Terminology in Visual Perception

Below are some concepts that are important to understand when reading this topic and its chapters.

Afterimage

An afterimage is a visual illusion or sensory impression that persists in your eyes or brain even after the original stimulus (like a bright light or a colored shape) is removed. It happens because the photochemical activity or neural processing in your retina continues after the external cause has ceased. There are two primary types of afterimages:

1. Negative Afterimages
These are the most common. When you stare at an object for an extended period, the photoreceptors in your eyes become fatigued. When you look away (such as at a blank white wall), you will see the same shape in its complementary color and opposite brightness.
Example:
Staring at a red object causes a green afterimage to appear when you look away. Staring at black text on a screen will temporarily leave a glowing white afterimage.

2. Positive Afterimages
These are much rarer and typically short-lived. Instead of changing colors, a positive afterimage retains the exact colors and brightness of the original image.
Example:
The lingering, bright, flash-shaped spot you see immediately after taking a photograph with a camera flash.

The previously mentioned term ‘afterimages’ is also referred to as: ‘phosphenes’, ‘entoptic phenomena’, or ‘form constants’.
In their article 'The Signs of All Times', J.D. Lewis-Williams and T.A. Dowson (1988) propose a 'neural bridge' in archaeological time span to the Upper Palaeolithic.
Through this neural bridge we can gain insight into the nature of the origin of art.
As far as we can tell, not much has changed in the last 100,000 years.

In our biological evolution, we may still physically be the hunter-gatherers we were before agrarianism.
In the signs of palaeolithic art (for example, cave paintings), Lewis-Williams and Dowson see entoptic phenomena that closely resemble those produced by humans in altered states of consciousness today.

Entoptics

'Entoptic' is derived from the Greek for 'inside sight', that is to say: within the optical system between and including the eye itself and the cortex, where signals from the optic nerve are interpreted.
Lewis-Williams and Dowson further subdivide these into:
a) 'phosphenes' that can be produced by physical stimulation (such as the patterns you see when you close your eyes and apply gentle pressure to your eyelids), and
b) 'shape constants' that are produced outside the eye in the cortex itself.
Lewis-Williams and Dowson (1988) focus primarily on the latter, although they do not exclude phosphenes and clearly group both under the general term 'entoptics'.

However, they distinguish between entoptics and hallucinations. Entoptics are geometric patterns whose origin lies in the moving self; whereas hallucinations are iconic and culturally determined and can be experienced in all respects {auditory, visual, tactile, olfactory (smell), and synesthetic}, thus not only visually. Hallucinations can arise from entoptics, as will be described below.

Phosphenes

Phosphenes can appear in your eye without you having looked into a light. With a blow to the eye, you can see phosphenes in the form of stars.
They are phantom light spots of many sizes and types.
Phosphenes can also be spots, lines, shapes, or patterns that ‘glow’ in visual memory, for example, when using hallucinogenic substances.

Entoptic phenomena

Entoptic phenomena are visual effects whose origin lies within the eye itself, or in the brain region that processes information from the optic nerves (the occipital lobe).

Shape constants

Shape constants are various geometric patterns that are recursively perceived during hallucinations and altered states of consciousness.
These terms are used interchangeably here, because many researchers have given them their own definitions.

In short:
Some spots are ‘specks’ in the eye.
Some figures are intrinsic patterns of the visual organ (retina) that are activated by light or deformation of the eyeball (hardware).
Some figures are intrinsic basic properties of the neuronal visual system in the brain, which is activated by seeing geometric patterns.
Some patterns are figures that we unconsciously like to see (software) and can easily shape ourselves in our imagination, because they are readily activated by our neuronal network (hardware).

Superstimulus

A superstimulus (short for supernormal stimulus) is a term from the domain of behavioral biology and indicates the following: Certain external characteristics in animals have a strong stimulating effect on the observer to exhibit a specific behavior; for example, in seagulls: a red spot on the mother's beak stimulates chicks to open their beaks and accept food. The color red in an essential spot on the caregiver initiates specific behavior in the young.

A superstimulus is a supernormal stimulus, that is to say: an exaggerated version of an ordinary stimulus to which there is usually a tendency to respond.
It can also be a stimulus that elicits a response more strongly than the stimulus for which it was developed.

When it comes to bird eggs, for example, birds can evolve to prefer artificial versions over their own eggs, which is particularly evident in brood parasitism.
Consider, for example, the parasitic cuckoo that lays an egg in the nest of small songbirds. The cuckoo's egg is actually larger than the eggs of the songbirds themselves; A cuckoo egg acts as a superstimulus on the songbird that incubates it.
Almost a century ago, the ethologist (= behavioral biologist) Niko Tinbergen (1907 - 1988) conducted research into animal behavior. For instance, he used artificial eggs, but a size larger, and let the songbirds choose which egg they wanted to incubate: the bird often preferred the large egg over an egg of normal size. His research into the function of the red spot on the beak of the herring gull is also famous.

Humans can be exploited in the same way by junk food, which looks bigger and more colorful on the packaging than the product inside.

Organisms tend to show a preference for certain properties of the stimulus (for example: size, color, shape, etc.) that have usually evolved in nature.
But when an artificial, exaggerated stimulus is presented, animals will exhibit targeted behavior in favor of the artificial stimulus over the naturally occurring stimulus. A variety of organisms that exhibit (or are sensitive to) supernormal stimuli include insects, birds, and humans.

Over many generations, selective evolutionary pressure occurs both among the animals that display characteristics of a supernormal stimulus and among the organisms that respond to these superstimuli. This biological process is called co-evolution. Thus, co-evolution takes place between animals that exhibit supernormal stimuli and the organisms that respond to these superstimuli, for example:
Flower and Bee:
The best-known example is flower pollination by bees: conspicuous flowers are pollinated more frequently by bees. Bees that recognize these flowers are better able to collect nectar. The flower serves as a superstimulus for the bee. The bee becomes more sensitive to this superstimulus. This feedback loop develops over thousands of years of co-evolution between certain plant species and certain insect species. This co-evolution depends on the evolutionary diffusion of genetic traits, behavioral patterns, and other biological factors.

Supernormal stimuli such as striking color, size, patterns, or shapes, are often successful for the following reasons:
An organism exhibiting these characteristics will often be sexually selected by an organism (of same species) that prefers these characteristics.
This ensures the survival of animals with superstimulus characteristics. These animals have an improved chance of reproduction in current and later generations. This process is an example of a positive cybernetic feedback loop, which entails a self-reinforcing (evolutionary) process, in this case of a genetically embedded trait.

Sources

- J.D. Lewis-Williams and T.A. Dowson (1988). The Signs of All Times.
- Entoptic phenomenon: https://en.wikipedia.org/wiki/Entoptic_phenomenon.
- Phosphene: https://en.wikipedia.org/wiki/Phosphene.
- Supernormal stimulus: https://en.wikipedia.org/wiki/Supernormal_stimulus.