Neurophysiology of Cognition and Behavior (SOWPSB3BC25E)
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Radboud Universiteit Nijmegen (RU)
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Neurophysiology of Cognition and Behavior (SOWPSB3BC25E)
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Neurophysiology of Cognition and Behaviour
Week 1: Attention by biased competition
Attention: navigating successfully in the real world: the neural resources available in a brain with
finite processing capabilities must be efficiently directed to the aspects of this overwhelming
information load that are likely to matter most from moment to moment.
The Concept of Attention
Arousal: a global state of the brain, broadest categorization is being awake or asleep, continuum
from deep sleep and full wakefulness, people who are asleep might be less attentive, but awake
individuals can be alert (attentive), or drowsy (not attentive).
Attention: is selectively focused! Selective attention: refers to the allocation of processing resources
to the analysis of certain stimuli or aspects of the environment at the expense for other resources.
Studying selective attention:
Cocktail party effect: phenomenon in which multiple sounds simultaneously, yet a listener can
selectively focus on one voice or conversation and effectively tune the others out.
Experiment: Subjects were presented with two verbal streams simultaneously, on to each ear, and
asked to verbally shadow (immediately repeat, requires attention) one of the streams. When tested
later, they could accurately report the content of the attended stream but could only report little of
the unattended one. The main feature reported for unattended was whether the speaker was male
or female. → Unattended inputs are filtered out at low levels of perceptual processing on the basis
of very basic physical characteristics, but: → Subjects noticed when name was mentioned in
unattended stream, which indicates that at least some information in an unattended stream is being
processed up to the level of semantic meaning and not complete at lower levels.
→ Ability varies across individual, deficits in ADHD and schizophrenia
Visual Spatial Attention: briefly flashed arrays of letters on a screen and asked subjects to report the
letter appearing at a particular location. When the subject is steadily fixated their gaze on a
particular point in the visual field but directed their covert attention to another region of the field,
the stimuli presented in the attended location could be reported much better than stimuli in the rest
of the field.
→ attention improves processing but in cost of processing other stimuli
Behavioral Studies of Attention Capacity and Selection
At which level does attention occur?
Early selection: low-level gating mechanism that can filter put or attenuate irrelevant information
before the completion of sensory and perceptual analysis
Late selection: proposed that all stimuli are processed through the completion of sensory and
perceptual processing before any selection occurs
→ more basic sensory analysis
filtered out early (e.g., physical
characteristics, brainstem, and
lower sensory cortices), more
complex (like semantics,
association cortices) in later stages
,Endogenous attention: ability to voluntarily direct attention depending on one’s goals, expectations,
and/or knowledge
Exogenous attention: stimuli attracting attention automatically (reflexive attention)
Experiment!
Endogenous attention
Exogenous attention:
→ faster and shorter than endogenous
attention, effects begin after 75ms after
the cue and only lasts few 100ms
→ Inhibition of return: at longer intervals
the effect of the target validity tends to
reverse, with subjects responding more
slowly to targets in the cued condition,
not observed in endogenous attention!
May promote exploration of new,
previously unattended places or objects in
the environment by slowing the return of
recently attended ones
Neuroscience Approaches to Studying Attention
Auditory Spatial Attention – Electrophysiological studies
→ The average ERP in response to a single stimulus can be divided into three phases: (A) brainstem-
evoked responses are the small waves in first 10ms, (B) early cortical responses from 10-50ms which
include initial activity in A1, and (C) slower-frequency late waves from higher-order auditory areas,
with N1 peaking at ms.
Auditory attentional stream paradigm: Participant hear tones in both ears and is instructed to pay
attention to only one and detect when there is a deviant stimulus (which is in both ears).
→ enhanced N1 elicited for all attended stimuli (early selection, between auditory channels),
detected deviant stimulus elicited longer latency, P300 (later selection, within auditory channel).
→ Early attentional selection (between): used contrasts is to which ear to attend. Purely by attending to
your left ear a particular sound produces more current in the auditory cortex for that ear purely as a
result of top-down auditory attention, even though the sounds in both ears are the same (endogenous
attention).
→ Late attentional selection (within): contrast used is whether the sound is deviant or not (standard or
target). Late attentional selection occurs when the participant distinguishes whether the sound is deviant
or not (signature of late attentional selection).
→ No earlier attentional effect before 70ms: all earlier sensory processing is immune to attentional
influences, brainstem not involved in attentional selection
→ P20-50, early cortical responses, early attentional selection can occur at this stage of processing!
Attention can affect stimulus processing in the sensory cortices very early in the auditory input
stream, thereby providing particularly strong support for early-selection models of attention
,Neuroimaging studies: difficult to study, activity not lasting long enough to be detected by fMRI:
effects of attention were seen mainly in the auditory belt areas and not in the primary cortex
Animal studies: little research, hard to train monkeys, but single neuron activity fits with P20-50 EEG
Auditory feature processing: Does this early enhancement lead to improvements in perceptual
discriminability of stimuli in the attended stream of input relative to that in the unattended stream?
Mismatch Negativity (MMN): deviant stimuli in a stream of otherwise identical sounds produce a
negative wave peaking at about 150-200ms after stimulus onset, elicited by any auditory feature
derived form the auditory cortex
→ MMN amplitude is lower within an unattended channel relative to an attended one, but there is
still somewhat an activity, which is good in the environment to not shut off the rest completely.
→ These results indicate not only that attention can modulate the overall amplitude of early neural
responses elicited by auditory stimuli, but that this early modulation leads to a large later effect on
auditory feature analysis and thus that auditory feature analysis is indeed susceptible to attentional
influence.
Visual Spatial Attention: Electrophysiological studies
After a light flash, P1 and N1 component peaking
at 100 and 180ms. When the subject attend to a
location either in the right or left visual field for
unilaterally presented visual flash stimuli on that
side and ignoring stimuli on the other side.
Attention enhances the amplitude of the sensory
P1 and N1 component and therefore induces a
gain enhancement in the response to stimuli
occurring in an attended region of space.
→ For both endogenous and exogenous attention: This reflects an early selection mechanism,
effects particularly visible in extrastriate cortex
→ later stages: Elicited P300, similarity to auditory processing, across sensory modalities
The attentional blink and late attentional selection: In the attentional blink paradigm stimuli are
presented in a rapid stream, in which occasional target stimuli are to be detected. When one target
occurs alone, it is detected very well, when a second target follows a first target within
approximately 150-400ms, the ability to report the occurrence of the second target is reduced.
Limitations of attentional capacity at some level of the system. Late selection
Neuroimaging studies
Combined ERPs and PET scans: Attention to one visual field enhanced activity in the
contralateral visual cortex. Visual spatial attention directly enhances stimulus processing
in the specific portions of the low-level visual areas that represent the particular
attended region of space.
→ Biased competition: when multiple stimuli are presented in the visual field, areas
concerned with object recognition in the temporal lobe tend to interact competitively, with each
inhibiting activations by the others. Directing attention to one of the stimuli counteracts the
suppressive influence from nearby stimuli, and thus may help filter out distracting irrelevant
information. Attentional bias toward the one thing being attended.
→ Activity in lower levels: visual cortex
Combining electrophysiological and neuroimaging studies: fMRI does not provide timing of effects
Results show that visual spatial attention affects the sensory processing of visual stimuli not only on
low level visual cortical areas, but also early on the sensory processing sequence.
Other studies have indicated that attention can also have an effect at longer latencies on sensory
processing activity, but in the lower-level sensory cortices, which suggests:
, → Reentrant process: attention related activity returns to the same low-level sensory areas that
were initially activated in the ascending pass through the system, presumably reflecting enhanced
late processing of the stimulus information in those areas. This feedback could enable more finely
tuned analysis after some interaction with higher brain areas, especially when there is a greater
need to extract more detailed information, such as when stimuli are closely spaced.
Animal studies: monkeys were trained to attend to stimuli at one
location in the visual field and ignore stimuli at another while the
activity of cells was recorded from visual area V4 (One was effective,
one ineffective for RF). Before each trial, the monkey was cued where to
attend. When the effective stimulus was attended, the cell fired
strongly. If the ineffective sensory stimulus was attended, the cell gave
much weaker response even though the effective stimulus was still
within the RF of the cell. This suggests that neuronal responses depend
on the locus of attention within the receptive field, at least in V4
neurons.
→ When the attention was directed to a location outside the RF of the cell, the response to
the effective stimulus within the RF was NOT modulated, so the neurons in V4 fired strongly.
In later stages of processing (inferior temporal cortex), this was different: attention
modulated the neuronal responses even if the ignored stimulus was far away from the
attended one, presumably because at this level the RF are much larger.
→ Spatial attention had no effect on the width or shape of a single V4 neuron’s tuning curve,
but rather enhanced responses to all stimulus orientations
→ Spatial attention increases Contrast sensitivity: the largest increase in firing rate were in
response to contrasts in the lower and middle portions, where amplification would be more useful
Feature processing: Subjects did easy or difficult task. When subjects had only an easy task to attend
to in one spatial location (less perceptual load), more processing capacity was available for stimuli in
unattended locations, leading to fuller processing of the stimulus features of those unattended-
location stimuli. In more difficult tasks, was less processing of the sensory features of those other
stimuli. → underscore the capacity limitations of attention
Nonspatial auditory features
Pitch: important for information regarding body size, gender, emotional state, the meaning of
words, beneficial for discriminating auditory streams
→ instead of having tones on one ear or another participant hear different auditory streams of
sounds of a particular pitch. They have to attend to one and detect deviation in pitch. When
attended, a Processing negativity follows deviant sound, 100 ms, feature processing starts later than
spatial processing
→ fMRI showed that attending to a particular feature (e.g. phonetic, tonal) enhances activity in the
brain areas that normally process that feature (phonetic left, tone = emotional state right)
Nonspatial visual features
→ Like the processing negativity, selection negativity begins later than visual spatial attention
effects and does not include P1 and N1 occipital components specific for spatial attention
→ fMRI studies show that attending to a feature enhances activity in the area responsible for that
feature (MT for motion, V4 for color
STUDY! Will neurons detecting a specific feature increase their firing rate if you were attending to the
feature vs. non-attending the feature but to another one? The monkeys were fixated, and the measured
neurons RF was detecting upward motion, however this part was task irrelevant. They were constructed
to either attend to the a or b (upward or downward motion). There was more activity in the neuron when
the motion attended to was the same as for its RF, even though it was outide the neurons RF and the
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