People adapt with remarkable flexibility to reversal of the visual field caused by prism spectacles. With sufficient time, this adaptation restores visually guided behaviour and perceptual harmony between the visible and tactile worlds. Although it has been suggested that seeing one's own body is crucial for adaptation, the underlying mechanisms are unclear. Here we show that a new representation of visuomotor mapping with respect to the hands emerges in a month during adaptation to reversed vision. The subjects become bi-perceptual, or able to use both new and old representations. In a visual task designed to assess the new hand representation, subjects identified visually presented hands as left or right by matching the picture to the representation of their own hands. Functional magnetic resonance imaging showed brain activity in the left posterior frontal cortex (Broca's area) that was unique to the new hand representations of both hands, together with activation in the intraparietal sulcus and prefrontal cortex. The emergence of the new hand representation coincided with the adaptation of perceived location of visible objects in space. These results suggest that the hand representation operates as a visuomotor transformation device that provides an arm-centred frame of reference for space perception.

A preliminary and two main experiments designed to examine the perceptual properties of electrocutaneous stimulation are reported. The stimuli used were single short pulses varying in intensity and duration. In Experiment 1, the exponents of power functions fitted to electrocutaneous magnitude estimation data were determined together with the sensory qualities induced by electrical stimulation. The results showed that there was no correlation between the exponent values and the sensory qualities. The mean exponent was 1.2. In Experiment 2, an intensity-duration trading function was constructed from the data obtained from identifying the induced sensory qualities. The results showed that the critical duration increases from 30 to 300 msec with increasing sensation level. These findings are compared with the properties of other sense modalities.

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Three experiments investigated the properties of temporal and spatial integration for electrocutaneous stimulation at absolute threshold level. The duration of pulses delivered to the skin were varied from .1 to 100 msec, and the spatial distribution of stimulation was varied by controlling separation, width, and length of electrodes. For temporal integration, the threshold currents were fitted by the equation (1-1 0 ) , t n = c, indicating that partial integration took place below the critical duration of 1 msec and that the integration index remained constant (n = .43) independent of the spatial distribution of stimulation. For spatial integration, the separation of electrodes was found to be the most effective determiner of threshold current. Furthermore, when the equation (1-1 0 ) • Am = k was fitted to the spatial integration data, the value m resulted in 1.33 with a critical separation of 8 rom, which was constant for any pulse duration.properties of temporal integration, therefore, it was necessary to confirm the previous findings by using different types of electrodes.In the studies of vision, touch, and hearing, the equationThe present study deals with temporal and spatial integration for electrocutaneous stimulation at absolute threshold level. Babkoff, Brandeis, and Bergman (1975), Hahn (1958), Rollman (1969, 1975), and Uttal (1958 showed how threshold varies with pulse duration and obtained the psychophysical .hyperbolic function:

Recent study of [Sugita, Y. (1996) Global plasticity in adult visual cortex following reversal of visual input. Nature, 380, 523-526.] demonstrated that prism adaptation to reversed retinal input generates the transfer of neuronal activities in monkey V1 to the opposite visual cortex. This raises the question if perceptual learning on one side of the visual field can transfer to the other side. We tested this in using the Gabor lateral masking paradigm. Before adaptation, long-range interaction was induced vertically on one side (i.e., the right) of the visual field with training (perceptual learning). Prism adaptation was achieved by wearing right-left reversing goggles. During adaptation period, perceptual learning transferred to a mirror symmetrical region across the vertical meridian. Results in the post adaptation period revealed that both learning and transfer persisted for over three months. These results provide direct evidence of transferred perceptual plasticity across the visual field, the underlying mechanism of which is supported by the mirror symmetrical connection between the right and left cortices.

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The hypothesis that there are two neural mechanisms for electrocutaneous stimulation-one that is sensitive to low current and is adaptive to repeated stimulation and another that is responsive to high current and is less adaptive-was tested in a control and four main experiments. In the main experiments, magnitude estimates obtained for single electrical pulses (of 2-msec duration) were described by a simple power function for each combination of high-and low-current levels and 10 trial blocks. The results were: (1) The slope of the power function for low current was steeper than was that for high current; (2) for low current, the intercept of the power function decreased with increasing block, whereas for high current, it remained constant over blocks; (3) this decrease of the intercept for low current disappeared when judgmental blocks were separated by a rest period of 8 min; (4) the modulus did not affect the slope; (5) for a large modulus combined with low current, the intercept decreased rapidly over trial blocks, whereas for a small modulus combined with high current, the intercept increased over trial blocks. The fIrst four fIndings support the two-mechanism hypothesis, but the last one may also be interpretable in terms of the regression to absolute scale values.Higashiyama and Tashiro (1987) obtained free-modulus magnitude estimates for single electrical pulses as a function of stimulus current, with the parameters of trial block and current level. For the high-current level, which produced pain responses, the magnitude estimates remained constant independently of block, whereas for the low-current level, which yielded tactile sensations, they decreased as a function of block. In addition, the exponents of power functions fItted to the magnitude estimates were smaller for the high-current level (2.02) than were those for the low-current level (4.06). These fIndings have led them to suggest that there are two neural mechanisms with different adaptation processes: One is sensitive to low current and is very adaptive to repeated stimulation, and another is responsive to high current and is less adaptive.However, these outcomes also could be explained in terms of a natural absolute scale. Zwislocki and Goodman (1980) argued that subjects tend to use absolute judgments rather than ratio judgments when making magnitude estimations or productions of sensation. In usual ratio scales, the unit of measurement is arbitrary and can be changed by multiplying all scale values by a constant. In absolute scales, on the other hand, the unit is not arbitrary