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Directional Asymmetries in Vowel Perception
- Nadine P.W.D. de Rue, Alejandrina Cristia, Paula Fikkert, Sho Tsuji
Directional asymmetries in vowel perception are attributed a key role in language acquisition. Therefore, it is of the outmost importance to understand why such asymmetries exist. In the theoretical portion of this hesis, we first provide an overview of current hypotheses. One of them suggests that directional asymmetries in vowel perception are caused by natural discontinuities in the general auditory system. If this hypothesis s correct, asymmetries should be elicited by linguistic stimuli as well as by non-linguistic analogues that reserve crucial acoustic information. In the empirical section, we conducted two perceptual tasks to verify his prediction. We tested discrimination of spoken vowel contrasts and their nonspeech analogues in adult Dutch listeners in two nonnative vowel pairs. All hypotheses predicted more efficient discrimination in linguistic stimuli when the vowel changed in peripheral direction than when the vowel changed towards the center of vowel space; but only the general auditory hypothesis predicted this bias to extend to nonlinguistic analogues. In fact, results showed no evidence of perceptual asymmetries in speech discrimination. We conclude that asymmetries are weak in adults, leading to small effect sizes. Regarding the non-linguistic analogues, results were promising as adults exhibited discrimination performance above chance level. Thus, further work with larger adult participant samples and/or with infant samples exploiting the same nonlinguistic analogues bears promise to answer the question of the etiology of vowel asymmetries.
What you see is What You’ve Learned: Reward Biases Visuospatial Attention
- Sebastiaan den Boer, Johanna Zumer, Sean Fallon, Ole Jensen
Reward can have a large impact on behavior. This could be due to a modulation of selective attention, but could also be explained by an increase in effort. The present study disentangles these two possible explanation, and investigates whether reward may directly affect attentional control by creating a perceptual bias. By orthogonalizing reward from task performance, we show that this is indeed the case. We show that reward creates a non-volitional perceptual bias that increases the amount of attention that is allocated towards a previously rewarded stimulus. This effect is reflected in reaction times and also in modulations of posterior alpha oscillations.
Do Alpha Oscillations Provide a Mechanism for Prioritizing Salient Unattended Stimuli?
- Yağmur Güçlütürk, Mathilde Bonnefond, Ole Jensen
Recently, it has been hypothesized that alpha oscillations allow the representations of competing unattended stimuli to be ordered in the visual cortex with respect to their saliency levels. According to this framework, alpha oscillations and gamma oscillations (>30 Hz) phase- locked to alpha oscillations produce a temporal phase code for saliency. Furthermore, power of alpha oscillations that increases with reduced attention, determines the number of unattended stimuli that can be processed, such that a higher alpha power would result in fewer representations of stimuli to activate, and vice versa. In this study we wanted to answer the question: ‘does alpha activity provide a mechanism for prioritizing and ordering unattended visual inputs with respect to the saliency levels of each input?’ To this end, we performed three experiments in which, we have taken advantage of the well-studied attentional phenomenon called the prior entry effect. In particular, the experiments involved visual temporal order judgement tasks with and without a spatial attention component, and an auditory task. We used magnetoenchephalography (MEG) to measure oscillatory activity in order to test our hypothesis. The analysis of the behavioural and MEG data revealed a number of differences between the task conditions, which suggests a stronger prioritization for higher alpha power in the occipital brain
regions, in line with the suggested mechanism for prioritization and ordering of salient unattended stimuli. Our results warrant further research on the suggested framework.
Studying the Acquisition of Emotion Words Over Time: a Longitudinal Behavioral and Electrophysiological Study
- Renée Middelburg, Agnes Sianipar, Ton Dijkstra
This paper investigated the sensitivity of second language learners to the emotional content of words. In addition, the potentially helpful role of cognates in accessing the emotional contents of words was examined. Thirty-two young adult German native speakers participated in four Dutch lexical decision experiments, combining reaction time (RT) measures with EEG recordings over their first six months of learning Dutch (L2). The learners already reacted differently to emotion words after only one to two weeks of language learning. Especially positive words seemed to have a special status in the earliest stages of second language acquisition: RTs to these words were faster, fewer errors were made on them, and a more positive-going Late Positive Complex was found in response to these words. Arousal of the words itself did not affect the ERPs, but it did influence the valence response. In sum, from the earliest stages of second language acquisition onwards, emotional valence played a role in L2 processing, and, as has been found previously, learning a new language was a fast process; i.e., processing words in a new language up to the semantic and emotion levels already occurs at a very early stage of learning. We did not find strong support for a facilitating role of cognates, neither in the ERP patterns, nor in the behavioral data.
Linearity of Spin-echo and Gradient-echo BOLD
- Nils Müller, David Norris, Markus Barth
The blood-oxygenation level dependent (BOLD) contrast is one of the most important means of measuring brain activity. For the analysis of most functional magnetic resonance imaging data it is assumed that the BOLD contrast behaves in a linear fashion. Recent literature suggests differences between gradient-echo (GE) and spin-echo (SE) based sequences in terms of SE showing a more linear response at short inter stimulus intervals (ISI). In case of densely spaced events this could result in spin echo being superior to GE despite its reduced sensitivity. We investigated this differential linearity in the visual cortex for SE and GE at 7 Tesla. We used a dual echo sequence, acquiring both GE and SE simultaneously, and a paired-stimulus paradigm. Based on our results we cannot conclude whether there is a difference in linearity. This could be a result of the unexpectedly low temporal signal to noise ratio (tSNR) of SE compared to GE.
The Effects of an Enriched Environment on the Intrinsic Properties and Neuromodulations of CA1 Pyramidal Cells
- María Jesús Valero Aracama, Motoharu Yoshida, Wim Scheenen
It has long been established that living in enriched environments (EE) improves learning and memory. While enhancement of hippocampal plasticity by EE has also been widely reported, the modification of intrinsic cellular properties and their interaction with neuromodulators are not well understood. Using whole cell atch clamp techniques in the hippocampal CA1 slice preparation from mice housed in EE and control environments (CE), I tested the modification of intrinsic cellular properties of CA1 pyramidal cells by an E. The EE manipulation increased the excitability and the sag amplitude and its ratio in response to a yperpolarizing current pulse. Additionally, I tested the acute effects of four neuromodulators that are crucial or learning and memory: acetylcholine (ACh) agonist, noradrenaline (NA), serotonin (5-HT) and brainderived neurotrophic factor (BDNF) agonist. EE-cells seem to have a higher sensitivity to NA and 5-HT n reducing the sag amplitude and ratio. The sag response has been reported as a measure for the amount f hyperpolarization-activated cation current (Ih) in the cell. Since the Ih is known to be modulated by cyclic adenosine monophosphate (cAMP) and NA and 5-HT modulate cAMP levels, these results suggest a regulation of cAMP actions in EEs. In addition, I tested the ability of CA1 cells to support persistent firing (PF) after a short current pulse as a neural mark of working memory. PF was observed with cholinergic and TrkB receptor agonists, but not with NA or 5-HT suggesting a role of ACh and BDNF in PF. Since previous studies found an increment of BDNF in the hippocampi from EE-animals, EE might improve learning by facilitating PF through increasing BDNF concentration in hippocampus. In summary, my data suggests that EE increases the intrinsic excitability and the Ih, modifies the cellular sensitivity to NA and 5-HT, and it probably increases PF through a BDNF concentration increment
MicroRNA-338 in Neuronal Growth and Development: Investigating the Role of microRNA-338 in on the Morphological Development of Cortical Neurons in vitro
- Mark van Kessel, Aron Kos, Armaz Aschrafi
Post-transcriptional regulation of gene expression is an important factor healthy neuronal development. One of the regulatory mechanisms that has received a lot of attention recently is miRNAs, small non-coding pieces of RNA that influence the translation of messenger RNA. In this study we specifically looked at miRNA-338-3p to establish its role in neuronal development in vitro. We show that expression levels for miRNA-338 vary with region and developmental time points and, that at specific time points, there are gross morphological differences in terms of dendritic structure as well as dendritic spine head diameter and spine length. Spine density and synaptogenesis on the other hand were unaffected. These results indicate miRNA-338 might increase somatic projections and a role for miRNA-338 in synapse maturation or synapse maintenance.