Contingent negative variation

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The contingent negative variation (CNV) is the reaction time between a warning and a go signal as measured by electroencephalography (EEG). The CNV was one of the first event-related potential (ERP) components to be described. The CNV component was first described by W. Grey Walter and colleagues in an article published in Nature in 1964. [1] The importance of this finding was that it was one of the first studies which showed that consistent patterns of the amplitude of electric responses could be obtained from the large background noise which occurs in EEG recordings and that this activity could be related to a cognitive process such as expectancy.

Contents

Main paradigms

Grey Walter and colleagues conducted the experiment in the chronometric paradigm. They had noticed that the electric response became attenuated, or habituated when a single stimulus is repeated. They also noticed that the amplitude of the electric response returned when a second stimulus was associated with the first stimulus. These effects were strengthened when a behavioral response was required for the second stimulus. In a chronometric paradigm, the first stimulus is called the warning stimulus and the second stimulus, often one that directs the subject to make a behavioral response, is called the imperative stimulus. The foreperiod is the time between the warning and imperative stimuli. The time between the imperative stimulus and the behavioral response is called the reaction time. The CNV, then, is seen in the foreperiod, between the warning and imperative stimulus.

Walter and colleagues also noticed that electric responses to warning stimuli seemed to have three phases: a brief positive component, a brief negative component, and a sustained negative component. They noticed that the brief components varied due to sensory modality, while the sustained component varied with the contingency between the warning and imperative stimuli and the attention of the subject. They labeled this component the "contingent negative variation" because the variation of the negative wave was contingent on the statistical relationship between the warning and imperative stimuli.

In their study, Walter et al. (1964) presented clicks or flashes, singly or in pairs, at intervals between 3–10 sec. The warning stimuli were single clicks or flashes and the imperative stimuli were repetitive clicks or flashes. The modality of the imperative stimuli was opposite that of the warning stimuli. The behavioral response was a button press which terminated the repetitive stimuli. [1]

In 1990 a bidirectional CNV paradigm was used by Liljana Bozinovska and her team to obtain a CNV-based brain-computer interface for control of a computer buzzer. [2] [3]

In 2009, a CNV flip-flop paradigm was used by Adrijan Bozinovski and Liljana Bozinovska in a CNV-based brain-computer interface experiment for control of a physical object, a robot. [4]

Component characteristics

Walter et al. (1964) showed that a single click elicits a brief positive peak and a brief negative peak. Repetitive flashes elicit brief positive and negative peaks. If these stimuli are separated by 1 sec the same individual patterns result. After around 50 presentations, these peaks are indistinguishable from noise. On the other hand, when a single click is followed by the repetitive flashes which are terminated by a button press, there is a large gradual negative peak which ends sharply with the button press. This is the contingent negative variation. Another classical study was described by Joseph Tecce in the Psychological Bulletin in 1972. [5] In this review, Tecce summarizes the development, morphology, and locus of appearance of the CNV.

Development

Studies have shown that the CNV appears after about 30 trials of paired stimuli, although this number can be reduced when the subject understands the task in advance. Light flashes, clicks, and tones have all been used to elicit the CNV. A response to the imperative stimulus is necessary to elicit a clear CNV. This response could be a physical or mental response. [5] The CNV is elicited when two, linked stimuli are presented. When the imperative stimulus is removed unexpectedly, the CNV attenuates until it is completely suppressed after about 20–50 trials. The CNV is immediately restored if paired with the imperative stimulus again.

Morphology

The negative CNV peak rises around 260–470 ms after the warning stimulus. It will rise quickly if the subject is uncertain about when the imperative stimulus will be, and it will rise gradually if the subject is confident about when the imperative stimulus will be. The maximum amplitude is usually around 20 microvolts. [5]

Topography

The CNV appears most prominently at the vertex and is bilaterally symmetrical. [5]

Functional sensitivity

There is much research which describes what stimulus characteristics can affect characteristics of the CNV. For example, intensity, modality, duration, stimulus rate, probability, stimulus relevance, and pitch discrimination can affect the CNV component. [6]

Attention and expectancy

Attention also affects the amplitude of the CNV. The following examples from various task conditions and studies show that the CNV is changed when the experimental protocol changes the attention needed to perform the tasks. [1] [5] First, when subjects were told that the imperative stimulus would be removed, the CNV was reduced. Second, in one condition subjects were allowed to choose whether they were going to press the button or not. In trials where the subject chose not to respond, there was no CNV. Third, when the subject was specifically told that there would not be repetitive flashes, no CNV was elicited. Fourth, another condition showed that a CNV was elicited in subjects who were told to estimate when the repetitive flashes would come even when no flashes were presented. Fifth, when subjects were asked to pay attention and respond quickly, CNV amplitude was increased. The results of these conditions suggest that the CNV is related to attention and expectancy.

Probability

When the probability of repetitive flashes is random and the repetitive flashes are removed in about 50% of the trials, the amplitude of the CNV is about half as that of normal.

Intensity

Some researchers have shown that the intensity of the stimulus may affect the CNV amplitude. It seems that the CNV component has a higher amplitude for stimuli that have low-intensity, i.e. is difficult to see or hear, as opposed to stimuli that have high-intensity. This could be because the subject must pay more attention to perceive the low-intensity stimulus. If the detection of the imperative task becomes too difficult, then the CNV amplitude is reduced. In other words, attention to the imperative stimulus is important for the development of the CNV and increased task difficulties distract the attention.

In related studies, researchers have also shown that the larger the motoric response needed, the larger the CNV. Studies with subjects that have a lack of sleep tend to show a reduced CNV. This provides further evidence that lack of attention might decrease the CNV amplitude. [5]

Interstimulus interval

The amplitude of the CNV changes when one changes the foreperiod, or interstimulus interval (ISI). The most frequent ISI used is between 1.0–1.5 seconds. Trials with an ISI between 0.5–1.5 elicit a robust CNV wave. When the ISI is reduced to 0.125 or 0.25 seconds, the CNV becomes suppressed. On the other hand, trials with an ISI of 4.8 seconds show reduced CNV amplitude.

O-wave and E-wave

Most researchers agree that the CNV component has been associated with information processing and response preparation. The main controversy is whether the CNV is composed of more than one component. After discovery of the CNV, researchers were able to distinguish between two main components of the CNV. Loveless and Sanford (1975) and Weerts and Lang (1973) increased the interstimulus interval to greater than 3 seconds and showed that two components can be visually distinguished from the CNV. The first wave followed the warning stimulus and was called the O wave, or orienting wave. [7] [8] This wave showed enhanced amplitude in the frontal regions. The second wave preceded the imperative stimulus and was called the E wave, or expectancy wave. A study conducted by Gaillard (1976) provided further evidence that the O wave was frontally distributed and was more strongly affected by auditory stimuli rather than visual stimuli. [9]

A related, important issue has been the question of whether all or part of the CNV corresponds to the readiness potential. The readiness potential is the neural preparation for motoric responses. Both components have a similar scalp distribution with a negative amplitude and are associated with a motor response. In fact, many researchers claimed that the terminal CNV, or E wave, was in fact the readiness potential, or Bereitschaftspotential. This was the general consensus until other work provided evidence that the CNV can be distinguished from the RP. [6] [10] First, the RP is usually lateralized to the contralateral side of the motoric response, while the CNV is usually bilateral. Second, the CNV can occur even when a motor response is not required. Third, a RP occurs without any external stimuli. This shows that the RP occurs for motor responses while the CNV occurs when two stimuli are contingent with each other. [5]

Localization

Another important topic in studying the CNV component is localizing the general source of the CNV. For example, Hultin, Rossini, Romani, Högstedt, Tecchio, and Pizzella (1996) used magnetoencephalography (MEG) to determine the location of the electromagnetic source of the CNV wave. Their experiment suggests that the terminal CNV is located within Brodmann's area 6 and corresponds to the premotor cortex. [11]

The work done by Zappoli and colleagues is another example of research completed to determine the generators of the CNV component. Zappoli (2003) studied the ERP patterns, including the CNV, of subjects with brain disorders or brain damage. [12] Zappoli reviews evidence which shows that in certain cases epileptic discharges affect the expectance waves and therefore decrease the CNV amplitude. Zappoli also described research which investigated the CNV characteristics in patients which had lobotomies of frontal regions. The CNV amplitudes were decreased or absent in these patients.

Theory

Many theories have been posited to account for cognitive processes underlying the CNV component. Walter and colleagues suggested that CNV amplitude varies directly with subjective probability or expectancy of the imperative stimuli. Other researchers suggested that the CNV amplitude varies with the intention to perform an act. Another theory is that CNV varies with the motivation of the subject to complete the task. Tecce suggests that the CNV is related to both attention and arousal level.

See also

Related Research Articles

An evoked potential or evoked response is an electrical potential in a specific pattern recorded from a specific part of the nervous system, especially the brain, of a human or other animals following presentation of a stimulus such as a light flash or a pure tone. Different types of potentials result from stimuli of different modalities and types. EP is distinct from spontaneous potentials as detected by electroencephalography (EEG), electromyography (EMG), or other electrophysiologic recording method. Such potentials are useful for electrodiagnosis and monitoring that include detections of disease and drug-related sensory dysfunction and intraoperative monitoring of sensory pathway integrity.

Event-related potential Brain response that is the direct result of a specific sensory, cognitive, or motor event

An event-related potential (ERP) is the measured brain response that is the direct result of a specific sensory, cognitive, or motor event. More formally, it is any stereotyped electrophysiological response to a stimulus. The study of the brain in this way provides a noninvasive means of evaluating brain functioning.

In neurology, the Bereitschaftspotential or BP, 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 brain leading up to voluntary muscle movement. The BP is a manifestation of cortical contribution to the pre-motor planning of volitional movement. It was first recorded and reported in 1964 by Hans Helmut Kornhuber and Lüder Deecke at the University of Freiburg in Germany. In 1965 the full publication appeared after many control experiments.

The N400 is a component of time-locked EEG signals known as event-related potentials (ERP). It is a negative-going deflection that peaks around 400 milliseconds post-stimulus onset, although it can extend from 250-500 ms, and is typically maximal over centro-parietal electrode sites. The N400 is part of the normal brain response to words and other meaningful stimuli, including visual and auditory words, sign language signs, pictures, faces, environmental sounds, and smells.

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 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.

Mental chronometry

Mental chronometry is the scientific study of processing speed or reaction time on cognitive tasks to infer the content, duration, and temporal sequencing of mental operations. Reaction time is measured by the elapsed time between stimulus onset and an individual’s response on elementary cognitive tasks (ETCs), which are relatively simple perceptual-motor tasks typically administered in a laboratory setting. Mental chronometry is one of the core methodological paradigms of human experimental, cognitive, and differential psychology, but is also commonly analyzed in psychophysiology, cognitive neuroscience, and behavioral neuroscience to help elucidate the biological mechanisms underlying perception, attention, and decision-making in humans and other species.

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 neuroscience and psychology. It can occur in any sensory system, but has most frequently been studied for hearing and for vision. In the case of auditory stimuli, the MMN occurs after an infrequent change in a repetitive sequence of sounds For example, a rare deviant (d) sound can be interspersed among a series of frequent standard (s) sounds. The deviant sound can differ from the standards in one or more perceptual features such as pitch, duration, or loudness. The MMN is usually evoked by either a change in frequency, intensity, duration or real or apparent spatial locus of origin. The MMN can be elicited regardless of whether the subject is paying attention to the sequence. During auditory sequences, a person can be reading or watching a silent subtitled movie, yet still show a clear MMN. In the case of visual stimuli, the MMN occurs after an infrequent change in a repetitive sequence of images.

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 body; in other words, it is a spike in the electrical activity of the brain that happens when a person gets ready to move one arm, leg, or foot. It is a special form of bereitschaftspotential. LRPs are recorded using electroencephalography (EEG) and have numerous applications in cognitive neuroscience.

In neuroscience, the N100 or N1 is a large, negative-going evoked potential measured by electroencephalography ; it peaks in adults between 80 and 120 milliseconds after the onset of a stimulus, and is distributed mostly over the fronto-central region of the scalp. It is elicited by any unpredictable stimulus in the absence of task demands. It is often referred to with the following P200 evoked potential as the "N100-P200" or "N1-P2" complex. While most research focuses on auditory stimuli, the N100 also occurs for visual, olfactory, heat, pain, balance, respiration blocking, and somatosensory stimuli.

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 (ERP) effect that appears in studies employing a subsequent memory paradigm, in which ERPs are recorded when a participant is studying a list of materials and trials are sorted as a function of whether they go on to be remembered or not in the test phase. For meaningful study material, such as words or line drawings, items that are subsequently remembered typically elicit a more positive waveform during the study phase. This difference typically occurs in the range of 400–800 milliseconds (ms) and is generally greatest over centro-parietal recording sites, although these characteristics are modulated by many factors.

The P3a, or novelty P3, is a component of time-locked (EEG) signals known as event-related potentials (ERP). The P3a is a positive-going scalp-recorded brain potential that has a maximum amplitude over frontal/central electrode sites with a peak latency falling in the range of 250–280 ms. The P3a has been associated with brain activity related to the engagement of attention and the processing of novelty.

In neuroscience, the visual P200 or P2 is a waveform component or feature of the event-related potential (ERP) measured at the human scalp. Like other potential changes measurable from the scalp, this effect is believed to reflect the post-synaptic activity of a specific neural process. The P2 component, also known as the P200, is so named because it is a positive going electrical potential that peaks at about 200 milliseconds after the onset of some external stimulus. This component is often distributed around the centro-frontal and the parieto-occipital areas of the scalp. It is generally found to be maximal around the vertex of the scalp, however there have been some topographical differences noted in ERP studies of the P2 in different experimental conditions.

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" indicates that the polarity of the component is negative with respect to an average mastoid reference. The "1" originally indicated that it was the first negative-going component, but it now better indexes the typical peak of this component, which is around 150 to 200 milliseconds post-stimulus. The N1 deflection may be detected at most recording sites, including the occipital, parietal, central, and frontal electrode sites. Although, the visual N1 is widely distributed over the entire scalp, it peaks earlier over frontal than posterior regions of the scalp, suggestive of distinct neural and/or cognitive correlates. The N1 is elicited by visual stimuli, and is part of the visual evoked potential – a series of voltage deflections observed in response to visual onsets, offsets, and changes. Both the right and left hemispheres generate an N1, but the laterality of the N1 depends on whether a stimulus is presented centrally, laterally, or bilaterally. When a stimulus is presented centrally, the N1 is bilateral. When presented laterally, the N1 is larger, earlier, and contralateral to the visual field of the stimulus. When two visual stimuli are presented, one in each visual field, the N1 is bilateral. In the latter case, the N1's asymmetrical skewedness is modulated by attention. Additionally, its amplitude is influenced by selective attention, and thus it has been used to study a variety of attentional processes.

The N200, or N2, is an event-related potential (ERP) component. An ERP can be monitored using a non-invasive electroencephalography (EEG) cap that is fitted over the scalp on human subjects. An EEG cap allows researchers and clinicians to monitor the minute electrical activity that reaches the surface of the scalp from post-synaptic potentials in neurons, which fluctuate in relation to cognitive processing. EEG provides millisecond-level temporal resolution and is therefore known as one of the most direct measures of covert mental operations in the brain. The N200 in particular is a negative-going wave that peaks 200-350ms post-stimulus and is found primarily over anterior scalp sites. Past research focused on the N200 as a mismatch detector, but it has also been found to reflect executive cognitive control functions, and has recently been used in the study of language.

Somatosensory evoked potential 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 combining SEP recordings at different levels of the somatosensory pathways, it is possible to assess the transmission of the afferent volley from the periphery up to the cortex. SEP components include a series of positive and negative deflections that can be elicited by virtually any sensory stimuli. For example, SEPs can be obtained in response to a brief mechanical impact on the fingertip or to air puffs. However, SEPs are most commonly elicited by bipolar transcutaneous electrical stimulation applied on the skin over the trajectory of peripheral nerves of the upper limb or lower limb, and then recorded from the scalp. In general, somatosensory stimuli evoke early cortical components, generated in the contralateral primary somatosensory cortex (S1), related to the processing of the physical stimulus attributes. About 100 ms after stimulus application, additional cortical regions are activated, such as the secondary somatosensory cortex (S2), and the posterior parietal and frontal cortices, marked by a parietal P100 and bilateral frontal N140. SEPs are routinely used in neurology today to confirm and localize sensory abnormalities, to identify silent lesions and to monitor changes during surgical procedures.

The C1 and P1 are two human scalp-recorded event-related brain potential components, collected by means of a technique called electroencephalography (EEG). The C1 is named so because it was the first component in a series of components found to respond to visual stimuli when it was first discovered. It can be a negative-going component or a positive going component with its peak normally observed in the 65–90 ms range post-stimulus onset. The P1 is called the P1 because it is the first positive-going component and its peak is normally observed in around 100 ms. Both components are related to processing of visual stimuli and are under the category of potentials called visually evoked potentials (VEPs). Both components are theorized to be evoked within the visual cortices of the brain with C1 being linked to the primary visual cortex of the human brain and the P1 being linked to other visual areas. One of the primary distinctions between these two components is that, whereas the P1 can be modulated by attention, the C1 has been typically found to be invariable to different levels of attention.

P3b

The P3b is a subcomponent of the P300, an event-related potential (ERP) component that can be observed in human scalp recordings of brain electrical activity. The P3b is a positive-going amplitude peaking at around 300 ms, though the peak will vary in latency from 250–500 ms or later depending upon the task and on the individual subject response. Amplitudes are typically highest on the scalp over parietal brain areas.

The N170 is a component of the event-related potential (ERP) that reflects the neural processing of faces, familiar objects or words. Furthermore, the N170 is modulated by prediction error processes.

N2pc refers to an ERP component linked to selective attention. The N2pc appears over visual cortex contralateral to the location in space to which subjects are attending; if subjects pay attention to the left side of the visual field, the N2pc appears in the right hemisphere of the brain, and vice versa. This characteristic makes it a useful tool for directly measuring the general direction of a person's attention with fine-grained temporal resolution.

The oddball paradigm is an experimental design used within psychology research. Presentations of sequences of repetitive stimuli are infrequently interrupted by a deviant stimulus. The reaction of the participant to this "oddball" stimulus is recorded.

References

  1. 1 2 3 Walter, W.G; Cooper, R.; Aldridge, V.J.; McCallum, W.C.; Winter, A.L. (1964). "Contingent Negative Variation: an electric sign of sensorimotor association and expectancy in the human brain". Nature. 203 (4943): 380–384. doi:10.1038/203380a0. PMID   14197376.
  2. ↑ L. Bozinovska, G. Stojanov, M. Sestakov, S. Bozinovski. CNV pattern recognition – a step toward cognitive wave observation. In: L. Torres, E. Masgrau, M. Lagunas, editors. Signal processing: theories and applications. Proceedings of the Fifth European Signal Processing Conference (EUSIPCO 90); 1990, Barcelona. 1990, Elsevier Science Publishers; 1990. p. 1659–1662
  3. ↑ L Bozinovska, S. Bozinovski, G. Stojanov. Electroexpectogram: experimental design and algorithms. Proceedings of the IEEE International. Biomedical. Engineering Days; 1992. Istanbul. p. 58–60
  4. ↑ A. Bozinovski, L. Bozinovska. Anticipatory Brain Potentials in a Brain-Robot Interface Paradigm. Proceedings of the 4th International IEEE EMBS Conference on Neural Engineering, Antalya, Turkey, p. 451-454, 2009
  5. 1 2 3 4 5 6 7 Tecce, J.J. (1972). "Contingent negative variation (CNV) and psychological processes in man". Psychological Bulletin. 77 (2): 73–108. doi:10.1037/h0032177. PMID   4621420.
  6. 1 2 Frost, B.G.; Neill, R.A.; Fenelon, B. (1988). "The determinants of the non-motoric CNV in a complex, variable foreperiod, information processing paradigm". Biological Psychology. 27 (1): 1–21. doi:10.1016/0301-0511(88)90002-6. PMID   3251557.
  7. ↑ Loveless, N.E; Sanford, A.J. (1975). "The impact of warning signal intensity on reaction time and components of the contingent negative variation". Biological Psychology. 2 (3): 217–226. doi:10.1016/0301-0511(75)90021-6. PMID   1139019.
  8. ↑ Weerts, T.C.; Lang, P.J. (1973). "The effects of eye fixation and stimulus and response location on the contingent negative variation (CNV)". Biological Psychology. 1 (1): 1–19. doi:10.1016/0301-0511(73)90010-0. PMID   4804295.
  9. ↑ Gaillard, AW (1976). "Effects of warning-signal modality on the contingent negative variation (CNV)". Biological Psychology. 4 (2): 139–154. doi:10.1016/0301-0511(76)90013-2. PMID   1276304.
  10. ↑ Ruchkin, D.S.; Sutton, S.; Mahaffey, D.; Glaser, J. (1986). "Terminal CNV in the absence of motor response". Electroencephalography and Clinical Neurophysiology. 63 (5): 445–463. doi:10.1016/0013-4694(86)90127-6. PMID   2420561.
  11. ↑ Hultin, L.; Rossini, P.; Romani, G. L.; Högstedt, P.; Tecchio, F.; Pizzella, V. (1996). "Neuromagnetic localization of the late component of the contingent negative variation". Electroencephalography and Clinical Neurophysiology. 98: 425–448.
  12. ↑ Zappoli, R. (2003). "Permanent or transitory effects on neurocognitive components of the CNV complex induced by brain dysfunctions, lesions, and ablations in humans". International Journal of Psychophysiology. 48 (2): 189–220. doi:10.1016/S0167-8760(03)00054-0. PMID   12763574.
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