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PSYB51H3 (300)
Lecture

PSYB51H3 Lecture Notes - Binding Problem, Temporal Lobe, Spatial Frequency


Department
Psychology
Course Code
PSYB51H3
Professor
Matthias Niemeier

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PSYB51 - Perception Lecture Slides
Textbook Notes
Lecture 7 & 8
Attention
-We are unable to read more than one thing at once because we do not have the
brains for it
-Attention: not a single thing; family of mechanisms that restrict processing in
various ways
-Selective attention is a cognitive brain mechanism that enables one to process relevant
inputs, thoughts, or actions while ignoring others that are less important, irrelevant, or
distracting; the ability to pick one (or a few) out of many stimuli
-Arousal: a global state of the brain reflecting an overall level of responsiveness
-Why we need attention:
oBottlenecks: it is impossible to process everything at once. Lack of brain, lack of
arms, …
oSensory – cognitive – motor (?)
-Why attention can help us:
-Where attention plays a role:
oAttention to vision
oAttention to audition/touch/smell
oAttention across modalities
oAttention to thoughts
oAttention to motor tasks
Studying Attention
-Measure attention
oReaction time: a measure of the time from the onset of a stimulus to a response
oPerceptual thresholds: change with attention
oMotor accuracy
oBrain activity
oEye movements: can reflect overt shifts of attention. But careful; attention can
shift without eye movements: covert attention
oPerceptual biases
-Simple probe detection experiment measures RT (or perceptual thresholds)
-Posner: adding a cue; Posner found that with a valid cue, the RT increases
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-Cue: a stimulus that might indicate where (or what) a subsequent stimulus will be: valid
(correct information) vs. invalid (incorrect) vs. Neutral (uninformative)
-Stimulus-driven cues: information conveyed through previous events at the same location
-Voluntary cues: (spatial) information conveyed through cognitions and memory, often
based on language or other symbols
-Difference between stimulus – driven/peripheral and voluntary/symbolic
oPartially independent neural structures
oStimulus onset asynchrony (SOA): the time between the onset of one stimulus and
the onset of another
Different time courses of SOAs; slower effects for voluntary cues
Inbition of return (IOR)
-Overt shifts of attention: a shift of attention accompanied by corresponding movements of
the eyes
-Covert shifts of attention: a shift of attention in the absence of corresponding movements
of the eyes
-Perceptual biases: asymmetries in perceptual between the left and right side of a stimulus;
varies with task (i.e. listening to speech)
-Grating scales:
oWhich bar has more of the thinner/thicker stripes?
-Electroencephalography: leftward bias associated with greater negativity over the right
hemisphere >320 ms, potentially reflecting interhemispheric competition
-Space-based cueing of attention
-Feature-based cueing of attention: attention is guided based on non-spatial information
about features
oCued feature becomes more β€œvisible” throughout the visual field
-Feature-based attention can be a disadvantage
-Zhang & Luck (2009): electrophysical signals in response to occasional luminance
decrements
oFeature dependent modulation of the P1 suggests early influence of feature-based
attention on extrastriate areas
-Stojanoski & Niemeier (submitted): attention aids perception of β€˜high-level’ features for
object perception, attention to contours modulates EEG later than attention to motion
Visual Search
-Visual search: looking for a target in a display containing distracting elements
-Target: the goal of visual search
-Distractor: any stimulus other than the target
-Set size: the number of items in a visual display
oHas no influence on search time for β€œefficient searches”
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oImpacts search time for β€œinefficient searches”
-Feature search: search for a target defined by a single attribute, such as colour or
orientation
-Basic features/obvious stimulus properties: colour, size, orientation, motion
-Less β€˜ basic’ (it seems) yet efficiently searched: lighting direction
oNo single feature defines a target, a target is defined by the co-occurrence of two
or more features
-Salience: the vividness of a stimulus relative to its neighbours (feature contrast β€œclearly”
above JND threshold)
oWhen an item is salient, no matter the number of distractors, the target will
β€œpop out” of the image
-Parallel: the processing of multiple stimuli at the same time
-When the target and distractors contain the same basic feature, the search in
inefficient
-Is conjunction search serial?
oYes – serial self-terminating search: items are examined one after another until
target is found or until all items are checked, similar to eye movements scanning a
scene but faster
oNo – limited capacity parallel process: watering garden with adjustable spray
nozzle idea
oCombo – neurophysiological evidence that both mechanisms co-exist
-Real World Searches
oGuided search theory (Wolfe): attention can be restricted to a subset of possible
items on the basis of information about the target’s basic features
oConjunction search: search for a target defined by the presence of two or more
attributes; no single feature defines the target
-Binding Problem in the Visual Search
oBinding problem: challenge of tying different attributes of visual stimuli to
the appropriate object so that we perceive a unified object
-Feature integration theory (Treisman and Gelade): a limited set of basic features can be
processed in parallel preattentively, but that other properties require attention
oPreattentive stage: parallel processing of basic features across entire visual field
before selective attention is deployed
oAttentive stage: spatial attention binds together features for one item at a time,
serial search
oIllusory conjunctions: false combination of the features from two or more
different objects
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