A New Method for Haptic Shape Discriminability Detection

Touch shape discrimination is not only closely related to tactile mechanoreceptors but also higher cognitive function. However, previous shape discrimination methods are difficult to complete in a short time, and the devices are complicated to operate and not user-friendly for nonprofessionals. Here, we propose a new method, the evaluation quantity of which is the angle discrimination threshold. In addition, to make this method easy to use for nonprofessionals, we designed a haptic angle sorting system, including the device and software. To evaluate this method, the angle sorting and two-angle discrimination experiments were compared, and it was found that participants spent significantly less time in the former experiment than in the latter. At the same time, there is a strong correlation between the performance of angle sorting and two-angle discrimination, which shows that the angle threshold obtained by the new method can also be used to evaluate the ability of touch discrimination. Moreover, the angle sorting results of different age groups also further demonstrate the feasibility of the method. The efficiency of this new method and the effectiveness of the system also provide a convenient means for evaluating haptic shape discrimination, which may have potential clinical application value in the early diagnosis of peripheral neuropathy and even in the evaluation of cognitive function.

Tactile Angle Discrimination Decreases due to Subjective Cognitive Decline in Alzheimer’s Disease

Background: Subjective Cognitive Decline (SCD) is the early preclinical stage of Alzheimer's Disease (AD). Previous study provided an invaluable contribution by showing that a tactile angle discrimination system can be used to distinguish between healthy older individuals and patients with mild cognitive impairment and AD. However, that study paid little attention to the relationship between tactile angle discrimination and SCD. Therefore, a means of differentiating Normal Controls (NCs), elderly subjects with SCD, patients with amnestic Mild Cognitive Impairment (aMCI), and AD is urgently needed. Methods: In the present study, we developed a novel tactile discrimination device that uses angle stimulation applied to the index finger pad to identify very small differences in angle discrimination between the NC (n = 30), SCD (n = 30), aMCI (n = 30), and AD (n = 30) groups. Using a three-alternative forced-choice and staircase method, we analyzed the average accuracy and threshold of angle discrimination. Results: We found that accuracy significantly decreased while thresholds of angle discrimination increased in the groups in the following order: NC, SCD, aMCI, and AD. The area under the receiver operating characteristic curve also indicated that the tactile angle discrimination threshold was better than Mini-Mental State Examination scores in distinguishing NC individuals and SCD patients. Conclusion: These findings emphasize the importance of tactile working memory dysfunction in explaining the cognitive decline in angle discrimination that occurs in SCD to AD patients and offer further insight into the very early detection of subjects with AD.

A jump to the left and a step to the right: A test of two accounts of peak shift

Abstract“Peak Shift” usually occurs following intradimensional-discrimination training and involves a shift of the peak of the generalization gradient away from the original discriminative stimulus (S+) in a direction away from an S-. Two theoretical accounts of peak shift, the gradient interaction theory (GIT) and adaptation level theory (ALT), were compared. The effects of asymmetric test stimuli and the impact of instructions to participants for them to treat stimuli as members of categories on generalization gradients were investigated. In Experiment 1, the relation between peak shifts obtained when an extended asymmetric set of test stimuli was employed and the occurrence of categorization of the stimuli involved was investigated in four separate conditions. Two involved temporal discrimination, one involved line-angle discrimination, and one involved a compound line-angle and temporal cue discrimination. If participants treated the stimuli as belonging to discrete categories, such as hands-on a clock, rather than as being on continuous dimensions then responding to the compound cue was expected to result in attenuation of blocking of a peak shift. However, the peak shift obtained to the three cue types were the same. In Experiment 2, an independent group of participants was given explicit instructions to treat the line angles as if they were the hands of a clock face and this eliminated peak shift. The results from the present experiments support an ALT interpretation, although the peak shifts were significantly smaller in magnitude than predicted by this account.

Tactile angle discriminability improvement: roles of training time intervals and different types of training tasks

Perceptual learning, which is not limited to sensory modalities such as vision and touch, emerges within a training session and between training sessions and is accompanied by the remodeling of neural connections in the cortex. However, limited knowledge exists regarding perceptual learning between training sessions. Although tactile studies have paid attention to between-session learning effects, there have been few studies asking fundamental questions regarding whether the time interval between training sessions affects tactile perceptual learning and generalization across tactile tasks. We investigated the effects of different training time intervals on the consecutive performance of a tactile angle discrimination (AD) task and a tactile orientation discrimination (OD) task training on tactile angle discriminability. The results indicated that in the short-interval training group, AD task performance significantly improved in the early stage of learning and nearly plateaued in the later stage, whereas in the long-interval training group, significant improvement was delayed and then also nearly plateaued in the later stage; additionally, improved OD task performance resulted in improved AD task performance. These findings suggest that training time interval affects the early stage of learning but not the later stage and that generalization occurs between different types of tactile tasks. NEW & NOTEWORTHY Perceptual learning, which constitutes important foundations of complicated cognitive processes, is learning better perception skills. We demonstrate that training time interval can affect the early stage of learning but not the later stage. Moreover, a tactile orientation discrimination training task can also improve tactile angle discrimination performance. These findings may expand the characteristics of between-session learning and help understand the mechanism of the generalization across tactile tasks.