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Chapter3.2_Theanatomyofthebrainandprimaryvisualpathway-revisedfor3rdedition.ppt

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Chapter 3.2:
The anatomy of the brain and primary visual pathway

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Overview

Explain the significance of the “turn to the brain” in cognitive science

Explain Mishkin and Ungerleider’s hypothesis that there are two distinct visual systems

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Classical CogSci and the brain

Neuroscience did not feature prominently in the early days of cognitive science

• Widespread view that neural details are “merely implementational”

• Top-down approach (e.g. Marr)

• Functional analysis of cognitive abilities

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

The turn to the brain

1. Development of new technologies for studying cognition in the brain (as opposed to neuroanatomy)

• single-neuron recording

• PET and fMRI

2. Neurally-inspired models of information-processing

• connectionism

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

2 visual systems hypothesis

Originally proposed by Mishkin and Ungerleider

Draws on both functional and anatomical data

• functional data derived from lesion studies on the brain

Illustrates a bottom-up approach to studying cognition - and illustrates how “boxology” can connect up with the brain

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Primary visual pathway

• Contralateral organization (relative to visual field)

• Projects to primary visual cortex (a.k.a striate cortex/V1)

• What happens next?

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

2 visual pathways

Dorsal – carries information relevant to object location

(the “where” pathway)

Ventral – carries information relevant to object identification (the “what” pathway)

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Two different levels of analysis

Functional analysis

• identifying two different and dissociable types of visual information-processing

Anatomical analysis

• identifying two different anatomical pathways within the brain

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Preliminary evidence

• Brain-damaged patients – Damage to parietal and temporal lobes produces different types of impairment

parietal = problems acting on and locating objects

e.g. visuospatial neglect

temporal = problems identifying objects

e.g. agnosia

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Visuospatial neglect

• Both images show patients with right parietal damage

• Lower image shows eye-tracking

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Note that this is not discussed in the text. The images are from Husain, M., and Rorden, C. (2003). Non-spatially lateralized mechanisms in hemispatial neglect. Nature Reviews Neuroscience, 4, 26–36. The original studies the images are based off of come from Eglin, M., Robertson, L. C. & Knight, R. T (1989). Visual search performance in the neglect syndrome. Journal of Cognitive Neuroscience. 1, 372–385.

The images come

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Visual agnosias

• Associated with damage to the temporal and/or occipital lobe

• Basic features of vision are preserved (acuity, brightness discrimination, color vision etc.)

• Impairment in copying, drawing or naming objects

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

A certain type of agnosia will lead people to report only one or two of the objects shown in the picture. This form of agnosia is caused by damage to the dorsal stream.

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

General questions

How do we move from functional analysis to anatomical analysis?

• dangerous to infer function of neural areas directly from what happens when they are damaged

• is the impairment due to the damaged area? Or to the fact that information fails to reach another area

How do we get a model of an information-processing pathway?

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Cross-lesion disconnection experiments - background

• The cerebrum is divided into two hemispheres

• Major cortical areas are duplicated in each hemisphere

• Hemispheres can communicate through the corpus callosum in order to compensate for damage in one hemisphere

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Basic idea

• Remove one of the stations on a postulated pathway from one hemisphere

• The corresponding area in the other hemisphere will typically compensate

• Subsequent transection of the corpus callosum allows experimenters to identify whether the station lies on the pathway

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Ventral lessions

• crossed striate and inferior temporal lesions

• pathways preserved via corpus callosum

• but performance on pattern discrimination tasks abolished by transection of corpus callosum

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Dorsal lesion study

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Implication: disorder of unilateral spatial neglect

Patients typically “neglect” one half of the space around them
Typically follows damage to the posterior parietal cortex in one hemisphere and the neglected region is contralateral to the damage
Possible explanation: the posterior parietal cortex in each hemisphere is specialized for processing information about the opposite region of space

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Two versions of the hypothesis

Mishkin and Ungerleider:

Dorsal = location (“Where?”

Ventral = identification (“What?”)

Milner and Goodale

Dorsal = vision for action

Ventral = vision for identification

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Evidence from monkeys

Bilateral temporal lobe lesions result in severe impairments of recognition, but basic visuomotor skills are preserved

• object avoidance

• judging distances when jumping

Electrophysiological studies revealed neurons in parietal cortex sensitive to different types of reaching movement

– neuronal enhancement

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Evidence from brain-damaged patients

Double dissociation between visual recognition and visuomotor control

Balint’s syndrome – visuomotor deficit (optic ataxia) with recognitional impairment

Visual form agnosia - impaired recognition with preserved visuomotor skills

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Visual form agnosia (DF)

• Damage to ventral stream

• Preserved ability to calibrate grip size

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Note that this is not discussed in the text.

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Contrast with optic ataxia

• Optic ataxia = deficit in reaching not explicable by motor, somatosensory or visual field deficits

• Grasp lines (i.e. where thumb and index finger make contact with shape

• No significant difference between DF and control

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Note that this is not discussed in the text.

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Evidence from normal subjects

• Ebbinhaus illusion is very robust for normal subjects

• But if asked to reach subjects typically make an accurate-sized grasp response

• Dissociation between action and conscious visual awareness?

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Note that this is not discussed in the text. These are known as Titchener circles, and are used in a wide variety of studies on the two visual streams.

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020

Important points

• Reveals interdisciplinary nature of cognitive science

• lesion experiments on monkeys

• single neuron neurophysiology

• cognitive psychology experiments on brain- damaged and normal subjects

• Reveals a basic challenge in cognitive science – integrating functional analysis and anatomical analysis

• Shows that this integration need not be top-down

Cognitive Science  José Luis Bermúdez / Cambridge University Press 2020