In the haptic DCT, 67 participants had to compare two simultaneously presented dot arrays with the palms of their hands in the visual DCT, participants inspected and compared dot arrays on a screen. We used a dot comparison task (DCT), in which participants compare two dot arrays and decide which one contains more dots. We investigated approximate number processing in the haptic modality and compared performance to that of the visual modality. In the present study, we test the assumption of a shared cross-sensory system. The representation of numbers is assumed to be abstract and not bound to a particular sense. The Approximate Number System (ANS) is conceptualized as an innate cognitive system that allows humans to perceive numbers of objects or events (>4) in a fuzzy, imprecise manner. The results of the SG task, however, are inconsistent with previous results and suggest that both spatial and intensive factors are involved in this task. The results of the GO task are consistent with the view that GO is a valid measure of spatial acuity. The largest increases occurred at the less sensitive locations. With a glove, the SG thresholds increased by 100% to more than 300% as in comparison with those in the no-glove condition. Without a glove, however, the SG thresholds were well below the GO thresholds, and changing the site of stimulation had little effect on the threshold. With the glove, increases in the GO thresholds were relatively uniform and modest. In the present study, without a glove, the GO thresholds varied as a function of location. Neurophysiological studies have suggested that the density of innervation of SAI fibers is a limiting factor in spatial acuity. Measures were made at three locations that varied in sensitivity and in density of innervation of the primary afferent fibers: the index fingerpad (fingertip), palmar surface of the proximal phalanx (fingerbase), and the thenar eminence (palm). Two psychophysical measures of tactile sensitivity-grating-orientation (GO) and smooth-grooved (SG) discrimination-were used to determine tactile spatial acuity with and without an intermediate surface (latex glove) interposed between the contactor and the skin. Qualitative comparisonsīetween the palm and fingerpad data indicate that spatial patterns are processed similarly at the two sites. Tasks on the palm can be predicted quantitatively from fingerpad data with a moderate degree of accuracy. Of density of innervation between the fingerpad and the palm is estimated to be 5.7: 1 and 8.8: 1.
For the two types of receptor systems sensitive to spatial information, the ratio
Of performance achieved on the fingerpad. Gratings had to be six to more than seven times larger on the palm to produce the same levels Performance similar to those on the fingerpad required letters on the palm 50mm in height, seven to nine times larger than The results from these measures were compared with results from similar studiesĬonducted on the fingerpad and with estimates of the density of innervation of the fingerpad and palm. Letter identification and grating orientation. Spatial sensitivity was examined on another site on the body, the palm, using two measures, It has been suggested that with appropriate scaling, these models would apply to the processing of spatial patterns Of these studies, models have been developed linking spatial pattern identification and resolution with underlying neural Studies of tactile spatial pattern perception have, for the most part, been carried out using the fingerpad.