Perceptual timing precision with vibrotactile, auditory, and multisensory stimuli

It is important to understand the perceptual limits on vibrotactile information-processing because of the increasing use of vibrotactile signals in common technologies like cell phones. To advance such an understanding, we examined vibrotactile temporal acuity and compared it to auditory and bimodal (synchronous vibrotactile and auditory) temporal acuity. In a pair of experiments, subjects experienced a series of empty intervals, demarcated by stimulus pulses from one of the three modalities. One trial contained up to 5 intervals, where the first intervals were isochronous at 400 ms, and the last interval varied from 400 by ±1-80 ms. If the final interval was < 400 ms, the last pulse seemed “early”, and if the final interval was > 400 ms, the last pulse seemed “late”. In Experiment One, each trial contained four intervals, where the first three were isochronous. Subjects judged the timing of the last interval by describing the final pulse as either “early” or “late”. In Experiment Two, the number of isochronous intervals in a trial varied from one to four. Psychometric modeling revealed that vibrotactile temporal processing was less acute than auditory or bimodal temporal processing, and that auditory inputs dominated bimodal perception. Additionally, varying the number of isochronous intervals did not affect temporal sensitivity in either modality, suggesting the formation of memory traces. Overall, these results suggest that vibrotactile temporal processing is worse than auditory or bimodal temporal processing, which are similar. Also, subjects need no more than one isochronous reminder per trial for optimal performance.

Left frontal white matter atrophy links to timing mechanisms relevant for apraxia of speech

ObjectiveIn some patients with apraxia of speech (AOS), we observed impaired perceptual timing abilities, which lead us to propose a shared mechanism of impaired perceptual timing underlying impaired rhythm discrimination (perceptual processing) and AOS (motor speech output). Given that considerable white matter damage is often observed in these patients, we here investigate whether white matter changes are related to impaired rhythm processing as one possible mechanism underlying AOS.MethodsWe applied deformation-based morphometry (DBM) and diffusion tensor imaging (DTI) in 12 patients with the nonfluent variant (NFV) of Primary Progressive Aphasia (PPA) with AOS, as well as 11 patients with the semantic variant and 24 controls.ResultsSeventy-five percent of the patients with NFV displayed impaired rhythm processing and the severity of their impairment correlated with their degree of AOS. Moreover, left frontal white matter volume loss adjacent to the supplementary motor area (SMA) correlated with impaired rhythm processing. In addition, we obtained tract-based metrics of the left Aslant tract, which is typically damaged in NFV. The structural integrity of the left Aslant tract also correlated with rhythmic discrimination abilities in NFV.ConclusionsOur data suggest that a shared white matter substrate adjacent to the SMA contributes to impaired rhythm perception and motor speech impairments. This indicates that impaired perceptual timing may be one of the neurocomputational mechanisms underlying AOS. Our observation that regional variations in left frontal lobe atrophy are linked to the phenotypical heterogeneity in NFV may lead the way for earlier diagnosis.

The perception of time is dynamically interlocked with the facial muscle activity

Time perception relies on the motor system. Involves core brain regions of this system, including those associated with feelings generated from sensorimotor states. Perceptual timing is also distorted when movement occurs during timing tasks, possibly by interfering with sensorimotor afferent feedback. However, it is unknown if the perception of time is an active process associated with specific patterns of muscle activity. We explored this idea based on the phenomenon of electromyographic gradients, which consists of the dynamic increase of muscle activity during cognitive tasks that require sustained attention, a critical function in perceptual timing. We aimed to determine whether facial muscle dynamic activity indexes the subjective representation of time. We asked participants to judge stimuli durations (varying in familiarity) while we monitored the time course of the activity of the zygomaticus-major and corrugator-supercilii muscles, both associated with cognitive and affective feelings. The dynamic electromyographic activity in corrugator-supercilii over time reflected objective time and this relationship predicted subjective judgments of duration. Furthermore, the zygomaticus-major muscle signaled the bias that familiarity introduces in duration judgments. This suggests that subjective duration could be an embodiment process based in motor information changing over time and their associated feelings.

Time perception deficits and its dose-dependent effect in methamphetamine dependents with short-term abstinence

Intake of addictive substances acutely modifies dopaminergic transmission in the striatum and prefrontal cortex, which is the neural substrate underlying time processing. However, the persistent effects of methamphetamine (meth) abuse (e.g., during abstinence) on temporal processing have not been fully elucidated. Here, we recruited different samples in two experiments. We first compared the potential differences in motor timing between healthy controls and meth dependents with varied length of abstinence and then examined the ability of perceptual timing between the healthy subjects and the meth group at short abstinence. We found that motor timing, but not perceptual timing, was altered in meth dependents, which persisted for at least 3 months of abstinence. Dose-dependent effects on time perception were only observed when short-term abstinent meth abusers processed long time intervals. We conclude that time perception alteration in meth dependents is task specific and dose dependent.