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Fast-Fourier Transform (FFT) transforms a signal from the time domain into the frequency domain. Basically, any time-dependent signal can be broken down in a collection of sinusoids. In this way, lengthy and noisy EEG recordings can be conveniently plotted in a frequency power-spectrum. By doing so, hidden features can become apparent. By adding all the ...


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Many EEG responses are swamped in random brain activity, artifacts and background noise. A single movement typically doesn't evoke measurable activity, because its amplitude is so small with respect to background noise. I think the potentials you are looking for are event-related potentials or ERPs (Fig. 1). During ERP recording, basically a regular EEG is ...


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Short answer The cochlea is a tonotopic map with certain physically determined boundaries that determine the range of frequencies perceived. Ultrasonic soundwaves simply do not have a correlate on this map. Background The cochlea is a frequency analyzer that basically translates acoustic frequencies into a place-map. High frequencies are encoded basally (...


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Any periodic waveform can be produced by adding up a series of sin waves of the appropriate frequency and amplitude. The FFT looks at a complex waveform and calculates those frequencies and amplitudes. The result is a new curve which plots amplitude vs frequency. Thus, it transforms the signal from the time domain into the frequency domain. I don't have ...


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Event-related potentials are an issue in many aspects of physiology, not just in EEG analysis, so this answer is more general. The main problem is that electrical or other signals that are associated with some "event" are typically much lower in magnitude than the background noise in the system being examined. Electrocardiograms are the exception in this ...


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Specific events, e.g. finger flexions, generate synchronized neuronal responses in the brain that can be measured on the scalp with EEG. However, a voltage response to a single event typically generates a low-amplitude response relative to the background EEG. One way to enhance the signal-to-noise ratio is to repeatedly record the EEG in response to the same ...


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EEGs are often analyzed in the frequency domain, where signals are subjected to spectral analysis, typically by Fast Fourier Transformation, or FFT. What an FFT basically does is decomposing a signal in the time domain into one in the frequency domain. It does this by decomposing the input signal (any signal, including EEG) into a series of sinusoids. ...


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Action potentials of single neurons (APs) are the building blocks of compound action potentials (CAPs). While each of the individual APs is a yes-or-no response with a clear-cut defined threshold, CAPs are not. CAPs are build up of hundreds or thousands of neuronal contributions in, e.g., the auditory nerve. Decreased responsiveness as well as ...


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Excellent question! The difference is the fact that the rheobase is an example of a threshold measure. The threshold, as you correctly suggest, is the minimal energy (typically current level and not voltage as you suggest) to excite neural tissue. The threshold applies only under the specific experimental parameter settings used. These parameters include the ...


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A number of cardiomyocytes is lost during an infarction. Instead, fibrous tissue forms, but it only preserves structural integrity, having no contractile function [1]. Myocardial infarction is an uncommon condition in pediatrics, happening very rare, when embolization occurs due to blood coagulation affections or heart congenital defects [2]. The fibrous ...


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There is no physical limitation whatsoever on the frequency band you wish to record, other than the hardware limitations on the sampling rate. Often electrophysiological recordings suffer from noise (mainly in the high-frequencies) and drifts in the baseline (low-frequency range). In the end, you wish to filter out as much noise as possible, without ...


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I think that you are misquoting Aliasing. Digital acoustics is explained in a mathematical sense, Aliasing is a maths concept. Real life acoustics is explained in a physical sense, which talks about reflection, absorption, phase change, harmonic modes, weights... the perception of sound is discussed as psychoacoustics and cortical structures and individual ...


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EEG 10-20 system. source: Wikipedia How many actual channels are there? 21 in the figure, i.e., the number of active electrodes. What's the difference between reference and active channels? The active electrode is the electrode under investigation. Basically this is arbitrary. Consider electrode F2 and F3. When you measure the potential ...


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ERPs are typically analyzed in terms of amplitude and latency. FFT is not really an option; it doesn't make sense. There may be some applications where it may be useful, but these are quite specific. For example, if repeated stimuli are presented and you are not averaging them, but you are collection an EEG, then FFT may help you to deduce whether stimulus ...


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For this answer, I'll use a very broad definition of "buffer" as a mechanism to integrate information at different delays. I have no interest in getting into specific computer science definitions of what a buffer is and I don't think it makes any sense to use them in biology. Parallel processing and predictive coding The brain is a massively ...


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So, are repetitions wanted in this kind of experiment? Yes: repetitions reduce random noise and increase the chance to tell artifact from response. Adaptation is a serious issue, typically becoming apparent by decreasing amplitudes, or even skipped responses. Reading the existing literature and/or performing experiments with various stimulus intervals may ...


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A-Flutter will have discernible waves that can be counted, usually. The R-R interval will be regular or maybe slightly irregular if there's a variable conduction block in the AV Node. A-Fib will ALWAYS be completely irregular without discernible pattern. You can also modify the position of your limb leads. There is an EKG placement called the S5-Lead that ...


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After developing and checking the algorithm with simulated ECG data, i found out that premature beats (as the name suggests) itself arrive prematurely i.e. their R-R peak interval is less then the R-R peak interval between normal beats. In that case, i am considering the averaged interval between normal beats and compare it to the interval between next ...


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In fact, filters can be damaged by heat. However, newer filter coatings are less prone to heat damage [details]. For the barrier filter, it's less likely to be heat damage. The older/less expensive filter coatings do degrade slowly over time and have to be replaced. So I would guess that the haze represents permanent, non-removable damage to the coating. ...


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Its probably not from heat. Filters are basically a glass substrate with some ionic compound deposited in thin layers. These won't oxidize at reasonable temperatures, and furthermore since you have it on the emission filter as well, its even less likely to be from the source. More likely its just accumulated organic material from the environment. 7 ...


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