Linear and non linear measures of pupil size as a function of hypnotizability.

Higher arousal and cortical excitability have been observed in high hypnotizable individuals (highs) with respect to low hypnotizables (lows), which may be due to differences in the activation of ascending activating systems. The present study investigated the possible hypnotizability-related difference in the cortical noradrenergic tone sustained by the activity of the Locus Coeruleus which is strongly related to pupil size. This was measured during relaxation in three groups of participants-highs (N = 15), lows (N = 15) and medium hypnotizable individuals (mediums, N = 11)-in the time and frequency domains and through the Recurrence Quantification Analysis. ECG and Skin Conductace (SC) were monitored to extract autonomic indices of relaxation (heart interbeats intervals, parasympathetic component of heart rate variability (RMSSD) and tonic SC (MeanTonicSC). Most variables indicated that participants relaxed throughout the session. Pupil features did not show significant differences between highs, mediums and lows, except for the spectral Band Median Frequency which was higher in mediums than in lows and highs at the beginning, but not at the end of the session.Thus, the present findings of pupil size cannot account for the differences in arousal and motor cortex excitability observed between highs and lows in resting conditions.

Effect of yoga on pulse rate variability measured from a venous pressure waveform.

The benefits of yoga have been studied in different fields, from chronic health conditions to mental disorders, showing that it can help to improve the overall health. In particular, it has been proven that yoga also improves the autonomic function. Heart rate variability (HRV) at rest is commonly used as a non-invasive measure of autonomic regulation of heart rate. Alternatively, pulse rate variability (PRV) has been proposed as a surrogate of HRV. VoluMetrix has developed a novel technology that captures venous waveforms via sensors on the volar aspect of the wrist, called NIVAband. This study aims to assess the effect of yoga in the autonomic nervous system by analyzing the PRV obtained from the NIVA signal. Temporal (statistics of the normal-to-normal intervals), spectral (power in low and high frequency bands) and nonlinear (lagged Poincaré Plot analysis) parameters are analyzed before and after a yoga session in 20 healthy volunteers. The PRV analysis shows an increase in parameters related to parasympathetic activity and overall variability, and a decrease in parameters related to sympathetic activity and mean heart rate. These results support the beneficial effect of yoga in autonomic nervous system, increasing the parasympathetic activity.

Tactile flow explains haptic counterparts of common visual illusions.

Interaction with the external world requires the ability to perceive dynamic changes in complex sensorial input and react promptly. Here, we show that perception of dynamic stimuli in the visual and tactile sensory modalities share fundamental psychophysical aspects that can be explained by similar computational models. In vision, optic flow provides information on relative motion between the individual and the content of percept. For instance, radial patterns of optic flow are used to estimate time before contact with an approaching object [J.J. Gibson, What gives rise to the perception of motion? Psychol. Rev. 75 (1968) 335-346]. Similarly, in the tactile modality, radial patterns of stimuli provide information on softness of probed objects [A. Bicchi, D. De Rossi, E.P. Scilingo, The role of the contact area spread rate (CASR) in haptic discrimination of softness, IEEE Trans. Rob. Autom. 16 (2000) 496-504]. Optic flow is also invoked to explain several visual illusions, including the well-known "barber-pole" effect [N. Fisher, J.M. Zanker, The directional tuning of the barber-pole illusion, Perception 30 (2001) 1321-1336]. Here, we introduce a computational model of tactile flow, which is intimately related to existing models for the visual counterpart. The model accounts for psychophysical aspects of dynamic tactile perception and predicts illusory phenomena in the tactile domain, analogous to the barber-pole effect. When subjects touched translating pads with differently oriented gratings, they perceived a direction of motion that was significantly biased towards the orientation of the gratings. Therefore, these findings indicate that visual and tactile flow share similarities at the psychophysical and computational level and may be intended for similar perceptive goals. Results of this analysis have impact on the engineering of better haptic and multimodal interfaces for human-computer interaction.

EEG Hyperconnectivity Study on Saxophone Quartet Playing in Ensemble.

A professional quartet of saxophonists playing in ensemble provides a perfect scenario to study the eventual occurrence of synchronous oscillatory brain activity across subjects. Here, we applied hyperscanning methodologies for simultaneously recordings of electroencephalographic (EEG) signals from four professional saxophonists while they observ an audiovideo recording of their own previous musical performance. An ad-hoc musical composition was written for the study. At debriefing, the subjects were asked to answer two questionnaires to assess their empathy trait and the musical leadership. In order to estimate the hyperconnectivity of each musician we proposed a measure which combines phase synchronization index of brain oscillations and graph theory framework. The inter-connectivity level of each musician was statistically compared. Statistical results revealed a significant lower hyperconnectivity in the left Brodmann area 44 for the Soprano with respect to the other three members. Recent theories attributed this brain region (Broca's area) to music generation, empathy processes and communication. We hypothesize a relationship between brain-to-brain connectivity level and the musical role within the quartet.

Nonlinear digital signal processing in mental health: characterization of major depression using instantaneous entropy measures of heartbeat dynamics.

Nonlinear digital signal processing methods that address system complexity have provided useful computational tools for helping in the diagnosis and treatment of a wide range of pathologies. More specifically, nonlinear measures have been successful in characterizing patients with mental disorders such as Major Depression (MD). In this study, we propose the use of instantaneous measures of entropy, namely the inhomogeneous point-process approximate entropy (ipApEn) and the inhomogeneous point-process sample entropy (ipSampEn), to describe a novel characterization of MD patients undergoing affective elicitation. Because these measures are built within a nonlinear point-process model, they allow for the assessment of complexity in cardiovascular dynamics at each moment in time. Heartbeat dynamics were characterized from 48 healthy controls and 48 patients with MD while emotionally elicited through either neutral or arousing audiovisual stimuli. Experimental results coming from the arousing tasks show that ipApEn measures are able to instantaneously track heartbeat complexity as well as discern between healthy subjects and MD patients. Conversely, standard heart rate variability (HRV) analysis performed in both time and frequency domains did not show any statistical significance. We conclude that measures of entropy based on nonlinear point-process models might contribute to devising useful computational tools for care in mental health.

Characterizing psychological dimensions in non-pathological subjects through autonomic nervous system dynamics.

The objective assessment of psychological traits of healthy subjects and psychiatric patients has been growing interest in clinical and bioengineering research fields during the last decade. Several experimental evidences strongly suggest that a link between Autonomic Nervous System (ANS) dynamics and specific dimensions such as anxiety, social phobia, stress, and emotional regulation might exist. Nevertheless, an extensive investigation on a wide range of psycho-cognitive scales and ANS non-invasive markers gathered from standard and non-linear analysis still needs to be addressed. In this study, we analyzed the discerning and correlation capabilities of a comprehensive set of ANS features and psycho-cognitive scales in 29 non-pathological subjects monitored during resting conditions. In particular, the state of the art of standard and non-linear analysis was performed on Heart Rate Variability, InterBreath Interval series, and InterBeat Respiration series, which were considered as monovariate and multivariate measurements. Experimental results show that each ANS feature is linked to specific psychological traits. Moreover, non-linear analysis outperforms the psychological assessment with respect to standard analysis. Considering that the current clinical practice relies only on subjective scores from interviews and questionnaires, this study provides objective tools for the assessment of psychological dimensions.

A Finite element model of tactile flow for softness perception.

Touch is an extremely dynamic sense. To take into account this aspect, it has been hypothesized that there are mechanisms in the brain that specialize in processing dynamic tactile stimuli, in a way not too dissimilar from what happens for optical flow in dynamic vision. The concept of tactile flow, related to the rate of expansion of isostrain volumes in the human fingerpad, was used to explain some perceptual illusions as well as mechanisms of human softness perception. In this paper we describe a computational model of tactile flow, and apply it to a finite element model of interaction between deformable bodies. The shape and material properties of the bodies are modeled from those of a human fingertip interacting with specimens with different softness properties. Results show that the rate of expansion of isostrain volumes can be used to discriminate different materials in terms of their softness characteristics.

The social perceptual salience effect.

Affective processes appraise the salience of external stimuli preparing the agent for action. So far, the relationship between stimuli, affect, and action has been mainly studied in highly controlled laboratory conditions. In order to find the generalization of this relationship to social interaction, we assess the influence of the salience of social stimuli on human interaction. We constructed reality ball game in a mixed reality space where pairs of people collaborated in order to compete with an opposing team. We coupled the players with team members with varying social salience by using both physical and virtual representations of remote players (i.e., avatars). We observe that, irrespective of the team composition, winners and losers display significantly different inter- and intrateam spatial behaviors. We show that subjects regulate their interpersonal distance to both virtual and physical team members in similar ways, but in proportion to the vividness of the stimulus. As an independent validation of this social salience effect, we show that this behavioral effect is also displayed in physiological correlates of arousal. In addition, we found a strong correlation between performance, physiology, and the subjective reports of the subjects. Our results show that proxemics is consistent with affective responses, confirming the existence of a social salience effect. This provides further support for the so-called law of apparent reality, and it generalizes it to the social realm, where it can be used to design more efficient social artifacts.

Mind-body relationships in elite apnea divers during breath holding: a study of autonomic responses to acute hypoxemia.

The mental control of ventilation with all associated phenomena, from relaxation to modulation of emotions, from cardiovascular to metabolic adaptations, constitutes a psychophysiological condition characterizing voluntary breath-holding (BH). BH induces several autonomic responses, involving both autonomic cardiovascular and cutaneous pathways, whose characterization is the main aim of this study. Electrocardiogram and skin conductance (SC) recordings were collected from 14 elite divers during three conditions: free breathing (FB), normoxic phase of BH (NPBH) and hypoxic phase of BH (HPBH). Thus, we compared a set of features describing signal dynamics between the three experimental conditions: from heart rate variability (HRV) features (in time and frequency-domains and by using nonlinear methods) to rate and shape of spontaneous SC responses (SCRs). The main result of the study rises by applying a Factor Analysis to the subset of features significantly changed in the two BH phases. Indeed, the Factor Analysis allowed to uncover the structure of latent factors which modeled the autonomic response: a factor describing the autonomic balance (AB), one the information increase rate (IIR), and a latter the central nervous system driver (CNSD). The BH did not disrupt the FB factorial structure, and only few features moved among factors. Factor Analysis indicates that during BH (1) only the SC described the emotional output, (2) the sympathetic tone on heart did not change, (3) the dynamics of interbeats intervals showed an increase of long-range correlation that anticipates the HPBH, followed by a drop to a random behavior. In conclusion, data show that the autonomic control on heart rate and SC are differentially modulated during BH, which could be related to a more pronounced effect on emotional control induced by the mental training to BH.