The OED first defines the noun form of “filter” as an obsolete word for the fabric felt. Indeed, the medieval Latin word given as filter’s etymological root, filtrum, is the one for “felt.” The OED next defines “filter” as “a piece of felt, woolen cloth, paper, or other substance, through which liquids are passed to free them from matter held in suspension.” The definition has substantially both broadened and narrowed its scope from the original, singular meaning as a specific fabric, felt, to any fabric or substance used in the specified act, i.e. of filtration. This shift in definition happened as filters, in the second sense, began to grow in popularity, and a multitude of other substances than filter, in the first sense, were found to be more effective at being used in the act, resulting in the first sense becoming obsolete. This occurred as a function of time, as is demonstrated by the gap of 175-odd years that exists between the earliest quotations supplied by the OED for the first and second definitions, and the coining of the verbal form of the word, i.e. “to filter,” which is defined as “to pass (a liquid) through a filter, or some porous medium, for the purpose of removing solid particles or impurities,” at roughly same time (mid-to-late 1500s) that the second usage of the noun form came to being.
“Filter,” the noun and the verb, and the act of “filtration” are strongly associated with purification, a concept championed by art critics and historians like Clement Greenberg, who championed the purification of the medium of painting through its purging of any qualities associated to other artistic media, such as music, sculpture and literature, and who advocated painting that self-consciously stressed that which most defined its identity as a painting, namely its flatness, which he thought characterized painting’s purest essence.1
While filters do appear in the art world, most commonly in the medium of photography, and in it are involved with purification, they do not operate in exactly the same way as what Greenberg has in mind, because Greenberg’s purification is ideological, and photographic filters are much more physical. A photographic filter is a “transparent, light-altering device used in front of a camera or enlarger lens or in the path of light falling on the subject.”2 These filters are often made of glass, plastic, gelatin or acetate such that they are heat resistant—the heat from lamps will not melt them—and they are uniform in color. Photographic filters are used in both the developing of film and the lighting of sets to tweak the image and create certain desired effects. The effect of photographic filters are myriad, as they can be designed to act upon color balance, interference, polarization, color compensation, light balancing, and neutral density, to name a few. “Most filters are colored and act subtractively; that is, they absorb from light wavelengths of the opposite (complementary) color and transmit wavelengths of their own color”3; that is, a red filter would block the color green and strengthen red. How much green is absorbed and red transmitted results from the strength of the filter, i.e. how red it is.
As a medium, a filter’s primary effect is to remove certain desired components from that which passes through it. In its most commonly associated applications, the components that are removed are physical; these applications abound, as the desire for a purified version of a substance is an essential component of modern life: the oil filters installed in automotive engines clean the oil that greases the pistons, allowing for more efficient lubrication and longer times and distances between oil changes; paper filters on cigarettes reduce each drag’s chemical intake; air filters in HVAC ducts and compressors work in much the same way, removing dust and other impurities; Brita water filters make our tap water “drinkable”; etc. What these examples share is a common denominator, the increase of the productivity of objects, which often arrives as the lessening of the dangerous effects objects have on humans. Simultaneously, filters also decrease man’s involvement in that productivity-increase process. In this way, filters are what Marshall McLuhan would call a “hot” medium.4
Perhaps a better way of considering filters under the rubric of McLuhan’s concept of hot and cold media is that they function by making other mediums hotter. The relationship between the filter and the object or medium it filters is co-dependent. As much as electronic media make things appear instantly, efficiently, and resolutely, filters figure strongly in their productivity. The quality of TV and radio reception, DSL and Cable data-streams, etc., all depends on reception and decoding of a signal, but in the transfer process from antennae or stream-source the broadcast is never without interference, which is then passed through electronic filters at the receiving end. However hot or cold the respective medium being filtered is, without the electronic filter operating to clean up and restore the initial purity of the medium, human involvement would be greater—e.g. the listener or viewer would have to fill in the gaps produced by static—and the medium colder. SPAM filters are installed in email applications to work in much the same way, to weed out the unwanted SPAM mail from the desired mail, allowing the desired mail to be accessed more efficiently and easily. On the other hand, filters also are tools used in the process of human involvement. “Virtual” filters in computer applications like PhotoShop, for instance, edit files by either removing, shifting or creating data in order to produce desired textures, effects, distortions, backgrounds, frames, you name it.
Nowhere is the sense that filters function as a medium between ourselves and the outside world in order to make that world accessible, efficient, and productive for our use more apparent than in Beyond the Pleasure Principle, in which Freud theorizes that the brain functions much like a vesicle in which a superficial membrane defending the nucleus from attack but allowing certain amounts of stimuli through in order to gather information.5 The nervous system, Freud argues by extension, serves as a “Protective Shield (Against Stimuli)” and filters the sensory bombardment of external excitations in order to allow the brain to operate at a normal level, i.e. not be hampered by continuous or over- stimulation.6 It operates as a medium between the outside and inside worlds, allowing in proportional quantities of stimuli such that the external can be represented realistically, but more moderately. This filtering allows for an efficiency of production with a less than actual level of excitation. If Freud’s theory holds up, then it shows how we ourselves operate neurologically as an a priori instance of heavily mediated filtering as a defense mechanism.
In her essay on Walter Benjamin’s “The Work of Art in the Age of Mechanical Reproduction,” Susan Buck-Morss traces the development of the nervous system, and extends that the circuit of that system out of the body’s limits to the external world (as the source of stimuli), arguing that the modern world is one of such excessive stimuli that man would succumb to shock and trauma if the stimuli, having already were not filtered, or blocked completely, by consciousness.7 She writes, “Of course, the eyes still see. Bombarded with fragmentary impressions they see too much—and register nothing.”8 The problem is that this necessitates a response to stimuli “without thinking”; the mind, in the narcissistic pursuit of self-preservation, filters experience to such a degree that a;; thought is deadened, which Buck-Morss argues opens the door to Fascism. 9
Henri Bergson, however, argues the body responds to stimuli in two ways: as a pure automaton or as voluntary action, i.e. through reflex triggered by the spinal cord or conscious choice developed in the cerebral cortex. 10 In the latter, consciousness stores, delays, and chooses the arrival of stimuli, such that conscious perception can occur when the animal anticipates the eventuality of stimuli.11 Memories, as the principal share of individual consciousness in perception, supplant actual perceptions, functioning as signs that recall the former images of perception, but do so negatively and reflectively, i.e. consciousness can never add anything to the image; only, if anything, subtract.12 Mark Hansen updates Bergson’s account of the sensorimotor basis of the human body, and argues for the importance of positive “affectivity”: the body experiences more than just perception, and thus more than itself, because it creates something positive in the interactions, associations and enfoldings of the images and memories; that is, an image is no longer restricted to the superficial, the reflective or the negative, but extends to encompass the entire process by which it is made perceivable through embodied experience, and becomes what Hansen terms a digital image. 13
The concept of filters have also entered common slang speech through the euphemism that a person may not “have a filter,” which means they speak incessantly and without regard for personal embarrassment, shame, or moral compass. This metaphorical filter shows an opposite role of or side to Freud’s psychoanalytic filter of the Protective Shield. That psyche not only creates shields that protect itself from external stimuli but also from itself.