Cortical processing of the periodicity of speech sounds

The periodicity of speech sounds which is produced by the vibration of the vocal folds, plays a significant role in speech communication. In the auditory system, sound periodicity is extracted along the neural pathway and is, according to several studies of the human brain, represented in the cortical level by a periodicity-specific neural population. Such a population could encode the periodicity of speech sounds. The evidence for cortical periodicity-sensitivity, however, rests mostly on measures of brain activity elicited by non-speech stimuli that differ from speech sounds with respect to their acoustic features and perceptual qualities. Thus, the generalizability of these results to natural speech communication may be limited. The work presented in this thesis investigated cortical processing of the periodicity of speech sounds by using controlled manipulations in the periodicity of vowel stimuli and by measuring brain activity elicited by these stimuli with magnetoencephalography. The results indicate larger amplitudes and more anterior source locations for the responses elicited by periodic as opposed to aperiodic vowel stimuli. While such an effect of periodicity was observed for a range of fundamental frequencies (F0), degrees of periodicity, and durations of the periodic vowel stimuli, the cortical periodicity-specific activity was also modulated by these parameters. Furthermore, evidence for aperiodicity-sensitive activity was found through stimulus-specific release from adaptation when aperiodic vowel stimuli were alternated with periodic rather than with aperiodic adaptors. The results of the thesis, thus, indicate that the degree of speech sound periodicity, determined by the vocal fold vibration, is represented in the auditory cortex. Such sensitivity to periodicity might reflect the activity of distinct neural populations that are selective to sound periodicity and aperiodicity. Importantly, this view of distinct feature-selective populations can, based on the current results, be generalized to describe the neural mechanisms of speech perception. The dependency of the observed periodicity-sensitivity on the acoustic features of the vowel stimuli, further, appears to reflect cortical encoding of auditory-perceptual aspects of voice quality

A graphical user interface for infant ERP analysis

Recording of event-related potentials (ERPs) is one of the best-suited technologies for examining brain function in human infants. Yet the existing software packages are not optimized for the unique requirements of analyzing artifact-prone ERP data from infants. We developed a new graphical user interface that enables an efficient implementation of a two-stage approach to the analysis of infant ERPs. In the first stage, video records of infant behavior are synchronized with ERPs at the level of individual trials to reject epochs with noncompliant behavior and other artifacts. In the second stage, the interface calls MATLAB and EEGLAB (Delorme & Makeig, Journal of Neuroscience Methods 134(1):9–21, 2004) functions for further preprocessing of the ERP signal itself (i.e., filtering, artifact removal, interpolation, and rereferencing). Finally, methods are included for data visualization and analysis by using bootstrapped group averages. Analyses of simulated and real EEG data demonstrated that the proposed approach can be effectively used to establish task compliance, remove various types of artifacts, and perform representative visualizations and statistical comparisons of ERPs. The interface is available for download from http://www.uta.fi/med/icl/methods/eeg.html in a format that is widely applicable to ERP studies with special populations and open for further editing by users. Electronic supplementary material The online version of this article (doi:10.3758/s13428-013-0404-4) contains supplementary material, which is available to authorized users

Psychophysiological responses to eye contact with a humanoid robot: Impact of perceived intentionality

Eye contact with a social robot has been shown to elicit similar psychophysiological responses to eye contact with another human. However, it is becoming increasingly clear that the attention- and affect-related psychophysiological responses differentiate between direct (toward the observer) and averted gaze mainly when viewing embodied faces that are capable of social interaction, whereas pictorial or pre-recorded stimuli have no such capability. It has been suggested that genuine eye contact, as indicated by the differential psychophysiological responses to direct and averted gaze, requires a feeling of being watched by another mind. Therefore, we measured event-related potentials (N170 and frontal P300) with EEG, facial electromyography, skin conductance, and heart rate deceleration responses to seeing a humanoid robot's direct versus averted gaze, while manipulating the impression of the robot's intentionality. The results showed that the N170 and the facial zygomatic responses were greater to direct than to averted gaze of the robot, and independent of the robot's intentionality, whereas the frontal P300 responses were more positive to direct than to averted gaze only when the robot appeared intentional. The study provides further evidence that the gaze behavior of a social robot elicits attentional and affective responses and adds that the robot's seemingly autonomous social behavior plays an important role in eliciting higher-level socio-cognitive processing.Peer reviewe

Dynamic Eye Tracking Based Metrics for Infant Gaze Patterns in the Face-Distractor Competition Paradigm

Peer reviewe

Individual differences in pupil dilation to others' emotional and neutral eyes with varying pupil sizes

Sensitivity to others' emotional signals is an important factor for social interaction. While many studies of emotional reactivity focus on facial emotional expressions, signals such as pupil dilation which can indicate arousal, may also affect observers. For example, observers' pupils dilate when viewing someone with dilated pupils, so-called pupillary contagion. Yet it is unclear how pupil size and emotional expression interact as signals. Further, examining individual differences in emotional reactivity to others can shed light on its mechanisms and potential outcomes. In the current study, adults' (N = 453) pupil size was assessed while they viewed images of the eye region of individuals varying in emotional expression (neutral, happy, sad, fearful, angry) and pupil size (large, medium, small). Participants showed pupillary contagion regardless of the emotional expression. Individual differences in demographics (gender, age, socioeconomic status) and psychosocial factors (anxiety, depression, sleep problems) were also examined, yet the only factor related to pupillary contagion was socioeconomic status, with higher socioeconomic status predicting less pupillary contagion for emotionally-neutral stimuli. The results suggest that while pupillary contagion is a robust phenomenon, it can vary meaningfully across individuals

Individual differences in pupil dilation to others’ emotional and neutral eyes with varying pupil sizes

Sensitivity to others’ emotional signals is an important factor for social interaction. While many studies of emotional reactivity focus on facial emotional expressions, signals such as pupil dilation which can indicate arousal, may also affect observers. For example, observers’ pupils dilate when viewing someone with dilated pupils, so-called pupillary contagion. Yet it is unclear how pupil size and emotional expression interact as signals. Further, examining individual differences in emotional reactivity to others can shed light on its mechanisms and potential outcomes. In the current study, adults’ (N = 453) pupil size was assessed while they viewed images of the eye region of individuals varying in emotional expression (neutral, happy, sad, fearful, angry) and pupil size (large, medium, small). Participants showed pupillary contagion regardless of the emotional expression. Individual differences in demographics (gender, age, socioeconomic status) and psychosocial factors (anxiety, depression, sleep problems) were also examined, yet the only factor related to pupillary contagion was socioeconomic status, with higher socioeconomic status predicting less pupillary contagion for emotionally-neutral stimuli. The results suggest that while pupillary contagion is a robust phenomenon, it can vary meaningfully across individuals.publishedVersionPeer reviewe

Investigating pupillometry to detect emotional regulation difficulties in post-traumatic stress disorder

Objective: Individuals with posttraumatic stress disorder (PTSD) have been found to exhibit emotional regulation difficulties. However, the specific neural mechanisms that underlie these difficulties remain understudied. This study aimed to use pupillometry as an index function of parasympathetic nervous system activation, to investigate the mechanisms underlying emotional regulation difficulties in individuals with PTSD. Method: A total of 87 trauma-exposed mothers (34 with PTSD and 53 non-PTSD controls) completed an eye tracking assessment in which pupillary dilation in response to emotionally valenced stimuli was measured. The participants also completed two self-report measures of emotional regulation, namely the Difficulties in Emotional Regulation Scale and the Emotional Regulations Questionnaire. Linear mixed-effect modelling was used to assess potential group differences. Results: The PTSD group exhibited increased pupillary dilation to positively valenced stimuli compared to the non-PTSD group. However, no significant associations between the self-report measures and pupillary response to emotionally valenced stimuli were found. Conclusion: Increased pupillary dilation in PTSD may reflect impaired parasympathetic nervous system processes. The lack of association of these measures with self-reported emotion regulation may suggest reporting biases. Larger studies with more generalised populations are required to consolidate these preliminary findings.acceptedVersionPeer reviewe