Ben Laposky, Electronic Abstraction 4, 1952. Gelatin silver print of an oscilloscope screen. Collection of Anne and Michael Spalter.
Computer art is often considered to begin with Laposky’s oscilloscope images. A mathematician and artist, in 1950 Laposky became the first person to use an analogue computer to create graphic images, though he had previously experimented with mathematically-based systems. To create Oscillation #4, he sent beams across the fluorescent face of a cathode-tube oscilloscope (or oscillograph), a device used to measure and graph the fluctuations in electric current. The voltage moves the beam up and down, tracing the image of the current on a screen. Laposky recorded the mathematical curves and waveforms of the manipulated light beams onto high-speed film, producing artworks he called ‘Electronic Abstractions’ or ‘Oscillons’. In 1953–4, fifty of Laposky’s Oscillons were the subject of the exhibition ‘Electronic Abstractions’, which opened at the Sanford Museum in Cherokee, Iowa, and traveled to thirteen other venues across the US. An oscillon served as the cover illustration for Jack Burnham’s classic book, Beyond Modern Sculpture: The Effects of Science and Technology on the Sculpture of Our Time (1968). Although Laposky did not employ a digital computer in his Oscillons, his use of algorithmic signals to programme and control imagery on a CRT monitor was an important precursor to computer art. 
Laposky explained his work in the book, Oscillons: Electronic Abstractions, 1954, a short excerpt of which appears below:OSCILLONS: ELECTRONIC ABSTRACTIONS
My work in computer art is a form of oscillography, the results of which I have called 'Oscillons' or 'Electronic Abstractions.' These are composed of combinations of basic electronic wave forms as displayed on a cathode ray oscilloscope and photographed. Color compositions are achieved by means of special filter arrangements. The resulting art works are presented in photographic exhibitions, kinetic oscilloscope displays, light boxes, or movies.
The relationship of the oscillons to computer art is that the basic waveforms are analogue curves, of the type used in analogue computer systems. The oscillons have been recognized as being the first major development in this field as abstract art creations, and the first to be widely exhibited and published in America and abroad (over 216 exhibitions, 160 publications since 1952).
I got into oscillographic art through a long-time interest in art or design derived from mathematics and physics. I had worked with geometric design, analytic and other algebraic curves, 'magic line' patterns from magic number arrangements, harmonograph machine tracings, pendulum patterns, and so on. The oscilloscope seemed to me to be a way of getting a wider variety of similar kinds of design and with controlled effects to produce even newer forms not feasible with previous techniques.
My interest in other kinds of art was to some extent in abstract geometric painting, cubism, synchronism and futurism. The oscillons are related to the newer developments of op art, Lumia (light) art, computer art, abstract motion pictures, video synthesizer (TV) art, and laser displays, such as Laserium.
Oscillographic art might be considered as a kind of visual music, as the basic waveforms resemble sound waves. I used sine waves, saw tooths, square waves, triangular waves, and others in various combinations, modulations, envelopes, sweeps, etc. Oscillons usually are not accidental or naturally occurring forms, but are composed by the selection and control of the oscilloscope settings and of varied input circuitry. I used especially modified oscilloscopes for this work, as well as some of my own specifically designed electronic instruments.
The oscillons may be created without the use of an analogue or a digital computer system. It may even be possible, of course, to imagine or to compose some of these patterns without the use of the electron beam tracing them on the cathode ray tube. However, the electronic method greatly extends the possibilities of obtaining new and aesthetically pleasing figures. The oscillons are intended to be a form of creative fine art.
 Image source: http://news.medill.northwestern.edu/chicago/news.aspx?id=75509
 Edward A. Shanken, Art and Electronic Media, 2009, p 78
The full book and other documentation is available as a .pdf via the Vasulka Archives