best regarded as a type of subjective phenomenon rather than as a description of an objective property. Unlike length (measured say in centimeters), yellow is not a property of physical objects. As a phenomenon, yellow is more like pain: you have to be a person who experiences it in order to know what it is.

For most people, this way of speaking is counterintuitive. We think that surely "yellow" is a property of the object itself, not a property of our seeing. However, the experimental evidence is overwhelmingly contrary to this common way of thinking. Different objects do indeed reflect different wavelengths of light. But the experience we call "yellow" is a particular way of interpreting a wide variety of visual stimuli under different conditions. Color researchers at the Eastman-Kodak company are always eager to note that color is not at all the physical property people think it is.

Acoustical versus Auditory Phenomena

As our understanding of perception has grown, psychologists have become increasingly careful to distinguish between subjective and objective phenomena. In an earlier chapter, we discussed some basic acoustical phenomena. Terms such as amplitude, frequency, phase, and waveform refer to physical properties. Psychoacousticians regard these as objective terms. These terms are used to characterize physical properties of the real world rather than to describe our internal experience of these sounds.

In this chapter we will discuss sound from an introspective point-of-view. We will discuss terms that refer exclusively to our subjective experience of stimuli. Some of the terms we use to characterize sounds are obviously value-laden -- such as "beautiful" and "dissonant." These adjectives clearly pertain to internal responses rather than objective properties of a sound. (There is no objectively "ugly" sound, for example.) However, there are a surprising number of other descriptive terms we use that are not value-laden -- such as "timbre" and "pitch" -- but still refer to subjective experiences rather than objective phenomena.

When a phenomenon pertains to the external physical world of sound, researchers call it an acoustical phenomenon. Conversely, when a phenomenon pertains to the internal subjective experience of sound, researchers call it an auditory phenomenon.

Primary Auditory Phenomena

Objective terms can normally be clearly defined by describing some way of measuring the phenomenon. By contrast, subjective terms are much more difficult to describe or define. Like laughter or regret, you have to experience the phenomenon in order to know what it is. At least eight basic subjective phenomena can be identified in auditory perception; we will refer to these as primary auditory phenomena:

1. Loudness. Loudness is the subjective sense of how energetic a sound is. Loudness ranges between the sense of "silence" or "quiet" to "loud".
2. Pitch. Pitch is the subjective sense of highness (or lowness) to a sound.
3. Timbre. Timbre is the subjective sense of tone-color by which one sound may be distinguished from another sound of equivalent loudness and pitch.
4. Toneness. Toneness is the subjective sense of how tone-like a sound is. When a sound evokes low toneness, we experience it as noisy or diffuse.
5. Apparent Location. Apparent location is the subjective sense of the position in space from which a sound is thought to emanate.
6. Streaming. Streaming is the subjective sense of connectedness -- where two or more successive sounds appear to arise from the same sound-generating activity or source.
7. Numerosity. Numerosity is the subjective sense of how many sounds are present in a sound experience.
8. Sensory Dissonance. Sensory dissonance is the subjective sense of lack of euphoniousness to a sound experience.

Acoustic Correlates of Primary Auditory Phenomena

For each of the above auditory phenomena, we'll discuss how these phenomena are correlated with various physical properties. As a first approximation, we can note the following correlations.

As we will see, these correlations are only rough approximations; each of the eight primary auditory phenomena is influenced by many more than one acoustical property.

A good question to ask is why the auditory system doesn't provide us with a direct experience of physical properties such as amplitude? Instead of experiencing a complicated phenomenon like loudness, why doesn't the auditory system generate a direct subjective correlate of amplitude? Remember that the biological purpose of a sensory system is not to give us accurate information about the world; the purpose is to give us biologically useful information about the world. Millions of years of evolution has established that amplitude is less adaptive than loudness. Similarly, frequency is less adaptive than pitch, waveform is less adaptive than timbre, and so on. It is even the case that apparent location is more adaptive than actual physical location. [1] In short, each of these primary auditory phenomena can be traced to an evolutionary adaptation. As we will see, there are excellent adaptive reasons why listeners should have the experience of sensory dissonance (say) rather than spectral density.

Secondary Auditory Phenomena

The eight phenomena identified above pertain directly to how we apprehend or experience sound. However, sound can also induce subjective phenomena that are more general or systemic in nature; these systemic subjective experiences can also arise from visual, tactile and other stimuli -- not just from sound. Four such secondary subjective phenomena are: arousal, attention, anxiety, and surprise. Later in this chapter, we will look in depth at these more general or systemic phenomena.

Review the following concepts or terms:

Idealism:

Realism:

Objective term:

Subjective term:

Perception:

Acoustical phenomenon:

Auditory phenomenon:

Loudness:

Pitch:

Timbre:

Toneness:

Apparent location:

Stream:

Numerosity:

Sensory dissonance:

Footnote

[1] For example, the auditory system is relatively insensitive to the location of distant sounds compared with sounds that are in close proximity. From an adaptive point of view, nearby sounds are on average more important than distant sounds.

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  © Copyright 2002, 2003 David Huron