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.
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:
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