NEUR2020 Lecture 5: Understanding Attention

• NEUR2020 Lecture 5 covers the topic of attention
• Attention includes properties, selectivity, early vs late selection, distractor interference, inattention blindness and neglect/extinction

Concept of Attention

• Attention involves taking possession of the mind, in clear and vivid form, of one of several possible objects or trains of thought
• Focalization and concentration of consciousness are key aspects of attention
• Attention implies withdrawal from some things to effectively deal with others
• Attention involves processes that enable a person to recruit resources for processing selected aspects of incoming sensory information more fully than non-selected aspects
• Attention includes allocating resources to relevant aspects of the environment, engaging, shifting, and re-engaging, while inhibiting irrelevant information
• Attention is not the same as alertness and arousal, which are functions of the reticular activating system in the brainstem
• Low alertness results in poor extraction of information from the environment
• The nervous system must be receptive to stimulation for attention to function
• Diffuse connections to most regions of the cortex
• Damage to these areas can result in coma, stupor, and chronic vegetative state

Properties of Attention

• Capacity refers to the amount of perceptual resources available for a task or process, and it varies with the task and individual
• Selectivity refers to how fixed perceptual resources can be allocated in a flexible way to different subsets of information
• Attention is selective in terms of what information gets processed

The Royal Exchange Effect

• Attention can focus on one source of information among many
• Attention can be redirected, and information is selected in specific ways
• A large amount of information can be filtered out
• Individuals can follow a sensible message, even when it switched ears
• One's own name is "special" information (salience)
• Some information can intrude under certain circumstances

Early vs. Late Selection

• The timing of the "gate" or filter determines when selection occurs
• Early selection suggests filtering occurs before extensive processing
• Late selection suggests filtering occurs after extensive processing
• Timing of the filter is task-dependent and can be early or late depending on task demands and instructions
• Distractor interference is an example of how "extra" or irrelevant information affects processing

Distractor Interference

• Distractor interference slows reaction times to targets and reduces accuracy
• Changes to trajectories in movements to targets
• Irrelevant information slows responses to the target, increasing response time
• The interference is particularly strong when the opposite response needs to be inhibited

Visual Spatial Attention

• Overt attention involves making eye movements
• Covert attention involves moving your attention without moving your eyes
• Timing of filter is task-dependent
• Can be early or late
• Example: Searching 'scenes' bit by bit

Selectivity

• Deals with busy scenes using several attention mechanisms
• Includes overt eye movements
• Includes shifting attention
• Top-down/bottom-up influences
• The overt and covert monitoring have consequences for neuronal activation
• The extent of neuronal activation differs, depending on the type of stimulus

Shifting Attention

• Involves three components:
  • Disengagement: attention is normally focused on a target and must first disengage to move.
  • Movement/Shifting: disengaged attention is free to move and must be directed to the new target.
  • Engagement: attention must be re-engaged on the new object after reaching the target.
• Neural substrates of shifting attention:
  • Damage to the parietal lobe (especially the right) results in loss of disengagement.
  • Damage to the superior colliculus impedes eye movement and compromises movement.
  • Damage to regions in the thalamus compromises engagement
• Shifting attention requires coordinated action from three separate brain areas

Posner Cuing Paradigm

• Examines the consequences of attending to specific locations in space
• Valid trials involve cues that correctly predict the location of a target
• Invalid trials involve cues that incorrectly predict the location of a target
• Neutral trials involve non predictive cues
• Enhanced processing in the attended area comes at a cost to the unattended area
• Observers covertly attend to either the left or right location as cued by the experiment
• Valid cues are associated with enhanced P1 and N1 ERPs relative to invalid cues, indicating enhanced processing of the validly cued target

Voluntary & Involuntary Shifts

• "Endogenous cues" are symbolic cues (central arrow) that require attention to be voluntarily pushed from a central cue to the cued location
• "Exogenous cues" draw attention to the location of the cue, are usually a flash or movement, and cannot be ignored involuntarily
• Top-down/bottom-up processes
• Interface between external environments and internal states (goals)
• Always an interaction between the two states

Visual Spatial Attention

• Ability to perceive letters within covertly attended region
• Attention is like a spotlight with a focus, fringe, and margin
• Illuminating the object in its focus region
• Distractor interference data support the spotlight analogy

Zoom-lens of Visual Attention

• Attention is likened to a zoom lens, a camera with variable spatial scope
• A wider field results in coarser detail
• A narrow field results in fine resolution
• Local/global tasks support the zoom lens metaphor

Divided VS Focused Attention

• Distributed attention involves parallel processing/visual 'pop-out'
• Visual processing occurs simultaneously over the whole visual field
• Focused attention involves serial processing, selecting a bit of the environment at a time
• Visual processing is a series of attentional "fixations" each covering a different region

Parallel Search

• Relies on single visual feature differences
• Perform the task, is the target present or absent?
• Note the number of distractors
• Serial Search involves more than one feature differences

Inattentional Blindness

• A state where features that pop out when searched for are not perceived under conditions of inattention
• Research shows that people rarely see what they are looking at unless attention is directed to it
• Demonstrates that attention helps avoid sensory overload
• Demonstrates the capacity limitations of attention
• Individuals pick up what they are "set" to pick up
• Instructions are crucial, as they are the interface between the environment and the goals/expectations

Change Blindness

• A (small) change in visual display is not detected
• Disorders of attention involve neglect and extinction

Neglect & Extinction

• Neglect and extinction arise from the posterior parietal lobe's role in disengaging attention, the superior colliculus's role in moving attention, and the pulvinar's role in enhancing attention.
• Patients do not acknowledge stimuli on the left
• Includes sensory, spatial, motor and attentional factors
• Multimodal
• Distinguish from visual field deficits such as hemianopia and quadrantanopia
• Occurs after damage to one side of the brain, usually the right hemisphere
• Right parietal lobe is damaged
• Patients behave as if the affected side of space has ceased to exist
• Characterized by:
  • Ignoring food on one side of their plate
  • Failing to shave/make up one side of the face.
  • Bumping into objects on one side.
  • Fail to read text form one side of the page
• Most common/severe after damage to the parietal lobe
• Parietal lobe damage causes severe attention deficits
• Damage to angular and parahippocampal gyri are also critical
• Frequently co-occurs with hemiplegia and visual deficits
• Commonly impaired in left-sided neglect are:
  • Disengagement from right-sided stimuli
  • Shifting to left-sided stimuli
  • Engagement with left-sided stimuli
  • Capacity Limits
  • Distributed Attention
• Also has effect on Internal representations & Unconscious processing

Visual Extinction

• Preserved detection of single contralesional left-sided stimuli
• Characterized by:
  • Better detection of left events when able to ignore right events.
  • Better detection of left events when they are presented better than right events
  • Often the next stage in the evolution / resolution after neglect
• Failure to report the more contralesional of two simultaneous, bilateral stimuli, with normal reporting on either side.
• Right hemisphere dominance for the distribution of attention in peripersonal hemispace
• Attention vector deployed mostly from the right hemisphere to left hemispace