The P600 is an
event-related potential
An event-related potential (ERP) is the measured brain response that is the direct result of a specific sense, sensory, cognition, cognitive, or motor system, motor event. More formally, it is any stereotyped electrophysiology, electrophysiologi ...
(ERP) component, or peak in electrical brain activity measured by
electroencephalography
Electroencephalography (EEG)
is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignal, bio signals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in ...
(EEG). It is a language-relevant ERP component and is thought to be elicited by hearing or reading
grammatical errors and other
syntactic anomalies. Therefore, it is a common topic of study in
neurolinguistic experiments investigating
sentence processing in the human brain.
The P600 can be elicited in both visual (reading) and auditory (listening) experiments, and is characterized as a positive-going deflection with an onset around 500 milliseconds after the stimulus that elicits it; it often reaches its peak around 600 milliseconds after presentation of the stimulus (hence its name), and lasts several hundred milliseconds.
[Different authors give slightly different time periods for the P600; for example, claim it may start as early as 400 milliseconds, and describes it as occurring "between 600–1000 ms.] In other words, in the EEG waveform it is a large peak in the positive direction, which starts around 500 milliseconds after the subject sees or hears a stimulus. It is typically thought of as appearing mostly on centro-
parietal electrodes (i.e., over the posterior part of the center of the scalp), but frontal P600s have also been observed in several studies.
In EEG, however, this distribution at the scalp does not mean the P600 is coming from that part of the brain; a 2007 study using
magnetoencephalography
Magnetoencephalography (MEG) is a functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electric current, electrical currents occurring naturally in the human brain, brain, using very sensitive magn ...
(MEG) speculates that the generators of the P600 are in the posterior
temporal lobe, behind
Wernicke's area.
The P600 was first reported by Lee Osterhout and Phillip Holcomb in 1992.
[ It is also sometimes called the syntactic positive shift (SPS), since it has a positive polarity and is usually elicited by syntactic phenomena.]
Elicitation
The P600 was originally considered a "syntactic" ERP component, as it is elicited by several types of syntactic phenomena, including ungrammatical stimuli, garden-path sentences that require reanalysis, complex sentences with a large number of thematic roles, and the processing of filler-gap dependencies (such as wh-words that appear at the beginning of a sentence in English but are actually interpreted somewhere else).
;Grammatical errors
A P600 may be elicited by several kinds of grammatical errors in sentences, such as problems in agreement, such as "the child *''throw'' the toy".[ In addition to this sort of subject-verb disagreement, P600s have also been elicited by disagreements in tense, ]gender
Gender is the range of social, psychological, cultural, and behavioral aspects of being a man (or boy), woman (or girl), or third gender. Although gender often corresponds to sex, a transgender person may identify with a gender other tha ...
, number
A number is a mathematical object used to count, measure, and label. The most basic examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with number words. More universally, individual numbers can ...
, and case, as well as phrase structure violations.[ A 2009 study has suggested that these errors elicit stronger P600s than the other syntactic stimuli that have been implicated.]
;Garden paths
P600s are also known to occur when a sentence contains no outright grammatical error, but must be parsed in a different way than the reader originally expects. These sentences are known as "garden path" sentences, because the reader follows one interpretation of the sentence only to realize later that this interpretation was wrong and he must backtrack to understand the sentence. For example, found P600s elicited by the word ''to'' in sentences such as The broker persuaded to sell the stock was tall.
In sentences such as this, the preferred reading is to interpret "persuaded" as the main verb of the sentence (i.e., "the broker persuaded me"), and upon seeing the word ''to'' the reader has to re-analyze the sentence to mean something more like "the broker that was persuaded to sell the stock, he was tall".[
;Syntactic errors in music
P600s are also elicited by errors in musical harmony, such as when a chord is played out of key with the rest of a musical phrase. This implies that P600s are not "language-specific," but "can be elicited in nonlinguistic (but rule-governed) sequences."]
;Dependencies and complexity
Some studies have found a P600 elicited by words where there is no grammatical error and no "garden path" (i.e., where the word is exactly what the reader would expect), but when the sentence is complex because there are a number of noun phrase
A noun phrase – or NP or nominal (phrase) – is a phrase that usually has a noun or pronoun as its head, and has the same grammatical functions as a noun. Noun phrases are very common cross-linguistically, and they may be the most frequently ...
s active. This has most often been the case when the reader has to "re-activate" a word that appeared earlier in the sentence. For example, in a sentence like "Who did you imitate?", the word ''who'' appears in the beginning of the sentence but is actually the direct object of ''imitate'', and must be interpreted in that way (i.e., as "you imitated who?"); several studies have found that after the reader sees the word ''imitate'' he or she has a P600 response, possibly as a result of re-activating ''who''. These sorts of P600s get stronger as the number of noun phrases active in the sentences increases, suggesting that the P600 generator is sensitive to the level of complexity in a sentence.
;Semantic attraction
demonstrated a so-called "semantic P600" in sentences that are grammatically correct but semantically anomalous, and in which syntactic reanalysis is more appealing than semantic reanalysis. For example, a P600 may be elicited in the following sentence: The hearty meal was devouring the kids.
This suggests that the reader would rather interpret the sentence as containing a morphosyntactic error (saying "devour''ing''" instead of "devour''ed by''") rather than a semantic one (meals can't devour kids, but can be devoured by them). The interpretation of "semantic P600s" has attracted considerable attention and controversy in the literature.
Interpretations
There are several theories about what computational processes the P600 may be triggered by. Because it often happens in response to grammatical violations or garden path sentences, one theory is that the P600 reflects processes of ''revision'' (i.e., trying to "rescue" the interpretation of a sentence that can't be processed normally because of structural errors) and ''reanalysis'' (i.e., trying to rearrange the structure of a sentence that has been interpreted incorrectly because of a garden path). On the other hand, other models suggest that the P600 may not reflect these processes in particular, but just the amount of time and effort in general it takes to build up coherent structure in a sentence, or the general processes of creating or destroying syntactic structure (not specifically because of repair). Another proposal is that the P600 does not necessarily reflect any linguistic processes per se, but is similar to the P300 in that it is triggered when a subject encounters "improbable" stimuli—since ungrammatical sentences are relatively rare in natural speech, a P600 may not be a linguistic response but simply an effect of the subject's "surprise" upon encountering an unexpected stimulus. Another account is that the P600 reflects error/surprisal propagation due to learning processes that take place during linguistic adaptation and this account has been implemented in a connectionist model that explains several P600/N400 results.
See also
* Bereitschaftspotential
In neurology, the Bereitschaftspotential or BP (German language, German for "readiness potential"), also called the pre-motor potential or readiness potential (RP), is a measure of activity in the motor cortex and supplementary motor area of the b ...
* C1 and P1
* Contingent negative variation The contingent negative variation (CNV) is a negative slow surface potential, as measured by electroencephalography (EEG), that occurs during the period between a warning stimulus or signal and an imperative ("go") stimulus. The CNV was one of the ...
* Difference due to memory Difference due to memory (Dm) indexes differences in neural activity during the study phase of an experiment for items that subsequently are remembered compared to items that are later forgotten. It is mainly discussed as an event-related potential ...
* Early left anterior negativity
The early left anterior negativity (commonly referred to as ELAN) is an event-related potential in electroencephalography (EEG), or component of brain activity that occurs in response to a certain kind of stimulus. It is characterized by a negativ ...
* Error-related negativity
Error-related negativity (ERN), sometimes referred to as the Ne, is a component of an event-related potential (ERP). ERPs are electrical activity in the brain as measured through electroencephalography (EEG) and time-locked to an external event (e. ...
* Late positive component The late positive component or late positive complex (LPC) is a positive-going event-related brain potential (ERP) component that has been important in studies of explicit recognition memory.Munte, T. F., Urbach, T. P., Duzel, E., & Kutas, M., (200 ...
* Lateralized readiness potential In neuroscience, the lateralized readiness potential (LRP) is an event-related brain potential, or increase in electrical activity at the surface of the brain, that is thought to reflect the preparation of motor activity on a certain side of the b ...
* Mismatch negativity
The mismatch negativity (MMN) or mismatch field (MMF) is a component of the event-related potential (ERP) to an odd stimulus in a sequence of stimuli. It arises from electrical activity in the brain and is studied within the field of cognitive neu ...
* N2pc N2pc refers to an ERP component linked to selective attention.Luck, S. J. (2005). "The operation of attention—millisecond by millisecond—over the first half second." In H. Ogmen & B. G. Breitmeyer (Eds.), ''The first half second: The microgen ...
* N100
* N170
* N200
* N400
* P3a
* P3b
* P200
* P300 (neuroscience)
* Somatosensory evoked potential Somatosensory evoked potential (SEP or SSEP) is the electrical activity of the brain that results from the stimulation of touch. SEP tests measure that activity and are a useful, noninvasive means of assessing somatosensory system functioning. By c ...
* Visual N1
The visual N1 is a visual evoked potential, a type of event-related electrical potential (ERP), that is produced in the brain and recorded on the scalp. The N1 is so named to reflect the polarity and typical timing of the component. The "N" ind ...
Notes
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External links
Video of the N400 and P600 visualized as animated scalp topographies
{{Neuroscience
Electroencephalography
Evoked potentials
Neurolinguistics