Brain asymmetry in directing attention during dichotic listening test: An fNIRS study.

In a classical dichotic listening paradigm, besides auditory brain asymmetry, cognitive functions such as attention and conflict resolution play a major role. The aim of this study is to reveal the possible haemodynamic mechanisms of higher attentional performance in prefrontal cortex during dichotic listening test. Twenty-six healthy participants underwent a dichotic listening task in three sessions; non-forced attention, attention focused to right ear, and attention focused to left ear. In each session, haemodynamic activity of prefrontal brain area was recorded using functional near-infrared spectroscopy (fNIRS). Effects of focused attention and performance level of the task on oxy-, deoxy-, and total haemoglobin levels were investigated. Oxy- and total haemoglobin levels in right prefrontal regions during forced-right and forced-left sessions were significantly higher than levels of the non-forced session. This might be an indicator of inhibition and orienting attentional functions of right inferior frontal gyrus. High performers had significantly higher deoxyhaemoglobin levels in the forced-left session compared to the non-forced session, while low performers' deoxyhaemoglobin levels did not differ among these sessions. Observing this difference only in the forced-left session but not in the forced-right session might suggest conflict resolution in top-down and bottom-up processes during the forced-left session for right-handed participants.

Meaning in meaninglessness: The propensity to perceive meaningful patterns in coincident events and randomly arranged stimuli is linked to enhanced attention in early sensory processing.

Perception of objectively independent events or stimuli as being significantly connected and the associated proneness to perceive meaningful patterns constitute part of the positive symptoms of schizophrenia, which are associated with altered attentional processes in lateralized speech perception. Since perceiving meaningful patterns is to some extent already prevalent in the general population, the aim of the study was to investigate whether the propensity to experience meaningful patterns in co-occurring events and random stimuli may be associated with similar altered attentional processes in lateralized speech perception. Self-reported and behavioral indicators of the perception of meaningful patterns were assessed in non-clinical individuals, along with EEG auditory evoked potentials during the performance of an attention related lateralized speech perception task (Dichotic Listening Test). A greater propensity to perceive meaningful patterns was associated with higher N1 amplitudes of the evoked potentials to the onset of the dichotically presented consonant-vowel syllables, indicating enhanced automatic attention in early sensory processing. The study suggests that more basic mechanisms in how people associate events may play a greater role in the cognitive biases that are manifest in personality expressions such as positive schizotypy, rather than that positive schizotypy moderates these cognitive biases directly.

Selective attention to emotional prosody in social anxiety: a dichotic listening study.

The majority of evidence on social anxiety (SA)-linked attentional biases to threat comes from research using facial expressions. Emotions are, however, communicated through other channels, such as voice. Despite its importance in the interpretation of social cues, emotional prosody processing in SA has been barely explored. This study investigated whether SA is associated with enhanced processing of task-irrelevant angry prosody. Fifty-three participants with high and low SA performed a dichotic listening task in which pairs of male/female voices were presented, one to each ear, with either the same or different prosody (neutral or angry). Participants were instructed to focus on either the left or right ear and to identify the speaker's gender in the attended side. Our main results show that, once attended, task-irrelevant angry prosody elicits greater interference than does neutral prosody. Surprisingly, high socially anxious participants were less prone to distraction from attended-angry (compared to attended-neutral) prosody than were low socially anxious individuals. These findings emphasise the importance of examining SA-related biases across modalities.

Can an observational method of assessing hand preference be used to predict language lateralisation?

The current study investigated (a) whether or not the WatHand Cabinet Test (WHCT, Bryden, Roy, & Spence, 2007) could be used as accurately as the Waterloo Handedness Questionnaire (WHQ) to classify individuals into language lateralisation groups based on their hand preference, and (b) the relationship between direction and degree of hand preference and language lateralisation. A total of 142 participants (82 right-handers and 60 left-handers) completed the WHQ and the WHCT, and performed a fused-words dichotic listening test. Findings indicated that the WHCT was robust alternative to the WHQ in providing a measure of hand preference as there was a high correlation between the WHCT and the WHQ, and individuals were divided into similar language lateralisation groups when using either the WHCT or the WHQ as the classifying variable. More specifically, there existed a predictable pattern of language lateralisation into which members of different handedness groups fell. The same pattern exists whether handedness is defined using subjective questionnaires or more objective observational measures of hand preference.

Effect of dichotic listening on self-reported state anxiety.

The present study examined the relationship between dichotic speech recognition and state anxiety. State anxiety, as determined by the State-Trait anxiety inventory (STAI), was measured pre- and post-dichotic testing in a group of young adults with normal hearing. Dichotic speech recognition was measured for three types of speech stimuli: 3-pair digits, monosyllabic words, and consonant-vowels. Results revealed significant increases in state anxiety as a function of dichotic testing for all stimulus types. There was not a significant difference, however, in state anxiety between the stimulus types. A subset of subjects (n=44) repeated the experiment a second time. There were no significant differences in state anxiety experienced due to dichotic listening between the two sessions. Results from the present study confirm that dichotic listening induces significant increases in state anxiety in a group of young adults with normal hearing. Although statistically significant, the mean increase in state anxiety does not exceed normative levels for college students. Further, the effect of anxiety on dichotic speech recognition performance appears minimal in this population.

Temporal dynamics of selective attention during dichotic listening.

The ability to selectively attend to one sound and ignore other competing sounds is essential for auditory communication. Subjects in our study detected occasional changes in the frequency of amplitude modulation in sounds presented to one ear while ignoring sounds in the other ear. Neuromagnetic source analysis revealed attention-related activity in a cortical network including primary auditory cortices, posterior superior temporal gyri, inferior parietal lobules (IPLs), inferior frontal gyri (IFG), and medial frontal gyri. Time courses of event-related magnetoencephalography responses were analyzed during the interval between stimulus presentation and behavioral response. Enhanced neural responses to targets and standards in the attended ear indicated early modulation of sensitivity in the attended sensory channel. A subsequent process of discriminative stimulus selection was indexed by a response increase over time for targets and decreasing activity for standards. Enhanced responses to deviants in the unattended ear indicated discriminative processing of unattended inputs as well, though to a lesser extent than for attended stimuli. Superior temporal gyrus, planum temporale, and the IPL were prominently involved in stimulus selection, whereas medial frontal regions were linked to initiation of behavioral responses and sustained activity in IFG suggested a role in attentional control.

Reliance on visible speech cues during multimodal language processing: individual and age differences.

The current study demonstrates that when a strong inhibition process is invoked during multimodal (auditory-visual) language understanding: older adults perform worse than younger adults, visible speech does not benefit language-processing performance, and individual differences in measures of working memory for language do not predict performance. In contrast, in a task that does not invoke inhibition: adult age differences in performance are not obtained, visible speech benefits language performance, and individual differences in working memory predict performance. The results offer support for a framework for investigating multimodal language processing that incorporates assumptions about general information processing, individual differences in working memory capacity, and adult cognitive aging.

Verbal dichotic listening in right and left-handed adults: laterality effects of directed attention.

Dichotic listening performance of consonant vowel stimuli was studied in 51 adult right- and left-handers in three attention conditions: non-directed and directed to either the right or left ear. In the non-directed condition, a significant right-ear advantage was found in both handedness groups with a stronger asymmetry in right-handers. There are at least three explanations for this ear bias. The classic or structural hypothesis suggests that to the right ear projects more strongly to the language dominant left hemisphere. The callosal relay hypothesis is based on the influence of inhibitory connections via the corpus callosum. The attentional hypothesis suggests that each hemisphere primarily directs attention to contralateral space and because the left hemisphere is dominant for language in both groups, and is aroused by speech stimuli, attention is primarily directed to the right ear. Neither hypothesis can explain why greater than 95% of right-handers have left hemisphere language dominance, but only 70-80% have a right ear bias. Our results demonstrate that in the directed attention conditions both groups increased their lateral biases when directed to either the right or left. The classic or structural hypothesis cannot account for these changes, thereby providing support for the attentional hypothesis. In addition, the right-handed subjects exhibited a greater shift of bias than did the left-handed subjects, when directing their attention leftward. This finding suggests that right-handed people are better able to shift their attention than left-handed people.

Increased cortisol and decreased right ear advantage (REA) in dichotic listening following a negative mood induction.

This study aimed to evaluate neuroendocrine responses and changes in perceptual asymmetry following an induced negative affect. Cortisol increasing in response to negative affect has been reported, while current brain models of emotion processing link negative affect to the right hemisphere. In this study, the Velten Mood Induction Procedure was used to generate neutral or negative affect in 44 healthy subjects. The PANAS scales were used to assess self-reported mood. A consonant-vowel dichotic listening (DL) test was applied after the neutral and negative affect inductions, and levels of salivary cortisol were determined by radioimmunoassay. For the negative affect condition, and congruent with the hypothesis tested, PANAS positive scores diminished (p<0.001) and PANAS negative scores increased (p<0.001), yielding an inverse correlation between them. A significant increase in cortisol levels was also seen (p<0.04). When taking cortisol reactivity into account, PANAS negative scores were higher for high-than for low-cortisol responders (p<0.02). Regarding DL, an increase in left ear items (p<0.04) and a decrease in right ear items (p<0.03) reported for those subjects who obtained a right ear advantage in the neutral condition. An explanation in terms of Kinsbourne's model for attentional-activation influences on DL is postulated and implications for the issue of affective illness are also discussed.

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.

Postrecognition of interleaved melodies as an indirect measure of auditory stream formation.

Primitive processes involved in auditory stream formation are measured with indirect, objective method. A target melody interleaved with a distractor sequence is followed by a probe melody that was identical to the target or differed by 2 notes. Listeners decided whether the probe melody was present or not in the composite sequence. Interleaved melody recognition is not possible when distractor sequences have the same mean frequency and maximum contour crossover with target melodies. Performance increases with mean frequency separation and timbral dissimilarity and is unaffected by the duration of the silent interval between composite sequence and probe melody. The relation between this indirect task measuring the interleaved melody recognition boundary and direct judgments measuring the fission boundary is discussed.

On the reliability of laterality effects in a dichotic emotion recognition task.

The present study examined the reliability of a dichotic emotion recognition task under three different conditions presumed to provide different levels of control of attention deployment. Sixty right-handed undergraduate students were randomly assigned to one of the three conditions. The task involved dichotic presentation of words pronounced in an angry, happy, sad, or neutral, emotional tone. The free recall condition applied no attention control. It required participants to report the emotion heard in each ear. Both the monitoring and ABX conditions presumably forced participants to divide their attention equally between the ears. In monitoring, participants were required to indicate when a target emotion was presented to either ear. Finally, the ABX condition required participants to indicate whether the emotional tone of a binaural stimulus matched either of the dichotic stimuli on the same trial. Results showed the expected left ear advantage (LEA). In addition, the monitoring and ABX procedures were found to be somewhat more reliable than the free recall procedure. The present study suggests that control of attention deployment strategies is critical in the reliable assessment of laterality. Issues related to task difficulty and its effect on the reliability and magnitude of laterality effects are also discussed.