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Chapter 4

Cog chap 4.doc

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University of Guelph
PSYC 2650

Cognition – Chapter 4 Selective Attention - William James Dichotic Listening  Participants wear headphones, hear one input in one here & a different input in the other. Instructed to pay attention to one (the attended channel) & ignore the unattended channel. - To ensure they were paying attention, they were usually given a task called shadowing; they were required to repeat the recording of someone speaking in the attended channel. It’s hard at first but gets easier after a minute. - Shadowing performance is usually almost 100%, & when asked to report what the unattended message was about, they say they have no idea – they can’t even tell if it was a message or just random words. - One experiment, the unattended message was in another language but pronounced in an English way – only 4 of the 30 participants detected the peculiar character of the message. - Similar pattern with visual input: participants wanted a TV screen with a team of players in white shirts passing a ball back & forth, & they had to signal each time the ball changed hands. Interwoven with these players was another team wearing black, also passing a ball back & forth, whom the participants were told to ignore. They failed to notice when a person in a gorilla costume walked through the middle of the game, pausing to thump his chest before exiting. - Physical attributes of the unattended channel are heard, even though participants seem oblivious to the content (can tell if voice was male/female, high/low pitch, speaking loudly/softly, etc.) Some Unattended Inputs are Detected - One study: embedded within the unattended message, roughly a 3 of participants could hear their own name when it was spoken, but nothing else. - Words with some personal important are often (but not always) noticed. - The cocktail party effect: at a party, you tune out everything except the conversation you’re engaged in, but if someone nearby mentions a friend of yours (or something) then you find yourself listening to that conversation & momentarily oblivious to your conversation. Perceiving & the Limits on Cognitive Capacity - Proposed that you block processing of the inputs you’re not interested in.  This proposal was central for theories of attention (“bottleneck theories”) which suggested that you create a filter that shields you from potential distractors. The attended channel (the desired info) goes on to receive further processing. - Evidence suggests that filtering is done on a distractor-to-distractor basis; you are able to inhibit your response to this distractor or that distractor but these efforts are of little value if a new, unexpected distractor comes along. - Evidence also suggests you are also able to promote the processing of desired stimuli. Inattentional Blindness - Study: Participants were instructed to point their eyes at the dot, and to make judgments about the cross shown just off to the side. However, the dot itself briefly changed to another shape. If participants were not warned about this (and so were not paying attention to the dot), they routinely failed to detect this change— even though they had been pointing their eyes right at the dot the whole time! If participants were warned, though, and so alert for possible changes, then virtually all detected the change.  Perception requires work (not seeing a cyclist when driving). Conscious Perception, Unconscious Perception - Mack & Rock argue that there is no conscious perception without attention. - Experiment: participants didn’t notice that the background dots changed into a geometric illusion while they were focusing on the length of the horizontal lines in the centre. However, the dot pattern still influenced them to perceive the top horizontal line as longer even though they are both the same size. Thus the participants were completely unaware of the patten but they were still influenced by this – they perceived the pattern in some way but they did not consciously perceive it. Change Blindness  Observers’ inability to detect changes in scenes they’re looking at directly (difference between 2 pictures) - Ex. in a video of 2 women having a conversation, aspects of the scene changed each time the camera angle changed, but most observers didn’t notice. - Ex. Investigator approaches pedestrians – switches places with another person who continues the conversation when momentarily hidden by a door – about half failed to notice. Early vs. Late Selection - Early selection hypothesis: attended input is identified from the start, so the unattended receives little to no analysis, & is therefore never perceived.  Electrical brain activity shows that attended & unattended inputs are distinguishable just 80ms after a stimulus is presented – early in sensory processing.  Complex attended input = many resources required for processing = fewer resources available to processs unattended input. - Late selection hypothesis: all inputs receive relatively complete analysis; selection is done after this analysis is finished.  People are unaware of distractors but they are still influenced by them (selection after the distractors are perceived).  Relatively simple attended input = fewer resources required for processing = more resources available for unattended input. - Even neurons in the visual cortex show more responsiveness to attended inputs.  Attention can literally change what we perceive. Selective Priming - It is proposed that people can ‘prepare’ themselves for perceiving by priming the suitable detectors, & that this priming requires some effort/resources which are in limited supply.  Why don’t participants notice the shapes in the inattentional blindness study? They don’t expect any stimulus to appear, so they have no reason to prepare for any stimulus. Thus, when the stimulus appears, it falls on unprepared, unprimed, unresponsive detectors, leading to lack of perception.  Selective listening: you don’t want to hear the distractor (unattended) channel, so devoting resources to that distractor would be a waste. Therefore, the detectors needed for the distractor receive no resources & are unprimed. - Some attention is given to the unattended input when, for example, you hear your name, because these distractors are already primed because it is a stimulus you encounter often. Two Types of Priming - 1) A matter of the stimuli you’ve encountered (recently or frequently) in the past – takes no effort & requires no resources. - 2) Under your control & dependent on your expectations – deliberately priming detectors for inputs you believe are upcoming. - Experiment: participants had to say whether stimulus was same (AA) or different (AB). 3 conditions = neutral (primed with a + sign), primed (primed with the letter of the upcoming pair) or unprimed (primed with the wrong letter).  Version 1: the warning sign was a poor predictor of the upcoming stimuli (low validity) - 20% of the time when the prime matches the stimulus, the participant can’t use the prime as a basis for predicting it because it is a poor indicator of things to come; however faster reaction times (RTs) are still expected because it has still primed the relevant detectors. - Results: priming is observed even in the absence of expectations; truly stimulus- based. - Performance in the misled condition was the same as performance in the neutral condition; priming the wrong detector takes nothing away from the other detectors; which supports the notion from chap3 that the various detectors work independently of the others.  Version 2: the warning sign was a good predictor (high validity) - High validity primes produce a warm-up effect and also an expectation effect; whereas low validity primes only produce the warm-up effect. Therefore, high validity primes lead to faster RTs. Explaining the Costs & Benefits - Expectation-based priming takes longer to kick in that stimulus-based priming. - Stimulus-based priming appears to be “free” – we can prime one detector without taking away from another (low-validity condition). - Expectation-based priming does have a cost – priming the wrong detector takes something away from the other detectors. This is because expectation-based priming has a limited “budget” – getting prepared for one target makes people less prepared for other targets. This reveals the presence of a limited-capacity system. Chronometric Studies & Spatial Attention - Study: even with the simplest tasks, it pays to be prepared.  What about the trials in which participants were misled? RTs in this condition were about 12% slower than those in the neutral condition. Therefore, we’re seeing evidence of a limited-capacity system: In order to devote more attention to (say) the left position, you have to devote less attention to the right. If the stimulus then shows up on the right, you’re less prepared for it— hence the cost of being misled. Attention as a Spotlight - Attention can be compared to a beam that can “shine” anywhere in the visual field, & which marks the region of space for which you are prepared, so that the inputs within the beam are processed more efficiently. - The spotlight idea refers to movements of attention, not movements of the eyes. The benefits of attention occur prior to any eye movement, & therefore cannot be a consequence of eye movements. - Control of attention actualy depends on a network of brain sites in the frontal & parietal cortexes, which send activity to other brain sites which do the analysis of the information.  Therefore, expectations are supported by one group of brain areas & are used to modulate activity in other areas that are directly responsible for handling the input. - Activity in the parietal cortex can modulate activity in regions crucial for memory, allowing you to pay attention to remembered events.  Thus, no spotlight beam. Instead, neural mechanisms allow you to adjust your sensitivity to certain inputs. Supports the proposal that “paying attention” involves priming. Attending to Objects or Attending to Positions - Alternative to spotlight beam: we pay attention to objects rather than to positions in space. Both views capture part of the truth. - Evidence 1 (unilateral neglect syndrome): ignore all inputs from one side of the body. These symptoms seem to support a space-based account of attention (the patient seems insensitive to all objects within a spatially defined region. - However, patients with the same syndrome were much more sensitive to targets appearing within the red cirlce (because it was on the r
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