Biomedical subjects

Takatsune Kumada

Publications and source records attributed to Takatsune Kumada.

8 recordsLinked to original sources

PubMed2006

Attribute-invariant orientation discrimination at an early stage of processing in the human visual system.

This study investigated event-related brain potentials (ERPs) during selective attention to the orientation of a bar comprised of two squares, which were defined by only color or motion (intra-attribute conditions) or both (interattribute condition). An early positive potential in association with orientation selection was elicited for all conditions in similar latency ranges but with different scalp distributions. These results suggest that attribute-invariant orientations can be discriminated at an early stage of processing in the human brain, which fills a gap between monkey electrophysiology and human psychophysics, while attribute-specific orientations are also available in a given context.

Adult↗

PubMed2006

An inter-item similarity model unifying feature and conjunction search.

We propose a model of visual search to address the hitherto unresolved issue of reconciling serial deployment of attention accounts with inter-item similarity effects. Target-distractor and distractor-distractor similarity were systematically varied in 85 (17x5) set type-size conditions over seven experiments, including univariate feature and bivariate conjunction search. The model, a power (square root) function of dimension-specific target-distractor and distractor-distractor similarity in linear combination with set size, accounted for 98% of the variance on type-size means. It suggests that much of efficient and inefficient search can be unified under a single theory involving item similarity.

Adult↗

PubMed2006

Attentional prioritization to contextually new objects.

Using a hybrid paradigm of a contextual cuing task and a probe detection task, we tested whether or not contextually new objects can be prioritized in visual search. After several hundred visual search practice trials with repeated and nonrepeated layouts, an additional distractor that was contextually new was presented in the repeated layouts. The results showed that detection of probe dots appearing at the location of a search target was faster in the repeated than in the nonrepeated layouts. More importantly, detection of probe dots at the new object locations was as fast as that of probe dots at the target locations in repeated layouts, suggesting that the attentional system implicitly prioritizes the processing of a location where a change in contextual information has occurred.

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↗

PubMed2003

Effects of pictorially-defined surfaces on visual search.

Three experiments of visual search for a cube (for a square pillar in Experiment 3) with an odd conjunction of orientation of faces and color (a cube with a red top face and a green right face among cubes with a green top face and a red right face, for example) showed that the search is made more efficient by arranging cubes (or square pillars) so that their top faces lie in a horizontal surface defined by pictorial cues. This effect shows the same asymmetry as that of the surface defined by the disparity cue did [Perception and Psychophysics, 62 (2000) 540], implying that the effect is independent of the three-dimensional cue and the global surface structure influences the control of attention during the search.

Adult↗

PubMed2003

Integration process of contours defined by different attributes.

We examined how contours defined by different attributes are integrated into a shape using the visual search paradigm and found that the search for the bar orientation is particularly difficult when each bar is composed of motion-defined and luminance- or color-defined contours. This does not support the view that the shape integration process is based on the unified contour representation entirely common to all attributes, but suggests that motion-defined contours are integrated through a different process.

Color Perception↗

PubMed2003

Attending to a location in three-dimensional space modulates early ERPs.

It has been reported that attending to a particular location can modulate incoming sensory signals, as reflected by the stimulus-evoked P1 and N1 components of the visual event-related potential (ERPs) in a two-dimensional (2D) display [Attention, Space, and Action: Studies in Cognitive Neuroscience, Oxford University Press, New York, 1999, p. 31]. In contrast, in this study we examined the effect of attention in 3D space using a stereoscopic display. Stimuli were presented randomly, one at a time, in an orthogonal combination of two depths (near, far) and two 2D locations (left, right) relative to the fixation point. The task was to attend selectively to one of these four positions and to respond to a target stimulus defined by shape in the attended 3D location. The effect of 2D location selection on the P1 amplitude was greater for stimuli in the near than the far depth plane, and the amplitude of N1 increased in response to stimuli in the attended combination of 2D location and depth. These results suggest that the effect of early spatial selection on the visual ERP is not simply based on retinotopic organization of the visual field, but also on intermediate stages that construct a 3D spatial representation of the external world.

Adult↗

PubMed2002

Cross-dimensional interference and cross-trial inhibition.

In two experiments, we examined whether one source of cross-dimensional interference in visual search involves cross-trial position priming. In Experiment 1, we demonstrated cross-dimensional interference in search for an orientation-defined target: Search for a left-tilted target among right-tilted non-targets was disrupted by the presence of a singleton color distractor. In all conditions, search was facilitated when a target was presented at the same position as a target in the previous trial (positive position priming). In addition, there were negative effects of position priming on orientation targets that fell on the same side as singleton distractors on the previous trial. In Experiment 2, to examine the impact of negative position priming on cross-dimensional interference, trials with and without singleton distractors were presented in a single trial block. The chance of a singleton distractor's being present on a preceding trial was then equated across displays when the distractor was and when it was not subsequently present. Cross-dimensional interference was eliminated under this mixed presentation condition, suggesting that the cost of cross-dimensional interference was not determined by the stimulus-driven factors in the current trial, at least when a limited number of target and distractor locations was used. We conclude that top-down selection is possible during visual search, and this leads to inhibition of the location of salient distractors. The cost of this is slowed detection of targets at inhibited locations on subsequent trials.

Adult↗