Best-phase alignment compensates for inter-individual shifts in neural response phase

Evidence

A performance measure was extracted for each tACS phase condition: For experiment 1, accuracy was extracted, defined as the number of correct responses divided by the number of trials. In experiment 2, the sensitivity index d’ was computed based on the overall time during which the participant correctly or erroneously reported the target, divided by the overall target or non-target time (respectively). Next, a ‘time series’ of the performance measure was reconstructed by concatenating the six phase conditions. To compensate for possible inter-individual variations in the phase for which performance was best, the maximum of the series was aligned to the 90°-point and the series was phase-wrapped (e.g., Ng et al. 2012 ). Following this ‘best-phase alignment’—under the main hypothesis that 4-Hz tACS phase modulates detection—phases 30–150° should delimit a positive 4-Hz half-cycle, whereas phases 210–330° should delimit the opposite (negative) half-cycle. To verify this prediction, performance was averaged across the hypothesized positive half-cycle (phases 30 and 150°) and the opposite half-cycle (phases 210, 270, and 330°), and the two resulting averages were compared. — Dijk, Pim van, Physiology, Psychoacoustics and…, 4777

Categorization

• DEFINE: Explains ‘best-phase alignment’: aligning each participant’s best-performance phase to 90° handles individual phase-offset variability before averaging.
• XREF: The phase-wrapping/alignment problem parallels best-pitch or best-frequency alignment used across psychoacoustic individual-difference studies.