Synaesthesia

Synesthesia (also spelled synæsthesia or synaesthesia, plural synesthesiae or synaesthesiae)?from the Ancient Greek (syn), "together," and (aisth?sis), "Category: wikt - :sensation|sensation"?is a neurologically based phenomenon in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway. People who report such experiences are known as synesthetes.

In one common form of synesthesia, known as grapheme ? color synesthesia or color-graphemic synesthesia, letters or numbers are perceived as inherently colored, while in ordinal linguistic personification, numbers, days of the week and months of the year evoke personalities. In spatial-sequence, or number form synesthesia, numbers, months of the year, and/or days of the week elicit precise locations in space (for example, 1980 may be "farther away" than 1990), or may have a (three-dimensional) view of a year as a map (clockwise or counterclockwise). Yet another recently identified type, visual motion ? sound synesthesia, involves hearing sounds in response to visual motion and flicker. Over 60 types of synesthesia have been reported by people,Day, Sean, Types of synesthesia. (2009) Types of synesthesia. Online: http://home.comcast.net/~sean.day/html/types.htm, accessed 18 February 2009. but only a fraction have been evaluated by scientific research. Even within one type, synesthetic perceptions vary in intensity and people vary in awareness of their synesthetic perceptions.Campen, Cretien van (2009) "The Hidden Sense: On Becoming Aware of Synesthesia" TECCOGS, vol. 1, pp. 1-13.[http://www.pucsp.br/pos/tidd/teccogs/artigos/pdf/teccogs_edicao1_2009_artigo_CAMPEN.pdf]

While cross-sensory metaphors (e.g., "loud shirt," "bitter wind" or "prickly laugh") are sometimes described as "synesthetic," true neurological synesthesia is involuntary. It is estimated that synesthesia could possibly be as prevalent as 1 in 23 persons across its range of variants. Synesthesia runs strongly in families, but the precise mode of inheritance has yet to be ascertained. Synesthesia is also sometimes reported by individuals under the influence of psychedelic drugs, after a stroke, during a temporal lobe epilepsy seizure, or as a result of blindness or deafness. Synesthesia that arises from such non-genetic events is referred to as "adventitious synesthesia" to distinguish it from the more common congenital forms of synesthesia. Adventitious synesthesia involving drugs or stroke (but not blindness or deafness) apparently only involves sensory linkings such as sound ? vision or touch ? hearing; there are few, if any, reported cases involving culture-based, learned sets such as graphemes, lexemes, days of the week, or months of the year.

Although synesthesia was the topic of intensive scientific investigation in the late 1800s and early 1900s, it was largely abandoned by scientific research in the mid-20th century, and has only recently been rediscovered by modern researchers. Psychological research has demonstrated that synesthetic experiences can have measurable behavioral consequences, while functional neuroimaging studies have identified differences in patterns of brain activation. Many people with synesthesia use their experiences to aid in their creative process, and many non-synesthetes have attempted to create works of art that may capture what it is like to experience synesthesia. Psychologists and neuroscientists study synesthesia not only for its inherent interest, but also for the insights it may give into cognitive and perceptual processes that occur in synesthetes and non-synesthetes alike.

Autism is a disorder of neural development that is characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their synapses connect and organize; how this occurs is not well understood. The two other autism spectrum disorders (ASD) are Asperger syndrome, which lacks delays in cognitive development and language, and PDD-NOS, diagnosed when full criteria for the other two disorders are not met.

Autism has a strong genetic basis, although the genetics of autism are complex and it is unclear whether ASD is explained more by rare mutations, or by rare combinations of common genetic variants. In rare cases, autism is strongly associated with agents that cause birth defects. Controversies surround other proposed environmental causes, such as heavy metals, pesticides or childhood vaccines; the vaccine hypotheses are biologically implausible and lacking convincing scientific evidence. The prevalence of autism is about 1?2 per 1,000 people; the prevalence of ASD is about 6 per 1,000, with about four times as many males as females. The number of people diagnosed with autism has increased dramatically since the 1980s, partly due to changes in diagnostic practice; the question of whether actual prevalence has increased is unresolved.

Parents usually notice signs in the first two years of their child's life. The signs usually develop gradually, but some autistic children first develop more normally and then regress. Although early behavioral or cognitive intervention can help autistic children gain self-care, social, and communication skills, there is no known cure. Not many children with autism live independently after reaching adulthood, though some become successful. An autistic culture has developed, with some individuals seeking a cure and others believing autism should be tolerated as a difference and not treated as a disorder.