Imagery

A mental image is the representation of an idea in a person's mind. The ability to form and recall mental images, to learn about the world from them, and to communicate to others about them is a defining characteristic of the human species.

Introduction
At the most literal level, human consciousness consists entirely of imagery of the world from the sense data that surrounds us. Light enters through our eyes and sound waves enter through our ears. We touch things to feel them and we put things in our mouth to taste them. We smell airborne particles through our noses. From all of this data our minds make mental images that help us to survive and to reproduce. The human mind is also able to remember mental images in order to associate them with each other, to compare them to others, and to form useful theories of how the world works based on likely sequences of mental images - whether other creatures have this capability is debated.

Mental images are not restricted to our perceptions of the environment. Humans also have the ability to recall images from the past, and to synthesize (integrate) various memories. We can imagine and create images, and sometimes confabulate images (confuse reality with dream). This ability includes being able to look inward, and to form a mental image of ourselves, and of our activities - this introspection is the basis of consciousness (see also "animal mind").

Sensory input tends to be dominated by visual data, and mental images are often visual in nature (the word 'image' itself implies the visual system). It is common in English to use the verb "to see" to mean "to understand", but the same process can also be applied to all other sense data and the mental images we form from them (eg. "sounds good", "feels right"). Some people find auditory or kinesthetic sensations far more prominent than visual sensations. Though the range of mental imagery includes pictures, sounds, textures, tastes, & smells, there are some limitations to this process. For example, most people consider it far easier to clearly remember the look or sound of something than to remember its taste or smell.

The synthesis of multiple senses is perhaps most strikingly experienced in the form of dreams. In certain forms of sleep, human minds synthesize new mental images at random in curious half-connected sequences. If the dreamer is only lightly asleep, they may become aware not only of images, but also experience emotions and sensations connected with them. Thus, we can enjoy a pleasant dream or be frightened by a nightmare. We may remember our dreams when fully awake, although such memories often fade rapidly.

Philosophical ideas about mental images
Mental images are an important topic in classical and modern philosophy, as they are central to the study of knowledge. The urtext is Plato's Republic book VII. Plato uses the metaphor of a prisoner in a cave, bound and unable to move, sitting with his back to a fire and watching the shadows cast on the wall in front of him by people carrying objects behind his back. The objects that they are carrying are representations of real things in the world. The prisoner, explains Socrates, is like a human being making mental images from the sense data that he experiences. To see the "real" world the prisoner would have to make a great effort in order to break his bonds, and to fight his way out of the cave. And when he did so, the bright daylight would dazzle him.

In more recent times, Bishop Berkeley's idea of idealism has been proposed. This idea is that reality is equivalent to mental images &mdash; our mental images are not a copy of another material reality, but that reality itself. Berkeley, however, sharply distinguished between the images that he considered to constitute the external world, and the images of individual imagination. Only the latter are considered "mental imagery" in the contemporary sense of the term.

Following modern scientific realist philosophers like Karl Popper and David Deutsch, we can look back to an eighteenth century British writer, Dr. Samuel Johnson, for the case against idealism. When asked what he thought about idealism (while out on a walk in Scotland) he is alleged to have replied "I refute it thus!" as he kicked a large rock and his leg rebounded. His point was that the idea that the rock was just another mental image and had no material existence of its own, was a poor explanation of the painful sense data he had just experienced.

As David Deutsch argues in The Fabric of Reality, if we judge the value of our mental images of the world by the quality and quantity of the sense data that they can explain, then the most valuable mental image — or theory — that we currently have is that the world has a real independent existence and that humans have successfully evolved by building up and adapting patterns of mental images to explain it. This is an important idea in scientific thought.

On the other hand, this scientific realism has led others to ask how the inner perception of mental images actually occurs. This is sometimes called the "homunculus problem" (see also the mind's eye). The problem is similar to asking how the images you see on a computer screen exist in the memory of the computer, or how a computer is able to perceive it's surroundings (see computer vision, machine vision, computer graphics). To scientific materialism, mental images and the perception of them must be brain-states. The problem comes when an attempt to show where the images and the perceiver of them exist in the brain — they cannot be found anywhere. Neither will any description of the brain's functions show where they are. To speak of a perceiver and his images requires a subjective mode of thought, and this seems incompatible with a purely objective and materialist worldview.

Training and Learning Styles
Mental imagery has been associated with learning styles. Trainers are encouraged to teach using material that works with the visual, auditory, and kinesthetic systems (where possible). Teaching styles frequently include spoken components with a whiteboard or overheads. The theory is that some people may learn far more from one system than another, and teaching in multiple overlapping sensory systems benefits learning.

Research has been done on the experience of mental imagery and the effect of the imagination on skill development. For example, imagining playing a 5-finger piano exercise (mental practice) resulted in a significant improvement in performance over no mental practice - though not as significant as that produced by physical practice. "However, mental practice alone led to the same plastic changes in the motor system as those occurring with the acquisition of the skill by repeated physical practice (...) Mental practice alone seems to be sufficient to promote the modulation of neural circuits involved in the early stages of motor skill learning." (Pascual-Leone et al). Other experiments have found similar results (significant neural development but not equal to physical practice).

Psychiatric ideas about mental images
Mental images, and particular images from dreams, are the basis for the theories of Sigmund Freud about human behavior. His basic thesis was that our childhood experiences strongly influence the mental images that we make in later life. He believed that humans form mental images unawares in the unconscious according to their "latent" desires; these, he claims, are as important as conscious mental images and desires as explanations for human behaviour. Interestingly Freud began his work thinking about Hamlet, a play that deals deeply with how mental images affect action.

The variation of mental images we can form is exemplified in Optical illusions, which are based on the ambiguity of interpretation of an image. Computer vision pioneer David Marr produced a famous photograph of a woman's face, which includes an ambiguous feature that could be either her nose or her finger.

Application to Design and Usability
Much more pragmatically, psychologists working with control systems and other computer systems study mental images in order to help create systems that are easy to use. When users interact with a complex system, like a computer program, a motor car, or a nuclear power station, they form mental images of how it works. If this mental image is a poor one or has significant differences from the designer's mental image, then the user is more likely to make mistake [!-this sounds more like forming a "mental model" than a "mental image"]