The effects of foreknowledge and task-set shifting as mirrored in cue- and target-locked event-related potentials

Abstract

The present study examined the use of foreknowledge in a task-cueing protocol while manipulating sensory updating and executive control in both, informatively and non-informatively pre-cued trials. Foreknowledge, sensory updating (cue switch effects) and task-switching were orthogonally manipulated in order to address the question of whether, and to which extent, the sensory processing of cue changes can partly or totally explain the final task switch costs. Participants responded faster when they could prepare for the upcoming task and if no task-set updating was necessary. Sensory cue switches influenced cue-locked ERPs only when they contained conceptual information about the upcoming task: frontal P2 amplitudes were modulated by task-relevant cue changes, mid-parietal P3 amplitudes by the anticipatory updating of stimulus-response mappings, and P3 peak latencies were modulated by task switching. Task preparation was advantageous for efficient stimulus-response re-mapping at target-onset as mirrored in target N2 amplitudes. However, N2 peak latencies indicate that this process is faster for all repeat trials. The results provide evidence to support a very fast detection of task-relevance in sensory (cue) changes and argue against the view of task repetition benefits as secondary to purely perceptual repetition priming. Advanced preparation may have a stronger influence on behavioral performance and target-locked brain activity than the local effect of repeating or switching the task-set in the current trial.

Figure 1. Stimulus material and experimental design.

Each trial consisted on a visual cue, either informative (Ic) or non-informative (NIc), followed by the target cards to be sorted. Target cards also contained a similar cue (this was a non-informative cue in informatively cued trials, and vice versa). Participants had to match the choice card with one of the four key cards according to either the color or shape of their elements. Examples of an Ic trial (left panel), and a NIc trial (middle panel) are shown on the figure.

Figure 2. Response times (RT) in milliseconds (ms) and percent hit rates (HR) across the three task conditions for both, Ic trials (light gray) and NIc trials (dark gray).

Mean RTs were faster in Ic trials compared to NIc trials, and faster in cue repeat trials compared to task switch trials. No effect on HR was found.

Figure 3. Cue-locked ERPs for the P2 (A) and P3 (B) components for informative and non-informative cue repeat and cue switch trials and their respective topographical distribution.

Figure 4. Cue-locked ERPs and topographical distributions for the respective waveforms of the P2 and P3 components.

Additionally, topographical maps of difference waveforms are presented. (A) Frontal P2 mean amplitudes were larger for task switch trials compared to task repeat trials and NIc trials. (B) The amplitude of the midparietal P3 component was enhanced for both, informative task repeat and task switch trials compared with NIc trials.

Figure 5. Target-locked ERPs and topographical distributions for the informatively and non-informatively cued waveforms in the N2 time window.

Moreover, the topographical map of their difference waveform is shown. Amplitudes were enhanced for Ic trials compared to NIc trials for both ERP components. Shortest N2 peak latencies occurred in repeat trials.