Perceiving is the process by which evanescent sensations are linked to environmental cause and made enduring and coherent through the assignment of meaning, utility, and value. Fundamental to this process is the establishment of associations over space and time between sensory events and other sources of information. These associations provide the context needed to resolve the inherent ambiguity of sensations. Recent studies have explored the neuronal bases of contextual influences on perception. These studies have revealed systems in the brain through which context converts neuronal codes for sensory events into neuronal representations that underlie perceptual experience. This work sheds light on the cellular processes by which associations are learned and how memory retrieval impacts the processing of sensory information. Collectively, these findings suggest that perception is the consequence of a critical neuronal computation in which contextual information is used to transform incoming signals from a sensory-based to a scene-based representation.
Perceiving is a common English word with a number of related colloquial meanings: it is the act of understanding, realizing, seeing, noticing, or becoming aware of. In modern neuroscience, our working definition of perception is captured well by the Oxford English Dictionary: “The action of the mind by which it refers its sensations to an external object as their cause.” This definition has roots in the corpus of eighteenth-century philosophy–beginning with George Berkeley and David Hume–was expanded upon by later British associationists, and became a foundation of both experimental psychology and modern neuroscience.
There are two essential features of this definition, the first being the distinction between perception and sensation. Sensation is the immediate neurobiological consequence of stimulating sensory transducers1 such as photoreceptors, mechanoreceptors, and chemoreceptors. Sensory events are ubiquitous and can affect behavior directly–the spinal reflex of pulling your hand back from a hot surface is one simple example–but they are fleeting, discontinuous, and lacking semantic content. Perception enriches sensation by reference to other knowledge or experience. . . .
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- 1Sensory transducers are specialized cellular mechanisms that enable various forms of environmental energy (mechanical, chemical, radiant) to be converted into energy that is communicated within and between neurons. Transduced energy leads to specific sensations. Photoreceptors, for example, transduce energy in the form of light into neuronal energy, which leads to visual sensation