Physiological Perception Filters

5211 WordsJun 8, 200421 Pages
"When a person glimpses the face of a famous actor, sniffs a favourite food or hears the voice of a friend, recognition is instant. Within a fraction of a second after the eyes, nose, ears, tongue or skin is stimulated, one knows the object is familiar and whether it is desirable or dangerous. How does such recognition, which psychologists call preattentive perception, happen so accurately and quickly, even when the stimuli are complex and the context in which they arise varies? Much is known about the way the cerebral cortex, the outer rind of the brain, initially analyses sensory messages. Yet investigations are only now beginning to suggest how the brain moves beyond the mere extraction of features-how it combines sensory messages with…show more content…
"PHASE PORTRAITS" made from electroencephalograms (EEGs) generated by a computer model of the brain reflect the overall activity of the olfactory system at rest (above) and during perception of a familiar scent (right). Resemblance of the portraits to irregularly shaped, but still structured, coils of wire reveals that brain activity in both conditions is chaotic: complex but having some underlying order. The more circular shape of the right-hand image, together with its greater segregation of colour, indicates that olfactory EEGs are more ordered-more nearly periodic-during perception than during rest. Also, how does the brain achieve what is called generalization-over- equivalent receptors? Because of turbulence in nasal airflow, only a few of the many receptors that are sensitive to an odorant are excited during a sniff, and the selection varies unpredictably from one sniff to the next. How does the brain recognize that signals from different collections of receptors all refer to the same stimulus? Our investigations begin to suggest answers to both problems. Many of our insights were derived from intensive studies of the olfactory bulb. Those experiments show clearly that every neuron in the bulb participates in generating each olfactory perception. In other words, the salient information about the stimulus is carried in some

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