Biomedical subjects

Rob H J Van der Lubbe

Publications and source records attributed to Rob H J Van der Lubbe.

5 recordsLinked to original sources

PubMed2006

Spatial attention triggered by unimodal, crossmodal, and bimodal exogenous cues: a comparison of reflexive orienting mechanisms.

The aim of this study was to establish whether spatial attention triggered by bimodal exogenous cues acts differently as compared to unimodal and crossmodal exogenous cues due to crossmodal integration. In order to investigate this issue, we examined cuing effects in discrimination tasks and compared these effects in a condition wherein a visual target was preceded by both visual and auditory exogenous cues delivered simultaneously at the same side (bimodal cue), with conditions wherein the visual target was preceded by either a visual (unimodal cue) or an auditory cue (crossmodal cue). The results of two experiments revealed that cuing effects on RTs in these three conditions with an SOA of 200 ms had comparable magnitudes. Differences at a longer SOA of 600 ms (inhibition of return for bimodal cues, Experiment 1) disappeared when catch trials were included (in Experiment 2). The current data do not support an additional influence of crossmodal integration on exogenous orienting, but are well in agreement with the existence of a supramodal spatial attention module that allocates attentional resources towards stimulated locations for different sensory modalities.

Acoustic Stimulation↗

PubMed2006

Are space and time automatically integrated in episodic memory?

The aim of the present study was to determine to what extent spatial and temporal features are automatically integrated during encoding in episodic memory. Both nameable and non-nameable stimuli were presented sequentially at different locations on a computer screen. Mixed and pure blocks of trials were used. In the mixed blocks participants were instructed to focus either on the spatial or the temporal order of the objects, as on the majority of the trials recall of this feature was tested (expected trials). However, on a few trials participants had to reproduce the other feature (unexpected trials). In the pure blocks either the spatial or the temporal order of the objects was tested on all trials. More errors were made on unexpected than on expected trials of the mixed blocks. Moreover, no primacy or recency effects were found when performance on the spatial task was plotted as a function of the temporal position. These results suggest that spatial information and temporal order information rely on separate encoding processes.

Adult↗

PubMed2005

Different effects of exogenous cues in a visual detection and discrimination task: delayed attention withdrawal and/or speeded motor inhibition?

Several studies examining spatial attention have found a discrepancy regarding the effects of exogenous cues on reaction times in visual detection and discrimination tasks. Namely, across a wide range of cue-target intervals, responses are slower for targets at cued than at uncued locations (inhibition of return) in detection tasks, whereas responses are faster for targets at cued than at uncued locations (facilitation) in discrimination tasks. Two hypotheses were proposed to account for this discrepancy. First, attention may dwell much longer on the exogenously cued location in discrimination tasks because stimuli have to be identified (i.e., the delayed attention withdrawal hypothesis). Secondly, due to increased motor preparation in detection tasks, cue-induced motor inhibition may rise much faster in these tasks than in discrimination tasks (i.e., the speeded motor inhibition hypothesis). We examined to what extent these hypotheses can account for effects of exogenous cues in a detection and discrimination task on the extrastriate P1 component, and the onset of motor activation, as indexed by the lateralized readiness potential. Some support was found for the delayed attention withdrawal hypothesis, as task-dependent cueing effects were found on the P1 component. Other aspects of our data, however, indicate that motor inhibition is also involved. Based on these findings, we propose that effects of exogenous cues in detection and discrimination tasks are determined by the interplay between two mechanisms, of which the time courses of activation may be modulated by the specific setting.

Adult↗

PubMed2004

Mechanisms underlying spatial coding in a multiple-item Simon task.

Choice responses are faster when target position and response side correspond than when they do not, even if target position is response-irrelevant. This "Simon effect" has also been observed in case of multi-item arrays. Generally, it is assumed that an automatically generated spatial response code is responsible for the effect. The referential-coding account assumes that this code is directly related to the target, although the moment of production of the code is not fully clear. The attention-shift account assumes that the code is directly related to the direction of the most recent attentional shift. An experiment was performed in which left or right target locations were indicated by arrows occurring before (precue), simultaneous with (simcue), or after (postcue) six-element arrays. Overt responses and EEG potentials were recorded. The Simon effect was present in all conditions, and decreased when responses were slower. No relation was found between amplitude of posterior lateralized components and the magnitude of the Simon effect. A posterior contralateral negativity was also found after presenting the arrays in the precue condition, which might reflect the reorienting of attention toward the target position. The results are more favorable to the referential-coding account although this account becomes very similar to the attention-shift hypothesis as the moment of formation of the spatial response code is related to effective target onset rather than to stimulus onset.

Adult↗

PubMed2004

Being prepared on time: on the importance of the previous foreperiod to current preparation, as reflected in speed, force and preparation-related brain potentials.

How do participants adapt to temporal variation of preparatory foreperiods? For reaction times, specific sequential effects have been observed. Responses become slower when the foreperiod is shorter on the current than on the previous trial. If this effect is due to changes in motor activation, it should also be visible in force of responses and in EEG measures of motor preparation, the contingent negative variation (CNV) and the lateralized readiness potential (LRP). These hypotheses were tested in a two-choice reaction task, with targets occurring 500, 1500, or 2500 ms after an acoustic warning signal. The reaction time results showed the expected pattern and were accompanied by similar effects on a fronto-central CNV and the LRP. In contrast, the increase of response force with brief current foreperiods did not depend on previous foreperiods. Thus, EEG measures confirm that sequential effects on RT are at least partially due to changes in motor activation originating from previous trials. Effects found on response force may be related to general response readiness rather than activation of motor-hand areas, which may explain the absence of a sequential effect on force in the current experiment.

Adult↗