Remote Subthreshold Stimulation Enhances Skin Sensitivity in the Lower Extremity

Foot sole skin interfaces with the ground and contributes to successful balance. In situations with reduced sensitivity in the glabrous foot skin, stochastic resonance (SR) improves skin sensitivity by adding tactile noise. Some situations, however, involve an interface comprised of hairy skin, which has higher thresholds for sensitivity. For example, in lower extremity amputation the residual limb is comprised of hairy leg skin. The main objective of this study was to determine if SR improves skin sensitivity in hairy skin, and whether a specific intensity of noise is most effective. Secondary objectives were to compare the effect between locations, ages and modalities. In 60 healthy participants a vibrotactile (test) input was delivered at the lower extremity concurrently with a second, noisy stimulus applied more proximally. The presence of a remote SR effect was tested in 15 young participants using electrotactile noise at the calf. Secondary objectives were tested in separate groups of 15 subjects and differed by substituting for one of the three variables: vibrotactile noise, heel site, and with older participants. A forced-choice protocol was used to determine detection ability of the subthreshold vibration test input with varying noise levels applied simultaneously (0, 20, 40, 60, 80, and 100% of perceptual threshold). An SR effect was identified when increased detection of the input was obtained at any level of noise versus no noise. It was found that all four test groups demonstrated evidence of SR: 33–47% of individuals showed better detection of the input with added noise. The SR effect did not appear consistently at any specific noise level for any of the groups, and none of the variables showed a superior ability to evoke SR. Interestingly, in approximately 33% of cases, threshold values fluctuated throughout testing. While this work has provided evidence that SR can enhance the perception of a vibrotactile input in hairy skin, these data suggest that the ability to repeatably show an SR effect relies on maintaining a consistent threshold.

Brain state and cortical layer-specific mechanisms underlying perception at threshold

Identical stimuli can be perceived or go unnoticed across successive presentations, producing divergent behavioral readouts despite similarities in sensory input. We hypothesized that fluctuations in neurophysiological states in the sensory neocortex, which could alter cortical processing at the level of neural subpopulations, underlies this perceptual variability. We analyzed cortical layer-specific electrophysiological activity in visual area V4 during a cued attention task. We find that hit trials are characterized by a larger pupil diameter and lower incidence of microsaccades, indicative of a behavioral state with increased arousal and perceptual stability. Target stimuli presented at perceptual threshold evoke elevated multi-unit activity in V4 neurons in hit trials compared to miss trials, across all cortical layers. Putative excitatory and inhibitory neurons are strongly positively modulated in the input (IV) and deep (V & VI) layers of the cortex during hit trials. Excitatory neurons in the superficial cortical layers exhibit lower variability in hit trials. Deep layer neurons are less phase-locked to low frequency rhythms in hits. Hits are also characterized by greater interlaminar coherence between the superficial and deep layers in the pre-stimulus period, and a complementary pattern between the input layer and both the superficial and deep layers in the stimulus-evoked period. Taken together, these results indicate that a state of elevated levels of arousal and perceptual stability allow enhanced processing of sensory stimuli, which contributes to hits at perceptual threshold.

Imagery adds stimulus-specific sensory evidence to perceptual detection

Internally generated imagery and externally triggered perception rely on overlapping sensory processes. This overlap poses a challenge for perceptual reality monitoring: determining whether sensory signals reflect reality or imagination. In this study, we used psychophysics to investigate how imagery and perception interact to determine visual experience. Participants were instructed to detect oriented gratings that gradually appeared in noise while simultaneously either imagining the same grating, a grating perpendicular to the to-be-detected grating, or nothing. We found that, compared to both incongruent imagery and no imagery, congruent imagery caused a leftward shift of the psychometric function relating stimulus contrast to perceptual threshold. We discuss how this effect can best be explained by a model in which imagery adds sensory signal to the perceptual input, thereby increasing the visibility of perceived stimuli. These results suggest that, in contrast to changes in sensory signals caused by self-generated movement, the brain does not discount the influence of self-generated sensory signals on perception.

A new adaptive procedure for estimating perceptual thresholds: the effects of observer bias and its correction.

Adaptive threshold estimation procedures sample close to a subject's perceptual threshold by dynamically adapting the stimulation based on the subject's performance. Yet, perceptual thresholds not only depend on the observers' sensory capabilities but also on any bias in terms of their expectations and response preferences, thus distorting the precision of the threshold estimates. Using the framework of signal detection theory (SDT), independent estimates of both, an observer's sensitivity and internal processing bias can be delineated from threshold estimates. While this approach is commonly available for estimation procedures engaging the method of constant stimuli (MCS), correction procedures for adaptive methods (AM) are only scarcely applied. In this article, we introduce a new AM that takes individual biases into account, and that allows for a bias-corrected assessment of subjects' sensitivity. This novel AM is validated with simulations and compared to a typical MCS-procedure, for which the implementation of bias correction has been previously demonstrated. Comparing AM and MCS demonstrates the viability of the presented AM. Besides its feasibility, the results of the simulation reveal both, advantages, and limitations of the proposed AM. The procedure has considerable practical implications, in particular for the design of shaping procedures in sensory training experiments, in which task difficulty has to be constantly adapted to an observer's performance, to improve training efficiency.

The perception of voicing contrast in assimilation contexts in minimal pairs: evidence from Hungarian

It has been long acknowledged that the perception and production of speech is affected by the presence or absence of higher levels of linguistic information, too. The recoverability of meaning heavily relies on semantic context, similarly, the precision of articulation is inversely proportional to the presence of semantic information. The present study explores the recoverability of the voice feature of word-final alveolar fricatives in minimal pairs in Hungarian in phonetic contexts that trigger regressive voicing assimilation. Specifically, it aims to clarify whether the acoustic differences found in earlier studies are perceptually salient enough to distinguish underlying voicing in minimal pairs in semantically ambiguous contexts. For this reason, a perception study with the synthesised minimal pair mész–méz ‘whitewash–honey’ was carried out where the amount of voicing in the fricative, and the duration of the fricative and vowel were manipulated. The target words appeared in the following three phonetic contexts: before /p/, before /b/ and before the vowel /a/. Our results suggest that the observed acoustic differences in most of the cases remain below the perceptual threshold which means that phonological contrast is indeed neutralised before obstruents in Hungarian, and this may cause semantic ambiguity.

123 Detrimental effects of acute sleep deprivation on perceptual metacognition

Introduction Sleep deprivation (SD) impairs cognitive performance but its impact on metacognition – i.e. the ability to introspect about cognitive performance – is less clear. A few studies have assessed metacognitive accuracy after acute sleep deprivation in tasks of executive functions and found no impairments. However, whether SD has no influence on metacognition of other cognitive domains such as perception has not been investigated. In this study, we examined how metacognitive accuracy in perceptual decision tasks is affected by 32 hours of sustained wakefulness. Methods 14 participants (3 males, aged 20-32) repeated four visual psychophysical tasks (orientation discrimination, two-flicker fusion, vernier acuity and a novel face/house discrimination in noise) at regular intervals during 32 hours of sustained wakefulness and once after 8 hours recovery sleep. In each task, we concurrently measured quantitative indices of perceptual threshold, confidence rating and metacognitive accuracy (i.e. how well confidence ratings discriminate correct vs incorrect perceptual judgements). Results We observed a gradual increase of perceptual threshold in all tasks with increased time awake. Furthermore, metacognitive accuracy gradually decreased during sustained wakefulness in all tasks. Specifically, the decrease in metacognitive accuracy was driven by over-estimated confidence in trials when participants made incorrect perceptual judgements. After recovery sleep, perceptual thresholds were reset to baseline for all tasks, while metacognitive accuracy was reset to baseline for the orientation discrimination and two-flicker fusion tasks only. Conclusion We showed that sustained wakefulness up to 32 hours increasingly impairs metacognitive accuracy in perceptual decision tasks. These results are consistent across different perceptual tasks, but are in contrast to previous studies showing preserved metacognition of executive functions after SD. Overall, this suggests that the fundamental mechanisms of perceptual metacognition may be similarly affected by sleep deprivation, but that SD selectively impacts different domains of metacognition, such as perceptual metacognition and metacognition of executive functions. Support (if any) MB - Cardiff University PhD Funding CS - Wellcome Trust 209192/Z/17/Z

Real-Time Compression for Tactile Internet Data Streams

The Tactile Internet will require ultra-low latencies for combining machines and humans in systems where humans are in the control loop. Real-time and perceptual coding in these systems commonly require content-specific approaches. We present a generic approach based on deliberately reduced number accuracy and evaluate the trade-off between savings achieved and errors introduced with real-world data for kinesthetic movement and tele-surgery. Our combination of bitplane-level accuracy adaptability with perceptual threshold-based limits allows for great flexibility in broad application scenarios. Combining the attainable savings with the relatively small introduced errors enables the optimal selection of a working point for the method in actual implementations.

Japanese Listeners’ Judgments of Prolongations: With Focus on the Effect of Phonemic Length Contrast

Purpose: This study examined 1) what the absolute minimal duration of the lengthened Japanese sounds /s/, /ss/, /i/, and /i:/ are that are perceived to be abnormal by native speakers of Japanese; 2) what the relative ratio of a stimulus sound’s original length to its absolute perceptual threshold is; 3) whether differences are observed between short and long fricatives and between short and long vowels; and 4) whether phonemic length contrast affects the perceived abnormality of lengthened speech sounds.Methods: Twelve native speakers of Japanese (2 males, 10 females) listened to the Japanese sounds /s/, /ss/, /i/, and /i:/, each of which was lengthened by 0–400 ms in 20 ms increments. The participants rated whether the sound was normal (0) or abnormal (1). The minimal duration for each lengthened sound to be perceived as abnormal by the participants was calculated by analyzing the receiver operating characteristic curves using Youden’s index.Results: The minimal prolongation duration to be perceived as abnormal was 70 ms for /s/, 130 ms for /ss/, 70 ms for /i/, and 170 ms for /i:/. The percentage increases in duration required to be perceived as abnormal were 106% for /s/, 129% for /ss/, 117% for /i/, and 138% for /i:/.Conclusion: Phonemic length contrast affects the minimal prolongation duration and the percentage increase thresholds at which Japanese listeners perceive speech sounds as abnormally long. The implications of these results were further discussed within a diagnostic context of sound prolongation as one of core behaviors of stuttering.