© 2000 Charly Herscovici, Brussels / Artists Rights Society (ARS), New York Reproduction, including downloading of Magritte works is prohibited by copyright laws and international conventions without the express written permission of Artists Rights Society (ARS), New York. Interactions between Dorsal and Ventral Pathways Objects exist in space

Vision: Outline Eye –Color vision –Receptive Field –Edge Detection Visual Path –thalamus (LGN) –primary visual cortex Orientation sensitive; Spatial frequency –Ventral Pathways Area MT (motion), Object Recognition, Area V4 (color) synesthesia –Dorsal Pathway Spatial Attention Hemispatial Neglect

Ventral Dorsal Visual Cortex Dorsal Dorsal Pathway

RetinaLGNV1 V4 Parietal Cortex Inferotemporal Cortex (Relay Station) (Detects Edges) (Color, Form) (Shape, Object Recognition) (Location, How to reach or act upon)

- Line-bisection task - Extinction hemispatial neglect syndrome - Drawing - Line cancellation

Self-portrait by Anton Raderscheidt, at different stages of his rehabilitation from neglect syndrome Tom Greenshield’s drawings pre- and post-stroke BeforeAfter

QDoes the disordered attentional mechanisms associated with visuospatial neglect alter patient’s representation of space ? normal neglect

move your eyes (& your attention) you ‘see’ the change -- you are ‘perceptually aware’-- at the attended location You are unaware at the unattended locations. Try to find the difference between these two pictures Attention contributes to object perceptual awareness

Looking for a target in neglect

‘look for blue horizontal line”

Inattentional blindness (here)here Count how many passes the ‘white’ team makes Continuity errors (Terminator 2)

time Mike Posner ++ Spatial cueing task (aka covert orienting task)

+++ invalid 20% Valid 80% 1 sec 0.5 sec Mike Posner Reaction time (ms)

Voluntary System of Atention (dorsal). <- Voluntary Attention <- 1 sec delay * Unattended stimulus is detected Automatic System of attention (ventral) Corbetta et al, nature neuroscience Bilateral IPS FEF Right TPJ

Interaction between voluntary and automatic system IPS left IPS right Right TPJ balance Modulated by expectations Warning by Unexpected stimulus

Arteria Cerebral Arterial Media y area de lesion por obstruccion

Resonancia Magnetica NormalAtrofiastroke

Sindrome de Negligencia Espacial Anatomia hemisferio derecho, plano horizontal Union temporo- parietal derecha, (vista lateral) A veces la lesion se extiende al lobulo frontal

Interaccion entre los dos sistemas despues de stroke SPI izq. SPI der. UTP der DESbalance Alerta por Estimulo Inesperado Muy disminuida LESION Sintomas:?? Effectos en tarea de flecha y asterisco

El sistema de atencion ejerce un efecto modulatorio en los procesos mentales (“vemos claramente”, Williams James) -Por ej. atencion a movimiento activa area MT Efecto

time Memory/Attention Task (fMRI / ERP)

Regions of Interest Right Visual Field Left Visual Field

Stim 1Stim 2 Single-Unit Recording “spike” = single neuron’s action potential (Macaque monkey) Signal Analysis Receptive Field

Attention Effects in Single Neuron Responses 100 msec Frequency of spikes Attended bar Unattended bar ( Robert Desimone, NIH)

Atypical Alzheimer ’ s Disease Also known as Posterior Cortical Atrophy (PCA) Similar pathology to AD, but: –Localized in Parietal cortex Some clinical similarities to: –Right parietal stroke (hemispatial neglect) –Bi-parietal stroke (Balint ’ s syndrome) Hemispatial neglect

Atypical AD Patient 68 y-old male Local bias ccc c c c c c c c Impaired drawing bilateral posterior parieto-temporal atrophy, most pronounced in right hemisphere Left visual field extinction

‘Perception’ Tasks: Can the patient ‘discriminate’ two simultaneous shapes? (circle, square) Can the patient ‘see’ two simultaneous shapes?

Buffer Shape Discrimination Task: same / different Display: Sequential (duration tailored for each subject) T 1 Ts 1 & 2 Mask Interval T 2 Simultaneous Buffer Mask Buffer Mask 88% correct 50% correct

Count Task: one / two Follow-up study - Single Figure Accuracy 61%46% Conclusion: - R.D. cannot ‘see’ two objects Control study: Single complex figure 90% accuracy

steps in the cueing task Arrow onset. Voluntarily attend to that side Target appears in opposite side. Detect unexpected location. Disengage attention from initial location. Redirect attention to the other side

Funcion: Atencion Espacial Anatomia: - Dorsal: Surco Parietal Inferior (SPI); Frontal Eye Field - ambos hemisferios Caracteristicas: - representacion espacial - se activa al preparar movimientos oculares o manuales El Sistema Voluntario de Atención

Funcion: Reorientacion & Alerta Anatomia: - Ventral: Union temporo-Parietal (UTP); Giro frontal inferior - hemisferio derecho Caracteristicas: - sin representacion espacial - es activado por: - estimulos inesperados - estimulos dolorosos - estimulo infrecuente El Sistema automatico de atencion