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Hele uitgebreide uitwerking van de lectures van Neurophysiology
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Met deze samenvatting heb ik een 8 gehaald bij de eerste kans. Heel fijn om ernaast te houden tijdens het kijken van de colleges.
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NeurophysiologyWeek 1 Lecture 1
Attention and the Effects on Stimulus Processing
Difference between arousal and attention: arousal is a global state of the brain (in the broadest sense, being
awake or asleep). 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 is the allocation of
processing resources to the analysis of certain stimuli or aspects of the environment at the expense for other
resources.
▪ When someone is sitting in a park on a bench and suddenly a loud sound is played both attention and
arousal will change within the person. When someone is sitting in a park on a bench, engaged in
watching his son playing football with some friends and suddenly a loud sound is played to the right
of the field, only attention will switch (to the right side of the field) but arousal will stay the same
because the individual is already aroused by the football game he is watching.
Cocktail party effect: phenomenon in which multiple conversations and other sounds are occurring
simultaneously, yet a listener can selectively focus on one voice or conversation and effectively tune out the
others. In an experiment, subjects were presented with two verbal streams simultaneously, on to each ear,
and asked to 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.
Unattended inputs are filtered out at low levels of perceptual processing on the basis of very basic physical
characteristics but noticing when a name is mentioned in the unattended stream indicates that at least some
information in an unattended stream is being processed up to the level of semantic meaning.
Visual spatial attention: a form of visual attention that involves
directing attention to a location in space. Selective attention to a
subset of a visual scene enhances the processing of information
from the attended portion at the expense of processing
information from the rest of the scene.
In the experiment, subjects were briefly presented with an array
of letters and asked afterwards to recall the letters they had seen.
It was observed that if a subject was asked to covertly attend to a
certain area of the visual field away from fixation, then the items
in the attended portion of the letter array could be accurately
reported, whereas items in the unattended locations could not.
,Information-processing model of Broadbent (A): in this
model, an early-selection gating mechanism under top-
down control determines which information is passed on
for higher-level analysis.
Information-processing model of Treisman (B): this early-
selection model is based on attenuation and/or modulation
rather than all-or-non gating.
Recent information-processing models (C): these models
incorporated the possibility of top-down selection at early,
middle, or later stages of stimulus processing, depending
on the circumstances.
Endogenous attention is the ability to voluntarily direct attention depending on one’s goals, expectations,
and/or knowledge. Exogenous attention refers to stimuli attracting attention automatically (reflexive
attention). To determine if attention is endogenous or exogenous, you will have to look at the predictive
value of the stimuli; in endogenous the stimuli does predict something and in exogenous it doesn’t.
▪ A cat has learned that a particular sound predicts the presence of a mouse in the high grass, when the
mouse hears that particular sound, the cat engages in endogenous attention. When a cat walks
through the grass and hears a sound she has never heard before, the cat engages in exogenous
attention. The cat has not yet learned the association between the sound and the mouse, so after
hearing the sound it will not stay attentive to the sound because it has no predictive value yet.
A cuing paradigm for studying
endogenous visual spatial attention:
(A) In this paradigm, a centrally
presented instructional cue indicates
where a target will most likely be
presented (validly cued), where it will
be less likely be presented (invalidly
cued), or the cue can provide no
information either way (neutrally cued).
,(B) Typical results show the benefits and costs in the reaction time for target detection after valid and invalid
cueing, relative to the neutral cue condition. Subject typically are faster to respond to validly cued targets
than to invalidly cued ones. Relative to the neutral-cue condition, subjects respond more quickly to validly
cued targets (reflecting the benefits of attention having been directed to the location where the target occurs)
and more slowly to invalidly cued targets (reflecting the costs of attention having been directed to another
location).
Exogenously triggered (reflexive) attention:
(A) In this paradigm a brief flash is
presented in one of two possible target
locations, serving as an exogenous cue
(sound of the mouse) for a target that might
follow at that location or at the other
location. The occurrence of a target at the
cued versus uncued location is random,
with the probability at each location being 50 percent. The task of the participant is to press a button as fast
as possible indicating where the target was presented.
(B) Shortly after the exogenous cue (green-shaded time period), stimulus processing at that location is
facilitated, as indicated by faster response times to cued targets. At longer intervals (red-shaded time period),
however, there is a decrement in performance for the cued targets, known as inhibition of return.
Inhibition of return: refers to a slower reaction time in an already seen cued location in comparison to an
unseen or uncued location. At longer intervals (delay) the effect of the target validity tends to reverse, with
subjects responding more slowly to targets in the cued condition (this is not seen in endogenous attention).
▪ In the cat and mouse example: if you increase the delay between the cue and the target, the effect
will be reversed. The cat responds faster to the uncued target compared to the cued target.
▪ Inhibition of return is a good revolutionary thing to have for survival.
In visual processing, visual information enters the occipital
cortex (V1), and then visual information is processed in
secondary processing areas (yellow stream, bottom-up stimulus
processing). The blue region and arrows represent an attentional
control network, where the blue arrows carry out an attentional
control function by means of top-down neural signals that
regulate stimulus processing at various levels in the sensory and
association cortices. So, yellow is where the stimulus is
processed, and blue is where the control of processing comes from.
, ▪ The neural effects of attention on stimulus processing are seen in the yellow part, thus the sensory
areas (this processing will be different depending on if the stimulus is attended or not).
▪ Brain areas are in control of the attentional modulations of stimulus processing is seen in the
attentional control network, which lies in the anterior, parietal, and frontal cortices. The more you go
from posterior to anterior parts of the brain in the dorsal stream, the more you end up in brain areas
that are involved in attentional deployment.
Event-related potentials (ERPs): extract specific time-
locked responses from the ongoing scalp EEG (ERPs
have great temporal precision). An ERP can be broken
down in three phases:
1. (A) Brainstem evoked responses (BERs): early
latency waves (first 10ms) reflect activity evoked
in the auditory brainstem nuclei as the sound
stimulus information reaches them along the
afferent pathways.
2. (B) Midlatency responses: reflects mainly the
early evoked activity in the auditory cortex (10 –
50ms), including waves N and P.
3. (C) Late waves: longer-latency waves that
continue for several hundred milliseconds,
reflecting extended activity in the secondary and
association auditory cortices.
▪ The calculations/measurements that are needed to produce an ERP: A lot of EEG measurements are
done in response to a stimulus presentation. This stimulus has to be presented multiple times to
calculate an average ERP so that unrelated data are not seen in the ERP.
The auditory stream paradigm: the stimuli are identical in
both attention conditions; the only difference is the covert
focusing of attention toward one input channel or the
other. The participants are instructed to detect when there
is a deviant stimulus (which occurs in both ears).
▪ Early attentional selection: contrasts is to which
ear to attend. (B) An identical stimulus is
presented in both ears, but when the left ear is
attended the N1 component has a higher
amplitude compared to the amplitude of the unattended ear.
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