Idiosyncratic Functions of Active Touch Strategies in Shape Perception.

Hand movements are essential for tactile perception of objects. However, the specific functions served by active touch strategies, and their dependence on physiological parameters, is unclear and understudied. Focusing on planar shape perception, we tracked at high resolution the hands of eleven participants during shape recognition task. Two dominant hand movements strategies were identified: Contour-following movements, either tangential to the contour or oscillating perpendicular to it, and exploration by scanning movements, crossing between distant parts of the shapes’ contour. Both strategies exhibited non-uniform coverage of the shapes’ contours. Idiosyncratic movement patterns were specific to the sensed object and could be explained in part by spatial and temporal tactile thresholds of the participant. Using simulations, we show how some strategy choices may affect receptors activation. These results suggest that motion strategies of active touch adapt to both the sensed object and to the perceiver’s physiological parameters.

Postextraction Ridge Width Alterations Following Socket Seal Surgery—A Retrospective Study

Background and objectives: Preservation of alveolar ridge contour following tooth extraction is important to allow for restoration with prosthetics and implants. Socket seal surgery was introduced more than two decades ago for preservation of the form, volume and bone quality of the postextraction ridge. The aim of this retrospective study was to assess the changes in alveolar ridge contour following socket seal surgery and to evaluate the survival of the soft tissue grafts sealing the extraction site. Materials and Methods: Digital images of the extraction sites treated with the socket seal surgery were obtained immediately after extraction and after a healing time of 6 months to measure the changes in the alveolar width. In addition, the sites were photographed 1 week postsurgery to evaluate the vitality of the soft tissue grafts. Results: The overall mean loss of buccal width following socket seal surgery was 5.3% (SD = 13.4%). The mean change in width at the incisor area (1.5% ± 13.1) was significantly lesser than those in the canine area (−17.0% ± 2.1, p < 0.01) or premolar area (−10.5% ± 11.2, p < 0.01). One-week post-surgery 69% of the grafts were vital, and 31% were partially vital. Complete necrosis of the grafts did not occur. Conclusions: Our results suggest that socket seal surgery has a beneficial effect on alveolar dimensional changes 6 months following tooth extraction and that the teeth that benefit mostly from socket seal surgery are incisors.

Active palpation underlying shape perception is shaped by physiological thresholds and experience

ABSTRACTHand movements are essential for tactile perception of objects. However, why different individuals converge on specific movement patterns is not yet clear. Focusing on planar shape perception, we tracked the hands of 11 participants while they practiced shape recognition. Our results show that planar shape perception is mediated by contour-following movements, either tangential to the contour or spatially-oscillating perpendicular to it, and by scanning movements, crossing between distant parts of the shapes’ contour. Both strategies exhibited non-uniform coverage of the shapes’ contours. We found that choice of strategy during the first experimental session was strongly correlated with two idiosyncratic parameters: participants with lower tactile resolution tended to move faster; and faster-adapting participants tended to employ oscillatory movements more often. In addition, practicing on isolated geometric features increased the tendency to use the contour-following strategy. These results provide insights into the processes of strategy selection in tactile perception.SIGNIFICANCE STATMENTHand movements are integral components of tactile perception. Yet, the specific motion strategies used to perceive specific objects and features, and their dependence on physiological features and on experience, are understudied. Focusing on planar shape perception and using high-speed hand tracking we show that human participants employ two basic palpation strategies: Contour-following and scanning. We further show that the strategy chosen by each participant and its kinematics depend strongly on the participant’s physiological thresholds – indicative of spatial resolution and temporal adaptation - and on their perceptual experience.