Biomedical subjects

Geoffrey F Woodman

Publications and source records attributed to Geoffrey F Woodman.

10 recordsLinked to original sources

PubMed2006

The time course of consolidation in visual working memory.

How long does it take to form a durable representation in visual working memory? Several theorists have proposed that this consolidation process is very slow. Here, we measured the time course of consolidation. Observers performed a change-detection task for colored squares, and shortly after the presentation of the first array, pattern masks were presented at the locations of each of the colored squares to disrupt representations that had not yet been consolidated. Performance on the memory task was impaired when the delay between the colored squares and the masks was short, and this effect became larger when the number of colored squares was increased. The rate of consolidation was approximately 50 ms per item, which is considerably faster than previous proposals.

Adolescent↗

PubMed2005

Fractionating working memory: consolidation and maintenance are independent processes.

In the present study, we required subjects to remember simple objects that were masked to interrupt consolidation and allow us to estimate the rate of information accrual in visual working memory. We compared a consolidation-baseline condition with a consolidation-during-maintenance condition in which subjects needed to remember a set of unmasked items and then were shown to-be-remembered masked items. We hypothesized that if the control processes of consolidation and maintenance are performed by common mechanisms, then consolidation should be less efficient when performed during maintenance than when performed alone. However, we found that an identical amount of information was encoded per unit time in the two conditions. These results indicate that working memory consolidation is not slowed by maintenance and suggest a two-step model of encoding in visual working memory.

Adolescent↗

PubMed2005

Pushing around the locus of selection: evidence for the flexible-selection hypothesis.

Attention operates at an early stage in some experimental paradigms and at a late stage in others, which suggests that the locus of selection is flexible. The present study was designed to determine whether the locus of selection can vary flexibly within a single experimental paradigm as a function of relatively modest variations in stimulus and task parameters. In the first experiment, a new method for assessing the locus of selection was developed. Specifically, attention can influence perceptual encoding only if it is directed to the target before a perceptual representation of the target has been formed, whereas attention can influence postperceptual processes even if attention is cued after perception is complete. Event-related potentials were used to confirm the validity of this method. The subsequent experiments used cueing tasks in which subjects were required to perceive and remember a set of objects, and the difficulty of the perception and memory components of the task were varied. When the task overloaded perception but not working memory, attention influenced the formation of perceptual representations but not the storage of these representations in memory; when the task overloaded working memory but not perception, attention influenced the transfer of perceptual representations into memory but not the formation of the perceptual representations. Thus, attention operates to select relevant information at whatever stage or stages of processing are overloaded by a particular stimulus-task combination.

Adolescent↗

PubMed2004

Neural fate of ignored stimuli: dissociable effects of perceptual and working memory load.

Observers commonly experience functional blindness to unattended visual events, and this problem has fuelled an intense debate concerning the fate of unattended visual information in neural processing. Here we used functional magnetic resonance imaging (fMRI) to demonstrate that the type of task that a human subject engages in determines the way in which ignored visual background stimuli are processed in parahippocampal cortex. Increasing the perceptual difficulty of a foveal target task attenuated processing of task-irrelevant background scenes, whereas increasing the number of objects held in working memory did not have this effect. These dissociable effects of perceptual and working memory load clarify how task-irrelevant, unattended stimuli are processed in category-selective areas in human ventral visual cortex.

Adult↗

PubMed2004

Visual search is slowed when visuospatial working memory is occupied.

Visual working memory plays a central role in most models of visual search. However, a recent study showed that search efficiency was not impaired when working memory was filled to capacity by a concurrent object memory task (Woodman, Vogel, & Luck, 2001). Objects and locations may be stored in separate working memory subsystems, and it is plausible that visual search relies on the spatial subsystem, but not on the object subsystem. In the present study, we sought to determine whether maintaining spatial information in visual working memory impairs the efficiency of a concurrent visual search task. Visual search efficiency and spatial memory accuracy were both impaired when the search and the memory tasks were performed concurrently, as compared with when the tasks were performed separately. These findings suggest that common mechanisms are used to process information during difficult visual search tasks and to maintain spatial information in working memory.

Fixation, Ocular↗

PubMed2003

Serial deployment of attention during visual search.

This study examined whether objects are attended in serial or in parallel during a demanding visual search task. A component of the event-related potential waveform, the N2pc wave, was used as a continuous measure of the allocation of attention to possible targets in the search arrays. Experiment 1 demonstrated that the relative allocation of attention shifts rapidly, favoring one item and then another. In Experiment 2, a paradigm was used that made it possible to track the absolute allocation of attention to individual items. This experiment showed that attention was allocated to one object for 100-150 ms before attention began to be allocated to the next object. These findings support models of attention that posit serial processing in demanding visual search tasks.

Adolescent↗

PubMed2003

Dissociations among attention, perception, and awareness during object-substitution masking.

When a visual target object is surrounded by four dots that onset at the same time as the target but remain visible after the target terminates, the four dots dramatically impair target discrimination performance. This phenomenon is called object-substitution masking, reflecting the hypothesis that both the target and the four dots are identified, but the representation of the four dots replaces the representation of the target object before the target can be reported. The present study used the event-related potential technique to demonstrate that a target masked in this manner is identified by the visual system and triggers a shift of attention. However, by the time attention is shifted to the target, only the mask remains visible, leading to impaired behavioral detection performance. These findings support the object-substitution hypothesis and provide new evidence that perception, attention, and awareness can be dissociated.

Adolescent↗

PubMed2003

Perceptual organization influences visual working memory.

Previous studies have demonstrated that top-down factors can bias the storage of information in visual working memory. However, relatively little is known about the role that bottom-up stimulus characteristics play in visual working memory storage. In the present study, subjects performed a change detection task in which the to-be-remembered objects were organized in accordance with Gestalt grouping principles. When an attention-capturing cue was presented at the location of one object, other objects that were perceptually grouped with the cued object were more likely to be stored in working memory than were objects that were not grouped with the cued object. Thus, objects that are grouped together tend to be stored together, indicating that bottom-up perceptual organization influences the storage of information in visual working memory.

Adult↗

PubMed2002

Lower region: a new cue for figure-ground assignment.

Figure-ground assignment is an important visual process; humans recognize, attend to, and act on figures, not backgrounds. There are many visual cues for figure-ground assignment. A new cue to figure-ground assignment, called lower region, is presented: Regions in the lower portion of a stimulus array appear more figurelike than regions in the upper portion of the display. This phenomenon was explored, and it was demonstrated that the lower-region preference is not influenced by contrast, eye movements, or voluntary spatial attention. It was found that the lower region is defined relative to the stimulus display, linking the lower-region preference to pictorial depth perception cues. The results are discussed in terms of the environmental regularities that this new figure-ground cue may reflect.

Cognition↗

PubMed2002

Voluntazy and automatic attentional control of visual working memory.

Previous studies of attention-directing cues have focused largely on the effects of cuing on perceptual processes, but cuing may also influence the transfer of perceptual representations into visual working memory. In the present study, we examined this potential role of cues, using both predictive and non-predictive cues in the context of a visual working memory task. Each trial began with a cue, followed by an array of six colored squares, a delay interval, and then a probe square presented at th e location of one of the squares in the previous array. The subjects were required to indicate whether the color of the probe square was the same as the color of the square that had previously been presented at the same location. Performance on this working memory task was more accurate when the cued location was probed than when an uncued location was probed, even when the cued location was no more likely to be probed than any of the uncued locations. An additional experiment using the abrupt-onset paradigm of Yantis and Jonides (1984) yielded similar results. Thus, visual transients may automatically influence the transfer of perceptual representations into visual working memory.

Adolescent↗