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Sensation and sensory processing
PS 1003
PS1003Introduction to Biological Psychology
Organisation of sensory systemsPS 1003
Peripheral sensory receptors
Sensory thalamus
Primary sensory cortex
Unimodal association cortex
Multimodal association cortex
[ Spinal cord ]
PS 1003
The senses
Touch Sight Hearing Taste Smell Sense
Skin Eye Ear Tongue Nose Organ
Spinal cord
Optic II Vestibulo-cochlear
VIII
Facial VII Glossoph.
IXVagus X
Olfactory I
Nerve
Somato-sensory Visual Auditory
Somato-sensory Olfactory Cortex
PS 1003
Gustatory (taste) perception
Taste• Salty, sour, sweet, bitter, umani
Taste map? – different areas of the tongue sensitive to different tastes• Myth!
All tastes are perceived over the full sensory area of the tongue.
PS 1003
Gustatory pathway
Taste buds
Taste receptor cells Touch, pain receptors
Brainstem
Thalamus
Taste centres of somatosensory cortex Somatosensory cortex
Facial (VII), Glosso-pharangeal (IX), Vagus (X)
PS 1003
Gustatory pathway (2)
PS 1003
Olfactory perception
Olfactory receptors in olfactory epithelium of nose
Olfactory nerve (II)
Olfactory bulb
Olfactory cortex
Hypothalamus
PS 1003
Hierarchical processing
Sensory processing is organised in a hierarchical manner• Different areas for specific function• Similar in all sensory modalities• Visual system is a good example
STS Superior temporal sulcusTEO Inferior temporal cortex TE Inferior temporal cortex
Eye
Superiorcolliculus
Dorsal LGN V1 V2
V3
V4
V3A STS
TEO
V5
TE
Posteriorparietal Cx
Striate Cortex
ExtrastriateCortex
Inferior TemporalCortex
Dorsal stream
Ventral stream
PS 1003
Area V1
Primary visual cortex (striate cortex)• First level of input to the visual cortex• Cells in V1 respond differently to different aspects of the visual
signal (e.g. orientation, size, colour)• Involved in characterisation not analysis
o Sends independent outputs to several other areas• Damage to V1 leads to total or partial blindness depending on
the extent of the damage
Blindsight• Subjects are blind due to damage to area V1• But can “guess” direction of travel of a moving object or colour• Movement and colour not analysed in V1• Information can bi-pass V1 to reach visual cortex
PS 1003
Area V3
First stage of building of object form
Code for component aspects of the object• e.g. edges, orientation, spatial frequency (= size)
Feeds information to V4, V5, TEO, TE, STS and to parietal cortex
PS 1003
Area V4
Colour recognition• Individual neurones in V4 respond to a variety of wavelengths
PET studies show• Activation in V4 to coloured patterns, but not to greyscale
Achromatopsia• damage to V4 causes an inability to perceive colour• patients “see the world in black and white”• also an inability to imagine or remember colour
PS 1003
Temporal lobe (TEO, TE, STS)
Highest level of processing of visual information
Recognition of objects dependent on their form• Independent of scale (distance), orientation, illumination.
Visual memory
Face recognition• Features of a face (subject specific)• Expressions on a face (independent of subject)• Gaze direction
Associative visual agnosia• Normal visual acuity, but cannot name what they see
Aperceptive visual agnosia Normal visual acuity, but cannot recognise objects visually by shape
PS 1003
Area V5
Movement perception• Movement is perceived in area V5
PET studies show• Activation in V5 to moving patterns, but not to stationary ones
Middle aged woman, who suffered a stroke causing bilateral damage to the area V5
• became unable to perceive continuous motion• rather saw only separate successive positions• unaffected in colour, perception, object recognition, etc• able to judge movement of tactile or auditory stimuli
PS 1003
Posterior parietal cortex
Analysis of spatial location of visual cues• Building of an image of multiple objects within space• Coordinates visually directed movement (reaching)• Receives information from all areas of the visual cortex
Balint’s syndrome (damage to PPCx) • Optic ataxia • deficit in reaching for objects (misdirected movement)
• Ocular apraxia• deficit in visual scanning• difficulty in fixating on an object• unable to perceive the location of an object in space
• No difficulty in overall perception or object recognition
PS 1003
V1
V2
V3
V4
V3A STS
TEO
V5
TE
PPCx
Summary of hierarchical processing
Primary visual input
Building object form
Colour recognitionHigher level processingof object form
Ventral stream
Movement recognition
Spatial analysis ofvisual information
Dorsal stream
PS 1003
Primary Auditory Pathway
Cochlea
Cochlear Nucleus
Superior Olivary Nucleus
Inferior Colliculus
Medial Geniculate Nucleus
Auditory Cortex
Ear
Pons
Thalamus
Cortex
Vestibulo-cochlear nerve(CN VIII)
PS 1003
Auditory processing
Cochlea
Cochlear Nucleus
Superior Olivary Nucleus
Inferior Colliculus
Medial Geniculate Nucleus
Auditory Cortex
Cochlea
Cochlear Nucleus
Superior Olivary Nucleus
Inferior Colliculus
Medial Geniculate Nucleus
Auditory Cortex
Bin
aura
l
PS 1003
Auditory processing (2)
PS 1003
Cochlea
Sound waves converted into vibration in basilar membrane
Hair cells in organ of Corti transduce movement of basilar membrane into electrical signal• High frequency sound transduced at base• Low frequency sound transduced at apex
Information is transmitted along vestibulo-cochlear nerve20kHz 5kHz
1kHz
500Hz
20Hz
Apex
Base
PS 1003
Auditory processing
Originally thought to be in auditory cortex• Intermediate stages only ‘stepping stones’
BUT • Auditory discrimination possible in the absence of auditory
cortex (e.g. direction, pitch, tunes)
THEREFORE• Initial processing occurs in pons and thalamus• Auditory cortex analyses complex aspects of sound
o Dorsal stream (parietal lobe) – spatial analysiso Ventral stream (temporal lobe) – component analysis
i.e. Where and What (similar to vision)
PS 1003
Localisation of sound
Dependent on different characteristics of a sound arriving at each ear
Intensity difference• Difference in intensity of the sound
between the two ears
Latency• Phase shift between the two ears
o Due to slightly different distance to reach each ear
Duplex theory – sound location depends on a combination of intensity
and latency
PS 1003
The vestibular organ
Semicircular canals:• Detect head rotation and tilt around three axes
Head movement
Movement of endolymph
Displacement of capula
Stimulation of hair cells
Activation of CN VIII
Informationtransmitted to brain
PS 1003
Vestibular pathways
Vestibulocochlear nerve (CN VIII)
Vestibular nuclei in the brainstem Cerebellum
Motor thalamus
Cortex
Vestibulo-ocularreflex
Balancereflex
PS 1003
The vestibulo-ocular reflex (VOR)
VOR• Works with eyes closed
• Not dependent on visual input• Dependent on vestibular input
PS 1003
The balance reflex
Vestibular organ
Vestibular nucleiMedial Lateral
Neck muscles Peripheral muscles
Head orientation Postural musclesBalance
Inner ear
Brainstem