Intruding male red swamp crayfish,Procambarus clarkii,immediately dominate members of established communities of smaller,mixed-sex conspecifics

The effects of competing asymmetries (intruder size advantage vs. prior residence) on dominance relationships were investigated in a laboratory setting. Sexually mature (Form I) male red swamp crayfish, 25%-27% larger than the average member of several mixedsex communities of 20-25 sexually mature conspecifics, individually intruded upon these communities on successive days. Each community was invaded once a day, with each of these large intruders invading every community once during the experiment. Five days after the last large intruder invasion, novel intruder group males, approximately the same size as the average community member, individually invaded the same communities, all communities being invaded once during a single day of testing. These novel intruders were used to differentiate the effects of intruder size from those effects of being put into a novel environment. During each intrusion, the frequencies of dominance, submission, aggressive standoffs, and nonaggressive interactions between the intruder and members of the community were recorded. The large intruders on each day immediately and virtually completely dominated all encountered community members, and the large intruders were significantly more dominant than the novel, smaller-sized intruders. The size advantage of the large intruders overwhelmed prior residence in influencing dominance outcomes, even in these well established communities. © 1995 Wiley-Liss, Inc.     

Hemispheric Asymmetries: Attention to Visual and Auditory Primitives

A computational theory of hemispheric asymmetries in perception (double filtering by frequency) is described. Its central tenet is that the cerebral hemispheres first perform symmetric filtering of visual and auditory information. Functional hemispheric asymmetry arises from a second filtering stage (containing filters skewed in different directions in the two hemispheres). The first stage selects a range of task-relevant spatial or auditory frequencies from the absolute values. This range is passed to the asymmetric filters. In this way, the hemispheric difference becomes one of relative rather than absolute information. Behavioral deficits due to unilateral lesions in neurological patients and neuroimaging and electrophysiological measures in normal subjects implicate posterior cortex in these hemispheric differences.     

Functional magnetic resonance imaging of human cognitive processes

Functional magnetic resonance imaging (fMRI) is now widely accepted as a tool for analyzing human brain function. Since the realization of fMRI in the early 1990s, numerous reports have been published. In this paper, we present three studies. The first examined syntactic processing of Japanese sentences and the results prove that Broca's area is involved in the use of grammar. The second study compared binocular with monocular stereopsis. There were significant activations in the right inferior parietal lobe. The third study concerned the encoding and retrieval processes underlying face recognition. It revealed activations mainly in the right prefrontal areas, which is contrary to the hemispheric encoding and retrieval asymmetry (HERA) theory. fMRI will continue to play an important role in the analysis of human brain function.     

Hemisphere-dependent holistic processing of familiar faces

In two behavioral experiments involving lateralized stimulus presentation, we tested whether one of the most commonly used measures of holistic face processing—the composite face effect—would be more pronounced for stimuli presented to the right as compared to the left hemisphere. In experiment 1, we investigated the composite face effect in a verbal identification task, similar to its original report (Young, Hellawell, & Hay, 1987). Aligning top and bottom halves of composite face stimuli led to performance decreases irrespective of hemifield, indicating holistic processing of comparable magnitude for inputs provided separately to either hemisphere. However, when matching of the same top parts was required in experiment 2, an alignment-dependent performance decrease was found for stimuli presented in the left, but not right visual field. These observations suggest that the right hemisphere dominates in early stages of holistic processing, as indexed by the composite face effect, but that later processes such as face identification and naming are based on unified representations that are independent of input lateralization. Moreover, the composite face effect may not rely on the exact same representation(s) when measured in matching and identification tasks.     

Fitts’ Law as a Function of System Dynamics and Target Uncertainty

Fitts’ law was found to hold for discrete movements executed by subjects controlling the velocity of a cursor with a control stick. The slope of movement time versus index of difficulty was approximately twice as large as for a comparable position control system. Target uncertainty also increased the slope of total time versus index of difficulty, and this effect is interpreted in terms of adaptive tuning of the human movement system.     

Hemispheric processing of anaphoric inferences: the activation of multiple antecedents

This research investigates the hemispheric processing of anaphors when readers activate multiple antecedents. Participants read texts promoting an anaphoric inference and performed a lexical decision task to inference-related target words that were consistent (Experiment 1) or inconsistent (Experiment 2) with the text. These targets were preceded by constrained or less constraining text and were presented to participants' right visual field-left hemisphere or to their left visual field-right hemisphere. In Experiment 1, both hemispheres showed facilitation for consistent antecedents and the right hemisphere showed an advantage over the left hemisphere in processing antecedents when preceded by less constrained text. In Experiment 2, the left hemisphere only showed negative facilitation for inconsistent antecedents. When readers comprehend text with multiple antecedents: both hemispheres process consistent information, the left hemisphere inhibits inconsistent information, and the right hemisphere processes less constrained information.     

Maternal cradling bias in baboons: The first environmental factor affecting early infant handedness development?

The most emblematic behavioral manifestation of human brain asymmetries is handedness. While the precise mechanisms behind the development of handedness are still widely debated, empirical evidences highlight that besides genetic factors, environmental factors may play a crucial role. As one of these factors, maternal cradling behavior may play a key role in the emergence of early handedness in the offspring. In the present study we followed 41 Papio anubis infants living in social groups with their mother for which direction (e.g., left- or right-arm) and degree of maternal cradling-side bias were available from a previous published study. We assessed hand preferences for an unimanual grasping task at three developmental stages: (A) 0–4, (B) 4—6, and (C) 9–10 months of age. We found that individual hand preferences for grasping exist as soon as the first months of age, with a population-level left-handedness predominance, being stable until 6 months; to wit the period during which juveniles are mainly carried by their mothers. More importantly, this early postnatal handedness is positively correlated with maternal cradling lateralization. Interestingly, hand preferences assessed later in the development, once juveniles are no longer carried (i.e., from 9 to 10 months of age), are less dependent from the maternal cradling bias and less consistent with the earlier developmental stages, especially in infants initially cradled on the right maternal side. Our findings suggest that the ontogenetic dynamics of the infant's hand preference and its changes might ultimately rely on the degree of infant dependence from the mother across development.     

Hemispheric asymmetries in processing L1 and L2 idioms: effects of salience and context

This study investigates the contribution of the left and right hemispheres to the comprehension of bilingual figurative language and the joint effects of salience and context on the differential cerebral involvement in idiom processing. The divided visual field and the lexical decision priming paradigms were employed to examine the activation of salient and nonsalient ambiguous idiom interpretations (i.e., literal vs. non-literal) in the two hemispheres. Literally plausible ambiguous idioms, L1 (Polish) and L2 (English), were embedded in unconstraining ambiguous (e.g., I knew he kept an ace up his sleeve) or constraining unambiguous context clearly favoring their conventional idiomatic interpretation (e.g., The debating president kept an ace up his sleeve). Idioms were presented centrally, followed by laterally presented targets related to the figurative (e.g., GAIN) or literal (e.g., SHIRT) meaning of the idiom and displayed at Interstimulus Intervals (ISIs) of 0 ms (Experiment 1), 300 ms (Experiment 2), and 800 ms (Experiment 3). Results indicate that context and salience effects are significantly modulated by the language (native vs. nonnative) of the stimulus materials being presented to each hemisphere. Literal facilitation was found for L2 idioms in all three ISI conditions, which supports the notion of the special status that literal meanings of L2 idioms enjoy in the course of their processing by nonnative language users. No significant differences were found between the right and left hemispheres in regards to their sensitivity to contextual constraints. Results are discussed in terms of the Graded Salience Hypothesis and the Fine/Coarse Coding Theory.     

Hemispheric asymmetry in recognition memory: effects of retention level on the recognition of Portuguese words

Early findings from Broca and Wernicke led to the classical view of hemispheric specialization, where the main idea relates to left-hemisphere language capabilities compared to right-hemisphere visual capabilities. Federmeier and Benjamin (2005) have suggested that semantic encoding for verbal information in the right hemisphere can be more effective when memory demands are higher. In light of this, our main goal was to study the effect of retention level of verbal information on hemispheric processes. However, regarding the cross-linguistic differences in orthography and their subsequent effects on word recognition (Frost, Katz, & Bentin, 1987), our intent was also to test prior predictions of Federmeier and Benjamin (2005) for a "shallow" orthography language, where words have a clear correspondence between graphemes and phonemes, as opposed to English, which is a "deep" orthography language. Portuguese concrete nouns were selected. The participants were submitted to a visual half-field word presentation using a continuous recognition memory paradigm. The retention level included 1, 2, 4, 8, 20 or 40 words. Results showed that recognition accuracy was higher for words studied in the right visual field, compared to those studied in the left visual field, when the retention interval included 2, 4, or 20 words. No significant differences were found for the remaining intervals. Further analysis on accuracy data for intermediate retention levels showed that recognition accuracy was higher for the 2 words retention level than for the levels including 4, 8, or 20 words; it was higher for left-hemisphere encoding as well. Our results also indicated that reaction times were slower for left-hemisphere encoding and for the 40 words retention level when compared to that of 20 words. In summary, the current results are in partial agreement with those of Federmeier and Benjamin (2005) and suggest different hemispheric memory strategies for the semantic encoding of verbal information.     

Asymmetric prefrontal cortex functions predict asymmetries in number space

Little is known about the neuropsychological factors that contribute to individual differences in the asymmetric orientation along the mental number line. The present study documents healthy subjects’ preference for small numbers over large numbers in a random number generation task. This preference, referred to as “small-number bias” (SNB), varied with prefrontal functional lateralization: it was larger in participants with over-proportionately better performance in design fluency compared to letter fluency than in participants with over-proportionately better performance in letter fluency when compared to design fluency. Asymmetries in learning and memory tasks (verbal vs. non-verbal) were not related to direction or size of the SNB. We conclude that hemispheric asymmetries of specifically prefrontal executive functions are predictive of an individual’s lateral orientation bias along the mental number line. Therefore, the focus on parietal contributions to spatial-numerical associations may not be justified. Random number generation may be a helpful method to further explore these associations uncontaminated by the asymmetric involvement of response effectors.