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Lecture 15

Lecture 15 & 16.docx

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Western University
Psychology 2115A/B

Lecture 15 Visual Attention The span of Apprehension - How many thing that are out there can you perceive at once - Miller o The span of short term memory  magic number is 7 (+/- two) George Sperling (1959) The whole Report Procedure o Wanted to know how many things you can perceive at one glance o Present displays fro a short period time and asked them to report back everything (there were different things in each display) o Found that people could recall 5 things no problem (in a 50ms window) o Once you go beyond 5 you can’t perceive them all o His displays only went up to 12 o Two reasons why this is limited (problems)  1. You can perceive them all, but you cant remember them in your short term memory (short term memory problems)  2. Output of interference: you see all 12, you only remember 7, but when you try and repeat them back the th experimenter you forget them (start saying the, by the 5 , cant remember the last few things) - Example of Sperlings trials  on board o Musical notes at the end are a cue to only report a part of the display (high pitch- report the top row, low pitch report the bottom row) o You wont know what row you will be asked to report –this means that you need to perceive as much as you can o You are never going to have to report more than 4 things o Graph showing the probability correct against the interstimulus interval – y axis (probability correct) o With a short interstimulus interval- probability hat was correct was nearly 100% o In order to do this you must have perceived all 9 letters in order to report three of them because you didn’t know which ones you were going to be asked to relay back - Conclusion: perception isn’t within our limits, we can perceive everything, we just cant contain it in our short term memory - No real perceptual attention everything gets in - When the stimulus is gone- perception is stopped—so when you delay the cue, you are tapping into short term memory, the longer you wait the more performance will go down - We need someone to answer the question does perception ends when the cue ends Ovarbach and Coriell - They presented two rows of 8 letters - Cued one of the letter positions with a bar marker - Trying to establish that they can produce sperlings pattern of data with a visual cue  doesn’t have to be an auditory cue to get the same effect - Early cue- good results, late cue- weaker results - Same type of graph, same example of a decline (decay) - Sperlings data don’t hinge on the auditory cue you get the same result with a visual cue - Another condition- they had a circle around the letter that had a bunch of cross hatch lines in it (the grid) that they wanted the person to remember - The purpose of the experiment – perception goes on after the stimulus is gone - The visual nature of the cue should be irrelevant- its all sitting in STM has nothing to do with your visual system o BUT this is not what you find o Short interstimulus interval- no one can report anything o If you delay the cue, the longer you do- the better the performance - When the stimulus is gone- perception is still going - SPERLINGS WORK DOES NOT HOLD o This re-opens the debate o Even though his assumption is wrong, does not mean that the conclusion is wrong, there may be other truths o SO- maybe he was right you perceive everything but can not contain it in you STM- BUT the cue helps o Maybe what that cue does- IS HELP YOU DURING PERCEPTION o You have a ¼ of a second to extract the info from your STM  So maybe the cue helps you retrieve the info o You put all of you perception on the thing that was cued so it increases the chances of you reporting the thing that the experimenter actually wants to report Is perception an unlimited perceptual process? Or is there a capacity limitation? Where in the system do we have limitations? Stimulus sensory memory (after image)perceptionSTM - If we have a capacity limitation, it would mean that we have a harder time seeing more things Estes and Taylor (1964) - If you can perceive anything and everything it wont matter how many things they put in front of you – there is a limitation, perception is better in the fovea, so that’s were most things are concentrated - They presented either 4, 8 or 16 things
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