Context Dependence Signature, Stimulus Properties and Stimulus Probability as Predictors of ERP Amplitude Variability

Abstract

Typically, in an oddball paradigm with two experimental conditions, the longer the time between novels the greater P3a amplitude. Here the research question is: Does an oddball paradigm maintain the greater P3a amplitude under several experimental conditions? An EEG study was carried out with an oddball number parity decision task having four conditions in control and schizophrenic participants. Contrary to previous findings (Gonsalvez and Polich, 2002; Polich, 2007) in control participants, non-correlation was found between the time of a novel (N) stimulus condition to the next novel condition and P3a amplitude. Moreover, with an innovative method for stimulus properties extraction features and EEG analysis, single trial across-subject averaging of participants' data revealed significant correlations (r > 0.3) of stimulus properties (such as probability, frequency, amplitude, and duration) on P300, and even r > 0.5 was found when N was an environmental sound in schizophrenic patients. Therefore, stimulus properties are strong markers of some of the features in the P3a wave. Finally, a context analysis of ERP waves across electrodes revealed a consistent modulation in novel appearance for MisMatch Negativity in schizophrenia. A supplementary analysis running linear modeling (LIMO) in EEG was also provided (see Supplementary Material). Therefore, in a multiple condition task: stimulus properties and their temporal properties are strong markers of some of the features in the P300 wave. An interpretation was done based on differences between controls and schizophrenics relate to differences in the operation of implicit memory for stimulus properties and stronger correlations were observed within groups related contextual and episodic processes.

Keywords: MisMatch Negativity (MMN); P3a; attention; event related potential (ERP); goal-driven network (GDN); schizophrenia; sound properties; stimulus-driven network (SDN).

FIGURE 1

Block diagram of data processing in the first study.

FIGURE 2

Effect of preceding (NG) and simultaneous (TNG) distractors on number parity decisions compared to simple number decision task (TG).

FIGURE 3

(A–D) Grand average ERP waveforms and trial by trial voltage plots at Pz electrode in 20 control participants in the standard goal (TG), novel preceding goal (NG), novel target (TN) and simultaneous novel and goal (TNG) conditions. (E–G) Waveforms generated by subtraction (in black) of novel conditions from control condition (TG in green) and corresponding t-values for successive time bins of 187.5 ms.

FIGURE 4

(A–D) Grand average ERP waveforms and trial by trial voltage plots at Pz electrode in 12 participants diagnosed with schizophrenia in the standard goal (TG), novel preceding goal (NG), novel target (TN) and simultaneous novel and goal (TNG) conditions. (E–G) Waveforms generated by subtraction (in black) of novel conditions from control condition (TG in green) and corresponding t-values for successive time bins of 187.5 ms.

FIGURE 5

Preceding novel stimuli (NG) vs. amplitude of the P300 peak in Fz, Cz, and Pz. P300 peak amplitudes between 250 and 450 ms (solid lines) and between 350 and 450 ms (dotted lines) computed for control participants.

FIGURE 6

Preceding novel stimuli (NG) vs. amplitude of the P300 peak in Fz, Cz, and Pz. P300 peak amplitudes between 250 and 450 ms (solid lines) and between 350 and 450 ms (indented lines) computed for schizophrenic patients.

FIGURE 7

Correlations in control participants and schizophrenic patients (shown in color) between amplitude of single trial across-subject P300 peak at channels Fz, Cz, Pz, CP6, and CP5 (horizontal axis) and 14 sound properties (vertical axis). P300 amplitude measured in the time range [250 450] ms. Difference of duration and spectrum calculations (LTAS and entropy) showed correlations across electrodes in the analysis only in schizophrenic patients.

FIGURE 8

Grand average for control group of the ERP conditions (top) subtracted from every ERP condition in the previous channels (middle), and the one-tailed t-test analysis between each condition and the standard followed by the standard (p < 0.001) (bottom).

FIGURE 9

Grand average for schizophrenic patients of the ERP in each condition (top) subtracted with the standard ERP condition in the previous channels (middle), and the multiple t-test analysis between each condition and the standard followed by the standard (p < 0.001) (bottom).

FIGURE 10

Initial hypothesis plotted with the first results and the route to the sound properties analysis. (A) Theory of habituation response to stimulus sequence. (B) Initial hypothesis about time dependence of novel amplitude. Found only in some left electrodes in controls. (C) Most of the amplitude channels explained by significant correlations with stimulus properties in both groups.

FIGURE 11

A general route of the sound properties analysis influencing P3a amplitude. Thickness shows strength of the correlations found.

FIGURE 12

The context interpretation about MisMatch Negativity in schizophrenic patients.