Abstract: Two modes of haptic length perception have been tested with themethod of constant stimuli:Thumb-index finger span (2F mode) andtouching of index finger along the surface of a wooden bar from one endto the other (1F mode). In addition to the DL, we also obtained d' and βaccording to the signal detection theory from the same data. In terms ofboth DL and d', the 2F mode is more accurate than the 1F mode. Theformer has lower DL and bigger d', while the latter has higher DL andsmaller d'. The DL data are consistent with d'. These two modes have nosignigicant difference in β. The results suggest that the two modes aredifferential not in the criterion of decision but in the sensitivity conditionedby the various ways of encoding in processing length information.

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