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Chapter 8 Attention and Scene Perception
Visual acuity is limited in the periphery. Hence you cant read more than 2 books at
a time. even if the letters are large.
^ general problem that the retinal array contains more information than that can be
Why cant we process everything at once?
We dont have the brains for it. recall recognizing a single object requires a
sizeable chunk of the brain and its processing power.
Processing everything all at once requires a brain that will not fit in the
human head.
If itisnt possible to process everything then what should be processesd?
--- we pay attention to some stimuli and not others.
Attention- is not a single thing and it doesnot have a single locus in the brain.but
attention is the name given to family of mechanisms that restrict processing in
various ways
Can be overt or covert
Overt attention- refers to directing a sense organ at a stimulus.
covert attention -refers to discreet attention while stimulus organ is pointed
somewhere else.
Divided attention paying attention simultaneously to two things
Sustained attention paying attention for prolonged period of time
In this chapter, mostly concerned with selective attention.
Selective attention - the form of attention involved when processing is
restricted to a subset of possible stimuli. The ability to pick one or few things
to focus on.
But these terms are not mutually exclusive.
Operational mechanisms operate in all of the senses not just visual attention
We can also use attentional mechanisms to give one sense priority over
Selection in Space
What does it mean to pay attention?
Michael Posner created the classic situation. The subject must hit the response
key as fast as possible when the probe appears.
Measure of interest is the reaction time (RT)- amount of time that elapses
between the point when probe appears and the point when the subject hits
the response key.
What if the subject is given a cue? Cue is a stimulus that might indicate
where(OR what) a subsequent stimulus will be.
Valid cue when the probe appears in the cued location.
RT decreases when valid cue.
RT is faster because the participant is paying attention to the
current location.
No cue condition RT is longe(=slower) compared to valid cue
Invalid cue –occurs when the probe id misleading. Appears in the area
opposite of the cued location.
RTs are slower here than in the control condition because the
subject has been fooled into attending to the wrong location.
The experimenter doesnot tell the participants whether the trial will be
valid or invalid
Peripheral cue vs symbolic cue
How long does it take for a cue to redirect our attention?
Depends on the nature of the cue.
Time 2: when the cue appears
Time 3: when the probe appears
Stimulus onset asynchrony: the time between the onset of one stimulus and
the onset of another. SOA
When SOA is o millisec, no time for it to be used to direct attention and there is no
diff between the effects of a valid or invalid cue.
When SOA is 150 ms, the magnitude of the cueing effect from a valid PERIPHERAL
cue increases and plateaus.
Symbolic cues take longer to work because we need to do ome work to interpret the
BUT some symbolic cue work like fast, peripheral cues.
The spotlight of attention
Does attention actually move from one point to another
Attention could be deployed from one point to the next in several ways.
1.It might move in the manner analogous to the movement of the eyes.when we
shift our gaze, our point of gaze sweeps across the intervening space
attention might sweep across space in similar manner like a spotlight beam.