Biomedical subjects

T Uka

Publications and source records attributed to T Uka.

5 recordsLinked to original sources

PubMed2001

Processing of shape defined by disparity in monkey inferior temporal cortex.

Neurons in the monkey inferior temporal cortex (IT) have been shown to respond to shapes defined by luminance, texture, or motion. In the present study, we determined whether IT neurons respond to shapes defined solely by binocular disparity, and if so, whether signals of disparity and other visual cues to define shape converge on single IT neurons. We recorded extracellular activity from IT neurons while monkeys performed a fixation task. Among the neurons that responded to at least one of eight random-dot stereograms (RDSs) containing different disparity-defined shapes, 21% varied their responses to different RDSs. Responses of most of the neurons were positively correlated between two sets of RDSs, which consisted of different dot patterns but defined the same set of eight shapes, whereas responses to RDSs and their monocular images were not correlated. This indicates that the response modulation for the eight RDSs reflects selectivity for shapes (or their component contours) defined by disparity, although responses were also affected by dot patterns per se. Among the neurons that showed selectivity for shapes defined by luminance or disparity, 44% were activated by both cues. Responses of these neurons to luminance-defined shapes and those to disparity-defined shapes were often positively correlated to each other. Furthermore the stimulus rank, which was determined by the magnitude of responses to shapes, generally matched between these cues. The same held true between disparity and texture cues. The results suggest that the signals of disparity, luminance, and texture cues to define the shapes converge on a population of single IT neurons to produce the selectivity for shapes.

Animals↗

PubMed2000

Disparity selectivity of neurons in monkey inferior temporal cortex.

The inferior temporal cortex (IT) of the monkey, a final stage in the ventral visual pathway, has been known to process information on two-dimensional (2-D) shape, color, and texture. On the other hand, the dorsal visual pathway leading to the posterior parietal cortex has been known to process information on location in space. Likewise, neurons selective for binocular disparity, which convey information on depth, have been found mainly in areas along the dorsal visual pathway. Here, we report that many neurons in the IT are also selective for binocular disparity. We recorded extracellular activity from IT neurons and found that more than half of the neurons changed their response depending on the disparity added. The change was not attributed to monocular responses or eye movements. Most neurons selective for disparity were "near" or "far" cells; they preferred either crossed or uncrossed disparity, and only a small population was tuned to zero disparity. Disparity-selective neurons were also selective for shape. Most preferred the same type of disparity irrespective of the shape presented. Disparity preference was also invariant for the fronto-parallel translation of the stimuli in most of the neurons. Finally, nearby neurons exhibited similar disparity selectivity, suggesting the existence of a functional module for processing of binocular disparity in the IT. From the above and our recent findings, we suggest that the IT integrates shape and binocular disparity information, and plays an important role in the reconstruction of three-dimensional (3-D) surfaces.

Animals↗

PubMed1999

Behavioral evidence for visual perception of 3-dimensional surface structures in monkeys.

Human subjects perceive two crossing bars, one in front of the other, when shown a cross with disparity added to its horizontal limbs, and they also perceive neon-color spreading when shown a stereoscopic Redies-Spillmann figure. It has thus been hypothesized that the human visual system follows the principle of generic image sampling in reconstructing 3-dimensional (3-D) surface structures. Here we examine whether monkeys also perceive these surface structures. The results indicate that monkeys, like humans, perceive two crossing bars and neon-color spreading and suggest that the principle of generic image sampling may also be applied to visual perception in monkeys.

Animals↗

PubMed1997

Prism adaptation of reaching movements: specificity for the velocity of reaching.

Accurate reaching toward a visual target is disturbed after the visual field is displaced by prisms but recovers with practice. When the prisms are removed, subjects misreach in the direction opposite to the prism displacement (aftereffect). The present study demonstrated that the severity of the aftereffect depends on the velocity of the movements during and after the visual displacement. Trained subjects were required to reach with one of four movement durations (<300, approximately 800, approximately 2000, and approximately 5000 msec) from a fixed starting point to a target that appeared at a random location on a tangent screen (400 mm away). The size of the aftereffect was largest when the movement after the removal was performed with the same duration as that performed with the prisms. It became smaller as the difference in velocity became larger. When the contralateral arm was used after visual displacement, the aftereffect was never significant. Because the adaptation does not generalize across velocities or to the other arm, we infer that the underlying changes occur at a later stage in the transformation from visual input to motor output, in which not only the direction but also the time-dependent parameters of movements, such as velocity, acceleration or force, are represented.

Adaptation, Physiological↗

PubMed1995

Effects of delayed visual information on the rate and amount of prism adaptation in the human.

Accurate reaching towards a visual target is initially disturbed when the visual field is displaced by prisms, but recovers with successive trials. To determine how the improvement depends on the visual error signals associated with the motor output, the time course of prism adaptation was studied with delayed visual information on the error. Subjects were trained to reach rapidly at a target on a tangent screen. Vision was always blocked during the movement, and allowed again only after the index finger touched the screen. One experiment consisted of three sets of 30 trials. In the first set, the subject wore no prisms and vision was allowed without delay. In the second, the visual field was displaced by prisms, and vision was available only after a delay period of 0-10,000 msec while the subjects maintained their final pointing position. Initially, the subject misreached the target by about the amount of visual displacement (60 mm). Errors decreased with trials by an amount proportional to the error in the preceding trial. The rate of decrease of error was generally largest when the delay was 0 msec, became significantly smaller when the delay was 50 msec, and showed only gradual change with longer delays. In the third set, the subject wore no prisms and vision was allowed without delay. Initial misreaching in the direction opposite to the visual displacement, reflecting the amount of adaptation in the second set, was generally largest with no delay (median of 46 mm) and significantly smaller with 50 msec and longer delays (17-33 mm).(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗