The influence of the global/local probability effect on the neural processing of cues and targets. A functional systems approach.

Global and local probability effects were explored in a visuo-auditory version of the central cue Posner's paradigm through the analysis of the neural Event-Related Potentials (ERPs) generated in the interaction between validity sequence effects (local probability) and block validity effects (global probability). Four behavioral measures (response times, correct/incorrect anticipations, and incorrect responses), three pre-target ERPs (visual P1/N1 and Contingent Negative Variation (CNV)), and six post-target ERPs (auditory N1, P2, Processing Negativity (PN), P3a, P3b and Late Slow Positivity (LSP)) were considered. Four types of trial-sequences (Valid-Valid, Invalid-Valid, Invalid-Invalid, Valid-Invalid) and three types of trial-blocks, with different validity/invalidity proportions (50%, 68%, and 86% of valid trials), were employed. Present data replicate previous reports on the validity sequence effects on ERPs (local probability): (i) higher CNV on trials preceded by valid trials; (ii) higher PN on valid trials preceded by invalid trials compared to valid trials preceded by valid trials; and (iii) higher P3a/P3b and LSP on invalid trials preceded by valid trials compared to invalid trials preceded by invalid trials. In summary, local probability showed more effects modulating the brain responses than global probability and/or their interaction. Among a number of other hypotheses, the functional systems theory would account for the ability of the previous trial to modify processing in the current trial.