He claimed that brain activity that is observed through the use of EEG can change in a consistent, reliable and recognizable fashion when the state of the patient changes, such as going from relaxation to alertness, sleep, lack of oxygen Bronzino This breakthrough gave rise for the research of the years to come and the varied applications of EEG use today.
Infant Eeg And Event Related Potentials (Studies In Developmental Psychology)
They are excitable cells with intrinsic electrical properties, and their activity results in magnetic as well as electrical fields, which can then be recorded with the use of recording electrodes. The EEG is the recording of the summed electrical activity of populations of neurons called pyramidal cells, measured with the use of electrodes placed on the scalp and graphed over time.
It is an alternating current that fluctuates from positive to negative depending on a number of factors, including changes in the permeability of the cell membrane that are induced by excitatory or inhibitory inputs from other neurons. There are two main types of neuronal activity: action potentials and postsynaptic potentials.
Action potentials are the result of the very rapid depolarization of a neuron mediated mainly by changes in permeability of the membrane to sodium and potassium ions. They occur when the cell depolarizes to a certain degree from its negative resting state potential. Postsynaptic potentials are mediated by a number of neurotransmitter systems and, as a result of synaptic activation, generally entail slower changes in membrane potentials Lopes da Silva They are voltages produced when the neurotransmitters bind to the receptors on the membrane of the postsynaptic cell, making ion channels open or close.
Reliably, EEG can only record postsynaptic potentials. Due to action potentials being very rapid and brief, in addition to having to travel down the axon at a fixed rate, the electrodes placed on the scalp simply cannot detect them. The extra-cellular electrical charge, positive or negative, is what is measured with electrodes placed on the scalp. Pyramidal cells are like little batteries in that they have polarity—if one end of the dendrite is positive, the other is negative. Whether the charge outside the dendrite at the top of a pyramidal cell is positive or negative depends on two factors; first, whether an inhibitory or excitatory stimulus has come to the synaptic junction from the axon of another cell and, second, whether that synapse is proximal or distal to the cell body.
The EEG electrode on the scalp will record a negative extracellular potential if the same thing is happening at the same time to a large number of pyramidal cells in the same macro-column of cells that lies below the electrode. The EEG thus represents the algebraic sum of excitatory and inhibitory postsynaptic potentials. It is used in medicine, where monitoring brain activity or the lack thereof is useful in determining brain death in patients, areas of damage following a stroke or head trauma, epileptic activity, sleep disorders, and many others.
In other research, it is useful in investigating various cognitive functions, such as memory or attention; it is also used in language and clinical research; for example, studies that investigate EEG patterns in individuals with aphasia. For decades, EEG recording was of great use in research and clinical settings. However, it is very difficult, if not impossible, to use the raw, continuous recording to examine the specific neural activity as a function of certain cognitive processes.
Event-related brain potentials are small parts of the continuous EEG recording, which are evoked in response to stimuli, such as viewing of pictures or words on the computer screen. In cognitive neuroscience experiments, it is not very informative to just use a continuous EEG recording. If we are interested in, for example, how the brain deals with language comprehension or production, we need the recording to reflect the modulation of brain activity by that particular task, in a precise moment in time.
ERPs are obtained by time-locking the stimuli so that we know at exactly which point in time the stimuli were presented and then we analyze the brain response to a particular stimulus, such as a sound, word, picture, and so on. ERPs are used in a range of psychological experiments that aim to investigate various aspects of cognitive processes, such as language comprehension and production, memory, attention, amongst many others. Therefore, they need to be singled out from the continuous recording by creating an average of recording periods, known as epochs, which are time-locked to repeated presentations of the same stimulus.
The spontaneous EEG fluctuations, unrelated to stimulus presentation, are averaged out, resulting in the ERP wave, which reflects only the activity persistently related to the time-locked presentation of stimuli.
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Therefore, it can be said that the ERPs mirror the neuronal activity evoked by the repeated presentation of a stimulus. Below is an example of an experimental setting used in ERP studies Fig. The participant is presented, in this case, with a visual stimulus a picture on a computer screen. Each time it appears, it evokes a response by the brain, which is continuously recorded on the computer.
This recording is then averaged, and individual ERPs, time-locked to the stimulus that was repeatedly presented, get extracted.
Infant EEG and Event-Related Potentials - Google Livres
EEG signal is obtained by recording the electrical activity, which is produced by the brain with the use of electrodes set at different sites on scalp see Fig. The EEG measures the difference in electrical potential between two sites usually termed active and reference measured over time.
The EEG recording can be visually inspected for eye-blinks as these are distributed across the scalp but have the most power in the frontal region, and inverse potentials are often found over the parietal and occipital sites. The point of extracting and analyzing ERP components from the continuous data in research is to average the activity over a number of trials in each condition. Only the activity that is recurrent and time-locked will not be cancelled out and therefore has some meaning.
The output which is obtained, resembles a wave, with a number of positive and negative peaks. Negative going waves are associated with activation, whereas positive going waves with inhibition. Medical experts, such as neurologists, usually read EEG with negative up and positive down. There are many known ERP components involved in language research. Some of the most commonly studied ERP components in language research. Solid line represents the basic perceptual components in an experiment involving any visual stimuli, such as words or pictures. Two dashed lines represent additional components, which are elicited in certain experimental designs.
Some, especially the early components P, N, P are generally linked with basic, low-level perception and are thought to be automatic in nature. This means, that as long as a perceptual stimulus such as a word or a picture is presented, they should be elicited. This distinction of early automatic and late more conscious components is made just to illustrate the general idea of ERP components. This generalization may not be valid in all cases, and the functional significance of each peak is often task-dependent and the experimental paradigm should always be considered.
N is one of the best and most studied language components. It was first reported by Kutas and Hillyard It was discovered by accident, in a modified experiment aimed at eliciting a P3b response for language materials Kutas and Hillyard As a result, a large negativity was elicited—largest for semantically anomalous sentences, but present also for those that had a strange, although theoretically possible, ending.
The N is found in a number of different experimental paradigms. Firstly, it has been well documented in lexical priming paradigms. The N effect created by the different waves of the congruent—incongruent stimuli is found when the target word is unrelated for example, semantically or categorically to the proceeding word prime. The unrelated pairs induce larger N amplitudes as opposed to the related ones. Secondly, it has been found in auditory word presentation Bentin et al. In those experiments, the N appears slightly earlier than in the case of visual word presentation but only in natural speech; when presented at a fixed rate, there is no shift in timing and lasts longer.
It also has a more frontal topography, less concentrated on the right Holcomb and Anderson It is important to note that the N is not elicited to just any unexpected language manipulations. The N effect is not elicited as a response to just any violation, linguistic or not, but rather is very closely linked with the processing of meaning.
It is especially powerful in language studies, however its application goes beyond that Kutas and Federmeier Kutas and Federmeier point out that out of a range of different studies, two main streams of findings are prevalent. Firstly, there is a disparity between the behavioral outcomes reaction times and the ERPs. That is, only rarely do those two behave in a similar pattern. This is perhaps not surprising given that with behavioral measures such as RTs, a number of cognitive processes take place and get consolidated by the time the individual makes a response; whereas with the ERPs, the components of interest reflect only a specific fraction of the whole process.
Secondly, the results obtained through the ERP analysis often fail to fully support an existing theory, thus supporting different elements of various theoretical approaches. The N has been reported across different modalities, such as speech production Strijkers and Costa sign language Kutas et al. However, it is important to mention that topographies of the N distributions can vary in each of those contexts Kutas and Federmeier That is, different types of stimuli can elicit the Ns, but those, although they have many broad similarities such as waveshape and timecourse , depend on the type of stimuli used and vary in terms of the specifics especially when it comes to topography.
And so, for example, written words elicit the N which is strongest in centro-parietal region, whereas pictures are concentrated in the fronto-central regions. Even though the N has been found in studies using sounds, the N effect does not reliably appear in classic music experiments. Instead, those consistently elicit a P3b response Besson and Macar Looking at the wide range of studies that incorporate the N as a measurement, it is difficult not to conclude that our unique ability to see the meaning in the world around us, to which the N is susceptible, is underpinned by a number of cognitive processes, such as attention, memory, language, perception, amongst many others.
The N therefore seems to be a very reliable and solid component with which we can study processes directly linked to semantic integration. It is an index of processing syntactically incorrect or non-preferred sentences Osterhout and Holcomb ; Hagoort et al. Osterhout and colleagues argue that the P component varies with the degree to which a syntactic continuation of a sentence is expected.
That is, grammatically incorrect continuations result in a larger P than those that are grammatical but non- preferred. It has also been found to be sensitive to continuations which are more difficult to process even though they are grammatically correct and preferred, compared to a control condition Kaan et al. Additionally, recently the P has been linked with monitoring and re-evaluation processes Kolk et al. In addition to syntax, the P has been found to be elicited in some situations outside of the language context, such as violations in music Besson and Macar ; Patel et al.
This implies that the P component is sensitive to a violation of any expected structure, whether linguistic or not.
Infant EEG and Event-Related Potentials
Some investigators took advantage of the fact that some syntactic violations can impact semantics, and investigated the processing of less clear-cut psycholinguistic aspects, such as the gender agreement between a pronoun her and its antecedent the boy. The results of such experiments clearly show that similar violations only modulate the P and possibly LAN rather than the N, suggesting that they were perceived as syntactic rather than lexico-semantic Osterhout and Mobley Another component, known to also index syntactic processing, is the left-anterior negativity LAN.
However, this location has not been found to be consistent across studies Hagoort et al. It is elicited by grammatical violations Kutas and Hillyard ; Friederici et al.
The ELAN has been implicated in automatic processing of phrase structure information and is elicited when phrase structure or word category is violated, such as when a passive participle not a noun follows a determiner for example, the stolen car Neville et al. The later component, LAN, has been initially implied by Friederici and colleagues to be elicited by problems with morpho-syntactic agreement process, but later this interpretation has been questioned. Hagoort and colleagues elicited it for phrase structure violations, and Deutsch and Bentin found it to be an early index for agreement violations.
There is a debate about the language specificity of the LAN, with some researchers claiming that it reflects processes specific to syntax, whilst others argue that it is a more general index of working memory load Kluender and Kutas a , b ; Coulson et al. In the literature, it is common to find E LAN component s followed by the P, with the P thought to reflect post-hoc integration of various streams of information and the repair of anomalies involving sentence structure, and possible semantic inconsistencies. This component reflects auditory deviance, and therefore is used in speech perception research.
It is a negative deflection, peaking around —ms after stimulus onset Luck MMN is observed if the difference between the standards and deviants has been registered. It can also be elicited when listening to music, watching a movie, reading a book, or sleeping, and individuals do not have to engage in a specific activity. MMN is believed to be a result of an automatic process, which compares actively incoming stimuli sounds to a sensory memory trace of previous sounds Luck MMN has been used extensively in first language acquisition research with neonates and infants.
Typically, behavioral research on speech perception in babies focuses on preferential looking or sucking rate Vouloumanos et al. However, such methods are sometimes difficult to quantify and their interpretation has, at times, caused controversy Cheour et al. Research involving ERPs has replicated those findings. Therefore, a conclusion can be drawn that infants become less sensitive to their non-native phonemic distinction as they grow. This example illustrates how ERPs can be used in language research with infants. ERPs, because of their good temporal resolution, are useful in language research because language processing happens at a very fast pace.
Only a method with an excellent temporal resolution can provide some insight into how language processing unfolds over time. ERPs are particularly useful when working with clinical populations, such as individuals with aphasia, or infants and children. It is a technique that enables researchers to present the stimuli in spoken form, rather than in writing. Additionally, participants are not required to perform an extra task, again making it particularly useful when testing special populations. For example, in studies involving language comprehension, it is possible to assess the processing of a particular word, which might appear in the middle of the sentence.
In classic behavioral experiments, it is necessary to wait until the sentence is fully presented for participants to make a response, thus relying on their memory. By that time, a number of cognitive processes are involved and it is not possible to accurately determine their effect. In experiments where an overt response by participants is needed, it is possible to establish which stage of processing is affected by a particular experimental manipulation, from the stimulus presentation to the response. This technique allows for the collection of continuous data, with very good temporal resolution.
The ERPs are multidimensional, allowing researchers to draw conclusions about the type of processes involved and their relationship.
An example might include studies involving the RTs and self-paced reading. In those cases, we do not know why people might struggle with reading, whereas with the ERPs we can say whether they are struggling with, for example, the semantics or syntax, as those are different components responsible for different processes and they are easily distinguishable in the ERPs. Another advantage is that the effects can be seen almost immediately upon presenting participants with a particular, for example semantic, manipulation. Additionally, every single stimulus, not just targets, can be time locked in ERP research, thus providing not only instantaneous, but also continuous look at language processing.
Finally, the cost of ERPs is important. ERPs are rather inexpensive, compared to other techniques. One of the main drawbacks of EEG research is the number of trials needed in an experiment. It is essential to have a large number of stimuli in each condition presented to participants, usually at least 40, because an individual ERP signal is such a small part of the continuous EEG recording that we need a larger sample size in a number of participants for meaningful interpretations.
The exact number depends on a number of things, but typically in sentence processing studies involving 20 participants, a minimum of 40 trials is needed in each condition Kaan This in itself can create a number of further problems. Firstly, the time it takes to prepare the stimuli. Stimuli used in experiments have to be closely matched on a number of characteristics, such as word length, familiarity, imageability, amongst many others.
Creating a set of such stimuli will take time, especially given that it is advisable that no stimulus is presented more than once to the same participant. Instead, different sets of items are created, and these are counterbalanced across participants to ensure that all versions of the stimuli are presented the same amount of time throughout the experiment, but no participant is presented with the same version of a stimulus more than once.
It can be very time consuming, especially in experiments that have a number of different conditions. Kaan suggests that in a study with four different conditions, it can take over a year to prepare a well-matched set of stimuli. Secondly, the large number of trials means longer experiments, especially if more conditions are needed, and that leads to tired participants. This in turn leads to a number of difficulties, such as possible alpha waves, participants paying less attention to the task, poor concentration, employing different processing and coping strategies, more missed trials, and so on.
It is important to remember that poor quality data leads to more noise, which in turn leads to more trials that might need to be rejected. Another important aspect is the human factor. Participants can often get tired and fed-up with long, monotonous studies. That is why frequent breaks are advisable.
Thirdly, a large number of trials often lead to more artefacts and more trials that will have to be removed. Eye blinks, muscle movements, accidental head turns, even swallowing can create artefacts which will affect the ERPs. A mathematical method, such as that proposed by Gratton and colleagues can be applied to the data in order to correct for the distortion of eye blinks, which can be especially useful in special populations, where specific instructions often cannot be given. However, using such method also has some drawbacks Luck A large number of trials make it impractical for the ERPs to be used in certain experiments, such as those in which each participant can only receive one trial in each condition Luck Another possible disadvantage of using ERPs is the poor spatial resolution.
ERPs show a good temporal resolution, but it is difficult to say where in the brain the activity occurs. Poor spatial resolution could be a result of limited spatial sampling or contamination of the reference electrode. Furthermore, ERPs only provide information about surface cortical sites, whereas other neuroimaging techniques, such as MRI, can go deeper in the cortex, or even subcortical, when looking at the activation patterns.
In sentence processing experiments involving visual presentation of stimuli, it is not advisable to present the whole sentence on the screen at once because of the eye movements. Also, because it would not be possible to time lock the ERPs to our target stimuli, sentences are usually presented on a word-by-word basis. This is different from typical reading and can therefore add some load to working memory and may introduce a confound Kaan However, results from experiments investigating natural speech are comparable with those using visual presentation of stimuli Gratton et al.
In comparison with classic behavioral studies, the interpretation of ERPs is less clear and requires much more inferences. However, in ERPs when peak latency is later in condition 1 in comparison to condition 2, it is difficult to draw a conclusion without making many assumptions and inferences Luck Despite those possible limitations, using ERPs in language research has proven to be popular and valuable and has added a great depth of knowledge to how language is processed in the human brain in real time.
Although not without some limitations, EEG has been successfully used in cognitive psychology research. What are VitalSource eBooks? For Instructors Request Inspection Copy. Infancy is a time of rapid growth, when brain plasticity is at a maximum. Event-related potentials ERPs are one of the few methods that can easily and safely be used to study this process, and have led to exciting discoveries about human brain functioning and the neural basis of cognition.
Over recent years, there has been a massive rise in the level of interest in ERPs and this book considers the advantages which they offer to researchers and clinicians. In particular, it looks at the benefits of this form of neuroimaging as a non-invasive tool for detecting impairments in brain and cognitive development very early in life. The potential use of ERPs for clinical settings is also explored in detail.
The contributions are all from eminent researchers in the field and represent the latest thought on the topic. Infant EEG and Event-Related Potentials explains the basics of event-related potentials for those less familiar with the procedures and terminology, as well as offering a valuable handbook of the latest theories and empirical findings for those working in the field.
This will be a valuable source for those interested in developmental psychology and neuropsychology, and for clinicians interested in application of ERPs. Scott, C. Johnson, H. Molfese, V. Molfese, N. Marshall, N. Stroganova, E. Csibra, M. Cownie, Glossary of Terms. She obtained her PhD in child psychology and neuroscience from the University of Minnesota in Her current research focuses on understanding the roles of brain development and life experience in normal and atypical development of memory and of perception of social information.
I anticipate that it will assume the reputation as the principal reference for this growing discipline. We provide complimentary e-inspection copies of primary textbooks to instructors considering our books for course adoption. Most VitalSource eBooks are available in a reflowable EPUB format which allows you to resize text to suit you and enables other accessibility features.