Selective impairment of sensorimotor representations following short-term upper-limb immobilization

In the present experiment, we examined whether short-term upper-limb immobilization would selectively affect the representation of the immobilized limb (using a hand laterality task) or whether the effect of immobilization would extend to another body part (using a foot laterality task). A rigid splint placed on the participants’ left hand was used for immobilization. A control group did not undergo the immobilization procedure. We compared the participants’ performances on the hand and foot laterality tasks before (T₁) and after (T₂) a 48-hour delay, corresponding to the immobilization period. For controls, response time analysis indicated a benefit of task repetition for the recognition of both hand and foot images. For the immobilized group, a slowdown of performance appeared in T₂ for hand images, but not for foot images. The reduced benefit of task repetition following left-hand immobilization appeared for both the immobilized and non-immobilized hand images. These findings revealed that the general cognitive representation of upper-limb movements is affected by the decrease in input/output signal processing due to the left-hand immobilization, while the cognitive representation of lower-limb movements is not.     

Hemispheric differences in the perception of words and faces in deaf and hearing children

The purpose of this study was to investigate hemispheric functional asymmetry in 18 normal hearing children and 18 congenitally deaf children aged 13-14 years. The task was identification of a visual stimulus (3-letter word or photograph of a face) presented in either the left or right visual field. The children responded by pointing to the target stimulus on a response card which contained four different words or three different faces. The percentage of errors for presentations to the two visual fields were analysed to determine hemispheric dominance. The pattern of hemispheric differences for the hearing children was consistent with that from previous investigations. The results for the deaf children differed from those of the normals. In word perception we observed a right hemisphere advantage and in the face recognition a lack of hemispheric differences. These results point to a lack of auditory experiences which is affecting the functional organization of the two hemispheres. It is suggested that the necessity to make use of visuo-spatial information in the process of communication causes right hemisphere dominance in verbal tasks. This may influence the perception of other visuo-spatial stimuli which may yield a lack of hemispheric asymmetry in face recognition.     

中国学生的自我面孔识别

已有研究表明大脑右半球具有自我面孔再认的优势。为了进一步验证这个观点,该研究使用面孔识别任务,以13名右利手的中国大学生为被试,测量被试对morphing面孔的左右手反应差异。给被试呈现第一张面孔向第二张面孔的morphing过程,当被试看到morphing的面孔更像第二张面孔时报告停止。研究有两个morphing过程：一个为由自我面孔向名人面孔morphing,另一个为好朋友面孔（熟悉的）向名人面孔morphing。结果表明当用左手反应时,被试倾向于把morphing的面孔识别为自己,研究中自我面孔再认的左手优势与已有的发现一致。另外,研究还发现在一定trials条件下,熟悉面孔再认也具有左手优势,这一结果与西方被试的结果不一致,但东西方被试对熟悉面孔再认的差异与独立型自我和互倚型自我的观点一致。该文认为神经心理学有关自我的研究可能需要考虑文化和情境的复杂性。     

Tympanic Membrane Temperature and Hemispheric Cognitive Style

The authors tested the hypothesis that there is a correlation between hemispheric cognitive style and ear temperature. A sample of 100 participants completed a measure of hemispheric cognitive style, the Hemispheric Consensus Prediction Profile. Ear temperatures were taken in 2 sessions, 2 times for each ear at each session. Average left ear temperature was subtracted from average right ear temperature as an index of dominant temperature. Only 56 of the participants showed a stable dominant ear temperature. For these 56 participants, there was a statistically significant positive correlation between scores on the Hemispheric Consensus Prediction Profile and tympanic member temperature (Spearman's ρ =.29, 95% CI [.04,.51]). Individuals with a left hemispheric cognitive style tended to have a warmer left tympanic membrane temperature while those with a right hemispheric cognitive style tended to have a warmer right tympanic membrane temperature. Tympanic membrane temperatures are easily obtained using inexpensive and noninvasive technology. The relationship suggested by these findings may open new opportunities for the study of cerebral asymmetry.     

Lateralisation of emotions: evidence from pupil size measurement

The way our brain processes emotional stimuli has been studied intensively. One of the main issues still under debate is the laterality of valence processing. Herein, we employed the fact that pupil size increases under conditions of higher mental effort and during emotional processing, in order to contrast three proposed hypotheses in the field. We used different manual response mapping for emotional stimuli: Participants responded with their right hand for positive and with their left hand for negative facial expressions, or vice versa. The hands position was either regular (Experiment 1) or crossed (Experiment 2) in order to rule out a “spatial-valence association” alternate explanation. A third experiment was conducted by employing a passive viewing procedure of peripheral emotional stimuli. In the first two experiments, pupil size was larger when participants responded to positive stimuli with their left hand and to negative with their right hand, compared with the opposite mapping. Results of Experiment 3 strengthen the findings of Experiments 1 and 2. These findings provide significant psychophysiological evidence for the valence hypothesis: Processing positive stimuli involves the left hemisphere, while processing negative stimuli involves the right hemisphere. These results are discussed in relation to contemporary theories of emotion processing.     

Human gestures trigger different attentional shifts in chimpanzees (Pan troglodytes) and humans (Homo sapiens)

Brain lateralization has been the matter of extensive research over the last centuries, but it remains an unsolved issue. While hand preferences have been extensively studied, very few studies have investigated laterality of eye use in non-human primates. We examined eye preference in 14 Campbell’s monkeys (Cercopithecus c. campbelli). We assessed eye preference to look at a seed placed inside a tube using monocular vision. Eye use was recorded for 100 independent and non-rewarded trials per individual. All of the 14 monkeys showed very strong preferences in the choice of the eye used to look inside the tube (mean preference: 97.6%). Eight subjects preferred the right eye and six subjects preferred the left eye. The results are discussed in light of previous data on eye preference in primates, and compared to data on hand preference from these subjects. Our findings would support the hypothesis for an early emergence of lateralization for perceptual processes compared to manual motor functions.     

Functional hemispheric differences for the categorization of global and local information in naturalistic stimuli

Up to now functional hemispheric asymmetries for global/local processing have mainly been investigated with hierarchical letters as stimuli. In the present study, three experiments were conducted to examine whether corresponding visual-field (VF) effects can also be obtained with more naturalistic stimuli. To this end, images of animals with a pattern placed on their body were displayed as stimuli. The task for the global level and for the local level was to categorize the animals and the patterns, respectively. As a result, VF-effects were also found for these stimuli and tasks. It is concluded that the hemispheric differences observed for hierarchical letters also hold for naturalistic stimuli.     

Behavioral and ERP measures of holistic face processing in a composite task

Holistic processing of faces is characterized by encoding of the face as a single stimulus. This study employed a composite face task to examine whether holistic processing varies when attention is restricted to the top as compared to the bottom half of the face, and whether evidence of holistic processing would be observed in event-related potentials. Analyses of behavioral data showed that spatial misalignment of the face halves disrupted holistic processing and enhanced detection of repeated attended halves. Effects of misalignment on the N170, VPP and N250 ERP components resembled effects of face inversion. Attention to the top half of the face was associated with faster P1, N170, VPP, and P2 latencies than attending to the bottom, suggesting automatic processing of the eye region. Further, N170 latency effects suggested that structural encoding of the face is facilitated during holistic processing. N250 latency effects reflected task difficulty. Finally, an overall right hemispheric asymmetry was most pronounced when holistic face processing was greatest. Results are discussed in light of recent proposals that holistic face processing is a subtype of configural face processing.     

Hemispheric asymmetries for temporal information processing: transient detection versus sustained monitoring

This study investigated functional differences in the processing of visual temporal information between the left and right hemispheres (LH and RH). Participants indicated whether or not a checkerboard pattern contained a temporal gap lasting between 10 and 40 ms. When the stimulus contained a temporal signal (i.e. a gap), responses were more accurate for the right visual field-left hemisphere (RVF-LH) than for the left visual field-right hemisphere (LVF-RH). This RVF-LH advantage was larger for the shorter gap durations (Experiments 1 and 2), suggesting that the LH has finer temporal resolution than the RH, and is efficient for transient detection. In contrast, for noise trials (i.e. trial without temporal signals), there was a LVF-RH advantage. This LVF-RH advantage was observed when the entire stimulus duration was long (240 ms, Experiment 1), but was eliminated when the duration was short (120 ms, Experiment 2). In Experiment 3, where the gap was placed toward the end of the stimulus presentation, a LVF-RH advantage was found for noise trials whereas the RVF-LH advantage was eliminated for signal trials. It is likely that participants needed to monitor the stimulus for a longer period of time when the gap was absent (i.e. noise trials) or was placed toward the end of the presentation. The RH may therefore be more efficient in the sustained monitoring of visual temporal information whereas the LH is more efficient for transient detection.     

The effects of bilateral presentations on lateralized lexical decision

We investigated how lateralized lexical decision is affected by the presence of distractors in the visual hemifield contralateral to the target. The study had three goals: first, to determine how the presence of a distractor (either a word or a pseudoword) affects visual field differences in the processing of the target; second, to identify the stage of the process in which the distractor is affecting the decision about the target; and third, to determine whether the interaction between the lexicality of the target and the lexicality of the distractor ("lexical redundancy effect") is due to facilitation or inhibition of lexical processing. Unilateral and bilateral trials were presented in separate blocks. Target stimuli were always underlined. Regarding our first goal, we found that bilateral presentations (a) increased the effect of visual hemifield of presentation (right visual field advantage) for words by slowing down the processing of word targets presented to the left visual field, and (b) produced an interaction between visual hemifield of presentation (VF) and target lexicality (TLex), which implies the use of different strategies by the two hemispheres in lexical processing. For our second goal of determining the processing stage that is affected by the distractor, we introduced a third condition in which targets were always accompanied by "perceptual" distractors consisting of sequences of the letter "x" (e.g., xxxx). Performance on these trials indicated that most of the interaction occurs during lexical access (after basic perceptual analysis but before response programming). Finally, a comparison between performance patterns on the trials containing perceptual and lexical distractors indicated that the lexical redundancy effect is mainly due to inhibition of word processing by pseudoword distractors.