Wavelet decomposition of event related potentials: toward the definition of biologically natural components

Transient time-voltage neural waveforms recorded at the scalp are elicited by discrete sensory or perceptual events and thought to be composed of fundamental waveform components. A new definition is proposed of ERP components as `wavepackets´, which are oscillating waveforms that extend throughout the ERP. The wavelet transform is used to extract orthogonal wavepacket components. Each component is restricted to its own frequency band, and may strongly influence the ERPs over local time regions. Unilateral visual field stimulation data from human subjects show that wavepacket components reveal visual processing events earlier than direct amplitude measurements on the ERPs. Wavepackets provide new insights into ERP morphology and its relationship to the timecourse of neural processes