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Lecture

PSYC*2650 Ch 4.doc

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Department
Psychology
Course
PSYC 2650
Professor
Anneke Olthof
Semester
Winter

Description
Tuesday, Jan 22, 2012 Chapter 4: Paying Attention - the stimulus you’re attending to is only one of many that are available to you 1) you could choose to pay attention to any of the other things in the room and if you did, you would be virtually oblivious to other things 2) there seems to be one thing you cannot do: you cannot pay attention to all of these things at once Selective Listening - many early studies employed a task called Shadowing - participants hear a tape recording of someone speaking and must echo this speech back word for word - it is initially challenging but becomes relatively easy - the message to be shadowed, the Attended Channel, is often presented through stereo headphones (the right headphone) - a different message - the Unattended Channel - is presented in the left earphone - the overall setup is referred to as Dichotic Listening - participants easily follow one message and their shadowing performance is near per- fect and they hear little from the unattended channel - more recent studies have documented a similar pattern with visual inputs - e.g. video of people passing a ball and gorilla walks through and no one notices - people are not altogether oblivious to the unattended channel, physical attributes are heard but the semantic content is not Some Unattended Inputs Are Detected - when the unattended channel said a series of names, including the participants’s own name, 1/3 of them heard their own voice - the name seemed to “catch” their attention - other things will also catch your attention if you are primed for them: mention of a movie you just saw, your favourite restaurant - words with personal importance - this is referred to as the Cocktail Party Effect Perceiving and the Limits on Cognitive Capacity - we have 2 options of how to think about attention - one focuses on what we do with the unattended input - we block the inputs we’re not interested in Tuesday, Jan 22, 2012 - suggests we erect a Filter that shields us from potential distractors - we can shut out distractors this way, but this “shutting out” seems to work on a distrac- tor-by-distractor basis - when a new distractor comes along, we need to develop a new skill aimed specifically at blocking it - we are also able to Promote the processing of Desired stimuli Inattentional Blindness - in a study, participants were supposed to pay attention to a “+” and in the second trial a shape flashed quickly after it - 89% of participants didn’t notice anything different between the 2 trials - first proposed explanation is that participants did see the target shapes but couldn’t re- member what they had just seen - second proposed expiation is that participants were not expecting any shapes to ap- pear and were not in any way prepared for these shapes and failed to see the shapes - this is called Inattentional Blindness - e.g. when you can’t find something in the fridge that’s right in front of you - which of these is correct? - they both have something in common: our normal ability to see what’s around us and to make use of what we see, is dramatically diminished in the absence of attention Conscious Perception, Unconscious Perception - Mack and Rock claim there is no conscious perception without attention - in an experiment, participants didn’t perceive the fins on the lines but did consciously perceive them as they said the top line was bigger than the bottom - perhaps you can unconsciously detect and be influenced by patterns in the world even in the absence of attention Change Blindness Tuesday, Jan 22, 2012 - observers’ inability to detect changes in scenes they are looking directly at - a related pattern emerges when participants watch movies and in live events Early Versus Late Selection - in several paradigms, people seem oblivious to stimuli that are directly in front of their eyes - there are 2 ways to think about these results: - they may reveal genuine limits on perception, so that participants literally don’t see the stimuli - or they may reveal limits on memory, so that people do see the stimuli but immediately forget what they have seen - which is correct? one approach to this question hinges on when the perceiver selects the desired input and when the perceiver ceases the processing of the unattended input - Early Selection Hypothesis - the attended input is identified and privileged from the start, so that the unattended input receives little analysis and is never perceived - Late Selection Hypothesis - all inputs receive relatively complete analysis, but it is only the attended input that reaches consciousness or that is remembered - each hypothesis captures part of the truth - recording form neurons in Area V4 of the visual cortex shows that the neurons are more responsive to attended inputs than to unattended ones - studies suggest that attention may modulate neural events even earlier in the stream of visual processing - perhaps as early as the lateral geniculate nucleus - these results argue that attention doesn’t just change what we remember or what we’re aware of, it can also literally change what we perceive - why is the pattern mixed between late and early selection? the answer depends in part not he nature of the attended input - if the input is complex, processing will demand a lot of effort, little effort will be left over for other stimuli leading to a data pattern consistent with early selection - if the attended input is simple, there is more effort available for the unattended inputs so the unattended inputs will see a pattern of late selection Selective Priming - whether selection is early or late, looking directly at an input isn’t by itself enough to al- low conscious perception - “resources” are needed for perceiving, but what are those resources? Tuesday, Jan 22, 2012 - proposal: people can literally prepare themselves for perceiving by priming the suitable detectors - why don’t participants notice the shapes in the inattentional blindness studies? it may be that they don’t expect any stimulus so they have no reason to prepare for any stimu- lus - what about selective listening? one does not want to hear the distractor, so devoting resources to it would be a waste of resources so detectors receive no resources and are unprimed - why does attention sometimes “leak”? the detectors for this stimulus (your name) are already primed because it is a stimulus you have often encountered in the past - activation level of these detectors is already high Two Types of Priming - resources are needed to prime detectors, and those resources are in limited supply - in a study, a pair of letters was shown and participants had to decide if the letters were the same or different - before each pair, participants saw a warning signal, in the neutral condition the warn- ing signal was a plus sign, in the primed condition, the warning signal was one of the let- ters that was about to be shown and in the misled condition, the signal was a letter that wasn’t about to be shown - accuracy rates are very high, but the speed of responding varies from condition to con- dition - by comparing Response Times (RTs) in the primed and neutral conditions, we can ask what benefit there is from the prime - by comparing the misled and neutral conditions, we can see what cost there is from being misled - there were 2 different versions of this: in one version, the warning signal was an excel- lent predictor of the upcoming stimuli (high validity primer) and in the other, the warning signal was a poor predictor of the upcoming stimuli (low validity condition) - in the low validity condition, the prime should not lead to any specific expectations but we do expect faster RTs in the primed condition than the neutral - RTs were reliably faster in the primed condition than in the neutral condition - apparently receptors can be primed by mere exposure to a stimulus - priming is observed even in the absence of expectation so it is truly stimulus-based - in the misled condition with a low-validity prime, misleading participants had no effect - performance was the same as in the neutral condition Tuesday, Jan 22, 2012 - priming the wrong detector takes nothing away from the other detectors - the high-validity primes produce a warm-up effect and also an expectation effect whereas low-validity primes produce only the warm-up - high-validity primes helped participants more than low-validity primes - faster respons- es - in the misled condition with high-validity primes, responses were slower than response in the neutral condition - misleading hurt performance Explaining the Costs and Benefits - the message is clear, there are 2 types of primes: one is stimulus-based (produced merely by presentation of the priming stimulus, with no role for expectations) the other is expectation-based - these can be distinguished in several ways: 1. expectation-based priming is larger in magnitude than the stimulus-based priming, leading to a greater benefit in the RT data 2. expectation-based priming takes longer to kick in 3. the two types of priming can also be distinguished in terms of their “cost”, stimulus- based priming appears to be “free” and so we can prime one detector without taking anything away from the other detectors, expectation-based priming does have a cost (priming the wrong detector in the high-validity condition takes something away from other detectors) - what produces this cost? an analogy is being on a limited budget Tuesday, Jan 22, 2012 - expectation based priming - if the Q-detector is primed, this takes something away form the other detectors, getting prepared for one target seems to make people less pre- pared for other targets - expectation-based priming reveals the presence of a Limited-Capacity System - now to explain Selective Attention: perceiving involves some work, and this requires some limited mental resources so you can only listen to one message at a time, - evidence for those limited resources comes from the limited-capacity system Chronometric Studies and Spatial Attention - what exactly is the nature of these expectations? - imagine the participants are told, “the next stimulus will be a T” or “the next stimulus will on the left side of the screen” - Spatial Attention - our ability to focus on a particular position in space and this to be better prepared for any stimulus that appear in that position - did the same type of experiment with high-validity and low-validity except using places and got the same results Attention as a Searchlight - studies of spatial attention suggests that visual attention can be compared to a search- light beam - the “beam” marks the regions of space for which one is prepared so inputs are pro- cessed more efficiently and more swiftly - the beam can be wide or narrowly focused - this idea is referring to movements of attention and not movement of the eyes - what does the “searchlight” accomplish? priming, the searching shining on a stimulus is just another way of saying that a person is priming the relevant detectors for that stim- ulus Attending to Objects, or Attending to Positions - there are important differences between attention and a searchlight beam - a beam of light might not be in the right position - we pay attention to objects, rather than to position in space - study of people who have suffered forms of brain damage (parietal cortex) that pro- duce problems in paying attention - patients with Unilateral Neglect Syndrome seem to ignore inputs coming from one side of the body, usually damage on the right side and neglect on the left Tuesday, Jan 22, 2012 - this may provide evidence that we pay attention to spatially define regions not object’s boundaries - other evidence demands further theory - in one study, patients with neglect syndrome had to respond to target that appeared within a barbell-shaped frame, the right was a red circle and the left was blue - while the patients watched, the barbell frame was slowly spun around so the circles switched - once they have “locked in” one of the circled, it is the object, and not the position in space that defines their focus of attention - they will continue attending to the initial circle they focused on even though it is now on their neglected side - to describe this, we need a two-part account: - first, the symptoms of neglect syndrome plainly reveal a spatially defined bias - second, once attention is directed toward a target, it is the target itself that defines the focus of attention - if the target moves, the focus moves with it - in this way, the focus of attention is object-based not space-based - normal participants also show a mix of space-based and object-based attention - study: participants look at a computer screen that showed 2 rectangles, one on the left, one on the right - they were asked to respond as soon as they saw the target on one end - in the majority of trials, a cue signaled in advance where the target would appear - in other trials, the cue was misleading Tuesday, Jan 22, 2012 - participants were faster when the cue accurately signaled where the target would be - what’s crucial is the comparison between misleading cues that at least signaled the proper rectangle and misleading cues that signaled the wrong rectangle - according to space-based account, there should be no difference between these 2 cases - according to an object-based account, these 2 cases will be different - this is true - the cues didn’t just draw attention to location, they drew attention to object Perceiving and the Limits on Cognitive Capacity: An Interim Summary - at the broadest level, we have suggested t
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