frontiersin | Sensory perception is often the most striking proof of something factual—when we perceive something, we interpret it and take it as “objective”, “real”. Most obviously, you can experience this with eyewitness testimonies: If an eyewitness has “seen it with the naked eye”, judges, jury members and attendees take the reports of these percepts not only as strong evidence, but usually as fact—despite the active and biasing processes on basis of perception and memory. Indeed, it seems that there is no better, no more “proof” of something being factual knowledge than having perceived it. The assumed link between perception and physical reality is particularly strong for the visual sense—in fact, we scrutinize it only when sight conditions have been unfortunate, when people have bad vision or when we know that the eyewitness was under stress or was lacking in cognitive faculties. When people need even more proof of reality than via the naked eye, they intuitively try to touch the to-be-analyzed entity (if at all possible) in order to investigate it haptically. Feeling something by touch seems to be the ultimate perceptual experience in order for humans to speak of physical proof (Carbon and Jakesch, 2013).
We can analyze the quality of our perceptual experiences by standard methodological criteria. By doing so we can regularly find out that our perception is indeed mostly very reliable and also objective (Gregory and Gombrich, 1973)—but only if we employ standard definitions of “objective” as being consensual among different beholders. Still, even by meeting these methodological criteria, we cannot give something in evidence about physical reality. It seems that knowledge about the physical properties of objects cannot be gained by perception, so perception is neither “veridical” nor “valid” in the strict sense of the words—the properties of the “thing in itself” remain indeterminate in any empirical sense (Kant, 1787/1998). We “reliably” and “objectively” might perceive the sun going up in the morning and down in the evening; the physical relations are definitely different, as we have known at least since Nicolaus Copernicus’s proposed heliocentricism—it might also be common sense that the Earth is a spheroid for most people, still the majority of people have neither perceived the Earth as spherical nor represented it like that; one reason for this is that in everyday life contexts the illusion of a plane works perfectly well to guide us in the planning and execution of our actions (Carbon, 2010b).
Limitations of the Possibility of Objective Perception
The limitations of perception are even more far reaching: our perception is not only limited when we do not have access to the thing in itself, it is very practically limited to the quality of processing and the general specifications of our perceptual system. For instance, our acoustic sense can only register and process a very narrow band of frequencies ranging from about 16 Hz–20 kHz as a young adult—this band gets narrower and narrower with increasing age. Typically, infrasonic and ultrasonic bands are just not perceivable despite being essential for other species such as elephants and bats, respectively. The perception of the environment and, consequently, the perception and representation of the world as such, is different for these species—what would be the favorite music of an elephant, which preference would a bat indicate if “honestly asked”? What does infrasonic acoustics sound and feel like? Note: infrasonic frequencies can also be perceived by humans; not acoustically in a strict sense but via vibrations—still, the resulting experiences are very different (cf. Nagel, 1974). To make such information accessible we need transformation techniques; for instance, a Geiger-Müller tube for making ionizing radiation perceivable as we have not developed any sensory system for detecting and feeling this band of extremely high frequency electromagnetic radiation.
But even if we have access to given information from the environmental world, it would be an illusion to think of “objective perception” of it—differences in perception across different individuals seem to be obvious: this is one reason for different persons having different tastes, but it is even more extreme: even within a lifetime of one person, the perceptual qualities and quantities which we can process change. Elderly people, for instance, often have yellowish corneas yielding biased color perception reducing the ability to detect and differentiate bluish color spectra. So even objectivity of perceptions in the sense of consensual experience is hardly achievable, even within one species, even within one individual—just think of fashion phenomena (Carbon, 2011a), of changes in taste (Martindale, 1990) or the so-called cycle of preferences (Carbon, 2010a)! Clearly, so-called objective perception is impossible, it is an illusion.
Illusory Construction of the World
The problem with the idea of veridical perception of the world is further intensified when taking additional perceptual phenomena, which demonstrate highly constructive qualities of our perceptual system, into account. A very prominent example of this kind is the perceptual effect which arises when any visual information which we want to process falls on the area of the retina where the so-called blind spot is located
Interestingly, visual information that is mapped on the blind spot is not just dropped—this would be the easiest solution for the visual apparatus. It is also not rigidly interpolated, for instance, by just doubling neighbor information, but intelligently complemented by analysing the meaning and Gestalt of the context. If we, for example, are exposed to a couple of lines, the perceptual system would complement the physically non-existing information of the blind spot by a best guess heuristic how the lines are interconnected in each case, mostly yielding a very close approximation to “reality” as it uses most probable solutions. Finally, we experience clear visual information, seemingly in the same quality as the one which mirrors physical perception—in the end, the “physical perception” and the “constructed perception”, are of the same quality, also because the “physical perception” is neither a depiction of physical reality, but is also constructed by top-down processes based on best guess heuristic as a kind of hypothesis testing or problem solving (Gregory, 1970).
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