PSY246 Lecture Notes - Lecture 4: Lesion, Prosopagnosia, Domain Specificity
2 Jun 2018
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PSY246: Week 4 Lecture
Visual Attention
• What is attention? What does it do?
• What is the relationship between eye movements and attention?
• How and why do we shift attention – exogenous and endogenous attention
• What can attention select?
• What can visual search tell us about attention?
• Impact of perceptual and working memory load on attention
- We can only attend to a small amount of our visual world at any one time:
choose wisely
What does attention do?
• Filtering mechanism (acts as a gate-keeper)
• Finding mechanism (spotlight moving through our world, selects different
spatial locations) and binding information together
• Favouring (weighting/bias)
• These are all interrelated processes and functions
Attention and eye movements:
• Eye movements can control the ‘spotlight’ of selective visual processing
• Camera-based eye trackers measure:
o Saccades – small, rapid eye movements
o Fixations – pauses in eye movements that indicate where a person is
attending
o Approximately 3 fixations per second
• Fine details are only represented in central vision (point of fixation)
o Eye movements control what high resolution information we can
access
• Is knowing where attention is simply a matter of knowing where one’s eyes
are looking?
o the bigger the fixation, the longer the person is looking
• Attention and eye movement are related but not the same thing
o Shifts of attention often precedes eye movements – shift attention
before ur eyes have actually moved
• Attending to something is NOT just meaning you have to look at it
o Covert attention → you can keep track of 4 dots without moving your
eyes, this ability is limited, impacting how much we can process at
once
o I.e. just because your eyes are on the road does not mean you are
attending properly to the road
• Eye movements are insightful when studying attention, but people’s eyes are
not always directed towards the focus of their attention
Favouring: Attention helps us keep track of what’s important
• We have an inherent bias (bottom-up) to attend to information that is relevant
for survival e.g. sudden onsets (e.g. a lion leaping at you)
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• We can also ‘tune’ our attention to the processing of task-relevant information
e.g. to find your friend in a crowd
• These reflect distinct ways in which we shift or control our attention
Shifting attention
• Endogenous → intentional, goal-directed shifting of attention to a location
o Goal-driven attention – can be directed without eye movements
o “Posner cueing task” – endogenous cue; arrow directs you to a box and
then a letter appears – the arrow is a valid cue; the opposite is the
invalid cue (when the arrow directs you to the right box, but letter
appears in the left box)
• Exogenous → reflexive, involuntary, shifting of attention; ‘attentional capture’
o Involuntary – attention directed by saliency i.e. a lion jumps out of
bush, attention occurs suddenly
o Posner cueing task – exogenous cue; valid cue with flash of target into
the box, invalid cue where red flash drags attention to other side of
screen, letter appears in other box
o Exogenous attention shifts are rapid
o Concept called ‘inhibition of return’
• Looking in the brain, both endogenous and exogenous have distinct networks
o Voluntary system (endogenous)
o Reflexive system – ‘circuit breaker’ (exogenous)
• Attention in the visual hierarchy
o Attentional enhancement is greater in higher visual areas
What can attention select?
• Spatial locations e.g. regions of space
• Features e.g. a colour, orientation
• Objects e.g. a person/thing
• Spatial-based selection → where’s Wally task
• Spatial attention
o Attention directed to a location in the visual field
o Spotlight metaphor
▪ Attention moves across the visual field highlighting spatial
locations
o Spotlight can scale in size
• Feature-based selection → looking for red in where’s wally task
• Feature-based attention
o Attention directed toward a feature
o E.g. colours like blue or red, orientation like 45 degrees
• Object-based selection → select objects in itself – find wally in picture from
last time
• Object-based attention
o Attention can select an entire object
o Including colour, shape etc. – not just one element of a component
• Evidence for object-based attention
o Observer views two rectangles
▪ Cue signals where target may appear
▪ Task was to press button when target appeared
find more resources at oneclass.com
find more resources at oneclass.com
▪ The debate: spatial vs. object based attention
o Results show
▪ Fastest reaction time at targeted position
▪ ‘Enhancement’ effect for non-target within the target rectangle
• Neural evidence for object based attention
o Attend to face –activation in face processing (FFA) increases
o Attend to house – activation in scene (PPA) processing area increases
o NO change to the stimulus but attention changes what object is
processed
Finding: Attention helps us find things
• Finding a friend in a crowd e.g. on the beach
• Why are some searchers more difficult? i.e. finding a car in a car park
• Spatial visual attention - How do we allocate attention and locate objects or
other info in complex arrays/scenes?
o Treisman devised the ‘visual search task’ to study spatial visual
attention
o Subjects search for a target among distractors; 50% of the time target
was present, subjects judge whether target is present or absent – she
measured how the decision time affected the number of items searched
• Search for conjuctions of features – the O ‘pops out’ if distractors are shapes
without curves
• Search time for a R (conjunction of features) among Ps and Qs varies with set
size
• Treisman and Gelade (1980)
o Found RT increased as a linear function of set size for conjunction
targets
o Argued that conjunction searches are serial and self-terminating
• Basic features which pop out in displays:
o Colour
o Orientation
o Curvature
o Vemier offset
o Size
o Motion
o Shape (not all do)
o Depth
o Gloss
• Why conjunctions are slow – because attention ‘binds’ the world together
o Binding → process by which features are combined to create coherent
objects
o For conjunction searches, object features must be bound by attention
• The binding problem
o Features of objects are processed separately in different areas of the
brain
• Feature Integration Theory
o Basic features e.g. colour, orientation are processed in parallel by pre-
attentive processing
o Pre-attentive features are ‘free-floating’
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Impact of perceptual and working memory load on attention. We can only attend to a small amount of our visual world at any one time: choose wisely. What does attention do: filtering mechanism (acts as a gate-keeper, finding mechanism (spotlight moving through our world, selects different spatial locations) and binding information together, favouring (weighting/bias, these are all interrelated processes and functions. Incorrect associations of features with objects, e. g. reporting a. Yellow triangle" occurred 18% of time: asking observers to focus on the target objects eliminated this effect (did not mix up the binding) Is face recognition different: face processing and visual expertise. Insights into face processing from the impact of emotional state. Is there a way to conduct this experiment that could separate these two hypotheses: unfamiliar object recognition is viewpoint-dependent (change the viewpoint, recognition gets slower and slower) inconsistent with the view that it is viewpoint-invariant.
