On the reliability and validity of noninvasive laterality measures

Opposite perceptual biases in analogous auditory and visual tasks are unique to consonant-vowel strings and are unlikely a consequence of repetition

Despite wide reporting of a right ear (RE) advantage on dichotic listening tasks and a right visual field (RVF) advantage on visual half-field tasks, we know very little about the relationship between these perceptual biases. Previous studies that have investigated perceptual asymmetries for analogous auditory and visual consonant-vowel tasks have indicated a serendipitous finding: a RE advantage and a left visual field (LVF) advantage with poor cross-modal correlations. In this study, we examined the possibility that this LVF advantage for visual processing of consonant-vowel strings may be a consequence of repetition by examining perceptual biases in analogous auditory and visual tasks for both consonant-vowel strings and words. We replicated opposite perceptual biases for consonant-vowel strings (RE and LVF advantages). This did not extend to word stimuli where we found RE and RVF advantages. Furthermore, these perceptual biases did not differ across the three experimental blocks. Thus, we can firmly conclude that this LVF advantage is unique to consonant-vowel strings and is not a consequence of the repetition of a relatively limited number of stimuli. Finally, a test of covariances indicated no cross-modal relationships between laterality indices suggesting that perceptual biases are dissociable within individuals and cluster on mode of presentation.

Accident proneness, laterality, and time estimation

Cerebral laterality has been linked to accident proneness and time perception, but the possible role of time estimation abilities has received little attention. Accordingly, the present study focused on this under-explored question while also aiming to replicate past work examining the relationship between measures of laterality and injury proneness. Participants reported on the number of accidents they have had in their lifetime requiring medical care and the number of minor accidents they had in the past month as outcome variables. They also completed the Waterloo Handedness Questionnaire, a left bias visual task (Greyscales task), a right bias auditory verbal task (Fused Dichotic Words Task), and an objective measure of time perception. Extensive examination of statistical model fit showed that a model assuming a Poisson distribution provided the best fit for minor injuries and an additional negative binomial provided the best fit to the lifetime accidents. Results showed a negative relation between the degree of verbal laterality (absolute right bias) and injuries requiring medical care. Furthermore, the number of accidents requiring medical care was positively related to the precision of time estimation and the direction of verbal laterality on response time (raw right bias). Interpretations of these findings emphasize their implications for interhemispheric communication and motor control in the context of time estimation and auditory verbal laterality. These aspects seem to provide promising avenues for future research.

The effects of alphabetic literacy, linguistic-processing demand and tone type on the dichotic listening of lexical tones

Brain lateralization of lexical tone processing remains a matter of debate. In this study we used a dichotic listening paradigm to examine the influences of the knowledge of Jyutping (a romanization writing system which provides explicit Cantonese tone markers), linguistic-processing demand and tone type on the ear preference pattern of native tone processing in Hong Kong Cantonese speakers. While participants with little knowledge of Jyutping showed a previously reported left-ear advantage (LEA), those with a good level of Jyutping expertise exhibited either a right-ear advantage or bilateral processing during lexical tone identification and contour tone discrimination, respectively. As for the effect of linguistic-processing demand, while an LEA was found in acoustic/phonetic perception situations, this advantage disappeared and was replaced by a bilateral pattern in conditions that involved a greater extent of linguistic processing, suggesting an increased involvement of the left hemisphere. Regarding the effect of tone type, both groups showed an LEA in level tone discrimination, but only the Jyutping group demonstrated a bilateral pattern in contour tone discrimination. Overall, knowledge of written codes of tones, greater degree of linguistic processing and contour tone processing seem to influence the brain lateralization of lexical tone processing in native listeners of Cantonese by increasing the recruitment of the left-hemisphere language network.

Combined fMRI Region- and Network-Analysis Reveal New Insights of Top-Down Modulation of Bottom-Up Processes in Auditory Laterality

Dichotic listening along with the right-ear advantage (REA) has been a standard method of investigating auditory laterality ever since it was first introduced into neuropsychology in the early 1960s. Beginning in the 1980s, authors reported that it was possible to modulate the bottom-up driven perceptual REA by instructing subjects to selectively attend to and report only from the right or left ear. In the present study, we investigated neuronal correlates of both the bottom-up and top-down modulation of the REA through two fMRI analysis approaches: a traditional region approach and a network connectivity approach. Blood-Oxygenation-Level-Dependent (BOLD) fMRI data were acquired while subjects performed the standard forced-attention paradigm. We asked two questions, could the behavioral REA be replicated in unique brain markers, and second if the profound instruction-induced modulation of the REA found in behavioral data would correspond to a similar modulation of brain activation, both region- and network-specific modulations. The subjects were 70 healthy adult right-handers, about half men and half women. fMRI data were acquired in a 3T MR scanner, and the behavioral results replicated previous findings with a REA in the non-forced (NF) and forced-right (FR) conditions, and a tendency for a left-ear advantage (LEA) in the FL-condition. The fMRI data showed unique activations in the speech perception areas of the left temporal lobe when directly contrasted with activations in the homologous right side. However, there were no remaining unique activations when the FR- and FL-conditions were contrasted against each other, and with the NF-condition, using a conservative significance thresholding. The fMRI results are conceptualized within a network connectivity frame of reference, especially with reference to the extrinsic mode network (EMN). The EMN is a generalized task-positive network that is upregulated whenever the task demands exceed a certain threshold irrespective of the specifics and demands of the task. This could explain the similarity of activations for the FR- and FL-conditions, despite the clear differences in behavior.

Frontal and parietal EEG alpha asymmetry: a large-scale investigation of short-term reliability on distinct EEG systems

EEG resting-state alpha asymmetry is one of the most widely investigated forms of functional hemispheric asymmetries in both basic and clinical neuroscience. However, studies yield inconsistent results. One crucial prerequisite to obtain reproducible results is the reliability of the index of interest. There is a body of research suggesting a moderate-to-good reliability of EEG resting-state alpha asymmetry, but unfortunately sample sizes in these studies are typically small. This study presents the first large-scale short-term reliability study of frontal and parietal EEG resting-state alpha asymmetry. We used the Dortmund Vital Study data set containing 370 participants. In each participant, EEG resting state was recorded eight times, twice with their eyes opened, twice with their eyes-closed, each on two different EEG systems. We found good reliability of EEG alpha power and alpha asymmetry on both systems for electrode pairs. We also found that alpha power asymmetry reliability is higher in the eyes-closed condition than in the eyes-open condition. The frontomedial electrode pair showed weaker reliability than the frontolateral and parietal electrode pairs. Interestingly, we found no population-level alpha asymmetry in frontal electrodes, one of the most investigated electrode sites in alpha asymmetry research. In conclusion, our results suggest that while EEG alpha asymmetry is an overall reliable measure, frontal alpha asymmetry should be assessed using multiple electrode pairs.

Dichotic listening abilities among liturgical teachers of the Ethiopian Orthodox Church

This study examines patterns of ear advantage and attentional capacity among religious teachers of the Ethiopian Orthodox Church versus adults who are not religious teachers. Religious education, rooted mainly in Christianity and Islam, has a long history in Ethiopia. Most of such education has been practised through recitations and oral presentations, which demand perceptual vigour particularly on the part of the teachers. The present study employed a dichotic listening paradigm, using monosyllabic word and CV-syllables listening tasks, administered in three attentional conditions: non-forced (NF), forced-right (FR) and forced-left (FL). 54 right-handed male adults (27 teachers and 27 non-teachers) served as participants. Percentages of correct responses per ear, as well as Laterality Index (LI) were calculated and analysed using a repeated measures analysis of variance (ANOVA) statistical procedure. Results showed that, on both listening tasks, the religious teachers demonstrated a higher ear advantage in all conditions, indicative of stronger language asymmetry (in non-forced condition) and better ability to focus on one specific ear (in forced conditions). The findings of the present study are very much in support of the theory of neuroplasticity in human cognition (Konorski, 1948).

Laterality 2020: Response to the article commentaries

In our recent opinion paper "Laterality 2020: entering the next decade", we highlighted trends that we thought are likely to shape laterality research in the 2020s. Our opinion paper inspired 11 commentaries by experts from several disciplines which discussed a wide range of topics complementing the 10 trends we identified in the opinion paper. In this reply, we summarize and discuss the 11 commentaries by clustering them into 3 different main topics. The topic that was covered by the largest number of commentaries was the role of comparative and evolutionary approaches in laterality research. Moreover, several comments focused on the ontogenesis of hemispheric asymmetries and the importance of reliability and validity in laterality research. Embracing the technical advances, research trends and controversies laid out in the commentaries will significantly improve our understanding of several of the core questions of laterality research.

Look to the future but remember the past: A commentary on Ocklenburg, Berretz, Packheiser, and Friedrich (2020)

This is a commentary on a paper by Ocklenburg et al. ([2020]. Laterality 2020: entering the next decade. Laterality). I discuss measurement and task selection issues that should not be neglected as we make our way through the next decade. I also comment further on a few pointed issues relevant to open science and meta-analysis.

Assessing the reliability of an online behavioural laterality battery: A pre-registered study

Studies of cerebral lateralization often involve participants completing a series of perceptual tasks under laboratory conditions. This has constrained the number of participants recruited in such studies. Online testing can allow for much larger sample sizes but limits the amount of experimental control that is feasible. Here we considered whether online testing could give valid and reliable results on four tasks: a rhyme decision visual half-field task, a dichotic listening task, a chimeric faces task, and a finger tapping task. We recruited 392 participants, oversampling left-handers, who completed the battery twice. Three of the tasks showed evidence of both validity and reliability, insofar as they showed hemispheric advantages in the expected direction and test-retest reliability of at least r = .75. The reliability of the rhyme decision task was less satisfactory (r = .62). We also confirmed a prediction that extreme left-handers were more likely to depart from typical lateralization. Lateralization across the two language tasks (dichotic listening and rhyme judgement) was weakly correlated, but unrelated to lateralization on the chimeric faces task. We conclude that three of the tasks, dichotic listening, chimeric faces and finger tapping, show considerable promise for online evaluation of cerebral lateralization.

An optimal dichotic-listening paradigm for the assessment of hemispheric dominance for speech processing

Dichotic-listening paradigms are widely accepted as non-invasive tests of hemispheric dominance for language processing and represent a standard diagnostic tool for the assessment of developmental auditory and language disorders. Despite its popularity in research and clinical settings, dichotic paradigms show comparatively low reliability, significantly threatening the validity of conclusions drawn from the results. Thus, the aim of the present work was to design and evaluate a novel, highly reliable dichotic-listening paradigm for the assessment of hemispheric differences. Based on an extensive literature review, the paradigm was optimized to account for the main experimental variables which are known to systematically bias task performance or affect random error variance. The main design principle was to minimize the relevance of higher cognitive functions on task performance in order to obtain stimulus-driven laterality estimates. To this end, the key design features of the paradigm were the use of stop-consonant vowel (CV) syllables as stimulus material, a single stimulus pair per trial presentation mode, and a free recall (single) response instruction. Evaluating a verbal and manual response-format version of the paradigm in a sample of N = 50 healthy participants, we yielded test-retest intra-class correlations of rICC = .91 and .93 for the two response format versions. These excellent reliability estimates suggest that the optimal paradigm may offer an effective and efficient alternative to currently used paradigms both in research and diagnostic.

Testing the interhemispheric deficit theory of dyslexia using the visual half-field technique

A deficit in interhemispheric transfer has been proposed as a neuropsychological theory of dyslexia. Interactions between the hemispheres during word recognition can be studied using the visual half-field paradigm. The well-established recognition advantage for right visual field (RVF) words over left visual field (LVF) words is thought to reflect the additional processing costs associated with callosal transfer of LVF word representations to the language-specialised left hemisphere. In addition, a further gain in recognition for bilateral presentation of a word has been attributed to cooperative interactions between the hemispheres. These recognition advantages can therefore be seen as behavioural indices of the efficiency of callosal transfer. This study aimed to replicate the finding of an absence of the bilateral advantage in developmental dyslexia, previously reported by Henderson et al. In all, 47 dyslexic and 43 control adult participants were tested, and no significant difference was found in the size of the bilateral advantage between the two groups. Our data did however replicate the previous finding of an increased RVF-LVF difference in dyslexic participants caused by poorer accuracy for LVF words (i.e., a greater LVF cost). This evidence is compatible with the interhemispheric deficit theory of dyslexia, suggesting an impairment in the transfer of visual word information from the right to the left hemisphere during reading.

Auditory semantic priming and the dichotic right ear advantage

The current study presents two experiments that aimed to explore the effects of auditory semantic priming on the dichotic right ear advantage. In Experiment 1, a classic fused dichotic words task was modified with the addition of auditory associative primes with three levels of relatedness (right, left, or neither ear). In Experiment 2, a new dichotic listening task was developed based on a binaural task used in a published auditory priming study. In both experiments, we expected that priming would produce a large right ear advantage when related to the right ear target but that the magnitude of this advantage would decrease for left ear related targets. Although evidence of priming (faster responses for related than unrelated primes) was found in both experiments, only Experiment 2 confirmed our prediction of an ear by prime relatedness interaction. Results are interpreted in the context of models concerned with the role of each cerebral hemisphere in semantic processing as well as models of perceptual asymmetries.

Right-lateralized unconscious, but not conscious, processing of affective environmental sounds

Much research on the laterality of affective auditory stimuli features emotional speech. However, environmental sounds can also carry affective information, but their lateralized processing for affect has been studied much less. We studied this in 2 experiments. In Experiment 1 we explored whether the detection of affective environmental sounds (from International Affective Digital Sounds) that appeared in auditory scenes was lateralized. While we found that negative targets were detected more rapidly, detection latencies were the same on the left and right. In Experiment 2 we examined whether conscious appraisal of the stimulus was needed for lateralization patterns to emerge, and asked participants to rate the stimuli's pleasantness in a dichotic listening test. This showed that when positive/negative environmental sounds were in the attended to-be-rated channel, ratings were the same regardless of laterality. However, when participants rated neutral stimuli and the unattended channel was positive/negative, the valence of the unattended channel affected the neutral ratings more strongly with left ear (right hemisphere, RH) processing of the affective sound. We link our findings to previous work that suggests that the RH may specialize in the unconscious processing of emotion via subcortical routes.

Schizotypy and hemispheric asymmetry: Results from two Chapman scales, the O-LIFE questionnaire, and two laterality measures

Schizotypy is a multidimensional personality construct representing the extension of psychosis-like traits into the general population. Schizotypy has been associated with attenuated expressions of many of the same neuropsychological abnormalities as schizophrenia, including atypical pattern of functional hemispheric asymmetry. Unfortunately the previous literature on links between schizotypy and hemispheric asymmetry is inconsistent, with some research indicating that elevated schizotypy is associated with relative right over left hemisphere shifts, left over right hemisphere shifts, bilateral impairments, or with no hemispheric differences at all. This inconsistency may result from different methodologies, scales, and/or sex proportions between studies. In a within-participant design we tested for the four possible links between laterality and schizotypy by comparing the relationship between two common self-report measures of multidimensional schizotypy (the O-LIFE questionnaire, and two Chapman scales, magical ideation and physical anhedonia) and performance in two computerised lateralised hemifield paradigms (lexical decision, chimeric face processing) in 80 men and 79 women. Results for the two scales and two tasks did not unequivocally support any of the four possible links. We discuss the possibilities that a link between schizotypy and laterality (1) exists but is subtle, probably fluctuating, unable to be assessed by traditional methodologies used here; (2) does not exist, or (3) is indirect, mediated by other factors (e.g., stress-responsiveness, handedness, drug use) whose influences need further exploration.

"Right on all Occasions?" - On the Feasibility of Laterality Research Using a Smartphone Dichotic Listening Application

Most psychological experimentation takes place in laboratories aiming to maximize experimental control; however, this creates artificial environments that are not representative of real-life situations. Since cognitive processes usually take place in noisy environments, they should also be tested in these contexts. The recent advent of smartphone technology provides an ideal medium for such testing. In order to examine the feasibility of mobile devices (MD) in psychological research in general, and laterality research in particular, we developed a MD version of the widely used speech laterality test, the consonant-vowel dichotic listening (DL) paradigm, for use with iPhones/iPods. First, we evaluated the retest reliability and concurrent validity of the DL paradigm in its MD version in two samples tested in controlled, laboratory settings (Experiment 1). Second, we explored its ecological validity by collecting data from the general population by means of a free release of the MD version (iDichotic) to the iTunes App Store (Experiment 2). The results of Experiment 1 indicated high reliability (r_ICC = 0.78) and validity (r_ICC = 0.76–0.82) of the MD version, which consistently showed the expected right ear advantage (REA). When tested in real-life settings (Experiment 2), participants (N = 167) also showed a significant REA. Importantly, the size of the REA was not dependent on whether the participants chose to listen to the syllables in their native language or not. Together, these results establish the current MD version as a valid and reliable method for administering the DL paradigm both in experimentally controlled as well as uncontrolled settings. Furthermore, the present findings support the feasibility of using smartphones in conducting large-scale field experiments.

Speech dominance is a better predictor of functional brain asymmetry than handedness: a combined fMRI word generation and behavioral dichotic listening study

An unresolved issue in behavioral studies of hemispheric asymmetry is why both left-handers and right-handers show a right ear advantage at the group level. In the present study we screened left-handers for left- versus right-hemisphere speech dominance with fMRI by comparing right versus left hemisphere frontal lobe activity (in Broca's area) in a silent word generation task. A left hemisphere dominant right-handed control group was included as well. All participants took part in a dichotic listening task with consonant-vowel syllables. The results showed that left-handers and right-handers with left-hemisphere speech dominance showed a right ear advantage. However, the left-handers with right hemisphere speech dominance had a left ear advantage. Thus, at the group level the direction of the ear advantage in dichotic listening was predicted by language dominance but not by hand preference. At the individual level, the dichotic task we used showed more variability than the fMRI results. Further research will have to indicate whether this is a feature inherent to dichotic listening, or whether the variability is due to alternative explanations such as a more bilateral representation of speech perception compared to speech production.

The sad, the angry, and the asymmetrical brain: dichotic listening studies of negative affect and depression

Dichotic Listening (DL) is a valuable tool to study emotional brain lateralization. Regarding the perception of sadness and anger through affective prosody, the main finding has been a left ear advantage (LEA) for the sad but contradictory data for the anger prosody. Regarding an induced mood in the laboratory, its consequences upon DL were a diminished right ear advantage (REA) for the induction of sadness and an increased REA for the induction of anger. The global results fit with the approach-withdrawal motivational model of emotional processing, pointing to sadness as a right hemisphere emotion but anger processed bilaterally or even in the left hemisphere, depending on the subject's preferred mode of expression. On the other hand, the study of DL in clinically depressed patients found an abnormally larger REA in verbal DL tasks which was predictive of therapeutic pharmacological response. However, the mobilization of the available left hemisphere resources in these responders (reflected in a higher REA) would indicate a remission of the episode but would not assure the absence of new relapses.

Reliability and magnitude of visual laterality effects: The influence of attention

Two studies investigated the test-retest reliability of laterality effects in visual tasks. In each of the studies, 160 right-handed participants were tested. In Experiment 1, a lexical decision task was used under four testing conditions: no control of attention, fixation control, bilateral presentation with endogenous cue, and bilateral presentation with exogenous cue. In Experiment 2, the same four conditions were used in a letter-matching task in which participants had to indicate whether two letters in a different case had the same name. Results showed a significant right visual field advantage in the first testing session. However, this advantage was eliminated in the second session, suggesting that attention was not fully controlled by any of the procedures. In addition, the reliability of laterality effects was greater when control of attention was applied. The discussion focuses on the importance of controlling attention when assessing laterality by means of a visual task. Alternative explanations of the present findings are also considered.

Beyond laterality: a critical assessment of research on the neural basis of metaphor

Metaphors are a fundamental aspect of human cognition. The major neuropsychological hypothesis that metaphoric processing relies primarily on the right hemisphere is not confirmed consistently. We propose ways to advance our understanding of the neuropsychology of metaphor that go beyond simple laterality. Neuropsychological studies need to more carefully control confounding lexical and sentential factors, and consider the role of different parts of speech as they are extended metaphorically. They need to incorporate recent theoretical frameworks such as the career of metaphor theory, and address factors such as novelty. We also advocate the use of new methods such as voxel-based lesion-symptom mapping, which permits precise and formal tests of hypotheses correlating behavior with lesions sites. Finally, we outline a plausible model for the neural basis of metaphor. (JINS, 2009, 16, 1-5.).

Atypical cerebral lateralisation in adults with compensated developmental dyslexia demonstrated using functional transcranial Doppler ultrasound

Functional transcranial Doppler ultrasound (fTCD) is a relatively new and non-invasive technique that assesses cerebral lateralisation through measurements of blood flow velocity in the middle cerebral arteries. In this study fTCD was used to compare functional asymmetry during a word generation task between a group of 30 dyslexic adults and a group of 30 non-dyslexic individuals. In light of previous evidence of atypical laterality in dyslexia, a reduced leftward asymmetry was predicted and confirmed. We know from previous research that most people with atypical language lateralisation have normal language and literacy skills: nevertheless, our results confirm that language laterality is reduced in those with dyslexia. Theoretical explanations for this apparent conundrum are discussed.

Response procedure and laterality effects in emotion recognition: implications for models of dichotic listening

The present study manipulated response procedure in a dichotic emotion recognition task as a means to investigate models of dichotic listening. Sixty-seven right-handed students were presented with dichotic pairs of the words bower, dower, power, and tower pronounced in a tone of sadness, anger, happiness, or neutrality. They were asked to identify the two emotional tones presented in each pair and completed the task twice, in two sessions separated by the administration of a handedness questionnaire. Participants completed the task under one of two response procedures. Thirty-four participants responded by crossing out face drawings corresponding to the emotions they perceived among four alternatives on a response sheet, whereas another group of 33 participants circled the corresponding words among four alternatives. Results revealed the expected left ear advantage (LEA) for emotion perception regardless of response procedure. However, the reliability of the LEA was greater with drawings than with words, whereas the magnitude of the LEA was substantially reduced in the second testing session for words when compared to drawings. These findings support a model of memory where the encoding and retrieval of nonverbal auditory material likely take place in the right cerebral hemisphere. Implications of these results for the representation of emotions in memory and models of dichotic listening are discussed.

A comparative analysis of functional cerebral asymmetry in lesbian women, heterosexual women, and heterosexual men

This study tested dichotic listening performance, a measure of functional cerebral asymmetry previously shown to be sexually dimorphic, in homosexual women (n=23), heterosexual women (n=27), and heterosexual men (n=24). All participants completed a verbal consonant-vowel dichotic listening task. On three laterality indices, heterosexual men displayed a significantly greater right-ear advantage compared to heterosexual women only. Homosexual women did not differ significantly from heterosexual men or from heterosexual women. Post-hoc comparisons (with a statistical correction) for each ear separately showed that heterosexual men displayed significantly greater right-ear scores compared to heterosexual women only. These data suggest that lesbian women are somewhat masculinized in their functional cerebral asymmetry. The results were interpreted in the context of sexual variation in models of linguistic hemispheric processing.

Visual half-field experiments are a good measure of cerebral language dominance if used properly: Evidence from fMRI

Traditional neuropsychology employs visual half-field (VHF) experiments to assess cerebral language dominance. This approach is based on the assumption that left cerebral dominance for language leads to faster and more accurate recognition of words in the right visual half-field (RVF) than in the left visual half-field (LVF) during tachistoscopic presentation. Information in the RVF is directly projected to the left hemisphere, whereas information presented in the LVF needs interhemispheric transfer to reach the left half of the brain. This interpretation of the RVF superiority for word recognition lacks direct evidence however, and a multitude of studies have lead to contradictory findings. To investigate this matter further we try to establish the ideal parameters for VHF experiments to measure language dominance, and subsequently compare laterality indices (LIs) obtained from RT patterns in bilateral VHF tasks to those LIs acquired in the same individuals during a mental word generation task in the fMRI scanner. Our results reveal a direct link between VHF advantages and individual language lateralization. Differences in behavioral performance between left-hemisphere dominant and right-hemisphere dominant individuals suggest that carefully designed VHF tests can be used as a reliable predictor of cerebral language dominance.

The influence of musical experience on lateralisation of auditory processing

The influence of musical experience on free-recall dichotic listening to environmental sounds, two-tone sequences, and consonant-vowel (CV) syllables was investigated. A total of 60 healthy right-handed participants were divided into two groups according to their active musical competence ("musicians" and "non-musicians"). In both groups, we found a left ear advantage (LEA) for nonverbal stimuli (environmental sounds and two-tone sequences) and a right ear advantage (REA) for CV syllables. Dichotic listening to environmental sounds was uninfluenced by musical experience. The total accuracy of recall for two-tone sequences was higher in musicians than in non-musicians but the lateralisation was similar in both groups. For CV syllables a lower REA was found in male but not female musicians in comparison to non-musicians. The results indicate a specific sex-dependent effect of musical experience on lateralisation of phonological auditory processing.

Fixation and attention control in lateralised target detection and free recall with words

The purpose of the present study was to test the hypothesis that lateralised target detection in the visual modality would produce results similar in magnitude, reliability, and validity to those obtained in the auditory modality with an analogue task. Thus, it was expected that it would produce laterality effects that are larger, more reliable, and more valid than those obtained in a free recall task. The claim that target detection provides its own attention control also led to the hypothesis that the magnitude of laterality effects should be affected by fixation control in free recall but not target detection. A total of 349 right-handed participants completed a word recognition task with either free recall or target detection with or without fixation control. Only the finding that free recall was generally more reliable than target detection went contrary to the hypotheses. This finding is interpreted as reflecting a consistent attentional bias that stems from task requirements. In general, the results suggest that target detection without fixation control has much potential as a measure of perceptual asymmetries in the visual modality.

Does Attentional Cueing Affect Dichotic Listening Performance in Children?

This study addresses the effects of verbal versus nonverbal (tone) shifts of attention on dichotic listening (DL) performance with children. Theoretically, a tonal cue may be more effective in increasing attention than a verbal cue following instruction. The inconsistency of studies reporting substantial effects of attention on ear asymmetries in children with or without learning disabilities (LDs) may be due to a developmental difference in their ability to use verbal or tone cues to select stimuli for recall. Participants included 30 right-handed children (15 control, 15 with LDs) with a mean age of 10.8 years. Each participant received 60 trials of a monaural tone cue task, 60 trials of a binaural verbal cue task, and 60 trials of a monaural verbal cue task, to direct attention to either the left or right ear before the presentation of consonant-vowel syllable pairs in a DL task. A factorial design analysis of variance yielded a significant right-ear advantage for both groups. More important, the Group x Task interaction was found to be significant, indicating that group performance on ear scores was dependent on type of cueing condition. Whereas all 3 cue conditions were effective in orienting attention for control participants, larger shifts were apparent under both binaural and monaural verbal instructional cue conditions. In contrast, participants with LD showed larger shifts of attention under the tonal cue condition. These results show that control participants have greater ability to focus attention with the use of a verbal cue, whereas participants with LD show greater ability to orient attention with the use of a tone cue in reducing error rates in DL performance.

Simultaneous masking in a dichotic emotion detection task

The present study investigated the possible role of ceiling effects in producing laterality effects of small magnitude in dichotic emotion detection. Twenty two right-handed undergraduate students participated in the present experiment. They were required to detect the presence of a target emotion in the expressions tones of happiness, sadness, anger, and neutrality presented dichotically. Stimuli were adjusted to 70 dB and occurred simultaneously with a white noise mask that had an intensity of 65, 70, 80, or 85 dB. Results showed a left ear advantage (LEA) for the 65 dB mask and a right ear advantage for the 85 dB mask, but only after two testing sessions. The possible existence of a generalized right ear bias that might affect the observed LEA for non-verbal tasks is discussed. Alternative explanations and limitations of the present experiment are also presented.

Sex influences on material-sensitive functional lateralization in working and episodic memory: Men and women are not all that different

Research investigating the effects of sex on the lateralization of language functions has produced mixed results to date, with some studies finding sex differences and others not [Shaywitz, B.A., Shaywitz, S.E., Pugh, K.R., Constable, R.T., Skudlarski, P., Fulbright, R.K., Bronen, R.A., Fletcher, J.M., Shankweiler, D.P., Katz, L., et al., 1995. Sex differences in the functional organization of the brain for language. Nature 373 607-609.; Frost, J.A., Binder, J.R., Springer, J.A., Hammeke, T.A., Bellgowan, P.S., Rao, S.M., Cox, R.W., 1999. Language processing is strongly left lateralized in both sexes. Evidence from functional MRI. Brain 122 (Pt 2) 199-208.]. Further, few studies have evaluated how any such sex effects extend to tasks involving cognitive functions that may utilize language processes such as working and episodic memory. This study examined sex difference in material-sensitive functional activation (using fMRI) in working memory and episodic memory that included either words and faces. We performed these analyses on two large groups of healthy subjects with the goal of attempting to replicate results across two independent data sets. The results indicated that both males and females showed strong and consistent evidence for material-sensitive lateralization for both working and episodic memory, such that word tasks resulted in greater left-sided activation and face tasks resulted in greater right-sided activation. Further, few of the sex differences in regions showing material specificity effects in at least one gender replicated across studies, providing little evidence for any differences in lateralization patterns between the sexes. In conclusion, our data suggest that males and females show a similar pattern of lateralized activation to material type during working memory and recognition tasks.

Dichotic target detection with words: a modified procedure

The purpose of the present study was to investigate the influence of attention on the magnitude and reliability of laterality effects in dichotic target detection. Twenty-five participants completed a dichotic target detection task requiring them to identify the ear to which a target word was presented. Correct left and right responses (LL and RR outcomes, respectively) produced a large and reliable right ear advantage (REA). Participants circled right when the target was presented to the left ear (LR outcomes) more often than they circled left when the target was presented to the right (RL outcomes). A combination of the LL+LR outcomes compared to RR+RL outcomes resulted in a reduced REA. Finally, cases where participants incorrectly responded left or right when the target was absent produced no systematic differences, reflecting the absence of a generalized bias to respond "right." The discussion emphasizes the usefulness of the approach presented here in producing a score that minimizes the attentional component of laterality effects.

Hemispheric asymmetry and deception detection

Previous research has indicated a possible right hemisphere advantage in deception detection including a possible left ear advantage in decoding deceptive statements. In this study, 32 undergraduate students listened to 112 true and false statements presented unilaterally to both the left and right ears. The participants responded using their left or right hand, indicating whether the statements they heard were true or false. It was found that there was a significant (p < .004) advantage for the left ear in detecting whether a statement was true or false. These findings replicate and extend previous research indicating a left ear/right hemisphere advantage in deception detection.

Reliability of non-verbal laterality effects in the visual modality

The present experiment investigated the reliability and magnitude of laterality effects in a non-verbal task in the visual modality. The use of a bilateral discrimination task in which participants indicated whether a centrally presented probe stimulus matched either of the bilaterally presented targets was presumed to provide control over attention deployment. This led to the prediction that a reliable left visual field advantage (LVFA) would be obtained. A total of 40 right-handed undergraduate students completed the bilateral discrimination task twice in a test-retest design. Although relatively large test-retest correlations suggested that the laterality effect was quite reliable, a significant LVFA was obtained in the first testing session, and a right visual field advantage in the second one. This finding parallels results obtained in previous work with non-verbal tasks and supports the notion that practice affects the direction of laterality effects. The discussion examines alternative explanations with emphasis on practice effects and possible attentional factors. A possible shift in the bivariate distribution of laterality scores is used as a tentative explanation of the apparent contradiction between the high test-retest reliability and the shift in laterality with practice.

Reliability and magnitude of perceptual asymmetries in a dichotic word recognition task

The hypothesis that control of idiosyncratic attention deployment and retrieval strategies would improve the reliability and magnitude of laterality effects obtained in an auditory word recognition task was investigated. Sixty participants completed a dichotic word recognition task under 1 of 3 conditions. In free recall, they reported the 2 words presented on each trial (1 to each ear). In focused attention, they reported only the word presented to a prespecified ear. In target detection, they indicated whether a target word was presented to either ear on each trial. Results showed that the target-detection condition produced the largest and most reliable laterality effects compared with the other 2 conditions. The mechanisms likely to be responsible for these findings are discussed.

Lateralized spatial processes and their lexical implications

Numerous lateralized tasks have been identified as involving spatial processing, but the extent to which they use the same spatial process is largely unknown. The present research investigated relationships among significant asymmetries from seven visuo-spatial and two verbal tasks, combining samples from previous factor analytic experiments with those from three new studies (combined N=789). All of the spatial intercorrelations were negligible (r<0.20), unlike previous outcomes finding robust correlations within certain clusters of verbal asymmetries. However, lateral differences involving spatial quantitative processing on the one hand and figure-ground separation on the other, showed significant but independent correlations with one from visual lexical processing (word recognition). The results support three major conclusions. First, there are at least several and possibly many lateralized spatial processes. Second, hemispheric processes follow a modular architecture in preference to a diffuse or parallel distributed architecture. Finally, the dissociated correlations are consistent with a visual lexical processing model having both occipital and parietal components, potentially reconciling a current controversy over the cerebral localization of language.

Reliability and magnitude of auditory laterality effects: the influence of attention

Three experiments investigated the effect of attention on the reliability and magnitude of laterality effects in a dichotic listening task. In Experiment 1, 40 undergraduate students were randomly assigned to either a free-recall or focused-attention condition. In Experiment 2, 40 undergraduate students completed a dichotic listening task with exogenous cueing. They were randomly assigned to either a 150-ms stimulus onset asynchrony (SOA) or a 450-ms SOA condition. In Experiment 3, 20 participants completed a task where the SOA for the exogenous cue was randomized on a trial to trial basis. Results indicated that focused attention increased the magnitude of the laterality effect. Contrary to predictions, this finding was not due to reduced variability in the focused-attention task compared to the free-recall task. In addition, a cueing tone was only effective at directing attention in Experiment 3. Specifically, a significant right ear advantage observed at the 150-ms SOA was reduced at the 450-ms SOA. It appears that, in Experiment 3, the tone was effective at controlling attention because it reduced the systematic bias that has been suggested to account for the laterality effects observed in dichotic tasks.

Gender differences in laterality on a dichotic task: the influence of report strategies

Four experiments were conducted to investigate the influence of report strategies on gender differences in laterality. Ten males and 10 females completed a dichotic consonant-vowels pairs task under four conditions manipulating reporting strategies. Free recall allowed participants to report syllables in any order they chose, whereas order of report control required the report of a pre-specified ear first. In focused attention, they reported only one response from a pre-specified ear. Finally, in ABX discrimination, participants were required to indicate whether a binaural probe was one of the stimuli presented dichotically on the same trial. It was hypothesized that improved control of report strategies would increase the likelihood of detecting significant gender differences in laterality. This was confirmed when results showed no significant gender differences in laterality for the free recall and order of report control conditions, whereas focused attention produced marginal gender differences and clearly significant differences were obtained in the ABX discrimination condition. These findings have implications for interpretations of gender differences in laterality based on strategy effects. Interpretations emphasize the role of attention deployment in the measurement of laterality.

Comparing the Fused Dichotic Words Test and the Intracarotid Amobarbital Procedure in children with epilepsy

The validity of the Fused Dichotic Words Test (FDWT) in predicting the nature of speech representation, as determined by the Intracarotid Amobarbital Procedure (IAP), was examined in a sample of 28 children with epilepsy. Various methods of analysis (difference score, lambda, and lambda(*)), for the FDWT data were calculated and compared. Results showed the validity of the FDWT did not change depending on the method of analysis. The difference scores showed that 18 of the 19 patients with left hemisphere speech obtained right-ear advantages, while the patient with right hemisphere speech showed a left-ear advantage. As a group, patients with left-hemisphere speech obtained a statistically significant right-ear advantage for the lambda and lambda(*) indices, while the patient with right-hemisphere speech showed a left-ear advantage that was also significant for both lambda measures. Patients with bilateral speech, as a group, displayed a non-significant ear advantage. Some of the scores from the left-hemisphere group overlapped with those from patients with bilateral speech representation. Controlling for stimulus dominance effects using the lambda(*) measure did not improve classification accuracy for nature of speech representation based on FDWT scores. Finally, comparison of our data using the laterality index from a similar study, showed scores smaller in magnitude than that found in adults with epilepsy.

Sex differences in functional cerebral asymmetries in a repeated measures design

The aim of the present study was to analyze whether task repetitions which are an inevitable part of repeated measures designs might induce performance alterations specific for gender and hemisphere. Male and female subjects conducted twice a lexical decision, a polygon recognition, and a face discrimination task as a visual half field paradigm with the two experimental sessions repeated by 2 weeks. The results show that only in female subjects can a session effect for the lexical decision and the polygon recognition task be demonstrated which is hemisphere specific. Thus, repeated measures designs seem to have a gender- and hemisphere-specific effects of their own which could confound with other variables under study.