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74-404: In their study, Grey Walter et al. (1964) presented a "warning stimulus" (e.g., a single click or flash of light) to a human subject. The warning stimulus was randomly followed (or not followed) by an "imperative stimulus" (repetitive clicks or flashes) 0.5-1 second later. In some situations, the subject simply experienced warning and imperative stimuli passively; in others, the subject could prevent

148-559: A BCI with sensory feedback with rhesus monkeys. The monkey controlled the position of an avatar arm while receiving sensory feedback through direct intracortical stimulation (ICMS) in the arm representation area of the sensory cortex . Other laboratories that have developed BCIs and algorithms that decode neuron signals include John Donoghue at the Carney Institute for Brain Science at Brown University , Andrew Schwartz at

222-516: A challenge for BCI control. Vidal's 1977 experiment was the first application of BCI after his 1973 BCI challenge. It was a noninvasive EEG (actually Visual Evoked Potentials (VEP)) control of a cursor-like graphical object on a computer screen. The demonstration was movement in a maze. 1988 was the first demonstration of noninvasive EEG control of a physical object, a robot. The experiment demonstrated EEG control of multiple start-stop-restart cycles of movement, along an arbitrary trajectory defined by

296-566: A first, second, and third-place winner, who receive awards of $ 3,000, $ 2,000, and $ 1,000, respectively. Invasive BCI requires surgery to implant electrodes under the scalp for accessing brain signals. The main advantage is to increase accuracy. Downsides include side effects from the surgery, including scar tissue that can obstruct brain signals or the body may not accept the implanted electrodes. Invasive BCI research has targeted repairing damaged sight and providing new functionality for people with paralysis. Invasive BCIs are implanted directly into

370-632: A grant from the National Science Foundation , followed by a contract from the Defence Advanced Research Projects Agency ( DARPA ). Vidal's 1973 paper introduced the expression brain–computer interface into scientific literature. Due to the cortical plasticity of the brain, signals from implanted prostheses can, after adaptation, be handled by the brain like natural sensor or effector channels. Following years of animal experimentation,

444-455: 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

518-419: A human brain implant that produced signals of high enough quality to simulate movement. Their patient, Johnny Ray (1944–2002), developed ' locked-in syndrome ' after a brain-stem stroke in 1997. Ray's implant was installed in 1998 and he lived long enough to start working with the implant, eventually learning to control a computer cursor; he died in 2002 of a brain aneurysm . Tetraplegic Matt Nagle became

592-487: A line drawn on a floor. The line-following behavior was the default robot behavior, utilizing autonomous intelligence and an autonomous energy source. In 1990, a report was given on a closed loop, bidirectional, adaptive BCI controlling a computer buzzer by an anticipatory brain potential, the Contingent Negative Variation (CNV) potential. The experiment described how an expectation state of

666-407: A patient's brain and used deep learning to synthesize speech. In 2021, those researchers reported the potential of a BCI to decode words and sentences in an anarthric patient who had been unable to speak for over 15 years. The biggest impediment to BCI technology is the lack of a sensor modality that provides safe, accurate and robust access to brain signals. The use of a better sensor expands

740-526: A robot arm. Their deeply cleft and furrowed brains made them better models for human neurophysiology than owl monkeys. The monkeys were trained to reach and grasp objects on a computer screen by manipulating a joystick while corresponding movements by a robot arm were hidden. The monkeys were later shown the robot and learned to control it by viewing its movements. The BCI used velocity predictions to control reaching movements and simultaneously predicted gripping force . In 2011 O'Doherty and colleagues showed

814-505: A robotic arm. The same group demonstrated that a monkey could feed itself pieces of fruit and marshmallows using a robotic arm controlled by the animal's brain signals. Andersen's group used recordings of premovement activity from the posterior parietal cortex , including signals created when experimental animals anticipated receiving a reward. In addition to predicting kinematic and kinetic parameters of limb movements, BCIs that predict electromyographic or electrical activity of

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888-403: A robotic arm. Lebedev and colleagues argued that brain networks reorganize to create a new representation of the robotic appendage in addition to the representation of the animal's own limbs. In 2019, a study reported a BCI that had the potential to help patients with speech impairment caused by neurological disorders. Their BCI used high-density electrocorticography to tap neural activity from

962-471: A series of 16 paying patients to receive Dobelle's second generation implant, one of the earliest commercial uses of BCIs. The second generation device used a more sophisticated implant enabling better mapping of phosphenes into coherent vision. Phosphenes are spread out across the visual field in what researchers call "the starry-night effect". Immediately after his implant, Jens was able to use his imperfectly restored vision to drive an automobile slowly around

1036-423: Is a direct communication link between the brain 's electrical activity and an external device, most commonly a computer or robotic limb. BCIs are often directed at researching, mapping , assisting, augmenting , or repairing human cognitive or sensory-motor functions . They are often conceptualized as a human–machine interface that skips the intermediary of moving body parts (hands...), although they also raise

1110-496: 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. In this review, Tecce summarizes the development, morphology, and locus of appearance of the CNV. Studies have shown that

1184-516: Is located within Brodmann's area 6 and corresponds to the premotor cortex . 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. Zappoli reviews evidence which shows that in certain cases epileptic discharges affect

1258-457: Is of importance because the difference in the interstimulus interval (ISI) can have major effects on learning. For example, it has been shown that the length of the ISI, as well as the variability, changes habituation in subjects. When ISI is short and constant, habituation will happen more rapidly. The changes in the gap of time can be minuscule, from tens of milliseconds to several seconds long, and

1332-408: 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

1406-749: The Altran Foundation for Innovation prize for developing a Brain Computer Interface with electrodes located on the surface of the skull, instead of directly in the brain. Research teams led by the BrainGate group and another at University of Pittsburgh Medical Center , both in collaborations with the United States Department of Veterans Affairs (VA), demonstrated control of prosthetic limbs with many degrees of freedom using direct connections to arrays of neurons in

1480-531: The University of Pittsburgh , and Richard Andersen at Caltech . These researchers produced working BCIs using recorded signals from far fewer neurons than Nicolelis (15–30 neurons versus 50–200 neurons). The Carney Institute reported training rhesus monkeys to use a BCI to track visual targets on a computer screen (closed-loop BCI) with or without a joystick. The group created a BCI for three-dimensional tracking in virtual reality and reproduced BCI control in

1554-401: The grey matter of the brain during neurosurgery. Because they lie in the grey matter, invasive devices produce the highest quality signals of BCI devices but are prone to scar-tissue build-up, causing the signal to weaken, or disappear, as the body reacts to the foreign object. In vision science , direct brain implants have been used to treat non- congenital (acquired) blindness. One of

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1628-493: The retina . Neuron firings were recorded from watching eight short movies. Using mathematical filters, the researchers decoded the signals to reconstruct recognizable scenes and moving objects. Duke University professor Miguel Nicolelis advocates using multiple electrodes spread over a greater area of the brain to obtain neuronal signals. After initial studies in rats during the 1990s, Nicolelis and colleagues developed BCIs that decoded brain activity in owl monkeys and used

1702-481: The 1970s established that monkeys could learn to control the firing rates of individual and multiple neurons in the primary motor cortex if they were rewarded accordingly. Algorithms to reconstruct movements from motor cortex neurons , which control movement, date back to the 1970s. In the 1980s, Georgopoulos at Johns Hopkins University found a mathematical relationship between the electrical responses of single motor cortex neurons in rhesus macaque monkeys and

1776-411: 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. The CNV is elicited when two, linked stimuli are presented. When

1850-438: The CNV component. 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. 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

1924-411: The CNV controlled a physical object, a robot. 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

1998-400: The CNV occurs when two stimuli are contingent with each other. 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

2072-399: The air. The timing between the conditioned and unconditioned stimulus is important. There are two types of approaches for eye blink conditioning when it comes to timing between the stimuli. The first is called delay conditioning, which is when the conditioned stimulus (tone) starts, then continues until the unconditioned stimulus (air puff) is released after a delay, then they both suspend at

2146-445: The brain's electrical activity and the development of electroencephalography (EEG). In 1924 Berger was the first to record human brain activity utilizing EEG. Berger was able to identify oscillatory activity , such as the alpha wave (8–13 Hz), by analyzing EEG traces. Berger's first recording device was rudimentary. He inserted silver wires under the scalps of his patients. These were later replaced by silver foils attached to

2220-566: The brain, manifested by CNV, used a feedback loop to control the S2 buzzer in the S1-S2-CNV paradigm. The resulting cognitive wave representing the expectation learning in the brain was termed Electroexpectogram (EXG). The CNV brain potential was part of Vidal's 1973 challenge. Studies in the 2010s suggested neural stimulation's potential to restore functional connectivity and associated behaviors through modulation of molecular mechanisms. This opened

2294-456: 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

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2368-487: The company had successfully enabled a monkey to play video games using Neuralink's device. In 1969 operant conditioning studies by Fetz et al. at the Regional Primate Research Center and Department of Physiology and Biophysics, University of Washington School of Medicine showed that monkeys could learn to control the deflection of a biofeedback arm with neural activity. Similar work in

2442-405: The context of a simple learning task, illumination of transfected cells in the somatosensory cortex influenced decision-making in mice. BCIs led to a deeper understanding of neural networks and the central nervous system . Research has reported that despite neuroscientists' inclination to believe that neurons have the most effect when working together, single neurons can be conditioned through

2516-415: 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. The amplitude of the CNV changes when one changes

2590-563: The devices to reproduce monkey movements in robotic arms. Monkeys' advanced reaching and grasping abilities and hand manipulation skills, made them good test subjects. By 2000, the group succeeded in building a BCI that reproduced owl monkey movements while the monkey operated a joystick or reached for food. The BCI operated in real time and could remotely control a separate robot. But the monkeys received no feedback ( open-loop BCI). Later experiments on rhesus monkeys included feedback and reproduced monkey reaching and grasping movements in

2664-532: The direction in which they moved their arms. He also found that dispersed groups of neurons, in different areas of the monkey's brains, collectively controlled motor commands. He was able to record the firings of neurons in only one area at a time, due to equipment limitations. Several groups have been able to capture complex brain motor cortex signals by recording from neural ensembles (groups of neurons) and using these to control external devices. Phillip Kennedy (Neural Signals founder (1987) and colleagues built

2738-464: The door for the concept that BCI technologies may be able to restore function. Beginning in 2013, DARPA funded BCI technology through the BRAIN initiative, which supported work out of teams including University of Pittsburgh Medical Center , Paradromics, Brown, and Synchron. Neuroprosthetics is an area of neuroscience concerned with neural prostheses, that is, using artificial devices to replace

2812-467: 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. 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

2886-523: The first neuroprosthetic devices were implanted in humans in the mid-1990s. Studies in human-computer interaction via the application of machine learning to statistical temporal features extracted from the frontal lobe ( EEG brainwave ) data has achieved success in classifying mental states (relaxed, neutral, concentrating), mental emotional states (negative, neutral, positive), and thalamocortical dysrhythmia . The history of brain-computer interfaces (BCIs) starts with Hans Berger 's discovery of

2960-457: The first intracortical brain–computer interface by implanting neurotrophic-cone electrodes into monkeys. In 1999, Yang Dan et al. at University of California, Berkeley decoded neuronal firings to reproduce images from cats. The team used an array of electrodes embedded in the thalamus (which integrates the brain's sensory input). Researchers targeted 177 brain cells in the thalamus lateral geniculate nucleus area, which decodes signals from

3034-485: The first person to control an artificial hand using a BCI in 2005 as part of the first nine-month human trial of Cyberkinetics 's BrainGate chip-implant. Implanted in Nagle's right precentral gyrus (area of the motor cortex for arm movement), the 96-electrode implant allowed Nagle to control a robotic arm by thinking about moving his hand as well as a computer cursor, lights and TV. One year later, Jonathan Wolpaw received

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3108-432: The first scientists to produce a working brain interface to restore sight was private researcher William Dobelle . Dobelle's first prototype was implanted into "Jerry", a man blinded in adulthood, in 1978. A single-array BCI containing 68 electrodes was implanted onto Jerry's visual cortex and succeeded in producing phosphenes , the sensation of seeing light. The system included cameras mounted on glasses to send signals to

3182-473: 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. Most researchers agree that the CNV component has been associated with information processing and response preparation. The main controversy

3256-485: The function of impaired nervous systems and brain-related problems, or of sensory or other organs (bladder, diaphragm, etc.). As of December 2010, cochlear implants had been implanted as neuroprosthetic devices in some 736,900 people worldwide. Other neuroprosthetic devices aim to restore vision, including retinal implants . The first neuroprosthetic device, however, was the pacemaker . The terms are sometimes used interchangeably. Neuroprosthetics and BCIs seek to achieve

3330-441: The gap of time between the start of the neutral or conditioned stimulus and the start of the unconditioned stimulus. An example would be the case of Pavlov's dog , where the time between the unconditioned stimulus , the food, and the conditioned stimulus , the bell, is considered the ISI. More particularly, ISI is often used in eyeblink conditioning (a widely studied type of classical conditioning involving puffs of air blown into

3404-421: 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. Brain-computer interface A brain–computer interface ( BCI ), sometimes called a brain–machine interface ( BMI ),

3478-406: 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. 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

3552-403: The imperative stimulus, if it occurred, by a behavioral response, e.g., pressing a button, but the button worked only if it was pressed after the imperative stimulus had occurred (i.e., premature button presses were ineffective). The process of warning stimulus optionally followed by imperative stimulus recurred at variable intervals between 3–10 sec. The experimenters found that EEG responses to

3626-400: The implant. Initially, the implant allowed Jerry to see shades of grey in a limited field of vision at a low frame-rate. This also required him to be hooked up to a mainframe computer , but shrinking electronics and faster computers made his artificial eye more portable and now enable him to perform simple tasks unassisted. In 2002, Jens Naumann, also blinded in adulthood, became the first in

3700-414: The interstimulus interval is simply the time between the two flashes. The ISI plays a large role in the phi phenomenon (Wertheimer) since the illusion of motion is directly due to the length of the interval between stimuli. When the ISI is shorter, for example between two flashing lines alternating back and forth, we perceive the change in stimuli to be movement. Wertheimer discovered that the space between

3774-399: The motor cortex of tetraplegia patients. In May 2021, a Stanford University team reported a successful proof-of-concept test that enabled a quadraplegic participant to produce English sentences at about 86 characters per minute and 18 words per minute. The participant imagined moving his hand to write letters, and the system performed handwriting recognition on electrical signals detected in

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3848-465: The motor cortex, utilizing Hidden Markov models and recurrent neural networks . Interstimulus interval The interstimulus interval (often abbreviated as ISI ) is the temporal interval between the offset of one stimulus to the onset of another. For instance, Max Wertheimer did experiments with two stationary, flashing lights that at some interstimulus intervals appeared to the subject as moving instead of stationary. In these experiments,

3922-431: The muscles of primates are in process. Such BCIs could restore mobility in paralyzed limbs by electrically stimulating muscles. Nicolelis and colleagues demonstrated that large neural ensembles can predict arm position. This work allowed BCIs to read arm movement intentions and translate them into actuator movements. Carmena and colleagues programmed a BCI that allowed a monkey to control reaching and grasping movements by

3996-435: The neuronal mass principle, the neural degeneracy principle, and the plasticity principle. BCIs are proposed to be applied by users without disabilities. Passive BCIs allow for assessing and interpreting changes in the user state during Human-Computer Interaction ( HCI ). In a secondary, implicit control loop, the system adapts to its user, improving its usability . BCI systems can potentially be used to encode signals from

4070-524: The parking area of the research institute. Dobelle died in 2004 before his processes and developments were documented, leaving no one to continue his work. Subsequently, Naumann and the other patients in the program began having problems with their vision, and eventually lost their "sight" again. BCIs focusing on motor neuroprosthetics aim to restore movement in individuals with paralysis or provide devices to assist them, such as interfaces with computers or robot arms. Kennedy and Bakay were first to install

4144-538: The patient's head by rubber bandages. Berger connected these sensors to a Lippmann capillary electrometer , with disappointing results. However, more sophisticated measuring devices, such as the Siemens double-coil recording galvanometer , which displayed voltages as small as 10 volt, led to success. Berger analyzed the interrelation of alternations in his EEG wave diagrams with brain diseases . EEGs permitted completely new possibilities for brain research. Although

4218-400: The periphery. These sensory BCI devices enable real-time, behaviorally-relevant decisions based upon closed-loop neural stimulation. The BCI Research Award is awarded annually in recognition of innovative research. Each year, a renowned research laboratory is asked to judge projects. The jury consists of BCI experts recruited by that laboratory. The jury selects twelve nominees, then chooses

4292-402: The possibility of erasing the distinction between brain and machine . BCI implementations range from non-invasive ( EEG , MEG , MRI ) and partially invasive ( ECoG and endovascular) to invasive ( microelectrode array ), based on how physically close electrodes are to brain tissue. Research on BCIs began in the 1970s by Jacques Vidal at the University of California, Los Angeles (UCLA) under

4366-422: 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

4440-502: The range of communication functions that can be provided using a BCI. Development and implementation of a BCI system is complex and time-consuming. In response to this problem, Gerwin Schalk has been developing BCI2000 , a general-purpose system for BCI research, since 2000. A new 'wireless' approach uses light-gated ion channels such as channelrhodopsin to control the activity of genetically defined subsets of neurons in vivo . In

4514-420: The same aims, such as restoring sight, hearing, movement, ability to communicate, and even cognitive function . Both use similar experimental methods and surgical techniques. Several laboratories have managed to read signals from monkey and rat cerebral cortices to operate BCIs to produce movement. Monkeys have moved computer cursors and commanded robotic arms to perform simple tasks simply by thinking about

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4588-425: The same time. The other is called trace conditioning, where the conditioned stimulus (tone) is shorter and stops before the unconditioned stimulus (air puff) begins, leaving a gap between the two stimuli. This type of conditioning forces the subject, in this particular example, a bunny, to remember to link the conditioned stimulus with the unconditioned stimulus. The distinction between the two types of conditioning

4662-444: The subject is confident about when the imperative stimulus will be. The maximum amplitude is usually around 20 microvolts. The CNV appears most prominently at the vertex and is bilaterally symmetrical. 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

4736-420: The subject's eyes) where the ISI can affect learning based on the size of the time gap. What is of interest in this particular type of classical conditioning is that when the subject is conditioned to blink after the conditioned stimulus (tone), the blink will take place within the time period between the tone and the air puff, making the subject's eyes close before the puff can reach the eyes, protecting them from

4810-416: The sustained component the "contingent negative variation" because the variation of the negative wave was contingent on the statistical relationship between the warning and imperative stimuli. They observed that: In 1990 Bozinovska et al devised a CNV-based brain-computer interface to control a computer buzzer. In 2009, Bozinovski and Bozinovska designed a CNV-based brain-computer interface experiment, where

4884-411: The task and seeing the results, without motor output. In May 2008 photographs that showed a monkey at the University of Pittsburgh Medical Center operating a robotic arm by thinking were published in multiple studies. Sheep have also been used to evaluate BCI technology including Synchron's Stentrode. In 2020, Elon Musk 's Neuralink was successfully implanted in a pig. In 2021, Musk announced that

4958-468: The term had not yet been coined, one of the earliest examples of a working brain-machine interface was the piece Music for Solo Performer (1965) by American composer Alvin Lucier . The piece makes use of EEG and analog signal processing hardware (filters, amplifiers, and a mixing board) to stimulate acoustic percussion instruments. Performing the piece requires producing alpha waves and thereby "playing"

5032-411: The two lines is filled in by our brains and that the faster the lines alternate, the more likely we are to perceive it as one line moving back and forth. When the stimuli move fast enough, this creates the illusion of a moving picture like a movie or cartoon. Phi phenomenon is very similar to beta movement . As it applies to classical conditioning , the term interstimulus interval is used to represent

5106-425: The use of BCIs to fire in a pattern that allows primates to control motor outputs. BCIs led to development of the single neuron insufficiency principle that states that even with a well-tuned firing rate, single neurons can only carry limited information and therefore the highest level of accuracy is achieved by recording ensemble firings. Other principles discovered with BCIs include the neuronal multitasking principle,

5180-440: The various instruments via loudspeakers that are placed near or directly on the instruments. Vidal coined the term "BCI" and produced the first peer-reviewed publications on this topic. He is widely recognized as the inventor of BCIs. A review pointed out that Vidal's 1973 paper stated the "BCI challenge" of controlling external objects using EEG signals, and especially use of Contingent Negative Variation (CNV) potential as

5254-425: The warning stimulus seemed to have three phases: a brief positive component, a brief negative component, and a sustained negative component. The brief components varied with sensory modality (e.g., visual vs auditory), while the sustained component varied with the time gap between the warning and imperative stimuli (and whether the imperative stimulus occurred) and the subject's attention/vigilance. Walter et al labeled

5328-424: Was called the O wave, or orienting wave. 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. A related, important issue has been

5402-419: Was increased. The results of these conditions suggest that the CNV is related to attention and expectancy. 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. Some researchers have shown that the intensity of the stimulus may affect the CNV amplitude. It seems that the CNV component has

5476-458: Was the general consensus until other work provided evidence that the CNV can be distinguished from the RP. 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

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