Week 9 Flashcards
Arousal
Global physiological and psychological state
• Asleep or awake but degrees – light sleep or low
arousal
• Also coma, locked-in syndrome, persistent
vegetative state
• Nervous system has to be receptive to stimulation
• Low arousal - poor extraction of information from
environment
Arousal
Transection of the cat brainstem at midbrain level (between
SC and IC) – continuous sleep-like state; transect mid pons
or lower – no effect
• Damage to reticular formation in cats – loss of wakefulness
• Stimulated reticular formation – sleeping EEG immediately
transforms to awake EEG
• Structures in rostral pons and caudal midbrain for arousal
• Ascending arousal system (not reticular activating system –
RAS - since additional structures important eg locus
coeruleus)
Arousal
• Project to virtually every part of the CNS • Dorsal pathway – thalamus to cortex • Ventral pathway – hypothalamus and basal forebrain to cortex
Attention
Attention is NOT Arousal – The What is it?
• Processing resources of the brain are finite
• Not all sensory information is equally important
• Not all thoughts are equally important
Prioritise to make best use of the available
processing resources
Attention
‘Everyone knows what attention is. It is the
taking possession by the mind … of one out of
what seem several simultaneously possible
objects or trains of thought. Focalization,
concentration, of consciousness are of its
essence. It implies withdrawal from some
things in order to deal effectively with others…’
William James
Visual Spatial Attention - Helmhotz
• Screen with letters – dark with brief flash to illuminate • Screen to big to view all without moving eyes • Could decide in advance where to pay attention – even with eyes fixed at centre – and identify letters at centre of attention better than anywhere else
Cocktail Party Effect
• Conversation at a party - selective auditory attention – perceive signal of interest in considerable noise • Dichotic listening task (Cherry, 1953) • Can’t report any detail of unattended ear – best they could report was gender of unattended voice
Attention – Important Concepts
• Selectivity - at any given moment the fixed
perceptual resources can be allocated to different
subsets of information in a flexible way (selective
attention)
• Capacity - the amount of perceptual resources
available for a task or process (varies with the task
and individual)
Attention – Important Concepts
• Overt attention – physically orient toward the
target of attention – head, eyes
• Covert attention – mentally direct attention
without orienting (e.g listen in on a conversation
behind you)
Attention – Important Concepts
• Voluntary attention – intentionally attend to
something – goal driven – internally driven –
endogenous - top-down (e.g. direct your attention
to reading this slide)
• Reflexive attention – external stimulus captures
attention – stimulus driven – externally driven –
exogenous - bottom-up (loud bang; flash of light;
movement in the periphery – recall MSI lecture and
SC)
Attention – Important Concepts
Three components of shifting attention
• Disengagement - attention is normally focused on
some target so to move, must first disengage from the
current target
• Movement - once disengaged, attention is free to move
and must be directed to the new target
• Engagement - after reaching the target, attention must
be re-engaged on the new object or feature
Selective Attention
Prioritise and attend to some things while ignoring
others – allocate resources
How is the brain able to select some information at
the expense of other information?
1. What determines the priority?
2. How does attention influence processing?
3. How is attention allocated?
What Determines the Priority?
• Many things – internal or external • Attend to stimuli relevant to current behaviour and goals • Goal driven; top-down • Endogenous • Top-down shaped by learned priorities from experience and evolution • Attend to salient stimuli • Stimulus driven; bottom-up • Exogenous • Warnings
What Determines the Priority?
• The interface between external environment and internal states (goals, expectations). • Always an interaction between the two states
Posner Cueing Paradigm
• Reaction time task to visual stimuli presented in either
the left or right visual field
• Just before the stimulus appears an attentional cue
appears to direct visual spatial attention either left or
right
• Exogenous cues – flash or similar presented left or right
• Endogenous cues – arrow presented centrally but
pointing left or right
• Combination of valid and invalid trials and usually no
cue trials for control
• Can be covert (keep focus central and respond) or overt
(make a saccade to the target)
Posner Cueing Paradigm
Typical Result Benefit - enhanced processing in the attended area Cost - the unattended area receives less processing
Posner Cueing - Predictiveness
• Endogenous cues must be predictive (say 80% valid
trials)
• In order to use the cue, must anticipate (after
presentation) that it is of value
• Exogenous cues can be non-predictive (i.e. random)
• Involuntary capture of attention regardless of value
• McCormick (1997) found that exogenous cues that
were reliably wrong provided a benefit with the cue
first involuntary capturing attention (to the wrong
place) but then subsequently being used to
strategically redirect attention to the correct place
Posner Cueing - Timing
• Exogenous cuing responses faster to subsequent stimuli at cued location • But only for 50-200ms after cue • After 300ms – pattern of effects reverses – inhibition of return (IOR) • Reflexive – quick but short lived • Voluntary – slower but sustained
Sensory Processing
• Think back to perception being constructed – how does attention influence the construction process? • Metaphors for attention • Spotlight • Zoom • Filter Each has merits Helps with conceptualising But They are all METAPHORS
Spotlight of Visual Attention
• William James (1880s), and Michael Posner (1980s)
• Attention is like a spotlight, it has a focus, a fringe
and a margin
• Illuminating the object in its focus region
• Interference data support this analogy
Zoom Lens of Visual Attention
• Attention is loosely likened to a zoom lens on a
camera that has variable spatial scope (Eriksen & St
James, Klein)
• However, the wider the field, the coarser the detail
• Local/global tasks support the zoom lens metaphor
Cocktail Party Effect
• Dichotic listening task (Cherry, 1953) • Can’t report any detail of unattended ear • Proposed attention results in better encoding of attended stimulus / loss of unattended stimulus • Processing bottlenecks • High-priority (selected) inputs get the resources
Filtering
• Filtering - early vs late selection models
• Select early
• Why process a bunch of information that will only be
ignored?
• But, how do you know what to select without some
processing?
• Select late
• Without sufficient early processing don’t know what to
select
• But, why bother selecting at all if going to do all the
processing anyway?
Selection
• Broadbent – information processing system with
limited capacity stages
• But – some information gets through – early not
blocked, only attenuated (Treisman)
Evidence for Early Selection
• Auditory pathway – two way all the way to cochlear
– attentional gating could be very early
• Hillyard et al (1973)
• Streams of sounds into headphones (dichotic)
• 10% deviant tone – attend to and count deviants in
one ear while ignoring the other ear
• Then reverse ears
Evidence for Early Selection
Auditory sensory ERPs larger amplitude for attended ear Early section of covert attention Physiological basis for the cocktail party effect
Evidence for Early Selection
• Visual spatial attention
• Typical ERPs - P1 (100ms), N1 (180ms) – both larger
in contralateral occipital cortex – early modulation
of sensory processing
Evidence for Late Selection
• Cocktail party effect – unattended information gets
through
• Endogenous attention can be interrupted by stimuli
• Distractor interference
• Early selection – irrelevant information should have
little influence on perceptual processing
• Late selection - increased interference from irrelevant
information since early processing resources divided
Distractor Interference
Irrelevant information slows responses to the target Particularly when the opposite response needs to be inhibited
Distractor Interference
• Reaching errors - changes in trajectory • Distractor is not a physical obstacle • Non-targets evoke competing responses • Inhibitory mechanisms resolve this competition
Distractor Interference
• Similar pattern with saccades • Reflexive and voluntary orienting • Upper and lower targets • Distractors on left had a bigger impact
Evidence for Late Selection
• Distractor interference
• Early selection – irrelevant information should have
little influence on perceptual processing
• Late selection - increased interference from irrelevant
information since early processing resources divided
• Slowed reaction times to targets
• Reduced accuracy to targets
• Changes to trajectories in movements to targets
Early or Late Selection
• Timing of filter is task-dependent
• Can be early or late
• Filter is a metaphor!!
• Boosting and attenuation of processing of different
stimuli likely occurs throughout the various
pathways/stages leading to conscious awareness
• Salience is important
• Different types of information likely have different
thresholds for activation (e.g. names or motion in the
periphery)
• Stimulus intensity influences
Visual Search
• How is attention deployed and how do voluntary and
reflexive attention interact when we are looking for
something?
• Distributed vs focused attention
• Distributed attention
• involves parallel processing and 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 of the visual field.
Visual Search – Distributed Attention
Single distinguishing stimulus feature
Visual Search – Focused Attention
More than one distinguishing stimulus feature
Target: black bar top right tilted conjunction search
Distributed Attention - Distractors
Single distinguishing stimulus feature - “pop out”
Focused Attention - Distractors
More than one distinguishing stimulus feature -
conjunction
Distributed vs Focused Attention
• Single stimulus feature - independent of number of distractors (pop out search) • If not single feature - distractor dependent (conjunctive search) • Elementary features analysed pre-attentively in parallel • Focused spatial attention to integrate features into an object – deployed sequential around the field
Attention
Control Mechanisms
• Sensory processing considered the sites of influence of
attention
• Consider now how the focus of attention is controlled
• Anatomy- interacting subcortical and cortical networks
• Superior colliculus and pulvinar (thalamus)
• Frontal, posterior parietal, posterior superior temporal,
anterior cingulate, posterior cingulate, and insula
cortex
• As is common with many systems – information comes
from patients with brain damage that influences the
behaviour of interest
Attention
Control Mechanisms
Three components of shifting attention
• Disengagement - attention is normally focused on
some target so to move, must first disengage from the
current target
• Movement - once disengaged, attention is free to move
and must be directed to the new target
• Engagement - after reaching the target, attention must
be re-engaged on the new object or feature
Control Mechanisms
Three components of shifting attention
• Disengagement - damage to the parietal lobe
(especially the right) results in impaired disengagement
• Movement - damage to the superior colliculus impedes
movement (eye movements are also compromised)
• Engagement - damage to regions in the thalamus
compromises engagement at a cued location
Parietal Cortex
• 2 separate frontoparietal cortical systems for
controlling attention – dorsal (spatial attention)
and ventral (non-spatial aspects of attention)
• Systems interact and cooperate
• Parietal central to both
systems
• Dorsal – intraparietal sulcus
and superior parietal lobule
• Ventral – temporoparietal
junction
• Ventral network - stimulus driven attention,
detection of salient targets, reorientation of
attention
• Selectively attending to a region of space and
stimulus appears elsewhere – ventral system
engages
• Alert – interrupt the current attentional focus
established by goal directed dorsal network
• Lesions to TPJ – deficits in disengaging spatial
attention
Superior Colliculus
• SC important in orienting – head and eye movements • Reflexive orienting (overt) to unisensory and multisensory stimuli • Certain neurons activated when attend to location of stimulus and prepare to move eyes to the target • Detect and guide orienting • Progressive supranuclear palsy (degeneration of SC and basal ganglia) • Difficulty shifting attention • Slow to respond to cued targets • Unilateral SC damage • Reduced IOR for inputs to damaged SC • Impaired visual search • Problems with moving attention
Pulvinar
• Thalamic nucleus • Inputs from SC and all over cortex • Visual neurons selective to colour, motion, orientation • Retinotopic maps of visual world • Enhanced activity when stimulus is target of a saccade or attended without eye movement • Voluntary and reflexive • Chemically deactivate in monkeys using muscimol (GABA agonist) • Difficulty orienting covertly to visual targets in contralateral visual field • Impaired at filtering distractions • Normal subjects – as number of distractors increases, activity in pulvinar increases • Pulvinar lesions – problems engaging attention at a cued location
Control Mechanisms
Three
Components
of shifting
attention
Parietal Cortex
• Parietal (frontoparietal networks) involved in much
more than simply disengagement
• Unilateral parietal damage and spatial neglect
• Impaired:
• Disengagement (from ipsilesional stimuli)
• Shifting (to contralesional stimuli)
• Engagement (with contralesional stimuli)
• Capacity limits
• Distributed attention
Spatial Neglect
• Unilateral (contralateral) - both sides possible but
more persistent and severe with right damage
• Patients do not acknowledge stimuli on the left
• Left regions of space
• Left part of objects
• Left side of body ignored
• Bias rather than complete loss of attention to
neglected field – can direct attention there – like
concentration – if work hard, can attend, but
slightest distraction and gone
• Not visual – map full visual field using single stimuli
• Occurs after damage to one side of the brain (usually the
right hemisphere)
• Patients behave as if the affected side of space (the
contralesional side) has ceased to exist
• ignore food on one side of their plate
• fail to shave/make-up one side of their face
• bump into objects on one side
• fail to read text from one side of the page – or one side of word
• Most common and severe after damage to the parietal lobe
(but can arise from cortical and subcortical damage
elsewhere)
Frequently following stroke
involving the middle cerebral
artery (MCA)
MCA patients with (a) and
without (b) neglect
Critical regions – angular gyrus,
parahippocampal gyrus
Image copy
Spontaneous drawing
Line bisection
Gaze bias – eye
tracking
At rest (light grey)
Searching for a
target letter (dark
grey)
Mental Imagery
Neglect not restricted to the physical environment Internal representations also impaired – but NOT memory
Visual Extinction
- Preserved detection of single contralesional left-sided stimuli
- Better detection of left events when allowed to ignore right events
- Better detection of left events when they are presented earlier than right events
- Not visual
Right Dominance
Attention vector deployed mostly from right hemisphere to left hemispace, but some deployed within same (right) hemispace Attention vector from left hemisphere deployed to right hemispace
Key Learnings
• Attention is not arousal – ascending arousal system
controls levels of wakefulness
• Attention - processing resources are finite so
prioritise
• Important concepts – selectivity and capacity;
overt vs covert; voluntary vs reflexive;
disengage/move/engage
• Interaction between internal goals and external
environment driving attention
• Posner – endogenous vs exogenous; valid vs
invalid; costs and benefits; IOR
• Evidence for early and late selection
• Visual search – pop out vs conjunction and effect of
distractors
• Control of disengage/move/engage
• Neglect
