This Lecture Unilateral Neglect Unilateral Neglect a representational deficit? a representational deficit? a deficit in orienting control? a deficit in orienting control? Single Unit response properties and selection Single Unit response properties and selection

The Definition of Unilateral (LEFT) neglect... a deficit in perceiving & responding to stimulation on the side opposite to the damaged hemisphere. a deficit in perceiving & responding to stimulation on the side opposite to the damaged hemisphere. a deficit in perceiving & responding: cannot be explained by primary sensory or motor disturbance a deficit in perceiving & responding: cannot be explained by primary sensory or motor disturbance Hemianopia and hemiparesis dissociate from neglect. Hemianopia and hemiparesis dissociate from neglect.

The Definition of Unilateral (LEFT) neglect... on the side opposite to: In what frame of reference does neglect occur? on the side opposite to: In what frame of reference does neglect occur? How do we define LEFT? How do we define LEFT? Reference Frame: system for representing locations relative to some standard Neglect affects multiple reference frames Neglect affects multiple reference frames

Reference Frames Retinotopic - left defined re visual midline Retinotopic - left defined re visual midline Hemispatial - left defined re body midline Hemispatial - left defined re body midline Gravitational - left defined re environment Gravitational - left defined re environment

Reference Frames... continued Object-centered- re the midline of the object Object-centered- re the midline of the object

Time 1 Time 2Time 3Object-based Viewer/environment -based Behrmann and Tipper TASK: Detect a signal presented in one of the shapes RESULT: Square extinguished in Upper sequence; Circle ext. in lower sequence.

The Definition of Unilateral (LEFT) neglect... damaged hemisphere: neglect is more severe and more common after RH than LH damage damaged hemisphere: neglect is more severe and more common after RH than LH damage Theories of Neglect must try to explain... Hemispheric asymmetry Hemispheric asymmetry Multiple reference frames Multiple reference frames

Imagine yourself in the Piazza del Doumo...

Clouds behind a slit... Are 2 consecutive clouds same or different? Are 2 consecutive clouds same or different? Differences can be on left or right of cloud. Differences can be on left or right of cloud. Neglect patients miss differences on left. Neglect patients miss differences on left. NOTE: All aspects of clouds are viewed from same spatial/retinal location! NOTE: All aspects of clouds are viewed from same spatial/retinal location! Neglect must affect the viewer’s image. Neglect must affect the viewer’s image. Bisiach and colleagues (1978) Full stimulus Viewed through slit

Representational Account LH represents right space / RH represents left space. LH represents right space / RH represents left space. Problem in forming a spatial representations by the damaged hemisphere. Problem in forming a spatial representations by the damaged hemisphere.

Problems with Representational View Why greater incidence of left neglect? Why greater incidence of left neglect? How to distinguish deficient representation from disordered covert scanning of intact representation? How to distinguish deficient representation from disordered covert scanning of intact representation?

Target: SOLID RED Distraction from the Right The more right-sided stimulation, the greater the left-sided neglect. The more right-sided stimulation, the greater the left-sided neglect. TARGET DETECTION TIME

Timed Search Task Stimulation on the left compensates for orienting imbalance Stimulation on the left compensates for orienting imbalance

Attentional Orienting Model Orienting: the process that "directs" attention to regions in space. Orienting: the process that "directs" attention to regions in space. Kinsbourne (1970): Kinsbourne (1970): each hemisphere directs overt & covert orienting contralaterally. each hemisphere directs overt & covert orienting contralaterally. mutual inhibitory balance mutual inhibitory balance

Neglect according to Kinsbourne’s hypothesis The hemispheres normally compete for attentional control. The hemispheres normally compete for attentional control. With damage, the bias of the intact hemisphere dominates. With damage, the bias of the intact hemisphere dominates. A release sign or positive symptom: left neglect involves “over attending” to the right. A release sign or positive symptom: left neglect involves “over attending” to the right. Bias of the LH is stronger than RH bias, in right handed individuals --> Left neglect is more prevalent. Bias of the LH is stronger than RH bias, in right handed individuals --> Left neglect is more prevalent.

Precuing Task to Measure Covert Attention Cue Valid TrialInvalid Trial

Posner Spatial Precuing Task VALIDINVALID CUE LVF TARGET Task: Press a key when target appears. Valid-Invalid RT difference reveals attentional abilities

Posner, Walker, Friedrich & Rafal (1984) Prediction for Orienting account of Left Neglect: If attention biased to the right --> STRONG disadvantage for left targets on INVALID trials. If attention biased to the right --> STRONG disadvantage for left targets on INVALID trials.Result: Prediction confirmed. Prediction confirmed. Disengage Deficit --> inability to disengage from current focus in order to direct attention leftward. Disengage Deficit --> inability to disengage from current focus in order to direct attention leftward.

Target Location: Contralesional LVF- Right Parietal Patients RVF-Left Parietal Patients VALIDINVALID Rparietal Lparietal Reaction Time Detection times for targets in Contralesional VF Norma l RESULT: Detection in “bad” field IMPAIRED by Invalid cue in good field.

Both groups impaired contralesionally. Right Par. more impaired than Left Par. ContralesionalIpsilesional V IVV Rparietal Lparietal Reaction Time

Neglect Summary A unilateral attention deficit A unilateral attention deficit LH- strong right bias; RH- possible bilateral control (can direct left or right) LH- strong right bias; RH- possible bilateral control (can direct left or right) Attention operates on representations Attention operates on representations Brain represents space in multiple frames of reference Brain represents space in multiple frames of reference Neglect can affect multiple representations Neglect can affect multiple representations Posterior parietal cortex critical for attention Posterior parietal cortex critical for attention

Attention at the neural level Enhancement and inhibition effects Identify the cells receptive field Identify the cells receptive field Determine how responsesare modified by Determine how responsesare modified by Target relevance Target relevance Attention Attention Response requirements Response requirements

Superior Colliculus Response ENHANCEMENT is specific to saccades Response ENHANCEMENT is specific to saccades Wurtz et al

Parietal Cells ENHANCEMENT from attending in order to saccade OR respond manually. ENHANCEMENT from attending in order to saccade OR respond manually. Enhancement effect is more general than in SC. Enhancement effect is more general than in SC. Wurtz et al.

V4 responses to shape modulated by spatial attention Moran & Desimone