The psychological differences between a frog’s vision and ours should not be overlooked. The frog’s vision is passive and its responses are automatic. The bug-shaped templates in its eyes, called receptive fields, will “capture” a bug that flies by and the frog will enjoy a meal.
Frogs can’t pay attention. Stimuli are never ambiguous. A frog will eat a poisonous tiger moth and learn too late of its misjudgment. On the other hand, we humans seek specific visual targets related to food and social contact, and these poisoned apples and faithless smiles may be highly ambiguous. We need top-down discrimination with our capacious brains to survive, though our great longevity—compared to a frog’s—may depend more on body size than brain size alone.
Our sensations need interpretation. Top-down processing puts sensations into context. That doesn’t mean that top-down is truer than bottom-up; in fact perception may not change the sensation, but it can make it less ambiguous. And then we’re often stuck with that interpretation; we can’t unsee it. There’s the difference between sensation and perception.
One implication of this is that, while psychology can make it clear that we all face the same problems of stimulus ambiguity in sensation, it can’t make sure we all have the same experiences in perception.
It’s even hard to prove that there is an external world to arouse our conscious awareness through sensation. To some extent, our consciousness creates our impression of the external world–as a kind of hallucination or illusion.
BIO: Our senses do not appear on anyone’s list of measuring instruments because they are calibrated for our survival rather than to the metric system.
What is it with light, that we should measure it, anyway? We use it to form images. Most life forms use it to set their biological clocks. Plants use it for energy!
But why not radio waves? X-rays? Anything but visible light? Radio, X-rays, microwaves: They’re all electromagnetic radiation, differing only in wavelength.
But some wavelengths are emitted weakly by the sun or won’t travel through the atmosphere, like microwaves and gamma radiation. And all the wavelengths are blocked by seawater–except visible light. If we suppose that all life originated in the oceans*, that’s a pretty big consideration.
As it happens, sunlight varies over a wide range of intensities, more than one billion to one, too much for any eye to measure directly. Instead, we adjust our vision to be sensitive just to the ambient light level, from noontime glare to a cave’s dimness, by a process called adaptation. Adaption influences almost every sensory judgment that we make. When we are adapted to a dark theater, we can’t see facial features when we leave the theater at noon. As dark-adapted viewers, we see only silhouettes. If we re-enter the theater after a few minutes, we can’t distinguish seats that were obvious in dim light earlier.
In that way, our vision keeps us sensitive to whatever is happening, wherever we are, even if we are failures as light meters.
The frog’s eye adapts to light as well, by the bleaching of rhodopsin in its retina, which reduces sensitivity. Humans can adapt as well using the brain, making it possible to adapt to contrast, detail, and other features of visual objects. In this way, adaptation and attention play complementary roles, decreasing and increasing the salience of visual features.
That is only the beginning of the survivalist senses that evolution has selected for. It’s a kind of compliment to evolution that we now try to duplicate evolutionary successes. However, it raises a serious question of whether the world we sense is reality or an invention of the brain.
*There are those who favor fresh water.
PSYCHO: Consider the extraordinary sensory and perceptual judgments in tasks that may be required to earn a living: Athletes, symphony conductors, wine tasters, chick sexers, cloth dyers, chefs, dermatologists, filmmakers, piano tuners, tightrope walkers and acrobats, dialect coaches, cholecystectomy surgeons, gumologists, and counterfeiters all make their living by their senses.
No one would imagine that these perceptual paragons simply add up the readings on their receptors to pursue their crafts. Instead, their interpretations of what they see, hear, and feel have been honed since infancy to respond to important aspects of what they work with.
In other words, we construct our perceptual reality. We make up what we see and hear to a surprising extent. Hallucinations are an everyday experience, as when we drink too much coffee or smell smoke when we enter a non-burning room or hear music without a source.
Psychologists since Piaget are likely to say that even our thoughts are constructed. Even recalling a single memory is a reconstruction. We don’t know what we know, true; but we bring what we know to mind not through recollection but active construction.
Our memories are made to fit a kind of story that we may call a thought. Our goal is not to preserve an archival record but to survive. This may have some awkward consequences, but it’s too late to argue with our evolution.
SOCIAL: We share a sense of reality with others around us as a result of social validation—signals from others that our view matters. The consensus is not a gauge of physical reality, or past ages would not have believed in ghosts and cultural influencers would not nurture hopes of persuading us that physical reality betokens supernatural visitors and lost worlds.
We perceive disabled (differently abled) people according to the way our culture views them. Disability is certainly in part an illusion. Sometimes disabled people win the Olympics. I suspect that some of the celebrities on this list were diagnosed after the fact, as when some sites label Einstein as autistic, but it does make a point.