Biomedical subjects

B Giesbrecht

Publications and source records attributed to B Giesbrecht.

5 recordsLinked to original sources

PubMed2003

Neural mechanisms of top-down control during spatial and feature attention.

Theories of visual selective attention posit that both spatial location and nonspatial stimulus features (e.g., color) are elementary dimensions on which top-down attentional control mechanisms can selectively influence visual processing. Neuropsychological and neuroimaging studies have demonstrated that regions of superior frontal and parietal cortex are critically involved in the control of visual-spatial attention. This frontoparietal control network has also been found to be activated when attention is oriented to nonspatial stimulus features (e.g., motion). To test the generality of the frontoparietal network in attentional control, we directly compared spatial and nonspatial attention in a cuing paradigm. Event-related fMRI methods permitted the isolation of attentional control activity during orienting to a location or to a nonspatial stimulus feature (color). Portions of the frontoparietal network were commonly activated to the spatial and nonspatial cues. However, direct statistical comparisons of cue-related activity revealed subregions of the frontoparietal network that were significantly more active during spatial than nonspatial orienting when all other stimulus, task, and attentional factors were equated. No regions of the frontal-parietal network were more active for nonspatial cues in comparison to spatial cues. These findings support models suggesting that subregions of the frontal-parietal network are highly specific for controlling spatial selective attention.

Adult↗

PubMed2003

Conflict monitoring in the human anterior cingulate cortex during selective attention to global and local object features.

Parallel processing affords the brain many advantages, but processing multiple bits of information simultaneously presents formidable challenges. For example, while one is listening to a speaker at a noisy social gathering, processing irrelevant conversations may lead to the activation of irrelevant perceptual, semantic, and response representations that conflict with those evoked by the speaker. In these situations, specialized brain systems may be recruited to detect and resolve conflict before it leads to incorrect perception and/or behavior. Consistent with this view, recent findings indicate that dorsal/caudal anterior cingulate cortex (dACC), on the medial walls of the frontal lobes, detects conflict between competing motor responses primed by relevant versus irrelevant stimuli. Here, we used a cued global/local selective attention task to investigate whether the dACC plays a general role in conflict detection that includes monitoring for conflicting perceptual or semantic representations. Using event-related functional magnetic resonance imaging (fMRI), we found that the dACC was activated by response conflict in both the global and the local task, consistent with results from prior studies. However, dACC was also activated by perceptual and semantic conflict arising from global distracters during the local task. The results from the local task have implications for recent theories of attentional control in which the dACC's contribution to conflict monitoring is limited to response stages of processing, as well as for our understanding of clinical disorders in which disruptions of attention are associated with dACC dysfunction.

Adult↗

PubMed2001

Cued shifts of attention and memory encoding in partial report: a dual-task approach.

This study explores how cued shifts of visual attention and rapid encoding of visual information relate to limited-capacity processing mechanisms. Three experiments were conducted placing a partial-report task within a dual-task paradigm. Experiments 1 and 2 involved a simple speeded visual discrimination (Task 1) and then an unspeeded partial-report task (Task 2). Generally, Task 2 accuracy declined as the temporal overlap between the two tasks increased. In addition, in Experiment 1, varying the number of items in the partial-report display had an effect on performance regardless of overlap. In contrast, in Experiment 2, varying the type of probe had an effect only at long task overlap. The generality of the interference effect was tested in Experiment 3 using an auditory discrimination as Task 1. Again, Task 2 accuracy declined as the temporal overlap between the two tasks increased. In all cases, the observed interference had the properties of a processing bottleneck. It is argued that encoding information into memory and response selection for the first task both require general-purpose processing. The results are discussed in terms of the functional relationship between attention and memory.

Adolescent↗

PubMed1999

Isolating the interference caused by cue duration in partial report: a quantitative approach.

In bar-probe partial report experiments, subjects are presented with a brief array of letters, followed by a cue that singles out a target letter. Using this procedure, V. M. Townsend (1973) reported a counterintuitive effect: As the duration of a cue was increased, target performance decreased dramatically. The aim of the present study was to isolate the locus of the cue-duration effect. To this end, several characteristics of the bar-probe display were manipulated in a single experiment: the interstimulus interval between the array and the cue, array density, the number of letters, and the number of symbols adjacent to the target. These factors were manipulated on a priori grounds so as to affect the different sources of information used in the bar-probe task--namely, durable storage, abstract identity information, and feature level information. The data were accurately fit by a simple quantitative, multinomial model that assumes that the different sources of information used in the bar-probe task make independent contributions to performance. The critical assumption of the model is that cue duration interferes with only one source of information--namely, feature level information.

Cues↗

PubMed1998

Beyond the attentional blink: visual masking by object substitution.

If 2 targets are to be identified among distractors displayed in rapid sequence, correct identification of the 1st target hinders identification of the 2nd. To obtain this attentional blink (AB), the 1st target must be masked with a simultaneous (integration) or a delayed (interruption) mask indifferently. In 3 experiments, it was shown that the 2nd target must also be masked, but that the precise form of masking is important: An AB occurs with interruption but not with integration masking. This nonequivalence of masking paradigms parallels that found in studies of masked priming, a phenomenon arguably related to the AB. The results are explained by a revised 2-stage model (M. M. Chun & M. C. Potter, 1995).

Adult↗