SENSATION 1 Flashcards
What is attention?
the ability to preferentially process some parts of a stimulus at the expense of processing other parts of the stimulus
Why is attention needed?
You can’t process everything in the visual scene
simultaneously
your perceptual system has a limited capacity
to avoid being overwhelmed
Overt attention
looking directly at an object
covert attention
looking at one object but attending to another object
What does it mean to fixate an object?
the look at it - eye movements between fixations are BALLISTIC (i.e. very fast)
these eye movements are called SACCADES
what are saccades?
when your eyes jump from point to point
what are fixations?
the rests b/w jumps, where the eyes stay looking directly at one part of the scene
What directs out attention?
- an initial involuntary process (mediated by attentional capture)
- a subsequent voluntary process (guided by your goals & expectations)
What is attentional capture?
when you r first presented w a scene, your fixations are captured by salient parts of the scene (this is involuntary)
What captures our attention?
contrast
- regions of colour / luminance contrast
- regions of size contrast
- regions of orientation contrast
- regions of motion / flicker contrast
What are the effects of attention?
- attention speeds responses
- can influence appearance
- can influence physiological responding
ATTENTION MAKES PERCEPTION MORE VIVID
Attention affects not only how quickly a person can respond to a stimulus but also the appearance of the stimulus.
what did carrasco et al 2004 show?
showed that attention can make objects appear to have a higher contrast (cued grating appeared to be higher contrast)
What is the binding problem?
- diff aspects of a stimulus are processed independently, often in separate brain areas
- e.g. motion is processed by DORSAL stream and form is processed by VENTRAL stream
The issue of how an object’s individual features are combined (i.e. bound) to create a coherent percept is known as the binding problem.
e.g. how can i associate the right object w the right colour?
What is feature integration theory?
suggests that the binding problem is solved by attending to only one location at a time - only features associated w that location are processed so only those features are bound together
- avoids binding features from dif objects
what is a prediction of FIT?
if attention is inhibited, features from dif objects will be incorrectly bound together
What did Treisman & Schmidt (1982) find
- showed that illusory conjunctions occur
- they presented character strings very briefly followed by noise mask
- the primary task was to report the 2 numbers
- then O’s were asked to report coloured letters
- O’s often associated the wrong colour with the wrong letter
- such incorrect bindings are called illusory conjunctions
Balint’s syndrome
- parietal lobe damage leads to condition here you cannot focus attention on a single object - very prone to illusory conjunctions due to inability to focus attention on a single object
What is a conjunction search?
when the target differs from the distractors only by its particular conjunction of features
- some forms of visual search require binding to occur
What does FIT predict about conjunction searches?
predicts that attention needs to be applied to each object in turn (one at a time) to determine whether or not the attended object is the target - VERY SLOW
What is a feature search?
the target contains a feature (e.g. red) that the distractors DO NOT contain
what does FIT predict about feature searches?
predicts that because binding does not need to occur, attention does not need to be applied to each item in turn - FAST
What is change blindness?
You can only remember a few parts of a scene at one time
If one of those parts change, you notice the change
If some other part of the scene changes, chances are you won’t notice the change
Why doesn’t change blindness occur all the time?
because changes usually generate motion transients that draw attention to the location change, thereby making it easy to spot the change
What are motion transients?
In the previous demonstration, a blank screen was
inserted between images.
This meant that when the second image was shown,
motion transients occurred for every part of the image -
not just the parts that changed.
This meant that motion transients did not guide attention
to the change
