Biomedical subjects

Kazuhiko Yokosawa

Publications and source records attributed to Kazuhiko Yokosawa.

11 recordsLinked to original sources

PubMed2006

Attentional awakening: gradual modulation of temporal attention in rapid serial visual presentation.

Orienting attention to a point in time facilitates processing of an item within rapidly changing surroundings. We used a one-target RSVP task to look for differences in accuracy in reporting a target related to when the target temporally appeared in the sequence. The results show that observers correctly report a target early in the sequence less frequently than later in the sequence. Previous RSVP studies predicted equivalently accurate performances for one target wherever it appeared in the sequence. We named this new phenomenon attentional awakening, which reflects a gradual modulation of temporal attention in a rapid sequence.

Adult↗

PubMed2006

Grouping and trajectory storage in multiple object tracking: impairments due to common item motions.

In our natural viewing, we notice that objects change their locations across space and time. However, there has been relatively little consideration of the role of motion information in the construction and maintenance of object representations. We investigated this question in the context of the multiple object tracking (MOT) paradigm, wherein observers must keep track of target objects as they move randomly amid featurally identical distractors. In three experiments, we observed impairments in tracking ability when the motions of the target and distractor items shared particular properties. Specifically, we observed impairments when the target and distractor items were in a chasing relationship or moved in a uniform direction. Surprisingly, tracking ability was impaired by these manipulations even when observers failed to notice them. Our results suggest that differentiable trajectory information is an important factor in successful performance of MOT tasks. More generally, these results suggest that various types of common motion can serve as cues to form more global object representations even in the absence of other grouping cues.

Cues↗

PubMed2006

Orthogonal stimulus-response compatibility effects emerge even when the stimulus position is task irrelevant.

The above-right/below-left mapping advantage with vertical stimuli and horizontal responses is known as the orthogonal stimulus-response compatibility (SRC) effect. We investigated whether the orthogonal SRC effect emerges with irrelevant stimulus dimensions. In Experiment 1, participants responded with a right or left key press to the colour of the stimulus presented above or below the fixation. We observed an above-right/below-left advantage (orthogonal Simon effect). In Experiment 2, we manipulated the polarity in the response dimension by varying the horizontal location of the response set. The orthogonal Simon effect decreased and even reversed as the left response code became more positive. This result provides evidence for the automatic activation of the positive and negative response codes by the corresponding positive and negative stimulus codes. These findings extended the orthogonal SRC effect based on coding asymmetry to an irrelevant stimulus dimension.

Adult↗

PubMed2004

Visual search and memory search engage extensive overlapping cerebral cortices: an fMRI study.

Previous studies have investigated neural correlates of visual search and memory search independently, but none of those studies examined whether cortical regions involved in these searches are overlapping or segregated by directly comparing the two types of search. In this study, we compared the cortical regions involved in visual search and memory search in the same functional magnetic resonance imaging (fMRI) experiment run on the same subjects, using identical stimuli and time courses of stimulus presentation. The right dorsolateral prefrontal cortex (DLPFC), the left frontal eye field (FEF), the right precuneus and cuneus, and the left cerebellum were activated by both visual search and memory search. We suggest that the right DLPFC is associated with the process of monitoring and manipulating multiple elements, while the left FEF is involved in cognitive planning. We also propose that the right precuneus and cuneus as well as the left cerebellum are responsible for both spatial and nonspatial shifts of attention, including attentional shifts in long-term memory, although each of these regions has a slightly different role.

Adult↗

PubMed2004

Texture segregation by motion under low luminance levels.

We examined the effect of average luminance level on texture segregation by motion. We determined the minimum presentation duration required for subjects to detect a target defined by motion direction against a moving background. The average luminance level and retinal position of the target were systematically varied. We found that the minimum presentation duration needed for texture segregation depends significantly on the average luminance level and on retinal position. The minimum presentation duration increased as the mean luminance decreased. At a very low (presumably scotopic) luminance level, the motion-defined target was never detected rapidly. Under scotopic conditions, the minimum presentation duration was shorter in the periphery than in a near foveal region when the task was simple detection of the target. When the task included identifying the shape of the target patch, however, the target presented near the fovea was identified faster at all luminance levels. These results suggest that the performance of texture segregation is constrained by the spatiotemporal characteristics of the early visual system.

Adult↗

PubMed2004

[Temporal characteristics of signal enhancement by visual attention].

The effects of spatial attention by precuing the location of the target stimulus are attributed to two mechanisms: noise reduction and stimulus signal enhancement. The signal enhancement hypothesis proposes that attention directly improves the quality of the stimulus representation. In this study, we examined the temporal characteristics of signal enhancement by combining an orientation discrimination sensitivity measurement and the Speed-Accuracy Trade-off procedure. To minimize the spatial uncertainty, target position was indicated in advance. We found that the valid precue improved the orientation discrimination sensitivity by speeding up the rate of information processing, while not affecting the asymptotic level of sensitivity. We conclude that the signal enhancement by the attention is observed only at the early stage of information processing, and it has different temporal characteristics from that of noise reduction.

Attention↗

PubMed2003

Efficient extrapolation of the view with a dynamic and predictive stimulus.

In the real-world, the retinal projection of an object changes as we move, or as a moving object passes in front of us. We have to recognise objects, despite such retinal-projection changes. Many studies have shown that the time required to identify objects after a change in the retinal projection is longer than when there is no retinal-projection change. This recognition cost is referred to as the view-dependent effect. Previous researchers have studied the view-dependent effect while disregarding the predictability of retinal-projection changes. Here, we demonstrate that there is no view-dependent effect when the predictability is introduced, in the case where participants track moving objects by head-turning or eye-movement in a virtual environment. Violation of the predictability, such as an unpredictable retinal-projection change or a movement of the first stimulus that was inconsistent with a subsequent retinal-projection change, caused a view-dependent effect. Moreover, we found that extraretinal information such as head-turning or eye-movement was unnecessary for view-independent recognition. These results indicate that humans can extrapolate to the tested view from the studied view in a view-independent way when retinal-projection change is predictable from the visual stimulus.

Adult↗

PubMed2003

Does disruption of a scene impair change detection?

When we view a scene, we generally feel that we have a rich representation of that scene. Recent research has shown, however, that we are unable to detect relatively large changes in scenes, which suggests an inability to retain the visual details from one scene view to the next. In the present study, we investigated whether we can retain and make use of global and semantic information from a scene in order to efficiently detect changes from one scene to the next. Results indicated that change detection was practically independent of scene disruption with one exception. Better performance in the meaningful scenes was observed only in the whole-scene presentation condition where the participants knew that the stimulus was extracted from the meaningful scene.

Adult↗

PubMed2003

Negative priming and stimulus familiarity: what causes opposite results?

There has been a discrepancy among past studies with regard to the relation between negative priming and familiarity of stimuli. That is, Malley and Strayer (1995; Strayer & Grison, 1999) reported that the more familiar the stimuli were, the larger negative priming became (i.e., a positive correlation), whereas DeSchepper and Treisman (1996; Treisman & DeSchepper, 1996) reported that the less familiar the stimuli were, the larger negative priming became (i.e., a negative correlation). These studies differ not only in their experimental tasks (identification vs. matching) but also in their respective manners of arranging unfamiliar stimuli (pure vs. mixed). In the present study, using an identical set of stimuli, we examined whether these factors caused the opposite results. An identification task with a pure arrangement produced a positive correlation, and a matching task with a mixed arrangement produced a negative correlation. These results suggest that the past opposing results are both replicable and that they have reflected the different causal mechanisms of negative priming.

Adolescent↗

PubMed2003

[The properties of visual short-term memory on change detection task].

Visual short-term memory (VSTM) has been investigated with a change detection task. Recent studies suggested that there might be some representations in VSTM even when a change was not detected. However, this is discrepant with the previous studies that estimated the representation by change detection. In this study, we investigated the properties of the representation to be retained between two stimuli in a change detection task combined with the probe method so as to explore what causes the discrepancy. The interval between the test and the comparison stimuli and the timing of a positional cue at the location of change were manipulated. The results of three experiments suggested that, before the comparison stimulus presentation, the representations in VSTM were retained more than representations estimated by a normal change detection task, that they decayed with time, and that their availability decreased when the representations of the comparison stimulus were formed. From these results, we discussed a model of VSTM with attention.

Adult↗

PubMed2002

How do the internal details of the object contribute to recognition?

Object recognition becomes difficult when the main axis of the object is foreshortened. It has previously been reported that this so-called foreshortened disadvantage is larger when the silhouette of the object is presented than when the line drawing of the object is presented. The pronounced foreshortened disadvantage in silhouette recognition indicates that the internal details of the object, which are absent in the silhouette, provide useful information, particularly when the main axis is foreshortened. But the role of these internal details remains controversial. One account for the pronounced disadvantage is that the internal details contribute to the derivation of the main axis. The other account is that internal details provide the distinctive features that are directly matched to the object represented in memory. The aim in the present study was to determine which of these two explanations best accounts for the differential foreshortened disadvantage between line drawings and silhouettes. To reduce the uncertainty regarding the axis orientation, a 3-D arrow indicating the orientation of the main axis was presented as a cue before the object itself was presented. As a result, the difference in the foreshortened disadvantage between silhouettes and line drawings disappeared. This indicated that the pronounced foreshortened disadvantage for silhouettes was caused by a lack of axis information. In other words, the internal details provided the information necessary for axis derivation when the axis was foreshortened.

Adult↗