The bilateral field advantage on a letter-matching task

Electrophysiological Evidence for Interhemispheric Connectivity and Communication in Young Human Infants

Little is known empirically about connectivity and communication between the two hemispheres of the brain in the first year of life, and what theoretical opinion exists appears to be at variance with the meager extant anatomical evidence. To shed initial light on the question of interhemispheric connectivity and communication, this study investigated brain correlates of interhemispheric transmission of information in young human infants. We analyzed EEG data from 12 4-month-olds undergoing a face-related oddball ERP protocol. The activity in the contralateral hemisphere differed between odd-same and odd-difference trials, with the odd-different response being weaker than the response during odd-same trials. The infants' contralateral hemisphere "recognized" the odd familiar stimulus and "discriminated" the odd-different one. These findings demonstrate connectivity and communication between the two hemispheres of the brain in the first year of life and lead to a better understanding of the functional integrity of the developing human infant brain.

Exploratory study of a screening measure for polycystic ovarian syndrome, quality of life assessment, and neuropsychological evaluation

Background

The universally adopted 2018 PCOS medical diagnostic and treatment guidelines for Polycystic Ovarian Syndrome (PCOS) cites the need for a brief screening measure that can be easily administered in the clinical care setting. We evaluate a 12-item questionnaire emphasizing the medical symptoms of PCOS with a group of women with PCOS as well as comparison samples of college women not diagnosed with PCOS.

Method

Of 120 undergraduate psychology women 18 to 41 years of age, 86 screened negative on a 12-item PCOS symptoms inventory. They were compared to a group of PCOS patients diagnosed medically in a manner consistent with the Teede et al. (2018) evidence-based diagnostic guidelines. The screen-positive, screen-negative, and PCOS-confirmed groups were compared on the PCOS Quality-of-Life (QoL) questionnaire, Zung Self-Rating Depression Scale (ZDS), Spielberg State-Trait Anxiety Inventory (STAI), Fatigue Symptom Inventory (FSI), Spiritual well-being and Spiritual Beliefs Inventories, the computerized Automated Neuropsychological Assessment Metric (ANAM) battery, and an experimental tachistoscopic Bilateral Perceptual Asymmetries Letter and Dots Matching Bilateral Field Advantage (BFA) test (to evaluate the effects of early brain androgenization possible from PCOS). For each questionnaire and neuropsychological performance principal outcome, the Linear Mixed Effects (LME) model was employed to evaluate the predictive significance of demographic characteristics and group membership (confirmed cases, screen negative and screen positive cases) for these outcomes.

Results

The PCOS-confirmed women scored more poorly than the screen-negative (reference) and screen-positive groups on all the measures of physical, emotional, social, and spiritual well-being measures. On the ANAM neuropsychological battery, PCOS-confirmed women did more poorly on Sternberg Memory and Stimulus Response throughput measures. They also had slower correct response speed for both the unilateral and bilateral dot- and letter-matching tachistoscopic stimulus presentations. However, the bilateral field advantage throughput performance ratio did not differ among groups, which is a global measure of bilateral versus unilateral brain/behavior asymmetries.

Conclusion

PCOS screening can be a feasible and important part of women’s healthcare. PCOS-confirmed women should receive not only the medical standard of care from the 2018 guidelines, but also comprehensive psychosocial and neurocognitive support to enhance their quality of life.

Inter-hemispheric dynamics revealed by reaction time in the Dimond paradigm

The Dimond paradigm (DP) consists of tachistoscopically presenting two stimuli to be discriminated--either both stimuli in a single visual hemifield or one in each. The DP has recently been implemented using predecessors to index homotopy of the callosal fibre projection with reaction time (RT) as the dependent measure. Using simple perceptual discrimination tasks, it has recently been reported that the advantage of the unilateral stimulation condition significantly decreases with practice. This effect has been interpreted as being due to the plasticity of the callosal network. Two experiments were designed to replicate these two little-known effects, namely callosal homotopy and callosal network plasticity. In addition, new evidence of another type of callosal network plasticity, termed "callosal network dispatching", was sought by introducing double manipulation of orientations of both stimulus-contours and inter-stimulus arrays to the DP. Strong support for the callosal homotopy and callosal network plasticity effects was obtained. In addition, evidence for a "callosal network dispatcher" effect accrued.

Intra and inter hemispheric dynamics revealed by reaction time in the Dimond paradigm: a quantitative review of the literature

In stimulus matching tasks requiring discrimination of two unilaterally or bilaterally presented stimuli (Dimond paradigm), a well established intrahemispheric processing bottleneck model predicts that an increase in task difficulty as measured by reaction time should provide an advantage to bilateral stimulations. The purpose of the current investigation was to review the entire relevant literature on the Dimond paradigm and identify the experimental variables which reliably yield such effects. Forty nine experimental effects compatible with the "intrahemispheric processing bottleneck" model and 26 contrary effects were found. Manipulation of the complexity of the stimulus matching criterion significantly produced intrahemispheric bottleneck effects. This effect was also significantly greater when non-target stimuli required heavier processing. These two findings support the intrahemispheric bottleneck model: computationally complex tasks seem to overload a hemisphere׳s processing capacity, an effect seen in the unilateral presentation conditions. However, manipulating the similarity of target stimuli produced contrary effects. Contrary effects were also obtained more readily when two physical matching tasks were compared. These two latter effects may best be explained as low level visual-perceptual limitations of interhemispheric transfer or integration.

Behavioural indexes of callosal functioning in Williams syndrome

Williams syndrome (WS) is a neurogenetic disorder that stems from a microdeletion on chromosome 7. Recent anatomical studies have found evidence for corpus callosum abnormalities in WS. However, to date, the impact of these structural differences on callosal functionality remains unclear. The aim of the present study was to investigate interhemispheric communication and hemispheric asymmetry in individuals with WS relative to mental age-matched controls. This was assessed using bilateral and unilateral presentations of visual stimuli in a picture-naming task. Results found both groups to exhibit a bilateral field advantage and a left visual advantage on unilateral presentations. However, while a significant performance increase with age was found for controls, no such correlation was found for individuals with WS. Taken together, these findings suggest that despite some evidence for an atypical developmental pathway in WS, both interhemispheric communication and hemispheric asymmetry are functionally intact in this population.

Bilateral attentional advantage on elementary visual tasks

We examined interactions between and within the left and right visual hemifields using elementary visual tasks. Each trial required identifying a letter at fixation and then either discriminating the orientation of (experiment 1) or detecting (experiment 2) peripheral Gabor targets. On half the trials Gabor distracters were presented between the Gabor targets, and were either restricted to one lateral hemifield (unilateral condition) or presented across the left and right hemifields (bilateral condition). Orientation discrimination and detection each exhibited bilateral superiority only when distracters were present. The results confirm bilateral superiority in attentional selection, even on these most elementary visual tasks.

Homotopy and heterotopy and the bilateral field advantage in the Dimond paradigm

Pairs of homotopic and heterotopic visual bilateral stimuli and pairs of unilateral visual stimuli were presented to 12 normal right-handed university students requiring a key press if they were of the same form. As predicted from the known histology of the corpus callosum (massive preponderance of homotopic fibers), homotopic presentations yielded significantly faster reaction times than heterotopic stimulations. Bilateral pairs of stimuli were also advantaged in comparison with unilateral trials, replicating Sereno and Kosslyn [Sereno, A. B., & Kosslyn, S. M. (1991). Discrimination within and between hemifields: a new constraint on theories of attention. Neuropsychologia, 29, 659-675]. Moreover, certain attentional processes have never been investigated in the Dimond paradigm and this study provides evidence to the effect that discriminative reaction times to stimulus pairs are strongly influenced by their proximity to the fixation point. In similar previous experiments, the homotopy/heterotopy observation and the bilateral field advantage may have been distorted by that particular confound, as well as several others.

Interhemispheric resource sharing: Decreasing benefits with increasing processing efficiency

Visual matches are sometimes faster when stimuli are presented across visual hemifields, compared to within-field matching. Using a cued geometric figure matching task, we investigated the influence of computational complexity vs. processing efficiency on this bilateral distribution advantage (BDA). Computational complexity was manipulated by requiring different types of match decision (physical identity vs. category identity) and processing efficiency was varied by on-task training A pronounced BDA, initially present in both tasks, completely disappeared in the course of training for the less complex and decreased for the more complex task. Thus, the size of the BDA is determined by both, processing efficiency and task complexity.

The stability of compromised interhemispheric processing in callosal dysgenesis and partial commissurotomy

The persistence and stability of selective deficits in interhemispheric processing resulting from known callosal pathology have been monitored over periods ranging from ten to thirty five years. The present study included five patients: two with complete agenesis of the corpus callosum, one with partial dysgenesis, and two with a partial section of the corpus callosum. A crossed-uncrossed difference task and four bilateral visual matching tasks were administered to these patients and to groups of normal individuals matched on age and intelligence. As expected, all of the patients showed deficits in speed or accuracy relative to the performance of their control groups. The profile of performance for each patient across the five tasks demonstrated a systematic (but not perfectly consistent) relationship with the location and extent of callosal pathology.

Normal development of bilateral field advantage and evoked potential interhemispheric transmission time

Implications of the developmental progression of myelination of the corpus callosum were studied using evoked potential interhemispheric transmission time (EP-IHTT) and the bilateral field advantage (BFA) in letter matching. Forty-two normal children aged 7 to 17 years were asked to respond regarding whether 2 letters matched when presented either unilaterally (both in the same visual field) or bilaterally (1 letter in each field). Evoked potentials were recorded with bilateral midparietal electrodes during unilateral presentations of the letter-matching task. Age-related changes were found for both EP-IHTT and BFA. BFA in reaction time in the visual letter-matching task increased significantly with age. Decreasing EP-IHTT with age was also evident (although only in a statistical trend). These findings lend support to the hypothesis that increased callosal myelination during late childhood has functional significance. Callosal maturation appears to result in faster interhemispheric transfer and increasing ability to integrate information across the midline.

Visuo-spatial neural response interactions in early cortical processing during a simple reaction time task: a high-density electrical mapping study

The timecourse and scalp topography of interactions between neural responses to stimuli in different visual quadrants, straddling either the vertical or horizontal meridian, were studied in 15 subjects. Visual evoked potentials (VEPs) were recorded from 64 electrodes during a simple reaction time (RT) task. VEPs to single stimuli displayed in different quadrants were summed ('sum') and compared to the VEP response from simultaneous stimulation of the same two quadrants ('pair'). These responses would be equivalent if the neural responses to the single stimuli were independent. Divergence between the 'pair' and 'sum' VEPs indicates a neural response interaction. In each visual field, interactions occurred within 72-86 ms post-stimulus over parieto-occipital brain regions. Independent of visual quadrant, RTs were faster for stimulus pairs than single stimuli. This replicates the redundant target effect (RTE) observed for bilateral stimulus pairs and generalizes the RTE to unilateral stimulus pairs. Using Miller's 'race' model inequality (Miller J. Divided attention: evidence for coactivation with redundant signals, Cognitive Psychology 1982;14:247-79), we found that probability summation could fully account for the RTE in each visual field. Although measurements from voltage waveforms replicated the observation of earlier peak P1 latencies for the 'pair' versus 'sum' comparison (Miniussi C, Girelli M, Marzi CA. Neural site of the redundant target effect: electrophysiological evidence. Journal of Cognitive Neuroscience 1998;10:216-30), this did not hold with measurements taken from second derivative (scalp current density) waveforms. Since interaction effects for bilateral stimulus pairs occurred within 86 ms and require interhemispheric transfer, transcallosal volleys must arrive within 86 ms, which is earlier than previously calculated. Interaction effects for bilateral conditions were delayed by approximately 10 ms versus unilateral conditions, consistent with current estimates of interhemispheric transmission time. Interaction effects place an upper limit on the time required for neuronal ensembles to combine inputs from different quadrants of visual space ( approximately 72 ms for unilateral and approximately 82 ms for bilateral conditions).

When does inter-hemispheric integration of visual events emerge in infancy? A developmental study on 19- to 28-month-old infants

Simultaneous attention in the two visual fields and interhemispheric integration of visual information was studied in 19-23 and 24-28-month-old infants. The stimuli were schematic faces within which the pair of eyes was made of either two identical (two circles or two triangles) or two different eyes (triangle-circle, circle-triangle). The faces were presented either in one visual hemifield, on the right or left side of a central fixation point (unilateral presentation), or across the two visual hemifields (bilateral presentation), with one eye of the stimulus on each side of the fixation point. The task was an operant conditioning task where the children had to decide whether the shapes of the two eyes were identical or not. The results show that even the younger subjects were able to perform the task when presented in the unilateral presentation condition, whereas only children aged 24 months and older could learn the task when presented in the bilateral condition. It is concluded that simultaneous attention to the two visual fields and inter-hemispheric co-ordination of visual information emerge very late in development at about the age of 24 months.

Benefits of interhemispheric integration on the Japanese Kana script-matching tasks

We tested Banich's hypothesis that the benefits of bihemispheric processing were enhanced as task complexity increased, when some procedural shortcomings in the previous studies were overcome by using Japanese Kana script-matching tasks. In Exp. 1, the 20 right-handed subjects were given the Physical-Identity task (Katakana-Katakana scripts matching) and the Name-Identity task (Katakana-Hiragana scripts matching). On both tasks, a pair of Kana scripts was tachistoscopically presented in the left, right, and bilateral visual fields. Distractor stimuli were also presented with target Kana scripts on both tasks to equate the processing load between the hemispheres. Analysis showed that, while a bilateral visual-field advantage was found on the name-identity task, a unilateral visual-field advantage was found on the physical-identity task, suggesting that, as the computational complexity of the encoding stage was enhanced, the benefits of bilateral hemispheric processing increased. In Exp. 2, the 16 right-handed subjects were given the same physical-identity task as in Exp. 1, except Hiragana scripts were used as distractors instead of digits to enhance task difficulty. Analysis showed no differences in performance between the unilateral and bilateral visual fields. Taking into account these results of physical-identity tasks for both Exps. 1 and 2, enhancing task demand in the stage of ignoring distractors made the unilateral visual-field advantage obtained in Exp. 1 disappear in Exp. 2. These results supported Banich's hypothesis.

The cerebral hemispheres cooperate to perform complex but not simple tasks

Three experiments were designed to examine whether task complexity determines the degree to which a division of processing across the hemispheres (i.e., across-hemisphere processing) underlies performance when within- and across-hemisphere processing are equally possible. When task complexity was relatively low, performance in a midline condition that allowed for either within- or across-hemispheric processing resembled within-hemisphere performance (Experiments 1 and 2). However, when task complexity was high, performance in a midline condition (Experiments 1 and 2) and a lateralized condition, which also allowed for either within- or across-hemisphere processing (Experiment 3), resembled across-hemisphere performance. Results complement and extend prior work (e.g., M. T. Banich & A. Belger, 1990) by indicating that the degree to which interhemispheric cooperation underlies performance changes with the complexity of the task being performed. This finding suggests that the hemispheres dynamically couple or uncouple their processing as a function of task complexity.

Bilateral field advantage and evoked potential interhemispheric transmission in commissurotomy and callosal agenesis

The role of the corpus callosum versus other cerebral commissures in the interhemispheric integration of visual information was studied in four individuals with complete agenesis of the corpus callosum, two individuals with partial agenesis, one total commissurotomy patient, and normal individuals. Evoked potential (EP) indices of interhemispheric transmission of visual sensory responses were observed during matching of unilateral and bilateral visual field letters and patterns. Neither the commissurotomy nor any of the acallosal patients had ipsilateral hemisphere visual EPs (P1 and N1), demonstrating that the posterior callosum is necessary for interhemispheric transmission of these components of visual evoked potentials. While the commissurotomy patient could not compare bilaterally presented letters, the anterior commissure of the acallosal patients appeared to be sufficient for interhemispheric comparison of single letters. However, bilateral comparison of more complex visual patterns resulted in considerable difficulty for complete agenesis patients, while comparison of patterns was more nearly normal when anterior callosal fibers were present (partial agenesis).

The role of attention in visual bilateral matching tasks

The consistent finding of studies employing visual matching tasks has been a reaction time and accuracy advantage for judgements about stimuli presented bilaterally when compared to the average performance of the two unilateral field presentations. As with recent studies showing the influence of attention on reaction times to unilateral presentations, we hypothesized that attentional mechanisms may also play a role in the speed advantage seen with bilateral letter presentations. The present study employed random dot-patterns ("dot-primes"), presented in the upper half of the LVF, RVF, Bilateral VF, or absent, as abrupt onset peripheral cues to attract attention automatically. Letter pairs followed immediately (14 msecs) after the dot-primes in the lower half of the LVF, RVF, or Bilateral VF. The results for unilateral dot-primes, followed by unilateral letter pairs, were consistent with previous studies showing that the field advantage for a particular task can be altered using abrupt onset attentional cues, with the advantage going to the field where the attentional prime is presented. Bilateral dot-primes did reduce latencies to subsequent bilateral letter pairs, but bilateral primes also reduced latencies to both LVF and RVF letter pairs, in nearly the same proportion as for bilateral letter pairs. Latencies for RVF-primes/Bilateral-letters were as fast as for Bilateral-primes/Bilateral-letters, and both of these conditions were significantly faster than LVF-primes/Bilateral-letters. The results suggest that attention plays a relatively minor role in the bilateral field advantage, and that non-attentional factors (i.e. interhemispheric dynamics) account for most of the asymmetric unilateral-prime influence on bilateral performance. Possible interhemispheric factors which may contribute to these results are discussed.

Stroop interference and facilitation in the cerebral hemispheres in schizophrenia

A divided visual field presentation of the Stroop colour-word test was used to study interhemispheric (transcallosal) function in schizophrenic and normal subjects. The modified test used a colour strip paired with either an incongruent, neutral or congruent colour word. Interference and facilitation were defined as the difference between the mean reaction times for incongruent stimuli and neutral stimuli and that between neutral stimuli and congruent stimuli, respectively. The stimuli were presented tachistoscopically with the two components either separated across the midline centrally, up or down from the midpoint (bilateral presentation), or presented to a single visual half-field (unilateral presentation). The inclusion of the 'up' and 'down' bilateral conditions controlled for the reaction time advantage for central compared with unilateral stimulus presentations noted in an earlier study (David, 1993a). The difference in reaction time to an incongruent compared with a congruent colour-word pairing, the Combined Stroop Effect (CSE), was not affected significantly by stimulus presentation position (bilateral vs. unilateral) in either the control or schizophrenic group, unlike in the earlier study of David. For controls, interference was significantly greater than facilitation for both bilaterally- and unilaterally-presented stimuli. Schizophrenics had a significantly smaller interference effect for bilaterally-presented stimuli, indicating reduced interhemispheric interference in this group. For the control group, there was no significant difference between right and left CSEs, interference being significantly greater than facilitation on both visual half-field presentations. For schizophrenics, the CSE for left-presented stimuli was significantly greater than that for right-presented stimuli. In addition, left-field facilitation was significantly greater than right-field. Reduced Stroop facilitation with right-field presentations in schizophrenic subjects may reflect increased vulnerability of colour-naming by word-reading in the left hemisphere-evidence for the non-unitary nature of attentional processes and disintegration of these in schizophrenia.

Maximizing the bilateral field advantage on verbal and nonverbal matching tasks

Research has established that response latencies are generally shorter on visual matching tasks when one target is projected to each hemifield (bilateral presentation) than when both targets are projected to the same hemifield (unilateral presentation). This effect, called the bilateral field advantage (BFA), has recently shown promise as a predictor of callosal dysfunction. As a step toward developing a reliable BFA index, the present study examined two factors that appear to influence the extent of BFA in normal subjects. Twenty-seven right-handed college students performed a verbal matching task (using letter pairs drawn from the set AaBb) and a nonverbal matching task (using dot pattern pairs constructed with 4 dots in a 3 x 3 matrix). Order of task varied across subjects (dots followed by letters, or letters followed by dots, or letter trials and dot trials interleaved at random). The targets were presented either unilaterally or bilaterally. Results revealed a robust BFA for the letter-matching task in all three task order conditions, suggesting that the letter task may be suitable for inclusion in a battery of tasks for clinical assessment. The dot-matching task did not yield a significant BFA when administered as the first task. The dot task BFA increased when the letter task preceded it, and became comparable to the letter task BFA in the interleaved condition.

Directional asymmetries in interhemispheric transmission time: evidence from visual evoked potentials

The hypothesis was tested that interhemispheric transfer time (IHTT), as measured in the latency of bilaterally recorded visual evoked potentials, is directionally asymmetric, i.e. that an IHTT is faster for transmission from right-to-left hemisphere, than from left-to-right. A meta-analysis of 18 experiments within the published literature reporting visual evoked potential IHTTs indicates a significant experiment-wise predominance of faster right-to-left IHTTs. A new experiment is also reported in which significantly faster right-to-left IHTT was found in visual evoked potentials recorded from parietal electrodes to lateral visual field presentations while subjects performed a task requiring complex stimulus recognition and analysis, and a choice response.