Hemispheric differences in semantic processing: Category matching is not the same as category membership

Two closely related semantic processing tasks were studied under identical procedural conditions in order to examine lateral visual field effects on reaction times. In Experiment 1, reaction times did not differ as a function of visual field when subjects decided whether a lateral word was a member of a foveally presented category word (category membership task). On the other hand, reaction times were faster for right than for left visual field stimulus presentations when subjects decided whether two words, one lateral and one foveal, belonged to the same category (category matching task), although this advantage did not occur immediately. In Experiment 2, the laterality effect in the category matching task was studied as a function of word familiarity. Two groups of subjects performed the matching task for two blocks of trials, one group receiving the same word list in each block and the other receiving different lists. No visual field differences in reaction times were observed for either group during the first block of trials, but a distinct right field advantage appeared for both during the second block. The data from these experiments suggest that category matching strategies rely upon structures or processes localized in the left hemisphere, although their influence is not immediate. Category membership strategies, on the other hand, do not depend upon such localized structures.     

Using event-related potentials to examine hemispheric differences in semantic processing

Event-related potentials (ERPs) were used as the dependent measure in a divided visual field study examining the processing of lexically ambiguous words in the cerebral hemispheres. The goal was to determine if the N400 ERP component is sensitive measure of hemispheric differences in semantic processing. ERP waveforms were examined for lateralized target words that were related to either the dominant (MONEY) or subordinate (RIVER) meanings of ambiguous words (BANK). These waveforms were compared to trials where the prime-target pairs were unrelated. Reliable N400s, reflecting a significant difference between related and unrelated trials, were seen when targets were presented to the right visual field/left hemisphere. However, there were no N400s observed for either the dominant or subordinate conditions when targets were presented to the left visual field/right hemisphere.     

新颖语义联结形成的右半球优势效应

新颖语义联结形成是创造性思维的重要加工过程。采用谜题型歇后语为材料,直接操控语义联结的新颖性,通过两个实验考察汉语新颖语义联结形成的神经机制。实验1采用fMRI记录谜题型歇后语阅读理解过程的神经活动,结果显示相对于寻常语义关联条件,新颖语义关联条件更强地激活了右侧颞上回,该脑区可能与新颖语义信息的激活有关。实验2采用ERP技术在语义关联性判断任务中考察新颖语义联结形成神经加工的时空特征,结果显示相对于寻常语义关联条件,新颖语义关联条件在右侧颞区和右侧额区诱发了更正的晚期正成分,可能分别反映了新颖语义信息的激活以及选择与整合。研究结果支持了新颖语义联结形成的右半球加工优势效应。     

Dual hemispheric processing in a letter matching task

It has been reported that performance on recognition, detection, and matching tasks is enhanced if stimuli are projected to both sides of the visual field rather than to one side alone (Dimond, 1972). The present study investigated the claim that this phenomenon is due to the distribution of the burden of perceptual processing between the hemispheres. Three experiments were carried out using a matching paradigm in which RT and response errors were recorded. In all experiments, subjects were required to match two letters that were displayed separately on either side of a central fixation point (bilateral presentation) or were displayed together on the same side of the visual field (unilateral presentation). It was found that although lateral interference between adjacent stimuli was significantly implicated in the phenomenon, a strong residual effect, which could be tentatively ascribed to hemispheric mechanisms, remained in relation to letter name matches. It is argued that a model based on parallel hemispheric decision processes provides a better account of the data than does one based upon the notion of distributed perceptual processing.     

Handedness and sex differences in hemispheric asymmetry

A study was designed to assess the contributions of the factors of sex and familial history to cerebral dominance, where cerebral dominance was inferred from laterality on a dichotic listening task. The 144 subjects were selected from a larger sample on the basis of handedness, sex, and familial history of sinistrality, and tested on a task involving the dichotic presentation of CV syllables. Analysis of the data indicated that in female subjects, the presence of familial sinistrality increased the likelihood that they present atypical left-ear superiorities, while in males the converse was the case. Moreover, there was a significant sex difference overall, such that males were more clearly lateralized than females. A review of other dichotic listening studies provided support for the reliability of this sex difference for dichotic tasks using verbal material. A review of the clinical literature indicated that the hypothesis of a sex difference is at least tenable and merits further investigation. However, the possibility that there is a sex difference in the cognitive strategy used in dichotic listening cannot be ruled out.     

Familiarity and organization of category terms in semantic memory

In order to determine production frequencies for various category terms, 219 college students were asked to generate category terms (e.g. Automobiles, Vegetables, Relatives) during a 4-rain period. The production frequency (i.e., the number of subjects who listed a particular term) for a given category term may be considered as reflecting the familiarity or amount of usage of that category term, and, as such, should be of value to memory researchers in designing experiments. Additionally, examination of the order in which terms were produced showed that subjects "clustered" related category terms, (e.g., "Countries" and "States" were often produced successively). This clustering of category terrms is supportive of the hypothesis that categories are organized in semantic memory in some kind of higher order structure.     

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.     

Multitask investigation of individual differences in hemispheric asymmetry

Right-handed subjects (N = 120) participated in four different laterality tasks designed to measure aspects of cerebral hemisphere asymmetry: identification of dichotically presented consonant-vowel syllables (CVs), examination of the effects of concurrent repetition of CVs and concurrent anagram solution on finger-tapping by the right and left hands, lateralized identification of CVs presented tachistoscopically to the left and right visual fields, and left/right biases on a free-vision face task involving judgments of emotion. Ear differences in the dichotic listening task were related to the pattern of lateralized interference in the dual-task finger-tapping paradigm. There were no other significant relations between pairs of tasks, but when the present results are considered in the light of other recent experiments, there appears to be a relation between lateral bias on the free-vision face task and visual field differences in tachistoscopic identification. The pattern of results has implications for hypothesized individual differences among right-handers in cerebral dominance for verbal processes, input pathway dominance, and asymmetric arousal of the two cerebral hemispheres.     

Automatic semantic priming with various category relations in Alzheimer's disease and normal aging.

The 6 experiments reported here tested the effects of various category relations on automatic semantic priming in 20 Alzheimer's disease (AD), 20 older control, and 22 younger control subjects. The tasks were either word pronunciation or lexical decision; the prime-target stimulus-onset asynchrony (SOA) was always 250 ms. A variety of category relationships between prime and target were examined: highly associated category comembers, subordinate-superordinate or superordinate-subordinate pairs, and pairs selected on the basis of category typically to form typical-typical, atypical-typical, typical-atypical, and atypical-atypical pairings. Both for AD versus older control subjects and for older versus younger control subjects, no significant group differences were found in the magnitude of overall semantic priming or in the effects on priming of factors pertaining to the prime-target relationship.     

Categorization reaction time,category structure,and category size in semantic memory using artificial categories

This study examined the effects of category structure and category size on categorization reaction time, artificial categories being used to obtain greater experimental control than is usually found in semantic memory research. Four artificial categories varying in structure (hierarchical and nonhierarchical) and size (8 or 16 instances) were introduced to 20 adolescent subjects over a 12-week period by means of stories, exercises, and discussions. Significantly longer categorization reaction times were required for instances from the hierarchical categories, but no set size effect was found. The application of clustering and multidimensional scaling procedures to subjects’ free recall data revealed that subjects had acquired the hierarchical structures but imposed their own structures on the other categories. These findings were interpreted within a spreading activation framework.     

Subject differences in cross-modality matching

Forty-eight Ss performed four tasks each: (1) magnitude estimation of area, (2) magnitude estimation of numerousness, (3) cross-modality matching of force of handgrip to area, and (4) cross-modality matching of force of handgrip to numerousness. An additional 48 Ss performed Tasks 2 and 4. Psychophysical power functions were fitted to the data of each S for each condition. Higher correlations between individual exponents were found for conditions employing a common response (i.e., estimating or squeezing) than were found for conditions with the same set of stimuli. Individual differences among exponents stem more from the idiosyncratic use of the dependent variable than from different sensory characteristics.     

The unification of mind: Integration of hemispheric semantic processing

Seventy-six participants performed a visual half-field lexical decision task at two different stimulus onset asynchronies (50 or 750 ms). Word targets were primed either by a highly associated word (e.g., CLEAN-DIRTY), a weakly associated word (e.g., CLEAN-TIDY), or an unrelated word (e.g., CLEAN-FAMILY) projected to either the same or opposite visual field (VF) as the target. In the short SOA, RVF-left hemisphere primes resulted in high associate priming regardless of target location (ipsilateral or contralateral to the prime) whereas LVF-right hemisphere primes produced both high and low associate priming across both target location conditions. In the long SOA condition, contralateral priming patterns converged, demonstrating only high associate priming in both VF locations. The results of this study demonstrate the critical role of interhemispheric transfer in semantic processing and indicate a need to elaborate current models of semantic processing.     

Neural correlates of audiovisual integration of semantic category information

Previous studies have found a late frontal-central audiovisual interaction during the time period about 150-220 ms post-stimulus. However, it is unclear to which process is this audiovisual interaction related: to processing of acoustical features or to classification of stimuli? To investigate this question, event-related potentials were recorded during a words-categorization task with stimuli presented in the auditory-visual modality. In the experiment, congruency of the visual and auditory stimuli was manipulated. Results showed that within the window of about 180-210 ms post-stimulus more positive values were elicited by category-congruent audiovisual stimuli than category-incongruent audiovisual stimuli. This indicates that the late frontal-central audiovisual interaction is related to audiovisual integration of semantic category information.     

Repetition priming reveals hemispheric differences in compound word processing

The left (LH) and right (RH) hemispheres are thought to implement different mechanisms for visual word recognition; the LH’s parallel encoding strategy is more efficient than the RH’s serial, letter-by-letter analysis. Here we examine differences in hemispheric language processing strategy by investigating repetition priming of compound words (e.g. buttercup) and their constituents (e.g. butter, cup). Eighty-eight right-handed participants (29 M, 59 F) completed a lexical decision experiment in which centrally-presented compounds primed related (whole compound, first constituent, second constituent) and unrelated targets presented laterally to the left or right visual field; participants made button-press word/nonword decisions. Consistent with the LH parallel/RH serial distinction, repetition priming prompted an RH advantage for first constituents, whereas the LH performed equally efficiently in response to both first and second constituents. These data thus highlight differences in the hemispheres’ language processing strategies, offering new evidence supporting a relative parallel/serial distinction in LH/RH visual word recognition.     

Sex differences in performance and hemispheric organization for a nonverbal auditory task.

Musically experienced and inexperienced men and women discriminated among fundamental-frequency contours presented either binaurally (i.e., same contour to both ears) or dichotically (i.e., different contours to each ear). On two separate occasions, males made significantly fewer errors than did females in the binaural condition, but not in the dichotic condition. Subjects with prior musical experience were superior to musically naive subjects in both conditions. The dichotic pitch task produced a left-ear advantage, which was unrelated to gender or musical experience. The results suggest that the male advantage on the binaural task reflects a sex difference in the coordination of the two hemispheres during conjoint processing of the same stimuli rather than a difference in the direction or degree of hemispheric specialization for these stimuli.     

About hemispheric differences in the processing of temporal intervals

The purpose of the present study was to identify differences between cerebral hemispheres for processing temporal intervals ranging from .9 to 1.4 s. The intervals to be judged were marked by series of brief visual signals located in the left or the right visual field. Series of three (two standards and one comparison) or five intervals (four standards and one comparison), marked by sequences of 4 or 6 signals, were compared. While discrimination, as estimated by d', was significantly better in the 4-standard than in the 2-standard condition when stimuli were presented in the left visual field (LVF), this number-of-standard effect on discrimination varied with the difficulty levels when the signals were presented in the LVF. Moreover, the discrimination levels were constant for the different base durations with stimuli presented in the LVF, but not with stimuli presented in the right visual field. This article discusses the implication of these findings for the study of hemispheric dominance for temporal processing and for a single-clock hypothesis.     

Masked priming effects in semantic categorization are independent of category size

The question whether subliminal primes can activate their semantic meaning or not is still of interest today. Three different competing theories have tried to account for the often inconsistent research results: The semantic categorization hypothesis, the direct motor specification hypothesis, and the category search model. The present study aimed to shed light on these different points of view by examining the role of category size in response congruency effects when novel primes are used. Three experiments were conducted and a transparent pattern of results emerged: Significant priming effects were obtained across different tasks, irrespective of category size and irrespective of stimulus set size. The findings are discussed in terms of the three theoretical frameworks. It becomes clear that the present results provide strong evidence in favor of the semantic categorization hypothesis, which assumes semantic processing of subliminal primes.