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Chapter 9: Attention and Awareness (selective attention and the limits of…
Chapter 9: Attention and Awareness
out of mind, out of sight
unilateral visual neglect- could see things outside of left visual field once things had been brought to his attention; was unable to notice/pay attention to things in left visual field
despite fact that many sources of stimulation are evoking activity in sensory system, have awareness of just small subset of them
awareness:
active thinking about or concentration on some source of stimulation
attention:
the selection of some source of sensory stimulation for increased cognitive processing
includes for use in guiding actions, sorting sensory input in memory, and increasing awareness of it
can pay attention to more than one thing at a time with divided attention
focused attention, alternatively, is being acutely aware of only one thing at a time
selective attention:
attention to some things and not to others
regardless of whether attention is divided or focused, it is always selective attention
acts of selective attention determine contents of thoughts
attention provides way to select what to be aware of, what to store in memory, and what information to use in guiding action
selective attention and the limits of awareness
dichotic listening
challenge of comprehending speech in noisy environment called cocktail party problem
dichotic listening:
listening to one message in the left ear and a different message in the right ear
asked to repeat back/shadow message in one ear as message unfolded; able to report almost nothing about conversation in other ear
didn’t notice when language changed or when message played in reverse, but did notice when tone placed message or when speaker’s gender changed
suggest that low-level sensory changes in ignored ear are noticed, but changes related to meaning aren’t
filter theory of attention:
the theory that all sensory information is registered as physical signals but that attention selects only some of those signals to be interpreted for meaning, with the rest being filtered out
only signals selected for access to ‘limited-capacity system’ interpreted for meaning
mechanism that performs the selection is attention, which serves as a filter and limited-capacity system is what permits awareness and the storage of information in memory
hypothesized filter process
sensory stimuli from desired input channel
sensory mechanisms (eyes, ears, skin, etc.)
desired information
attentional filter (based on physical features of signals)
desired information
1 more item...
other information
.
other sensory stimuli
.
however, raises question of how you hear your own name in cocktail party if not registering meaning of unattended conversations
later studies suggest that certain words have default high priority- when they occur, tend to capture attention
suggests that semantic content of ignored message processed to some degree, but unless that message has particular importance for you, content is discarded and unavailable for later recall
inattentional blindness
inattentional blindness:
failure to perceive a fully visible but unattended visual object
in experiment, participants asked to fix gaze on fixation point at center of display and that large cross would appear briefly somewhere in display and asked to judge whether vertical or horizontal line of cross was longer
in critical trial, small diamond (critical stimulus) unexpectedly appeared at fixation point at same time as large cross appeared
asked if had seen anything in display other than large cross; 60-80% indicated that they hadn’t
when told to ignore large cross and report shape/location of anything else in display, were nearly perfect, showing that small shape was easy to see and identify when attended to
shows that even when looking directly at something, likely not to see if it you’re paying attention elsewhere
attentional blink
attentional blink:
unawareness of stimuli in an attended location if the stimuli occur when we are processing something else
rapid serial visual representation (RSVP):
an experimental procedure in which visual stimuli such as letters or photos are presented very rapidly, one after the other, in fixation
view stream of letters presented rapidly at fixation that contains target letter (green letter in stream of red letters) and in 50% of trials, a subsequent probe letter (an ‘X’)
in some trials, asked if detected the probe
when participants must identify the target, detection of the probe is sharply reduced if the probe appears 2-6 letters after the target, as if participants’ ability to attend to the letter at fixation briefly ‘blinks’ while they are busy identifying the target
ability to process incoming information shuts down briefly
able to detect probe when it is right after or one after target because some significant amount of processing of the subsequent letters after the target ‘gets in’ before the attentional blink starts (before participants realizes target has been presented)
when aren’t required to identify target, highly successful at detecting the probe no matter when it appears in the stream
just as attention is limited to portion of space, it is also limited in time dimension
change blindness
another example suggests that selective attention isn’t simply matter of choice, but is unavoidable
when asked to find small difference between two pictures, suggests that don’t have detailed simultaneous awareness of everything in the two pictures
when shown two pictures in quick alternation with blank between them, often took 10-20 seconds (12 or more alternation cycles) to detect difference
typically keep attention focused on one object in scene for one alternation cycle to determine whether change involves that object
inability to immediately detect single big difference between scenes viewed in alternation indicates that aren’t simultaneously aware of everything in scene
alternating-photos task shows that this isn’t merely effect of limited visual acuity, where it’s difficult to see things in periphery because often fail to notice difference between two scenes even when eyes pointed right at critical object
even if eyes don’t move from fixation point, might be paying attention to another object or a single feature of fixated object
change blindness:
inability to quickly detect changes in complex scene
reflects limited ability to pay attention to multiple things at same time
typically fail to recognize continuity errors in movies when switch camera angles between takes and objects are in slightly different positions
don’t notice when giving directions and two white males who differ in height, hairstyle, clothing, and other aspects switch place, even though had spoken to original confederate for 10-20 seconds and looked at their face multiple times
looking at something isn’t same as seeing it, just as letting sound of conversation into ears isn’t same thing as hearing it; have to pay attention to be aware of and fully understand what eyes are pointed at or what ears take in
in any given moment, really aware of details in only very limited parts of scene
must choose which streams of information to focus on and which to ignore
attention to locations, features, and objects
attention to locations
constantly move gaze from one spatial location to another in patterns that depend a great deal on what kind of information you’re looking for
overt attention:
selectively attending to some information by moving one’s eyes
reflects changes in visual attention
covert attention:
selectively attending to some information without moving one's eyes
also changes location of attention, as when trying to see something out of corner of eye or shifting attention to another conversation while still engaging with person you’re talking to
covertly directing attention to spatial locations enhances ability to detect/recognize things in attended location and impairs perception of things in other locations
experiments in 50-60s aimed at determining what is involved in process of selecting some signals while ignoring others
when playing different messages in each ear, person will often follow the message if ears are switched and start paying attention to the message in the ear they were told to ignore
when asked to shadow list of words they had heard in one ear and then asked what they had heard in other ear, failed to notice when ignored message consisted of same set of words repeated many times and noticed about 1/3 of the time when their own name appeared in ignored message
suggests that meaning of ignored message must be processed to some extent and that when meaning is either of great personal interest or highly related to message being shadowed, message in unattended ear can ‘break through’ and enter awareness
attentional cuing:
providing a cue (e.g., an arrow or tone) about the location and timing of an upcoming stimulus
used to examine how spatial location of person’s attention affects speed with which they can become aware of something and respond to it
measured covert movements in attention with experiment where told to keep eyes fixated on fixation point while either a left or right arrow would appear, indicating that stimulus was likely to appear in indicated direction, or a plus sign, indicating that stimulus was equally as likely to appear in either direction; had to press button as soon as saw stimulus
when arrow appeared, target appeared on indicated side 80% of the time (valid cues) and on other side 20% of the time (invalid cues)
results showed that response time was much longer when target appeared on unattended side than when target appeared on attended side and that response time when neutral cross appeared was in the middle, even though stimuli are equally distant from fixation point and therefore equally visible
as if attentional spotlight is directed to the cued location and results in faster perception
question of what changes occur in the brain when attention is directed to a location
recorded activity of single neurons in area V4 (tuned to particular color and orientation) of monkey’s brain in response to presentation of two stimuli in neuron’s receptive field
one stimuli was ‘effective’ because when presented alone, evoked strong response from neuron; ‘ineffective’ stimuli evoked only weak response when presented along
trained to direct attention to one or the other stimuli when both present, while keeping gaze fixated on center point
neuron’s response depended on where monkey was attending; response stronger when monkey attended to effective stimuli than when attended to ineffective stimuli; neuron’s response was similar to what it was when attended stimulus was presented alone
as if attention could select which of the two stimuli would drive the neural response in visual system
another experiment compared response rate of V4 neuron under two conditions- when attention shifts from a location outside receptive field to location inside receptive field versus when attention shifts from inside receptive field to outside receptive field
trained to attend to blue bars when fixation dot was blue and red bars when fixation dot was red while keeping gaze fixated on fixation point
blue bar always presented within receptive field
sometimes cue would change from red to blue as bars were presented and sometimes would change from blue to red
at end of each trial, four bars would disappear, leaving one blue one and one red one, tilted in different directions, and monkey had to press button to indicate tilt of bar whose color matched that of cue
firing rate of neuron decreased when monkey told to change attention from blue bar (in receptive field) to red bar (outside receptive field) and increased when told to change attention from red bar (outside receptive field) to blue bar (in receptive field)
shows that attention affects the firing rate of neurons in V4 in response to stimuli in receptive field, probably via feedback from higher areas of brain that are involved in directing attention
studies on humans used fMRI to measure changes in brain activity as people directed attention to different spatial locations
in one experiment, kept eyes fixated at center as directed attention to rapidly changing letters/digits on either left or right side of display
if attending to stimuli on left side, letter ‘R’ would cue participant to switch attention to right side and vice versa
activity was greater in the left hemisphere when attention was directed to the right and greater in the right hemisphere when attention was directed to the left
directing attention to particular spatial location without moving eyes causes corresponding changes in brain activity
show not only that attention can be directed to different spatial locations, enhancing awareness of and other cognitive responses to stimuli that appear in those locations, but also that attention affects responses of sensory neurons with receptive fields in attended locations
attention selects which of competing stimuli will be represented for further cognitive operations
attention to features
can also direct attention to features such as color, depth, motion, and others of both visual and non visual stimuli
perhaps most distinguishing feature of voice is range of pitches over which the voice tends to vary
could attend to friend’s voice at party by attending to the range of pitches, which would generally be different from range of nearby voices
experiments shown that ability to detect very faint sound is enhanced if know beforehand what pitch the will would have and can direct our attention toward listening for a sound with that pitch
with vision, looking for object of particular color would be more efficient if guided by attention to color of object, especially if all other objects in scene were not that color
visual search:
searching for a specific target in a scene containing one, a few, or many objects
used to investigate feature-based attention
told to look through scene for object with one or more specific features; object there half the time and absent the other half of the time
feature search:
searching a display for an item that differs in just one feature from all other items in the display
find that for feature search, item ‘pops out’ and response time in determining whether it is present or not is fast regardless of number of items in display
suggests that observer can detect the unique feature by attending to the entire visual scene
conjunction search:
searching a display for an item that differs from all other items in the display by having a particular combination of two or more features
response time in determining whether object is in scene or not increases as number of items increases
suggests that observer is required to direct attention to one item at a time, sequentially, to determine whether each item contains required combination of features
together, provides evidence that binding features together required attention to the spatial location of those features, to make sure that the features are in the same location and belong to the same object
attention to features affects brain activity
in human fMRI experiment, measured brain activity in area MT, part of brain that responds to visual motion
required to keep gaze constantly focused on center of display consisting of randomly arranged stationary black dots and moving white dots
would hear word ‘white’ or ‘black’ every 20 seconds, meaning had to shift attention to either white or black dots
found that average brain activity in area MT increased after attention shifted to moving dots and decreased after attention shifted to stationary dots
change in brain activity likely due to shifts in attention to particular features (motion or rest) and not to shifts in spatial location of attention since dots always present on display and mixed together
attention to objects
usually, when move attention around scene, interested in things that are there, even if interests is in some feature of an object, and feel as if we’re taking in object as a whole
object-based attention:
attentional selection of an entire object when attention is directed to part of the object
results from experiments suggest that we do take in entire objects as move attention around
in experiment, viewed fixation dot with two vertical bars on either side
one end of one object was cued by brightening that end, which quickly returned to normal
then, target was presented (white square filling one end of one object) and participants had to push button when they detected it
quickest to detect target when appeared in cued location, because cuing drew participants’ attention to that location
next quickest to detect the target at the other end of the cued object, which suggests that attention drawn to part of the object spreads to include the entire object
suggests that we seem to automatically attend to object as a whole when attend to part of an object in a scene
behavioral and neurophysiological evidence about how attention works in three important domains- attention to spatial locations like an attentional spotlight; attention to features such as an object’s shape, color, or motion, or pitch or loudness of a sound; attention to objects as a whole
why attention is selective
the binding problem
most objects composed of many features, including color, size, shape, texture, motion, etc.
full representation of complex object requires information that is represented in the firing rates of neurons in many distinct regions of the brain
distributed representation is representation that is distributed across multiple regions of the brain- come together to represent object and all of its features
works well for scenes containing a single object since visual system knows that signals coming from the many different active regions must all relate to the features of that lone object
binding problem:
the problem faced by the visual system of perceiving which visual features belong to the same object
feature integration theory (FIT):
the theory that scene perception takes place in two stages; resolves the binding problem by proposing that attention is directed to one object at a time
preattentive stage- visual system sense all basic visual features in the scene, such as edge orientations, shapes, and colors
at this point, when features exist in unbound state, errors in binding can occur
illusory conjunctions:
erroneously perceiving objects that consist of the features present in a scene, but in the wrong combinations
focussed attention stage- as attention directed to specific locations in scene, neurons with a receptive field at each location respond only to the features of the object at that location and not to the features of ignored objects
after the focussed attention stage, an accurate representation of the objects in the scenes exists with the various object features properly bound together
FIT implies that people must selectively attend to one object at a time during conjunction search
predicts the linear increase in response times
competition for neural representation
second issue requiring selective attention has to do with fact that many neurons in visual regions of brain have receptive fields large enough to contain multiple objects/parts of objects
frequently, features of one object in neuron’s receptive field match the neuron’s preference while features of other objects don’t
competition for neural representation occurs when features that match preference produce strong response while features that don’t produce weak response
neuron’s response is not average because that wouldn’t respond to either of the features
higher in the visual hierarchy, more intense competition becomes because of larger receptive fields and more objects in them
biased competition theory:
the theory that the brain resolves the competition for neural representation by selectively attending to one object and representing the features of just that object
attention biases the competition so that only the features of the attended object are represented, as if only attended object was present
in experiment, measured receptive field of V4 neuron of monkey while presented either effective or ineffective stimulus or both
neuron responded strongly to effective stimulus and weakly to the ineffective stimulus
when both in receptive field, neuron’s response was a compromise since monkey wasn’t attending specifically to either of them
while still looking at fixation point, while monkey directed attention to one object or the other, neuron’s response was same as it would have been if just that object was in the receptive field
when person looking at cluttered scene, choose to attend to an object and all the neurons with that object in their receptive field will respond as if only that object were there
neurons throughout visual hierarchy respond to the attended object, forming distributed representation of that object
still has background awareness of gist of entire scene, but detailed awareness of other objects in scene would require redeployment of attention
attention control
three different forms of attentional control (how brain directs attention to things that are of interest to person)
top-down and bottom-up attentional control
top-down attentional control (or voluntary attentional control):
deliberately paying attention to something in order to get information needed to achieve goals
bottom-up attentional control (or stimulus-driven attentional control):
the involuntary, unavoidable capture of attention by a salient perceptual stimulus
bottom-up attentional control can be evoked by certain types of stimuli that might seem more likely to lead to top-down control
in experiment where had to find target after face on screen that was looking either right or left randomly, found target faster when it appeared on side where eyes pointed even though no more likely to appear on that side than on the other
suggests that seeing another person looking in a particular direction functions to automatically direct attention in same direction
evolved because sudden changes in environment are often accompanied by salient perceptual stimuli and might require rapid response
rapid, automatic response or ‘perceptual reflex’ bypasses relatively slow mechanisms for deliberately directing attention via top-down control
individuals with autism less able to make inferences about intentions of others, involves reduced sensitivity to where others are looking
experiment assessed difference in speed and efficiency between top-down and bottom-up attentional control
searched through display for target letters; one letter suddenly appeared (was perceptually salient)
when target was present but wasn’t abrupt onset, response time increased as number of letters to search increased
when target was abrupt-onset item, response time was fast and didn’t increase as number of letters to search increased
suggests that abrupt-onset item is frequently first item to be searched because captures attention
shows bottom-up attentional control can produce a quick response to sudden events
value-driven attentional control
value-driven attentional control:
the capture of attention by the learned reward value of a stimulus
is influenced by stimulus features that aren’t related to current goals or physical salience
value might not even be relevant in current situation
experiment where participants told to search stimulus for red or green circle and then report the orientation or bar in target; would get either 1c or 5c depending on color of circle
in test phase, told red/green was irrelevant to task and had to search for other colors, no reward
average response time to stimuli with high-value distractor was significantly longer than to stimuli with low-value distractor, and stimuli with neutral distractors produced shortest average response time
suggested that high-value distractors tended to capture participants’ attention, delaying search for and response to target, even though valuable feature of distractor (color) was irrelevant to goal in current situation and was no more salient than other colors
value-driven attentional control evolved to make us more likely to notice objects that are important to us
sources of attentional control in the brain
two areas in brain thought to be source of signals that control attention- posterior parietal cortex (PPC) and area in frontal cortex called frontal eye field (FEF)
evidence for involvement of PPC comes from patients who suffer stroke and damage to right RRP, resulting in difficulty attending to objects in left visual field
unilateral visual neglect:
a condition in which a person has difficulty attending to stimuli in one hand of the visual field (almost always the left half), as a result of damage to the contralateral posterior parietal cortex
is still possible to get them to see sufficiently salient visual stimuli there, suggesting that attention, not vision, is the issue
research on monkeys has shown that activity in many PPC neurons is correlated with where monkey is attending
four tasks- fixation task, saccade task, reach task, peripheral attention task
in fixation task, continued to fixate on center when stimulus appeared and ignored it, waited for fixation point to dim; PPC neuron continued to fire at baseline rate
in saccade task, required to shift visual attention toward stimulus; PPC neuron’s firing rate increased soon after stimulus appeared before eye movement occurred, when attention was switched
in reach task, stimulus was cue to make hand movement to stimulus while maintaining gaze on fixation point; firing rate increased soon after stimulus appeared, before hand movement occurred, when attention was shifted
in peripheral attention task, stimulus was cue for monkey to wait for stimulus to dim without changing direction of gaze and wait for stimulus to dim; firing rate increased with shift of attention
FEF involved in control of eye movements, also plays role in controlling shifts of attention without eye movements
with reduced FEF stimulation, monkey could detect dimmer spot of light in response field than it could without FEF stimulation, presumably because the stimulation had directed attention there
awareness and the neural correlates of consciousness
'the hard problem’ of consciousness is determining how activities of physical things (like neurons) produce conscious, subjective experiences like the awareness of objects
involves ‘first-person data’ that cannot be observed by others and that have been difficult/impossible to address scientifically
neural correlates of consciousness (NCCs):
correspondences between neural activity and conscious awareness
goal is to find brain activity that is correlated with conscious experience and how it functions differently from brain activity that is not correlated with consciousness
two different approaches to this
first focusses on situations in which visual awareness fluctuates while visual stimulus and retinal image do not change; brain activities that fluctuate systematically with fluctuations in awareness are candidates for NCCs
other approach focuses on people with brain damage who lack aspects of conscious awareness
seeking the NCCs in perceptual bistability
perceptual bistability:
a phenomenon in which an unchanging visual stimulus leads to repeated alternation between two different perceptual experiences
examples include many different perceptual illusions
retinal image remains constant, but conscious experience changes over time
when look at illusion, activity in some parts of visual system corresponds to unchanging retinal image, while activity in other parts of visual system correspond to perceptual experience (activity changes when perceptual experience flips from one form to the other)
binocular rivalry:
a phenomenon in which two different images presented to the two eyes result in perceptual bistability
don’t see blending of images, but images alternate every few seconds on regular basis; produce perceptual bistability
when switching between seeing house and face, activity in FFA and PPA alternates and is more like observer’s experience than like the stimulus
theories about what is required in addition to activation of visual areas to create conscious visual awareness
one possibility is involvement of areas in posterior parietal cortex that can direct attention to visual objects
supported by fact that damage to posterior parietal cortex can result in visual neglect
another proposal is that conscious perceptual experience requires a closed loop of neural activity that begins with stimulus-driven activity in lower-level visual areas, which leads feed-forward sweep of activity into higher-level visual areas, followed by a feedback
another idea is that synchronized neural firing rates within and across many distinct brain regions may be key property of conscious awareness
what blindsight reveals about awareness
when V1 is destroyed, report that they can see nothing; evidence to suggest that V1 is necessary for conscious vision
however, respond in certain ways to presence of light
DB had right V1 removed, couldn’t see anything in left visual field, but could point to spots of light in left visual field when required to
blindsight:
the ability to point to and sometimes discriminate visual stimuli without any conscious awareness of them
suggests that area V1 is necessary for awareness, but that other aspects of vision, including the guidance of reaching movements, do not require functional area V1
TN was completely blind but had emotional responses when shown faces depicting emotions and could navigate down hallway with obstacles
good evidence that residual vision in blindsight demonstrated by DB and TN is based on signals that pass from retina to superior colliculus, through thalamus, on to visual cortex
cannot provide conscious vision, but provides sufficient visual information to support visually guided action and sometimes categorization of emotional charged objects