Abstract:
The invention is a method to aid analysis of signals, such as electroencephalograms, pursuant to modern mathematical theories of nonlinear dynamical processes, sometimes referred to as chaotic dynamics or chaos theory. It employs graphic display and visual inspection of relatively less filtered, non-averaged raw test data, including raw data heretofore considered random or asynchronous `noise`. The invention enables reversible decomposition of selected elements of graphic portraits of raw signal data to identify subsets of the depicted raw data which correspond to visually-identified, manually-selected patterns from within the graphic portrait. The identified subsets of raw data can be segregated even though a precise mathematical description of the visually identified pattern is unknown. The invention further comprises a variety of techniques for displaying four or more variables and for enhancing visual discrimination of patterns within computer generated graphic phase space portraits, and conceptions for overlaying symbols onto graphic points representing stimulus and response events concurring with particular signal samples in the phase space portrait. The invention also comprises subsets of pattern-generating signal data identified by the method of the invention and thus made available for further computer or other operations separately from the full data set.

Description:
There are no related applications. No federally-sponsored research and development is involved. 
     SUMMARY OF THE INVENTION 
     The invention is a method for applying the new theories of chaotic dynamics to brain signals. It enables a computer operator to automatically identify in a recorded stream of brain signal data the subsets of signal data which correspond to manually-selected patterns observed in multi-variable, reversibly-transformable, phase space portraits. The data selection is enabled even though no algorithm describing the observed pattern is known. This data selection capability is combined with enhanced capabilities to display and manipulate multi-variable phase space portraits, thereby increasing the ability to visually discriminate patterns in the stream of data for selection. 
     The invention draws a large number of variables into a graphic phase space portrait for display on a computer monitor. It then enables manual selection of subsets of drawing elements from within the displayed portrait corresponding to visually identified patterns, and automatically decomposes the selected drawing elements to identify the subset of signal data corresponding to the visually-identified patterns. Each phase space portrait can simultaneously display multiple variables, including three spatial coordinates corresponding to three separate signal detectors, plus scalar magnitude, direction of change, and color-coded time sequence. In principle, such portraits also could display another variable corresponding to drawing line type and could superpose symbols to depict stimulus and response events relative to the time sequence of recorded signals, though the current model does not implement these features. 
     The invention also creates and depicts composite phase space portraits of larger sets of four or more signal detectors by means of overlays of simultaneous phase space portraits from a plurality of three-detector subsets. Variable colors serve to visually distinguish the contributions of each layer to the composite, thus enabling visual discrimination of the particular subsets of detectors which provide the signals of most interest. In principle, variable line types also could be used to distinguish layers. 
     One aspect of the invention may be viewed as a computer-assisted manual sieve to identify from a stream of data the subsets of data which correspond to an observed pattern where no algorithm describing the observed pattern is known. The resulting subsets of pattern-containing data then are available for more intensive analysis and other operations, including efforts to define a descriptive algorithm for the observed pattern and efforts to create a `template` for automated computer-aided pattern recognition. 
     BACKGROUND OF THE INVENTION 
     The field of this invention is analytic methods for depiction and analysis of brain signals. Electric potentials have been measured on scalps or with implanted electrodes for decades. The subjects of such measurements have been both human and animal. The current method, commonly called an electroencephalogram or EEG, measures and records a data stream comprised of the electric potentials between each of a plurality of detection electrodes distributed across the subject&#39;s scalp and a reference electrode attached to some other portion of the subject&#39;s head. A common reference electrode, such as one on an earlobe, may be used. 
     The relationship between a given electrode and the reference electrode is customarily called a &#34;channel&#34;. It has been recognized that the placement of the plurality of electrodes affects the signal collection. Therefore, conventions, such as the &#34;ten-twenty&#34;, have been agreed upon to guide the geographic distribution of electrodes about the scalp for collection of EEGs for clinical use. 
     The data stream of electric potentials from each channel is electronically amplified to strengths suitable for computer analysis and recorded. In modern practice the data stream usually is digitized for use in digital computers, but the data stream can be analyzed by analog computer if desired. The amplified electric potentials usually are electronically `filtered` to limit the collected signal to selected electronic frequencies. The data stream also frequently is `averaged` to eliminate more-random or asynchronous data that has been assumed to be meaningless `noise`. 
     In digital computer analysis the data stream sometimes is passed through a Fast Fourier Transform, or FFT. Less commonly, the data may be analyzed through a Mellin or `double` Fourier Transform. 
     The Fourier Transform and related transforms assume as a mathematical premise that the collected signal can be represented as the sum of a series of sine waves. The Fast Fourier Transform is a computer-implemented technique employing this mathematical premise. 
     The electroencephalogram has a number of characteristics which limit its discrimination among brain signals. The `filtering` and `averaging` both eliminate portions of the collected signal. This elimination process employs the unverified assumption that the data which is thereby eliminated is meaningless `noise`. That is, it commonly is assumed that the signal of interest is `non-random` and that data which is &#34;random&#34; is meaningless `noise`. The filtering and averaging have as their purpose the extraction of the `non-random` signal from `noise`. This assumption has been driven by the practical necessity that no better way of analyzing and depicting the entire data set has existed. That is, the discarded data was arbitrarily treated as `meaningless` due to the lack of a method of ascertaining its meaning, but with no practical method of evaluating whether or not the discarded data in fact is intrinsically meaningless. 
     A compelling practical reason for use of filtering and averaging is the lack of computer-implemented algorithms which can represent a mathematically true transform of the entire data set of collectible electric potentials without such filtering and averaging. 
     Some filtering is designed to eliminate signals external to the subject. An example is the 60 hertz `notch` filter which is intended to eliminate radiated signals from electric transmission lines and devices that transmit about the 60 hertz frequency. However, other filtering is employed to eliminate portions of the collected signal which truly emanate from the human or animal subject. 
     An analytic disadvantage of the current computer techniques is that discarding portions of the raw data set through filtering and averaging renders the transform of the raw data into the displayed signal irreversible. That is, a depicted EEG image cannot be reversibly re-transformed into the original raw data from which it was drawn due to the destruction of part of the original data set by &#34;filtering&#34; and &#34;averaging&#34;. Consequently, mathematically precise, reproducible decompositions of differing graphic depictions of mathematical transforms of the identical raw data stream can not readily be analytically verified to be true equivalents. 
     In recent years new mathematical techniques have been developed for analysis of nonlinear dynamical processes, sometimes referred to as the mathematics of chaos or chaotic dynamics. These new techniques search for patterns, and frequently for those patterns mathematically defined as strange attractors. These new techniques employ computer generated `phase space portraits` to visually depict a data stream, and then attempt to infer an appropriate mathematical description of the data stream from patterns visually detected in the graphic `phase space portraits`. Early examples of this technique are as follows: N. H. Packard, J. P. Crutchfield, J. Doyne Farmer, and R. S. Shaw, &#34;Geometry of a Time Series&#34;, Physical Review Letters, 47 (1980), p. 712; F. Takens, &#34;Detecting Strange Attractors in Turbulence&#34; in Lecture Notes in Mathematics 898, D. A. Rand and L. S. Young, eds., (Berlin: Springer-Verlag, 1981), p. 336; J. P. Crutchfield, J. Doyne Farmer, N. H. Packard, and R. S. Shaw, &#34;On Determining the Dimension of Chaotic Flows&#34;, Physica 3D, (1981), pp. 605-17. 
     Recent publications disclose efforts to apply phase space portraits to both electrocardiograms, EKGs, and electroencephalograms, EEGs. &#34;Is it Healthy to be Chaotic&#34; and &#34;The Footprints of Chaos&#34;, Science, Vol. 243, pp. 604-607, 8 Feb. 1989. &#34;Chaos Theory: How Big an Advance&#34;, Science, Vol. 245, pp. 26-28, 7 Jul. 1989. 
     THE PROBLEMS ADDRESSED BY THE INVENTION 
     A problem experienced in efforts to apply the new mathematics of nonlinear or chaotic dynamics to brain signals is that the signals must be taken at extremely short time intervals, on the order of milliseconds or less, resulting in an extremely high volume of data in a very short period of time. This necessitates use of a computer to collect and record such signals and to correlate the data stream with stimulus and response events. 
     The signals recorded from scalp electrodes appear to be a complex composite of several different biological processes of poorly defined origin. Signals reflecting muscular processes, including heartbeat, breathing and voluntary muscle contraction, are mixed in with and to a large extent obscure other signals of interest concerning brain function. In addition, signals from multiple processes within the brain itself may form a portion of the composite signal. Furthermore, the electrodes, or the subject&#39;s body, may also be acting antennas collecting signals from the environment. 
     Prior methods of extracting signals from the background have generally employed some form of averaging to limit the signal to nonrandom patterns, thereby deliberately discarding more random data from the signal. These prior methods also employ `artifact rejection` which in practice means that signals exceeding a pre-defined amplitude are assumed to be &#34;artifact&#34;, such as the signal of a muscular movement, and are &#34;rejected&#34; or deleted from the data stream before averaging. According to the new mathematics of nonlinear or chaotic dynamics it may be postulated that such `random` and `artifact` data is in fact part of the genuine brain signal, the meaning of which must be deciphered to understand the entire signal. Under these postulates, &#34;averaging&#34; to eliminate non-random portions of the signal eliminates chaotic data which is in fact a part of the true signal of brain function. In particular, averaging may obscure the transitions from chaotic to ordered states, and vice versa. However, programmable algorithms describing such chaotic data sufficient to employ automated computer pattern recognition or signal analysis have not yet been found. 
     Thus, the problem is to identify nonlinear dynamic characteristics of cognitive and other brain signals which distinguish such elements from the composite signal when no descriptive, programmable algorithms are known. Since the characteristic attributes of signals denoting cognitive brain functions are not yet known, empirical tools are needed to search for such distinctive characteristics so that such signals can be extracted from the background data. The invention is conceived as such a tool. 
     It is known that patterns sometimes can be visually recognized in phase space portraits even though such patterns cannot be described with mathematical precision sufficient to define an algorithm for automatic computer recognition of such patterns. The invention is designed to allow manual screening of raw data for visually recognizable patterns, manual selection of the drawing elements which form such patterns, and identification of the raw data which is reflected in the selected patterns. 
     Because the subset of raw data so identified contains the visually recognized pattern extracted to some degree from the background data, that subset of data can be subjected to more intensive and more efficient processing and analysis to find the best mathematical description to describe the observed pattern. 
     Once a pattern has been visually recognized and the data including that pattern segregated, it is possible to guide the search for an algorithm describing the pattern by reference to the known phase space portraits of a variety of mathematical formulae. See &#34;Geometry from a Time Series&#34;. 
     It is known that patterns sometimes may appear in graphic phase space portraits of data reflecting nonlinear dynamic processes only when a sufficiently large number of variable dimensions is reflected in the graphic portrait. For this reason it is desirable in phase space portraits to visually depict as many variable dimensions as can be achieved. 
     OBJECTIVES AND FEATURES OF THE INVENTION 
     A feature of the invention is the methods employed to increase the number of visually distinctive dimensions which can be displayed in a mathematically precise graphic portrait. In addition to the three physical dimensions which can be displayed in Cartesian coordinates, the invention enables other visually-distinctive dimensions by use of layers to create composite phase space portraits, use of colors to denote time sequence, use of colors to distinguish between the layers in a composite portrait, and use of time-linked color sequences to visually display time sequence and to seek periodicities within graphic phase space drawings. In principle, distinctive line types also could be employed to distinguish between layers in a composite portrait. 
     The power of the invention to point out subsets of raw data corresponding to visually-identified patterns thus is combined with enhanced ability to display patterns which arises from the capacity to graphically depict a large number of variable dimensions. 
     It is known that patterns sometimes can be made to appear more visibly distinctive when the phase space diagram is rotated in three dimensions, or otherwise manipulated through mathematically precise transformations. It is a feature of the invention that the graphic portraits can be passed into commercially available computer-aided drawing, design and engineering programs wherein they can be rotated, viewed in mirror image, and otherwise viewed after mathematically precise, reversible transformations. 
     It is an objective of the invention to enable analytic depiction of the `raw` amplified stream of electric potentials collected from a plurality of electrode channels, while reducing filtering of the raw data stream and eliminating the mathematical processing called `averaging`. It is a feature of the invention that it enables analytic depiction of the entire data stream, including within the analytically depicted data set so-called `random` data which prior analytic methods discarded as non-analyzable. 
     It is an objective of the invention to enable testing of the assumption that apparently `random` brain signal data, heretofore eliminated as `noise` or `artifact` through filtering and averaging, are meaningless. It is a feature of the invention that it reflects visually detectible patterns in the data stream, without first imposing patterns on the data by the assumption that it can properly be represented by a Fourier transform. It also displays signals of large magnitude heretofore rejected as &#34;artifact&#34;. 
     It is a further objective of the invention to enable the depiction of brain signal data in more than three dimensions, e.g. more than wave amplitude and phase over time as previously enabled by the continuous sine-like wave in an electroencephalogram. It is a feature of the invention that it enables depiction of change over time of a unique point in two or three dimensional space defined by simultaneously-recorded electric potentials, respectively, of two or three different electrode channels. It is a further feature of Applicant&#39;s invention that a single drawing line entity can simultaneously depict three drawing coordinates, a direction, an amplitude corresponding to line length, a unique color and a unique line type. Two successive drawing line entities also form an angle, which may be employed in pattern characterization. Each drawing line entity can be placed within a color-coded time sequence in the phase space portrait. In principle, symbols denoting stimulus and response events could also be superposed upon the time sequence. In principle, another variable dimension could be depicted by use of unique line types. See AutoCAD Manual, Sec. 7.9, et seq., pp. 192-195. 
     It is a further feature of the invention that it enables composite depiction of a plurality of layers wherein each such layer reflects the data stream from a unique different subset of two or three signal channels drawn from a larger set of channels. For example, from a set of four electrodes, layer one can depict a three-electrode combination 1,2,4; layer 2 can depict electrode combination 3,2,4; layer 3 depict electrode combination 2,1,3; and layer 4 depict electrode combination 4,1,3. In this example, a compound visual image can be assembled by overlays of layers 1 through 4, or any subset of them. 
     A particular layer might be thought of as a &#34;slice&#34; through the skull on a plane defined by the physical placement of the three detection electrodes, relative to the reference electrode, whose data streams are employed to define that particular layer. The composite graphic phase space portrait formed by the overlay of two or more layers might be thought of as a series of slices cut at different angles through the skull. 
     Each layer in a composite image can be assigned a different color so that the comparative contributions of different layers to the composite image can be visually distinguished on a color computer monitor. This enables rapid visual focus on those layers which produce the most dramatic display of distinctive patterns. Because layers can be turned on and off in any combination, the most dramatic presentations can quickly be identified, while parsimony in data presentation can be achieved by turning off those layers which contribute least to visual discrimination of patterns. 
     The limitation on the number of electrode combinations which can be so depicted in a composite image is practically limited by the number of channels recorded, by the capacity of the computer, and by the graphic capacity of its monitor, but not by the analytic method. The permutations of electrode combinations which can be depicted rises as a function of the number of electrodes recorded. 
     It is a feature of the invention that it enables visual inspection for empirically reproducible patterns in a stream of signal data, with less restrictive assumptions than previously employed concerning the mathematical formula which will best describe the data stream. That is, patterns are allowed to manifest themselves in the graphic portrait even though algorithms which describe the visible patterns are unknown. 
     It is a feature of the invention that it enables mathematically reversible transformations of the raw data set, without discarding any of the data set. It is a feature of the invention that it enables reversible transforms of the identical raw data set into a wide variety of mathematically-comparable, visually-inspectible graphic portraits. The transformations available in commercial CAD software include mirror imaging, and three-dimensional rotations. See AutoCAD Manual, Sec. 5.25, p. 117 and Chap. 14, pp. 309-311; AutoCAD Reference Manual Supplement, Release 9.0, Sec. 1.13, p. 9. This enables identification of those transforms which provide more distinctive depictions of unique features or patterns in the data set. 
     It is a feature of the invention that distinctive drawing &#34;entities&#34; depicted in the visual image can be &#34;selected&#34; and decomposed with mathematical precision into the subset of the raw data from which the selected drawing entity was created. For example, a drawing structure from within a phase space portrait displayed on the computer monitor can be selected by pointing with a computer mouse to the drawing entities which compose the structure. A computer program specially developed by the Inventors for this purpose then identifies the precise subset of raw data points upon which the selected drawing structure is based. See the PICK.LSP program listing appended hereto. 
     Visually identified distinctive patterns can be extracted as a &#34;block&#34; from the displayed phase diagram and decomposed into the subset of raw data which produced that block, thus enabling visually-directed identification of pattern-producing subsets of the raw data. See the GRAB.LSP program listing appended hereto. 
     Identification of the raw data point which produced a pattern enables segregation of that subset of raw data for more efficient, intensive analysis to find a descriptive algorithm. This feature of the invention enhances efforts to focus the search for a descriptive algorithm on classes of mathematical formulae whose graphs are known to approximate the pattern segregated from the phase space portrait. See &#34;Geometry from a Time Series&#34;, above. 
     A feature of the invention allows correlation of a subset of raw data with presentation of an external stimulus to the brain being monitored. &#34;Event flags&#34; or markers, indicating by their content the type of stimulus and by their location in the data sequence the time of presentation of stimuli to the human or animal whose brain signals are being recorded, could be inserted into the recorded stream of raw data. For example, if there were four detector channels being simultaneously recorded in parallel, the recorded computer data file would contain sets of four data points each time the detectors are simultaneously sampled, one point for each detector. The four-point data sets would be iterated for as many sampling times as desired. The data sets could be expanded to six points per set, assigning one additional point to stimulus events and the other additional point to response events. When a distinctive drawing structure displayed on screen was decomposed into the raw data it then could be temporally related with mathematical precision to stimulus and response events through inspection of the stimulus and response data points embedded in the raw data stream. These same flags embedded in the data stream could also be employed to place a distinctive marker in the graphic phase portrait on or close to the point entity formed from the signals in the data set in which the flag appears. 
     A feature of the invention is that the elements of the graphic display of the data may be considered virtual vectors calculated from the data streams of electrodes which are geographically dispersed over the subject&#39;s scalp. That is, a given drawing line entity possesses both a scalar magnitude and a direction. This allows inferences to be drawn from such virtual vectors about the geographic distribution within the head of the electric phenomena which are being graphically depicted. 
     A further feature of the invention is that a series of permutations, comprised of combinations of different sets of three electrodes drawn from a larger set of electrodes distributed over the whole head, can be depicted as overlays in a composite image. The resulting composite image reflects the virtual vectors of a broader geography of the head than can a subset of only three electrodes, thus enabling the drawing of more sophisticated inferences about the geographic distribution of phenomena within the head. 
     A feature of the invention is that the data stream can be depicted as a `tree` structure emanating radially from the center of a three dimensional phase space. Alternatively, the data stream can be depicted as emanations from corners of a cube along the cube&#39;s walls and within the interior space of the cube. The `tree` or center-based structure tends to reduce overlapping of the larger magnitude elements of the drawing structure making such larger magnitude images more readily distinguishable. The cube corner structure tends to reduce overlapping near the origins at the corners of the cube thus making lower amplitude drawing structures near the origins more readily discernable. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic diagram of a signal collection system. 
    
    
     THE INVENTION 
     The invention employs specially developed computer programs to format a stream of raw electronically-recorded brain signal data into ASCII DXF, or Drawing eXchange Files. See the DXFROW.EXE and DXFBOX.EXE computer program listings appended hereto. A data &#34;point entity&#34; in three dimensional space is defined by assigning from the raw data stream the signals recorded substantially simultaneously from three different detection electrodes as the `x`, `y`, and `z` coordinates, respectively. For example, the potential recorded from electrode 1 is the `x` dimension, that from electrode 2 is the `y` dimension, and that from electrode 4 is the `z` dimension, thereby defining a unique point in the three dimensional phase space. A &#34;line entity&#34; then is defined as the line connecting two successive data &#34;point entities&#34;. These point and line entities are defined within recognized conventions for graphic computer displays, such as the Drawing eXchange Format standard or DXF convention. Alternatively, various curved drawing entities instead of lines could be employed to connect the data points. The drawing &#34;line entity&#34; so defined can be thought of as a virtual vector reflecting the scalar value and the direction of the change over time of the electric potential from one data point to the succeeding data point. It is, of course, possible in principle to transform the drawing structures from Cartesian coordinates to polar coordinates, though the current software does not do so. 
     When so formatted the signal data can be imported into commercially available computer-aided design or CAD computer software programs. Formatting in accord with the ASCII DXF definition system enables mathematically reversible graphic display of the raw data in a wide variety of engineering computer-aided design programs such as AutoCad (R). It further enables manipulations of the raw data stream through three dimensional rotations and other image transformations using the capabilities of commercially available CAD programs. In principle, the formatted data could be translated into Initial Graphics Exchange Standard (IGES) files for use on other systems. See AutoCAD Manual, Sec. C.3, p. 383. 
     A variety of capabilities within such commercial CAD software is employed to enhance the number of visually displayed variable dimensions within the phase space portrait. From within the commercial CAD program a computer mouse is employed to manually point out the drawing entities within a graphic portrait which form visually identified patterns. A set of commands within the CAD program then forms a `selection-set` of the identified drawing entities. 
     The invention then employs specially developed computer programs to decompose the `selection-set` of drawing entities to identify the subset of raw signal data from which the manually-selected patterns were constructed. See the PICK.LSP computer program listing appended hereto. 
     DETAILED DESCRIPTION 
     &#34;Signal detector&#34; means a device for detection of phenomena of interest such that signal data can be collected through the device. A signal detection device in the case of electroencephalograms means metallic electrodes; and the signal is the electric potential measured between a pair of electrodes, one attached to the scalp and compared to a reference electrode attached elsewhere on the subject&#39;s head. An example of an electrode is the type E6GH gold disc electrode from Grass Instrument Company, Quincy, Mass. 02169. 
     &#34;Automatic collection of signal data&#34; by computer means detection of the signal through electrodes and electronic amplification to voltages suitable for computer processing. Drawing 1 is a schematic diagram of a signal collection system. The amplified signal is digitized for use in digital computers. Signal amplification and digitization are both well known electronic techniques. Electronic circuits for analog to digital conversions of a stream of signals, commonly called A/D circuits, are well known. A plurality of A/D converters in parallel under the control of a single timer can be employed for substantially simultaneous, parallel data collection from a plurality of signal detectors for display and analysis according to the invention. The Inventors estimate that the time intervals currently employed are approximately 1500 microseconds more or less between trigger signals. That is, that a data sample set is latched approximately every 1500 microseconds, though this time interval can be adjusted if desired. The Inventors estimate that the amplitude of scalp signal resolution currently employed for signal collection is approximately 3200 nanovolts, or 3.2 microvolts, though the gain is adjustable in a range above and below that value if desired. 
     &#34;Substantially simultaneous&#34; collection of signal data from several detectors is achieved by a common triggering signal from a timer controlled by a central or &#34;host&#34; processor to each of the several data detector &#34;channels&#34; which operate in parallel, resulting in substantially simultaneous initiation of data gathering and `latching` of a data value in every channel. This is followed by serial polling of the parallel data channels by a central processor to collect the latched data from each channel for recordation and/or further processing. The signal data then is serially written to storage media, such as a hard disk, in sets comprising a data value for each detector plus one or more additional items per set to represent any stimulus or other event which occurred during the same sampling period. The required file structure into which the collected raw data must be written to enable operation of the listed computer programs is described in the &#34;RAW DATA FILE FORMAT&#34; in Appendix 1 hereto. 
     Construction of computer graphic drawing entities, including drawing point entities and drawing line entities among others, is defined in accord with recognized computer conventions such as the ASCII DXF file format. 
     The invention employs computer software programs specially written for the invention to translate the collected raw signal data into computer graphic drawing &#34;point&#34; and &#34;line&#34; entities, to define drawing &#34;layers&#34;, and to assign color attributes to the drawing layers. See the DXFROW.EXE and DXFBOX.EXE computer program listings appended hereto. Where it is desired that a single drawing line entity have a separate color, that single drawing line entity is drawn on its own separate layer and the color is assigned to the layer. See the DXFCOL.EXE computer program listing appended hereto. 
     The image resulting from translation of a set of signal values into a series of computer graphic drawing entities is referred to as a &#34;graphic phase space portrait&#34; of such set of signal values. 
     Coordinates means a Cartesian, polar or relative coordinate system. See AutoCAD Manual, sec. 2.9, et seq., pp. 39-40. Thus, in a three dimensional Cartesian coordinate system, a point P would be defined by &#34;x&#34;, &#34;y&#34; and &#34;z&#34; coordinates. 
     The Inventors limit each individual phase space portrait or &#34;frame&#34; to approximately 100 samples, or less, to avoid excessive overlapping of drawing entities, enhance visual discrimination of drawing patterns, and permit more reliable selection of particular drawing entities with the computer mouse. The number of samples per frame is adjustable. Individual frames are then lined up in rows and columns according to time sequence. Within AutoCAD an individual frame, or any portion of it, can be `windowed` for `zoom` magnification to inspect smaller details of the phase space portrait. 
     Visual identification of patterns means to visually inspect the computer generated graphic image as displayed on the computer monitor screen. The invention employs commercially available AutoCAD (R) software to process ASCII DXF files into the computer, display the graphic images, to manually point to and select drawing entities, to turn layers on and off in connection with composite phase space portraits, and to rotate and otherwise manipulate the graphic images. References herein to AutoCAD commands and functions refer to the AutoCAD (R) Drafting Package Reference Manual, Jul. 11, 1986, (Copyright 1982, 1983, 1984, 1985, 1986 Autodesk, Inc.), referred to herein as &#34;AutoCAD Manual&#34;. The invention currently employs AutoCAD Release 9.0, AutoCAD Reference Manual Supplement Release 9.0, and AUTOLISP (™) Version 2.6 Programmer&#39;s Reference. 
     The invention currently employs a Compaq DESKPRO 386 (™) personal computer with math-co-processor and extended memory to operate both AutoCAD and the invention&#39;s special software programs. 
     Manual selection of drawing entities is achieved by use of a `pointing device` such as a computer mouse or the cursor control keyboard keys. A variety of drawing &#34;entity selection&#34; commands is available in publicly available drawing programs, such as those in the AutoCAD Manual, Sec. 2.10, pp. 45-49. The collection of drawing objects so identified is referred to as a &#34;selection-set&#34; in AutoCAD. 
     The invention employs specially developed copyrighted computer software to compare the AutoCAD &#34;selection-set&#34; to the ASCII DXF file and the original raw data file and to identify the subset of raw data which was used to create the selected drawing entities. See the PICK.LSP computer program listing appended hereto. The identified subset of raw data could then be written to a separate file if desired for further processing. 
     Colors, line types and layers are defined on pages 14 and 16 of the AutoCAD Manual and generally explained in Chapter 7, pp. 181-195 of the AutoCAD Manual. 
     Examples of point drawing symbols, which could be employed to mark the timing of events within a graphic portrait, may be found in the AutoCAD Manual, Section 4.2, p. 75. Note that the reference is to the types of symbols, not necessarily to the PDMODE and PDSIZE commands of AutoCAD, though those commands could be employed to some extent within their limitations. 
     As used in the claims the term &#34;event&#34; which is flagged within a data stream can refer to either a stimulus or a response. For example, one type of flag could be inserted into the data stream to reflect the triggering of a stimulus, such as presentation of a visual image to the test subject; and another type of flag could be inserted to reflect the time at which the test subject activates a trigger or some recording device detects a signal in response to perception or recognition of the stimulus. The detection device could be any of a wide variety of mechanical or biometric detectors for such things as respiration, blood pressure, muscular contraction or relaxation or motion. Various categories of events can be given unique, visually distinctive point symbols within a graphic phase space drawing. 
     COMPUTER PROGRAM AND FILE LISTINGS 
     APPENDIX 1 hereto contains a listing of computer programs and files employed in connection with one or more aspects of the invention. These programs and files were programmed by G. E. Somerville under directions from the inventors. The listings are as follows: 
     ACAD.LSP; COLBAR.LSP; GET.LSP; GRAB.LSP; LAYER.LSP; PICK.LSP; RAW FILE FORMAT; CHGCOLOR; DXFCOL; DXFROW; CRT03MN; CVN03MN; IOR03MN; and VIEW. 
     Programs with the .LSP suffix are written in accord with AUTOLISP (™) Version 2.6 PROGRAMMER&#39;S REFERENCE, copyright Autodesk, Inc. 1985, 1986, 1987. They are designed to employ the invention with AUTOCAD (R). 
     Programs with the .EXE suffix are written in binary code, executable format, for use on an IBM-compatible personal computer. IBM is a registered trademark of International Business Machines. The listed programs perform the following functions: 
     The RAW DATA FILE FORMAT describes the structure of file into which raw data must be written to enable the DXFROW.EXE program to opera on the raw data. User-defined data conversion programs may be necessary to convert the file format of various collection devices to the RAW DATA FILE FORMAT before DXFROW.EXE can be employed. Drawing 1 appended hereto is a schematic generally illustrating data collection. 
     DXFROW.EXE transforms raw data from files already formatted in the RAW DATA FILE FORMAT into ASCII DXF drawing entities, and creates rows of phase space portraits, one for each &#34;trial&#34;. Within the RAW DATA FILE a &#34;trial&#34; means a stimulus flag and its concurrent data sample set, plus data sample sets immediately following it up to but not including the next stimulus flag. DXFROW.EXE creates four subfiles: 
     [FILENAME]H.DXF which creates a `header` structure required by AutoCAD; 
     [FILENAME]E.DXF is an `entities` file which contains the drawing entities defined from the raw data; 
     [FILENAME].LSP which includes the LOADPARAM data required for PICK.LSP to identify raw data from selected drawing entities; 
     [FILENAME].SCR is a `script` file written for use by invoking the AutoCAD command &#34;script&#34; from within the AutoCAD program and entering [FILENAME].SCR at the AutoCAD command prompt. It automatically calls into AutoCAD the header and entity files, and loads the LOADPARAM data for use by the PICK.LSP program, resulting in display of the phase space portraits ready for manipulation within an AutoCAD drawing. 
     DXFCOL.EXE restructures drawing files created by DXFROW.EXE to impose a color-code in according with signal time sequence upon the drawing entities on a selected layer. DXFCOL.EXE employs whatever color code is in a data file named COLORS.DAT which defines the desired sequence in a color code. 
     CHGCOL.EXE is employed to define color codes in the format required for the COLORS.DAT file. It enables definition of a series of color codes. The color code of choice is copied to the COLOR.DAT file prior to running DXFCOL.EXE. 
     ACAD.LSP contains a series of definitions in a file format which is automatically read by AutoCAD when initiating a drawing. These definitions enable operation with AutoCAD of various programs developed under the direction of the inventors. 
     COLBAR.LSP allows display of the current color code sequence as a bar on the graphics monitor when a color-coded time sequence is imposed on a phase space portrait. 
     GET.LSP enables selection or deletion of a series of drawing entities in a time sequence between two selected drawing entities. 
     GRAB.LSP is employed in conjunction with AutoCAD to segregate a plurality of `blocks` of drawing entities. It must be loaded into AutoCAD by the command LOADGRAB. Then the command GRABBASE is given, which refers to all drawing entities displayed on the screen by AutoCAD at the time the command is given. Various commands from within AutoCAD can be employed to turn off layers, zoom to larger or smaller windows, delete drawing entities and otherwise eliminate unwanted drawing entities from the screen either before or after the GRABBASE command is given. Then those remaining entities for which raw data identification is sought can be pointed out by use of a computer mouse and a `window` to select the entities, and the command GRABVIEW is given, resulting in automatic identification of the raw data points. 
     LAYER.LSP facilitates rapid switching of groups of drawing layers on or off within AutoCAD. It is loaded into AutoCAD by the command LOADLAYER, following which the command SETLAYER is given. Thereafter the commands ONLAYER and OFFLAYER are available. 
     PICK.LS is employed in conjunction with AutoCAD (R) (C) to manually point out a single drawing entity displayed on the computer monitor screen and to automatically identify the raw data points from which the selected drawing structure is formed. It must be loaded into AutoCAD by the command LOADPICK. Thereafter its operating commands are SETPICK, which refers to drawing entities displayed on screen by AutoCAD at the time the command is given, and PICKENT which thereafter is employed to point out and automatically identify the raw data from which selected entities are drawn. 
     CRT03MN.LIB, CVN03MN.LIB and IOR03MN.LIB comprise a library of standardized subroutines called by the main program. They are written in accord with Microsoft (R) Macro Assembler Version 5.10. The use of these subroutines is transparent to the user. They are copyrighted programs of G. E. Somerville, who has licensed them to the inventors, and they are included herein with his permission. 
     VIEW.EXE parses a GRAB VIEW file. 
     CONCEIVED USES OF THE INVENTION 
     One of the Inventors&#39; conceptions is that a human subject can be given a switch to insert flags or markers into the signal data stream corresponding to the moment the subject experiences conscious thoughts, perceptions of external stimuli, or other conscious processes. Similarly, the host computer can trigger a stimulus and simultaneously insert a flag denoting the stimulus into the collected data stream. Thus, both stimulus and response events can be recorded within the data stream in conjunction with simultaneously collected brain signals. 
     Another of the Inventors&#39; conceptions is that the invention enables computer-assisted manual identification of pattern-generating subsets of raw data. The identified subsets of raw data can then be segregated to serve as empirical data patterns against which computer-aided pattern comparison can be made, even though no precise mathematical description of the segregated raw data can be programmed into the computer. The Inventors further conceive, for example, that such segregated subsets of pattern-generating raw data can be used to `train` computer neural networks to recognize the patterns in such raw data subsets without first defining a descriptive mathematical formula for such raw data subsets. 
     The Inventors conceive that an empirical library of subsets of raw data comprising brain activity reflecting responses to stimuli, perceptions, and thought processes, can be created by so selecting such visually distinctive, patterned subsets of raw data out of the displayed phase space portraits. The Inventors further conceive that such subsets can be employed as computer-recognizable patterns pattern recognition programs. 
     The Inventors conceive that the development of computer recognizable patterns in brain signals, in turn, will enable `on-the-fly` or real time analysis of brain signals by computer-aided pattern comparison to such an empirical library of brain signal patterns. 
     SYNTAX CONVENTIONS 
     The following conventions are employed in the syntax of the claims: 
     &#34;Signal detectors&#34; are assigned the capital letter &#34;D&#34;, followed by a numeral indicating a particular detector in the sequence, such as, D1, D2 and D3. 
     &#34;Discrete times&#34; are indicated by lower case &#34;t&#34; followed by a numeral indicating the particular place in the time sequence, such as, t1, t2, and t3. Signal values are assigned a capital letter &#34;S&#34; followed by a numeral indicating the time the signal was taken. For example signal S1 was collected at time t1. Signal values are further assigned a letter and number to indicate the particular detector from which the signal was collected, such as, D1S1, meaning the signal value collected from detector D1 at time t1. 
     A &#34;series&#34; of indeterminate length is indicated by listing the first few members of the series followed by four periods and the `nth` member of the series. 
     An example is the time series &#34;t1, t2, t3, . . . . tn. 
     Another example is the signal detector series &#34;D1, D2, D3, . . . . Dn&#34;. Alphabetic series of indefinite length are denoted by the first few letters followed by four periods and the letter `x`. An example is the alphabetic series &#34;Da, Db, Dc, . . . . Dx.&#34; 
     Drawing &#34;point entities&#34; are referred to by the capital letter &#34;P&#34; followed by a numeral indicating the time at which the signal data establishing the coordinates of the point was collected. Thus, point &#34;P1&#34; is defined by the signal data collected at time t1. The three coordinates of a point are defined by signal data collected substantially simultaneously from three different detectors. For example, &#34;x&#34; could be the signal data from detector D1, &#34;y&#34; the signal data from detector D2, and &#34;z&#34; the signal data from detector D3. 
     Drawing &#34;line entities&#34; are referred to by the capital letters &#34;LI&#34; followed by a numeral indicating the time of the first point entity, such as &#34;LI1&#34; referring to the line connecting points P1 and P2, which starts at time t1 and extends to time t2. &#34;LI2&#34; refers to the line connecting points P2 and P3, starting at time t2. 
     Drawing &#34;layers&#34; are referred to by the capital letters &#34;LA&#34; followed by a numeral indicating place in the sequence of a series of layers, such as LA1, LA2, and LA3. Point entities drawn on different layers are designated by a capital &#34;P&#34; followed by a numeral designating time, by the capital letters &#34;LA&#34; and a numeral indicate which layer in the sequence. For example, &#34;P1LA2&#34; means Point 1 on Layer 2, whose coordinates are defined by signal data taken at time t1, from the unique subset 2 of detectors whose signal data is employed to define the points on Layer 2. 
     &#34;Color-time&#34; sequences employ the syntax capital &#34;C&#34; followed by a numeral for a distinctive color, followed by lower case &#34;t&#34; followed by a numeral for a discrete time. Thus, &#34;C1t1&#34; means the color 1 is assigned to time t1 in a pre-determined table. Where colors are employed to visually illustrate a time sequence, the sequence of colors is pre-determined in a table. The relationship of a particular color to a particular discrete time in the table is entirely arbitrary. For example, one might choose to arrange the colors in accord with the natural spectrum or rainbow because of the intuitive ease of following the colors of the rainbow in the correct sequence. The first seven numbers have been assigned to standard colors by convention. AutoCAD Manual, sec. 7.1.2, p. 181. For computer programming purposes, colors are identified by numbers in accord with generally recognized color conventions for computer graphics. For non-spectral colors, a possible arrangement is the chromatic sequence in the color circle employed in the Farnsworth-Munsell 100 hue test. 
     &#34;Prime number&#34; means a number divisible only by the number 1 and itself. Examples are 2, 3, 5, 7, 11, and 13. 
     In principle, periodicities might appear in the graphic portraits corresponding to multiples of one of the prime numbers, providing either (i) that the period is nearly an exact multiple of the time interval (t2-t1) between data samples, or (ii) that such time interval (t2-t1) is extremely small relative to the period. ##SPC1##