Stimulus Modality
Labelled line theory
Premises:
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individual receptors transduce information about a single type of stimulus
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individual primary afferent fibres carry information from a single type of receptor
Conclusions:
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pathways carrying sensory information centrally are therefore also specific, forming a "labelled line" regarding a particular stimulus
Evidence:
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the brain associates a specific modality with a signal coming from a specific receptor (e.g., "light" is detected by the photoreceptors, even if the stimulus is pressure on the eye)
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in the cortex , perception is localized by modality, resulting in specific cortical areas for each sensation
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within each sensory area, sensations are "mapped" in ways that maintain an orderly representation of the stimulus (e.g. the humunculus that is maintained within somatosensory cortex; tonotopic maps that are formed in the auditory system; topographic maps in the visual cortex)
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Cortical sensory areas S&G Figure 10.4 |
Humunculus |
Pattern theory
Premises:
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some sensory systems (esp. taste and olfaction) integrate information across multiple primary afferents
- a few types of afferent endings are multimodal (more than one sensation can be evoked by their activation)
Conclusions:
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a single ascending pathway can convey information regarding sensory modalities by altering the temporal pattern of action potentials
- under this theory, it is the pattern of activation of neural networks that forms the basis of perception
Evidence:
- examples are found in the olfactory system, and in the colour perception
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Olfactory receptor codes |