Because of the Internet, people with unusual abilities have been able to contact one another. Some were surprised to find out that others had the same abilities, while others were surprised to discover that not everyone had the same abilities as they did. In the case of synesthesia, individuals have two or more senses that are involuntarily joined in some circumstances. For example, an individual with synesthesia may always perceive a certain number as tinged with green, while another number may be tinged with yellow. Someone with synesthesia may see colors when he or she hears the sound of a certain instrument. According to the website for the American Synesthesia Association, Inc., the ability may not be as rare as once thought. Synesthesia has been identified for about 300 years, but only in the last 20 years has it been a topic of serious study. Internet resources are available for individuals with synesthesia to learn about and discuss their abilities. Artists frequently perceive the physical world in unusual ways, so it is sometimes thought that people who describe synesthetic experiences are simply indulging artistic visions. Researchers have found that synesthesia does occur more often among creative individuals than in the general population. Additional information about synesthesia can be found on the Belgian Synesthesia Association website and on the Synesthesia Battery, which offers tests for the condition online.