Sensation and sensory processing

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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 ]

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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

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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.

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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)

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Gustatory pathway (2)

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Olfactory perception

Olfactory receptors in olfactory epithelium of nose

Olfactory nerve (II)

Olfactory bulb

Olfactory cortex

Hypothalamus

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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

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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

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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

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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

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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

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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

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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

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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

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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)

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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

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Auditory processing (2)

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Cochlea

Sound waves converted into vibration in basilar membraneHair 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 nerve

20kHz 5kHz

1kHz

500Hz20Hz

Apex

Base

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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)

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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

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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

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Vestibular pathways

Vestibulocochlear nerve (CN VIII)

Vestibular nuclei in the brainstem Cerebellum

Motor thalamus

Cortex

Vestibulo-ocularreflex

Balancereflex

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The vestibulo-ocular reflex (VOR)

VOR• Works with eyes closed

• Not dependent on visual input• Dependent on vestibular input

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The balance reflex

Vestibular organ

Vestibular nucleiMedial Lateral

Neck muscles Peripheral muscles

Head orientation Postural musclesBalance

Inner ear

Brainstem