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Chapter 8

PSYB51 Chapter 8


Department
Psychology
Course Code
PSYB51H3
Professor
Matthias Niemeier
Chapter
8

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Chapter 8: Attention and Scene Perception
-The retinal array contains far more information than we can process
-Processing everything, everywhere, all at once requires a brain that will not fit into
the human had
Attention
-Any of the very large set of selective processes in the brain. To deal with the
impossibility of handling all inputs at once, the nervous system has evolved
mechanisms that are able to restrict processing to a subset of things, places, ideas,
or moments in time
Overt attention, covert attention, divided attention, sustained attention
Selective attention
-The form of attention involved in processing is restricted to a subset of the possible
stimuli
-Potential mechanisms operate in all of is the senses
Selection in Space
-A queuing experiment by Michael Pozner in which an individual fixates on a central
point and must respond as soon as possible when a probe appears
The measure of interest is the average reaction time (a measure of the time
from the onset of a stimulus to a response)
-In another trial of this experiment a queue is provided during the waiting period; it
can be a peripheral or a symbolic cue it can be a valid or invalid cue
-Reaction times are slower with an invalid queue than in the control condition
because the subject was fooled into attending to the wrong stimulus
-Stimulus onset a synchrony the time between the onset of one stimulus and the
onset of another
Its SOA is 0 ms, the cue and probe appear simultaneously; if this time
increases to about 150 ms, the magnitude of the cueuing effect from a valid
peripheral cue increases and after that the effect of the cue levels off
-Symbolic cues take longer to work presumably because we need to do some work to
interpret the arrow
The Spotlight of Attention
-The best evidence suggests that attention is not moving from point to point the way a
physical spotlight would move
Visual Search
-Visual search - looking for a target in a display containing distracting elements
-The beach world the display shows a different set size the number of items in the
visual display; as a rule it is harder to find a target as the number of items increases
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One of the standard measures of the ease of search is to ask how much time is
added for each item added to display
In a typical experiment the target is present and 50% of the trials been absent
and the other 50% an experimenter averages the reaction times
-One might compare search tasks is to talk about the efficiency
Feature Searches Are Efficient
-Feature search - search for a target to find a single attribute, such as a salient color
or orientation
-Its salience the vividness of a stimulus relative to its neighbors
-Parallel individual attention, referring to the processing of multiple stimuli at the same
time
-Between one dozen and two dozen basic attributes seem to be able to support
parallel visual search
Many Searches Are Inefficient
-When the target and distractors in a visual search task contain the same basic
features, search is in efficient
-Each additional distractor can add about 20 to 30 ms to a successful search for a
target and about twice that amount of time to a search that ends without finding a
target
-Serial self terminating search - a search from item to item, ending when a target is
found
On average a person will have to search through about half of the items on each
trial before the search can be terminated
In Real-World Searches, Basic Features Guide Visual Searches
-Guided search search in which attention can be restricted to the subset of possible
items on the basis of information about the target items basic features
-Conjunction search search for a target defined by the presence of two or more
attributes
-Two feature convention searches tend to lie between the very efficient feature
searches and the inefficient serial searches
The Binding Problem in Visual Search
-Binding problem the challenge of time different attributes of visual stimuli which are
handled by different brain circuits, to the appropriate object to that we perceive a
unified object
-Pre-attentive stage the processing of a stimulus that occurs before selective
attention is deployed to that stimulus
The idea that there is a pre-attentive stage of basic feature processing followed
by a second, attention demanding stage is the core of Anne Treismans feature
integration theory which holds that a limited set of basic features can be
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