Attention and hemispheric differences in reaction time during simultaneous audio-visual tasks

The effect of different types of competing auditory tasks on laterality differences in visual perception was investigated. Right-handed subjects were presented with digits which occurred randomly in the left or right visual fields. They responded vocally to previously specified digits in a go, no-go reaction time situation. In the absence of any competing auditory task, digits presented in the right visual field were processed more quickly. This visual field difference in reaction time was in the same direction while subjects performed a secondary musical task. However, when a secondary verbal task had to be performed, digits in the left visual field received faster responses. The results support the view that the right hemisphere is capable of some language functions, and that hemispheric differences in performance have at their basis a quantitative asymmetry, which can be reversed even in normal subjects by overloading their limited capacity.     

Electrographic correlates of lateral asymmetry in the processing of verbal and nonverbal auditory stimuli

A veraged evoked potentials (AEP) to verbal (digits) and nonverbal (clicks) auditory stimuli were recorded from left and right temporal leads in ten right-handed Ss. With dichotic presentation, there was no significant difference in accuracy of report of the clicks heard in each ear, but significantly more digits were identified correctly from the right ear than from the left. Dichotic verbal stimuli elicited AEP whose early components were of greater amplitude, and whose later components were of shorter latency, from the left hemisphere than from the right. No consistent latency or amplitude differences were observed between AEP from the left and right hemispheres when clicks were presented dichotically.     

Verbal and nonverbal recognition memory in aphasic and nonaphasic stroke patients

The ability to retain lists of verbal and nonverbalizable items across recurrent recognition tasks was tested in three groups: (1) stroke patients with a left-brain lesion and aphasia, (2) stroke patients with a right-brain lesion and left hemiplegia, and (3) nonneurologically impaired outpatients. As determined with signal detection measures, aphasics were deficient in discriminating words that were to be remembered from those that were not; their recognition of nonverbal visual (geometric art) or auditory (bird calls) patterns, however, was unimpaired. Left hemiplegics showed the opposite pattern. After a long-term interval (<10 min), correct recognition of words was diminished in all groups whereas recognition of visual patterns increased. Both groups of stroke patients adopted material-specific decision criteria which in part accounted for the dissociation of verbal and nonverbal recognition memory by laterality of lesion. Item analysis indicated that aphasics' verbal memory difficulties were affected by acoustic-semantic confusion of list words.     

Right hemisphere comprehension of verbs in patients with complete forebrain commissurotomy: Use of the dichotic method and manual performance

The paradigm of dichotic listening was used to investigate verbal comprehension in the right, so-called “nonverbal,” hemisphere. Verbal commands were presented to the right and left ears in the simultaneous (dichotic) paradigm. There were striking instances, especially when the left hemisphere was occupied with some extraneous task, in which the right hemisphere understood the verbal command and executed the appropriate motor responses. In those instances the left hemisphere gave no overt response. Although the left hemisphere was usually dominant, it can be nevertheless concluded that not only can the right hemisphere understand verbal commands but can also express itself manually by executing actions more complex than object retrieval or pointing. As has been known for some time, the blockage of the ipsilateral pathway seems so complete during dichotic listening in the commissurotomy patient that there is no report of the words in the left ear—only of those presented to the right. At the same time there is normal report when words are presented to the left ear alone. It was found in the present study, however, that this model is too simple and only applies to the verbal response paradigm of dichotic listening. Under circumstances of dichotic presentation where the stimulus in the left ear (ipsilateral pathway) is necessary or important to the left hemisphere for completing a task, words from both pathways are reported. One may conclude that there exists a gating mechanism in each hemisphere that controls the monitoring of each auditory pathway and the degree of ipsilateral suppression.     

Task relevant effects on the assessment of cerebral specialization for facial emotion

Hemispheric specialization for processing different types of rapidly exposed stimuli was examined in a forced choice reaction time task. Four conditions of recognition were included: tacial emotion, neutral faces, emotional words, and neutral words. Only the facial emotion condition produced a significant visual field advantage (in favor of the left visual field), but this condition did not differ significantly from the neutral face condition's left visual field superiority. The verbal conditions produced significantly decreased latencies with RVF presentation, while the LVF presentation was associated with decreased latencies on the facial conditions. These results suggested that facial recognition and affective processing cannot be separated as independent factors generating right hemisphere superiority for facial emotion perception, and that task parameters (verbal vs. nonverbal) are important influences upon effects in studies of cerebral specialization.     

Hemispheric specialization in reading and word recognition

Three experiments dealing with hemispheric specialization are presented. In Experiment 1, words and/or faces were presented tachistoscopically to the left or right of fixation. Words were more accurately identified in the right visual field and faces were more accurately identified in the left visual field. A forced choice error analysis for words indicated that errors made for word stimuli were most frequently visually similar words and this effect was particularly pronounced in the left visual field. Two additional experiments supported this finding. On the basis of the results, it was argued that word identification is a multistage process, with visual feature analysis carried out by the right hemisphere and identification and naming by the left hemisphere. In addition, Kinsbourne's attentional model of brain function was rejected in favor of an anatomical model which suggests that simultaneous processing of verbal and nonverbal information does not constrict the attention of either hemisphere.     

Shift of visual field preference for Hebrew words in native speakers learning to read

Lateralization for Hebrew words was tested in both the visual and auditory modalities in Israeli children learning to read their native language, Hebrew. A left visual field preference for tachistoscopically presented words was found in the second graders in contrast to a right visual field preference for the same words in the third graders. Children in both grades showed a right ear dominance for similar words presented dichotically. These data suggest right hemisphere involvement in acquiring reading skills of a native language.     

Hemispheric Differences in the Recognition of Environmental Sounds

ABSTRACT— Recent work has found support for two dissociable and parallel neural subsystems underlying object and shape recognition in the visual domain: an abstract-category subsystem that operates more effectively in the left cerebral hemisphere than in the right, and a specific-exemplar subsystem that operates more effectively in the right hemisphere than in the left. Evidence of this asymmetry has been observed for linguistic stimuli (words, pseudoword forms) and nonlinguistic stimuli (objects). In the auditory domain, we previously found hemispheric asymmetries in priming effects using linguistic stimuli (spoken words). In the present study, we conducted four long-term repetition-priming experiments to investigate whether such hemispheric asymmetries would be observed for nonlinguistic auditory stimuli (environmental sounds) as well. The results support the dissociable-subsystems theory. Specificity effects were obtained when sounds were presented to the left ear (right hemisphere), but not when sounds were presented to the right ear (left hemisphere). Theoretical implications are discussed.     

Rhyming and the right hemisphere

Subjects determined whether two successively presented and orthographically different words rhymed with each other. The first word was presented at fixation and the second was presented either to the left or to the right of fixation, either alone (unilateral presentation) or accompanied by a distractor word in the other visual hemifield (bilateral presentation). Subjects were more accurate when the words did not rhyme, when presentation was unilateral, and when the target was flashed to the right visual hemifield. It was predicted that bilateral presentation would produce interference when information from both visual fields was processed by one hemisphere (callosal relay), but not when each of the two hemispheres performed a task independently (direct access). That is, callosal relay tasks should show greater laterality effects with bilateral presentations, whereas direct access tasks should show similar laterality effects with both bilateral and unilateral presentations. Greater laterality effects were observed for bilaterally presented rhyming words, but nonrhyming words showed similar laterality effects for both bilateral and unilateral presentations. These results suggest that judgment of nonrhyming words can be performed by either hemisphere, but that judgment of rhyming words requires callosal relay to the left hemisphere. The absence of a visual field difference with nonrhyming word pairs suggests further that judgment of nonrhyming word pairs may be accomplished by the right hemisphere when presentation is to the left visual field.     

Stimulus modality and working memory performance in Greek children with reading disabilities: Additional evidence for the pictorial superiority hypothesis

This study investigated the effects of stimulus presentation modality on working memory performance in children with reading disabilities (RD) and in typically developing children (TDC), all native speakers of Greek. It was hypothesized that the visual presentation of common objects would result in improved learning and recall performance as compared to the auditory presentation of stimuli. Twenty children, ages 10–12, diagnosed with RD were matched to 20 TDC age peers. The experimental tasks implemented a multitrial verbal learning paradigm incorporating three modalities: auditory, visual, and auditory plus visual. Significant group differences were noted on language, verbal and nonverbal memory, and measures of executive abilities. A mixed-model MANOVA indicated that children with RD had a slower learning curve and recalled fewer words than TDC across experimental modalities. Both groups of participants benefited from the visual presentation of objects; however, children with RD showed the greatest gains during this condition. In conclusion, working memory for common verbal items is impaired in children with RD; however, performance can be facilitated, and learning efficiency maximized, when information is presented visually. The results provide further evidence for the pictorial superiority hypothesis and the theory that pictorial presentation of verbal stimuli is adequate for dual coding.     

Hemisphere differences in the effects of cuing in visual recognition tasks.

In Experiment 1 uncued recognition of single letters presented in left or right visual fields showed no hemispheric asymmetry, but cuing by alternatives produced a left-hemisphere advantage. Uncued recognition of words was better in the right visual field (left hemisphere), and this advantage was unchanged by cuing by alternatives or cuing by class. In Experiment 2 a mixed series of words, digits, and dots was presented. Uncued trials showed no asymmetry, but when a precue indicated which type or stimulus would appear next, a left-hemisphere advantage for words was evident. Cuing also produced a nonsignificant shift toward a left-hemisphere advantage for digits and a right-hemisphere advantage for dots. The asymmetrical effects of cuing can be explained by Kinsbourne's attentional model of lateralization, which suggests that cuing may selectively activate one hemisphere, and so bias attention toward the contralateral visual field. Repetition effects within and between visual fields were analyzed but no asymmetries were found.     

Speech dominance and handedness in the normal human

Spectral analysis was used to measure the coherence or similarity of form between occipital and temporal evoked potentials. In both right- and left-handers, coherence was greater in the left hemisphere for click stimuli and in the right hemisphere for flash stimuli. Similar asymmetries occurred in left but not right speech dominant patients whose speech lateralization has been determined by the intracarotid amytal test. Right-handers and males, however, showed significantly larger amplitudes of auditory responses in the right hemisphere. Left-handers and females reversed this pattern. It was concluded that within a basically left speech dominant organization, males and right-handers would emphasize the verbal, temporal structure of auditory information and the nonverbal, spatial structure of visual information. Females and left-handers would tend to reverse this emphasis.     

Visual span of apprehension in patients with unilateral cerebral lesions

The visual span of apprehension for random letter and digit sequences, approximations to English sequences and non-symbolic line stimuli was measured in patients with unilateral cerebral lesions. The left hemisphere group was significantly impaired relative to the right hemisphere group and a control group on all three types of visual span task. The deficit was most marked in patients with left posterior lesions. The visual span deficits were not related to other language deficits. The findings are discussed in terms of a modality-specific defect of visual short-term memory.     

Hemispheric differences in object identification

Although the right hemisphere is thought to be preferentially involved in visuospatial processing, the specialization of the two hemispheres with respect to object identification is unclear. The present study investigated the effects of hemifield presentation on object and word identification by presenting objects (Experiment 1) and words (Experiment 2) in a rapid visual stream of distracters. In Experiment 1, object images presented in the left visual field (i.e., to the right hemisphere) were identified with shorter display times. In addition, the left visual field advantage was greater for inverted objects. In Experiment 2, words presented in the right visual field (i.e., to the left hemisphere) under similar conditions were identified with shorter display times. These results support the idea that the right hemisphere is specialized with regard to object identification.     

Reading disability and hemispheric interaction on a lexical decision task

The assumptions tested were that the relative contribution of each hemisphere to reading alters with experience and that experience increases suppression of the simultaneous use of identical strategies by the non-dominant hemisphere. Males that were reading disabled and phonologically impaired, reading disabled and phonologically normal, or with no reading disability were presented familiar words, orthographically correct pseudowords, and orthographically incorrect non-words for lexical decision. Accuracy and response times in all groups showed a shift from no asymmetry in processing non-words to a stable left hemisphere advantage and clear suppression of the right hemisphere in processing words. In the pseudoword condition, accuracy scores were higher when both hemispheres were free to engage, especially in those with a reading disability and responses slowed in the phonologically impaired group but not the phonologically normal groups when the right hemisphere was disengaged. As familiar words typically invoke lexical processing by both hemispheres while pseudowords invoke lexical processing by the right and non-lexical processing by the left hemisphere, and as non-lexical processing is weak in the phonologically impaired, the results support the assumptions that were tested.     

Hemispheric asymmetry in the processing of negative and positive words: A divided field study

Research on the lateralisation of brain functions for emotion has yielded different results as a function of whether it is the experience, expression, or perceptual processing of emotion that is examined. Further, for the perception of emotion there appear to be differences between the processing of verbal and nonverbal stimuli. The present research examined the hemispheric asymmetry in the processing of verbal stimuli varying in emotional valence. Participants performed a lexical decision task for words varying in affective valence (but equated in terms of arousal) that were presented briefly to the right or left visual field. Participants were significantly faster at recognising positive words presented to the right visual field/left hemisphere. This pattern did not occur for negative words (and was reversed for high arousal negative words). These results suggest that the processing of verbal stimuli varying in emotional valence tends to parallel hemispheric asymmetry in the experience of emotion.     

Phonological processing of words in right- and left-handers

It is commonly accepted that phonology is the exclusive domain of the left hemisphere. However, this pattern of lateralization, which posits a right visual field advantage, has been questioned by several studies. In fact, certain factors such as characteristics of the stimuli and subjects' handedness can modulate the right visual field advantage. Thus, the goal of this study was to compare the hemispheric dynamics of right-handers and left-handers during a divided visual field presentation of words that varied in terms of their phonological transparency. For non-transparent words, the left hemisphere seems more competent in both handedness groups. With regard to transparent words, the right hemisphere of both groups also appears competent. Surprisingly, left-handers achieved optimal processing with a functionally isolated left hemisphere, whereas right-handers needed the participation of both hemispheres. The pattern of performance cannot be fully explained by either the callosal or the direct access model.     

Hemispheric asymmetry in the processing of negative and positive words: a divided field study

Research on the lateralisation of brain functions for emotion has yielded different results as a function of whether it is the experience, expression, or perceptual processing of emotion that is examined. Further, for the perception of emotion there appear to be differences between the processing of verbal and nonverbal stimuli. The present research examined the hemispheric asymmetry in the processing of verbal stimuli varying in emotional valence. Participants performed a lexical decision task for words varying in affective valence (but equated in terms of arousal) that were presented briefly to the right or left visual field. Participants were significantly faster at recognising positive words presented to the right visual field/left hemisphere. This pattern did not occur for negative words (and was reversed for high arousal negative words). These results suggest that the processing of verbal stimuli varying in emotional valence tends to parallel hemispheric asymmetry in the experience of emotion.     

Is Happy Facial Expression Identified by the Left or Right Hemisphere？

1IntroductionCorrectly identifying other people′s facial ex-pressions of emotions is important to human socialinteraction in all societies.Many studies suggestthat the identification of facial expressions in par-ticular and perceptual processing of emotional infor-mation is carried out mainly by the right hemi-sphere of the brain[1￣7].Damage to the righthemisphere generally produces more significant im-pairment in recognition of all facial expressions ofemotion than damage to the left hemisp…     

Visual field differences in the processing of numerical stimuli

Twenty-four right-handed subjects received random presentations of the numbers 1-6 in the form of words, digits, and dot patterns, to the left and right visual fields. Accuracy and reaction time were recorded for an odd-even judgment requiring a manual response. A significant stimulus type of visual field interaction was obtained, with words showing a left-hemisphere advantage and digits and dot patterns showing a right-hemisphere advantage. This pattern supports Coltheart's (1980, Deep dyslexia: A right hemisphere hypothesis, In M. Coltheart, K. Patterson, & J.C. Marshall (Eds.), Deep dyslexia, London: Routledge & Kegan Paul) right hemisphere reading hypothesis, which suggests that the left hemisphere's general advantage in processing linguistic material may be specific to stimuli which involve phonological processing. When phonological processing is not possible (e.g., for arabic digits and other ideographic orthographies), the right hemisphere may have an advantage because of its superior visuospatial processing capabilities.