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Background: Representation of objects can be obtained through tactual perception alone. The previous studies showed that there were no significant differences between the index finger and middle finger when the participants perceived the length of the presented objects, however, the length perception characteristics between the thumb and each of the four other fingers remains unclear. Objective: To investigate the length perception characteristics between the thumb and each of the four other fingers, the current study using a four-degree-of-freedom (4DOF) length display device with an adjustable distance conducted length perception experiments. Methods: We performed two experiments: experiment I, perception of different lengths (natural position), and experiment II, perception of the same length (same length position). In experiment I, the length presented to each pair of fingers was different. In experiment II, the length presented to finger pairs of the participants was the same. Results: The results showed that in both experiments, the perceived length was relatively shorter than the presented length, and when the presented length was longer than 70 mm, the error becomes smaller. The comparison of results indicated that for the perception of the index finger, no significant differences existed between the two experiments under any condition; for the middle and ring fingers, significant differences were found only when the presented length was approximately 100 mm; for the little finger, significant differences were found for lengths ranging from 45 mm to 90 mm. Conclusion: These results indicated that the perceptual accuracy at the natural position of the fingers is worse than that when the finger is in a bent position, and when the finger is spread beyond the neutral position, the relative positon affects the length perception.

The basal ganglia, which have been shown to be a significant multisensory hub, are disordered in Parkinson’s disease (PD). This study was to investigate the audiovisual integration of peripheral stimuli in PD patients with/without sleep disturbances. Thirty-six age-matched normal controls (NC) and 30 PD patients were recruited for an auditory/visual discrimination experiment. The mean response times for each participant were analyzed using repeated measures ANOVA and race model. The results showed that the response to all stimuli was significantly delayed for PD compared to NC (all p<0.01). The response to audiovisual stimuli was significantly faster than that to unimodal stimuli in both NC and PD (p<0.001). Additionally, audiovisual integration was absent in PD; however, it did occur in NC. Further analysis showed that there was no significant audiovisual integration in PD with/without cognitive impairment or in PD with/without sleep disturbances. Furthermore, audiovisual facilitation was not associated with Hoehn and Yahr stage, disease duration, or the presence of sleep disturbances (all p>0.05). The current results showed that audiovisual multisensory integration for peripheral stimuli is absent in PD regardless of sleep disturbances and further suggested the abnormal audiovisual integration might be a potential early manifestation of PD.