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62-501: In 1975 Squires and colleagues conducted a study attempting to resolve some of the questions surrounding what neural process the P300 reflects. At the time, several researchers suggested that there needed to be active attention towards the target stimuli in order to elicit a P300, in part because stimuli that were ignored resulted in a P300 with a smaller amplitude or no P300 at all. On the other hand, some research had shown that subjects exhibit

124-410: A periodic variable is a measure of its change in a single period (such as time or spatial period ). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplitude (see below), which are all functions of the magnitude of the differences between the variable's extreme values . In older texts, the phase of a periodic function

186-608: A P300 to unpredictable stimuli in an ongoing repetitive series of stimuli, even when the stimuli were classified as irrelevant and subjects were asked to ignore them while completing another task (i.e. reading a book). It was intriguing that you could elicit a P300 in conditions with active attention and those of non-attention. Upon further investigation it turned out that when comparing the two types of P300 potentials, they differed in latency and scalp topography. This led Squires et al. to suggest that there were two distinct psycho-physiological entities that had been referred to collectively as

248-480: A P3b, the improbable event must be related to the task at hand in some way (for example, the improbable event could be an infrequent target letter in a stream of letters, to which a subject might respond with a button press). The P3b can also be used to measure how demanding a task is on cognitive workload . Since the initial discovery of the P300, research has shown that the P300 has two subcomponents. The subcomponents are

310-411: A design wherein subjects would receive finger taps to hand digits 2-5 and electric shocks to the wrist. Taps on the 2nd finger were considered standards (76% probability) while taps on the 5th finger were targets (12% prob.). Taps occurring on the 3rd and 4th digits were considered “tactile novel” stimuli (6% prob.) and electric shocks to the wrist were shock novels (6% prob.). They found that both types of

372-452: A drum, slamming a door, etc. where the amplitude is transient and must be represented as either a continuous function or a discrete vector. Percussive amplitude envelopes model many common sounds that have a transient loudness attack, decay, sustain, and release. With waveforms containing many overtones, complex transient timbres can be achieved by assigning each overtone to its own distinct transient amplitude envelope. Unfortunately, this has

434-403: A flash, or a cue which required subjects to guess whether the following stimulus would be a click or a flash. They found that when subjects were required to guess what the following stimulus would be, the amplitude of the "late positive complex" was larger than when they knew what the stimulus would be. In a second experiment, they presented two cue types. For one cue there was a 2 in 3 chance that

496-578: A positive deflection in voltage with a latency (delay between stimulus and response) of roughly 250 to 500 ms. In the scientific literature a differentiation is often made in the P3, which is divided according to time: Early P3 window (300-400 ms) and Late P3 window (380-440 ms). The signal is typically measured most strongly by the electrodes covering the parietal lobe . The presence, magnitude, topography and timing of this signal are often used as metrics of cognitive function in decision-making processes. While

558-404: A sinusoidal waveform. One property of root mean square voltages and currents is that they produce the same heating effect as a direct current in a given resistance. The peak-to-peak value is used, for example, when choosing rectifiers for power supplies, or when estimating the maximum voltage that insulation must withstand. Some common voltmeters are calibrated for RMS amplitude, but respond to

620-430: A specified reference and therefore should be modified by qualifiers, such as average , instantaneous , peak , or root-mean-square . Pulse amplitude also applies to the amplitude of frequency - and phase -modulated waveform envelopes . In this simple wave equation The units of the amplitude depend on the type of wave, but are always in the same units as the oscillating variable. A more general representation of

682-400: Is important in the search for exoplanets (see Doppler spectroscopy ). In general, the use of peak amplitude is simple and unambiguous only for symmetric periodic waves, like a sine wave, a square wave, or a triangle wave. For an asymmetric wave (periodic pulses in one direction, for example), the peak amplitude becomes ambiguous. This is because the value is different depending on whether

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744-416: Is no longer amplitude since there is the possibility that a constant ( DC component ) is included in the measurement. Peak-to-peak amplitude (abbreviated p–p or PtP or PtoP ) is the change between peak (highest amplitude value) and trough (lowest amplitude value, which can be negative). With appropriate circuitry, peak-to-peak amplitudes of electric oscillations can be measured by meters or by viewing

806-442: Is presented to the subject, and various columns or rows are highlighted. When a column or row contains the character a subject desires to communicate, the P300 response is elicited (since this character is "special" it is the target stimulus described in the typical oddball paradigm). The combination of the row and column which evoked the response locates the desired character. A number of such trials must be averaged to clear noise from

868-426: Is sometimes called the amplitude. For symmetric periodic waves, like sine waves or triangle waves , peak amplitude and semi amplitude are the same. In audio system measurements , telecommunications and others where the measurand is a signal that swings above and below a reference value but is not sinusoidal , peak amplitude is often used. If the reference is zero, this is the maximum absolute value of

930-413: Is suspected to also reflect interactions between the frontal lobe and the hippocampus , as patients with focal hippocampal lesions have reduced P3a amplitude from novel distracters. P300 (neuroscience) The P300 ( P3 ) wave is an event-related potential (ERP) component elicited in the process of decision making. It is considered to be an endogenous potential, as its occurrence links not to

992-446: Is target discrimination. It is interesting that although the P3a is elicited by non-target deviant stimuli, the nature of the target stimuli affect the P3a response. It seems that the amplitude of the P3a may be affected by an individual’s ability to distinguish target stimuli from standard stimuli. When this discrimination is easy, non-target deviant stimuli produce a P300 that is smaller than

1054-426: The orienting , involuntary shifts to changes in the environment), and the processing of novelty. The P3b has a positive-going amplitude (usually relative to a reference behind the ear or the average of two such references) that peaks at around 300 ms, and the peak will vary in latency from 250 to 500 ms or more, depending upon the task and the individual subject response. Amplitudes are typically highest on

1116-562: The square root of the mean over time of the square of the vertical distance of the graph from the rest state; i.e. the RMS of the AC waveform (with no DC component ). Mathematically the RMS can be defined as: R M S = E [ y 2 ] {\displaystyle RMS={\sqrt {\mathbb {E} [y^{2}]}}} Where y is the amplitude of the signal. For complicated waveforms, especially non-repeating signals like noise,

1178-556: The EEG. The speed of the highlighting determines the number of characters processed per minute. Results from studies using this setup show that normal subjects could achieve a 95% success rate at 3.4–4.3 chars/min. Such success rates are not limited to non-disabled users; a study conducted in 2000 revealed that 4 paralyzed participants (one with complete paraplegia, three with incomplete paraplegia) performed as successfully as 10 normal participants. Scientific research often relies on measurement of

1240-425: The P300 (P3b) elicited by rare target stimuli. The 3 stimulus oddball paradigm provides a flexible way to examine the P3a across stimulus modality and tasks. Yamaguchi and Knight conducted a study using mechanical tactile stimuli (finger taps) and electric shocks to the wrist within a 3-stimulus oddball paradigm. They were interested in seeing if subjects would elicit a P3a to novel somatosensory stimuli. They devised

1302-402: The P300 is that the amplitude of the waveform requires averaging of multiple recordings to isolate the signal. This and other post-recording processing steps determine the overall speed of an interface. The algorithm proposed by Farwell and Donchin provides an example of a simple BCI that relies on the unconscious decision making processes of the P300 to drive a computer. A 6×6 grid of characters

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1364-520: The P300 to examine event related potentials, especially with regard to decision making. Because cognitive impairment is often correlated with modifications in the P300, the waveform can be used as a measure for the efficacy of various treatments on cognitive function. Some have suggested its use as a clinical marker for precisely these reasons. There is a broad range of uses for the P300 in clinical research. Some research groups have performed fMRI combined to EEG in order to achieve inner-speech dictation and

1426-405: The P300. More specifically, Squires et al. recorded EEG during an auditory odd-ball paradigm with various conditions. The two types of stimuli were 90 dB and 70 db tone bursts that occurred 1.1 sec apart. Loud tones occurred with a probability of .9, .5, or .1, while the soft tones occurred with complementary probability. In addition, subjects completed blocks of stimuli under instruction to count

1488-403: The P3a have been hypothesized to arise from frontal lobe functioning and to involve frontal lobe attention mechanisms. Magnetic resonance imaging (MRI) studies looking at gray matter volume and P3a amplitude show stronger correlations when non-target, startling stimuli are viewed. Lesion studies indicate that prefrontal and temporal-parietal cortex contribute to auditory P3a generation. The P3a

1550-531: The P3a in order to distinguish it from its relative, the P3b , which was a positive-going potential that occurred at 310–380 ms when the infrequent tones were attended to. Scalp distribution helped them differentiate the two potentials as well. The newly coined "P3a" had a peak amplitude occurring at frontal midline sites while the P3b peak amplitude occurred over parietal midline sites. Consistent with this historical separation of

1612-420: The RMS amplitude is usually used because it is both unambiguous and has physical significance. For example, the average power transmitted by an acoustic or electromagnetic wave or by an electrical signal is proportional to the square of the RMS amplitude (and not, in general, to the square of the peak amplitude). For alternating current electric power , the universal practice is to specify RMS values of

1674-401: The air or the diaphragm of a speaker ) is described. The logarithm of the amplitude squared is usually quoted in dB , so a null amplitude corresponds to − ∞  dB. Loudness is related to amplitude and intensity and is one of the most salient qualities of a sound, although in general sounds it can be recognized independently of amplitude . The square of the amplitude is proportional to

1736-420: The approach of inner-speech recognition. The P300 wave obtained by visual stimulation is used to assess cognitive processes in humans, and the value of the latency and amplitude of the P300 wave can be a measure of the severity of dementia processes. The analysis of P300 wave latency seems to be particularly useful in the diagnosis of mild cognitive impairment (MCI). Amplitude The amplitude of

1798-481: The average value of a rectified waveform. Many digital voltmeters and all moving coil meters are in this category. The RMS calibration is only correct for a sine wave input since the ratio between peak, average and RMS values is dependent on waveform . If the wave shape being measured is greatly different from a sine wave, the relationship between RMS and average value changes. True RMS-responding meters were used in radio frequency measurements, where instruments measured

1860-526: The effect of modulating the loudness of the sound as well. It makes more sense to separate loudness and harmonic quality to be parameters controlled independently of each other. To do so, harmonic amplitude envelopes are frame-by-frame normalized to become amplitude proportion envelopes, where at each time frame all the harmonic amplitudes will add to 100% (or 1). This way, the main loudness-controlling envelope can be cleanly controlled. In Sound Recognition, max amplitude normalization can be used to help align

1922-514: The environment. Some have suggested that the P3a and P3b are variants of the same ERP response that varies in scalp topography as a function of attention and task demands. In other cases, however, the two can be dissociated: for example, patients with temporal-parietal lesions and an absent visual P3a response have partial preservation of their visual target P3b. These results indicate that at least partially non-overlapping neural circuits may be engaged during P3a and P3b generation. Neural sources of

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1984-461: The event has been created, and for this reason the event no longer generates a response when repeated. Each time a novel event is experienced, it is compared to the previously created neural representation, and, if it is sufficiently deviant, then the process begins again. If this event is not sufficiently deviant (i.e., it is the same) then habituation occurs. The P3a's rapid amplitude reduction with exposure to repeated trials of novel stimuli supports

2046-421: The following stimulus would be a click and a 1 in 3 chance that the following stimulus would be a flash. The second cue type had probabilities that were the reverse of the first. They found that the amplitude of the positive complex was larger in response to the less probable stimuli, or the one that only had a 1 in 3 chance of appearing. Another important finding from these studies is that this late positive complex

2108-417: The frontal and central areas of the brain is produced in response to auditory , visual , and somatosensory stimuli. Deviant stimuli from auditory, visual, and somatosensory modalities are all sufficient for eliciting a P3a. For example, Grillon and colleagues used this design when they tested for the effects of rare non-target (deviant) auditory stimuli on subjects' EEG activity. They used 1600 Hz tones as

2170-415: The heating effect in a resistor to measure a current. The advent of microprocessor -controlled meters capable of calculating RMS by sampling the waveform has made true RMS measurement commonplace. In telecommunications, pulse amplitude is the magnitude of a pulse parameter, such as the voltage level, current level, field intensity , or power level. Pulse amplitude is measured with respect to

2232-497: The idea that the P3a is the electrophysiological representation of the orienting response (which also habituates in behavior). For example, Grillon and colleagues used a 3 stimulus odd-ball paradigm wherein they presented subjects with a condition in which the deviant stimuli were constant and a condition in which the deviant stimuli were always novel. Their results showed the largest P3a amplitude in response to deviant stimuli that were novel. Another factor that affects P3a amplitude

2294-421: The intensity of the wave. For electromagnetic radiation , the amplitude of a photon corresponds to the changes in the electric field of the wave. However, radio signals may be carried by electromagnetic radiation; the intensity of the radiation ( amplitude modulation ) or the frequency of the radiation ( frequency modulation ) is oscillated and then the individual oscillations are varied (modulated) to produce

2356-413: The interval between clicks might be, and in this case, the late positivity occurred 300 ms after the second click. This shows two important findings: first, that this late positivity occurred when uncertainty about the type of click was resolved, and second, that even an absence of a stimulus would elicit the late positive complex, if said stimulus was relevant to the task. These early studies encouraged

2418-468: The maximum positive signal is measured relative to the mean, the maximum negative signal is measured relative to the mean, or the maximum positive signal is measured relative to the maximum negative signal (the peak-to-peak amplitude ) and then divided by two (the semi-amplitude ). In electrical engineering, the usual solution to this ambiguity is to measure the amplitude from a defined reference potential (such as ground or 0 V). Strictly speaking, this

2480-491: The neural substrates of this ERP component still remain hazy, the reproducibility and ubiquity of this signal makes it a common choice for psychological tests in both the clinic and laboratory. Early observations of the P300 (more specifically, the component that would later be named the P3b) were reported in the mid-1960s. In 1964, researchers Chapman and Bragdon found that ERP responses to visual stimuli differed depending on whether

2542-487: The novel somatosensory stimuli did in fact produce P3a’s that had a more frontal distribution than responses to target stimuli. Shock novels also resulted in a significantly shorter P3a latency. Two important factors for determining the amplitude of the P3a include habituation and target discrimination. One major difference between the P3b and the P3a is that only the P3a habituates with repeated presentation. The habituation indicates that some sort of memory encoding for

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2604-487: The novelty P3, or P3a , and the classic P300, which has since been renamed P3b . Since the mid-1980s, one of the most discussed uses of ERPs such as the P300 is related to lie detection . In a proposed "guilty knowledge test" a subject is interrogated via the oddball paradigm much as they would be in a typical lie-detector situation. This practice has recently enjoyed increased legal permissibility while conventional polygraphy has seen its use diminish, in part owing to

2666-410: The number of loud tones, count the number of soft tones, or ignore the tones and quietly read. Therefore, each set of instructions was performed at each of the probability combinations. Squires et al. found that when subjects were told to ignore the tones, the less frequent or rare tone (probability of .1) elicited a positive-going potential which occurred between 220 and 280 ms. They termed this potential

2728-492: The numbers and the flashes elicited the expected sensory responses (e.g., visual N1 components), and that the amplitude of these responses varied in an expected fashion with the intensity of the stimuli. They also found that the ERP responses to the numbers, but not to the light flashes, contained a large positivity that peaked around 300 ms after the stimulus appeared. Chapman and Bragdon speculated that this differential response to

2790-409: The numbers, which came to be known as the P300 response, resulted from the fact that the numbers were meaningful to the participants, based on the task that they were asked to perform. In 1965, Sutton and colleagues published results from two experiments that further explored this late positivity. They presented subjects with either a cue that indicated whether the following stimulus would be a click or

2852-409: The oddball task that is used to elicit a P3b. In this task, infrequent-nontarget stimuli are dispersed throughout a sequence of task-relevant target and standard stimuli. When these infrequent, novel stimuli (for example, the sound of dog barks or color forms) are presented in the series of more typical target and standard stimuli (for example, tones or letters of the alphabet), a P3a that is larger over

2914-406: The physical attributes of a stimulus, but to a person's reaction to it. More specifically, the P300 is thought to reflect processes involved in stimulus evaluation or categorization. It is usually elicited using the oddball paradigm , in which low-probability target items are mixed with high-probability non-target (or "standard") items. When recorded by electroencephalography (EEG), it surfaces as

2976-404: The scalp over parietal brain areas. The P3b has been a prominent tool used to study cognitive processes, especially psychology research on information processing. Generally speaking, improbable events will elicit a P3b, and the less probable the event, the larger the P3b amplitude. This was shown to be true both for the overall probability and for the local probability. However, in order to elicit

3038-408: The scalp, such as FCz/Cz in the international 10-20 system , which is the standard electrode placement system of many ERP labs around the world. P3b amplitudes are generally greater at sites like Pz. Latency is another distinguishing characteristic. While many things can affect the latency of the P3b, P3a latencies often occur 75-100 ms earlier than P3b peak latencies, and around 250-280 ms. Finally,

3100-519: The signal. Amplitude envelope refers to the changes in the amplitude of a sound over time, and is an influential property as it affects perception of timbre. A flat tone has a steady state amplitude that remains constant during time, which is represented by a scalar. Other sounds can have percussive amplitude envelopes featuring an abrupt onset followed by an immediate exponential decay. Percussive amplitude envelopes are characteristic of various impact sounds: two wine glasses clinking together, hitting

3162-473: The signal; if the reference is a mean value ( DC component ), the peak amplitude is the maximum absolute value of the difference from that reference. Semi-amplitude means half of the peak-to-peak amplitude. The majority of scientific literature employs the term amplitude or peak amplitude to mean semi-amplitude. It is the most widely used measure of orbital wobble in astronomy and the measurement of small radial velocity semi-amplitudes of nearby stars

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3224-416: The standard stimuli, while a 900 Hz tone represented the rare target stimuli. In the “Novel” condition, they added a rare non-target tone at 700 Hz. In their results it was apparent that the P300 they recorded to the rare non-target tones was in fact a P3a. The rare non-target tones resulted in a P300 (P3a) with a shorter latency that was distributed more towards the front of the scalp when compared to

3286-494: The stimuli had meaning or not. They showed subjects two kinds of visual stimuli: numbers and flashes of light. Subjects viewed these stimuli one at a time in a sequence. For every two numbers, the subjects were required to make simple decisions, such as telling which of the two numbers was numerically smaller or larger, which came first or second in the sequence, or whether they were equal. When examining evoked potentials to these stimuli (i.e., ERPs), Chapman and Bragdon found that both

3348-791: The target P3b and is largest over parietal sites. However, if target discrimination is difficult, the P3a to non-target stimuli is larger and more frontally-skewed with a shorter latency—in other words, the more "canonical" P3a response Although the P3a has been dissociated from the P3b, its amplitude and latency may be affected by factors that also modulate the P3b. Some of these factors include stimulus probability, stimulus evaluation difficulty, natural state variables (such as circadian and menstrual cycles ), and environmentally induced state variables (such as drugs and exercise ). John Polich and Albert Kok have written up an extensive review that covers many of these variables. The P3a has been linked with novelty or orienting and involuntary shifts to changes in

3410-401: The two components, typically if a stimulus is a rare non-target then the recorded EEG waveform has characteristics associated with the P3a, whereas attended targets elicit a P3b . With now-extensive research, it is also possible to dissociate these components even when the experimental context is different and/or less well-studied. P3a amplitudes tend to be maximal over frontal/central sites on

3472-412: The two responses have different functional sensitivities and associated psychological correlates. The 3-stimulus oddball paradigm is one of the primary paradigms used to elicit a prominent P3a. As the name implies, the paradigm includes three types of stimuli: frequent, attended "standards", less frequent, attended "target" stimuli and a third "deviant" stimulus type. This paradigm is a modification of

3534-444: The unconscious and uncontrollable aspects of the P300. The technique relies on reproducible elicitation of the P300 wave, central to the idea of a Memory and Encoding Related Multifaceted Electroencephalographic Response (MERMER) developed by Dr. Lawrence Farwell . Applications in brain-computer interfacing (BCI) have also been proposed. The P300 has a number of desirable qualities that aid in implementation of such systems. First,

3596-418: The use of ERP methods to study cognition and provided a foundation for the extensive work on the P300 in the decades that followed. The P3a, or novelty P3, has a positive-going amplitude that displays maximum amplitude over frontal/central electrode sites and has a peak latency in the range of 250–280 ms. The P3a has been associated with brain activity related to the engagement of attention (especially

3658-410: The wave equation is more complex, but the role of amplitude remains analogous to this simple case. For waves on a string , or in a medium such as water , the amplitude is a displacement . The amplitude of sound waves and audio signals (which relates to the volume) conventionally refers to the amplitude of the air pressure in the wave, but sometimes the amplitude of the displacement (movements of

3720-407: The waveform is consistently detectable and is elicited in response to precise stimuli. The P300 waveform can also be evoked in nearly all subjects with little variation in measurement techniques, which may help simplify interface designs and permit greater usability. The speed at which an interface is able to operate depends on how detectable the signal is despite "noise." One negative characteristic of

3782-410: The waveform on an oscilloscope . Peak-to-peak is a straightforward measurement on an oscilloscope, the peaks of the waveform being easily identified and measured against the graticule . This remains a common way of specifying amplitude, but sometimes other measures of amplitude are more appropriate. Root mean square (RMS) amplitude is used especially in electrical engineering : the RMS is defined as

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3844-442: Was observed for both the clicks and flashes, indicating that the physical type of the stimulus (auditory or visual) did not matter. In later studies published in 1967, Sutton and colleagues had subjects guess whether they would hear one click or two clicks. They again observed a positivity around 300 ms after the second click occurred – or would have occurred, in the case of the single click. They also had subjects guess how long

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