Haptic discrimination of distance

Where Is the Action in Perception? An Exploratory Study With a Haptic Sensory Substitution Device

Enactive cognitive science (ECS) and ecological psychology (EP) agree that active movement is important for perception, but they remain ambiguous regarding the precise role of agency. EP has focused on the notion of sensorimotor invariants, according to which bodily movements play an instrumental role in perception. ECS has focused on the notion of sensorimotor contingencies, which goes beyond an instrumental role because skillfully regulated movements are claimed to play a constitutive role. We refer to these two hypotheses as instrumental agency and constitutive agency, respectively. Evidence comes from a variety of fields, including neural, behavioral, and phenomenological research, but so far with confounds that prevent an experimental distinction between these hypotheses. Here we advance the debate by proposing a novel double-participant setup that aims to isolate agency as the key variable that distinguishes bodily movement in active and passive conditions of perception. We pilot this setup with a psychological study of width discrimination using the Enactive Torch, a haptic sensory substitution device. There was no evidence favoring the stronger hypothesis of constitutive agency over instrumental agency. However, we caution that during debriefing several participants reported using cognitive strategies that did not rely on spatial perception. We conclude that this approach is a viable direction for future research, but that greater care is required to establish and confirm the desired modality of first-person experience.

Enhancing general spatial skills of young visually impaired people with a programmable distance discrimination training: a case control study

BACKGROUND

The estimation of relative distance is a perceptual task used extensively in everyday life. This important skill suffers from biases that may be more pronounced when estimation is based on haptics. This is especially true for the blind and visually impaired, for which haptic estimation of distances is paramount but not systematically trained. We investigated whether a programmable tactile display, used autonomously, can improve distance discrimination ability in blind and severely visually impaired youngsters between 7 and 22 years-old.

METHODS

Training consisted of four weekly sessions in which participants were asked to haptically find, on the programmable tactile display, the pairs of squares which were separated by the shortest and longest distance in tactile images with multiple squares. A battery of haptic tests with raised-line drawings was administered before and after training, and scores were compared to those of a control group that did only the haptic battery, without doing the distance discrimination training on the tactile display.

RESULTS

Both blind and severely impaired youngsters became more accurate and faster at the task during training. In haptic battery results, blind and severely impaired youngsters who used the programmable display improved in three and two tests, respectively. In contrast, in the control groups, the blind control group improved in only one test, and the severely visually impaired in no tests.

CONCLUSIONS

Distance discrimination skills can be trained equally well in both blind and severely impaired participants. More importantly, autonomous training with the programmable tactile display had generalized effects beyond the trained task. Participants improved not only in the size discrimination test but also in memory span tests. Our study shows that tactile stimulation training that requires minimal human assistance can effectively improve generic spatial skills.

Radial trunk-centred reference frame in haptic perception

The shape of objects is typically identified through active touch. The accrual of spatial information by the hand over time requires the continuous integration of tactile and movement information. Sensory inputs arising from one single sensory source gives rise to an infinite number of possible touched locations in space. This observation raises the question of the determination of a common reference frame that might be employed by humans to resolve spatial ambiguity. Here, we employ a paradigm where observers reconstruct the spatial attributes of a triangle from tactile inputs applied to a stationary hand correlated with the voluntary movements of the other hand. We varied the orientation of the hands with respect to one another and to the trunk, and tested three distinct hypotheses regarding a reference frame used for integration: a hand-centred, a trunk-centred or an allocentric reference frame. The results indicated strongly that the integration of movement information and tactile inputs was performed in a radial trunk-centred reference frame.

Evaluation of Direct Haptic 4D Volume Rendering of Partially Segmented Data for Liver Puncture Simulation

This work presents an evaluation study using a force feedback evaluation framework for a novel direct needle force volume rendering concept in the context of liver puncture simulation. PTC/PTCD puncture interventions targeting the bile ducts have been selected to illustrate this concept. The haptic algorithms of the simulator system are based on (1) partially segmented patient image data and (2) a non-linear spring model effective at organ borders. The primary aim is to quantitatively evaluate force errors caused by our patient modeling approach, in comparison to haptic force output obtained from using gold-standard, completely manually-segmented data. The evaluation of the force algorithms compared to a force output from fully manually segmented gold-standard patient models, yields a low mean of 0.12 N root mean squared force error and up to 1.6 N for systematic maximum absolute errors. Force errors were evaluated on 31,222 preplanned test paths from 10 patients. Only twelve percent of the emitted forces along these paths were affected by errors. This is the first study evaluating haptic algorithms with deformable virtual patients in silico. We prove haptic rendering plausibility on a very high number of test paths. Important errors are below just noticeable differences for the hand-arm system.