封闭性知觉在大范围优先性中的特殊性

本文研究当封闭性作为被试分辨的图形性质时,空间位置不确定性和视野位置对大范围优先性有何影响。实验发现：（１）无论复合刺激呈现在视野的中央或外周．分辨复合刺激的整体性质的反应时（ＲＴ）比分辨局部性质的ＲＴ短,整体性质对分辨局部性质的反应有较强的干扰作用。相反,局部性质对分辨整体性质的反应的影响较小;（２）刺激位置的不确定对大范围优先性没有显著影响;（３）与周边刺激相比,分辨视野中央的复合刺激的ＲＴ较短,但整体性质的ＲＴ优势和对局部性质的干扰作用,不受刺激在视野中的位置的影响。这些实验结果揭示了封闭性知觉在大范围优先性中的特殊性。     

注意和非注意条件下的整体和局部性质加工

以往关于整体和局部知觉的研究通常要求被试直接对出现在复合刺激整体或局部水平上的靶目标做反应,因此复合刺激与任务相关并被注意。该研究通过测量复合字母的整体和局部性质对随后出现的探测刺激的启动效应来研究在非注意条件下整体和局部性质加工的差异。实验一发现复合刺激的整体和局部性质对探测刺激产生负启动效应,但二者没有显著差异。实验二缩短了启动刺激与探测刺激之间的时间间隔,复合刺激的整体和局部性质对探测刺激都不再产生启动效应。在实验一、二中,当要求被试直接对复合刺激做反应时,其分辨局部性质的错误率都比分辨整体性质的错误率高。根据这些结果,讨论了在注意和非注意下的整体和局部性质加工的差异。     

刺激的知觉辨认难度与大脑两半球间的分布式加工

采用半视野速示术将标准刺激在中间视野呈现,比较刺激以不同偏心视角（3.5°,5°和6.5°）在左或右视野同时呈现,以检查不同偏心视角引起比较刺激知觉辨认难度的改变对汉字大写数字奇－偶概念同/异判断任务在大脑两半球间分布式加工的影响。结果显示：随偏心视角的增大正确反应时和错误百分数均显著提高;三种视角条件下左右手的正确反应时均有明显的右视野（左半球）优势;3.5°视角右视野（左半球）呈现时右手反应明显快于左手,5°视角右视野（左半球）与左视野（右半球）呈现时均为右手反应明显快于左手,6.5°视角右视野（左半球）与左视野（右半球）呈现时均为左手反应明显快于右手。这些结果提示：本研究条件下只有比较刺激在6.5°偏心视角呈现时刺激和反应可能出现大脑两半球间分布式加工,3.5°和5°视角呈现时可能为左半球单独加工。6.5°视角刺激呈现的分布加工明显由于大视角呈现时比较刺激辨认难度与注意要求的提高所致。     

刺激呈现时间对汉字语义加工脑偏侧化的影响

以往关于汉字字词识别脑功能偏侧化的研究发现了左半球优势、右半球优势或者大脑两半球均势三种不同的结果。该研究采用一侧化Stroop范式(刺激分别只呈现于左视野、中央视野或右视野中),通过系统地改变刺激呈现时间以期探讨刺激呈现时间是可以解释这些不一致结果的可能因素之一。结果显示:对于右利手被试,在刺激呈现时间为60 ms时右半球出现了较强的Stroop效应,在刺激呈现200 ms时左右半球的Stroop效应没有表现出差异,在刺激呈现时间较长时左半球表现出较强的Stroop效应。该结果提示,随着刺激呈现时间的延长,语义优势发生了从右半球到左半球的转换。     

范畴异同判断中大脑两半球功能不对称性的实验研究

本实验利用汉字单词和图片为刺激材料,要求被试判断同时呈现在左视野和中央视野或右视野与中央视野的二个刺激是否属同一范畴,对范畴异同判断中大脑两半球功能不对称性进行研究。实验结果表明:(1)对汉字单词的处理为大脑左半球占优势,对图片材料的处理为大脑右半球占优势;(2)判断方式(异判断和同判断)在左半球和右半球之间未显示出不对称性。     

影响视觉复合刺激中整体和局部性质加工的几种因素

文章研究了视知觉组织,空间位置不确定性和视野位置等因素对复合刺激中整体和局部性质加工的影响。实验发现,（１）当复合刺激呈现在白背景上时,反应时和干扰作用都表明复复合刺激中大图的加工优于小图,刺激位置的不确定削弱大图对小图的干扰作用;而当复合刺激呈现在由“＋”组成的背影或时,小图的加工优于大图,刺激位置的不确定延长分辩小图的ＲＴ;（２）与周国刺激相比,分辨视野中央的复合刺激的ＲＴ较短,这种影响对分辨     

字母识别任务中左、右视野的视听整合差异

采用事件相关电位(ERP)探索字母识别过程中视听整合的神经机制。结果揭示,当刺激呈现在右视野时,整合差异波中存在两个显著的ERP成分:N136以及N262;当刺激呈现在左视野时,并没有显著的整合成分出现。该结果表明,呈现在右视野的视听字母信息更容易被整合。     

字母异同判断中场依存-独立性与大脑右半球机能专门化关系的研究

本研究根据大脑两半球机能专门化的基本知识和《镶嵌图形测验》的特点,提出了关于场独立性个体与场依存性个体之间在大脑右半球机能专门化程度上存在着差异的假设,并预言在一侧半视野速示条件下,当要求被试以有利于大脑右半球专门化机能的方式来判断字母形体异同时,场独立性样组的左侧半视野反应时将显著短于场依存性样组的,同时前者的两个半侧视野间的反应时也会有显著差异。实验证实了预言,从而支持了上述假设。     

汉字认知过程中大脑两半球机能不对称性的实验研究

以往我们的实验表明,大脑两半球在认知单个汉字时,没有表现出任何认知优势,但这并没有使我们得出最后的结论。 该项实验中,我们选出八个汉字并把它们放在四种噪音背景上,它们的信噪比分别为∞,6.66,4,和2.85。被试为20名大学生,男10名,女10名,年龄在19至20岁。刺激呈现时间为60ms。 实验结果如下: (1)无噪音干扰情况下,左、右视野在认知上无差别。信噪比为6.6时,差异不明显。 (2) 只是信噪比为4时,认知难度达到相当水平以后,右视野的优势才变得明显起来。 (3)无论在哪种难度水平上,左视野的反应时都比右视野快,但反应的准确度,右视野却占有优势。     

语篇主题表征在大脑两半球的存贮

使用半视野速示技术和启动—再认探测方法,采用包含两个句子的短语篇作为前行信息、通过主题启动、歧义词启动探测语段阅读时主题表征在大脑两半球的存贮情况,结果发现,无论是主题启动还是歧义词启动,左视野／右半脑和右视野／左半脑对语境相关的目标词反应时间都比不一致目标词更长,说明语段阅读后两半脑对主题表征都有存贮。     

Interlateral asymmetry in the time course of the effect of a peripheral prime stimulus

Evidence exists that both right and left hemisphere attentional mechanisms are mobilized when attention is directed to the right visual hemifield and only right hemisphere attentional mechanisms are mobilized when attention is directed to the left visual hemifield. This arrangement might lead to a rightward bias of automatic attention. The hypothesis was investigated by testing male volunteers, wherein a "location discrimination" reaction time task (Experiments 1 and 3) and a "location and shape discrimination" reaction time task (Experiments 2 and 4) were used. Unilateral (Experiments 1 and 2) and unilateral or bilateral (Experiments 3 and 4) peripheral visual prime stimuli were used to control attention. Reaction time to a small visual target stimulus in the same location or in the horizontally opposite location was evaluated. Stimulus onset asynchronies (SOAs) were 34, 50, 67, 83 and 100 ms. An important prime stimulus attentional effect was observed as early as 50 ms in the four experiments. In Experiments 2, 3 and 4, this effect was larger when the prime stimulus occurred in the right hemifield than when it occurred in the left hemifield for SOA 100 ms. In Experiment 4, when the prime stimulus occurred simultaneously in both hemifields, reaction time was faster for the right hemifield and for SOA 100 ms. These results indicate that automatic attention tends to favor the right side of space, particularly when identification of the target stimulus shape is required.     

Visual field differences in the magnitude of the Oppel-Kundt illusion vary with processing time

Three experiments were performed to investigate hemispheric differences in susceptibility to the Oppel-Kundt illusion presented tachistoscopically to the two visual hemifields. Experiment 1 used a successive comparison mode, in which 16 undergraduate students indicated whether the second of two successive extents looked shorter or longer than the first. Experiment 2 (20 under-graduates) and Experiment 3 (1 commissurotomy patient) required judgments of two extents presented simultaneously. The first experiment found no significant visual field differences, although females were more susceptible than males. In the second experiment, the illusion magnitude was greater in the left visual field, and in the third experiment, it was greater in the right visual field. Post hoc analyses resolve the conflicting results and show that in all three experiments, the susceptibility of the right hemisphere declined more than that of the left hemisphere during illusion processing. An interpretation is offered in terms of two parallel processes, one that is fast, uses feature extraction, and is performed more effectively in the left hemisphere, and one that is slow, uses visuospatial analysis to compute distances between parts of the illusion figure, and is performed more effectively in the right hemisphere.     

Right hemisphere specialization for color detection

Three experiments were carried out to investigate hemispheric asymmetry in color processing among normal participants. In Experiment 1, it was shown that the reaction times (RTs) of the dominant and non-dominant hands assessed using a visual target presented at the central visual field, were not significantly different. In Experiment 2, RTs of ipsilateral hands to lateralized chromatic stimuli revealed that the processing time was 17 ms shorter in the right hemisphere (RH) than that in the left hemisphere among the right-handed participants, whereas no significant difference was found among the left-handed participants. On the other hand, RTs to lateralized achromatic stimuli showed no such asymmetry among both the right- and left-handed participants (Experiment 3). These findings strongly suggest RH superiority for detection of color among right-handed individuals.     

Dissociating prelexical and postlexical processing of affective information in the two hemispheres: effects of the stimulus presentation format

Using a lexical decision task, the authors investigated whether brain asymmetries in the detection of emotionally negative semantic associations arise only at a perceptually discriminative stage at which lexical analysis is accurate or can already be found at crude and incomplete levels of perceptual representation at which word-nonword discrimination is based solely on guessing. Emotionally negative and neutral items were presented near perceptual threshold in the left and right visual hemifields. Word-nonword discrimination performance as well as the bias to classify a stimulus as a "word" (whether or not it actually is a word) were assessed for a normal, horizontal stimulus presentation format (Experiment 1) and for an unusual, vertical presentation format (Experiment 2). Results show that while the two hemispheres are equally able to detect affective semantic associations at a prelexical processing stage (both experiments), the right hemisphere is superior at a postlexical, perceptually discriminative stage (Experiment 2). Moreover, the findings suggest that only an unusual, nonoverlearned stimulus presentation format allows adequate assessment of the right hemisphere's lexical-semantic skills.     

Asynchronous stimulus presentation in visual extinction: A psychophysical study

Patients showing visual extinction as a consequence of a unilateral brain lesion can correctly detect a single stimulus in either hemifield but fail to detect the contralesional stimulus (or at least process the stimulus less efficiently) when it is presented simultaneously with an ipsilesional stimulus. In an attempt to uncover the nature of the underlying deficit, some studies have manipulated the temporal characteristics of stimulus presentation. Contra- and ipsilesional stimuli with different stimulus onset asynchronies are typically used. In the present study, visual extinction was investigated in a group of left neglect patients (N=10) using a psychophysical paradigm with different stimulus onset asynchronies of target and distractor stimuli presented in different hemifields. Contrast thresholds for a target grating were determined with the target either in isolation or in the presence of an irrelevant distractor grating. When target and distractor gratings were presented simultaneously, neglect patients showed a significant extinction effect, i.e., a significant interference from the right hemifield distractor with left hemifield contrast sensitivity. When the right hemifield distractor preceded the left hemifield target stimulus by 250 ms, two different patterns of results were observed in the neglect patients. Five patients showed a significant improvement compared to the simultaneous presentation condition, five other patients showed a significant increase of the extinction effect. The results suggest that different underlying mechanisms, maybe due to different lesion locations, can cause extinction in neglect patients.     

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.     

Developmental changes in the processing of hierarchical shapes continue into adolescence

The present study was designed to trace the normal development of local and global processing of hierarchical visual forms. We presented pairs of hierarchical shapes to children and adults and asked them to indicate whether the two shapes were the same or different at either the global or the local level. In Experiments 1 (6-year-olds, 10-year-olds, adults) and 2 (10-year-olds, 14-year-olds, adults), we presented stimuli centrally. All age groups responded faster on global trials than local trials (global precedence effect), but the bias was stronger in children and diminished to the adult level between 10 and 14 years of age. In Experiment 3 (10-year-olds, 14-year-olds, adults), we presented stimuli in the left or right visual field so that they were transmitted first to the contralateral hemisphere. All age groups responded faster on local trials when stimuli were presented in the right visual field (left hemisphere); reaction times on global trials were independent of visual field. The results of Experiment 3 suggest that by 10 years of age the hemispheres have adult-like specialization for the processing of hierarchical shapes, at least when attention is directed to the global versus local level. Nevertheless, their greater bias in Experiments 1 and 2 suggests that 10-year-olds are less able than adults to modulate attention to the output from local versus global channels-perhaps because they are less able to ignore distractors and perhaps because the cerebral hemispheres are less able to engage in parallel processing.     

Visual search for global/local stimulus features in humans and baboons

Fagot and Deruelle (1997) demonstrated that, when tested with identical visual stimuli, baboons exhibit an advantage in processing local features, whereas humans show the “global precedence” effect initially reported by Navon (1977). In the present experiments, we investigated the cause of this species difference. Humans and baboons performed a visual search task in which the target differed from the distractors at either the global or the local level. Humans responded more quickly to global than to local targets, whereas baboons did the opposite (Experiment 1). Human response times (RTs) were independent of display size, for both local and global processing. Baboon RTs increased linearly with display size, more so for global than for local processing. The search slope for baboons disappeared for continuous targets (Experiment 2). That effect was not due to variations in stimulus luminance (Experiment 3). Finally, variations in stimulus density affected global search slopes in baboons but not in humans (Experiment 4). Overall, results suggest that perceptual grouping operations involved during the processing of hierarchical stimuli are attention demanding for baboons, but not for humans.