As we have seen, there are many ways of conceptualizing dissonance: as pleasant, unpleasant, euphonious, beautiful, ugly, rough, smooth, fused, diffuse, tense, relaxed, etc. Dissonance is foremost a negative valence emotional response. We hear some sound and experience a sense of ugliness or repulsiveness. We might well understand why various sounds (like the cries of someone in pain) would evoke certain emotional responses. But how is it that combinations of simple sine tones can evoke experiences of pleasantness or unpleasantness? How is it that some sounds can be experiences as sounding `bad'?

Nesse (1991) draws our attention to why pain (both physical and psychological) is important from an evolutionary point of view. From a survival point of view, tissue damage is one of the worst things that can happen to an organism. The physical pain that ensues (such as from stubbing one's toe) provides a strong incentive for an individual to be careful in situations where physical damage is possible.

Similarly, Nesse points out that psychological pain (such as feelings of sadness due to loss) are also important evolutionary adaptations. A person who does not feel some anxiety in the presence of their boss is in danger of behaving in inappropriate and maladaptive ways. Fear, sadness, anxiety, anger, and other emotions serve important functions.

Research on consonance and dissonance has tended to focus solely on the causes. Accordingly we ask questions such as does dissonance arises from complex frequency ratios? from beating? from critical band interactions? An alternative approach is to focus on the purpose of dissonance: what is dissonance for? why do we experience some sounds as more pleasant than others? Why isn't our experience the reverse? Why don't we experience nominally dissonant sounds as pleasant and nominally consonant sounds as unpleasant?

A Gibsonian approach to dissonance allows us to reinterpret possible sources (causes) of dissonance:

1. Tonotopic Dissonance. The component of dissonance that arises when pure tones are separated by roughly 40% of a critical band. (Greenwood, 1961; Plomp & Levelt, 1965; Kameoka & Kuriyagawa, 1969a, 1969b).
   
   
2. Temporal Dissonance. The component of dissonance that arises due to rapid beating or amplitude fluctuations. (Helmholtz, 1877).
   
   
3. Virtual Pitch Dissonance. The component of dissonance that arises from competing (unclear) viritual pitches. (Terhard, 1974).
   
   
4. Expectation Dissonance. The component of dissonance that arises due to the thwarting or delaying of a (learned) expectation. According to this view, "even a single tone may engender that urgent expectation of resolution that is the essence of dissonance." (Cazden, 1980; p.157) Cazden argued that there are three levels of expectation-related dissonance: Dissonating Tone where a nonharmonic or non-chordal tone has a tendency to resolve within the framework of an underlying chord or harmony, Dissonant Chord Moment where a chord may be dissonant to the extent that it arouses the expectation of resolving to another chord within a harmonic progression, and Tonal Center Dissonance where a passage may retain a tonic or dominant tonal center, and dissonance arises is resolved when the dominant tonal area ultimately moves to the original tonic area.
   
   
5. Interval Category Dissonance. The component of dissonance that arises when a two pitches form an interval that is categorically ambiguous for a listener. That is, where the interval lies near a learned categorical boundary.
   
   
6. Absolute Pitch Category Dissonance. The component of dissonance that arises when a pitch is categorically ambiguous for a listener posessing absolute pitch. That is, where the pitch lies close to a learned categorical boundary.
   
   
7. Stream Incoherence Dissonance. The component of dissonance that arises due to confusion regarding streaming. (Wright & Bregman, 1987).
   
   
8. Relative Dissonance. The component of dissonance that arises from the context of dissonant successions. A sonority might sound relatively consonant when it is preceded by by other sonorities that are highly dissonant.