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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 fields
Contrast
Luminance
Spatial frequency
Orientations
Colors
Movement direction and/or speed
Textures
Shapes
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
Contrast
Spatial frequency
Integration
over space.
Spatial frequency
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 nuclei
Colliculus
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