Biomedical subjects

Katsumi Watanabe

Publications and source records attributed to Katsumi Watanabe.

12 recordsLinked to original sources

PubMed2004

Visual grouping by motion precedes the relative localization between moving and flashed stimuli.

A flashed stimulus is perceived as spatially lagging behind a moving stimulus when they are spatially aligned. When several elements are perceptually grouped into a unitary moving object, a flash presented at the leading edge of the moving stimulus suffers a larger spatial lag than a flash presented at the trailing edge (K. Watanabe. R. Nijhawan. B. Khurana, & S. Shimojo. 2001). By manipulation of the flash onset relative to the motion onset, the present study investigated the order of perceptual operations of visual motion grouping and relative visual localization. It was found that the asymmetric mislocalization was observed irrespective of physical and/or perceptual temporal order between the motion and flash onsets. Thus, grouping by motion must be completed to define the leading-trailing relation in a moving object before the visual system explicitly represents the relative positions of moving and flashed stimuli.

Cues↗

PubMed2004

Accumulation and degradation of thiamin-binding protein and level of thiamin in wheat seeds during seed maturation and germination.

Changes in the levels of thiamin-binding globulin and thiamin in wheat seeds during maturation and germination were studied. The thiamin-binding activity of the seed proteins increased with seed development after flowering. The thiamin content of the seeds also increased with development. Thiamin-binding activity decreased during seed germination. On the other hand, immunological analysis using an antibody directed against the thiamin-binding protein isolated from wheat seeds showed that the thiamin-binding globulin accumulated in the aleurone layer of the seeds during maturation, and then the protein was degraded and disappeared during seed germination. These results suggested that the thiamin-binding globulin of wheat seeds was synthesized and accumulated in the aleurone layer of the seeds with seed development, similar to the thiamin-binding albumin in sesame seeds, and that thiamin bound to the thiamin-binding globulin in the dormant wheat seeds for germ growth during germination.

Carrier Proteins↗

PubMed2003

Neural correlates of rewarded and unrewarded eye movements in the primate caudate nucleus.

The prospect of immediate reward elicits goal-oriented behavior. However, animals often have to perform actions that do not immediately lead to reward in the pursuit of a long-term goal. Here we identify neural activity in monkey caudate nucleus that specifically correlates with rewarded and unrewarded eye movements. The monkey performed a visually guided saccade task in which only one position was associated with positive reinforcement. To advance in the experimental session, however, the monkey had no choice but to complete a saccade to an unrewarded position as well as to a rewarded position. Some caudate saccadic neurons showed enhanced activity around the time of the saccade in rewarded trials (rewarded-saccade neurons). Another subset of neurons discharged selectively around the execution of the saccade in unrewarded trials (unrewarded-saccade neurons). In both rewarded and unrewarded trials, stronger activity of these neurons was associated with reduced saccade latency. These results suggest that both rewarded and unrewarded saccades are facilitated by caudate saccadic activity. The neuronal activity of unrewarded-saccade neurons might reflect the required execution of unrewarded eye movements on the way to future reward.

Action Potentials↗

PubMed2003

Effects of motivational conflicts on visually elicited saccades in monkeys.

The prospect of reward evoked by external stimuli is a central element of goal-oriented behavior. To elucidate behavioral effects of reward expectation on saccade latency, we employed a visually guided saccade task with asymmetrical reward schedule. The monkey had to make an immediate saccade to a peripheral visual target in every trial, but was rewarded for a correct saccade to only one of four possible target positions. Reward availability was predictable on the basis of the spatial position of the target throughout a daily session. Compared with the condition where all positions were rewarded with a smaller amount, the mean saccade latency in the asymmetrical reward schedule was significantly shorter when the saccade was made toward the position associated with reward than when it was directed to no-reward positions. Furthermore, a divergence-point analysis on cumulative latency distributions showed that the expectation of reward facilitated saccades at all latency ranges. In contrast, the expected lack of reward delayed the initiation of saccades with latencies longer than about 200 ms, irrespective of whether the saccade was made to a position orthogonal or opposite to the reward position. For saccades with latencies of more than approximately 240 ms, an additional delay was observed when the saccade was made to a position opposite, as compared to orthogonal, to the reward position. These results suggest that the facilitation by predictive reward is mediated by a preparatory process that is location-specific, whereas the inhibition by the absence of reward takes about 200 ms after the target onset to become effective and is initially location nonspecific but turns location-specific over time.

Animals↗

PubMed2003

Effect of target-distractor similarity on FEF visual selection in the absence of the target.

We tested the hypothesis that frontal eye field (FEF) visual activity integrates visual information with a template of a target by examining whether a target that is not present in a search display influences the target selection in FEF. Neural activity was recorded in FEF of macaque monkeys performing visual search for a singleton target defined by color or direction of motion. The target remained constant throughout, but not across experimental sessions. Trials with distractors dissimilar to the target were interleaved with trials with distractors similar to the target. The hypothesis was tested by measuring the magnitude of activity in randomly interleaved trials with the target absent and only distractors in the display. We found that the response to the distractors was significantly greater when presented with displays consisting of distractors that resembled the absent target than when presented with displays consisting of distractors most different from the absent target. The influence of target-distractor similarity on FEF activity was also observed when the target was present, as reported previously. These data suggest that a template of the absent target can influence the selection process in FEF. This provides more direct evidence that FEF integrates visual information and knowledge of the target to determine the goal of a saccade.

Action Potentials↗

PubMed2003

Differential effect of distractor timing on localizing versus identifying visual changes.

When visual changes are accompanied by visual transients, such as in the case of saccades, eye blinks, and brief flickers, they often go unnoticed; this phenomenon is called change blindness (Rensink, R. A. (2002). Change detection. Annual Review of Psychology 53, 245; Simons, D. J., & Levin, D. T. (1997). Change blindness. Trends in Cognitive Sciences 1, 261). Change blindness occurs even when the position of visual transients does not cover the location of the change (as in the 'mudsplash' paradigm) (O'Regan, J. K., Rensink, R. A., & Clark, J. J. (1999). Nature 398, 34). By using a simplified mudsplash display, the present study investigated whether change blindness depends on (a). the timing of visual transients, and (b). the task that observers perform. Eight Gabor elements with random orientations were presented. One element (target) was rotated 45 degrees clockwise or counterclockwise without a temporal gap. High contrast visual transients, not overlapping with the elements, appeared at various times with respect to the target change. Observers reported where the change was (change localization), or in which direction the target rotated (change identification). Change localization was impaired primarily when the onset of the transient was at or after the change. In contrast, change identification was impaired mainly when the transient preceded the change. These results suggest that change localization and change identification are mediated in part by different mechanisms.

Adult↗

PubMed2003

Perceived shifts of flashed stimuli by visible and invisible object motion.

Perceived positions of flashed stimuli can be altered by motion signals in the visual field-position capture (Whitney and Cavanagh, 2000 Nature Neuroscience 3 954-959). We examined whether position capture of flashed stimuli depends on the spatial relationship between moving and flashed stimuli, and whether the phenomenal permanence of a moving object behind an occluding surface (tunnel effect; Michotte 1950 Acta Psychologica 7 293-322) can produce position capture. Observers saw two objects (circles) moving vertically in opposite directions, one in each visual hemifield. Two horizontal bars were simultaneously flashed at horizontally collinear positions with the fixation point at various timings. When the movement of the object was fully visible, the flashed bar appeared shifted in the motion direction of the circle. But this position-capture effect occurred only when the bar was presented ahead of or on the moving circle. Even when the motion trajectory was covered by an opaque surface and the bar was flashed after complete occlusion of the circle, the position-capture effect was still observed, though the positional asymmetry was less clear. These results show that movements of both visible and 'hidden' objects can modulate the perception of positions of flashed stimuli and suggest that a high-level representation of 'objects in motion' plays an important role in the position-capture effect.

Attention↗

PubMed2002

Neuromagnetic responses to chromatic flicker: implications for photosensitivity.

Excessive cortical excitation due to visual stimulation often leads to photosensitive epilepsy. Here we demonstrate that even in normal subjects, prolonged stimulation with low-luminance chromatic (equiluminant) flicker evokes neuromagnetic activity in the primary visual cortex, which develops slowly (up to 1000 ms) and depends on the color combination of flicker. This result suggests that chromatic sensitivity is a critical factor of cortical excitation, which can be amplified over time by a flickering stimulus. We further show that transient activity occurs in the parieto-occipital sulcus as early as 100-400 ms after flicker onset, which is negatively correlated with the later occipital activity. The early parieto-occipital activity may reflect a defensive mechanism that suppresses cortical hyperactivity due to chromatic flicker.

Adult↗

PubMed2002

A neural correlate of response bias in monkey caudate nucleus.

Primates are equipped with neural circuits in the prefrontal cortex, the parietal cortex and the basal ganglia that predict the availability of reward during the performance of behavioural tasks. It is not known, however, how reward value is incorporated in the control of action. Here we identify neurons in the monkey caudate nucleus that create a spatially selective response bias depending on the expected gain. In behavioural tasks, the monkey had to make a visually guided eye movement in every trial, but was rewarded for a correct response in only half of the trials. Reward availability was predictable on the basis of the spatial position of the visual target. We found that caudate neurons change their discharge rate systematically, even before the appearance of the visual target, and usually fire more when the contralateral position is associated with reward. Strong anticipatory activity of neurons with a contralateral preference is associated with decreased latency for eye movements in the contralateral direction. We conclude that this neuronal mechanism creates an advance bias that favours a spatial response when it is associated with a high reward value.

Action Potentials↗

PubMed2002

Shifts in perceived position of flashed stimuli by illusory object motion.

Moving stimuli cause the position of flashed stimuli to appear shifted in the direction of motion (position capture). To examine whether position capture depends on low-level motion interactions or perception of integrated object motion, we employed a slit-view display. Two line-drawn diamonds translated horizontally in opposite directions, one above and one below the fixation cross, either behind an occluding surface with a narrow slit or without occluding surface. When the diamonds were in vertical alignment, two vertical bars were flashed, one in the center of each diamond. In the slit-view condition, the diamonds were visible through a 4-, 2-, or 1-pixel vertical slit; the width of the flashed bars always matched the width of the slit. Even though the horizontal component of physical motion was greatly reduced or absent in the slit-view conditions, observers perceived diamonds moving behind the occluding surface. Furthermore, the position of the flashed bar was captured by the moving diamonds such that each bar appeared shifted in the direction of perceived motion. We conclude that the position capture reported here has a component based on high-level motion processing that is responsible for dynamically integrating object motion and shape.

Analysis of Variance↗

PubMed2001

Cloning and sequence analysis of cDNA encoding thiamin-binding proteins from sesame seeds.

The amino acid sequences of the large polypeptides of thiamin-binding proteins (TBPs) from sesame (Sesamum indicum L.) seeds (STBP-I, -II and -III) were analyzed. The large polypeptides of STBP-I, -II and -III had the same amino acid sequences as did their small polypeptides. The peptide sequence information obtained from STBPs was used to synthesize DNA primers for amplification of the gene(s) encoding STBPs. A 200-bp fragment was amplified from cDNA synthesized from RNA from sesame seeds 4 weeks after flowering. The 200-bp fragment was used to clone full-length cDNA(s) encoding STBP(s) with RACE techniques. A 644-bp fragment was amplified, cloned and sequenced. The cDNA was a full-length clone encoding STBP(s). It contained an open reading frame, which defined a 143-residue polypeptide. The identified small and large polypeptide sequences of STBPs exactly matched the sequence encoded within the cDNA clone. These results indicated that the small and large polypeptides of STBPs were encoded on the mRNA as a single large proprotein precursor and that the final mature forms were generated by post-translational processing in the same manner as the other 2S albumins of plant seeds.

Journal Article↗

PubMed2001

Perceptual organization of moving stimuli modulates the flash-lag effect.

When a visual stimulus is flashed at a given location the moment a second moving stimulus arrives at the same location, observers report the flashed stimulus as spatially lagging behind the moving stimulus (the flash-lag effect). The authors investigated whether the global configuration (perceptual organization) of the moving stimulus influences the magnitude of the flash-lag effect. The results indicate that a flash presented near the leading portion of a moving stimulus lags significantly more than a flash presented near the trailing portion. This result also holds for objects consisting of several elements that group to form a unitary percept of an object in motion. The present study demonstrates a novel interaction between the global configuration of moving objects and the representation of their spatial position and may provide a new and useful tool for the study of perceptual organization.

Fixation, Ocular↗