Biomedical subjects

Katsumi Watanabe

Publications and source records attributed to Katsumi Watanabe.

At least 19 recordsLinked to original sources

PubMed2006

Effects of explicit knowledge of workspace rotation in visuomotor sequence learning.

Previous experimental and theoretical studies have suggested that two separate neural networks contribute to visuomotor learning of spatial sequences, one to the accuracy of performance and the other to the speed of performance (Nakahara et al. in J Cogn Neurosci 13:626-647, 2001). This study examined the influence of explicit knowledge of stimulus configuration (workspace) in visuomotor sequence learning. Twenty-eight right-handed subjects learned the sequences of button presses by trial and error (Hikosaka et al. in J Neurophysiol 76:617-621, 1996) in the course of two sessions. In the first session, both the number of completion failures (accuracy measure) and the performance time to complete a sequence (speed measure) decreased. In the second session, the workspace was rotated without notifying the subjects. About half the subjects remained unaware of the workspace rotation, and no transfer of learning occurred (i.e., neither accuracy nor speed of performance was preserved in the second session). The remaining subjects spontaneously noticed the rotation and they were able to use this knowledge to perform the task with less completion failures in the second session. However, the knowledge of workspace rotation did not decrease the performance time in the second session. The lack of influence of explicit knowledge on the speed of performance is consistent with the two-loop model of visuomotor sequence learning (Nakahara et al. in J Cogn Neurosci 13:626-647, 2001).

Analysis of Variance↗

PubMed2006

Flash-lag chimeras: the role of perceived alignment in the composite face effect.

Spatial alignment of different face halves results in a configuration that mars the recognition of the identity of either face half (). What would happen to the recognition performance for face halves that were aligned on the retina but were perceived as misaligned, or were misaligned on the retina but were perceived as aligned? We used the 'flash-lag' effect () to address these questions. We created chimeras consisting of a stationary top half-face initially aligned with a moving bottom half-face. Flash-lag chimeras were better recognized than their stationary counterparts. However when flashed face halves were presented physically ahead of moving halves thereby nulling the flash-lag effect, recognition was impaired. This counters the notion that relative movement between the two face halves per se is sufficient to explain better recognition of flash-lag chimeras. Thus, the perceived spatial alignment of face halves (despite retinal misalignment) impairs recognition, while perceived misalignment (despite retinal alignment) does not.

Face↗

PubMed2006

Object-based anisotropies in the flash-lag effect.

The relative visual position of a briefly flashed stimulus is systematically modified in the presence of motion signals. We investigated the two-dimensional distortion of the positional representation of a flash relative to a moving stimulus. Analysis of the spatial pattern of mislocalization revealed that the perceived position of a flash was not uniformly displaced, but instead shifted toward a single point of convergence that followed the moving object from behind at a fixed distance. Although the absolute magnitude of mislocalization increased with motion speed, the convergence point remained unaffected. The motion modified the perceived position of a flash, but had little influence on the perceived shape of a spatially extended flash stimulus. These results demonstrate that motion anisotropically distorts positional representation after the shapes of objects are represented. Furthermore, the results imply that the flash-lag effect may be considered a special case of two-dimensional anisotropic distortion.

Adult↗

PubMed2005

Immediate changes in anticipatory activity of caudate neurons associated with reversal of position-reward contingency.

The primate caudate nucleus plays a crucial role in transforming cognitive/motivational information into eye movement signals. A subset of caudate projection neurons fire before a visual target's onset. This anticipatory activity is sensitive to position-reward contingencies and correlates with saccade latency, which is shorter toward a rewarded position. We recorded single-unit activity of caudate projection neurons to examine the dynamics of change in anticipatory activity immediately after switches of the position-reward contingency. Two monkeys performed a visually guided saccade task where only one position was associated with reward. The position-reward mapping remained constant within a block, but was reversed frequently between blocks without any indication to the monkey. Therefore the switch could be detected only by unexpected reward delivery or unexpected lack of reward. After the switch, both saccade latency and anticipatory activity showed reliable changes already in the second trial, whether or not the first trial was rewarded. However, anticipatory activity in the second trial was generally higher if the first trial was rewarded, and the measured saccade latencies could be better explained by the difference in anticipatory activity between the two caudate nuclei. We suggest that anticipatory activity of caudate neurons reflects the reversal set of reward-position contingency.

Action Potentials↗

PubMed2005

The motion-induced position shift depends on the visual awareness of motion.

Visual motion signals distort the perceived positions of briefly presented stimuli; a briefly-flashed, stationary stimulus appears spatially displaced in the direction of a nearby motion. The present study examined the role of the visual awareness of motion in the motion-induced position shift by using exclusive dominance and suppression of binocular rivalry. Observers dichoptically viewed a flickering radial checkerboard and two sinusoidal gratings that drifted vertically in opposite directions. When observers viewed exclusively either the checkerboard or motion stimulus, two horizontal lines were flashed, one for each side of the rivalry stimulus. During the exclusive dominance of the grating motion, the lines appeared to shift in the directions of the nearby motions. The position shift was identical to that during non-rivalry, monocular viewing of the motion stimulus. However, when the grating motions were completely suppressed, no position shift was observed. These results demonstrate that the motion-induced position shift depends on the visual awareness of motion.

Awareness↗

PubMed2005

Eccentric perception of biological motion is unscalably poor.

Accurately perceiving the activities of other people is a crucially important social skill of obvious survival value. Human vision is equipped with highly sensitive mechanisms for recognizing activities performed by others [Johansson, G. (1973). Visual perception of biological motion and a model for its analysis. Perception and Psychophysics, 14, 201; Johansson, G. (1976). Spatio-temporal differentiation and integration in visual motion perception: An experimental and theoretical analysis of calculus-like functions in visual data processing. Psychological Research, 38, 379]. One putative functional role of biological motion perception is to register the presence of biological events anywhere within the visual field, not just within central vision. To assess the salience of biological motion throughout the visual field, we compared the detectability performances of biological motion animations imaged in central vision and in peripheral vision. To compensate for the poorer spatial resolution within the periphery, we spatially magnified the motion tokens defining biological motion. Normal and scrambled biological motion sequences were embedded in motion noise and presented in two successively viewed intervals on each trial (2AFC). Subjects indicated which of the two intervals contained normal biological motion. A staircase procedure varied the number of noise dots to produce a criterion level of discrimination performance. For both foveal and peripheral viewing, performance increased but saturated with stimulus size. Foveal and peripheral performance could not be equated by any magnitude of size scaling. Moreover, the inversion effect--superiority of upright over inverted biological motion [Sumi, S. (1984). Upside-down presentation of the Johansson moving light-spot pattern. Perception, 13, 283]--was found only when animations were viewed within the central visual field. Evidently the neural resource responsible for biological motion perception are embodied within neural mechanisms focused on central vision.

Discrimination, Psychological↗

PubMed2005

Asymmetric mislocalization of a visual flash ahead of and behind a moving objectt.

When subjects localize a flash relative to another stationary stimulus, the flash appears displaced in the direction of nearby motion signals (position capture; Whitney and Cavanagh, 2000 Nature Neuroscience 3 954-959). Our previous study had suggested that the position capture is larger for a flash presented ahead of a moving stimulus than for a flash behind it (Watanabe et al, 2003 Perception 32 545-559). In the present study, I investigated the spatial asymmetry of position capture. Experiment 1 demonstrated that asymmetric position capture occurs primarily in a moving-object-centered coordinate. Experiment 2 showed evidence that the asymmetric position capture operates after individuation of single visual objects. Finally, experiment 3 demonstrated that, when attention was reduced with a dual-task procedure, the asymmetric position capture increased. These results suggest that the spatial asymmetry of position capture occurs without attention but the spatial bias can be reduced by attention. Therefore, the underlying mechanism for the asymmetric spatial bias may be different from attentive tracking (Cavanagh, 1992 Science 257 1563-1565) and mislocalization during smooth pursuit (Brenner et al, 2001 Vision Research 41 2253-2259).

Attention↗

PubMed2004

Preserved gain control for luminance contrast during binocular rivalry suppression.

Binocular rivalry elevates contrast increment thresholds for the detection of a transient stimulus presented to the suppressed eye, while thresholds measured during dominance are identical to those during monocular viewing (e.g. [Wales, R., & Fox, R. (1970). Increment detection thresholds during binocular rivalry suppression. Perception and Psychophysics, 8, 90-94]). It is well established that contrast increment thresholds depend on reference (pedestal) contrast. With high contrasts, increment thresholds increase with pedestal contrast, reflecting a gain control with sigmoidal non-linearity. We examined how this gain control mechanism operates during binocular rivalry (i.e., with and without perception of a pedestal mask). Subjects viewed a horizontal sine-wave grating (steady pedestal) and a radial checkerboard dichoptically. When the grating achieved a pre-specified phenomenal state (dominance or suppressed), subjects initiated the transient presentation (500-ms Gaussian pulse) of a contrast increment of the same spatial frequency. The pulse appeared in either the upper or lower half of the pedestal. Subjects indicated which half of the pedestal contained the pulse. Contrast increment thresholds were measured using a staircase method with various pedestal contrasts, which yielded threshold versus contrast (TvC) functions during dominance and suppression. The measured thresholds were reliably higher during suppression, but the rising slopes of TvC functions did not differ significantly between dominance and suppression (i.e., constant upward shift of TvC function). A control experiment demonstrated that the TvC function during dominance was identical to that during non-rivalry, monocular viewing. Evidently, the contrast gain control for transient luminance increment does not require the perception of pedestal contrast.

Contrast Sensitivity↗

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↗