Single-event-related potential analysis by means of fragmentary decomposition

A recently developed fragmentary decomposition method is employed to analys e single-trial event-related potentials (ERPs), thereby extending the tradi tional method of averaging. Using a conventional auditory oddball paradigm with 40 target stimuli, single-trial ERPs in 40 normal subjects were analys ed for midline scalp (Fz, Cz and Pz) recording sites. The normalization eff ect, reported in our previous study of eye blink EMGs and proposed to be a characteristic property of a wide class of non-stationary physiological pro cesses, was found to apply to these single-trial ERPs. Fragmentary decompos ition of single-trial ERPs may be regarded as re-statement of the normaliza tion effect. This allows both pre-stimulus EEGs and post-stimulus ERPs to b e regarded as overlapping generic mass potentials (GMPs), with a characteri stic Gaussian amplitude spectrum. On theoretical and empirical grounds we u niquely deduce a model GMP using an introduced "bud" function, and physical ly support it by the resting and transient conditions. The model takes into account the shape of the component, which suggests a simple relationship b etween the peak latency and the time of the component onset. Given that GMP s may be manipulated and sorted out, we present principles of the fragmenta ry synthesis, i.e. probabilistic ERP reconstructions on the basis of indivi dual and ensemble properties of its identified components. Summarizing the component quantification in the form of the dynamic model provides for the first time the opportunity to quantify all significant components in single -trial ERPs. This method of single-trial analysis opens up new possibilitie s of exploring the dynamical ERP changes within a recording trial, particul arly in late component "cognitive" paradigms.