Social Haptic Communication mimicked with vibrotactile patterns:an evaluation by users with deafblindness

Many devices, such as smart phones, implement vibration motors for tactile feedback. When multiple vibration motors are placed on, for instance, the backrest of a chair it is possible to trace shapes on the back of a person by sequentially switching motors on and off. Social Haptic Communication (SHC) is a tactile mode of communication for persons with deafblindness that makes use of tracing shapes or other types of spatiotemporal patterns with the hand on the back of another person. This could be emulated using vibrotactile patterns. Here we investigated whether SHC users with deafblindness would recognize the vibrotactile patterns as SHC signs (Haptices). In several cases the participants immediately linked a vibrotactile patterns to the Haptice that is was meant to imitate. Together with the participants we improved and expanded the set of vibrotactile patterns.</p

Haptic pleasantness, naturalness, and complexity, of geometric raised line drawings

In vision, stimulus pleasantness has been shown to relate to complexity following an inverted U-curve or a linear relationship. At the same time, geometric patterns that are more associated with nature are found to be perceived as more pleasant. However, little is known about how pleasantness relates to naturalness and complexity of tactile geometric patterns. Therefore, we investigated whether haptic pleasantness depends on complexity, and naturalness of a geometric pattern. Because exploratory hand movements have been shown to depend on the haptic property to be extracted and can depend on complexity we also recorded hand movements. We examined the influence of perceived naturalness and complexity on movement speed

No need to touch this: Bimanual haptic slant adaptation does not require touch

In our daily life, we often interact with objects using both hands raising the question the question to what extent information between the hands is shared. It has, for instance, been shown that curvature adaptation aftereffects can transfer from the adapted hand to the non-adapted hand. However, this transfer only occurred for dynamic exploration, e.g. by moving a single finger over a surface, but not for static exploration when keeping static contact with the surface and combining the information from different parts of the hand. This raises the question to what extent adaptation to object shape is shared between the hands when both hands are used in static fashion simultaneously and the object shape estimates require information from both hands. Here we addressed this question in three experiments using a slant adaptation paradigm. In Experiment 1 we investigated whether an aftereffect of static bimanual adaptation occurs at all and whether it transfers to conditions in which one hand was moving. In Experiment 2 participants adapted either to a felt slanted surface or simply be holding their hands in mid-air at similar positions, to investigate to what extent the effects of static bimanual adaptation are posture-based rather than object based. Experiment 3 further explored the idea that bimanual adaptation is largely posture based. We found that bimanual adaptation using static touch did lead to aftereffects when using the same static exploration mode for testing. However, the aftereffect did not transfer to any exploration mode that included a dynamic component. Moreover, we found similar aftereffects both with and without a haptic surface. Thus, we conclude that static bimanual adaptation is of proprioceptive nature and does not occur at the level at which the object is represented

The effect of feature saliency on haptic subitizing

‘Subitizing’ refers to fast and error-free numerosity judgment for small (<4) sets of items. For larger sets, the slower process of ‘counting’ is used. Counting has a serial character, whereas subitizing is believed to have a parallel character. While subitizing was initially found in vision, it has been shown to exist in touch as well. In vision, it has been demonstrated that adding distractor items to a set of target items influences numerosity judgment of the target items. Subitizing was in this case only possible if the distractor item is highly salient among the targets. In the present study, we investigated the effect of adding a distractor item on haptic judgement of a set of target items. To this end, we asked subjects to judge the number of spheres grasped in their hand. Either a cube or an ellipsoid could be added to the set. A cube among spheres has been shown to be highly salient, while an ellipsoid among spheres is not. Our results show that adding a distractor item led to an increase in the response time slopes regardless of the distractor shape. Subitizing was, however, only possible in the case of a salient distractor. This is in agreement with results from vision

Haptic subitizing across the fingers

Numerosity judgments of small sets of items (≤ 3) are generally fast and errorfree, while response times and error rates increase rapidly for larger numbers of items. We investigated an efficient process used for judging small numbers of items (known as subitizing) in active touch. We hypothesized that this efficient process for numerosity judgment might be related to stimulus properties that allow for efficient (parallel) search. Our results showed that subitizing was not possible forraised lines among flat surfaces, whereas this type of stimulus could be detected in parallel over the fingers. However, subitizing was possible when the number of fingers touching a surface had to be judged while the other fingers were lowered in mid-air. In the latter case, the lack of tactile input is essential, since subitizing was not enabled by differences in proprioceptive information from the fingers. Our results show that subitizing using haptic information from the fingers is possible only whensome fingers receive tactile information while other fingers do not

Grabbing subitizing with both hands: bimanual number processing

Visual judgment of small numerosities (<4) is generally assumed to be done through subitizing, which is a faster process than counting. Subitizing has also been shown to occur in haptic judgment of the number of spheres in the hand. Furthermore, interactions have been shown to exist between visually perceived numbers and hand motor action. In this study, we compare enumeration of a set of spheres presented to one hand (unimanual) and enumeration of the same total number of spheres presented divided over the two hands (bimanual). Our results show that, like in vision, a combination of subitizing and counting is used to process numbers in active touch. This shows that numbers are processed in a modality-independent way. This suggests that there are not only interactions between perception of numbers and hand motor action, but rather that number representation is modality-independent

Number magnitude to finger mapping is disembodied and topological

It has been shown that humans associate fingers with numbers because finger counting strategies interact with numerical judgements. At the same time, there is evidence that there is a relation between number magnitude and space as small to large numbers seem to be represented from left to right. In the present study, we investigated whether number magnitude to finger mapping is embodied (related to the order of fingers on the hand) or disembodied (spatial). We let healthy human volunteers name random numbers between 1 and 30, while simultaneously tapping a random finger. Either the hands were placed directly next to each other, 30 cm apart, or the hands were crossed such that the left hand was on the right side of the body mid-line. The results show that naming a smaller number than the previous one was associated with tapping a finger to the left of the previously tapped finger. This shows that there is a spatial (disembodied) mapping between number magnitude and fingers. Furthermore, we show that this mapping is topological rather than metrically scaled

Range dependent processing of visual numerosity: similarities across vision and haptics

‘Subitizing’ refers to fast and accurate judgement of small numerosities, whereas for larger numerosities either counting or estimation are used. Counting is slow and precise, whereas estimation is fast but imprecise. In this study consisting of five experiments we investigated if and how the numerosity judgement process is affected by the relative spacing between the presented numerosities. To this end we let subjects judge the number of dots presented on a screen and recorded their response times. Our results show that subjects switch from counting to estimation if the relative differences between subsequent numerosities are large (a factor of 2), but that numerosity judgement in the subitizing range was still faster. We also show this fast performance for small numerosities only occurred when numerosity information is present. This indicates this is typical for number processing and not magnitude estimation in general. Furthermore, comparison with a previous haptic study suggests similar processing in numerosity judgement through haptics and vision

Perceptual Grouping Affects Haptic Enumeration Over the Fingers

Spatial arrangement is known to influence enumeration times in vision. In haptic enumeration, it has been shown that dividing the total number of items over the two hands can speed up enumeration. Here we investigated how spatial arrangement of items and non-items presented to the individual fingers impacts enumeration times. More specifically, we tested whether grouping by proximity facilitates haptic serial enumeration (counting). Participants were asked to report the number of tangible items, amongst non-items, presented to the finger pads of both hands. In the first experiment, we divided the tangible items in one, two, or three groups that were defined by proximity (i.e., one nonitem in between two groups) and found that number of groups and not number of items were the critical factor in enumeration times. In a second experiment, we found that this grouping even takes place when groups extend across fingers of both hands. These results suggest that grouping by proximity affects haptic serial enumeration and that this grouping takes place on a spatial level possibly in addition to the somatotopic level. Our results support the idea that grouping by proximity, a principle introduced in vision, also greatly affects haptic processing of spatial information