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2 Acta Neurobiologiae Experimentalis

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Expectation of an important event affects responses to irrelevant stimuli of different modalities

100%

Michalski A.

tom 60

nr 4

Periodic alterations of event-related potentials (ERPs) were studied during "oddball" tasks. Sequences of randomly intermixed frequent (non-target) and rare (target) stimuli were presented. In visual experiments, these were flashes of light of two different colors. In auditory tests there were two tones of different frequencies. The instruction was to keep a mental count of each target stimulus. To study the alterations of the "state of the brain" produced by target detection, responses to non-targets immediately following targets were compared with responses to an eighth subsequent non-target stimulus. To evaluate the effect of such "brain states" on responses to stimuli of a different modality, additional visual stimuli (probes) were delivered after both auditory and visual "oddball" stimuli. It was found that responses to the eighth presentation of non-target stimulus were preceded by significant negative shift of recorded potential. This shift was smaller before the responses to non-targets immediately following the presentation of target stimuli. The difference was significant both in auditory and visual tests. Responses to "oddball" stimuli were little affected: only the reduction of P200 peaks in "after target" responses was significant in visual tests. Responses to probes showed stronger effects: when visual probes followed visual "oddball" stimuli, all three components measured (N100, P130 and P200) were shifted positively in responses to eighth presentations of non-targets. When visual probes were presented in auditory tests, only the amplitude of the N100 component was significantly affected.

Sequential P3 effects in a Posner's spatial cueing paradigm: Trial-by-trial learning of the predictive value of the cue

67%

Gomez C. M. , Flores A. , Digiacomo M. R. , Vazquez-Marrufo M.

nr 2

155-167

The neurocognitive consequences of correct or incorrect spatial prediction in a sequential S1-S2 paradigm were assessed. Sequential dependence on previous trial outcome (valid or invalid) was assessed by late Event-Related Potentials (ERPs) and behavioural responses. Two different experiments were performed, situating the target in the vertical (Experiment 1) or in the horizontal (Experiment 2) meridian. RTs and late positivities (P3a and P3b) were recorded. ERPs showed that posterior positivity (probably a P3b) was greater in invalid-valid trials than in valid-valid trials but lower than in valid- invalid trials. However, at the frontal electrodes, late positivity (probably a P3a) only appeared in valid-invalid trials, indicating that invalid trials are analyzed as novel-like stimuli. The P3b results suggest trial-by-trial learning of the predictive value of the cue, which needs to be updated as indicated by the pattern of P3b amplitudes: valid-invalid > invalid-valid > valid-valid.