IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-20, NO. 1, JANUARY 1973 [31 M. M. Ter-Pogossian, J. 0. Eichling, D. 0. Davis, and M. J. Welch, "The measure in vivo of regional cerebral oxygen utilization by means of oxyhemoglobin labeled with radioactive oxygen-15," J. Clin. Invest., vol. 49, pp. 381-391, 1970. [4] J. A. Jacques, "Tracer kinetics," in Principles of Nuclear Medi- cine, H. N. Wagner, Jr., Ed. Philadelphia, Pa.: Saunders, 1968. [51 C. W. Sheppard, Basic Principles of the Tracer Method. New York: Wiley, 1962. [6] D. R. Cox and P. A. W. Lewis, The Statistical Analysis of Series ofEvents. New York: Wiley, 1966. [71 D. R. Cox and H. D. Miller, The Theory of Stochastic Processes. New York: Wiley, 1965. [8] D. L. Snyder, "Nonrecursive smoothing for Gaussian modulated point processes," in Proc. 9th Annu. Allerton Conf. Circuit and System Theory, Oct. 1971. 19] B. Hoop, Jr., R. G. Ojemann, and G. L. Brownell, "A stochastic model of regional cerebral circulation," J. Nucl. Med., vol. 12, no. 8, pp. 540-546, Aug. 1971. [10] M. Rockoff, "Notes on the interpretation of a clearance curve in terms of compartmental analysis," in Proc. Workshop Computer Processing of Dynamic Images from an Anger Scintillation Cam- era (Washington Univ., St. Louis, Mo.), Jan. 18-22,1971,ch. 20. 111 K. Larson, "Some aspects of mathematical modeling of regional and organ blood flow," in Proc. Workshop Computer Processing of Dynamic Images from an Anger Scintillation Camera, Jan. 18-22, 1971, ch. 19. [12] D. L. Snyder, "Filtering and detection for doubly stochastic Pois- son processes,' Biomed. Comput. Lab., Washington Univ. School of Medicine, St. Louis, Mo., monogr. 145; also IEEE Trans. Inform. Theory, vol. IT-18, pp. 91-102, Jan. 1972. [131 L. J. Savage, The Foundations of Statistics. New York: Wiley, 1954. [141 P. Meier and K. L. Zierler, "On the theory of the indicator- dilution method for measurement of blood flow and volume," J. Appl. Physiol., vol. 12, no. 6, pp. 731-744, June 1954. 115] H. L. Van Trees, Detection, Estimation, and Modulation Theory: Part I. New York: Wiley, 1968. 1161 T. Sandor, M. Conroy, and N. Hollenberg, "The application of the method of maximum likelihood to the analysis of tracer kinetic data," Math. Biosci., vol. 9, pp. 149-159, 1970. 17] S. Haber, "Numerical evaluation of multiple integrals," SIAM Rev., vol. 12, no. 4, pp. 481-526, Oct. 1970. A Computer Analysis of BEG Spectral Signatures from Normal and Dyslexic Children BERNARD SKLAR, JOHN HANLEY, AND WILLIAM W. SIMMONS Abstract-We have been able to differentiate between 12 dyslexic children and 13 normal age- and sex-matched children on the basis of spectral estimates of their electroencephalograms (EEG's). The children were monitored during various mental tasks and rest situations. Data dimensionality was reduced by "banding" various spectral components and eliminating others. The reduced spectral vectors were used as an input to a stepwise discriminant analysis program which, in effect, selected the variables most disparate between the two groups (dyslexic and normal). The most prominent spectral differences appeared in the parieto- occipital region during the rest, eyes-closed phase. The dyslexic children on the average had more energy in the 3-7-Hz band and the 16-32-Hz band, the normals in the 9-14-Hz band. During the reading tasks, the autospectral disparity between the two sample populations was reversed at 16-32-Hz; normals tended to have greater energy. The coherences of all activity between various scalp leads displayed a par- ticular pattern and were used as the most prominent discriminating feature during reading. Within the same hemisphere, coherences be- tween leads were higher in dyslexics than in normals on the average, and, between symmetrical regions across the midline of the head, coherence tended to be higher in normals. F statistics are tabulated. However, since the discriminating variables were gleaned from a search technique, other techniques are employed for providing confidence to the findings. Manuscript received December 6, 1971; revised May 5, 1972 and July 31, 1972. The research was supported in part by The Aerospace Corporation, El Segundo, Calif., under their Advance Study Grant, 1971. B. Sklar is with The Aerospace Corporation, El Segundo, Calif. 90245. J. Hanley is with the Space Biology Laboratory, Brain Research Institute, University of California, Los Angeles, Calif. W. W. Simmons is with the Lawrence Livermore Laboratory, Univer- sity of California, Livermore, Calif. THE PROBLEM YSLEXIA, a neurological symptom known to medicine D for over half a century, manifests itself as an inability to acquire reading and spelling skills commensurate with the individual's intelligence. It is particularly insidious since a large number of dyslexics are very intelligent and many are well endowed with the ability for abstract thinking [1 ] -[3] . These children can learn by all the usual methods except reading. Many of them partially surmount their reading deficiencies by developing highly refined oral memories, just as the blind con- centrate on development of refined hearing ability [1] . A typical characteristic of the dyslexic's reading impairment is his difficulty in recognition and recall of the orientation of letters and the order of letters in words. Sometimes there are semantic substitutions in his reading, such as "funny" for "laugh," or "chicken" for "duck." Also, there are inversions such as "saw" for "was," or ".pot" for "top."' Frequently, mirror-image letters such as "p" and "q," "b" and "d," and upside-down equivalents such as "m"i and "vw," "n" and "u,"' are confused [4] -[6] .' Hoffman (1964) developed a differen- tial equation model of the visual cortex and postulated that the dyslexic's reversal manifestation may be mathematically ex- pressed as an instability in the rest state of the visual cortex 1Makita (1968) reported the incidence of dyslexia in Japan was some ten times lower than the figure quoted for Western countries. At least one noteworthy characteristic of the Japanese Kana script is that it contains no mirror-figure symbols [7] . 20