The philosophy of perception is concerned with the nature of perceptual experience and the status of perceptual data, in particular how they relate to beliefs about, or knowledge of, the world. Any explicit account of perception requires a commitment to one of a variety of ontological or metaphysical views. Philosophers distinguish internalist accounts, which assume that perceptions of objects, and knowledge or beliefs about them, are aspects of an individual's mind, and externalist accounts, which state that they constitute real aspects of the world external to the individual. The position of naïve realism—the 'everyday' impression of physical objects constituting what is perceived—is to some extent contradicted by the occurrence of perceptual illusions and hallucinations and the relativity of perceptual experience as well as certain insights in science. Realist conceptions include phenomenalism and direct and indirect realism. Anti-realist conceptions include idealism and skepticism. Recent philosophical work have expanded on the philosophical features of perception by going beyond the single paradigm of vision.
Within visual perception, an optical illusion is an illusion caused by the visual system and characterized by a visual percept that arguably appears to differ from reality. Illusions come in a wide variety; their categorization is difficult because the underlying cause is often not clear but a classification proposed by Richard Gregory is useful as an orientation. According to that, there are three main classes: physical, physiological, and cognitive illusions, and in each class there are four kinds: Ambiguities, distortions, paradoxes, and fictions. A classical example for a physical distortion would be the apparent bending of a stick half immerged in water; an example for a physiological paradox is the motion aftereffect. An example for a physiological fiction is an afterimage. Three typical cognitive distortions are the Ponzo, Poggendorff, and Müller-Lyer illusion. Physical illusions are caused by the physical environment, e.g. by the optical properties of water. Physiological illusions arise in the eye or the visual pathway, e.g. from the effects of excessive stimulation of a specific receptor type. Cognitive visual illusions are the result of unconscious inferences and are perhaps those most widely known.
An altered state of consciousness (ASC), also called altered state of mind or mind alteration, is any condition which is significantly different from a normal waking state. By 1892, the expression was in use in relation to hypnosis, though there is an ongoing debate as to whether hypnosis is to be identified as an ASC according to its modern definition. The next retrievable instance, by Dr Max Mailhouse from his 1904 presentation to conference, however, is unequivocally identified as such, as it was in relation to epilepsy, and is still used today. In academia, the expression was used as early as 1966 by Arnold M. Ludwig and brought into common usage from 1969 by Charles Tart. It describes induced changes in one's mental state, almost always temporary. A synonymous phrase is "altered state of awareness".
Ecstasy is a subjective experience of total involvement of the subject, with an object of their awareness. In classical Greek literature, it refers to removal of the mind or body "from its normal place of function."
A phosphene is the phenomenon of seeing light without light entering the eye. The word phosphene comes from the Greek words phos (light) and phainein. Phosphenes that are induced by movement or sound may be associated with optic neuritis.
Hypnagogia is the experience of the transitional state from wakefulness to sleep: the hypnagogic state of consciousness, during the onset of sleep. Its opposite state is described as hypnopompic —the transitional state from sleep into wakefulness. Mental phenomena that may occur during this "threshold consciousness" phase include hypnagogic hallucinations, exploding head syndrome, lucid dreaming, and sleep paralysis. The latter two phenomena are themselves separate sleep conditions that are sometimes experienced during the hypnagogic state.
Megalithic art refers to art either painted or carved onto megaliths in prehistoric Europe. Elizabeth Shee Twohig has coined the term Megalithic art in her study of 'The Megalithic Art of Western Europe'. Her original definition of Megalithic art focused on paintings or carvings found on the structural elements, like the kerbstones, orthostats, or capstones of megalithic tombs, but recent investigations have included decorations on stelae and menhirs.
Psychedelic art is art, graphics or visual displays related to or inspired by psychedelic experiences and hallucinations known to follow the ingestion of psychedelic drugs such as LSD, psilocybin, and DMT. The word "psychedelic" means "mind manifesting". By that definition, all artistic efforts to depict the inner world of the psyche may be considered "psychedelic".
A psychedelic experience is a temporary altered state of consciousness induced by the consumption of a psychedelic substance. For example, an acid trip is a psychedelic experience brought on by the use of LSD, while a mushroom trip is a psychedelic experience brought on by the use of psilocybin. Psychedelic experiences feature alterations in normal perception such as visual distortions and a subjective loss of self-identity, sometimes interpreted as mystical experiences. Psychedelic experiences lack predictability, as they can range from being highly pleasurable to frightening. The outcome of a psychedelic experience is heavily influenced by the person's mood, personality, expectations, and environment.
Entoptic phenomena are visual effects whose source is within the human eye itself.
Closed-eye hallucinations and closed-eye visualizations (CEV) are hallucinations that occur when one's eyes are closed or when one is in a darkened room. They can be a form of phosphene. Some people report CEV under the influence of psychedelics; these are reportedly of a different nature than the "open-eye" hallucinations of the same compounds. Similar hallucinations that occur due to loss of vision are called visual release hallucinations.
A form constant is one of several geometric patterns which are recurringly observed during hypnagogia, hallucinations and altered states of consciousness.
Hypnopompia is the state of consciousness leading out of sleep, a term coined by the psychical researcher Frederic Myers. Its mirror is the hypnagogic state at sleep onset; though often conflated, the two states are not identical and have a different phenomenological character. Hypnopompic and hypnagogic hallucinations are frequently accompanied by sleep paralysis, which is a state wherein one is consciously aware of one's surroundings but unable to move or speak.
James David Lewis-Williams is a South African archaeologist. He is best known for his research on southern African San (Bushmen) rock art, of which it can be said that he found a 'Rosetta Stone'. He is the founder and previous director of the Rock Art Research Institute and is currently professor emeritus of cognitive archaeology at the University of the Witwatersrand (WITS). Lewis-Williams is recognised by the National Research Foundation (NRF) of South Africa as a leading international researcher, with an A1 rating.
Trance is a state of semi-consciousness in which a person is not self-aware and is either altogether unresponsive to external stimuli or is selectively responsive in following the directions of the person who has induced the trance. Trance states may occur involuntarily and unbidden.
Ideasthesia is a neuropsychological phenomenon in which activations of concepts (inducers) evoke perception-like sensory experiences (concurrents). The name comes from the Ancient Greek ἰδέα and αἴσθησις, meaning 'sensing concepts' or 'sensing ideas'. The notion was introduced by neuroscientist Danko Nikolić as an alternative explanation for a set of phenomena traditionally covered by synesthesia.
Inside the Neolithic Mind: Consciousness, Cosmos and the Realm of the Gods is a cognitive archaeological study of Neolithic religious beliefs in Europe co-written by the archaeologists David Lewis-Williams and David Pearce, both of the University of the Witwatersrand in Johannesburg, South Africa. It was first published by Thames and Hudson in 2005. Following on from Lewis-Williams' earlier work, The Mind in the Cave (2002), the book discusses the role of human cognition in the development of religion and Neolithic art.
The San religion is the traditional religion and mythology of the San people. It is poorly attested due to their interactions with Christianity.
In the Neolithic and Bronze Age British Isles, rock art was produced across various parts of the islands. Petroglyphic in nature, the majority of such carvings are abstract in design, usually cup and ring marks, although examples of spirals or figurative depictions of weaponry are also known. Only one form of rock art in Europe, this late prehistoric tradition had connections with others along Atlantic Europe, particularly in Galicia.
DeepDream is a computer vision program created by Google engineer Alexander Mordvintsev that uses a convolutional neural network to find and enhance patterns in images via algorithmic pareidolia, thus creating a dream-like appearance reminiscent of a psychedelic experience in the deliberately overprocessed images.
