Biomedical subjects

Rob H J van der Lubbe

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

13 recordsLinked to original sources

PubMed2006

Divergence of categorical and coordinate spatial processing assessed with ERPs.

The spatial relation between two objects may be described either precisely or more coarsely in abstract terms, denoted as coordinate and categorical descriptions, respectively. These descriptions may reflect the outcomes of two spatial coding processes, which are realized in the left- and right-hemisphere. Support for this account comes from visual field effects in categorical and coordinate judgment tasks and from patient studies. In the current study, this hypothesis was tested by using event-related potentials (ERPs) and source localization. ERPs yield information about the processing stage at which the hypothesized categorical and coordinate processing diverge due to different task demands, especially in our S1-S2 version of the Bar Dot task. A centrally presented Bar Dot (S1) was followed after 2.5s by a second one (S2) in the left or right visual field; participants had to judge whether S2 matched S1 at the categorical, or, in a second task, at the coordinate level. Behavioral measures revealed a left-field advantage in the coordinate task that was absent in the categorical task. S1s elicited stronger early and late bilateral posterior responses in the coordinate than in the categorical task, possibly related to a compensatory strategy at the level of encoding and spatial memory. S2s elicited only stronger early contralateral responses, and stronger late right-hemisphere responses in the categorical task. It is proposed that the left-field advantage in the coordinate task may be due to differences in spatial resolution in perceptual encoding of the left- and right-hemispheres that are largely unaffected by the task at hand.

Adult↗

PubMed2006

Spatiotemporal overlap between brain activation related to saccade preparation and attentional orienting.

Recent brain imaging studies provided evidence that the brain areas involved with attentional orienting and the preparation of saccades largely overlap, which may indicate that focusing attention at a specific location can be considered as an unexecuted saccade towards that location (i.e. the premotor theory of attention). Alternatively, it may be proposed that attentional orienting is simply relevant for preparing saccades, but the two processes may also be completely unrelated. In two experiments, we examined temporal activation of brain areas by measuring the electroencephalogram. Central cues indicated the likely side (left or right) at which a to-be-attended target would occur, or to which a saccade had to be prepared. Cue direction-related activity was determined, time-locked to cue onset. In addition, in our second experiment, delayed saccades had to be carried out, which allows to focus on processes strongly related to saccade execution. In nearly all tasks, an early directing attention negativity (EDAN), an anterior directing attention negativity (ADAN), and a late directing attention positivity (LDAP) were observed, time-locked to cue onset. Source analyses supported the view that this activity probably originates from areas within the ventral intraparietal sulcus (vIPS) and the frontal eye fields (FEF). The saccade-locked analysis also indicated that the FEF plays an important role in triggering saccades, but the role of vIPS appears to be minimal. The latter finding disfavors the premotor theory of attention, as it suggests that the relation between attention and action is less direct.

Adult↗

PubMed2006

Task-dependent exogenous cuing effects depend on cue modality.

Task-dependent exogenous cuing effects on reaction time in detection and discrimination tasks have been ascribed to delayed withdrawal of attention in discrimination tasks. Alternatively, these differences may be due to cue-induced response inhibition in detection tasks. Unimodal and crossmodal versions of the Posner paradigm were examined with short cue-target intervals. Targets above or below fixation required either detection or discrimination responses. Cuing effects were determined for the target-elicited P1 component and for the lateralized readiness potential (LRP). Task-dependent cuing effects on reaction time were found in the unimodal but not in the crossmodal version, but not for the P1 component. The LRP data indicated that inhibition of return in the unimodal detection task had a premotoric locus. These findings suggest that inhibition in the unimodal detection task resulted from speeded motor inhibition triggered by the visual cue.

Acoustic Stimulation↗

PubMed2006

Delayed response to animate implied motion in human motion processing areas.

Viewing static photographs of objects in motion evokes higher fMRI activation in the human medial temporal complex (MT+) than looking at similar photographs without this implied motion. As MT+ is traditionally thought to be involved in motion perception (and not in form perception), this finding suggests feedback from object-recognition areas onto MT+. To investigate this hypothesis, we recorded extracranial potentials evoked by the sight of photographs of biological agents with and without implied motion. The difference in potential between responses to pictures with and without implied motion was maximal between 260 and 400 msec after stimulus onset. Source analysis of this difference revealed one bilateral, symmetrical dipole pair in the occipital lobe. This area also showed a response to real motion, but approximately 100 msec earlier than the implied motion response. The longer latency of the implied motion response in comparison to the real motion response is consistent with a feedback projection onto MT+ following object recognition in higher-level temporal areas.

Adult↗

PubMed2005

Interruption from irrelevant auditory and visual onsets even when attention is in a focused state.

The common view on the interplay between exogenous and endogenous orienting holds that abrupt onsets are not capable of attracting attention when they occur outside the current focus of attention. Does this also apply to sudden irrelevant auditory onsets and when irrelevant visual onsets occur far in the periphery? In addition, does focused attention also reduce the alerting effect of auditory onsets, or vice versa, do highly alerting stimuli distort the attentional state? Crossmodal and unimodal variants of the Posner paradigm were examined in two experiments with targets and irrelevant onsets occurring at 28.3 and 19.3 degrees from fixation. Either centrally presented arrows indicated the forthcoming position of visual targets to be discriminated, or warning cues signaled the likely moment of target occurrence. The targets could be preceded by peripheral auditory or visual onsets that were to be ignored. Crossmodal and unimodal exogenous orienting effects of these irrelevant onsets were observed while participants focused at the relevant side. In addition, no evidence was found that the alerting effect of auditory onsets was dependent on focused attention. Our findings indicate that, at least under the current conditions, neither crossmodal nor unimodal orienting effects of peripheral events dissipate when attention is in a focused state.

Acoustic Stimulation↗

PubMed2005

Delayed attentional engagement in the attentional blink.

Observers often miss the 2nd of 2 visual targets (first target [T1] and second target [T2]) when these targets are presented closely in time; the attentional blink (AB). The authors hypothesized that the AB occurs because the attentional response to T2 is delayed by T1 processing, causing T2 to lose a competition for attention to the item that follows it. The authors investigated this hypothesis by determining whether the AB is attenuated when T2 is precued. The results from 4 experiments showed that the duration and magnitude of the AB were substantially reduced when T2 was precued. The observed improvement in T2 report did not occur at the expense of T1 report, suggesting that processing of T1 was already completed or was at least protected when the cue was presented. The authors conclude that, during the AB, there is a delay between detection and the selection of target candidates for consolidation in short-term memory.

Attention↗

PubMed2004

Strategic and automatic components in the processing of linguistic spatial relations.

The objective of the present study was to determine the extent to which strategies influence the representational format of a linguistic spatial relation. The propositional model assumes that a sentence describing a spatial relation is always represented as a set of propositions, whereas the strategic model claims that a spatial sentence can be represented either as a set of propositions or as a mental image, depending on the strategy (verbal or visual-spatial) an individual follows. Participants read a sentence (spatial or non-spatial) followed by a picture or sentence, which did or did not exemplify the information of the first sentence. In order to examine the involvement of strategic and automatic components the probability (20% or 80%) of the nature (sentence or picture) of the second stimulus was varied. Participants had slower verification RTs for unexpected stimuli than for expected stimuli, but this cost was significantly larger for an unexpected picture than an unexpected sentence. Furthermore, this asymmetric cost for the unexpected visual-spatial stimulus only occurred with spatial sentences and not with non-spatial sentences. Surprisingly, these data do not support a strictly propositional or a strategic model. Instead, we propose a third option: a dual representational model, in which people automatically represent the spatial sentence propositionally. In addition, depending on the context, a pictorial strategy is employed, which results in a supplementary visual-spatial representation.

Adult↗

PubMed2004

Quantifying the interactions between allo- and egocentric representations of space.

Under many circumstances, humans do not judge the location of objects in space where they really are. For instance, when a background is added to a target object, the judged position of a target with respect to oneself (egocentric position) is shifted in the opposite direction as the placement of such a background with respect to the body midline. It is an ongoing debate whether such effects are due to a uni- or bi-directional interaction between allo- and egocentric spatial representations in the brain, or reflect a response strategy, known as the perceived midline shift. In this study, the effects of allocentric stimulus coordinates on perceived egocentric position were examined more precisely and in a quantitative manner. Furthermore, it was investigated whether the judged allocentric position (with respect to a background) is also influenced by the egocentric position in space of that object. Allo- and egocentric coordinates were varied independently. Also, the effect of background luminance on the observed interactions between spatial coordinates was determined. Since background luminance had an effect on the size of the interaction between allocentric stimulus coordinates and egocentric judgments, and no reverse interaction was found, it seems that interactions between ego- and allocentric reference frames is most likely only unidirectional, with the latter affecting the former. This interaction effect was described in a quantitative manner.

Adult↗

PubMed2004

Qualitative differences between conscious and nonconscious processing? On inverse priming induced by masked arrows.

In general, both consciously and unconsciously perceived stimuli facilitate responses to following similar stimuli. However, masked arrows delay responses to following arrows. This inverse priming has been ascribed to inhibition of premature motor activation, more recently even to special processing of nonconsciously perceived material. Here, inverse priming depended on particular masks, was insensitive to contextual requirements for increased inhibition, and was constant across response speeds. Putative signs of motor inhibition in the electroencephalogram may as well reflect activation of the opposite response. Consequently, rather than profiting from inhibition of primed responses, the alternative response is directly primed by perceptual interactions of primes and masks. Thus there is no need to assume separate pathways for nonconscious and conscious processing.

Adult↗

PubMed2004

Spatial tapping interferes with the processing of linguistic spatial relations.

Simple spatial relations may be represented either in a propositional format that is dependent on verbal rehearsal or in a picture-like format that is maintained by visual-spatial rehearsal. In sentence-picture and picture-picture verification tasks, we examined the effect of an articulatory suppression and a spatial tapping dual task on the encoding of simple spatial relations (e.g., triangle left of circle). Articulatory suppression did not interfere, while spatial tapping lowered performance in both tasks. Apparently, both linguistic and perceptual inputs of simple spatial relations engaged the visual-spatial working memory. In the sentence-picture verification experiments, spatial tapping only hampered performance of participants who were classified on the basis of their RT patterns as having used a visual-spatial strategy, while it had no effect for those who were classified as having applied a verbal strategy. Therefore, this study provides converging evidence, using a dual-task methodology, that both separate verbal and visual-spatial strategies exist for the processing of simple spatial sentences.

Analysis of Variance↗

PubMed2003

Delay improves performance on a haptic spatial matching task.

Systematic deviations occur when blindfolded subjects set a test bar parallel to a reference bar in the horizontal plane using haptic information (Kappers and Koenderink 1999, Perception 28:781-795; Kappers 1999, Perception 28:1001-1012). These deviations are assumed to reflect the use of a combination of a biasing egocentric reference frame and an allocentric, more cognitive one (Kappers 2002, Acta Psychol 109:25-40). In two experiments, we have examined the effect of delay between the perception of a reference bar and the parallel setting of a test bar. In both experiments a 10-s delay improved performance. The improvement increased with a larger horizontal (left-right) distance between the bars. This improvement was interpreted as a shift from the egocentric towards the allocentric reference frame during the delay period.

Adolescent↗

PubMed2002

Aging and the Simon task.

A visual Simon task was used to study the influence of aging on visuospatial attention and inhibitory control processes. Responses were much slower for elderly than for young participants. The delay in trials in which stimulus and response side did not correspond as compared to when they did correspond (the Simon effect) was larger for older people, even after correcting for general slowing due to aging. The slowing of responses reflected a slowing of internal processing, as indicated by progressively larger delays of the peak latencies of the N1, the posterior contralateral negativity (PCN), and P3. A comparison between the amplitudes of the PCN and early lateralized readiness potential (pre-LRP) indicated that transmission from posterior sites (PCN) to the motor cortex may be affected by age. The data support the view that aging affects an inhibitory process that controls direct visuomotor transmission.

Adult↗

PubMed2002

Traces left on visual selective attention by stimuli that are not consciously identified.

Briefly presented information, even if unidentifiable, may speed or delay required responses to following events. It has been assumed that this priming of the motor system may occur without affecting attention to priming and following stimuli. In contrast to this notion, the present study reports that such unidentified stimuli have effects on a physiological indicator of the attentional system. A lateral posterior electroencephalogram component was evoked by laterally presented relevant shapes, reflecting shifts of attention to those shapes. This component was absent, however, when the relevant shape was preceded by a similar shape at the same location, even if this shape was completely masked by metacontrast. The attentional shift evidently became unnecessary in this situation. Thus, unidentifiable information may leave some trace for attention-controlled selection of the following event.

Attention↗