Mental image
In the philosophy of mind, neuroscience, and cognitive science, a mental image is an experience that, on most occasions, significantly resembles the experience of "perceiving" some object, event, or scene but occurs when the relevant object, event, or scene is not actually present to the senses. There are sometimes episodes, particularly on falling asleep and waking up, when the mental imagery may be dynamic, phantasmagoric, and involuntary in character, repeatedly presenting identifiable objects or actions, spilling over from waking events, or defying perception, presenting a kaleidoscopic field, in which no distinct object can be discerned. Mental imagery can sometimes produce the same effects as would be produced by the behavior or experience imagined.
The nature of these experiences, what makes them possible, and their function have long been subjects of research and controversy in philosophy, psychology, cognitive science, and, more recently, neuroscience. As contemporary researchers use the expression, mental images or imagery can comprise information from any source of sensory input; one may experience auditory images, olfactory images, and so forth. However, the majority of philosophical and scientific investigations of the topic focus on visual mental imagery. It has sometimes been assumed that, like humans, some types of animals are capable of experiencing mental images. Due to the fundamentally introspective nature of the phenomenon, it has been difficult to assess whether or not non-human animals experience mental imagery.
Philosophers such as George Berkeley and David Hume, and early experimental psychologists such as Wilhelm Wundt and William James, understood ideas in general to be mental images. Today, it is widely believed that much imagery functions as mental representations, playing an important role in memory and thinking. William Brant traces the scientific use of the phrase "mental images" back to John Tyndall's 1870 speech called the "Scientific Use of the Imagination". Some have suggested that images are best understood to be, by definition, a form of inner, mental, or neural representation. Others reject the view that the image experience may be identical with any such representation in the mind or the brain, but do not take account of the non-representational forms of imagery.
Mind's eye
The notion of a "mind's eye" goes back at least to Cicero's reference to mentis oculi during his discussion of the orator's appropriate use of simile.In this discussion, Cicero observed that allusions to "the Syrtis of his patrimony" and "the Charybdis of his possessions" involved similes that were "too far-fetched"; and he advised the orator to, instead, just speak of "the rock" and "the gulf" —on the grounds that "the eyes of the mind are more easily directed to those objects which we have seen, than to those which we have only heard".
The concept of "the mind's eye" first appeared in English in Chaucer's Man of Law's Tale in his Canterbury Tales, where he tells us that one of the three men dwelling in a castle was blind, and could only see with "the eyes of his mind"; namely, those eyes "with which all men see after they have become blind".
Physical basis
The biological foundation of mental imagery is not fully understood. Studies using fMRI have shown that the lateral geniculate nucleus and the V1 area of the visual cortex are activated during mental imagery tasks. Ratey writes:The visual pathway is not a one-way street. Higher areas of the brain can also send visual input back to neurons in lower areas of the visual cortex. As humans, we have the ability to see with the mind's eye—to have a perceptual experience in the absence of visual input. For example, PET scans have shown that when subjects, seated in a room, imagine they are at their front door starting to walk either to the left or right, activation begins in the visual association cortex, the parietal cortex, and the prefrontal cortex—all higher cognitive processing centers of the brain.
A biological basis for mental imagery is found in the deeper portions of the brain below the neocortex. In a large study with 285 participants, Tabi, Maio, Attaallah, et al. investigated the association between an established measure of visual mental imagery, Vividness of Visual Imagery Questionnaire scores, and volumes of brain structures including the hippocampus, amygdala, primary motor cortex, primary visual cortex and the fusiform gyrus Tabi et al. found significant positive correlations between visual imagery vividness and the volumes of the hippocampus and primary visual cortex.
Significant positive correlations were also obtained between VVIQ scores and hippocampal structures including Bilateral CA1, CA3, CA4 and Granule Cell and Molecular Layer of the Dentate Gyrus. Follow-up analysis revealed that visual imagery was in particular correlated with the four subfields presented in the above illustration.
The thalamus has been found to be discrete to other components in that it processes all forms of perceptional data relayed from both lower and higher components of the brain. Damage to this component can produce permanent perceptual damage, however when damage is inflicted upon the cerebral cortex, the brain adapts to neuroplasticity to amend any occlusions for perception. It can be thought that the neocortex is a sophisticated memory storage warehouse in which data received as an input from sensory systems are compartmentalized via the cerebral cortex. This would essentially allow for shapes to be identified, although given the lack of filtering input produced internally, one may as a consequence, hallucinate—essentially seeing something that isn't received as an input externally but rather internal.
Not all people have the same mental imagery ability. For some, when the eyes are closed, the perception of darkness prevails. However, some people are able to perceive colorful, dynamic imagery. The use of hallucinogenic drugs increases the subject's ability to consciously access mental imagery including synaestesia.
Furthermore, the pineal gland is a hypothetical candidate for producing a mind's eye. Rick Strassman and others have postulated that during near-death experiences and dreaming, the gland might secrete the hallucinogenic chemical N,''N-Dimethyltryptamine to produce internal visuals when external sensory data is occluded. However, this hypothesis has yet to be fully supported with neurochemical evidence and plausible mechanism for DMT production.
The condition where a person lacks mental imagery is called aphantasia. The term was first suggested in a 2015 study.
Common examples of mental images include daydreaming and the mental visualization that occurs while reading a book. Another is of the pictures summoned by athletes during training or before a competition, outlining each step they will take to accomplish their goal. When a musician hears a song, they can sometimes "see" the song notes in their head, as well as hear them with all their tonal qualities. This is considered different from an after-effect, such as an afterimage. Calling up an image in our minds can be a voluntary act, so it can be characterized as being under various degrees of conscious control.
There are several theories as to how mental images are formed in the mind. These include the dual-code theory, the propositional theory, and the functional-equivalency hypothesis. The dual-code theory, created by Allan Paivio in 1971, is the theory that we use two separate codes to represent information in our brains: image codes and verbal codes. Image codes are things like thinking of a picture of a dog when you are thinking of a dog, whereas a verbal code would be to think of the word "dog". Another example is the difference between thinking of abstract words such as justice or love and thinking of concrete words like elephant or chair. When abstract words are thought of, it is easier to think of them in terms of verbal codes—finding words that define them or describe them. With concrete words, it is often easier to use image codes and bring up a picture of a human or chair in your mind rather than words associated or descriptive of them.
The propositional theory involves storing images in the form of a generic propositional code that stores the meaning of the concept not the image itself. The propositional codes can either be descriptive of the image or symbolic. They are then transferred back into verbal and visual code to form the mental image.
The functional-equivalency hypothesis is that mental images are "internal representations" that work in the same way as the actual perception of physical objects. In other words, the picture of a dog brought to mind when the word dog'' is read is interpreted in the same way as if the person was observing an actual dog before them.
Research has occurred to designate a specific neural correlate of imagery; however, studies show a multitude of results. Most studies published before 2001 suggest neural correlates of visual imagery occur in Brodmann area 17. Auditory performance imagery have been observed in the premotor areas, precunes, and medial Brodmann area 40. Auditory imagery in general occurs across participants in the temporal voice area, which allows top-down imaging manipulations, processing, and storage of audition functions. Olfactory imagery research shows activation in the anterior piriform cortex and the posterior piriform cortex; experts in olfactory imagery have larger gray matter associated to olfactory areas. Tactile imagery is found to occur in the dorsolateral prefrontal area, inferior frontal gyrus, frontal gyrus, insula, precentral gyrus, and the medial frontal gyrus with basal ganglia activation in the ventral posteriomedial nucleus and putamen. Research in gustatory imagery reveals activation in the anterior insular cortex, frontal operculum, and prefrontal cortex. Novices of a specific form of mental imagery show less gray matter than experts of mental imagery congruent to that form. A meta-analysis of neuroimagery studies revealed significant activation of the bilateral dorsal parietal, interior insula, and left inferior frontal regions of the brain. Causal evidence from neurological patients with brain lesions demonstrates that vivid visual mental imagery is possible even when occipital visual areas are lesioned or disconnected from more anterior cortex. Visual mental imagery can instead be impaired by left temporal damage. Consistent with these findings, a meta-analysis of 27 neuroimaging studies demonstrated imagery-related activity in a region of the left ventral temporal cortex, which was dubbed the Fusiform Imagery Node. An additional Bayesian analysis excluded a role for occipital cortex in visual mental imagery, consistent with the evidence from neurological patients.
Imagery has been thought to cooccur with perception; however, participants with damaged sense-modality receptors can sometimes perform imagery of said modality receptors. Neuroscience with imagery has been used to communicate with seemingly unconscious individuals through fMRI activation of different neural correlates of imagery, demanding further study into low quality consciousness. A study on one patient with one occipital lobe removed found the horizontal area of their visual mental image was reduced.