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S Shimojo

Publications and source records attributed to S Shimojo.

At least 37 records · Page 2Linked to original sources
PubMed2000

Primary LAMP-2 deficiency causes X-linked vacuolar cardiomyopathy and myopathy (Danon disease).

"Lysosomal glycogen storage disease with normal acid maltase" which was originally described by Danon et al., is characterized clinically by cardiomyopathy, myopathy and variable mental retardation. The pathological hallmark of the disease is intracytoplasmic vacuoles containing autophagic material and glycogen in skeletal and cardiac muscle cells. Sarcolemmal proteins and basal lamina are associated with the vacuolar membranes. Here we report ten unrelated patients, including one of the patients from the original case report, who have primary deficiencies of LAMP-2, a principal lysosomal membrane protein. From these results and the finding that LAMP-2-deficient mice manifest a similar vacuolar cardioskeletal myopathy, we conclude that primary LAMP-2 deficiency is the cause of Danon disease. To our knowledge this is the first example of human cardiopathy-myopathy that is caused by mutations in a lysosomal structural protein rather than an enzymatic protein.

Antigens, CD↗
PubMed2000

A slowly moving foreground can capture an observer's self-motion--a report of a new motion illusion: inverted vection.

We investigated interactions between foreground and background stimuli during visually induced perception of self-motion (vection) by using a stimulus composed of orthogonally moving random-dot patterns. The results indicated that, when the foreground moves with a slower speed, a self-motion sensation with a component in the same direction as the foreground is induced. We named this novel component of self-motion perception 'inverted vection'. The robustness of inverted vection was confirmed using various measures of self-motion sensation and under different stimulus conditions. The mechanism underlying inverted vection is discussed with regard to potentially relevant factors, such as relative motion between the foreground and background, and the interaction between the mis-registration of eye-movement information and self-motion perception.

Adult↗
PubMed2000

Repetition priming reveals sustained facilitation and transient inhibition in reaction time.

Reaction time (RT) in a detection or a location discrimination task increases when a target is repeatedly presented at the same location (inhibition), whereas RT decreases in feature (color or orientation) discrimination tasks (facilitation; Y. Tanaka & S. Shimojo, 1996a). Here, the time course of inhibition and facilitation was examined, using a repetition priming paradigm. Results indicate that inhibition occurred only in the immediately successive trial, whereas facilitation accumulated over several trials with location repetition. Moreover, inhibition and facilitation occurred in a task-relevant manner: Detection-location discrimination tasks produced transient RT increase, whereas feature discrimination tasks produced cumulative RT decrease. These results suggest a functional dissociation between spatial orienting and feature analysis, as well as top-down modulations by tasks leading to different types of visual memory.

Adult↗
PubMed2000

Changing objects lead briefly flashed ones.

Continuous, predictable events and spontaneous events may coincide in the visual environment. For a continuously moving object, the brain compensates for delays in transmission between a retinal event and neural responses in higher visual areas. Here we show that it similarly compensated for other smoothly changing features. A disk was flashed briefly during the presentation of another disk of continuously changing color, and observers compared the colors of the disks at the moment of flash. We also tested luminance, spatial frequency and pattern entropy; for all features, the continuously changing item led the flashed item in feature space. Thus the visual system's ability to compensate for delays in information about a continuously changing stimulus may extend to all features. We propose a model based on backward masking and priming to explain the phenomenon.

Adaptation, Physiological↗
PubMed2000

In space, the past can be recast but not the present.

We address the relationship between perception and spatial, working memory. Specifically, we argue that perceptual experience following the creation of a representation of target location affects it in a systematic way. We designed a motor task in which observers had to point to the initial or final position of a horizontally drifting target embedded in a vertically drifting background. The target was perceived as having an illusory motion component in a direction opposite that of the inducer dots [Duncker, 1938, Source Book of Gestalt Psychology (London: Kegan Paul, Trench, Trubner and Co)]. For both positions, there was an identical time delay before the observer could respond. Nonetheless, estimates of the initial target position were significantly biased by the illusion in a direction opposite the perceived target motion, and both bias and variability were significantly greater than those of the target's final position. In prior studies on positional accuracy with induced displacement, a delay before a pointing response led to an unbiased position estimate obtained without delay to become biased, leading investigators to argue for a long-lasting, inaccurate cognitive system that overrules an accurate, nonetheless transient, motor one (Bridgeman et al, 1997, Perceptual Psychology 59 456-469). Since the same motor task with identical delay on either position yielded different outcomes, a hypothesis based on distinct motor and cognitive representations of visual space is untenable here. Instead, we argue that an online representation of the target's original position is updated in an ongoing fashion in order to reconcile the perceived illusion with the veridically perceived present (current target location).

Humans↗
PubMed2000

Telemedicine for evaluation of brain function by a metacomputer.

A method of evaluating brain function using the metacomputer concept of the Globus system combined with a message-passing interface is described. The proposed method has the ability to exploit various geographically distributed resources and parallel computing linked to a high-technology medical instrumentation system, magnetoencephalography, to analyze the functional state of the brain. It is envisaged that the method will lead to the realization of an efficient telemedicine system for health care.

Brain↗
PubMed2000

[Lysosomal glycogen storage disease with normal acid maltase (Danon) without apparent cardiomyopathy and mental retardation].

A 29-year-old male who had a past history of mild ECG abnormality of arrhythmia at the age of 14 years, was referred to our hospital because of elevated serum creatine kinase (CK) level. He had never been aware of muscular weakness nor cardiac symptoms. Neurological examination revealed normal muscle strength of all extremities except marked back muscle weakness. He had normal intelligence. On laboratory examination, serum AST, ALT, LDH, aldolase, CK and myoglobin levels were elevated. Both lactate and pyruvate levels were normally responded after an ischemic exercises test. Acid maltase activity was normal in white blood cells. A muscle biopsy obtained from rectus femoris muscle revealed vacuolar myopathy with mildly increased PAS positive material. On electron microscopy, there were autophagic vacuoles scavenging glycogen particles and cytoplasmic debris, and sarcolemmal indentation, compatible with the findings of lysosomal glycogen storage disease with normal acid maltase. This patient had unusual clinical features of absent mental retardation and no apparent cardiomyopathy. Accordingly, mental retardation is probably not necessary to see later onset of cardiac muscle involvement.

Adult↗
PubMed1999

Manifestation of scotomas created by transcranial magnetic stimulation of human visual cortex.

Reduced visual performance under transcranial magnetic stimulation (TMS) of human visual cortex demonstrates suppression whose spatial extent is not directly visible. We created an artificial scotoma (region missing from a visual pattern) to directly visualize the location, size and shape of the TMS-induced suppression by following a large-field, patterned, visual stimulus with a magnetic pulse. The scotoma shifted with coil position according to known topography of visual cortex. Visual suppression resulted in pattern-dependent distortion, and the scotoma was filled in with temporally adjacent stimuli, suggesting spatial and temporal completion mechanisms. Thus, perceptual measurements of TMS-induced suppression may provide information about cortical processing via neuronal connections and temporal interactions of neural signals.

Humans↗
PubMed1999

Critical role of foreground stimuli in perceiving visually induced self-motion (vection).

The effects of a foreground stimulus on vection (illusory perception of self-motion induced by a moving background stimulus) were examined in two experiments. The experiments reveal that the presentation of a foreground pattern with a moving background stimulus may affect vection. The foreground stimulus facilitated vection strength when it remained stationary or moved slowly in the opposite direction to that of the background stimulus. On the other hand, there was a strong inhibition of vection when the foreground stimulus moved slowly with, or quickly against, the background. These results suggest that foreground stimuli, as well as background stimuli, play an important role in perceiving self-motion.

Adult↗
PubMed1998

Attentional modulation in perception of visual motion events.

Identical visual targets moving across each other with equal and constant speed can be perceived either to bounce off or to stream through each other. This bistable motion perception has been studied mostly in the context of motion integration. Since the perception of most ambiguous motion is affected by attention, there is the possibility of attentional modulation occurring in this case as well. We investigated whether distraction of attention from the moving targets would alter the relative frequency of each percept. During the observation of the streaming/bouncing motion event in the peripheral visual field, visual attention was disrupted by an abrupt presentation of a visual distractor at various timings and locations (experiment 1; exogenous distraction of attention) or by the demand of an additional discrimination task (experiments 2 and 3; endogenous distraction of attention). Both types of distractions of attention increased the frequency of the bouncing percept and decreased that of the streaming percept. These results suggest that attention may facilitate the perception of object motion as continuing in the same direction as in the past.

Attention↗
PubMed1998

Surface discontinuity is critical in a moving observer's perception of objects' depth order and relative motion from retinal image motion.

The visual system perceptually decomposes retinal image motion into three basic components that are ecologically significant for the human observer: object depth, object motion, and self motion. Using this conceptual framework, we explored the relationship between them by examining perception of objects' depth order and relative motion during self motion. We found that the visual system obeyed what we call the parallax-sign constraint, but in different ways depending on whether the retinal image motion contained velocity discontinuity or not. When velocity discontinuity existed (e.g. in dynamic occlusion, transparent motion), the subject perceptually interpreted image motion as relative motion between surfaces with stable depth order. When velocity discontinuity did not exist, he/she perceived depth-order reversal but no relative motion. The results suggest that the existence of surface discontinuity or of multiple surfaces indexed by velocity discontinuity inhibits the reversal of global depth order.

Depth Perception↗
PubMed1998

Stimulus size and eccentricity in visually induced perception of horizontally translational self-motion.

The effects of the size and eccentricity of the visual stimulus upon visually induced perception of self-motion (vection) were examined with various sizes of central and peripheral visual stimulation. Analysis indicated the strength of vection increased linearly with the size of the area in which the moving pattern was presented, but there was no difference in vection strength between central and peripheral stimuli when stimulus sizes were the same. Thus, the effect of stimulus size is homogeneous across eccentricities in the visual field.

Adult↗
PubMed1998

Orientation of selective effects of body tilt on visually induced perception of self-motion.

We examined the effect of body posture upon visually induced perception of self-motion (vection) with various angles of observer's tilt. The experiment indicated that the tilted body of observer could enhance perceived strength of vertical vection, while there was no effect of body tilt on horizontal vection. This result suggests that there is an interaction between the effects of visual and vestibular information on perception of self-motion.

Humans↗
PubMed1998

[Three cases of Munchausen's syndrome mimicking connective tissue diseases].

Three young women were admitted to our hospital because of severe anemia and fever of unknown origin. The patients had a long history of frequent hospitalizations and operations. During hospitalization, the patients complained of hematemesis, hematuria and fever, which were sometimes discrepant with their physical and laboratory findings. After the careful observation, the patients were diagnosed as Munchausen syndrome because of either discovery of the tools used to make their symptoms or the patient's confession that these symptoms were made by herself. The patients with Munchausen syndrome sometimes show various symptoms and signs of multisystem inflammatory diseases, which mimick the clinical feature of connective tissue diseases. It is important for rheumatologists to be aware of the existence of Munchausen syndrome among the differential diagnosis of connective tissue diseases.

Adult↗
PubMed1997

Visual motion sensation yielded by non-visually driven attention.

When a visual stimulus (the "cue") is presented and followed by a line, the line is perceived to grow rapidly from the cued side even when it is presented physically simultaneously (the "line-motion effect"). We now report that the same line motion can be observed when the cue is presented in a non-visual modality, such as auditory or somatosensory. A beep sound was presented either from the left or the right speaker as an auditory cue, or an electric pulse was applied to a finger put on the left or the right side of a CRT display as a somatosensory cue. A line probe was then presented between the two possible cue positions. Both the auditory and the somatosensory cues led to line motion, thus the line motion could not be interpreted as a variation of within-modality effects, such as visual apparent motion. When the cue lead time was manipulated, the obtained time courses of the effects were similar across the three cue modalities (Experiment 1). The minor differences could be explained simply in terms of latency of detection, according to results of another experiment (Experiment 2). Finally, the line-motion task was compared with a task of temporal order judgment, where two targets were presented simultaneously at the cued and the uncued sides, and the subject was asked to judge which of the targets had appeared first. As a result, similar dependencies on cue lead time were obtained between the two tasks within subjects (Experiment 3). Thus, the non-visual cue seems to facilitate "prior entry" of a visual stimulus nearby in the spatial representation, much the same way as a visual cue does. These effects should be attributed to modality non-specific spatial attention, i.e., a "gradient" of information processing efficiency across various locations.

Acoustic Stimulation↗
PubMed1997

Suppressive effect of multimodal surface representation on ocular smooth pursuit of invisible hand.

A human observer can smoothly pursue her/his own voluntarily moved hand with the eyes in total darkness. The effects of a perceived stationary surface during ocular pursuit of the invisible hand were investigated. The task was to track the invisible hand smoothly with the eyes in a Ganzfeld (experiment 1), with a stationary visual surface in the light (experiment 2), or with a solid stationary surface in total darkness (experiment 3). It was found that smooth pursuit of the invisible hand occurred in the Ganzfeld as well as in total darkness, but was replaced by frequent saccades when a stationary surface was perceived through either the visual or the tactile sense. The results obtained with a Ganzfeld suggest that light alone does not prevent smooth pursuit of the invisible hand, and those obtained with a stationary surface suggest that perception of such a surface prevents smooth pursuit of the invisible hand and evokes saccades, regardless of the sense modality.

Adult↗
PubMed1996

Location vs feature: reaction time reveals dissociation between two visual functions.

Reaction time in a detection or a location discrimination task was longer when a target appeared at the same location as in the previous trial (inhibition of return; IOR). However, it became shorter when the task was color or orientation discrimination (facilitation of return: FOR). This dichotomy was observed in the single target as well as in the popout displays. In additional experiments, vernier, size, and luminance discriminations all led to FOR, whereas eye-movement and arm-reaching tasks led to IOR. Moreover, identical stimuli could lead to the opposite patterns of result depending on the nature of the task: inhibition in global location tasks, and facilitation in feature analysis tasks. These may correspond to "where" vs "what" or "action" vs "recognition" pathways neurophysiologically.

Analysis of Variance↗