In the visual domain, there are several possible ways of expression tension and resolution including confusion to recognition, incoherence to coherence, complexity to simplicity, asymmetry to symmetry, imbalance to balance.
Rhythms and other repetitions in time can be directly represented by repetition through one or more dimensions of space, although the temporal experience of repetition is linear, whereas the spatial experience is inherently non-linear. Repetition perhaps has a useful relationship with visual symmetry. Symmetry in music is more often a compositional device than a directly expressive feature.
Melody and harmonic movement are functions of relationships between pitches. The experience of these features is based in the various qualities of consonance and dissonance produces by different mixtures of frequencies. There is no direct spatial equivalent, however it is tempting to explore shape and colour as possible replacements, in part because these in turn have no real equivalent in sound. A number of composer have claimed to feel associations between certain colours and certain musical keys, including Alexandr Scriabin.
Individual events are probably most appropriately represented by discrete objects or coherent segments of objects within an image. The spacing of events in time can be related to the spacing of objects in one or more dimensions of space.
Envelopes have a natural relationship to spatial trajectory or profile, although it seems that something significant is lost when an envelope is unleashed from time.
There is some sense in relating pitch to colour, as pitch and colour are both related to frequencies of oscillating waves. Because of our conventional use of high and low to denote the extremes of frequency, there is also a natural mapping of pitch to vertical position (as is found in musical notation. Relative pitch can also be expressed graphically with various kinds of patterns at various frequencies.
Different mixes of harmonically-related frequencies create a coherent and unified sonic impression. Although the number of harmonics in a sound can be quite large, our experience of a sound spectrum seems to be largely a function of the particular mix of 10 to 15 lowest harmonics and the fundamental. The most direct analogue in vision may be texture, however the relationship between audible spectrum and texture is not direct. In particular, the mathematical relationships of harmonics is not very substantially reflected in texture. The presence or absence of a moirŽ effect is related to harmonic alignment. Colour is another candidate, and indeed the terms colour, darkness and brightness are sometimes used to express attributes of sonic spectra, but the expressive nature of colour feels quite different from spectra. Our experience of combinations of different frequencies of light does not have the same kinds of features as our experience of combinations of different frequencies of sound.