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Lecture notes (extensive) Cognitive neuroscience
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Summary Principles of Cognitive Neuroscience for course UU Cognitive Neuroscience (200300074)
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Samenvatting Principles of Cognitive Neuroscience hoofdstuk 8 t/m 15 (200300074)
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PRINCIPLES OF COGNITIVE NEUROSCIENCE, PURVESChapter 6: Attention and its effects on stimulus processing
Neural arousal describes a global state of the brain. The broadest categorization of arousal is
whether an individual is awake or asleep a continuum whose extremes are deep sleep and
full wakefulness.
A key distinction between arousal and attention is that attention can be, and typically is,
selectively focused. Selective attention refers to the allocation of processing resources to the
analysis of certain stimuli of aspects of the environment, generally at the expense of resources
allocated to other concurrent stimuli or aspects.
Cocktail party effect a listener can selectively focus on one voice or conversation and
effectively tune out other simultaneously occurring ones.
A visual example is visual spatial attention selective attention to a subset of a visual scene
enhances the processing of information from the attended proportion at the expense of
processing information from the rest of the scene.
Covert attention is moving your attention to a particular point of the visual field without
moving your eyes.
Overt attention is moving your attention to a visual stimulus of location of interest with
explicitly moving your eye gaze towards it.
Models of early attentional selection postulate that there is a low-level gating mechanism that
can filter out or attenuate irrelevant information before the completion of sensory and
perceptual analysis.
Models of late attentional selection propose that all stimuli are processed through the
completion of sensory and perceptual processing before any selection occurs.
Anne Treisman’s theory of attentional selection proposes an early-stage gate that is simply
open or closed to be a more adaptable early-filtering system that could attenuate the inputs
from concurrent sensory channels in a flexible manner. In this model, some unattended
semantic information reaches higher levels, although it might be substantially attenuated. In
an unattended channel, only highly salient information would exceed the threshold to be
selected, reach conscious awareness, and be reportable by the individual.
Endogenous attention entails voluntary attention. Exogenous attention entails involuntary
attention. Although we voluntary direct attention to events that interest us because of
behavioral goals and other intrinsic factors, it is more often the case that stimuli arising from
the environment attract our attention involuntarily. However, we are always attending to
something (externally or internally) while we are awake, and all manner of stimulus
characteristics and combinations can determine what attracts our attention at any given
moment.
Endogenous and exogenous cuing have important functional differences:
- In endogenous cuing information about the likelihood that the target stimulus will
occur in the cued location is provided by prior knowledge.
- Exogenous attention is not driven by any explicit information about a likely target
location.
, - Time courses also differ between endogenous (target 300ms after cue) and exogenous
(target 75ms after cue) cuing.
At longer intervals the effect of the target validity tends to reverse with subjects actually
responding somewhat more slowly to targets in the cued location inhibition of return. This
is NOT observed with endogenous cuing!
The modulatory effects on stimulus processing presumably underlie the effects of attention on
performance observed in behavioral studies.
Some higher-level brain areas are involved in attentional control, particularly relatively
specific regions in the frontal and parietal cortices. This network of regions appears to carry
out this attentional control function by means of top-down neural signals that regulate
stimulus processing at various levels in the sensory and association cortices.
ERP = event related potentials.
BER = brainstem evoked responses
All the earlier sensory processing, including early cortical processing from 20 to 70 ms, is
immune to attentional influence.
High-resolution fMRI scans have shown that attention tends to modulate activity in specific
regions of the auditory cortex auditory belt areas.
The mismatch negativity (MMN) is an ERP component that is elicited by deviations in any
basic auditory feature. The MMN becomes larger as the feature deviation increases.
For auditory stimulus first ERP = N1, for visual stimulus first ERP = P1.
When multiple stimuli are presented simultaneously in the visual field, their cortical
representations in the areas concerned with object recognition in the temporal lobe tend to
interact competitively, with each inhibiting activations by the others. biased competition
P1 attention effect originates in the dorsal contralateral occipital cortex, thus following the
retinotopic organization of the visual sensory pathways.
Sensory neurons are typically rather selective about the stimuli to which they respond. Certain
stimuli are especially effective at activating a visual neuron when they fall within its receptive
field, whereas other stimuli without that feature are rather ineffective.
Spatial attention increases contrast sensitivity attention increases the likelihood of eliciting
a neuronal response near the contrast threshold level.
Studies have shown that behavioral responses are faster when there is strong gamma-band
synchronization in the neurons activated by the relevant stimulus, and slower when tehre is
strong gamma-band synchronization among the neurons sensitive to distracters, suggesting
that these neural oscillatory effects are related to successful selection of the relevant stimulus.
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