Target contact and exploration strategies in haptic search

In a haptic search task, one has to detect the presence of a target among distractors using the sense of touch. A salient target can be detected faster than a non-salient target. However, little is known about the exploration strategies that are used, especially in 3D search tasks where items are held in the hand. In this study, we investigated which parts of the hand were used to contact the target and which strategies were performed. Blindfolded participants performed search tasks in four conditions, where the targets differed in relevant property and saliency. The positions of the target and the hand were tracked during exploration. It was found that target saliency had a large effect on the use of the hand parts and the strategies. In the non-salient target conditions, the fingers, especially the thumb, contacted the target more often than in the salient target conditions. This could also be seen in the strategies, where the thumb was used to explore the items in a serial way by moving them in the hand or touching them individually. In the salient target conditions, more parallel strategies like grasping or shuffling of the items in the hand were used.