Last LectureLast Lecture

History of disconnection History of disconnection syndromessyndromes

The structure of the The structure of the corpus callosumcorpus callosum

Independent minds in the Independent minds in the same head?same head?

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Redundant Mixed

ControlsJ.W.

REMINDERREMINDER

THIS WEEK’S THIS WEEK’S

DISCUSSION SECTION DISCUSSION SECTION

READING AT READING AT EXCELEXCEL

This LectureThis Lecture

Hemispheric differences in Hemispheric differences in the Bisected Brainthe Bisected Brain

Functions of the corpus Functions of the corpus callosumcallosum

Hemispheric Asymmetries in Hemispheric Asymmetries in the Normal Brainthe Normal Brain Methods and theoriesMethods and theories

The corpus callosum and The corpus callosum and resource allocationresource allocation

Right Hemisphere Spatial Abilities RevealedRight Hemisphere Spatial Abilities Revealed

PREOPERATIVE

POSTOPERATIVE

RIGHT HANDLEFT HAND

RH superiority onBlock design

RH superiority onDrawing tasks

Language Language

LH Dominance:LH Dominance:Note: Language abilities vary Note: Language abilities vary

greatly among patientsgreatly among patients

Speech production Speech production single word by RH in some single word by RH in some

patientspatients

speech/reading speech/reading comprehension: comprehension: RH vocab ~ age 10 RH vocab ~ age 10

grammar comprehension: grammar comprehension: RH fails at more difficult RH fails at more difficult

grammatical constructions.grammatical constructions.

Active: The horse kicked the cow.Passive: The cow was kicked by the horse.

Hemispheric Differences in Matching Letters and LocationsHemispheric Differences in Matching Letters and Locations

Compare verbal vs. spatial matching by LH and RHCompare verbal vs. spatial matching by LH and RH Task: Present target items (letters or location) followed by Task: Present target items (letters or location) followed by

a probea probe Does probe match a target item?Does probe match a target item?

(Reuter-Lorenz & Miller 1998)(Reuter-Lorenz & Miller 1998)

Hemispheric Asymmetries on Basic Visual TasksHemispheric Asymmetries on Basic Visual Tasks

Verbal Spatial

percentcorrect

LH

RH

Corpus Callosum permits access to specialized processingCorpus Callosum permits access to specialized processing

LH dominanceLH dominance Language (comprehension/ production, reading)Language (comprehension/ production, reading) fine motor skills (writing, coordinated fine motor skills (writing, coordinated

movements/gestures)movements/gestures)

RH dominanceRH dominance Visuospatial/constructive abilitiesVisuospatial/constructive abilities

manipulo-spatial tasksmanipulo-spatial tasks

Face processingFace processing Emotion perceptionEmotion perception

Why did previous studies miss these disconnection effects?Why did previous studies miss these disconnection effects?

Sperry’s lab ensured lateralized inputSperry’s lab ensured lateralized input Sperry’s patients had complete callosal Sperry’s patients had complete callosal

section**section** This success inspired study of laterality in This success inspired study of laterality in

the normal brain.the normal brain.

Hemispheric Differences

in the Normal Brain

Hemispheric Differences

in the Normal Brain

Major DichotomiesMajor Dichotomies

LEFTLEFT VERBAL VERBAL ANALYTIC ANALYTIC SEQUENTIAL SEQUENTIAL LOCALLOCAL RATIONAL RATIONAL

RIGHT RIGHT NONVERBAL/SPATIAL NONVERBAL/SPATIAL HOLISTICHOLISTIC PARALLELPARALLEL GLOBALGLOBAL IMPRESSIONISTIC/ IMPRESSIONISTIC/

EMOTIVEEMOTIVE

Examples of Global/LocalExamples of Global/Local

Behavioral Asymmetries in Normal SubjectsBehavioral Asymmetries in Normal Subjects

Visual Laterality MethodVisual Laterality Method

Tachistoscopic presentation (less than 200 msec)Tachistoscopic presentation (less than 200 msec) lateralized stimulus exposurelateralized stimulus exposure Compare performance for left visual field (LVF) vs. Compare performance for left visual field (LVF) vs.

RVF presentations.RVF presentations. Dependent variables: reaction time, accuracyDependent variables: reaction time, accuracy

Visual Field AsymmetriesVisual Field Asymmetries

Task: Does display Task: Does display contain H or L ?contain H or L ?

Independent variables:Independent variables:

1) target level: local or 1) target level: local or global.global.

2) visual hemifield: LVF 2) visual hemifield: LVF or RVFor RVF

Dependent variable: RTDependent variable: RT 460

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Local Global

LVF

RVF

XX XXXX

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LL

LL L

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LSample displays

Split versus Together ...Split versus Together ...

Why do Why do performance performance asymmetries asymmetries

emerge emerge with an with an

intact intact corpus corpus

callosum?callosum?

Info is processed by the Info is processed by the hemisphere hemisphere specialized for the specialized for the material or task.material or task. input transferred to input transferred to

specialized hemispherespecialized hemisphere VF Differences reflect VF Differences reflect

interhemispheric transfer interhemispheric transfer timetime and and info degradationinfo degradation..

Callosal relay modelCallosal relay modelCallosal relay modelCallosal relay model

Direct access modelDirect access modelDirect access modelDirect access model

The hemisphere that The hemisphere that gets the stimulus gets the stimulus (directly) processes it(directly) processes it

VF differences reflect VF differences reflect relative ability/efficiency of relative ability/efficiency of hemispheres.hemispheres.

Both hemispheres do Both hemispheres do everything more or less welleverything more or less well

Attention is directed Attention is directed contralateral to the more contralateral to the more active hemisphere.active hemisphere.

Engaging LH verbal processes Engaging LH verbal processes biases attention rightward --> biases attention rightward --> RVFadvantageRVFadvantage

Engaging RH spatial/nonverbal Engaging RH spatial/nonverbal processes biases attention processes biases attention leftward--> LVF advantageleftward--> LVF advantage

Activation-orienting model Activation-orienting model (Kinsbourne)(Kinsbourne)Activation-orienting model Activation-orienting model (Kinsbourne)(Kinsbourne)

bog + bog

bogbog bogbog