Chapter 8 - Study notes

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19 Dec 2010
Quiz: wat is the univariance problem in color perception? u have a photoreceptor that
contribute to colour sensing but it doesnt see colour ..cuz itz ambiguous, dont noe which
wavelength it is. Come combo of wavelength and light energy can contribute to same
photoreceptor. How does our colour system solved the problem. by having more than one
photoreceptor.. ie red, green, blue. Only combo can tell us wat color we look at
What is a horopter? 2 eyes that have 2 diff image.. 2 version.. double vision, unless u
focus on smt. If u converge on it, the fovea not have double image, that is one point of the
horopter, but there are many points in space where eye dont have double vision. Like a
cylinder area where we dont have double vision = horopter
3)SOA stands for stimulus Onset asynchrony 10) we cant move our eyes w/o shifting in that
Attention = attention is the name we give to a family of mechanisms that restrict
processing in various ways. Overt vs covert attention: overt refers to directing a sense organ
at a stimulus fixating the eyes on a single word for ex. If you point your eyes at this page,
while directing attention to a person to left, you are engaging in covert attention. Reading
this text while listening to music is divided attention. Watching the pot for water to boil is
sustained attention. Selective attention = ability to pick one or few out of many stimuli.
One can be involved in more than one type of attention.
Experiment where subjects are fixated on a point and when the test probe appears they are
to react. Reaction time (RT) = amount of time that elapses /b/ point when the probe
appears and pt when subject hits response key. cue = stimulus that might indicate where
or wat a subsequent stimulus will be. Cues can be valid, invalid, or neutral. Cues could be
symbolic (voluntary) or peripheral (stimulus-driven) leds to IOR, inhibition of return cuz
then valid cue be SOA = 0
How long does it take for a cue to redirect our attention? Symbolic cues direct attention
more slowly cuz we have to process the cue. But some symbolic cues ie watching another
persons eyes can behave like fast peripheral cues. SOA = Stimulus onset asynchrony =
time /b/ onset of one stimulus and the onset of another. We can measure timing of attention
shift by varying the interval /b/ when cue appears and when test probe appears. If SOA is
0ms then cue and probe appear at same time, for this there is no diff between the effects of
valid or invalid cue.
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Attention starts at fixation point and somehow ends up at cued location. Does it actually
move from one pt to next? When we shift our gaze, our pt of fixation sweeps across the
intervening space, attention might sweep across space too like spotlight beam metaphor.
Other possibilities are that attention might expand from fixation, growing to fill the whole
region from fixation spot to the cued location and then shrink to include just cued location =
zoom lens model of attention. Or when attention is withdrawn from fixation spot, it might
not move at all. It might simply melt away at that location and then reappear at cued
location. No correct metaphor. However evidence suggests tat attention is not moving from
pt to pt like spotlight would.
Visual search = lookin for a target in a display containing distract(or)ing elements, this
provides a closer approximation of actions of attention in real world.
What makes some search tasks easier than others. set size = # of items in a visual display.
One of the standard measure of the ease of search is to ask how much time (reaction time),
on average, is added for each item added to display. When target is absent it takes much
longer for subject to say it is not present than to say it is present. If we direct attention to
target as soon as display appears, regardless of set size, then we have an efficient search. If
we must examine each item in turn until we find target, then we have an inefficient search.
Different types of search tasks differ in efficiency
Feature search = search for a target defined by a single attribute. If the target is salient
than it doesnt matter wat itz set size of distractor is. We can process the feature of all items
at once, in parallel. so when we measure RT it not change w/set size like normally.
When the target and distracters in a visual search task contain same basic features =
inefficient search. serial self-terminating search = search from item to item, ending
when a target is found or all items checked. Thus on average one has to search through half
of the distractors before finding target.
Guided search = search in which attention can be restricted to a subset of possible items
on the basis of information about the target items basic features ie itz color
Conjunction search = search for a target defined by the presence of 2 or more attributes
ie red & small). This 2 feature conjunction searches tend to lie /b/ efficient features and
inefficient serial searches.
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