Editing Evoked potential (section)

===The "sweep" technique===
The sweep technique is a hybrid frequency domain/time domain technique.<ref name="Rapid">{{cite journal | author = Regan D | year = 1973 | title = Rapid objective refraction using evoked brain potentials | journal = Investigative Ophthalmology | volume = 12 | issue = 9| pages = 669–79 | pmid = 4742063 }}</ref> A plot of, for example, response amplitude versus the check size of a stimulus checkerboard pattern plot can be obtained in 10 seconds, far faster than when time-domain averaging is used to record an evoked potential for each of several check sizes.<ref name="Rapid"/>
In the original demonstration of the technique the sine and cosine products were fed through lowpass filters (as when recording a SSEP )  while viewing a pattern of fine checks whose black and white squares exchanged place six times per second. Then the size of the squares was progressively increased so as to give a plot of evoked potential amplitude versus check size (hence "sweep"). Subsequent authors have implemented the sweep technique by using computer software to increment the spatial frequency of a grating in a series of small steps and to compute a time-domain average for each discrete spatial frequency.<ref name="Infant">{{cite journal |author1=Norcia A. M. |author2=Tyler C. W. | year = 1985 | title = Infant VEP acuity measurements: Analysis of individual differences and measurement error | journal = Electroencephalography and Clinical Neurophysiology | volume = 61 | issue = 5| pages = 359–369 | doi = 10.1016/0013-4694(85)91026-0 | pmid = 2412787 }}</ref><ref>{{cite journal |author1= Strasburger, H. |author2=Rentschler, I. | year = 1986 | title = A digital fast sweep technique for studying steady-state visual evoked potentials| url = http://webdoc.sub.gwdg.de/pub/med/2007/strasburger-86-digital.pdf | journal = Journal of Electrophysiological Techniques| volume = 13 | issue = 5| pages = 265–278}}</ref>
A single sweep may be adequate or it may be necessary to average the graphs  obtained in several sweeps with the averager triggered by the sweep cycle.<ref name="pattern">{{cite journal | author = Regan D | year = 1975 | title = Colour coding of pattern responses in man investigated by evoked potential feedback and direct plot techniques | journal = Vision Research | volume = 15 | issue = 2| pages = 175–183 | doi = 10.1016/0042-6989(75)90205-9 | pmid = 1129975 | s2cid = 42218073 }}</ref> Averaging 16 sweeps can improve the signal-to-noise ratio of the graph by a factor of four.<ref name="pattern"/>
The sweep technique has proved useful in measuring rapidly adapting visual processes<ref>{{cite journal |author1=Nelson J. I. |author2=Seiple W. H. |author3=Kupersmith M. J. |author4=Carr R. E. | year = 1984 | title = A rapid evoked potential index of cortical adaptation | journal = Investigative Ophthalmology & Visual Science | volume = 59 | issue = 6| pages = 454–464 |pmid=6209112 | doi=10.1016/0168-5597(84)90004-2}}</ref> and also for recording from babies, where recording duration is necessarily short. Norcia and Tyler have used the technique to document the development of visual acuity<ref name="Infant"/><ref name="Spatial">{{cite journal |author1=Norcia A. M. |author2=Tyler C. W. | year = 1985 | title = Spatial frequency sweep VEP: Visual acuity during the first year of life | journal = Vision Research | volume = 25 | issue = 10| pages = 1399–1408 | doi = 10.1016/0042-6989(85)90217-2 | pmid = 4090273 |s2cid=23557430 }}</ref> and contrast sensitivity<ref name="Electrophysiological">{{cite journal |author1=Norcia A. M. |author2=Tyler C. W. |author3=Allen D. | year = 1986 | title = Electrophysiological assessment of contrast sensitivity in human infants | journal = American Journal of Optometry and Physiological Optics | volume = 63 | issue = 1| pages = 12–15 | pmid = 3942183 | doi=10.1097/00006324-198601000-00003|s2cid=19809242 }}</ref> through the first years of life. They have emphasized that, in diagnosing abnormal visual development, the more precise the developmental norms, the more sharply can the abnormal be distinguished from the normal, and to that end have documented normal visual development in a large group of infants.<ref name="Infant"/><ref name="Spatial"/><ref name="Electrophysiological"/> For many years the sweep technique has been used in paediatric ophthalmology ([[electrodiagnosis]]) clinics worldwide.