Brillouin Optical Correlation Domain Analysis in Composite Material Beams.

Structural health monitoring is a critical requirement in many composites. Numerous monitoring strategies rely on measurements of temperature or strain (or both), however these are often restricted to point-sensing or to the coverage of small areas. Spatially-continuous data can be obtained with optical fiber sensors. In this work, we report high-resolution distributed Brillouin sensing over standard fibers that are embedded in composite structures. A phase-coded, Brillouin optical correlation domain analysis (B-OCDA) protocol was employed, with spatial resolution of 2 cm and sensitivity of 1 °K or 20 micro-strain. A portable measurement setup was designed and assembled on the premises of a composite structures manufacturer. The setup was successfully utilized in several structural health monitoring scenarios: (a) monitoring the production and curing of a composite beam over 60 h; (b) estimating the stiffness and Young's modulus of a composite beam; and (c) distributed strain measurements across the surfaces of a model wing of an unmanned aerial vehicle. The measurements are supported by the predictions of structural analysis calculations. The results illustrate the potential added values of high-resolution, distributed Brillouin sensing in the structural health monitoring of composites.

Brillouin optical spectrum analyzer monitoring of subcarrier-multiplexed fiber-optic signals.

Optical spectral analysis of closely spaced, subcarrier multiplexed fiber-optic transmission is performed, based on stimulated Brillouin scattering (SBS). The Brillouin gain window of a single, continuous-wave pump is scanned across the spectral extent of the signal under test. The polarization pulling effect associated with SBS is employed to improve the rejection ratio of the analysis by an order of magnitude. Ten tones, spaced by only 10 MHz and each carrying random-sequence on-off keying data, are clearly resolved. The measurement identifies the absence of a single subcarrier, directly in the optical domain. The results are applicable to the monitoring of optical orthogonal frequency domain multiplexing and radio over fiber transmission.

The bodily self from psychosis to psychedelics.

The sense of self is a foundational element of neurotypical human consciousness. We normally experience the world as embodied agents, with the unified sensation of our selfhood being nested in our body. Critically, the sense of self can be altered in psychiatric conditions such as psychosis and altered states of consciousness induced by psychedelic compounds. The similarity of phenomenological effects across psychosis and psychedelic experiences has given rise to the "psychotomimetic" theory suggesting that psychedelics simulate psychosis-like states. Moreover, psychedelic-induced changes in the sense of self have been related to reported improvements in mental health. Here we investigated the bodily self in psychedelic, psychiatric, and control populations. Using the Moving Rubber Hand Illusion, we tested (N = 75) patients with psychosis, participants with a history of substantial psychedelic experiences, and control participants to see how psychedelic and psychiatric experience impacts the bodily self. Results revealed that psychosis patients had reduced Body Ownership and Sense of Agency during volitional action. The psychedelic group reported subjective long-lasting changes to the sense of self, but no differences between control and psychedelic participants were found. Our results suggest that while psychedelics induce both acute and enduring subjective changes in the sense of self, these are not manifested at the level of the bodily self. Furthermore, our data show that bodily self-processing, related to volitional action, is disrupted in psychosis patients. We discuss these findings in relation to anomalous self-processing across psychedelic and psychotic experiences.

Continuously variable long microwave-photonic delay of arbitrary frequency-chirped signals.

A generic method for the continuously variable, long microwave-photonic delay of the impulse response of arbitrarily chirped waveforms is proposed and demonstrated. Nonlinear-frequency-modulated waveforms of 500 MHz bandwidth are delayed by tens of nanoseconds. The principle relies on the specific phase-time relations of the waveforms, and is applicable to chirped pulses of arbitrary durations, central radio frequencies, and bandwidths. The approach is suitable for beam steering in large phased-array antennas.

The dynamic boundaries of the Self: Serial dependence in the Sense of Agency.

The feeling of control over one's actions, termed the Sense of Agency (SoA), delineates one's experience as an embodied self. Although this embodied experience is typically perceived as stable over time, recent theoretical accounts highlight the experience-dependent and dynamic nature of the embodied self. In this study we examined how recent experiences modulate SoA (i.e., serial dependence), and disambiguated the unique contributions of previous stimuli and choices on subsequent SoA judgments. In addition, we examined whether these effects persist across different domains of perceptual alteration. We analyzed two independent datasets of the Virtual Hand (VH) task (N = 100 participants) in which a sensorimotor conflict is introduced between the presented visual feedback and the actual movement performed. In Dataset 1, which included only temporal alterations, we found that previous stimuli recalibrate current perception, increasing the likelihood of the current choice to be different than the previous choice. Whereas previous choices induce a repetition bias increasing the likelihood to repeat choices across trials. Thus, previous external stimuli and self-generated choices exert opposing influences on SoA. We replicated these findings in Dataset 2, in which the VH task was tested with alterations in both temporal and spatial domains. In addition, we discovered that previous stimuli from a different perceptual domain exert a recalibration effect similar to stimuli from the same domain. Thus, SoA is constantly shaped by our previous subjective choices and objective stimuli experienced even across different perceptual domains. This highlights how SoA may act as unifying construct organizing our experience of the self over time and across perceptual experiences.

Impaired sense of agency and associated confidence in psychosis.

The Sense of Agency (SoA), our sensation of control over our actions, is a fundamental mechanism for delineating the Self from the environment and others. SoA arises from implicit processing of sensorimotor signals as well as explicit higher-level judgments. Psychosis patients suffer from difficulties in the sense of control over their actions and accurate demarcation of the Self. Moreover, it is unclear if they have metacognitive insight into their aberrant abilities. In this pre-registered study, we examined SoA and its associated confidence judgments using an embodied virtual reality paradigm in psychosis patients and controls. Our results show that psychosis patients not only have a severely reduced ability for discriminating their actions but they also do not show proper metacognitive insight into this deficit. Furthermore, an exploratory analysis revealed that the SoA capacities allow for high levels of accuracy in clinical classification of psychosis. These results indicate that SoA and its metacognition are core aspects of the psychotic state and provide possible venues for understanding the underlying mechanisms of psychosis, that may be leveraged for novel clinical purposes.

Explicit Sequence Memory in Recall of Temporally-structured Episodes.

The order in which events unfold over time is an important scaffold aiding recollection. This study asks whether explicit order memory is enhanced for items sharing similar internally-driven temporal contexts. To tap internally-driven temporal context, we capitalized on the Temporal Contiguity Effect whereby recollection of one item promotes recall of adjacently-encoded items. We compared pairs encoded and retrieved contiguously (cont-enc-ret), whose items share internally-driven temporal contexts, to pairs retrieved, but not encoded, contiguously (cont-ret) and to pairs encoded, but not retrieved, contiguously (cont-enc). Cont-enc-ret pairs exhibited superior relative order over cont-ret pairs, supporting accounts emphasizing shared temporal context as opposed to temporal distinctiveness in driving sequence memory. No difference was found in absolute order between the pair types, in line with theories suggesting a dissociation between relative and absolute order. Additionally, cont-enc-ret and cont-enc pairs exhibited equivalent relative order, supporting the role of encoding as opposed to retrieval in the enhancement of relative order. Finally, cont-enc-ret pairs were perceived as closer than cont-enc pairs, supporting the claim that cont-enc-ret pairs constitute part of a temporally-coherent episode. Together, these results implicate internally-driven temporal context in the formation of temporally-structured episodes that enhances sequence memory of the items within the episode.

Assessing the Relationship between Sense of Agency, the Bodily-Self and Stress: Four Virtual-Reality Experiments in Healthy Individuals.

The bodily-self, our experience of being a body, arises from the interaction of several processes. For example, embodied Sense of Agency (SoA), the feeling of controlling our body's actions, is a fundamental facet of the bodily-self. SoA is disturbed in psychosis, with stress promoting its inception. However, there is little knowledge regarding the relationship between SoA, stress, and other facets of the bodily-self. In four experiments manipulating embodied SoA using a virtual hand (VH), we examined (1) How is embodied SoA related to other facets of the bodily-self?; and (2) How is SoA impacted by stress? We found that increased alteration of the VH significantly decreased subjective ratings of SoA and body ownership (Exp. 1), supporting the close relation between SoA and body ownership. Interoceptive accuracy and SoA were positively correlated (Exp. 3), connecting awareness to one's actions and cardiac signals. Contrary to our expectations, SoA was not related to trait anxiety (Exp. 3), nor did induced stress impair SoA (Exp. 4). Finally, we found a negative correlation between self-reported prodromal symptoms and SoA. These results strongly support the connection between SoA and the bodily-self. Whereas, SoA was not impaired by stress, and weakly related to psychotic symptoms.

UnReal? Investigating the Sense of Reality and Psychotic Symptoms with Virtual Reality.

Distortions of reality, such as hallucinations, are common symptoms of many psychiatric conditions. Accordingly, sense of reality (SoR), the ability to discriminate between true and false perceptions, is a central criterion in the assessment of neurological and psychiatric health. Despite the critical role of the SoR in daily life, little is known about how this is formed in the mind. Here, we propose a novel theoretical and methodological framework to study the SoR and its relation to psychotic symptoms. In two experiments, we employed a specialized immersive virtual reality (VR) environment allowing for well-controlled manipulations of visual reality. We first tested the impact of manipulating visual reality on objective perceptual thresholds (just noticeable differences). In a second experiment, we tested how these manipulations affected subjective judgments of reality. The results revealed that the objective perceptual thresholds were robust and replicable, demonstrating that SoR is a stable psychometric property that can be measured experimentally. Furthermore, reality alterations reduced subjective reality judgments across all manipulated visual aspects. Finally, reduced sensitivity to changes in visual reality was related to self-reported prodromal psychotic symptoms. These results provide evidence for the relevance of SoR in the assessment of psychosis and other mental disorders in which reality is distorted.

Metacognition strengthens the association between neurocognition and attenuated psychosis syndrome: Preliminary evidence from a pilot study among treatment-seeking versus healthy adolescents.

BACKGROUND: In a pilot study, we assessed the potential value of deficits at the metacognitive versus the neurocognitive level of functioning for identifying adolescents with attenuated psychotic syndrome (APS). METHOD: Twenty-two treatment-seeking adolescents with APS, 42 treatment-seeking comparisons, and 34 age-matched healthy comparisons were evaluated using the Prodromal Questionnaire, the Structured Interview for Prodromal Syndromes, and the Mood and Anxiety Symptom Questionnaire. Neurocognitive and metacognitive functioning were assessed in two non-social (verbal memory and executive functioning) and two social (facial emotion perception and theory of mind) cognitive domains. In addition to the standard neurocognitive administration of the tasks, subjects were asked to rate their confidence level on each answer and to choose whether they wanted it "counted" toward their overall task performance score on the task. Choices were rewarded. RESULTS: As hypothesized, APS among treatment-seeking adolescents was more strongly associated with impaired neurocognition than with impaired metacognition. Likewise, as hypothesized, impaired metacognition was shown to significantly improve the APS prediction beyond the contribution of impaired neurocognition alone, even after controlling for general intellectual ability, negative symptoms, social functioning, and depression. CONCLUSIONS: These results suggest that metacognitive monitoring and control play a strengthening role in the association between neurocognition and APS. One possible explanation is that metacognition serves as an indicator of insight into the condition, accounting for differences in insight not explained by neurocognition alone. However, further research with larger samples that include non-treatment seeking individuals, established measures of insight, and follow-up data is required to assess this possibility.

A Remember/Know Examination of Free-recall Reveals Dissociative Roles of Item- and Context-Information over Time.

It is well-established that the ability to freely recall information is driven by the extent to which the context at encoding is reinstated at retrieval. Still, when asked to judge the subjective quality of one's memories giving Remember/Know (R/K) judgments, people tend to classify a substantial proportion of recalls as being devoid of context. We suggest that R- and K-recalls differ with regard to their reliance on context- and item-information, with R-recalls driven primarily by contextual-information (e.g., associations evoked by the study-items) and K-recalls driven primarily by information pertaining to the items (e.g., semantic information). Memory was tested both immediately after study and in a final free-recall test conducted ~20 minutes after encoding-a timescale which is akin to real-life events. In line with our predictions, as compared to K-recalls, R-recalls show stronger contextual effects, but similarly strong item-related effects over these timescales. Furthermore, drawing on theories regarding the forgetting of item- and contextual information, we hypothesized and found that R- and K-recalls are differentially affected by the passage of time. Our findings provide several converging pieces of evidence for differential roles of item and contextual information in driving recall and thus highlight the need to extend longstanding theories of free-recall to account for cases in which recall relies less on context.