Post on 24-Feb-2016
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Sensory systems basics
Sensing the external world
Sensory transduction
Transforming external physical forces/energy into electrical impulses that are mediated by neural spikes.
Neural “encoding”
Encoding stimulus amplitude
Responses of a photoreceptor to light at different intensities.
Information is encoded by both amplitude and length of the response.
Encoding stimulus location
The location of the stimulus in space is encoded by the identity of responding receptors.
Encoding stimulus location
Encoding stimulus location
Distribution of receptors
Different organs (or organ locations) contain different amounts and types of receptors.
Distribution of receptors
Distribution of receptors
Sensory pathways
Sensory pathways
Central nervous system
Vision
Topographical organization
Photoreceptors responding to the left visual field innervate the right LGN.
Topographical organization
Both the thalamus and early visual cortices contain retinotopic maps of visual space.
Occular dominance
Information from the left and right eyes remains segregated in the LGN.
Occular dominance
Also in primary visual cortex.
Cortical magnification
Cortical magnification
Acuity
Columnar organization
Selectivity to stimulus attributes
Spatial receptive fieldsContrastLuminanceSpatial frequencyOrientationsColorsMovement direction and/or speedTexturesShapes
Receptive field
Many visual neurons have excitatory and inhibitory parts to their receptive field.
Examples of retinal and LGN cells.
Retino-topic mapping
Luminance & Contrast
Orientation selectivity
Orientation selectivity in primary visual cortex.
Orientation selectivity
Pinwheels(only in primates)
Hierarchy and integration
LGN
V1 Neurons
Invariance and Gain
Contrast invariant orientation tuning.
Response gain
Spatial frequency
Spatial frequency
Cont
rast
Integration over space.
Movement direction
Integration over time.
Overlapping representations of orientations and directions
Hierarchy and integration
Low, mid, and high level vision
Functional specialization
Face selectivity
Invariance (abstractness)
Is this vision or abstract memory?
Audition
Choclear output
Selectivity to specific frequencies.Louder stimuli generate less selective responses.
Sound localization
Interaural time differences (ITD)
Sound localization
Brainstem areas:Olivary nucleiColliculus
Sound localization
Auditory brainstem response
Tonotopy
But no spatial encoding…
Language system
Lateralized !
Language structure
Phonetics: ‘ba’, ‘da’, ‘pa’
Words, Grammar, Intonation
How is all this encoded?
Language hierarchy?
Invariance across hearing and reading?
Specific white matter tracts
Aphasias
Somatosensation
Parallel pathways
Parallel pathways
Each pathway conveys a different “part” of the information.
Redundancy…
Topographic organization
Homonculus
Secondary Somatosensory areas
How does all this develop?
Genetics
Experience
Flexibility/Plasticity