Biomedical subjects

Hannes Ruge

Publications and source records attributed to Hannes Ruge.

5 recordsLinked to original sources

PubMed2006

Attentional set mixing: Effects on target selection and selective response activation.

Performance is impaired under set mixing conditions that require frequent readjustments of attentional focus over an extended time period. We compared set repetitions within pure blocks (constant focus of attention) to physically identical repetitions within mixed blocks (changing focus of attention). The aim was to investigate how set mixing affects target selection, indexed by the N2pc component, and selective response activation, indexed by the lateralized readiness potential (LRP). We found that set mixing prolonged the evolution of the N2pc while leaving its onset unaffected. Impaired target selection indicated by the N2pc mixing effect also delayed the start of response planning indexed by an onset delay of the stimulus-locked LRP, explaining one part of the behavioral mixing cost. A larger part of mixing cost could be attributed to a prolonged response planning phase, indexed by an earlier onset of the response-locked LRP.

Adult↗

PubMed2005

Advance preparation and stimulus-induced interference in cued task switching: further insights from BOLD fMRI.

To switch from one cognitive task to another is thought to rely on additional control effort being indicated by performance costs relative to repeating the same task. This switch cost can be reduced by advance task preparation. In the present experiment the nature of advance preparation was investigated by comparing a situation where an explicit task cue was presented 2000 ms in advance of the target stimulus (CTI-2000) with a situation where cue and target were presented in close succession (CTI-100). We mapped the blood-oxygenation-level-dependent (BOLD) activation correlates of switch-related control effort and advance task preparation to test alternative explanations why advance preparation is reducing switch costs. A previously reported control-related cortical network of frontal and parietal brain areas emerged that was more strongly activated for switching between tasks. However, this was true exclusively for CTI-100 where no advance task preparation was possible. At CTI-2000 these same brain areas were equally engaged in both switch and repeat trials. For some of these areas, this common activation was time-locked to the presentation of both the cue as well as the target. Other areas were exclusively associated with target processing. The overall pattern of results suggests that advance task preparation is a common process of pre-activating (cue-locked activation) the currently relevant task set which does not face interference from a persisting N - 1 task set. During target processing the same brain areas are re-engaged (subsequent target-locked activation) to apply the pre-activated task set. Though being common to repeat and switch trials, advance preparation has a differential benefit for switch trials. This is because the instructed task set has time to settle into a stable state, thus becoming resistant against disruption from the previous task set, which is retrieved by the current target stimulus.

Adult↗

PubMed2003

Event-related analysis for event types of fixed order and restricted spacing by temporal quantification of trial-averaged fMRI time courses.

PURPOSE: To develop a method for event-related fMRI that allows rapidly presented event sequences to be analyzed, without requiring transitions of different event-types to be counterbalanced. MATERIALS AND METHODS: A cued task switching procedure was investigated with an experimental trial comprising a visual task cue that indicated how to process a subsequent visual target stimulus. Cue and target were either presented quasi-simultaneously, separated by a 100 msec cue-target-interval (CTI100), or the target presentation was delayed by 2000 msec (CTI2000). To characterize the trial-related BOLD-response in terms of its temporal relation to the underlying event structure, the pattern of onset latency differences and peak latency differences for CTI2000 minus CTI100 was evaluated. Independent estimates of onset latencies and peak latencies were determined for preprocessed trial-averaged time courses by jackknife resampling. RESULTS: Validating results were obtained for two brain areas with known characteristics: the visual cortex (cue-locked plus target-locked activation) and the motor cortex (response-locked activation). Extending the analysis to prefrontal areas with a priori unknown characteristics differentiated between several meaningful temporal activation patterns. CONCLUSION: The method yielded a fine-grained temporal description of trial-related BOLD-responses that could be successfully used for the event-related analysis of an experimental design that was highly restricted with respect to event order and event spacing.

Adult↗

PubMed2003

Equivalence of cognitive processes in brain imaging and behavioral studies: evidence from task switching.

A growing number of studies on the higher-order cognitive functions of the human brain use brain-imaging techniques, such as functional magnetic resonance imaging (fMRI). For the validity and generality of fMRI results, it is important that the relevant cognitive processes are equivalent to those functioning in typical settings used in behavioral research. This equivalence could be, for example, endangered by different spatial frames of reference when lying in the scanner. In the present study, we tested whether the cognitive processes, as reflected in behavioral data in brain-imaging settings, are indeed functionally equivalent to those reflected in "purely" behavioral settings. To this end, we used a task-switching paradigm with a spatial component, increasing the likelihood to find effects of experimental setting. We compared the data of three different groups that only differed in testing environments (real, operating fMRI vs simulated fMRI vs standard behavioral with upright position of participants) but used otherwise strictly equivalent experimental conditions. Of importance for our validation purposes, unlike previous studies, we included a group with a behavioral setting, and we tested whether we would replicate a nontrivial, complex three-way interaction across all three groups. We replicated the predicted complex data pattern in all groups, suggesting functional equivalence of the underlying cognitive processes. We also found strongly increased reaction time (RT) levels in the two fMRI groups. We attribute this increase to unspecific distracting factors affecting late motor processes and discuss potential methodological implications of this increased baseline RT in the scanner.

Adolescent↗

PubMed2003

When the same response has different meanings: recoding the response meaning in the lateral prefrontal cortex.

The ability to adapt our behavioral repertoire to different situations and tasks is crucial for our behavioral control. Since the same motor behavior can have different meanings in different task situations, we often have to change the meaning of our responses when we get into a different task context. In a functional MRI experiment we manipulated this response recoding process. Subjects were required to execute two simple spatial tasks in a task switching paradigm. In one condition both tasks required the same set of responses, hence each response had two different meanings depending on the relevant task (bivalent condition). In the other condition subjects used a separate set of responses for each task (univalent condition). While subjects were required to recode the meaning when switching from one task to the next in the bivalent condition, response recoding was not required in the univalent condition. We demonstrate that the lateral prefrontal cortex is involved in recoding of response meaning. These results extend previous assumptions on the role of the prefrontal cortex in behavioral control.

Adult↗