Visual field asymmetries in attention vary with self-reported attention deficits

The purpose of this study was to determine whether an index of self-reported attention deficits predicts the pattern of visual field asymmetries observed in behavioral measures of attention. Studies of “normal” subjects do not present a consistent pattern of asymmetry in attention functions, with some studies showing better left visual field (LVF) performance, others showing no asymmetry or even a right visual field (RVF) advantage. Here we found that a participant variable (a measure of self-reported attention problems) may help to explain these inconsistencies. We used Conners’ Adult ADHD Rating Scales to measure self-reported attention problems in a group of 36 normal (non-ADHD) subjects, and we used two behavioral tasks to directly measure their attentional abilities: a lateralized Attention Network Task (ANT) and a visual search task. Comparing subjects with relatively Low versus High scores on the attention-deficit (AD) scale, we found that subjects with High scores were less efficient in orienting attention to the left visual field. When LVF targets were preceded by a valid spatial cue, response times were positively correlated with AD scores, indicating slower covert-attention shifts as attention-deficit scores increased. Right visual field data showed a different pattern of results. Subjects with High AD scores were at least as efficient as those with Low AD scores in orienting attention to the RVF. This study provides evidence that visual field asymmetries in orienting attention vary across individuals, and that level of self-reported attention problems correlates with behavioral deficiencies in orienting attention to the left visual field.     

Geometry,landmarks and the cerebral hemispheres: 2D spatial reorientation in split‐brain patients

A right‐hemispheric superiority in spatial encoding based on geometric cues has been largely documented in a variety of species, together with a left‐hemispheric specialization for encoding based on landmarks. In humans, hemispheric asymmetries for spatial encoding have been little explored. In this study, we compared a patient with a complete callosal resection (D.D.C.) and a patient with a wide callosal resection saving the splenium (A.P.), with healthy participants. In two 2D versions of the ‘reorientation task’, participants were asked to find the target corner of a rectangle‐shaped environment, by exploiting either geometric information alone or the combination of geometric and landmark information. In Experiment 1, the landmark consisted of a coloured side of the rectangle; in Experiment 2, this cue was replaced by a coloured disc located inside the rectangle. In both experiments, the rectangular shape ensured the geometric cue. D.D.C. was always unable to recall the target, whereas A.P. correctly solved the task when only the geometric information was available, without difference with respect to the controls. Importantly, the performance of A.P. did not differ from controls’ when the right hemisphere was tested with the landmark cues (the task being carried out using the left hand), whereas when the left hemisphere was tested (right‐hand session) his performance was worse than controls’ with the coloured side of the space, but it was better than controls’ with the coloured disc. The results are discussed comparing them with data collected on other species, and with theories of spatial processing.     

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.     

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.     

Valence-specific laterality effects in vocal emotion: interactions with stimulus type, blocking and sex

Valence-specific laterality effects have been frequently obtained in facial emotion perception but not in vocal emotion perception. We report a dichotic listening study further examining whether valence-specific laterality effects generalise to vocal emotions. Based on previous literature, we tested whether valence-specific laterality effects were dependent on blocked presentation of the emotion conditions, on the naturalness of the emotional stimuli, or on listener sex. We presented happy and sad sentences, paired with neutral counterparts, dichotically in an emotion localisation task, with vocal stimuli being preceded by verbal labels indicating target emotions. The measure was accuracy. When stimuli of the same emotion were presented as a block, a valence-specific laterality effect was demonstrated, but only in original stimuli and not morphed stimuli. There was a separate interaction with listener sex. We interpret our findings as suggesting that the valence-specific laterality hypothesis is supported only in certain circumstances. We discuss modulating factors, and we consider whether the mechanisms underlying those factors may be attentional or experiential in nature.     

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 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.     

Valence specific laterality effects in free viewing conditions: the role of expectancy and gender of image

Recent research has looked at whether the expectancy of an emotion can account for subsequent valence specific laterality effects of prosodic emotion, though no research has examined this effect for facial emotion. In the study here (n=58), we investigated this issue using two tasks; an emotional face perception task and a novel word task that involved categorising positive and negative words. In the face perception task a valence specific laterality effect was found for surprise (positive) and anger (negative) faces in the control but not expectancy condition. Interestingly, lateralisation differed for face gender, revealing a left hemisphere advantage for male faces and a right hemisphere advantage for female faces. In the word task, an affective priming effect was found, with higher accuracy when valence of picture prime and word target were congruent. Target words were also responded to faster when presented to the LVF versus RVF in the expectancy but not control condition. These findings suggest that expecting an emotion influences laterality processing but that this differs in terms of the perceptual/experience dimension of the task. Further, that hemispheric processing of emotional expressions appear to differ in the gender of the image.     

Evidence for dissociable neural mechanisms underlying inference generation in familiar and less-familiar scenarios

In this study, we investigated whether the left and right hemispheres are differentially involved in causal inference generation. Participants read short inference-promoting texts that described either familiar or less-familiar scenarios. After each text, they performed a lexical decision on a letter string (which sometimes constituted an inference-related word) presented directly to the left or right hemisphere. Response-time results indicated that hemisphere of direct presentation interacted with type of inference scenario. When test stimuli were presented directly to the left hemisphere, lexical decisions were facilitated following familiar but not following less-familiar inference scenarios, whereas when test stimuli were presented directly to the right hemisphere, facilitation was observed in both familiar and less-familiar conditions. Thus, inferences may be generated in different ways depending on which of two dissociable neural subsystems underlies the activation of background information.     

A critical boundary to the left-hemisphere advantage in visual-word processing

Two experiments explored boundary conditions for the ubiquitous left-hemisphere advantage in visual-word recognition. Subjects perceptually identified words presented directly to the left or right hemisphere. Strong left-hemisphere advantages were observed for UPPERCASE and lowercase words. However, only a weak effect was observed for AlTeRnAtInG-cAsE words, and a numerical reversal of the typical left-hemisphere advantage was observed for words in a visual prototype font (a very unfamiliar word format). Results support the theory that dissociable abstract and specific neural subsystems underlie visual-form recognition and fail to support the theory that a visual lexicon operates in the left hemisphere.