Snake pictures draw more early attention than spider pictures in non-phobic women: evidence from event-related brain potentials.

Snakes were probably the first predators of mammals and may have been important agents of evolutionary changes in the primate visual system allowing rapid visual detection of fearful stimuli (Isbell, 2006). By means of early and late attention-related brain potentials, we examined the hypothesis that more early visual attention is automatically allocated to snakes than to spiders. To measure the early posterior negativity (EPN), 24 healthy, non-phobic women watched the random rapid serial presentation of 600 snake pictures, 600 spider pictures, and 600 bird pictures (three pictures per second). To measure the late positive potential (LPP), they also watched similar pictures (30 pictures per stimulus category) in a non-speeded presentation. The EPN amplitude was largest for snake pictures, intermediate for spider pictures and smallest for bird pictures. The LPP was significantly larger for both snake and spider pictures when compared to bird pictures. Interestingly, spider fear (as measured by a questionnaire) was associated with EPN amplitude for spider pictures, whereas snake fear was not associated with EPN amplitude for snake pictures. The results suggest that ancestral priorities modulate the early capture of visual attention and that early attention to snakes is more innate and independent of reported fear.

Distinct brain systems underlie the processing of valence and arousal of affective pictures.

Valence and arousal are thought to be the primary dimensions of human emotion. However, the degree to which valence and arousal interact in determining brain responses to emotional pictures is still elusive. This functional MRI study aimed to delineate neural systems responding to valence and arousal, and their interaction. We measured neural activation in healthy females (N=23) to affective pictures using a 2 (Valence) x 2 (Arousal) design. Results show that arousal was preferentially processed by middle temporal gyrus, hippocampus and ventrolateral prefrontal cortex. Regions responding to negative valence included visual and lateral prefrontal regions, positive valence activated middle temporal and orbitofrontal areas. Importantly, distinct arousal-by-valence interactions were present in anterior insula (negative pictures), and in occipital cortex, parahippocampal gyrus and posterior cingulate (positive pictures). These data demonstrate that the brain not only differentiates between valence and arousal but also responds to specific combinations of these two, thereby highlighting the sophisticated nature of emotion processing in (female) human subjects.

Nonlinear changes in brain activity during continuous word repetition: an event-related multiparametric functional MR imaging study.

BACKGROUND AND PURPOSE: Changes in brain activation as a function of continuous multiparametric word recognition have not been studied before by using functional MR imaging (fMRI), to our knowledge. Our aim was to identify linear changes in brain activation and, what is more interesting, nonlinear changes in brain activation as a function of extended word repetition. MATERIALS AND METHODS: Fifteen healthy young right-handed individuals participated in this study. An event-related extended continuous word-recognition task with 30 target words was used to study the parametric effect of word recognition on brain activation. Word-recognition-related brain activation was studied as a function of 9 word repetitions. fMRI data were analyzed with a general linear model with regressors for linearly changing signal intensity and nonlinearly changing signal intensity, according to group average reaction time (RT) and individual RTs. RESULTS: A network generally associated with episodic memory recognition showed either constant or linearly decreasing brain activation as a function of word repetition. Furthermore, both anterior and posterior cingulate cortices and the left middle frontal gyrus followed the nonlinear curve of the group RT, whereas the anterior cingulate cortex was also associated with individual RT. CONCLUSION: Linear alteration in brain activation as a function of word repetition explained most changes in blood oxygen level-dependent signal intensity. Using a hierarchically orthogonalized model, we found evidence for nonlinear activation associated with both group and individual RTs.

Corpus callosum size correlates with asymmetric performance on a dichotic listening task in healthy aging but not in Alzheimer's disease.

Alzheimer's disease (AD) involves not only gray matter but also white matter pathology, as reflected by atrophy of the corpus callosum (CC). Since decreased CC size may indicate reduced functional interhemispheric connectivity, differences in callosal size may have cognitive consequences that may become specifically apparent in neuropsychological tasks that tap hemispheric laterality. In the present study, we examined callosal functioning with a dichotic listening task in 25 Alzheimer patients, 20 healthy elderly and 20 healthy elderly with subjective memory complaints. We found decreased performance, increased ear asymmetry, and decreased callosal size in the AD group compared to healthy elderly. As expected, in the healthy elderly, we found significant negative correlations between ear asymmetry and callosal size, specifically in the anterior and posterior callosal subareas. While the association with the posterior subareas (isthmus and splenium) points at involvement of temporal areas mediating language processing, the association with the anterior subarea (the rostrum and genu) points at involvement of frontal areas mediating attention and executive functions. Remarkably however, in contrast to the healthy elderly, callosal size was not related to ear asymmetry in the AD group. The absence of an association between callosal atrophy and ear asymmetry implies that other pathological processes, next to reduced callosal functioning, attribute to ear asymmetry in AD. Difficulties to attend specifically to the left ear during dichotic listening in some of the AD patients, points at decreased attention and executive functions and suggests that pathology of specifically the frontal areas is involved.

Increased prevalences of left-handedness and left-eye sighting dominance in individuals with Williams-Beuren syndrome.

Handedness and eye sighting dominance were assessed in a sample of 50 individuals (25 male, 25 female; aged 5-38 years) with Williams-Beuren syndrome (WBS). The prevalences of left-handedness and left-eyedness were compared to the normative prevalences in the general population. We found significantly higher prevalences of left-handedness and left-eyedness in the WBS sample. The higher prevalences were more salient in younger than in older individuals and in male than in female individuals. We suggest that the increased prevalence of left-handedness in WBS is a consequence of a slower maturation rate, which allows deviation from a predetermined laterality pattern.

Ratings of emotion in laterally presented faces: sex and handedness effects.

Sixteen right-handed participants (8 male and 8 female students) and 16 left-handed participants (8 male and 8 female students) were presented with cartoon faces expressing emotions ranging from extremely positive to extremely negative. A forced-choice paradigm was used in which the participants were asked to rate the faces as either positive or negative. Compared to men, women rated faces more positively, especially in response to right visual field presentations. Women rated neutral and mildly positive faces more positively in the right than in the left visual field, whereas men rated these faces consistently across visual fields. Handedness did not affect the ratings of emotion. The data suggest a positive emotional bias of the left hemisphere in women.

Hemispheric facilitation as a result of threatening and nonthreatening words: blocked vs mixed presentation effects and order effects.

Sixteen right-handed participants (eight male and eight female students) were administered a tachistoscopic unilateral letter-naming task. The design contained three valance conditions and two types of presentation. In baseline conditions no concurrent task was given. In threat and nonthreat conditions, each unilateral stimulus was preceded by a threatening or nonthreatening word in central vision. Participants were instructed to recall this word after reporting the unilateral letter string. With blocked presentations, a series of trials had the same emotional valence (threatening or nonthreatening), whereas with mixed presentations the valences were alternating within a series. Analysis of order effects for the blocked presentations revealed sustained effects of the initial block valence on visual field asymmetries. The sustained effect of the initial threatening block was a reduction of the right visual-field advantage. Mixed presentations resulted in a enhanced right visual-field advantage following the presentation of threatening information and an enhanced left visual-field advantage following the presentation of nonthreatening information. The research suggests that tonic and phasic reactions to emotional stimuli may affect visual field asymmetry in different ways.

Verbal-to-manual and manual-to-verbal dual-task interference in left-handed and right-handed adults.

Verbal-manual interference was investigated with 80 students who were divided into four groups by sex and hand preference. Unilateral finger-tapping was measured during no-load conditions and during two concurrent tasks of word reading (aloud) and sentence reading (silent). During concurrent tasks, no selective interference effects for the preferred hand were found; however, when participants were classified according to consistent handedness instead of hand preference, consistent right-handers exhibited selective right-hand tapping interference during concurrent word reading, whereas consistent left-handers showed generalized interference. During concurrent sentence reading, men showed selective right-hand interference, irrespective of handedness. The influence of tapping on word reading was also examined. Concurrent tapping lowered word-reading performance substantially, showing that finger-tapping and word reading interfered reciprocally.

Altered visual field asymmetry for lexical decision as a result of concurrent presentation of music fragments of different emotional valences.

Sixteen right-handed male students were administered a unilateral lexical decision task in 4 conditions: a baseline condition and three sound conditions. In the sound conditions, the participants listened to noise, to music with a positive emotional valence, and to music with a negative emotional valence, while performing the visual half-field task. In the baseline condition, the noise condition, and the positive music condition, lexical decision latencies were shorter to right than to left visual field presentations. In the negative music condition, there was a selective enhancement of left visual field performance, which cancelled the visual field advantage completely. None of the concurrent sounds affected autonomic arousal as measured by heart rate. The results demonstrated that music with a negative emotional valence can alter the half-field asymmetry of a verbal task. The outcome was discussed in terms of right hemisphere priming due to negative emotional experience.

Altered visual field asymmetries for letter naming and letter matching as a result of concurrent presentation of threatening and nonthreatening words.

Thirty-two right-handed subjects (16 male and 16 female students) were administered a unilateral letter-naming task and two unilateral letter-matching tasks: physical-identity letter matching (shape task) and nominal-identity letter matching (name task). Each task contained three conditions. In control conditions, no concurrent task was given. In threat and nonthreat conditions, each unilateral stimulus was preceded by a centrally presented threatening or nonthreatening word. Subjects were instructed to recall this word after their response to the lateral stimulus. With letter naming, each trial consisted of three consonants presented horizontally to the left or right visual field. Across conditions, subjects identified more letters correctly in the right visual field than in the left visual field. The concurrent presentation of threatening words resulted in a selective enhancement of left visual-field performance. In the control condition of the shape task, same letter pairs were identified faster than different pairs when they were presented to the right visual field. The concurrent presentation of threatening words resulted in a selective shortening of left visual-field latencies to same pairs. In the name task, the concurrent presentation of threatening words resulted in improved accuracy on left visual field trials. No sex differences in perceptual asymmetries and in emotional priming effects were found. The results demonstrate that threatening stimuli can activate the right hemisphere and alter the laterality patterns for several tasks.

Sex and familial sinistrality differences in cognitive abilities.

Cognitive functioning was assessed in 69 left-handed males and females with a positive family history of left-handedness and in 77 left-handed and 55 right-handed males and females without familial left-handedness. Compared to females, males performed better on numerical reasoning and on two visuospatial tasks involving spatial manipulations (Figure Rotation and Surface Development). Within the group of left-handers, the multivariate effect for Familial Sinistrality was significant. Left-handers with familial left-handedness exhibited better scores on numerical reasoning, on verbal reasoning, and on two visuospatial tasks involving visual closure (Hidden Figures, Picture Completion) than did left-handers without left-handed relatives. The nonfamilial left-handers also exhibited lower scores on both inductive reasoning tasks when they were compared to their right-handed counterparts. The outcome runs contrary to the prevalent conclusion that left-handers with left-handed relatives are more likely to exhibit lower performances on visuospatial tasks than left-handers without such relatives.

Hemisphere-specific treatment of dyslexia subtypes: better reading with anxiety-laden words?

Twenty children (12 boys, 8 girls; mean age = 10.4 years) with P-type dyslexia (accurate but slow and fragmented reading) and 20 children (12 boys, 8 girls; mean age = 10.3 years) with L-type dyslexia (hurried, inaccurate reading) were treated with visual hemisphere-specific stimulation employing the HEMSTIM computer program. Stimulation was produced by presenting words to the left (L-dyslexia) or to the right (P-dyslexia) visual field. Children in the control condition received treatment with neutral words, whereas children in the experimental condition received treatment with anxiety-laden words. After treatment, the children with L-dyslexia in the experimental group made fewer substantive errors and more fragmentations on a text-reading task than did the children with L-dyslexia in the control group. The results are explained as being the consequence of additional activation of the right hemisphere caused by the anxiety-laden words. It is concluded that children with L-dyslexia can benefit from the use of such words in the HEMSTIM program.

Lexical decision performances in P-type dyslexic, L-type dyslexic, and normal reading boys.

Lexical decision performances in P-type dyslexic, L-type dyslexic, and normal reading boys were investigated using three-letter and four-letter words (familiar words) and nonwords presented in the central visual field. For words, P-type dyslexics displayed significantly longer latencies for four-letter than for three-letter word decisions, whereas L-type dyslexics and normal readers did not. For nonwords, all subject groups showed significantly larger mean latencies for four-letter than for three-letter nonword decisions. In general, the error data corresponded to the latency data. L-type dyslexics, however, made more errors during four-letter words than during three-letter words, although they had similar latencies in both conditions. The results are discussed with reference to the hypothesis that P-type dyslexics would use a sequential processing mode for reading familiar words, whereas L-type dyslexics would employ a parallel processing mode for reading familiar words.

Opposite hemispheric activations as a result of emotionally threatening and non-threatening words.

Twenty right-handed males participated in a tachistoscopic unilateral letter recognition task with three conditions. In the control condition, each trial consisted of three consonants that were flashed horizontally to the left or to the right visual field. In the threat and non-threat conditions, each lateral three-letter presentation was preceded by an emotionally threatening or non-threatening word presented in central fixation. Across conditions, subjects identified more letters correctly in the right visual field than in the left visual field. The concurrent presentation of threatening words resulted in a selective enhancement of left visual-field performances. The concurrent presentation of non-threatening words resulted in a selective right visual-field enhancement. Our conclusion is that threatening stimuli prime the right hemisphere and can alter predicted laterality patterns.

Familial resemblance for cognitive abilities in families with P-type dyslexic, L-type dyslexic, or normal reading boys.

P-type dyslexic, L-type dyslexic, and normal reading boys, and their parents were administered a number of cognitive tasks. The P- and L-type dyslexic boys showed impaired performances on tasks representing a verbal/memory dimension. In addition, L-type dyslexics performed worse on a figure-rotation task, a result that supported the notion of a visuospatial deficit in this type of reading disturbance. The parents of P- and L-type dyslexics exhibited lowered performances on verbal/memory tasks, but they showed no evidence of impaired visuospatial functioning. Indices of familial resemblance revealed differential familial resemblances in the three types of families. In the families of P-type dyslexics, a high father-son effect was found for the visuospatial dimension. In the families of L-type dyslexics, moderately high single-parent/child effects were found for both fathers and mothers and for both the verbal/memory dimension and the visuospatial dimension. In the families of normal readers, only small single-parent/child effects were found.

Lateralized effects of subclinical epileptiform EEG discharges on scholastic performance in children.

The interaction between lateralization of subclinical epileptiform discharges and cognitive tasks was investigated in 21 children (12 girls and 9 boys, mean age 10.6 years). Seventeen had a diagnosis of epilepsy (partial or secondarily generalized). Testing was by reading, arithmetic, and intelligence subtests during continuous telemetric EEG and video monitoring. Children with left-sided discharges had significantly lower reading performance than children with right-sided discharges. During reading, epileptiform discharges occurred relatively less frequently and with a shorter total duration over the left hemisphere than the right. This supports the view that cognitive tasks suppress epileptiform discharges when they activate a region of the brain within the epileptogenic zone. Discharges from other epileptogenic zones not directly activated by the tasks are increased, however.

Selective activation effects of concurrent verbal and spatial memory loads in left-handed and right-handed adults.

Thirty-two left-handed subjects, divided into four groups according to sex and familial sinistrality, and 16 right-handed subjects without familial sinistrality (8 male, 8 female) participated in a tachistoscopic unilateral letter-identification task with concurrent verbal- and spatial-memory loads. Across groups, a significant right visual field advantage for letter-identification was found. In the majority of both left-handed and right-handed subjects, the concurrent verbal-memory load resulted in a selective activation, with the right visual field performance showing improvement. However, the group of left-handed males with a positive family history of sinistrality gave less evidence of selective left-hemispheric activation as a consequence of the verbal-memory load. The concurrent spatial-memory load did not result in a consistent pattern of selective activation.

Mental rotation of laterally presented random shapes in males and females.

Eighteen right-handed subjects (9 males, 9 female) were to decide if laterally presented random shapes were identical or a mirror image of a centrally presented standard shape. The lateral shapes were rotated over 0 degrees, 60 degrees, 120 degrees, 180 degrees, 240 degrees, or 300 degrees. For unrotated (0 degrees) mirror image stimuli, females showed a significant right visual-field advantage, whereas males showed no significant hemifield effect. The rate of rotation was equivalent for both sexes. Field of presentation did not affect the rotation rate either. The present results support a growing number of findings that indicate that the interpretation of mental rotation as a typical right-hemispheric spatial-processing task is questionable.

Event-related potentials during word-reading and figure-matching in left-handed and right-handed males and females.

In two experiments, event-related potentials at left and right occipital, parietal, and temporal sites were studied in 16 left-handers (8 male, 8 female) and 16 right-handers (8 male, 8 female). Subjects displayed extreme handedness, had a normal writing hand position, reported no left-handed relatives, and reported no perinatal traumata. In Experiment 1, centrally presented words had to be read, and nonverbal stimuli had to be matched. Condition-dependent asymmetries were found for P340 and SW components. Word-reading elicited a N500 component, whereas figure-matching did not. In Experiment 2, words presented to either the left or right visual field had to be read. It was found that N160 measures were larger, and P240, P400, and SW measures were smaller to words presented in the contralateral visual field compared to words in the ipsilateral field. Sex affected these pathway effects. In both experiments, hand preference did not significantly influence the ERP results.