Ideasthesia

Ideasthesia (alternative spelling ideaesthesia) is a neuropsychological phenomenon in which activations of concepts (inducers) evoke perception-like sensory experiences (concurrents). The name comes from the Ancient Greek ἰδέα (idéa) and αἴσθησις (aísthēsis), meaning 'sensing concepts' or 'sensing ideas'. The notion was introduced by neuroscientist Danko Nikolić, but can be seen in examples in the Ethics of Spinoza (especially in the third part of the Ethics), as an alternative explanation for a set of phenomena traditionally covered by synesthesia.

While synesthesia meaning 'union of senses' implies the association of two sensory elements with little connection to the cognitive level, empirical evidence indicated that most phenomena linked to synesthesia are in fact induced by semantic representations. That is, the linguistic meaning of the stimulus is what is important rather than its sensory properties. In other words, while synesthesia presumes that both the trigger (inducer) and the resulting experience (concurrent) are of sensory nature, ideasthesia presumes that only the resulting experience is of sensory nature while the trigger is semantic.

Research has later extended the concept to topics other than synesthesia, and since it turned out to be applicable to everyday perception, the concept has developed into a theory of how we perceive. For example ideasthesia has been applied to the theory of art and could bear important implications in explaining human conscious experience, which, according to ideasthesia, is grounded in how we activate concepts.

A common example of synesthesia is the association between graphemes and colors, usually referred to as grapheme–color synesthesia. Here, letters of the alphabet are associated with vivid experiences of color. Studies have indicated that the perceived color is context-dependent and is determined by the extracted meaning of a stimulus. For example, an ambiguous stimulus '5' that can be interpreted either as 'S' or '5' will have the color associated with 'S' or with '5', depending on the context in which it is presented. If presented among numbers, it will be interpreted as '5' and will associate the respective color. If presented among letters, it will be interpreted as 'S' and will associate the respective synesthetic color.

Evidence for grapheme-color synesthesia comes also from the finding that colors can be flexibly associated to graphemes, as new meanings become assigned to those graphemes. In one study synesthetes were presented with Glagolitic letters that they had never seen before, and the meaning was acquired through a short writing exercise. The Glagolitic graphemes inherited the colors of the corresponding Latin graphemes as soon as the Glagolitic graphemes acquired the new meaning.

In another study, synesthetes were prompted to form novel synesthetic associations to graphemes never seen before. Synesthetes created those associations within minutes or seconds – which was time too short to account for creation of new physical connections between color representation and grapheme representation areas in the brain, pointing again towards ideasthesia. Although the time course is consistent with postsynaptic AMPA receptor upregulation or NMDA receptor coactivation, or both, which would imply that the realtime experience is invoked at the synaptic level of analysis prior to establishment of novel wiring per se, a very intuitively appealing model.

For lexical–gustatory synesthesia evidence also points towards ideasthesia: in lexical-gustatory synesthesia, verbalisation of the stimulus is not necessary for the experience of concurrents. Instead, it is sufficient to activate the concept.

Another case of synesthesia is swimming-style synesthesia in which each swimming style is associated with a vivid experience of a color. These synesthetes do not need to perform the actual movements of a corresponding swimming style. To activate the concurrent experiences, it is sufficient to activate the concept of a swimming style (e.g., by presenting a photograph of a swimmer or simply talking about swimming).