An Examination of the Factors that Dictate the Relative Weighting of Feedback and Feedforward Input for Speech Motor Control

Speech is arguably the most important form of human communication. Fluent speech production relies on auditory feedback for the planning, execution, and monitoring of speech movements. Auditory feedback is particularly important during the acquisition of speech, however, it has been suggested that over time speakers rely less on auditory feedback as they develop robust sensorimotor representations that allow speech motor commands to be executed in a feedforward manner. The studies reported in this thesis recorded speaker’s vocal and neural responses to altered auditory feedback in order to explore the factors that dictate the relative importance of auditory feedback for speech motor control. More specifically, studies 1 through 3 examined how the role of auditory feedback changes throughout development, while studies 4 and 5 examined the relationship between vocal variability and auditory feedback control, and lastly study 6 looked at how the predictability of auditory feedback errors influences the role of auditory feedback for speech motor control. Results of the first study demonstrated that toddlers use auditory feedback to regulate their speech motor commands, supporting the long held notion that auditory feedback is important during the acquisition of speech. While mapping out the developmental trajectory of vocal and event related potential responses to altered auditory feedback, the second study demonstrated that vocal variability, rather than age, best predicts responses to altered auditory feedback. Importantly, this suggests that the maturation of the speech motor control system is not strictly dependent on age. The third study in this thesis demonstrated that children and adults show similar rates of sensorimotor adaptation, suggesting that once speech is acquired, speakers are proficient at using sensory information to modify the planning of future speech motor commands. However, since adults produced larger compensatory responses, these results also suggested that adults are more proficient at comparing incoming auditory feedback with the feedback predicted by their sensorimotor representations, as a result of possessing more precisely mapped sensorimotor representations. The results of studies four and five demonstrated that vocal variability can be used to predict the size of compensatory responses and sensorimotor adaptation to changes in one’s auditory feedback, respectively. Furthermore, these studies demonstrated that increased variability was related to increased auditory feedback control of speech. Finally, the sixth study in this thesis demonstrated that experimentally induced predictability and variability can be used to induce increases in feedforward and auditory feedback control, respectively. In conclusion, the results reported in this thesis demonstrate that age and vocal variability, both naturally occurring and experimentally induced, are important determinants of the role of auditory feedback in speech motor control

The Role of Auditory Feedback at Vocalization Onset and Mid-Utterance

Auditory feedback plays an important role in monitoring and correcting for errors during speech production. Previous research suggests that at vocalization onset, auditory feedback is compared to a sensory prediction generated by the motor system to ensure the desired fundamental frequency (F0) is produced. After vocalization onset, auditory feedback is compared to the most recently perceived F0 in order to stabilize the vocalization. This study aimed to further investigate whether after vocalization onset, auditory feedback is used strictly to stabilize speakers’ F0, or if it is also influenced by the sensory prediction generated by the motor system. Event-related potentials (ERP) were recorded while participants produced vocalizations and heard the F0 of their auditory feedback perturbed suddenly mid-utterance by half a semitone. For half of the vocalizations, at vocalization onset, participants’ F0 was also raised by half a semitone. Thus, half of the perturbations occurred while participants heard their unaltered auditory feedback, and the other half occurred in auditory feedback that had also been perturbed 50 cents at vocalization onset. If after vocalization onset auditory feedback is strictly used to stabilize speakers’ F0, then similarly sized vocal and ERP responses would be expected across all trials, regardless of whether the perturbation occurred while listening to altered or unaltered auditory feedback. Results indicate that the perturbations to the participants’ unaltered auditory feedback resulted in larger vocal and N1 and P2 ERP responses than perturbations to their altered auditory feedback. These results suggest that after vocalization onset auditory feedback is not strictly used to stabilize speakers’ F0, but is also used to ensure the desired F0 is produced

Collapse of the Mott gap and emergence of a nodal liquid in lightly doped Sr2_2IrO4_4

Superconductivity in underdoped cuprates emerges from an unusual electronic state characterised by nodal quasiparticles and an antinodal pseudogap. The relation between this state and superconductivity is intensely studied but remains controversial. The discrimination between competing theoretical models is hindered by a lack of electronic structure data from related doped Mott insulators. Here we report the doping evolution of the Heisenberg antiferromagnet Sr$_2$IrO$_4$, a close analogue to underdoped cuprates. We demonstrate that metallicity emerges from a rapid collapse of the Mott gap with doping, resulting in lens-like Fermi contours rather than disconnected Fermi arcs as observed in cuprates. Intriguingly though, the emerging electron liquid shows nodal quasiparticles with an antinodal pseudogap and thus bares strong similarities with underdoped cuprates. We conclude that anisotropic pseudogaps are a generic property of two-dimensional doped Mott insulators rather than a unique hallmark of cuprate high-temperature superconductivity

Phytochrome Mediated Responses in Agrobacterium fabrum: Growth, Motility and Plant Infection

The soil bacterium and plant pathogen Agrobacterium fabrum C58 has two phytochrome photoreceptors, Agp1 and Agp2. We found that plant infection and tumor induction by A. fabrum is down-regulated by light and that phytochrome knockout mutants of A. fabrum have diminished infection rates. The regulation pattern of infection matches with that of bacterial conjugation reported earlier, suggesting similar regulatory mechanisms. In the regulation of conjugation and plant infection, phytochromes are active in darkness. This is a major difference to plant phytochromes, which are typically active after irradiation. We also found that propagation and motility were affected in agp1− and agp2− knockout mutants, although propagation was not always affected by light. The regulatory patterns can partially but not completely be explained by modulated histidine kinase activities of Agp1 and Agp2. In a mass spectrometry-based proteomic study, 24 proteins were different between light and dark grown A. fabrum, whereas 382 proteins differed between wild type and phytochrome knockout mutants, pointing again to light independent roles of Agp1 and Agp2

Exploring sensory phenotypes in autism spectrum disorder

Background: Atypical reactions to the sensory environment are often reported in autistic individuals, with a high degree of variability across the sensory modalities. These sensory differences have been shown to promote challenging behaviours and distress in autistic individuals and are predictive of other functions including motor, social, and cognitive abilities. Preliminary research suggests that specific sensory differences may cluster together within individuals creating discrete sensory phenotypes. However, the manner in which these sensory differences cluster, and whether the resulting phenotypes are associated with specific cognitive and social challenges is unclear. Methods: Short sensory profile data from 599 autistic children and adults between the ages of 1 and 21 years were subjected to a K-means cluster analysis. Analysis of variances compared age, adaptive behaviour, and traits associated with autism, attention-deficit and hyperactivity disorder, and obsessive and compulsive disorder across the resultant clusters. Results: A five-cluster model was found to minimize error variance and produce five sensory phenotypes: (1) sensory adaptive, (2) generalized sensory differences, (3) taste and smell sensitivity, (4) under-responsive and sensation seeking, and (5) movement difficulties with low energy. Age, adaptive behaviour, and traits associated with autism, attention-deficit and hyperactivity disorder, and obsessive and compulsive disorder were found to differ significantly across the five phenotypes. Limitations: The results were based on parent-report measures of sensory processing, adaptive behaviour, traits associated with autism, attention-deficit and hyperactivity disorder, and obsessive and compulsive disorder, which may limit the generalizability of the findings. Further, not all measures are standardized, or psychometrically validated with an autism population. Autistic individuals with an intellectual disability were underrepresented in this sample. Further, as these data were obtained from established records from a large provincial database, not all measures were completed for all individuals. Conclusions: These findings suggest that sensory difficulties in autistic individuals can be clustered into sensory phenotypes, and that these phenotypes are associated with behavioural differences. Given the large degree of heterogeneity in sensory difficulties seen in the autistic population, these sensory phenotypes represent an effective way to parse that heterogeneity and create phenotypes that may aid in the development of effective treatments and interventions for sensory difficulties

Attention Capture by Trains and Faces in Children with and Without Autism Spectrum Disorder

This study examined involuntary capture of attention, overt attention, and stimulus valence and arousal ratings, all factors that can contribute to potential attentional biases to face and train objects in children with and without autism spectrum disorder (ASD). In the visual domain, faces are particularly captivating, and are thought to have a ‘special status’ in the attentional system. Research suggests that similar attentional biases may exist for other objects of expertise (e.g. birds for bird experts), providing support for the role of exposure in attention prioritization. Autistic individuals often have circumscribed interests around certain classes of objects, such as trains, that are related to vehicles and mechanical systems. This research aimed to determine whether this propensity in autistic individuals leads to stronger attention capture by trains, and perhaps weaker attention capture by faces, than what would be expected in non-autistic children. In Experiment 1, autistic children (6–14 years old) and age- and IQ-matched non-autistic children performed a visual search task where they manually indicated whether a target butterfly appeared amongst an array of face, train, and neutral distractors while their eye-movements were tracked. Autistic children were no less susceptible to attention capture by faces than non-autistic children. Overall, for both groups, trains captured attention more strongly than face stimuli and, trains had a larger effect on overt attention to the target stimuli, relative to face distractors. In Experiment 2, a new group of children (autistic and non-autistic) rated train stimuli as more interesting and exciting than the face stimuli, with no differences between groups. These results suggest that: (1) other objects (trains) can capture attention in a similar manner as faces, in both autistic and non-autistic children (2) attention capture is driven partly by voluntary attentional processes related to personal interest or affective responses to the stimuli

Negative first impression judgements of autistic children by non-autistic adults

IntroductionAlthough autism inclusion and acceptance has increased in recent years, autistic people continue to face stigmatization, exclusion, and victimization. Based on brief 10-second videos, non-autistic adults rate autistic adults less favourably than they rate non-autistic adults in terms of traits and behavioural intentions. In the current study, we extended this paradigm to investigate the first impressions of autistic and non-autistic children by non-autistic adult raters and examined the relationship between the rater's own characteristics and bias against autistic children.MethodSegments of video recorded interviews from 15 autistic and 15 non-autistic children were shown to 346 undergraduate students in audio with video, audio only, video only, transcript, or still image conditions. Participants rated each child on a series of traits and behavioural intentions toward the child, and then completed a series of questionnaires measuring their own social competence, autistic traits, quantity and quality of past experiences with autistic people, and explicit autism stigma.ResultsOverall, autistic children were rated more negatively than non-autistic children, particularly in conditions containing audio. Raters with higher social competence and explicit autism stigma rated autistic children more negatively, whereas raters with more autistic traits and more positive past experiences with autistic people rated autistic children more positively.DiscussionThese rapid negative judgments may contribute to the social exclusion experienced by autistic children. The findings indicate that certain personal characteristics may be related to more stigmatised views of autism and decreased willingness to interact with the autistic person. The implications of the findings are discussed in relation to the social inclusion and well-being of autistic people

High frequency magnetic oscillations of the organic metal θ\theta-(ET)4_4ZnBr4_4(C6_6H4_4Cl2_2) in pulsed magnetic field of up to 81 T

De Haas-van Alphen oscillations of the organic metal $\theta$-(ET)$_4$ZnBr$_4$(C$_6$H$_4$Cl$_2$) are studied in pulsed magnetic fields up to 81 T. The long decay time of the pulse allows determining reliable field-dependent amplitudes of Fourier components with frequencies up to several kiloteslas. The Fourier spectrum is in agreement with the model of a linear chain of coupled orbits. In this model, all the observed frequencies are linear combinations of the frequency linked to the basic orbit $\alpha$ and to the magnetic-breakdown orbit $\beta$.Comment: 6 pages, 4 figure

Ex-ante assessment of returns on research investments to address the impact of Fusarium Wilt tropical race 4 on global banana production

The spread of Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), causal agent of Fusarium wilt of banana (FWB), has been projected to reach 17% of the global banana-growing area by 2040 equaling 36 million tons of production worth over US$10 billion. This potential loss has fueled (inter)national discussions about the best responses to protect production and small-scale growers’ livelihoods. As part of a multi-crop ex ante assessment of returns on research investments conducted by the CGIAR Research Program on Roots, Tubers, and Bananas (RTB) from 2012 to 2016, four FWB research options were assessed: (i) improved exclusion, surveillance, eradication, and containment (ESEC) measures to reduce Foc TR4 spread, (ii) integrated crop and disease management (ICDM) to facilitate production of partially FWB resistant cultivars on Foc-infested soils, (iii) conventional breeding of FWB-resistant cultivars (CBRC), and (iv) genetically modified (GM) FWB-resistant cultivars (GMRC). Building on a risk index (Foc scale) predicting the initial occurrence and internal spread of Foc TR4 in 29 countries, an economic surplus (ES) model, cost-benefit analysis, and poverty impact simulations were used to assess impact under two adoption scenarios. All options yield positive net present values (NPVs) and internal rates of return (IRRs) above the standard 10% rate. For the conservative scenario with 50% reduced adoption, IRRs were still 30% for ICDM, 20% for CBRC, and 28% for GMRC. ESEC has IRRs between 11 and 14%, due to higher costs of capacity strengthening, on-going surveillance, farmer awareness campaigns, and implementation of farm biosecurity practices, which could be effective for other diseases and benefit multiple crops. The research investments would reach between 2.7 million (GMRC) and 14 million (ESEC) small-scale beneficiaries across Asia/Pacific, Sub-Saharan Africa, and Latin America/Caribbean. The options varied in their potential to reduce poverty, with the largest poverty reduction resulting from CBRC with 850,000 and ESEC with 807,000 persons lifted out of poverty (higher adoption scenario). In the discussion, we address the data needs for more fine-grained calculations to better guide research investment decisions. Our results show the potential of public investments in concerted research addressing the spread of Foc TR4 to yield high returns and substantially slow down disease spread

The stable free rank of symmetry of products of spheres

A well known conjecture in the theory of transformation groups states that if p is a prime and (Z/p)^r acts freely on a product of k spheres, then r is less than or equal to k. We prove this assertion if p is large compared to the dimension of the product of spheres. The argument builds on tame homotopy theory for non simply connected spaces.Comment: 30 pages; improved exposition, some details adde