The Time Course of Negative Priming

Abstract

Selective attention enables goal-directed behavior despite the permanent, immense input to the sensory system. Contradicting early speculations of an active attending and passive ignoring, the active nature of ignoring was revealed by the negative priming paradigm. The present thesis will describe our multi-level approach to reveal the temporal structure of negative priming. Accompanied by computational modeling, we run sophisticated psychological experiments and record and analyze EEG data.The common denominator of all negative priming paradigms is the simultaneous presentation of targets that have to be attended to, and distractors that are to be ignored. A slowdown in the response to a formerly ignored stimulus is labeled negative priming. Because of negative priming being robust and sensitive at the same time, a variety of different theoretical accounts have been developed. But until now none of the theoretical accounts is able to explain all aspects of the negative priming effect. In order to clarify the situation of diverging explanatory accounts, the time course of negative priming is crucial. The mechanisms postulated by the different theories act in different stages of trial processing. In order to advance the debate on theoretical accounts, we provide two quantitative implementations. First we take up a single theory of negative priming and build a minimal model producing realistic effects on the basis of the postulated mechanism. We show how the model can be extended to generate hypotheses in a more complex paradigm. The second computational approach is more ambitious with respect to the discussion about the applicability of the theories of negative priming in specific situations. We build a computational model comprising most of the mechanisms suspected to play a role in the neural processing in negative priming tasks. The outcome is not only a meta-model for negative priming, termed General Model, but in itself a simplified model of the brain as a framework for action selection based on perception. We address the tradeoff between biological realism and understandability by modeling each assumed mechanism separately but keeping the internal dynamics of each of the corresponding layers very simple.The computational implementation of theories is accompanied by a series of behavioral experiments intended to decide about the temporal localization of the negative priming effect relative to the processing of a single trial. Adapting the voicekey paradigm, we present an EEG experiment that replicates findings from one of the few studies on event-related potentials related to negative priming, i.e. a left lateralized modulation of the P300 in a similar manner for both negative as positive priming trials and a differentiation in the late positive complex which points to a late ocuring of the negative priming effect. To access the timing of the effect not only through brain recordings but behavioral measures, we design a paradigm which requires a button press between stimulus identification and target selection phase. The results locate negative priming as well in the later part of a trial. This remainder of a trial still contains both the target selection and response generation process. Therefore, we construct another trial splitting paradigm which now singles out the response generation phase. We finally find the devotion of negative priming to the target selection phase of a trial.