Independent gains from 0.95 to 1.05 on stored channels permitted both F3/F4 alpha signs in 57 of 88 ds004504 records after a 19-channel mean reference

We tested the sign of frontal alpha asymmetry under independent gains on stored EEG channels. The source was OpenNeuro ds004504 v1.0.9, with 88 people and 19 channels. Each gain stayed fixed over time. Gains from 0.95 to 1.05, followed by a mean of all 19 channels, permitted both F3/F4 score signs in 57 records. The band was 8 to below 13 Hz. Of 56 records with a baseline larger-to-smaller power ratio above 1.1, 25 permitted both signs. We give a finite method that finds the exact attained power-difference limits over positive gain intervals. A separate exhaustive solver checked all 5280 bounds from 60 fixed settings. Fresh source replay checked three complete records. A full repeat matched seven analysis files byte for byte. The package contains the proof, code, matrices, source hashes, attaining gain vectors, results, figures, and repeat instructions. The result applies to constant gains on fixed processed signals. It does not measure recording-system errors or diagnostic accuracy.

frontal alpha asymmetry · EEG · channel gain · mean reference · cross-power matrix · sign sensitivity · exact bounds · measurement sensitivity