Chapter Three Flashcards
Representations:
properties of the world that are manifested in cognitive systems (mental) and neural systems (neural)
Single-cell recordings:
measure the responsiveness of a neuron to a given stimulus (in terms of AP/sec)
Electroencephalography (EEG):
measurements of the electrical signal generated by the brain through electrodes placed on different points on the scalp
What characteristic makes EEG methods highly useful?
changes are conducted instantaneously making it useful when measuring relative timing of cognitive events and neural activity
Event-related potentials:
The average amount of change in voltage at the scalp that is linked to the timing of a particular cognitive events
EX: stimulus, response
Reaction time:
the time taken between the onset of a stimulus/event and the production of a behavioral response (button press)
Functional imaging methods (fMRI) have better temporal/spatial resolution than temporal/spatial resolution.
spatial; temporal
Lesion methods tend to rely on measuring […] than […].
error rates; time-based processes
The AP is directly measured in the method of […].
single/multi cell recording
How can single-cell recording be obtained?
Why is it impossible to measure AP from a single neuron noninvasively?
electrode implanted intra or extracellularly
signal is too weak and the noise from other neurons is too high
Multi-cell recordings:
electrical activity (AP/sec) of many individually recorded neurons recorded at one or more electrodes
Grandmother cell:
hypothetical neuron that just responds to one particular stimulus
EX: the sight of one’s grandmother
What are the three different types of representation that may be found at the neural level?
- local: all information about a stimulus/event is carried in one of the neurons (grandmother cell)
- fully distributed: all information about a stimulus/event is carried in all the neurons of a given population
- sparse: a distributed representation in which a small proportion of the neurons carry information about a stimulus/event
Rate coding:
the informational content of a neurons may be related to the number of AP per second
given stimulus/event is associated with a change (typically increase) in the rate of neural firing
Temporal coding:
synchrony of firing may be used by a population of neurons to code the same stimulus or event
given stimulus/events is associated with greater sychronization of firing across different neurons
Both multi and single-cell recordings representation of information dependson what type of coding?
Why?
sparse distributed coding
- conserves energy
- high memory capacity
- protect against losing information if synapses or neurons die
- generalize/categorize (deja vu)
Th physiological bases of the EEG signal originates in the […] current rather than the axonal currents.
postsynaptic dendritic (passive)
In order for an electrical signal to be detectable at the scalp, what basic requirements need to be met?
Based on these requirements, what region is the most optimal space for EEG recording?
- whole population of neurons must be active in synchrony to generate a large enough electrical field
- population must be aligned in a parallel orientation so they can summate together (not cancel out)
cerebral cortex
EEG: The greater the electrical activity of neurons…
the greater the voltage change at the scalp
To gain an EEG measure one needs to compare the …
voltage between two or more different sites
What are some types of reference sites for EEG voltage comparisons?
- nasal
- mastoid bone behind ear
- average of all electrodes
Electrode placement labeling:
right side = even numbers
left side = odd numbers
midline = z
frontal = f
parietal = p
occipital = o
temporal = t
central = c
What are the limitations of ERPs?
Poor spatial resolution– don’t know the source of the signal we only know scalp distributions
- electrical signal is filtered/distorted by body tissue
- summed postsynaptic potentials; ERP loses identity of individual neurons/layers
- cannot distinguish IPSPs and EPSPs; polarity at the scalp depends on the location and the type of PSP
- inverse problem; have the output but that could be created through a variety of combinations
Incomplete measure of the brain
- ERP generated by synchronous firing of open field neurons
- ERPs are blind to close sources and asynchronous firing
- Electrical fields in sulci cancel out
- Distant and small activity will cancle out
The most common use of EEG in cognitive neuroscience is the method known as […].
ERP
How do you get an enhanced signal-to-noise ratio?
when different EEG waves are averaged relative to the presentation of a stimulus (a tone)
more trials = more observable ERP
Polarity significance in EEG recordings:
What does polarity depend on?
NONE: can’t infer which is excitation or inhibition so N and P peaks mean nothing
spatial arrangement/summation of dipoles of the neurons that are giving rise to the signal at that particular moment in time
The EEG signal tends to oscillate at different rates aka …
Alpha waves reflect oscillations in the […] range.
Beta waves reflect oscillations in the […] range.
Gamma waves reflect oscillations in the […] range.
Theta waves reflect oscillations in the […] range.
Delta waves reflect oscillations in the […] range.
frequency bands
7-14 Hz
15-30 Hz
30-100 Hz
4-7 Hz
Increases in the alpha band have been linked to […].
What specifically happens to the waves in this range?
increased attention OR filtering out of irrelevant information
the neurons become more synchronized in their electrical activity, especially at the 7-14 Hx range
Increases in the gamma band have been linked to […].
binding or grouping: a perceptual integration of parts into wholes (IMPORTANT FOR OBJECT RECOGNITION)
Mental chronometry:
study of the time-course of information processing in the human nervous system
Additive factors method:
What is the strength of this method?
general method for dividing reaction times into different stages
one could take an unknown factor (sleep deprivation, Parkinson’s, reading ability) and determine whether this has an additive effect or interactive effect
Use the additive factors method to develop the general steps for 4+2
visual recognition (2 and 4)
computing the sum (addition)
producing a response (6)
Stenberg’s experiment involved a
working memory task in which participants were given an array of one, two or four digits to hold in mind (e.g., 5, 9, 3, 2). They were then shown a single probe digit (e.g., 9) and asked to press one of two buttons (labeled “yes” and “no”) to indicate whether this item had been in the previous array.
Sternberg proposed the task could be divided into a number of separate stages:
- encoding
- comparing
- deciding
- responding
If different factors from different stages of the additive factors method were affected, this would be termed as a […].
If only one processing stage of the additive factors method were affected, this would be called […].
additive effects
interactive effect
Difference between reactive time and ERP waveform
RT is a single measure that is assumed to reflect different stages/components
ERP consists of a series of waves that vary continuously through time
ERP:
Early peaks in a task may reflect…
Later peaks…
Early– perceptual encoding
Later– comparison stage
What are some aspects of ERP waveforms that can correspond with different cognitive stages of processing?
- early vs later peaks
- amplitude of those peaks vary
- effect of a new variable on earlier or later peaks
N170:
How is this component affected?
an ERP component/deflection linked to perceiving facial structure (NP at 170 ms)
affected by perceptual changes to image
N250:
How is this component affected?
ERP component that reflects face recognition and identity processing
affected by familiarity; not affected by view changes (like N170)
SPECIFIC FACE NOT SPECIFIC IMAGE
Later, positive-going components of facial recognition/processing:
How is this component affected?
ERP component for person recognition (faces and names)
affected by both faces and names
are also sensitive to the repetition
and familiarity of specific person identities, and
the effects generalize to names as well as faces
Associative priming:
reaction times are faster to stimulus X after being presented to stimulus Y if X and Y have previously been associated together (if they tend to co-occur)
Exogenous components:
Another name for this is…
components that appear to depend on the physical properties of a stimulus (sensory, modality, size, intensity)
evoked potentials
Endogenous components:
appear to depend on properties of the task (what the participant is required to do with the stimulus)
Why is the spatial of ERP methods poor?
inverse problem
Inverse problem:
the difficulty of locating the source of electrical activity from measurements taken at the scalp
KNOWN: electrical potential at the scalp
UNKNOWN: number, location, and magnitude of the electrical sources
How could one attempt to solve the inverse problem?
dipole modeling
or use a fMRI to collect data at the same time as the EEG/ERP
Dipole modeling:
an attempt to solve the inverse problem
involves assuming how many dipoles (regions of electrical activity) contribute to the signal recorded at the scalp
ERP components: Early negatives
What are they? What can they tell us?
between period 100-300
the attention effect: a larger response to stimuli when the subject’s attention is directed to some of the stimulus features than when the subject attention is directed elsewhere.
ERP components: Mismatch negativity (MNN)
What are they? What can they tell us?
onset latency: 50 msec
peak latency: 100-200 msec
brain response to violations of a rule
Advantages of ERP technique
DIRECT MEASURE OF BRAIN
ACTIVITY
* Non-invasive
* Continuous data over time
* Excellent temporal resolution
(milliseconds)
* No response required
* Time-lock brain activity to any
stimulus or response event
* Multidimensional measures of
activity in space and time
* Easy, fast, and cheap to use
-INFERENCES IN ERP DATA-
Difference in topography implies …
different neural sources: qualitative difference
The opposite is not always true; the same distribution does not always equal the same sources because of the inverse problem
-INFERENCES IN ERP DATA-
A difference in the start of component (onset): the brain has…
detected a difference at least by that point – but maybe earlier and not
detected
-INFERENCES IN ERP DATA-
Difference in latency on the same component implies …
same process but with different time course
-INFERENCES IN ERP DATA-
Difference in amplitude implies …
increase in neural activity…but from the same or new sources unknown
-INFERENCES IN ERP DATA-
NO difference in ERP does not mean …
no difference in brain activity; it is an incomplete measure of neural activity
What is the benefit of an ECoG implant?
- removes sources of electrical interference or
filtering. - Result is cleaner signal that is better localizable than scalp EEG
ECoG is often used preoperatively to…
localize the source of epileptic seizures.
A change in ERP always means …
there was a change in neural
activity
How can an ERP change?
- time
- amplitude
- polarity
- distribution across scalp
What are the three uses of ERP as a tool:
- How does the brain respond to different stimuli?
- When in time does the brain respond to a stimulus?
- Dependent Measure as a Psychological too
