Towards an Optimized Dichotic-Listening Paradigm

Dikotisk lytting (DL) er en veletablert non-invasiv test, ofte brukt til å undersøke hemisfærisk dominans for tale og språkprosessering. Til tross for den utbredte bruken både innen forskning og diagnostikk, tydes det på at DL-paradigmer har lidd av middelmådig reliabilitet, et problem som utvilsomt svekker konklusjoner trukket fra testenes målinger. I denne forstand tok den aktuelle studien sikte på å designe og evaluere et nytt DL-paradigme, optimalisert for reliabel vurdering av hemisfæriske forskjeller i taleprosessering. Etter en omfattende litteraturgjennomgang ble designfunksjoner foreslått. Disse var basert på de viktigste eksperimentelle faktorene kjent for å tilføye systematisk bias til oppgaveutførelsen eller for å påvirke tilfeldig feilvarians. Et sentralt designprinsipp var å redusere oppgaveinduserte kognitive krav i forsøket på å undersøke stimulusdrevne lateralitetsestimater. De viktigste designfunksjonene som ble implementert inkluderte bruken av stopp-konsonant vokalstavelser (CV) som stimulansmateriale, et enkelt stimuluspar i hver prøve, og en enkel, fri tilbakekalling som responsinstruksjon. Friske, høyrehendte unge og middelaldrende voksne (N = 50) deltok i en test-retestevaluering av en verbal og en manuell responsformatversjon av paradigmet. Uavhengig av responsformat, avslørte intra- klassekorrelasjonskoeffisientene (ICC) «gode» til «utmerkede» reliabilitetsestimater for hele paradigmet. De aktuelle resultatene indikerer at det foreliggende paradigmet kan tilby et effektivt alternativ til eksisterende paradigmer, både i eksperimentelle og kliniske områder.Masteroppgave i psykologiMAPSYK360INTL-SVINTL-MNINTL-HFINTL-PSYKINTL-MEDMAPS-PSYKINTL-KMDINTL-JU

Left ear advantage in speech-related dichotic listening is not specific to auditory processing disorder in children: A machine-learning fMRI and DTI study

AbstractDichotic listening (DL) tests are among the most frequently included in batteries for the diagnosis of auditory processing disorders (APD) in children. A finding of atypical left ear advantage (LEA) for speech-related stimuli is often taken by clinical audiologists as an indicator for APD. However, the precise etiology of ear advantage in DL tests has been a source of debate for decades. It is uncertain whether a finding of LEA is truly indicative of a sensory processing deficit such as APD, or whether attentional or other supramodal factors may also influence ear advantage. Multivariate machine learning was used on diffusion tensor imaging (DTI) and functional MRI (fMRI) data from a cohort of children ages 7–14 referred for APD testing with LEA, and typical controls with right-ear advantage (REA). LEA was predicted by: increased axial diffusivity in the left internal capsule (sublenticular region), and decreased functional activation in the left frontal eye fields (BA 8) during words presented diotically as compared to words presented dichotically, compared to children with right-ear advantage (REA). These results indicate that both sensory and attentional deficits may be predictive of LEA, and thus a finding of LEA, while possibly due to sensory factors, is not a specific indicator of APD as it may stem from a supramodal etiology

How brain asymmetry relates to performance – a large scale dichotic listening study

All major mental functions including language, spatial and emotional processing are lateralized but how strongly and to which hemisphere is subject to inter- and intraindividual variation. Relatively little, however, is known about how the degree and direction of lateralization affect how well the functions are carried out, i.e., how lateralization and task performance are related. The present study therefore examined the relationship between lateralization and performance in a dichotic listening task for which we had data available from 1839 participants. In this task, consonant-vowel syllables are presented simultaneously to the left and right ear, such that each ear receives a different syllable. When asked which of the two they heard best, participants typically report more syllables from the right ear, which is a marker of left-hemispheric speech dominance. We calculated the degree of lateralization (based on the difference between correct left and right ear reports) and correlated it with overall response accuracy (left plus right ear reports). In addition, we used reference models to control for statistical interdependency between left and right ear reports. The results revealed a u-shaped relationship between degree of lateralization and overall accuracy: the stronger the left or right ear advantage, the better the overall accuracy. This u-shaped asymmetry-performance relationship consistently emerged in males, females, right-/non-right-handers, and different age groups. Taken together, the present study demonstrates that performance on lateralized language functions depends on how strongly these functions are lateralized. The present study further stresses the importance of controlling for statistical interdependency when examining asymmetry-performance relationships in general

Quantifying cerebral asymmetries for language in dextrals and adextrals with random-effects meta analysis

Speech and language-related functions tend to depend on the left hemisphere more than the right in most right-handed (dextral) participants. This relationship is less clear in non-right handed (adextral) people, resulting in surprisingly polarized opinion on whether or not they are as lateralized as right handers. The present analysis investigates this issue by largely ignoring methodological differences between the different neuroscientific approaches to language lateralization, as well as discrepancies in how dextral and adextral participants were recruited or defined. Here we evaluate the tendency for dextrals to be more left hemisphere dominant than adextrals, using random effects meta analyses. In spite of several limitations, including sample size (in the adextrals in particular), missing details on proportions of groups who show directional effects in many experiments, and so on, the different paradigms all point to proportionally increased left hemispheric dominance in the dextrals. These results are analyzed in light of the theoretical importance of these subtle differences for understanding the cognitive neuroscience of language, as well as the unusual asymmetry in most adextrals

The neuromodulatory properties of gonadal steroid hormones with regard to individual differences in cognition and brain organisation.

Sex hormones exert powerful modulatory effects throughout the nervous system and influence various aspects of behaviour. For example, estrogen and progesterone have been shown to influence sex-sensitive cognitive abilities, such as verbal and visuo-spatial abilities (Hampson, 1990a, 1990b). More recently it has been suggested that estradiol can influence executive functioning abilities, such as cognitive control, working memory and selective attention (Colzato et al., 2012; Hampson, 1990a, 1990b; Hampson & Morley, 2013; Hjelmervik et al., 2012; Rosenberg & Park, 2002). Sex hormones have also been shown to affect functional brain organisation, in particular, cerebral lateralisation. Cerebral lateralisation is a fundamental principle of functional brain organisation, referring to the asymmetrical representation of a specific cognitive process in a particular cerebral hemisphere. For example, the left hemisphere is typically dominant for language, while the right hemisphere is dominant for visuo-spatial processes in the healthy brain (Broca, 1861; Hellige, 1993; Kimura, 1967). While men typically demonstrate pronounced, stable patterns of lateralisation, women are assumed to be less lateralised and demonstrate a higher level of intra- and inter-individual variation in the degree of lateralisation (e.g., Bibawi et al, 1995; Cowell et al., 2011; Hampson, 1990a, 1990b; Hausmann et al., 2002; Hausmann & Güntürkün, 2000; Hjelmervik et al., 2012; Wadnerkar et al., 2008; Weis et al., 2008). The present thesis focuses on the influence of estrogen (particularly estradiol) and progesterone on cerebral lateralisation, functional connectivity, and cognition in naturally cycling women. Young, naturally cycling women, free of hormonal contraceptives, were tested during specific phases of their menstrual cycles across a series of behavioural studies and a resting state functional magnetic resonance imaging study. Hormone levels (estradiol and progesterone) were directly measured in each study. The results showed that while both cerebral lateralisation and executive functioning could be modulated by sex hormones, such effects may be smaller and more specific than previously suggested. Firstly, while estradiol (and progesterone) influenced language lateralisation, this effect was dependent on the degree of asymmetry produced by the task used. Specifically, a task that yields a large degree of asymmetry (presumably due to strong bottom-up effects) is likely to mask any sex hormonal effect on other processes underpinning lateralisation, such as interhemispheric inhibition. Secondly, and similarly, the effects of estradiol on executive function and cognitive control were smaller and more specific than previously demonstrated. As such, it was argued that estradiol effects on cognition are likely dependent upon individual differences in neurophysiology, such as those that underpin different levels of schizotypy. Finally, the rs-fMRI findings demonstrate that functional connectivity in the DMN fluctuates according to different phases of the menstrual cycle, while connectivity in the auditory network is stable. Taken together, the findings presented here highlight the extensive effects of sex hormones on the brain, and on behaviours beyond those related to sexual reproduction. Furthermore, they suggest that sex hormonal effects are more complex than previously hypothesised, underpinned by their capacity to interact with task demands, other hormones, and individual differences in neurophysiology

Auditory Hallucinations in Schizophrenia: The Role of Cognitive, Brain Structural and Genetic Disturbances in the Left Temporal Lobe

In this article we review research in our laboratory on auditory hallucinations using behavioral and MRI measure. The review consists of both previously published and new data that for the first time is presented together in a cohesive way. Auditory hallucinations are among the most common symptoms in schizophrenia, affecting more than 70% of the patients. We here advance the hypothesis that auditory hallucinations are internally generated speech perceptions that are lateralized to the left temporal lobe, in the peri-Sylvian region. From this we predict that hallucinating patients should have problems identifying a simultaneously presented external speech sound, as measured through performance on the dichotic listening (DL) paradigm with consonant–vowel syllables, since this technique lateralizes the stimulus input. Across a series of behavioral experiments, we have shown that patients with schizophrenia who experience frequent auditory hallucinations fail to demonstrate an expected right ear advantage on the dichotic listening test. Absence of a right ear advantage is indicative of a functional deficit in the left peri-Sylvian region. The results also revealed that patients with ongoing auditory hallucinations were more impaired than patients with previous hallucinations, and that a higher score on the hallucination item in a standard symptom rating scale (BPRS) correlated negatively with number of correct reports for the right ear stimulus. Moreover, we have found that schizophrenia patients fail to shift attention to the left ear stimulus, when explicitly instructed to focus on the right or left ear stimulus only, thus showing a deficit in inhibition of attention and response-inhibition. The behavioral DL data are substantiated in two MR morphometry studies that revealed significant reductions in grey matter density in the left peri-Sylvian region in hallucinating patients, and patients with reduced left temporal lobe grey matter density. Hallucinating patients also failed to show a right ear advantage in the dichotic listening test. Ongoing fMRI studies are focused on the underlying synaptic and molecular mechanisms by investigating the effects of the glutamate antagonist drug memantine on auditory perception and speech lateralization, and examination of temporal cortex-specific gene expression in the left peri-Sylvian region

The relationship between behavioral language laterality, face laterality and language performance in left-handers

Left-handers provide unique information about the relationship between cognitive functions because of their larger variability in hemispheric dominance. This study presents the laterality distribution of, correlations between and test-retest reliability of behavioral lateralized language tasks (speech production, reading and speech perception), face recognition tasks, handedness measures and language performance tests based on data from 98 left-handers. The results show that a behavioral test battery leads to percentages of (a) typical dominance that are similar to those found in neuropsychological studies even though the incidence of clear atypical lateralization (about 20%) may be overestimated at the group level. Significant correlations were found between the language tasks for both reaction time and accuracy lateralization indices. The degree of language laterality could however not be linked to face laterality, handedness or language performance. Finally, individuals were classified less consistently than expected as being typical, bilateral or atypical across all tasks. This may be due to the often good (speech production and perception tasks) but sometimes weak (reading and face tasks) test-retest reliabilities. The lack of highly reliable and valid test protocols for functions unrelated to speech remains one of the largest impediments for individual analysis and cross-task investigations in laterality research