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Carolina S Araujo, Givago S Souza, Luiz Carlos L Silveira; Visual evoked cortical potential kernels elicited by m-sequences: a principal component analysis. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3507. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the contribution of principal components of the second order kernels of pseudo-random VECP waveform in different combinations of achromatic contrast and spatial frequency.
Nine normal subjects were tested (24.1±6.2 yo). Achromatic sinusoidal gratings (8° visual angle) were temporally controlled by an m-sequence in order to simulate pattern reversal presentation mode. Six levels of Michelson contrast (3% to 99%) and seven spatial frequencies (0.4 cpd to 10 cpd) were used. The Veris system was used for visual stimulation, electrophysiological recording, and extraction of the first and second slice of the second order kernel (K2.1 and K2.2, respectively). Principal component analysis was applied in the K2.1 and K2.2 waveforms using singular value decomposition. We estimated the gain of the RMS amplitude of the principal components from K2.1 and K2.2 as a function of contrast and compared with data from retinal ganglion cells published by Kaplan & Shapley (1986).
Two principal components (PC) explained most of the variance from each slice of the second order kernel. The variance explained by the PC extracted from the K2.1 was 49±5% for the first PC and 20±3% for the second PC, whereas the variance explained by the PC extracted from K2.2 was 44±3% for the first PC and 22±2% for the second PC. The K2.1 first PC was very similar to the original K2.1, with the same N1, P1, and P2 components. The K2.1 second PC showed lower amplitudes and were similar to K2.1 first PC. The waveforms of the two PC extracted from K2.2 were dominated by negative polarity waveforms. The contrast-response function of the K2.1 first PC showed higher gain than K2.1 second PC, and both PCs from K2.2, mainly at low and intermediate spatial frequencies. The mean RMS amplitude function versus contrast of K2.1 first PC co-varied well with M cell responses from Kaplan & Shapley (1986), while contrast-response functions of K2.1 second PC and both PCs from K2.2 co-varied well with P cell responses from Kaplan & Shapley (1986).
K2.1 first principal component seems to be generated by the activity of a high contrast sensitivity pathway, while the other major K2.1 and K2.2 components seem to be generated by a mechanism of low contrast sensitivity. Visual system M and P parallel pathways are natural candidates to represent the generating mechanisms of the second order kernels principal components.
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