Cerebral lateralization for the processing of spatial coordinates and categories in left-and right-handers

Subjects judged whether a tachistoscopially lateralized drawing was identical or different to a drawing seen immediately before in free vision. The drawings depicted natural objects (e.g. animals). On half of the trials the tachistoscopic drawing presented the same objects but either the categorical or the coordinate spatial relations (according to Kosslyn's definitions [23]) between the objects were transformed. In the first experiment 38 right-handed subjects (half males and half females) were tested. Categorical judgements were faster when the match drawing appeared in the right visual field, whereas coordinate judgements were faster when the match drawing appeared in the left visual field. In the second experiment 26 right-handed and 40 left-handed subjects participated. Almost all the subjects were female. Right-handed subjects replicated the findings of the subjects in the first experiment. However, the LHs did not show any difference in response times between spatial conditions and visual fields. These findings support Kosslyn's hypothesis that the left and right hemispheres are specialized respectively for processing categorical and coordinate spatial relations. Moreover, they also suggest that this lateralization pattern is not typical of left-handers.     

The ontogeny of right cerebral lateralization of spatial mental set.

Tested the manner in which right-hemisphere function lateralizes in childhood based on the left-hemisphere bias in visual orientation that results from inducing spatial mental set. 49 male and 49 female 5–12 yr olds identified tachistoscopically presented digits in either half field, given either verbal or spatial priming. The spatial priming even diminished the right-field advantage in the verbal condition when it was conducted in the 2nd session several days later. No evidence of progressive lateralization for the left hemisphere (verbal identification) or for the right hemisphere (spatial priming) process was found. Minor sex differences could be due to strategic factors. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Right visual field superiority for letter recognition with partial report.

Experiments using partial report techniques have typically failed to find left-right visual field differences in the recognition of tachistoscopically presented letter rows. Such data represent a difficulty for theories that emphasize the relevance of cerebral hemispheric asymmetry. It is contended that the end items of a display are critical, and that a truly symmetric display should have both a left and a right end item in each visual field. In the present experiments with 36 righthanded university students, partial report procedures were employed, but a gap was placed between the left and right halves of the display. In the 1st experiment, a single-letter spatial probe procedure was used, and a clear right visual field superiority was found. In the 2nd experiment, a hemifield report procedure was used; the presence of a gap in the display enhanced the right visual field superiority, especially for shorter strings of letters. Results indicate that right visual field superiority can be obtained with partial report procedures under appropriate conditions. (French summary) (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The up–right/down–left advantage for vertically oriented stimuli and horizontally oriented responses: A dual-strategy hypothesis.

C. Umiltà's (1991) proposal that the up–right/down–left advantage for up and down stimuli mapped to left and right responses is due to verbal coding was evaluated. Two approaches were used in separating spatial from verbal codes. The 1st approach used a reaction time distribution bin analysis to examine the effect of response speed on the up–right/down–left advantage. The 2nd approach attempted to create task conditions that would promote either a verbal or visual strategy. Results show that the up–right/down–left advantage increased as response speed slowed down. This finding was interpreted in terms of the dual-strategy hypothesis, which asserts that participants may use the visual or the verbal stimulus code and that, depending on the task constraints, a visual or verbal strategy may prevail. With a visual strategy, no compatibility effect arises. With a verbal strategy, the up–right/down–left advantage emerges. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sustained visual-spatial attention produces costs and benefits in response time and evoked neural activity

This study investigated the simple reaction time (RT) and event-related potential (ERP) correlates of biasing attention towards a location in the visual field. RTs and ERPs were recorded to stimuli flashed randomly and with equal probability to the left and right visual hemifields in the three blocked, covert attention conditions: (i) attention divided equally to left and right hemifield locations; (ii) attention biased towards the left location; or (iii) attention biased towards the right location. Attention was biased towards left or right by instructions to the subjects, and responses were required to all stimuli. Relative to the divided attention condition, RTs were significantly faster for targets occurring where more attention was allocated (benefits), and slower to targets where less attention was allocated (costs). The early P1 (100-140 msec) component over the lateral occipital scalp regions showed attentional benefits. There were no amplitude modulations of the occipital N1 (125-180 msec) component with attention. Between 200 and 500 msec latency, a late positive deflection (LPD) showed both attentional costs and benefits. The behavioral findings show that when sufficiently induced to bias attention, human observers demonstrate RT benefits as well as costs. The corresponding P1 benefits suggest that the RT benefits of spatial attention may arise as the result of modulations of visual information processing in the extrastriate visual cortex.     

Form-specific explicit and implicit memory in the right cerebral hemisphere.

Results from 2 divided visual field (DVF) experiments indicate that in some conditions both explicit and implicit memory are greater when same-letter-case stimuli are presented directly to the right cerebral hemisphere (in the left visual field) than when they are presented directly to the left (in the right visual field). Explicit memory was measured with word-stem cued recall, and implicit memory was measured with word-stem completion priming. Words were presented centrally during encoding, and word stems were presented directly to the right hemisphere or to the left hemisphere during testing. Results for explicit memory contrast with findings from a previous DVF study that used a different procedure, those for implicit memory replicate previous DVF findings, and both results corroborate positron emission tomography findings. It is suggested that a form-specific system in the right hemisphere may contribute to both explicit and implicit memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Right hemisphere performance and competence in processing mental images, in a case of partial interhemispheric disconnection

The objective of this study was to analyze dynamic aspects of right hemisphere implementation in processing visual images. Two tachistoscopic, divided visual field experiments were carried out on a partial split-brain patient with no damage to the right hemisphere. In the first experiment, image generation performance for letters presented in the right visual field (/left hemisphere) was undeniably optimal. In the left visual field (/right hemisphere), performance was no better than chance level at first, but then improved dramatically across stimulation blocks, in each of five successive sessions. This was interpreted as revealing the progressive spontaneous activation of the right hemisphere's competence not shown initially. The aim of the second experiment was to determine some conditions under which this pattern was obtained. The experimental design contrasted stimuli (words and pictures) and representational activity (phonologic and visuo-imaged processing). The right visual field (/left hemisphere: LH) elicited higher performance than the left visual field (/right hemisphere, RH) in the three situations where verbal activity was required. No superiority could be found when visual images were to be generated from pictures: parallel and weak improvement of both hemispheres was observed across sessions. Two other patterns were obtained: improvement in RH performance (although LH performance remained superior) and an unexpectedly large decrease in RH performance. These data are discussed in terms of RH cognitive competence and hemisphere implementation.     

Hemiface contributions to hemispheric dominance in visual speech perception.

Lateralized displays are used widely to investigate hemispheric asymmetry in language perception. However, few studies have used lateralized displays to investigate hemispheric asymmetry in visual speech perception, and those that have yielded mixed results. This issue was investigated in the current study by presenting visual speech to either the left hemisphere (LH) or the right hemisphere (RH) using the face as recorded (normal), a mirror image of the normal face (reversed), and chimeric displays constructed by duplicating and reversing just one hemiface (left or right) to form symmetrical images (left-duplicated, right-duplicated). The projection of displays to each hemisphere was controlled precisely by an automated eye-tracking technique. Visual speech perception showed the same, clear LH advantage for normal and reversed displays, a greater LH advantage for right-duplicated displays, and no hemispheric difference for left-duplicated displays. Of particular note is that perception of LH displays was affected greatly by the presence of right-hemiface information, whereas perception of RH displays was unaffected by changes in hemiface content. Thus, when investigated under precise viewing conditions, the indications are not only that the dominant processes of visual speech perception are located in the LH but that these processes are uniquely sensitive to right-hemiface information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interhemispheric transfer of visual discriminations in split-chiasm monkeys (Macaca nemestrina) and its measurement.

The interhemispheric transfer of visual discriminations in split-chiasm monkeys (Macaca nemestrina) was assessed by training with one eye to a criterion level, then testing either with that same eye (control) or with the other eye (transfer). The difference between these 2 values was the loss due to transfer. A computer simulation suggested that the usual savings score could grossly misestimate transfer ability. In addition, stimuli with comparable left and right halves were used to minimize the effect of the bilateral hemianopia caused by chiasm section. Performance with the untrained eye was slightly, but statistically significantly, poorer than with the trained eye. No evidence of the phenomena of "learning to transfer" was found (i.e., there was no improvement in transfer ability in relation to concurrent intrahemispheric controls). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Video-task assessment of stimulus novelty effects on hemispheric lateralization in baboons (Papio papio).

In a video matching-to-sample task, we examined the effects of stimulus novelty on hemispheric specialization in 6 baboons (Papio papio). After familiarization with a set of 8 composite stimuli, baboons were tested with either familiar stimuli paired in a novel way, novel stimuli composed of familiar elements, or novel stimuli differing in structure from the previous stimuli. Analyses focused on visual field differences between initial and later trials in each condition. The findings reflected shorter left than right visual half-field response times for initial but not for terminal trials. With regard to accuracy, scores were smaller for the initial trials than for the later ones, but there was no significant difference between left and right visual half-fields. Overall, this study suggests that hemispheric lateralization changes with practice and that the right hemisphere of the baboon plays a critical role in the processing of novelty. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Covert orienting biases in scene-based reference frames: Orientation priming and visual field differences.

Performance advantages for stimuli presented in the right versus the left visual field have been found in a variety of attentional tasks. Such advantages were exploited in the present set of studies to examine orientation priming and directional biases in retinotopic and scene-based spatial coordinates. The results demonstrate that directional biases occur within spatial coordinates across orientation transformations that dissociate retinotopic from scene-based visual half fields. The results are discussed concerning the representation of spatial maps in higher visual analysis, the role of spatial coordinates in guiding covert orienting, and methods of presenting stimuli in the right or left visual field to test for functional hemispheric asymmetries. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pointage d'une position mémorisée et contexte visuel.

Determined whether a sensorimotor or cognitive encoding is used to encode a target position and save it into iconic memory. The methodology consisted of disrupting a manual aiming movement to a memorized visual target by displacing the visual field containing the target. The target was presented either centrally or in the right periphery. Participants moved their hand from the left to the right of fixation. The visual field was either stationary throughout the trial or was displaced to the right or left at the extinction of the target or at the start of the hand movement. Results showed three major effects: (1) Vision of the hand during the gesture improved the final accuracy; (2) visual field displacement produced an underestimation of the target distance only when the hand was not visible during the gesture and was always in the same direction displacement; and (3) the effect of the stationary structured visual field on aiming precision when the hand was not visible depended on the distance to the target. These results suggest that a stationary structured visual field is used to support the memory of the target position. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Right hemisphere superiority in visual orientation matching.

"Same" or "different" judgments were made by 22 right-handed college students in 2 orientation matching tasks. In 1 task pairs of lines were presented 4. left or right of fixation. Reaction times for both "same" and "different" judgments were faster if stimulus pairs were presented to the left visual field, indicating superiority of the right hemisphere for handling spatial information. In the other task the orientation of a standard line, held in memory, was compared with the orientation of a single test line projected to the left or right of fixation. Results were in the same direction as before, although the right hemisphere superiority was significant only for the "different" responses. Data do not support the idea that "same" and "different" judgments need be differentially lateralized. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Line bisection in a man with complete forebrain commissurotomy.

In judging whether horizontal lines flashed for 100 ms extended farther to the left or right of a central fixation mark, a man (L.B.) with complete forebrain commissurotomy showed a marked bias to judge the right side longer, which is consistent with left hemineglect. Normal controls were considerably more accurate and were slightly biased toward the left, which is consistent with right pseudoneglect. L.B. showed no rightward bias when viewing the lines freely or when asked in free vision to locate the center of a horizontal line, although his performance varied more than that of controls. Therefore, commissurotomy may induce strong but transient left hemineglect that is rapidly overcome in free vision. One explanation is that control is initially left-hemispheric and subcortical transfer results in the left hemisphere receiving a spatially compressed representation of information in the left visual field. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pseudoneglect and embryonic light stimulation in the avian brain.

A bias to allocate attention to the left hemispace, similar to the well-known pseudoneglect phenomenon shown by humans, has been recently reported in domestic chicks and other species of birds. Asymmetrical light exposure of the embryo of the domestic chick in a critical period before hatching is known to be responsible for a structural asymmetry in the visual ascending projections of the thalamofugal pathway and for lateralization of some visual behaviors. Thus the animal model provided by the chick makes possible investigation of the prenatal factors that may influence asymmetry in spatial attention. Here chicks coming from eggs exposed to light (light incubated, Li-chicks) and chicks incubated in darkness (dark incubated, Di-chicks) were tested in a task in which they were required to explore an area in front of them and to sample grains of food. The results showed that Li-chicks attended more to target stimuli located in the left hemispace, whereas no asymmetry was shown by Di-chicks. When grains of food were presented with small novel pebbles as distractors, both Li- and Di-chicks tended to allocate attention toward the left hemispace. When, however, chicks were tested after familiarization with pebbles, no bias was shown by either Li- and Di-chicks. Hence it seems that cerebral lateralization associated with right hemispheric involvement in response to novelty, interacts with the modulatory effect of asymmetric embryonic light stimulation on preferential allocation of spatial attention in the left hemispace (right hemisphere) and right eye (left hemisphere) control of visual discrimination during feeding. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Word repetition within- and across-visual fields: an event-related potential study

A divided visual field (DVF) procedure was used to investigate the scalp distribution of the event-related potential (ERP) repetition effect. ERPs were recorded from 27 scalp sites whilst subjects (n = 20) discriminated between words and non-words presented to either the left (LVF) or the right (RVF) visual field. A proportion of the words were repeated on the trial immediately following their first presentation. In two within-field repetition conditions the two encounters with a word occurred in the same visual field (LVF or RVF). In two across-field repetition conditions, the two encounters with a word occurred in different visual fields. For both words and non-words, task performance was better for RVF presentations than for LVF presentations. In each repetition condition there was a positive-going shift in the ERP elicited by repeated words compared to that elicited by words on their first presentation. This ERP repetition effect was equivalent in magnitude and lateralised to the right hemisphere to an equivalent degree in all four repetition conditions. It is suggested that the ERP effects largely reflect the processing of visual form thought to occur predominately in the right hemisphere.     

Sex differences in the relationship between visual memory and MRI hippocampal volumes.

This study investigated sex differences in the relationships between visual memory and MRI-determined hippocampal volume data before and after right and left temporal lobectomy (TL). Preoperative visual memory and postoperative visual memory change were evaluated by the Wechsler Memory Scale-Revised, and MRI hippocampal volumes were obtained in 54 right (28 men and 26 women) and 75 left (33 men, 42 women) TL patients. Preoperative visual memory and postoperative visual memory change were significantly related to the difference between hippocampal volumes (DHV) in right TL women but not right TL men. That is, extirpation of a large right hippocampus was significantly associated with a visual memory decline, but only in women. These findings support the presence of sexually dimorphic brain function and suggest that visual memory ability in women may be less plastic after a developmentally early right mesial temporal insult. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hemispheric asymmetries in vigilance and cerebral arousal mechanisms in younger and older adults.

Younger and older adults responded to an asterisk presented to either the left or right visual field, with delay interval between onset of a fixation cross and onset of the asterisk varied. At delay intervals longer than 3 s, reaction time was faster when the same visual field was stimulated on 2 successive trials than when different visual fields were stimulated. This prefield effect was larger in the left visual field (right hemisphere), consistent with hypotheses of hemispheric asymmetry for arousal and vigilance. For older adults, these results were obtained only when participants responded with the left hand, suggesting that some aspects of hemispheric asymmetry for attention-related processing or the efficiency of interhemispheric transfer may change in an age-related fashion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rotation of mental images and asymmetries in word recognition in disabled readers.

Two experiments with 72 right-handed children (9–11 yrs old) revealed marked dissimilarities in perceptual coding between impaired and fluent readers. In Exp I, 26 boys with reading disabilities and average intelligence were compared to 26 good readers on a test of visual–spatial, short-term memory. Both groups performed equally well in their spatial recall on transformed visual fields. However, poor readers coded the test stimuli differently, in a nonanalytic and synchronous fashion. In a follow-up experiment, 10 disabled readers compared with 10 good readers showed a lower right- over left-field advantage when reporting single words presented tachistoscopically. Taken together, results disconfirm the widely held ideas that poor readers are suffering from spatial disorientation, left–right confusion, mirror-image equivalence, or lack of cerebral dominance. Findings suggest that the perceptual "anormalies" often linked with reading disability may result from nonpathological variations in the structural operations used to encode visual information. This difference in the organization of encodings in visual memory may be related to asymmetries in brain functioning. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)