Cross-sensory calibration of one sense by another is an important multi-sensory function. Our recent studies suggest that the haptic system is important for calibration of visual judgements of size, particularly during development. If true, on would expect that the calibration should work only for distances within the haptic workspace. We studied size matching in 40 young subjects (6 - 24) of balls (about 5 cm diam) placed at various distances inside and outside the haptic workspace (42, 60, 85 and 120 cm). 6-10 year-old children consistently underestimated object size by 2-3 mm for distances outside their haptic workspace (85 & 120 cm), implying incomplete size-constancy. Adults (20-30 years), on the other hand, showed the opposite trend, overestimating object size by 2 - 4 mm at 85 & 120 cm, thereby exaggerated size-constency. Our results show that both children (as young as 6) and adults have quite good size constancy, but that it is imperfect for distances outside the haptic workspace. Interestingly, the bias in size perception outside the haptic workspace is in different directions for adults and children, suggesting that the mechanisms subserving size constancy are not fully developed even at 10-years of age. In a separte experiment we showed that in adults the size perception bias outside the haptic workspace could be reduced or even eliminated when subjects observed an actor grasping the ball stimulus. This has fascinating implications, suggesting that a??calibrationa?? of vision can be achieved by observation of haptic action, possibly implicating the a??mirror systema??.
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