Visual Attention: Outline Levels of analysis 1.Subjective: perception of unattended things 2.Functional: tasks to study components of attention 3.Neurological: hemi-spatial neglect

“Everyone knows what attention is… William James, Subjective level: What is visual attention?... It is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects” if you don’t pay attention to it, you don’t see* it * perceptual awareness Go mist Change blindness

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

Which are the cognitive processes of attention? 2. Functional level: How does attention work? Tasks to study the components of attention

Look for Waldo Visual Search Task Combination of features (e.g., lines that are red AND horizontal) arranged in a certain way (e.g. blue below red) Finding Waldo requires that we combine these features (redness, horizontal line, location) Such ‘binding’ of features requires focused attention, and is called ‘conjunction search’

Visual Search Task: Conjunction Search ‘Find the blue square’ (a waldo-like search)

Conjunction Search

“Conjunction Search” # of items in display Reaction Time (speed)

Look for Whitey Feature Search the target is defined by a single feature (the white item)

Feature Search the target is defined by a single feature (e.g., the blue item)

Doesn’t require attention. Parallel processing of simple visual features (e.g., color). Feature Search

Typical Results for “Feature Search” # of items in display Reaction Time (msec)

Subjective level: If you don’t attend to it, you are unaware of it Summary so far Functional level: - Focused Attention ‘binds’ features into objects - The binding is spatially coded (space as the anchor to other features) Prediction: - If your focused attention gets ‘stuck’ in one location, you will neglect (i.e, be unaware of) objects in other parts of the visual field

3. Neurological Deficits in Visuo-spatial attention: Hemi-spatial Neglect Right hemisphere lesion: - where temporal lobe meets with parietal lobe (temporo-parietal junction) - Sometimes in frontal lobe Middle Cerebral Artery: lesion area

drawings Hemispatial neglect Inability to attend to the left side of visual space, and thus to be aware of visual stimulus in the left visual field

Hemispatial neglect

Line-bisection task

normal neglect

Self portrait by Anton Raderscheidt, at different stages of recovery Drawings by Tom Greenshields pre- and post-stroke BeforeAfter

Visual search: Eye movements

- Extinction

Subjective level: unaware of things in the left side of visual field Hemispatial neglect: Functional level: - Focused Attention is biased toward the right side (in visual search task) - Disengagement deficit: Attention is ‘stuck’ in right side (extinction) Next steps: - Explore disengagement deficit in more detail (spatial cueing task) -Explore its neural substrates

time Spatial cueing task Mike Posner ++

+++ invalid 20% Valid 80% 1 sec 0.5 sec Mike Posner RT (ms) Spatial cueing task

Arrow Onset. Voluntary engagement of attention Target onset at opposite location (invalid trial). Detect surprising event. Disengage attention from initial site. Move it to the opposite location Spatial cueing task

Voluntary Attentional System (dorsal). <- Attention at the cued location <- 15 sec delay * Detect stimulus at unattended location Automatic attentional system (ventral) Corbetta et al, nature neuroscience

Interaction between the two systems Left IPS Right IPS. Right TPJ balance Modulated by expectations Alerted by Unexpected stimulus

Hemispatial Neglect Anatomy TPJ, horizontal cut Temporo-parietal junction (right) Lesion can extend toward frontal lobe

Interaction between the two systems post-stroke Left IPS. Right IPS Right TPJ IMBALANCE Alert by unexpected stimulus Greatly reduced LESION

Visual Attention: Outline Levels of analysis 1.Subjective: perception of unattended things 2.Functional: tasks to study components of attention 1.Visual search 2.Spatial Cueing 3.Other clinical assessments (e.g., extinction task) 3.Neurological: hemi-spatial neglect 1.Brain areas 2.Voluntary vs. Automatic system