Haptic exploratory behavior during object discrimination: a novel automatic annotation method

Mental Rotation Skill Shapes Haptic Exploration Strategies

Haptic exploration strategies have been traditionally studied focusing on hand movements and neglecting how objects are moved in space. However, in daily life situations touch and movement cannot be disentangled. Furthermore, the relation between object manipulation as well as performance in haptic tasks and spatial skill is still little understood. In this study, we used iCube, a sensorized cube recording its orientation in space as well as the location of the points of contact on its faces. Participants had to explore the cube faces where little pins were positioned in varying number and count the number of pins on the faces with either even or odd number of pins. At the end of this task, they also completed a standard visual mental rotation test (MRT). Results showed that higher MRT scores were associated with better performance in the task with iCube both in term of accuracy and exploration speed and exploration strategies associated with better performance were identified. High performers tended to rotate the cube so that the explored face had the same spatial orientation (i.e., they preferentially explored the upward face and rotated iCube to explore the next face in the same orientation). They also explored less often twice the same face and were faster and more systematic in moving from one face to the next. These findings indicate that iCube could be used to infer subjects' spatial skill in a more natural and unobtrusive fashion than with standard MRTs.

Frequency of Switching Touching Mode Reflects Tactile Preference Judgment

We can judge affective aspects of objects by actively exploring them with our hands. Previous studies have mainly focused on how the physical properties of an object’s surface affect tactile preference evaluations. However, despite the widely accepted notion that the participant’s strategy has a great impact on how they explore an object, there is a lack of investigations of hand motion during preference judgment and its impact on preference rating. This paper recruits the recurrence plot technique to illustrate the temporal dynamics of explorative hand motion. In an experiment, participants were asked to freely explore the surface of tactile stimuli and rate their tactile preference for them. The temporal dynamics of finger velocity and force were visualized and characterized by using recurrence quantification analysis. We found correlations between preference ratings and recurrence features that represent the temporal dynamics of explorative hand motion, in addition to correlations between preference ratings and conventional time-averaged features (e.g., averaged finger velocity). One unique feature that correlated with preference ratings was TREND, which represents to what extent similar motion patterns repeatedly occur. The results of a subsidiary analysis supported the possibility that the TREND difference can be interpreted as the frequency of switching touching modes (e.g., stroking and pushing motions). Taken together, these results suggest that participants tend to perform the same hand motion repeatedly for preferable objects, while they tend to combine different touching modes for less preferable objects. They also indicate that the recurrence plot scheme is a promising way to extract humans’ strategies for tactile exploration.

Visuo-Haptic Exploration for Multimodal Memory

When faced with a novel object, we explore it to understand its shape. This way we combine information coming from different senses, as touch, proprioception and vision, together with the motor information embedded in our motor execution plan. The exploration process provides a structure and constrains this rich flow of inputs, supporting the formation of a unified percept and the memorization of the object features. However, how the exploration strategies are planned is still an open question. In particular, is the exploration strategy used to memorize an object different from the exploration strategy adopted in a recall task? To address this question we used iCube, a sensorized cube which measures its orientation in space and the location of the contacts on its faces. Participants were required to explore the cube faces where little pins were positioned in varying number. Participants had to explore the cube twice and individuate potential differences between the two presentations, which could be performed either haptically alone, or with also vision available. The haptic and visuo-haptic (VH) exploratory strategies changed significantly when finalized to memorize the structure of the object with respect to when the same object was explored to recall and compare it with its memorized instance. These findings indicate that exploratory strategies are adapted not only to the property of the object to be analyzed but also to the prospective use of the resulting representation, be it memorization or recall. The results are discussed in light of the possibility of a systematic modeling of natural VH exploration strategies.

Haptic Exploratory Procedures of Children and Youth with and without Cerebral Palsy

Aims: Compare haptic exploratory procedures (EPs) and exploratory movements (EMs) of children. This study also tested the interrater reliability of a novel digital recording method. Methods: Participants were 31 children with typical development (TD) (aged 6 years 1 month to 15 years 9 months; 14 male) and 23 children with spastic unilateral cerebral palsy (CP) (aged 6 years to 15 years 5 months; 13 males; right hemiplegia, n = 12). Results: There were no statistically significant differences between groups for expected EP (p = .15), additional EPs (p = .78), or EMs (p = .69) but there was for mean duration of exploration (p < .001) and accuracy (p < .001). This suggests that although children with CP performed similar haptic EPs for each object as children with TD, they took more time and were less accurate in their identification. There was substantial agreement between the two raters' observations of expected EP, κ = .64, p < .0005. Conclusion: Children with CP performed similar haptic EPs as their TD peers. However, despite similarities, the results indicate that for children with CP manual ability was not the primary determinant of accuracy or speed of identification. This study provides evidence for a reliable method of recording haptic EPs.

Estimating Tactile Perception by Observing Explorative Hand Motion of Others

When we acquire tactile information about an object's surface, we actively move our hands. Past studies have shown a correlation between participants' (i.e., touchers') hand motion in tactile exploration and the evaluated tactile attributes of the object, which suggests that tactile perception can be estimated from statistical analysis of touchers' hand motion. Though it has been reported that the statistical analysis of hand motion can indeed estimate tactile perception, whether humans can estimate tactile perception by observing the hand motion of others remains unclear. To investigate this, we conducted experiments wherein observers watched point-light moving hands of touchers in tactile exploration and evaluated the material being touched. Our results show that, although observers' estimation of touchers' perception was not accurate, observers extracted information from touchers' hand motion for estimation, and the correlations within observers' estimation were high. These results suggest that human observers can estimate tactile perception through visual observation of the hand motion of others by adopting common strategies about the relationships between touchers' hand motion and tactile perception.

Modeling Touch and Palpation Using Autoregressive Models

OBJECTIVE

The human haptic system uses a set of reproducible and subconscious hand maneuvers to identify objects. Similar subconscious maneuvers are used during medical palpation for screening and diagnosis. The goal of this work was to develop a mathematical model that can be used to describe medical palpation techniques.

METHODS

Palpation data were measured using a two-dimensional array of force sensors. A novel algorithm for estimating the hand position from force data was developed. The hand position data were then modeled using multivariate autoregressive models. Analysis of these models provided palpation direction and frequency as well as palpation type. The models were tested and validated using three different data sets: simulated data, a simplified experiment in which participant followed a known pattern, and breast simulator palpation data.

RESULTS

Simulated data showed that the minimal error in estimating palpation direction and frequency is achieved when the sampling frequency is five to ten times the palpation frequency. The classification accuracy was for the simplified experiment and for the breast simulator data.

CONCLUSION

Proper palpation is one of the vital components of many hands-on clinical examinations. In this study, an algorithm for characterizing medical palpation was developed. The algorithm measured palpation frequency and direction for the first time and provided classification of palpation type.

SIGNIFICANCE

These newly developed models can be used for quantifying and assessing clinical technique, and consequently, lead to improved performance in palpation-based exams. Furthermore, they provide a general tool for the study of human haptics.