Visual half-field presentations of incongruent color-words reveal mirror-reversal of language lateralization in dextral and sinistral subjects

Two experiments are reported concerning identification of left and right hemisphere dominance for language in dextral and sinistral subjects. A visual half-field (VHF) incongruent color-words paradigm was used. Color-words written in incongruent colors were presented either to the right or left half-field. Subjects were instructed to report the color, ignoring the color-word. Vocal reaction time (VRT) and frequency of errors were measured. Twenty dextral adult males were tested in Experiment 1. Results showed significantly more errors and a trend towards longer VRT:s when the words were presented in the right half-field, i.e. initially to the left hemisphere. No differences between half-fields were observed to color-stripes serving as control-stimuli. The results were followed up in Experiment 2 with a preselected sinistral group. All subjects in the sinistral group had revealed a left-ear-advantage (LEA) in a previous dichotic listening test, i.e. right hemisphere language dominance. The results from the VHF inconguent color-words test showed a reverse pattern of responding compared to the dextral group, i.e. more errors and longer VRTs when the color-words were initially presented to the right hemisphere.     

Stuttering, dichotic listening, and cerebral dominance.

Fully right-sided stutterers (35) and fully right-sided nonstutterers (35) had a dichotic listening task to test hypotheses that stutterers have incomplete cerebral lateralization or reversed lateralization of speech function, or both. An assumption of the procedure is that a right-ear preference indicates left-cerebral dominance for speech. Six stutterers and no nonstutterers showed a reversal, ie, a left-ear preference. As a group, the remaining stutterers who showed no such reversal were the same as nonstutterers in the magnitiude of the right-ear preference. This suggests that a subset of stutterers may have an anomaly in the lateralization of speech functions. A nonsignificant tendency emerged for stutterers to show smaller between-ear differences on the test, consistent with the hypothesis that stutterers have less or incomplete lateralization of speech function than nonstutterers.     

Regional cerebral blood flow correlates of a dichotic listening task

This investigation was designed to test the hypothesis that ear advantage on a dichotic listening (DL) task of pitch discrimination reflects asymmetries in the metabolic activities of the temporal lobes. Fourteen normal subjects, with either a left-ear advantage (LEA) (n = 9) or a right-ear advantage (REA) (n = 5) on the DL task, underwent measurements of regional cerebral blood flow (rCBF) during a resting baseline condition and during performance on the DL task. For both groups, the DL task was associated with selective and significant increases in rCBF to the contralateral posterior temporal lobe. Our finding of selective rCBF activation with dichotic stimulation may have potential implications for an understanding of the functional organization of the cerebral hemispheres.     

Occupation and dichotic listening performance

A previous study has shown that dichotic listening performance was related to occupation (Govier & Bobby, 1994). That experiment used subjects drawn from a variety of professional occupations. The experiment described here tested the dichotic performance of male and female subjects in a single professional setting; medicine. Male and female doctors and male and female nurses were tested on a dichotic listening task. The results indicated that pattern of dichotic performance was more closely associated with occupation than biological sex, and were interpreted as supporting the view that both occupational choice and dichoticlistening asymmetries depend on biologically determined aspects of brain organisation.     

The effect of asymmetrically focused attention upon subsequent ear differences in dichotic listening

In a series of four experiments, normal right-handed adults engaged in dichotic listening with free-report instructions after having completed a selective listening task. The usual right-ear advantage (REA) for dichotic digit names was altered accordingto the ear previously monitored. Most notably, the REA was absent subjects who had monitored the left ear. Additional experiments showed that the “priming bias” is material-specific; it did not occur if consonant-vowel nonsense syllables (CV's) were subtituted for digit names in either the selective listening task or the subsequent free-report test. The findings help clarify the nature of one of the attentional mechanisms that influence auditory laterality.     

Ultradian rhythms in cerebral laterality tested by a verbal dichotic listening paradigm

Dichotic listening (DL) performance of normal (healthy) adults was tested every 15 minutes continuously during 8-12 hours of daytime. The dichotic material consisted of 8 blocks, each containing 40 pairs of monosyllabic, concrete nouns in German. The subjects heard one block per each 15-min trial. DL performances determined by the number of correct free recalls gave no evidence for periodic variations, neither of right nor of left-ear performance. However, when determined by the number of first, but correctly recalled nouns DL performance showed distinct periodicities of about 3-4 hours at least in some subjects. Such periodicities were obvious in both right and left-ear DL performance and oscillated in counter-phase. This suggests that competitive processing of dichotic verbal stimuli mediated by the cerebral hemispheres could be modulated by an endogenous oscillatory system. Some subjects slept in the laboratory after they had performed in a long-term dichotic listening task. Since sleep stage was scored by means of electroencephalographic recordings phase relationships between ultradian cycles of DL performance and the sleep cycle could be analyzed. These findings suggest that sleep cycle of about 1 1/2-2 hours and the 3-4 hour periodicities of DL performance are organized in an approximately 1:2 period ratio of an intrinsic multi-oscillatory system.     

Flow-cytometric analysis of T-lymphocyte subsets in sinistral and dextral patients with gingivitis

The aim of this study was to determine whether there was any change in T-lymphocyte subsets in sinistral and dextral patients with gingivitis. The study was carried out on 36 patients (16 males and 20 females) with gingivitis. The age of the patients ranged from 16 to 25 (mean age = 18.50 +/- 3.85). Patients were divided into two equal groups according to their right or left hand use. Being right- or left-handed was determined with Edinburgh Handedness Inventory (Oldfield). At the beginning of the study, gingival index (GI-L?e-Silness) and plaque index (PI-Silness-L?e) scores were recorded in order to assess the gingival tissue health in patients. At the same time, the biopsy samples were taken from the gingival pocket wall tissues at sites of gingivitis. Then, CD4+ and CD8+ lymphocyte and CD4/CD8 ratio values were determined using flow-cytometry in the biopsy samples. The two groups were compared by using Student's t-test. The normal value in peripheral blood of CD4+ lymphocyte and that of CD8+ lymphocyte are 25-29% and 19-48%, respectively. According to flow cytometry findings, in both sinistrality and dexterity with gingivitis, CD+ and CD8+ lymphocyte values were under the normal value while the CD4/CD8 rate was within normal distribution interval. CD4+ lymphocyte values observed in the sinistral patients were found to be lower than those in the dextral patients. The difference between the CD8+ lymphocyte values in left-handed patients and that obtained in right-handed patients was not found to be statistically significant while the difference between the CD4+ lymphocyte values in left-handed patients and that obtained in right-handed patients was found to be statistically significant (p < .05). In addition, the difference between the CD4/CD8 rate obtained in left-handed patients and that obtained in right-handed patients was found to be statistically very significant (p < .001). Consequently, these findings suggested CD4+ lymphocyte value and CD4/CD8 rate was lower in sinistrality. Sinistrality and dexterity may play an important role in local immune response.     

Auditory extinction and dichotic listening CV task in cerebral infarction: preliminary report

Six stroke patients were studied using a dichotic listening CV task, 4 with left hemisphere infarction, 2 with right hemisphere infarction. It was observed a "lesion-effect", a shift of hemisphere prevalence to the side opposite a brain lesion. The authors suggest that the lesion-effect can be explained by the auditory extinction phenomenon at the linguistic level.     

Verbal and nonverbal dichotic listening test. Influence of the hemispheric activation state in normal subjects

The dichotomic listening test provides data for assessment of cerebral hemisphere activities in response to a given stimulus. Variations in results following verbal and non-verbal dichotomic listening tests to familiar sounds are described, as well as modifications when the activity of one or other hemisphere has been previously altered. Findings demonstrate that voluntary excentration of gaze modifies inter-hemispheric equilibrium and affects the results of the non-verbal dichotomic listening test.     

Material type and attention control in dichotic listening

The present study investigated the effects of semantic and emotional content on laterality effects found in focused attention dichotic listening tasks. A total of 80 right-handed participants completed one of four conditions. They were presented either with dichotic pairs of consonant-vowel (CV) syllables (ba, da, ga, ka, pa, or ta) or words (bower, dower, power, or tower), pronounced in either a neutral tone or one of four emotional tones (happy, sad, angry, neutral). In all conditions, participants were instructed to circle the stimulus presented to the attended ear on each trial. The attended ear was randomised between blocks of trials for each participant. A significant condition by ear attended by ear of presentation interaction emerged. The typical right ear advantage (REA) was found in the neutral conditions, regardless of ear attended. In contrast, the emotional conditions revealed an REA when participants focused on the right ear, whereas a left ear advantage was found when they focused on the left ear. These findings suggest that the emotional component resulted in a shift in ear advantage coinciding with instructions possibly because of the influence of this component on attention and task difficulty. The role of semantic processing in words versus syllables is also discussed.     

Material type and attention control in dichotic listening

The present study investigated the effects of semantic and emotional content on laterality effects found in focused attention dichotic listening tasks. A total of 80 right-handed participants completed one of four conditions. They were presented either with dichotic pairs of consonant-vowel (CV) syllables (ba, da, ga, ka, pa, or ta) or words (bower, dower, power, or tower), pronounced in either a neutral tone or one of four emotional tones (happy, sad, angry, neutral). In all conditions, participants were instructed to circle the stimulus presented to the attended ear on each trial. The attended ear was randomised between blocks of trials for each participant. A significant condition by ear attended by ear of presentation interaction emerged. The typical right ear advantage (REA) was found in the neutral conditions, regardless of ear attended. In contrast, the emotional conditions revealed an REA when participants focused on the right ear, whereas a left ear advantage was found when they focused on the left ear. These findings suggest that the emotional component resulted in a shift in ear advantage coinciding with instructions possibly because of the influence of this component on attention and task difficulty. The role of semantic processing in words versus syllables is also discussed.     

A signal detection procedure eliminates priming biases in dichotic listening

Dichotic digit names were presented to normal right-handed adults in two experiments, the first of which used a standard free report procedure and the second of which used a signal detection procedure. Prior to each test, a priming bias was generated by having subjects monitor either the left or right ear for 30 selective listening trials. The expected priming effect was found in Experiment 1: ear asymmetry and order of report were altered according to the ear previously monitored. In contrast, no priming effect was observed with the signal detection procedure used in Experiment 2. There was a right-ear advantage in sensitivity irrespective of the ear previously monitored. The findings suggest that priming biases act by altering the order in which multiple stimuli are processed and reported.     

Effects of attention on dichotic listening: an 15O-PET study

The present study investigated the effect of attention on brain activation in a dichotic listening situation. Dichotic listening is a technique to study laterality effects in the auditory sensory modality. Two different stimuli were presented simultaneously, one in each ear. Twelve subjects listened to lists of consonant-vowel syllables, or short musical instrument passages, with the task of detecting a "target" syllable or musical instrument by pressing a button. The target stimulus appeared an equal number of times in the left and right ear. The subjects were instructed to either concentrate on the stimuli presented in both ears, or only on the left or right ear stimulus. Brain activation was measured with 15O-PET, and significant changes in regional normalized counts (rNC) were evaluated using statistical parametric mapping (SPM96) software. Concentrating on either the right or left ear stimulus significantly decreased activity bilaterally in the temporal lobes compared to concentrating on both ear stimuli, at the expense of an increased activation in the right posterior and inferior superior parietal lobe. The CV-syllables activated areas corresponding to the classic language areas of Broca and Wernicke. The musical instrument stimuli mainly activated areas in visual association cortex, cerebellum, and the hippocampus. An interpretation of the findings is that attention has a facilitating effect for auditory processing, causing reduced activation in the primary auditory cortex when attention is explicitly recruited. The observed activations in the parietal lobe during the focused attention conditions could be part of a modality non-specific "attentional network".     

Motor correlates of dichotic listening asymmetries in children

The purpose of this study was to determine the predictive relation between incidence of unintended motor overflow and degree of asymmetry on a dichotic word identification task in children. Seventy-eight third grade girls and 67 fifth grade boys were seen longitudinally over a 2-yr period. Among girls, incidence of overflow, primarily contralateral, accounted for nearly 20% of the variance in dichotic listening scores; but the results were not reliable for boys. The findings support the contention that suppression of the non-dominant hemisphere is an important mechanism underlying dichotic listening performance.     

Replication of a premenstrual decrease in right-ear advantage on language-related dichotic listening tests of cerebral laterality

Five fused dichotic word tasks measured perceptual asymmetry in 30 women at 4 weekly intervals. The five tasks varied according to whether the stimuli presented were word-word pairs or nonsense word-pairs, or whether they consisted of neutral words paired with positive emotion-evoking words (e.g. hug-tug), neutral words paired with negative emotion-evoking words (e.g. till-kill), or neutral words paired with neutral words (e.g. bean-dean). Overall right-ear advantage (REA) decreased in the premenstrual week relative to the postmenstrual week, replicating previous results using identical measures. In addition, REA scores were similar at menstrual, postmenstrual and midcycle weeks. Additional data from 12 men suggests sex differences in task performance were small or non-existent. In both women and men, there were no effects of repeated testing on REA, but emotional proclivity indices, defined as the tendency to recall words of positive or negative affective tone, increased across the four test sessions. As found previously, there was a trend for women to hear fewer positive words during the premenstrual week. These data are consistent with other research suggesting that a progesterone-mediated decrease in functional asymmetry occurs in the luteal phase. Future research manipulating task demands (e.g. memory load) or the affective valence of the stimuli may be useful in understanding the observed changes in hemispheric advantage.     

Left ear performance in dichotic listening following commissurotomy

Contribution of the left ear stimulus to dichotic listening performance following commissurotomy was studied in five patients. In two tasks, subjects were asked to identify in writing both members of a pair of competing stimuli, either digits or CV syllables. A third task required subjects to integrate high and low frequency components of a single word presented dichotically. Left ear performance was at chance level for CV syllables but exceeded 80% for four out of five patients on the digit stimuli. All patients showed evidence of being able to utilize left ear information in the dichotic fusion task. Results indicate that apparent supression of left ear material in the dichotic task is a function of spectral-temporal overlap between competing stimuli.