The two sides of the mental clock: the Imaginal HemiSpatial Effect in the healthy brain

When subjects are asked to compare the mental images of two analog clocks telling different times (the mental clock test), they are faster to process angles formed by hands located in the right than in the left half of the dial. In the present paper, we demonstrate that this Imaginal HemiSpatial Effect (IHSE) can be also observed in two modified versions of the mental clock test: in Experiment 1 subjects had to imagine the position occupied by two numbers within a clock face and to judge if the subtended angle was smaller or greater than 90 degrees , while in Experiment 2 subjects were asked to match two imagined positions on a clock face with two visually presented locations. The finding of the IHSE in these tasks suggested that it is a genuine phenomenon related to spatial imagery tasks, and is consistent with recent neuroimaging evidence that the left parietal lobe is mainly involved in the generation of spatial mental images.     

A computational analysis of mental image generation: evidence from functional dissociations in split-brain patients

Recent efforts to build computer simulation models of mental imagery have suggested that imagery is not a unitary phenomenon. Rather, such efforts have led to a modular analysis of the image-generation process, with separate modules that can activate visual memories, inspect parts of imaged patterns, and arrange separate parts into a composite image. This idea was supported by the finding of functional dissociations between the kinds of imagery tasks that could be performed in the left and right cerebral hemispheres of two patients who had previously undergone surgical transection of their corpus callosa. The left hemisphere in both subjects could inspect imaged patterns and could generate single and multipart images. In contrast, although the right hemisphere could inspect imaged patterns and could generate images of overall shape, it had difficulty in generating multipart images. The results suggest a deficit in the module that arranges parts into a composite. The observed pattern of deficits and abilities implied that this module is not used in language, visual perception, or drawing. Furthermore, the results suggest that the basis for this deficit is not a difficulty in simply remembering visual details or engaging in sequential processing.     

Imagery and verbal encoding in left and right hemisphere damaged patients

Neuropsychological aspects of imaginal and verbal encoding in memory were explored in two forced-choice recognition memory experiments with patients suffering from left and right anterior cerebral hemisphere damage. In the first experiment stimulus type and rate of presentation were varied. Predictions of patient performance based on the hypothesis that left anterior hemisphere pathology impairs verbal memory coding and right anterior hemisphere pathology impairs imaginal coding were confirmed. In a second recognition memory experiment for pictures of common objects, system-specific (imaginal or verbal) interference and distractor effects were demonstrated by analyzing the effects of interpolated tasks and the nature of false-recognition errors.     

Space-time compatibility effects in the auditory modality

Previous research suggests that past and future temporal concepts are spatially represented from left to right along a mental line. And these concepts can both prime motor responses to left or right space and direct visual spatial attention. The present study aimed at investigating the nature of this space-time conceptual metaphor in different auditory tasks. In the first experiment, subjects categorized time-related words (past or future) that were presented binaurally. In the second experiment, subjects detected left-ear or right-ear targets following time-related words. The similar space-time compatibility effects were found in these two experiments. Our results demonstrate that the activation of temporal concepts can both prime motor responses to left or right space and influence the orientation of auditory spatial attention, suggesting that the modality of the stimulus input is unimportant for the left-right mapping of time. These results are explained by the "intermediate coding" account.     

An investigation of immune system disorder as a "marker" for anomalous dominance

Geschwind and Galaburda (1987) proposed that immune disorder (ID) susceptibility, along with left handedness and familial sinistrality (FS), is a "marker" for anomalous dominance. The theory predicts lesser left lateralization for language processes, lessened left hemisphere abilities, and enhanced right hemisphere abilities. We assessed language laterality (dichotic consonant vowel task) and performances on spatial and verbal tasks. Subjects were 128 college students. The factors of handedness, sex, FS, and immune disorder history (negative or positive) were perfectly counterbalanced. Left-handers were significantly less lateralized for language and scored lower than right-handers on the spatial tasks. Females scored lower on mental rotation than males, but performed comparably to males on the spatial relations task. The only effect of ID was by way of interaction with FS on both spatial tasks--subjects who were either negative or positive on both FS and ID status factors scored significantly higher than subjects negative for one but positive for the other factor. A speculative explanatory model for this interaction was proposed. The model incorporates the notion that FS and ID factors are comparably correlated, but in opposite directions, with hormonal factors implicated by other research as relevant for spatial ability differences. Finally, no support for the "anomalous dominance" hypothesis predictions was found.     

视觉表象产生的大脑半球专门化效应

采用Kosslyn单侧视野速示技术, 以英文字母图片为学习材料, 通过三个实验考察了视觉表象产生的大脑半球专门化效应。实验一提出在两种类型的视觉表象产生任务中, 有两种截然不同的加工起作用, 但却不能直接证实这两种不同加工机制的存在。实验二和实验三则进一步证实了两种表象产生任务具有不同的认知加工机制, 并表现出不同的大脑半球专门化效应。上述研究表明: 大脑两半球均参与产生视觉心理表象, 但分工不同, 并表现出不同的单侧化效应: 大脑左半球通过运用类别空间关系产生表象更有效, 大脑右半球运用数量空间关系产生表象更有效。结果进一步拓展了Kosslyn关于视觉空间关系加工的大脑半球专门化观点。     

Autonomic and behavioral evidence of "implicit" memory in amnesia

A profoundly amnesic patient with a left retrosplenial-fornix lesion was tested on a recognition task that evaluated both verbal and electrodermal aspects of new learning. In addition, "implicit memory" tasks (mirror reading and perceptual identification) were given. The patient displayed strong evidence of learning on all tasks although the results of this learning were not represented in explicit recall or recognition. These findings suggest that autonomic as well as behavioral evidence can index spared memory functions in amnesia. The specific meaning of electrodermal recognition and its possible place in the distinction between implicit and explicit memory is discussed.     

Visual imagery and knowledge about the visual appearance of objects in patients with posterior cerebral artery lesions

The purpose of this study was to explore whether patients with left posterior cerebral artery (PCA) lesions have defective mental visual imagery and to differentiate whether such a deficit stems from a loss of knowledge about the visual appearance of objects or from an inability to create mental visual images out of preserved visual knowledge. Normal controls and patients with either left or right PCA lesions were asked to verify low- and high-imagery sentences and then to verify pictorial representations of the predicates of high-imagery sentences. High-imagery questions concerned either the shape or the color of objects. In addition, perceptual discrimination of shape and color was assessed. Patients with right PCA lesions were impaired on the perceptual discrimination tasks. Left PCA patients did not significantly differ from controls on low-imagery sentences but scored significantly lower on shape and color questions. Their impairment was distinctly more severe with the pictorial than with the verbal versions of shape and color questions. In comparison to patients with occipital left PCA lesions, patients with temporo-occipital left PCA lesions were selectively impaired on verbal and visual color questions. It is concluded that patients with left PCA lesions lack knowledge about shape and color of objects, but that their ability to convert visual knowledge into mental images is preserved.     

Sex differences in spatial task performance of patients with and without unilateral cerebral lesions

Two visuospatial tasks, the WAIS Block Design and the Street Gestalt Completion Test, were administered to men and women with and without unilateral cerebral lesions. These two tasks represent different categories of visuospatial functions. The Street test is a visual-perceptual gestalt task, requiring the closure of fragmented pictures, whereas Block Design is an analytical, manipulospatial task requiring rotation of spatial coordinates. For the non-brain-damaged group, the men showed a nonsignificant trend toward better Block Design performance relative to the women, whereas there was no sex-related difference in Street performance. For the brain-damaged groups, patients with right hemisphere lesions performed significantly worse than patients with left hemisphere lesions on both the Street test and Block Design, indicating that both tasks were more sensitive to right hemisphere functioning. There was, however, a significant sex X side of lesion interaction on Block Design only, with the men showing a more asymmetrical pattern of scores. These results suggest that sex differences in functional lateralization may underlie sex differences in visuospatial ability, and that sex differences in functional lateralization may be present for only certain visuospatial processes.     

自我和物体为参照系的心理旋转分离：内旋效应

采用虚拟的旋转不同角度左、右手模型,构建“左右手判断(Left and right hand judgment: LR)”任务和“相同－不同判断(same and different judgment: SD)”任务,考察这两种实验任务是否都存在内旋效应和角度效应,以此推论被试采用何种旋转策略。结果发现：（1） 两种实验任务结果均表现出显著的角度效应。（2）在LR任务条件下,存在显著的内旋效应,而在SD任务中不存在内旋效应。从而表明当人手图片作为心理旋转材料时,它具有双重角色。被试心理旋转加工时究竟选用何种参照系的旋转策略,与实验材料和实验任务两者都密不可分     

The visual basis of category effects in object identification: evidence from the visual hemifield paradigm

The basis for the category specific living things advantage in object recognition (i.e., faster and more accurate identification of living compared to nonliving things) was investigated in two experiments. It was hypothesised that the global shape of living things on average provides more information about their basic level identity than the global shape of nonliving things. In two experiments subjects performed name-picture or picture-name verification tasks, in which blurred or clear images of living and nonliving things were presented in either the right or the left visual hemifield. With blurred images, recognition performance was worst for nonliving things presented to the right visual field/left hemisphere, indicating that the lack of visual detail in the stimulus combined with a left hemisphere bias toward processing high frequency visual elements proved detrimental for processing nonliving stimuli in this condition. In addition, an overall living things advantage was observed in both experiments. This advantage was considerably larger with blurred images than with clear. These results are compatible with the global shape hypothesis and converge with evidence using other paradigms.     

Frontal brain asymmetry in depression with comorbid anxiety: a neuropsychological investigation

The approach-withdrawal model posits that depression and anxiety are associated with a relative right asymmetry in frontal brain activity. Most studies have tested this model using measures of cortical brain activity such as electroencephalography. However, neuropsychological tasks that differentially use left versus right frontal cortical regions can also be used to test hypotheses from the model. In two independent samples (Study 1 and 2), the present study investigated the performance of currently depressed individuals with or without a comorbid anxiety disorder and healthy controls on neuropsychological tasks tapping primarily left (verbal fluency) or right (design fluency) frontal brain regions. Across both samples, results indicated that comorbid participants performed more poorly than depressed only and control participants on design fluency, while all groups showed equivalent performance on verbal fluency. Moreover, comorbid participants showed "asymmetrical" performance on these two tasks (i.e., poorer design [right frontal] relative to verbal [left frontal] fluency), whereas depressed only and control participants showed approximately symmetrical profiles of performance. Results from these two samples suggest an abnormal frontal asymmetry in neurocognitive performance driven primarily by right frontal dysfunction among anxious-depressed individuals and highlight the importance of considering comorbid anxiety when examining frontal brain functioning in depression.     

Apparent shift in visual field preference after unilateral stroke

Patients with either a left- or a right-hemisphere stroke lesion scored higher in tasks of word-picture matching and of nonverbal shape matching when information was presented tachistoscopically (120 msec) to the visual field (VF) projecting to their undamaged hemisphere. Left-hemisphere stroke patients (n = 13) were dissociated from right-hemisphere stroke patients (n = 15) by low word recognition from memory and by low right VF but nearly normal left VF accuracy in word-picture matching or shape matching; the former appeared to rely upon processing of word meaning by the right hemisphere. In contrast, right-stroke patients had higher right than left VF scores in both tasks, and their discrimination of nonverbal shapes via the right VF was not different from that of controls (n = 15). Preferred processing by the VF projecting to the undamaged hemisphere appeared as a shift in perceptual asymmetry but may indicate, in support of a "direct access" model, that each hemisphere responds more or less efficiently to word and to nonverbal shape discriminations.     

汉语背景下横纵轴上的心理时间线

采用反应区分范式, 以表示过去和未来的时间词为刺激, 对汉语背景下横、纵两轴上的时间表征情况进行了探讨。结果发现, (1)横、纵轴方向上都出现了STEARC效应; (2)右对角线方向上, 出现了服从横轴的减弱的STEARC效应, 且STEARC效应值呈正态分布。以上结果表明, 汉语背景下既存在从左向右的心理时间线, 也存在从上到下的心理时间线, 两种时间表征同时存在, 且横轴表征倾向于占优势。     

Temporal discrimination in the split brain

Divided visual field studies of neurologically normal adults indicate that the left hemisphere is superior to the right in making temporal judgments. Some neuroimaging and neuropsychological studies, however, have suggested a role for the right hemisphere in temporal processing. We tested the divided hemispheres of a split-brain patient in two tasks requiring temporal judgments about visually presented stimuli. In one task, the patient judged whether two circles presented to one visual field appeared for the same or different durations. In the second task, the patient judged whether the temporal gaps in two circles occurred simultaneously or sequentially. In both tasks, the performance of the right hemisphere was superior to that of the left. This suggests that the right hemisphere plays an important role in making temporal judgments about visually presented stimuli.     

Right hemisphere participation in reading

This study examined whether the right hemisphere's contribution to lexical semantic processing is greatest when it is "disinhibited." Skilled reading may require the controlled modulation of interhemispheric interaction: the left hemisphere (or some other control mechanism) may regulate the subprocesses of reading by selectively "inhibiting" and "disinhibiting" right hemisphere function. Right-handed undergraduates concurrently performed two tasks: a lateralized semantic or rhyme task and a verbal memory task. It was hypothesized that right hemisphere reading processes would be disinhibited when the left hemisphere was "occupied" with the memory task. This hypothesis was supported for a subgroup of subjects who showed evidence of inhibition of right hemisphere function (i.e., left hemisphere dominance for lexical processing) when the lateralized semantic task was performed alone. Across subjects, there was a strong correlation between the degree of left hemisphere dominance in the single-task semantic conditions and the degree of disinhibition of right hemisphere function in the dual-task semantic condition.     

Bilateral capacity for speech sound processing in auditory comprehension: evidence from Wada procedures

Data from lesion studies suggest that the ability to perceive speech sounds, as measured by auditory comprehension tasks, is supported by temporal lobe systems in both the left and right hemisphere. For example, patients with left temporal lobe damage and auditory comprehension deficits (i.e., Wernicke's aphasics), nonetheless comprehend isolated words better than one would expect if their speech perception system had been largely destroyed (70-80% accuracy). Further, when comprehension fails in such patients their errors are more often semantically-based, than-phonemically based. The question addressed by the present study is whether this ability of the right hemisphere to process speech sounds is a result of plastic reorganization following chronic left hemisphere damage, or whether the ability exists in undamaged language systems. We sought to test these possibilities by studying auditory comprehension in acute left versus right hemisphere deactivation during Wada procedures. A series of 20 patients undergoing clinically indicated Wada procedures were asked to listen to an auditorily presented stimulus word, and then point to its matching picture on a card that contained the target picture, a semantic foil, a phonemic foil, and an unrelated foil. This task was performed under three conditions, baseline, during left carotid injection of sodium amytal, and during right carotid injection of sodium amytal. Overall, left hemisphere injection led to a significantly higher error rate than right hemisphere injection. However, consistent with lesion work, the majority (75%) of these errors were semantic in nature. These findings suggest that auditory comprehension deficits are predominantly semantic in nature, even following acute left hemisphere disruption. This, in turn, supports the hypothesis that the right hemisphere is capable of speech sound processing in the intact brain.     

Reversing spoken items--mind twisting not tongue twisting

Using 12 participants we conducted an fMRI study involving two tasks, word reversal and rhyme judgment, based on pairs of natural speech stimuli, to study the neural correlates of manipulating auditory imagery under taxing conditions. Both tasks engaged the left anterior superior temporal gyrus, reflecting previously established perceptual mechanisms. Engagement of the left inferior frontal gyrus in both tasks relative to baseline could only be revealed by applying small volume corrections to the region of interest, suggesting that phonological segmentation played only a minor role and providing further support for factorial dissociation of rhyming and segmentation in phonological awareness. Most importantly, subtraction of rhyme judgment from word reversal revealed activation of the parietal lobes bilaterally and the right inferior frontal cortex, suggesting that the dynamic manipulation of auditory imagery involved in mental reversal of words seems to engage mechanisms similar to those involved in visuospatial working memory and mental rotation. This suggests that reversing spoken items is a matter of mind twisting rather than tongue twisting and provides support for a link between language processing and manipulation of mental imagery.     

Role of the left hemisphere in sign language comprehension

We investigated the relative role of the left versus right hemisphere in the comprehension of American Sign Language (ASL). Nineteen lifelong signers with unilateral brain lesions [11 left hemisphere damaged (LHD) and 8 right hemisphere damaged (RHD)] performed three tasks, an isolated single-sign comprehension task, a sentence-level comprehension task involving simple one-step commands, and a sentence-level comprehension task involving more complex multiclause/multistep commands. Eighteen of the participants were deaf, one RHD subject was hearing and bilingual (ASL and English). Performance was examined in relation to two factors: whether the lesion was in the right or left hemisphere and whether the temporal lobe was involved. The LHD group performed significantly worse than the RHD group on all three tasks, confirming left hemisphere dominance for sign language comprehension. The group with left temporal lobe involvement was significantly impaired on all tasks, whereas each of the other three groups performed at better than 95% correct on the single sign and simple sentence comprehension tasks, with performance falling off only on the complex sentence comprehension items. A comparison with previously published data suggests that the degree of difficulty exhibited by the deaf RHD group on the complex sentences is comparable to that observed in hearing RHD subjects. Based on these findings we hypothesize (i) that deaf and hearing individuals have a similar degree of lateralization of language comprehension processes and (ii) that language comprehension depends primarily on the integrity of the left temporal lobe.     

Perceptual biases in processing facial identity and emotion

Normal observers demonstrate a bias to process the left sides of faces during perceptual judgments about identity or emotion. This effect suggests a right cerebral hemisphere processing bias. To test the role of the right hemisphere and the involvement of configural processing underlying this effect, young and older control observers and patients with right hemisphere damage completed two chimeric faces tasks (emotion judgment and face identity matching) with both upright and inverted faces. For control observers, the emotion judgment task elicited a strong left-sided perceptual bias that was reduced in young controls and eliminated in older controls by face inversion. Right hemisphere damage reversed the bias, suggesting the right hemisphere was dominant for this task, but that the left hemisphere could be flexibly recruited when right hemisphere mechanisms are not available or dominant. In contrast, face identity judgments were associated most clearly with a vertical bias favouring the uppermost stimuli that was eliminated by face inversion and right hemisphere lesions. The results suggest these tasks involve different neurocognitive mechanisms. The role of the right hemisphere and ventral cortical stream involvement with configural processes in face processing is discussed.