Differential visual field-interhemispheric transfer: can it explain sex and handedness differences in lateralization?

104 men and women were tested for visual field-hemispheric transfer of spatial information on a dot-localization task. Right-handed subjects showed significant improvement when stimuli were presented to the left visual field of the right hemisphere (LVF-RH) after practice on the same task presented to the right visual field of the left hemisphere (RVF-LH) first. No improvement was found when the task was presented in the reverse order (LVF-RH first followed by RVF-LH). It was concluded that, for right-handers, transfer of spatial information to the right hemisphere is facilitated while transfer to the left hemisphere is inhibited. Left-handed subjects demonstrated no significant improvement in either condition, suggesting inhibition or lack of transfer of spatial information in either direction. No sex differences were found in either right-handed or left-handed subjects. The findings suggest that there may be different mechanisms underlying the similarities in functional lateralization of women and left-handers.     

Hemispheric differences in the time-course of semantic priming processes: evidence from event-related potentials (ERPs)

To investigate hemispheric differences in the timing of word priming, the modulation of event-related potentials by semantic word relationships was examined in each cerebral hemisphere. Primes and targets, either categorically (silk-wool) or associatively (needle-sewing) related, were presented to the left or right visual field in a go/no-go lexical decision task. The results revealed significant reaction-time and physiological differences in both visual fields only for associatively related word pairs, but an electrophysiological difference also tended to reach significance for categorically related words when presented in the left visual field. ERP waveforms showed a different time-course of associative priming effects according to the field of presentation. In the right visual field/left hemisphere, both N400 and Late Positive Component (LPC/P600) were modulated by semantic relatedness, while only a late effect was present in the left visual field/ right hemisphere.     

Response bias and hemispheric differences in dot localization

A series of studies investigated the accuracy of dot localization in left and right visual fields. The left visual field superiority previously reported for this task was found to be small and statistically inconsistent. It was unaffected by the presence of a frame of reference, the location of the response card, or the sex of the subject. It was observed, however, that the majority of subjects showed a response bias favoring the report of items in the left visual field. This suggests that the right hemisphere is less critical than the left in its assessment of incoming information, and may provide a basis for understanding previous reports of right hemispheric superiority on dot localization. It is concluded that dot localization does not provide a reliable measure of right hemisphere performance.     

Right hemisphere sensitivity to arousal and depression.

Several lines of evidence show impaired right hemisphere function in depression. Lateralized simple reaction time tasks show impaired left visual field responses both in normals experiencing a depressed mood and in patients with mild unipolar depression. One interpretation for these findings is that depression impairs right hemisphere function by interfering with right hemisphere arousal and vigilance mechanisms. In order to test this hypothesis, subjects receiving either depression or relaxation mood suggestions performed an uncued reaction time task that has been shown to be sensitive to right posterior brain damage. Level of alertness was varied by contrasting uncued blocks with blocks in which targets were preceded by a warning tone. The results showed the predicted slowing of left visual field responses in the depressed mood, but only in women. The effect was significant only for the uncued blocks. The left visual field impairment was significantly larger during depression than in the relaxation state, but a smaller left visual field slowing was present in women in the relaxed state as well. These results may be consistent with the notion that depression interferes with right hemisphere function in part by influencing right hemisphere arousal mechanisms.     

Hemisphere differences for components of mental rotation

The hemispheric functional lateralization of components of mental rotation performance was investigated. Twenty right-handed males were presented with rotated alphanumerics and unfamiliar characters in the left or right visual field. Subjects decided if the laterally presented stimulus was identical to or a mirror image of a center standard stimulus. Reaction time and errors were measured. Previous mental rotation findings were replicated and the visual field variable produced significant effects for both dependent measures. An overall right visual field advantage was observed in the latency data, suggesting a left hemisphere superiority for at least one component process of the task. A significant interaction in the error data showed that alphanumerics produced less errors in the right visual field than in the left visual field, consistent with a left hemisphere superiority for processing verbal symbolic material. No such hemispheric difference in accuracy was found for unfamiliar characters.     

EFFECTS OF PERCEPTUAL QUALITY AND TASK DIFFERENCE ON THE HEMISPHERIC PROCESSING OF WORD STIMULI

Three experiments were conducted to examine the effects of stimulus exposure duration, retinal eccentricity, visual noise and task differences (physical classification and semantic classification) on the processing of Kana (Japanese phonetic symbol) words presented to the left and right visual fields. The primary findings of the three experiments were as follows. The right visual field advantage was found in the shorter exposure duration but no visual field difference was shown in the longer exposure duration condition (experiment 1). Stimulus presentation to large and small retinal eccentricity conditions revealed similar visual field difference (experiment 2). No significant visual field difference was shown in both clear and blurred stimulus presentation conditions (experiment 3). Semantic classification task revealed a right visual field advantage in all experiments whereas no visual field difference was shown in physical classification task in experiments 2 and 3. These results were discussed in terms of spatial frequency hypothesis and levels of processing hypothesis.     

Effects of type of cognitive demand on bilateral advantage in interhemispheric processing

The relationship between cognitive task demand and effect of bilateral advantage (BLA) was examined. In Experiment 1, the task demand based upon visual stimulus complexity was manipulated. One-digit and two-digit numbers were presented in the left, right or both visual fields tachistoscopically and subjects were requested to identify the numbers. The results showed no BLA, although a right visual field advantage was demonstrated. In Experiment 2, cognitive demand in terms of memory was manipulated. Subjects were asked to recall one-digit numbers that were presented successively once, three and five times in the left, right or the both visual fields. The results did not show any sign of BLA in the recall of numbers. In Experiment 3, a greater memory load task was given than that in Experiment 2, where two-digit numbers were presented successively (once, three and five times). Subjects were asked to recall the numbers. The results showed a significant BLA in the recall of numbers, i.e., the correct numbers in the correct temporal positions. These results strongly suggest that a benefit of redundant bilateral visual fields presentation is shown only in a highly cognitively demanding task, especially when it involves phonological memory loads.     

Sex differences in functional brain activation during a lexical visual field task

Functional MRI was used to investigate sex differences in brain activation during a paradigm similar to a lexical-decision task. Six males and 6 females performed two runs of the lexical visual field task (i.e., deciding which visual field a word compared with a pseudoword was presented to). A sex difference was noted behaviorally: The reaction time data showed males had a marginal right visual field advantage and women a left visual field advantage. Imaging results showed that men had a strongly left-lateralized pattern of activation, e.g., inferior frontal and fusiform gyrus, while women showed a more symmetrical pattern in language related areas with greater right-frontal and right-middle-temporal activation. The data show evidence of task-specific sex differences in the cerebral organization of language processing.     

Lexical decisions in the right and left cerebral hemispheres

Subjects performed a lexical decision task in which letter-strings were presented unilaterally and tachistoscopically to the right and left visual fields. Four types of letter-strings were used: high frequency words, low frequency words, pronounceable nonwords, and unpronounceable nonwords. Measures of reaction time and error rate both showed a right visual field advantage for both classes of words and no difference between the hemispheres for either class of nonword. It was concluded that meaning is a more salient parameter of wordness than is pronounceability. Possible mechanisms for processing words presented to the left visual field were discussed.     

Asymmetry in reception and retention of colors.

In Experiment 1 a same-different comparison task involving simultaneous discrimination of colors differing by 2.5 steps in hue and presented 2° in the left or right visual field was given to 24 male and 24 female familial righthanders. A significant left visual field superiority was obtained. In a color naming task, the higher the number of color pairs for which both members were given the same name, the larger the left visual field superiority. In Experiment 2 the tasks were replicated with a 10-sec memory interval inserted between the stimuli in each color pair. No significant effects were obtained.     

Probing hemispheric processes in an on-line reading task

Coney (1998) used a priming procedure to obtain evidence that the left and right hemispheres contributed equally to lexical processing of concrete nouns in a continuous reading task. In that study, however, there was no direct validation of the involvement of the right hemisphere in the task, and the possibility of left hemisphere processing of left visual field target stimuli could not be ruled out. The present study was designed to obtain validating evidence by using abstract and concrete noun primes in a similar reading task on the assumption that if the right hemisphere was contributing to the task there would be demonstrable differences between the visual fields in processing targets primed by abstract nouns. The results supported this expectation. While concrete targets projected to each visual field were primed by concrete nouns, there was significant priming by abstract nouns only in respect of targets presented to the right visual field. It is argued that this finding supports the involvement of the right hemisphere in continuous reading and further delimits the scope of its contribution to this process. Somewhat unexpectedly, the results also revealed that absolute response times were faster to left visual field targets when they were preceded by abstract nouns, even when there was no semantic relationship between the two words. It was suggested that this effect derives from the inability of the right hemisphere to process abstract nouns in that the failure of abstract nouns to engage lexical processing mechanisms leaves the right hemisphere relatively unencumbered when required to process a subsequent target.     

Categorical perception of colour in the left and right visual field is verbally mediated: evidence from Korean

In this study we demonstrate that Korean (but not English) speakers show Categorical perception (CP) on a visual search task for a boundary between two Korean colour categories that is not marked in English. These effects were observed regardless of whether target items were presented to the left or right visual field. Because this boundary is unique to Korean, these results are not consistent with a suggestion made by Drivonikou [Drivonikou, G. V., Kay, P., Regier, T., Ivry, R. B., Gilbert, A. L., Franklin, A. et al. (2007) Further evidence that Whorfian effects are stronger in the right visual field than in the left. Proceedings of the National Academy of Sciences 104, 1097-1102] that CP effects in the left visual field provide evidence for the existence of a set of universal colour categories. Dividing Korean participants into fast and slow responders demonstrated that fast responders show CP only in the right visual field while slow responders show CP in both visual fields. We argue that this finding is consistent with the view that CP in both visual fields is verbally mediated by the left hemisphere language system.     

Effects of concurrent spatial and verbal memory loads on serial position functions of laterally presented letter strings

In this study the influence of visuospatial and verbal memory loads on the identification of laterally presented letter strings was investigated. In the asymmetry task without concurrent loads, a clear right visual field advantage for letter identification was obtained. Hemisphere-specific effects due to concurrent loads were particularly observed when the difficulty of the load tasks was increased. The effects of visuospatial loads were found to be sex related, suggesting that under heavy load conditions mental rotation selectively overloads the processing capacity of the right hemisphere in males, while in females capacity limitations were observed in both hemispheres. Concurrent visuospatial loads produced more facilitation (or less interference) for letters in the outermost positions of each visual field than for letters in the innermost positions of each visual field. The results of the verbal memory load tasks revealed that an easy verbal load task facilitated performance which was particularly manifest for the right-most letter of both the left visual field and the right visual field. A difficult verbal memory load task interfered with recognition accuracy of letters which was most marked for the center letter in the right visual field. Letter position effects obtained in this study were interpreted in terms of various processing mechanisms influencing the serial position curves.     

知觉加工中存在颜色类别知觉效应的证据

对于颜色的辨别具有类别知觉效应：类间两种颜色的辨别能力比同等颜色空间距离的类内两种颜色的辨别能力更高。对于类别知觉效应的产生机制存在两种观点：知觉特性假设、语言标签假设。以往的研究范式由于实验任务涉及到工作记忆成分,被试在完成任务时会自动地对颜色命名以利于记忆,因此所得证据大多支持语言标签假设,而对知觉特性假设的支持证据则很少。本文利用目标觉察范式最大限度去掉了工作记忆成分,通过测量被试辨别两种颜色的反应时,得到了类别知觉效应。并通过语言干扰任务进一步证实在该实验范式下类别知觉效应与语言的无关性。从而,为知觉特性假设提供了证据     

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.     

The effect of orthographic uniqueness and deviation points on lexical decisions: evidence from unilateral and bilateral-redundant presentations

Words with an early or late orthographic uniqueness point and nonwords with an early or late orthographic deviation point were presented to the left, right, or both visual fields simultaneously. In Experiment 1, 20 participants made lexical decision judgements to horizontal stimulus presentations. In Experiment 2, a further 20 participants completed the task using vertical presentations to control for attentional biases. Consistent with previous research, words with earlier orthographic uniqueness points prompted faster responses across visual fields, regardless of stimulus orientation. Although research has suggested that the left hemisphere's superiority for language processing stems from a comparatively parallel processing strategy, with the right hemisphere reliant upon a serial mechanism, left and right visual field presentations were not differentially affected by orthographic uniqueness point. This suggests that differential sequential effects previously reported result during processes other than retrieval from the lexicon. The overall right visual field advantage observed using horizontal presentations disappeared when stimuli were presented vertically. Contrary to expectations, there was a facilitatory effect of late orthographic deviation point for horizontal nonword presentations. Overall, the results were interpreted as being consistent with predictions of a cohort model of word recognition, and they highlighted the effect of stimulus orientation on left and right hemisphere word recognition.     

Hemisphere differences in conscious and unconscious word reading

Hemisphere differences in word reading were examined using explicit and implicit processing measures. In an inclusion task, which indexes both conscious (explicit) and unconscious (implicit) word reading processes, participants were briefly presented with a word in either the right or the left visual field and were asked to use this word to complete a three-letter word stem. In an exclusion task, which estimates unconscious word reading, participants completed the word stem with any word other than the prime word. Experiment 1 showed that words presented to either visual field were processed in very similar ways in both tasks, with the exception that words in the right visual field (left hemisphere) were more readily accessible for conscious report. Experiment 2 indicated that unconsciously processed words are shared between the hemispheres, as similar results were obtained when either the same or the opposite visual field received the word stem. Experiment 3 demonstrated that this sharing between hemispheres is cortically mediated by testing a split-brain patient. These results suggest that the left hemisphere advantage for word reading holds only for explicit measures; unconscious word reading is much more balanced between the hemispheres.     

Grouping reduces visual extinction: Neuropsychological evidence for weight-linkage in visual selection

Abstract

We tested two subjects following damage to right parietal cortex to see if their failure to detect a left visual stimulus in the presence of a simultaneous right stimulus (visual extinction) could be modulated by perceptual grouping between the left and right stimuli. Subjects performed a simple detection task for brief displays in which items could appear in the left or right visual field, both fields, or neither field. On trials in which items appeared in both fields, we found that left omissions (extinction errors) were dramatically reduced when the two items formed a good perceptual group, either on the basis of Gestalt factors such as similarity and symmetry (Experiment 1). or by forming a familiar configuration (Experiment 2). We suggest that extinction may be a spatially specific exaggeration of a normal attention limitation, in which the contralesional item is disadvantaged in the competition for selection. However, this obstacle to selection can be overcome if, as a result of grouping, ipsilesional and contralesional items become allies rather than competitors for selection.     

Useful visual field in patients with schizophrenia: a choice reaction time study

This study examined the size of the useful visual field in patients (9 men, 6 women) with schizophrenia. A choice reaction task was conducted, and performances at 2.5, 5, 7, 10, and 25 degrees in both visual fields were measured. Three key findings were shown. First, patients had slower choice reaction times (choice RTs) than normal controls. Second, patients had slower choice RTs in the right visual field than in the left visual field. Third, patients and normal controls showed the same U-shaped choice RT pattern. The first and second findings were consistent with those of other studies. The third finding was a clear indication of the patients' performance in peripheral vision, and a comparison with normal controls suggested that there was no difference in the size of the useful visual field, at least within     

The lateralized emotional stroop task: left visual field interference in women

In a visual hemifield emotional Stroop task, 54 women were asked to name the color of laterally flashed emotional and neutral words while ignoring their semantic content. Vocal reaction times for color naming were recorded. The participants exhibited significant emotional interference effects in the left visual field, which tended to be larger for negative words than for positive words. Participants with higher trait anxiety scores exhibited larger interference for positive words in the left relative to the right visual field. The outcome indicates that, in women, emotional Stroop interference arises in the right rather than in the left hemisphere, with a larger impact of negative than of positive words, and with trait anxiety modulating the lateralized interference for positive words.