Abstract
In three experiments participants haptically discriminated object shape using unimanual (single hand explored two objects) and bimanual exploration (both hands were used, but each hand, left or right, explored a separate object). Such haptic exploration (one versus two hands) requires somatosensory processing in either only one or both cerebral hemispheres; previous studies related to the perception of shape/curvature found superior performance for unimanual exploration, indicating that shape comparison is more effective when only one hemisphere is utilized. The current results, obtained for naturally shaped solid objects (bell peppers, Capsicum annuum) and simple cylindrical surfaces demonstrate otherwise: bimanual haptic exploration can be as effective as unimanual exploration, showing that there is no necessary reduction in ability when haptic shape comparison requires interhemispheric communication. We found that while successive bimanual exploration produced high shape discriminability, the participants’ bimanual performance deteriorated for simultaneous shape comparisons. This outcome suggests that either interhemispheric interference or the need to attend to multiple objects simultaneously reduces shape discrimination ability. The current results also reveal a significant effect of age: older adults’ shape discrimination abilities are moderately reduced relative to younger adults, regardless of how objects are manipulated (left hand only, right hand only, or bimanual exploration).
Highlights
We humans explore and manipulate environmental objects primarily with our hands
A 2-way within-subjects analysis of variance (ANOVA) conducted upon the results shown in Fig. 6 revealed significant effects of both haptic exploration mode (simultaneous versus successive comparison, F(1, 4) = 11.0, p < 0.03; η2p = 0.73) and surface curvature magnitude (F(2, 8) = 54.7, p < 0.0001; η2p = 0.93)
Previous research by Kappers and Koenderink[17] and Kappers et al.[18] indicated that unimanual haptic exploration produced superior judgments of shape, at least for simple curved surfaces. These initial results were certainly interesting, because they suggested that shape performance was best if the required somatosensory cortical processing were limited to one cerebral hemisphere
Summary
We humans explore and manipulate environmental objects primarily with our hands. Multiple studies over the past half century[1,2,3,4,5] have demonstrated that for some tactile and proprioceptive tasks, performance for two hands is as good, or better, than that obtained from the usage of a single hand. The importance of the corpus callosum for the human sense of touch was behaviorally demonstrated by Gazzaniga, Bogen, and Sperry[16] These researchers studied the tactile abilities of a man whose cerebral hemispheres had been disconnected as a treatment for severe epilepsy. One purpose of the current study is to remedy this deficit–at the moment, we do not know the extent to which the two cerebral hemispheres can cooperate in order to bimanually perceive and discriminate natural solid shape At this point, it is important to note that psychophysical findings obtained for simple geometric objects do not necessarily generalize to objects that possess more complex and/or naturalistic geometrical structure. An Apple PowerMacintosh G4 computer was used to randomly order the presentation of the experimental stimuli
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