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Patent US7937157 - Electrical nerve stimulation based on channel specific sequences - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA method of activating at least two electrodes in a multichannel electrode array using channel specific sampling sequences is presented. A channel specific sampling sequence is defined for each electrode, the sequence having a particular duration, pulse amplitude distribution, and number of pulses. A...http://www.google.com/patents/US7937157?utm_source=gb-gplus-sharePatent US7937157 - Electrical nerve stimulation based on channel specific sequencesAdvanced Patent SearchPublication numberUS7937157 B2Publication typeGrantApplication numberUS 11/685,887Publication dateMay 3, 2011Filing dateMar 14, 2007Priority dateAug 26, 1999Also published asCA2382964A1, CA2382964C, DE60036875D1, DE60036875T2, EP1207938A1, EP1207938B1, EP1854504A2, EP1854504A3, EP1854504B1, EP2208507A1, EP2208507B1, US6594525, US7209789, US8798758, US20030105504, US20070156202, US20110230934, WO2001013991A1Publication number11685887, 685887, US 7937157 B2, US 7937157B2, US-B2-7937157, US7937157 B2, US7937157B2InventorsClemens M. ZierhoferOriginal AssigneeMed-El Elektromedizinische Geraete GmbhExport CitationBiBTeX, EndNote, RefManPatent Citations (27), Non-Patent Citations (45), Referenced by (2), Classifications (8), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetElectrical nerve stimulation based on channel specific sequencesUS 7937157 B2Abstract A method of activating at least two electrodes in a multichannel electrode array using channel specific sampling sequences is presented. A channel specific sampling sequence is defined for each electrode, the sequence having a particular duration, pulse amplitude distribution, and number of pulses. A weighting factor is applied to the channel specific sampling sequence. Each electrode in the multichannel electrode array is then simultaneously activated using sign-correlated pulses, the sign-correlated pulses based on parameters of spatial channel interaction reflecting geometric overlapping of electrical fields from each electrode, non-linear compression, and each electrode's weighted channel specific sampling sequence.
PRIORITY This application is a continuation of U.S. application Ser. No. 10/303,568 filed Nov. 25, 2002, entitled Electrical Nerve Stimulation Based on Channel Specific Sampling Sequences, now U.S. Pat. No. 7,209,789, which in turn is a continuation of U.S. application Ser. No. 09/648,687 filed Aug. 25, 2000, entitled Electrical Nerve Stimulation Based on Channel Specific Sampling Sequences, now U.S. Pat. No. 6,594,525, which claims priority from U.S. provisional patent application Ser. No. 60/150,773 filed Aug. 26, 1999, entitled Concept for Electrical Stimulation of the Acoustic Nerve Based on Channel Specific Sampling Sequences (CSSS). Each of the above described applications are hereby incorporated herein by reference.
a. 6-channel CSSS b. 6-channel CIS DETAILED DESCRIPTION OF THE INVENTION A cochlear implant with stimulation patterns containing enhanced temporal information, especially in the low frequency range up to 1 kHz, is described. It is known from literature that the neurons are able to track analogue electrical sinusoidals up to about 1 kHz. This ability is not exploited in the present CIS strategy, since the sampling rate is too low to represent high frequency envelope waveforms.
r ( t ) = 0 , for t < a , and r ( t ) = 1 - exp ( - t - t a τ ) , for t > t a , ( 1 ) with an absolute refractory period ta≈700 μs, and a time constant τ≈1250 μs for the relative refractory period. For example, if two supra-threshold stimulation pulses are applied, and the second pulse falls into the absolute refractory period after the first, no additional action potential can be elicited. If the second pulse occurs during the relative refractory period, an enhanced amplitude is necessary to generate an action potential.
( x 1 x 2 x 3 ⋯ x N - 2 x N - 1 x N ) = H ( y 1 y 2 y 3 ⋯ y N - 2 y N - 1 y N ) , ( 2 ) where Matrix H is
H = ( 1 ⅇ - d λ ⅇ - 2 d λ ⋯ ⅇ - ( N - 3 ) d λ ⅇ - ( N - 2 ) d λ ⅇ - ( N - 1 ) d λ ⅇ - d λ 1 ⅇ - d λ ⋯ ⅇ - ( N - 4 ) d λ ⅇ - ( N - 3 ) d λ ⅇ - ( N - 2 ) d λ ⅇ - 2 d λ ⅇ - d λ 1 ⋯ ⅇ - ( N - 5 ) d λ ⅇ - ( N - 4 ) d λ ⅇ - ( N - 3 ) d λ ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ ⅇ - ( N - 3 ) d λ ⅇ - ( N - 4 ) d λ ⅇ - ( N - 5 ) d λ ⋯ 1 ⅇ - d λ ⅇ - 2 d λ ⅇ - ( N - 2 ) d λ ⅇ - ( N - 3 ) d λ ⅇ - ( N - 4 ) d λ ⋯ ⅇ - d λ 1 ⅇ - d λ ⅇ - ( N - 1 ) d λ ⅇ - ( N - 2 ) d λ ⅇ - ( N - 3 ) d λ ⋯ ⅇ - 2 d λ ⅇ - d λ 1 ) , ( 3 ) The coefficients of matrix H reflect spatial channel interaction. A coefficient at row i and column j describes the fraction of the single channel potential caused by electrode #j at the position of electrode #i.
( y 1 y 2 y 3 ⋯ y N - 2 y N - 1 y N ) = H - 1 ( x 1 x 2 x 3 ⋯ x N - 2 x N - 1 x N ) , ( 4 ) where H−1 is the inverse matrix of H. Fortunately, matrix H−1 in general is a tri-diagonal matrix with non-zero elements only in the main-, the upper and lower neighboring diagonals (see Section A of the specification).
H ( z ) = 1 ( 1 - α z - 1 ) + - 1 ( 1 - α - 1 z - 1 ) , ( A3 ) which can be expressed as
H ( z ) = ( α + 1 α ) ( z + 1 - ( α + 1 α ) + z - 1 ) . ( A4 ) Transformation of (A1) into the z-domain yields
Y ( z ) = 1 ( α + 1 α ) ( z + 1 - ( α + 1 α ) + z - 1 ) X ( z ) . ( A7 ) The inverse z-transform immediately yields
y n = 1 ( α + 1 α ) - ( δ n - 1 ( α + 1 α ) δ n + δ n - 1 ) * x n , ( A8 ) where δn is the unit impulse, i.e., δn=1 for n=0, and δn=0 elsewhere. The first term of the convolution product (A8) is a finite impulse response (FIR). Equation (A8) can be expressed as
y n = 1 ( α + 1 α ) - ( x n - 1 ( α + 1 α ) x n + x n - 1 ) , ( A9 ) which is a set of linear equations. To calculate yn at positions n=1 and n=N requires to know amplitudes x0 and xN+1. Since sequence yn can have non-zero elements only at positions n=1, 2, . . . N, it follows with (A1)
( y 1 y 2 y 3 ⋯ y N - 2 y N - 1 y N ) = H - 1 ( x 1 x 2 x 3 ⋯ x N - 2 x N - 1 x N ) , ( A12 ) where matrix H−1 is a tri-diagonal matrix given by
H - 1 = ( b 0 - a 0 ⋯ 0 0 0 - a b - a ⋯ 0 0 0 0 - a b ⋯ 0 0 0 ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ 0 0 0 ⋯ b - a 0 0 0 0 ⋯ - a b - a 0 0 0 ⋯ 0 - a b 0 ) , ( A13 ) with coefficients
b 0 = 1 ( 1 α - α ) 1 α , b = 1 ( 1 α - α ) ( α + 1 α ) , and a = 1 ( 1 α - α ) . ( A14 ) It shall be mentioned that the analysis can simply be expanded to the case, if the infinite sequence hn (A2) is of the form
0 = - ax k 0 ′ + bx k 0 + 1 ′ - ax k 0 + 2 ′ 0 = - ax k 0 ′ + bx k 0 + 1 ′ - ax k 0 + 2 ′ � � 0 = - ax k 0 + L - 3 ′ + bx k 0 + L - 2 ′ - ax k 0 + L - 1 ′ 0 = - ax k 0 + L - 2 ′ + bx k 0 + L - 1 ′ - ax k 0 + L . ( A17 ) Elements xk0−1 and xk0+L, and coefficients a and b are known, and thus for L>1, (A17) can be written as
( x k 0 ′ x k 0 + 1 ′ x k 0 + 2 ′ ⋯ x k 0 + L - 3 ′ x k 0 - L - 2 ′ x k 0 + L - 1 ′ ) = 1 a Q L - 1 ( x k 0 - 1 0 0 ⋯ 0 0 x k 0 + L ) ( A18 ) with matrix square QL Q L = 1 a 2 ( b - a 0 ⋯ 0 0 0 - a b - a ⋯ 0 0 0 0 - a b ⋯ 0 0 0 ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ 0 0 0 ⋯ b - a 0 0 0 0 ⋯ - a b - a 0 0 0 ⋯ 0 - a b ) . ( A19 ) The number of lines (and rows) of matrix QL is L (L>1). Note that amplitudes x′k are fully determined by the �neighboring� amplitudes xk0−1 and xk0+L. In particular, amplitudes x′k0 and x′k0+L−1 can be calculated with
x k 0 ′ = c ( L ) a x k 0 - 1 + d ( L ) a x k 0 + L , and x k 0 + L - 1 ′ = d ( L ) a x k 0 - 1 + c ( L ) a x k 0 + L , ( A20 ) where coefficients c(L) and d(L) are the elements at the left- and right upper corner of matrix Q−1, respectively, i.e., at matrix positions (1,1) and (1,L). For each length L, there exists one unique pair of coefficients c(L) and d(L). For L=1, evaluation of (A17) yields
y k 0 - 1 ′ = - ax k 0 - 2 + bx k 0 - 1 - ax k 0 ′ = = - ax k 0 - 2 + ( b - c ( L ) ) x k 0 - 1 - d ( L ) x k 0 - L , and y k 0 + L ′ = - ax k 0 + L - 1 ′ + bx k 0 + L - ax k 0 + L + 1 = = - d ( L ) x k 0 - 1 + ( b - c ( L ) ) x k 0 + L - ax k 0 + L - 1 . ( A21 ) Thus, setting the amplitudes y′k=0 for a zero-sequence results in a modification of the elements in yn only at positions, which are neighboring to the zero-sequence. Note that other elements of yn are not concerned. Equation (A21) can be implemented by means of the following steps:
( x 1 ′ x 2 ′ ⋯ x L ′ ) = ( α L x L + 1 α L - 1 x L + 1 ⋯ α x L + 1 ) . ( A22 ) Regarding the matrix operation, the coefficient b of line L+1 of H−1 has to be replaced by coefficient b0. Then all lines and rows with indices k have to be removed, and the elements of xn with indices k can be ignored.
( x k 0 ′ x k 0 - 1 ′ ⋯ x N ′ ) = ( α x k 0 - 1 α 2 x k 0 - 1 ⋯ α L x k 0 - 1 ) . ( A23 ) Regarding the matrix operation, the coefficient b of line k0−1 of H−1 has to be replaced by coefficient b0. Then all lines and rows with indices k have to be removed, and the elements of xn with indices k can be ignored.
(1) Compute yn by multiplication of H−1 and xn. (2) Select elements yn=k<0 and set yk′=0. (3) Modify elements of H−1 according to (A21), (A22), (A23) (4) Remove all lines and rows of H−1 with indices k, and remove all elements xk. (5) Compute elements yn′, which are neighboring to zero-sequences. Example Let the result of the matrix multiplication yn=H−1xn, (matrix H−1 defined by coefficients b0, b, and a, for a 12-channel system (N=12) be a vector containing negative elements at positions k=[1, 2, 6, 7, 9, 10, 11]. Then the modified vector y′n is
y n ′ = ( 0 0 y 3 ′ y 4 ′ y 5 ′ 0 0 y 8 ′ 0 0 0 y 12 ′ ) , ( A24 ) and the unknown elements are computed by
( y 3 ′ y 4 ′ y 5 ′ y 8 ′ y 12 ′ ) = ( b 0 - a 0 0 0 - a b - a 0 0 0 - a b - c ( 2 ) - d ( 2 ) 0 0 0 - d ( 2 ) b - c ( 2 ) - c ( 3 ) - d ( 3 ) 0 0 0 - d ( 3 ) b 0 - c ( 3 ) ) ( x 3 x 4 x 5 x 8 x 12 ) . ( A25 ) Note that element y′4=y4, because position n=4 is not neighboring to a zero-sequence. Element y′8 is neighboring to two zero-sequences. Therefore, the corresponding element in the main diagonal is b−c(2)−c(3), reflecting the influence of both zero-sequences. Coefficients c(2), d(2) and c(3), d(3) are computed by inverting matrices Q2, and Q3, which themselves only depend on coefficients a and b.
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