Monocular deprivation alters the direction of functional and morphological asymmetries in the pigeon's (Columba livia) visual system.

One-day-old pigeons (Columba livia) were monocularly deprived by occluding the left or the right eye for 10 days. Up to 3 years later, degree and direction of functional and morphological asymmetries of deprived and control pigeons were analyzed. In control pigeons, the usual right-eye superiority was obtained in a visual discrimination task. In left-eye deprived pigeons, this behavioral asymmetry was strengthened, whereas the direction of lateralization was reversed in right-eye deprived birds. A morphological tectum analysis revealed that control and left-eye deprived pigeons displayed similar asymmetries, with the left-monocular deprived pigeons exhibiting more pronounced left-right differences. Tectal morphometry of right-eye deprived pigeons displayed a reversed pattern. Overall, the present study shows that a short period of posthatch monocular deprivation is sufficient to alter behavioral and morphological visual asymmetry for several years. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lateral asymmetry in face perception.

The tachistoscope was used to examine cerebral asymmetries in the perception of human faces by having 64 right-handed Ss make same–different comparisons between 2 faces or 2 objects (shoes) presented in the left or right field. A consistent left visual field advantage in response times (suggesting right-hemisphere processing) was found for the face presentations across all 3 experiments. There was no consistent field difference for the object presentations. Results suggest a right-hemisphere system specialized specifically to human faces. Some mechanisms are proposed for this apparent specificity. (French abstract) (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Asymmetries of representation in the visual system of pigeons

Although functional asymmetries in the course of visual information processing have been known for a long time in humans as well as in non-human species, the structural basis of these asymmetries is largely unknown. We now report that due to an asymmetry of commissural projections in the pigeon the left nucleus rotundus of the ascending tectofugal visual system predominantly represents inputs from both eyes while the right nucleus rotundus mainly represents the contralateral left eye. We suggest that a comparable organization exists for several asymmetries in humans. A representation of both hemifields can provide the dominant hemisphere with direct access to all stimulus features when objects cross the vertical meridian.     

Bihemispheric processing of redundant bilateral lexical information

Cerebral asymmetries in lexical ambiguity resolution were studied. In 2 experiments, targets related to the dominant and subordinate meanings of ambiguous word primes were presented for lexical decision after a 750-ms stimulus onset asynchrony. Experiment 1 compared presentation of target words to the left visual field/right-hemisphere (LVF/RH), to the right visual field/left-hemisphere (RVF/LH), or after redundant bilateral visual field (BVF) presentation. Experiment 2 examined unilateral priming in the absence of a BVF condition. On unilateral trials, priming was observed for dominant meanings in both the LVF/RH and RVF/LH, whereas subordinate priming was obtained only in the RVF/LH. These results suggest a possible role of hemispheric interaction in the availability of ambiguous word meanings. BVF performance evidenced a bilateral redundancy gain and priming that resembled that obtained on RVF/LH trials. Additional BVF analyses were not consistent with a strict race model interpretation and appear to implicate hemispheric cooperation in the bihemisperic processing of lexical information.     

Hand, space and attentional asymmetries in goal-directed manual aiming

Two experiments were conducted to explore the interaction of the two cerebral hemispheres in motor control, by examining hand, space and attentional asymmetries in goal-directed aiming. In Experiment 1, right-handed subjects moved to targets more quickly with their right hand than their left hand. In addition, each hand was faster when moving in its own hemispace. Although in a control condition, movements were initiated more quickly with the left hand, visual distractors disrupted left hand performance more than right hand performance. For contralateral aiming, ipsilateral distractors caused the greatest interference. In Experiment 2, when targets and distractors were all presented at the midline, a right hand advantage was found for movement time along with a left hand advantage for reaction time, independent of target and distractor location. Our findings are discussed in terms of a right hemisphere role in movement preparation and the allocation of attention in space, and greater left hemisphere involvement in movement execution.     

Form-specific priming and functional brain asymmetries in perceptual identification

Word form representations in intact cerebral hemispheres were studied by a lateralized perceptual identification priming task. During the study phase, word forms were primed by displaying words visually in uppercase or lowercase letters. During the test phase, perceptual identification of non-studied baseline words and studied words (presented in same or different lettercase as studied) was tested by displaying targets in the left or right visual field. Experiment 1 showed that the hemispheric pattern of priming effects was dependent on the lettercase at test. For uppercase test items, only the left visual field/right hemisphere was sentitive to study-test changes in lettercase, replicating an earlier result obtained in word-stem completion (Marsolek, Kosslyn and Squire, 1992). However, lowercase test items did not reveal any asymmetries in the form-dependent priming component indicating that in some conditions form-specific representations are computed in the left hemisphere also. No asymmetries were found in the abstract, form-independent component of priming. Experiment 2 revealed that use of explicit memory in the perceptual identification task eliminated the form-specific priming effects and suggested that the results of Experiment 1 were uncontaminated by explicit memory.     

Visual and semantic processing in reading Kanji.

A. Nakagawa (see record 1992-15549-001) showed hemispheric asymmetries during semantic processing of single English words. The right hemisphere passively maintained both strong and weak associations, whereas the left hemisphere maintained only strong associations when Ss were left free to attend. The present study extends the methodology to the study of Kanji characters. Contrary to the study of English characters, there was a general right-hemisphere advantage in single-character Kanji words. A study using a visual cue to direct attention suggested that the right-hemisphere advantage of Kanji was due to better representation of visual features by the posterior right hemisphere. However, the pattern of semantic priming found in English was replicated. Semantic analysis, mediated by more anterior systems, appears similar in the 2 languages. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual half-field Stroop effects with spatial separation of words and color targets

Past inconsistencies in the occurrence of differential visual half-field Stroop effects were addressed in two experiments using a visual half-field presentation technique incorporating brief displays (100 ms) and a fixation task designed to ensure proper eye fixation at display onset. Experiment 1 used displays in which distractor words and color targets were presented in contralateral visual fields. Experiment 2 compared contralateral with ipsilateral displays where words and color targets appeared one above the other in the same visual field. Stroop effects were larger whenever a word occupied the right as opposed to the left visual field, regardless of whether the color target was left or right. Results are consistent with the idea that words are processed more efficiently or automatically in right visual field/left hemisphere presentations.     

Lateral eye movements and hemispheric asymmetry: A critical review.

Eye movements to the left or right have been hypothesized to reflect activation of the cerebral hemisphere contralateral to the direction of gaze. This hypothesis was tested by comparing the direction of lateral eye movements (LEMs) following questions designed to engage the left or right hemisphere. The evidence from such studies was equivocal. Fewer than half found the predicted pattern of more right LEMs for left-hemisphere questions, and conceptual and methodological ambiguities in the questions, scoring, and experimental situation made interpretation of these studies difficult. In addition, findings showing more upward eye movements and more stares for right-hemisphere questions cannot be incorporated into the hemispheric asymmetry model of LEMs. Studies on individual differences in LEM patterns indicated a fair degree of stability and some consistency in their correlates. However, since "right" and "left movers" do not differ in verbal or spatial abilities, there is little justification for linking LEM patterns with "hemisphericity." It is concluded that further research on the relationship between directional ocular events and cognitive-affective processes is required before inferences about hemispheric function can be drawn from studies of lateral eye movements. (2? p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Avian visual lateralization: a review

Cerebral asymmetries represent an important principle of the organization of nervous systems. The asymmetries of the avian visual system, with their partly complementary domains in the left and the right hemisphere, offer an excellent window for the lateralized learning and cognitive processes. These behavioural experiments are accompanied by biochemical, synaptic, electrophysiological and neuroanatomical studies which have clarified to some extent the neuronal foundations of this asymmetry. Additionally they show that most, but not all, aspects of visual lateralization depend on a minute asymmetry of prehatch visual stimulation which triggers a cascade of events transforming the embryonic nervous system into lateralized structure and functioning.     

The contribution of attention to the right visual field advantage for word recognition

Perceptual asymmetries have been explained by structural, attentional bias and attentional advantage models. Structural models focus on asymmetries in the physical access information has to the hemispheres, whereas attentional models focus on asymmetries in the operation of attentional processes. A series of experiments was conducted to assess the contribution of attentional mechanisms to the right visual field (RVF) advantage found for word recognition. Valid, invalid and neutral peripheral cues were presented at a variety of stimulus onset asynchronies to manipulate spatial attention. Results indicated a significant RVF advantage and cueing effect. The effect of the cue was stronger for the left visual field than the RVF. This interaction supports the attentional advantage model which suggests that the left hemisphere requires less attention to process words. The attentional asymmetry is interpreted in terms of the different word processing styles used by the left and right hemispheres. These results have ramifications for the methodology used in divided visual field research and the interpretation of this research.     

Age differences and similarities in patterns of cerebral hemispheric asymmetry.

Younger (M age?=?20.4 years) and older (M age?=?70.7 years) adults participated in 3 visual half-field experiments. These were designed to examine specific aspects of hemispheric asymmetry: (a) hemispheric dominance for phonetic–linguistic processing (as measured by identification of nonword trigrams), (b) hemispheric differences in trigram processing strategy, (c) characteristic perceptual biases thought to reflect hemispheric arousal asymmetries, and (d) hemispheric dominance for processing emotions shown on faces. Patterns of left–right asymmetries were comparable for older and younger participants, and intercorrelations among the various measures of asymmetry were similar for both groups. In view of the present results, it seems unlikely that changes in hemispheric asymmetry contribute significantly to age-related changes in cognitive functioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Equivalence in periodontal trials: a description for the clinician

AIMS: To describe the clinical picture and electrophysiological findings in Müller cell sheen dystrophy, a recently reported retinal dystrophy. METHOD: A basic ophthalmological evaluation as well as recording of standard electro-oculography and electroretinography were performed in one patient at the onset of visual loss and after 1 year of follow up. RESULTS: A 61 year old woman presented with visual loss in the right eye. Multiple folds at the level of the internal limiting membrane were seen at the posterior pole in both eyes. Macular oedema was present in the right eye. The visual acuity of the right eye was 6/30 and of the left 6/9. A paracentral scotoma was found in the right eye. Electro-oculographic examination of both eyes gave normal results. Electroretinography (ERG) revealed reduced b-wave and flicker amplitudes in the right eye; these potentials were normal for the left eye. The ON response in the right eye was reduced and delayed; it was normal in the left eye. A further loss of visual function was noted 1 year later in the right eye, but the ophthalmoscopic findings were unchanged. The ERG of the right eye had a negative waveform when dark adapted. Light adapted responses showed an unusual delayed b-wave, broad and delayed ON and OFF responses and a missing flicker response, suggesting a Müller cell dysfunction. Light adapted responses were slightly reduced in the left eye. CONCLUSIONS: Electrophysiological data indicate Müller cell dysfunction as a background of functional loss in Müller cell sheen dystrophy. This is in agreement with previously reported histological findings in this disorder.     

Infants' understanding of the link between visual perception and emotion: "If she can't see me doing it, she won't get angry."

Two experiments investigated 18-month-olds' understanding of the link between visual perception and emotion. Infants watched an adult perform actions on objects. An emoter then expressed neutral affect or anger toward the adult in response to the adult's actions. Subsequently, infants were given 20 s to interact with each object. In Experiment 1, the emoter faced infants with a neutral expression during each 20-s response period but looked at either a magazine or the infant. In Experiment 2, the emoter faced infants with a neutral expression, and her eyes were either open or closed. When the emoter visually monitored infants' actions, the infants regulated their object-directed behavior on the basis of their memory of the emoter's affect. However, if the previously angry emoter read a magazine (Experiment 1) or closed her eyes (Experiment 2), infants were not governed by her prior emotion. Infants behaved as if they expected the emoter to get angry only if she could see them performing the actions. These findings suggest that infants appreciate how people's visual experiences influence their emotions and use this information to regulate their own behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Leukocyte migration inhibition test under agarose--a practical method for the recognition of cell-mediated reactivity

Morphological speech zone asymmetry in man cannot be due to environmental or developmental factors after birth. The functional implication of such a finding is not yet clear. Morphological asymmetry of the human brain is paralleled by electrophysiological evidence of cerebral hemispheric asymmetries. The results of our analysis of 50 infants suggest that clear occipital-temporal coherency asymmetry similar, but not identical to the adult pattern, also exists at or near birth. These asymmetries are generated by stimuli with no verbal content and in infants who presumably have no or an undeveloped capability for language. It is suggested that language is only a part of much more fundamental asymmetries which include the processing of auditory and visual information. Our results, and those of other, are consistent with the assumption that the left hemisphere is more able to relate stimuli to past experience, either short or long-term, while the right hemisphere is more able to process, stimuli which are not easily identifiable or referable. These capabilities would not be based on language, and hence would be expected to develop independently and possibly before speech. The demonstration that reversing electrophysiological asymmetries can be generated with non-speech stimuli in the visual and auditory modalities, and in neonates, supports such an assumption.     

Early versus late stages of processing and their relation to functional hemispheric asymmetries in face recognition

To determine whether perceptual asymmetries for faces occur at early or late stages of stimulus analysis, subjects compared the members of a pair of faces which appeared in the right or left visual field, either to each other or to a previously presented sample. The first two experiments established that manual reaction times were consistently shorter to left-field presentation only when test faces were compared for identity to a memorized sample (Experiment 2), but not when they were compared to each other (Experiment 1). By varying the interstimulus interval between the sample and test (Experiment 3), it was found that a consistent left-field superiority was absent for at least the first 50 msec following sample offset, suggesting that during that time both hemispheres have access to a short-lived, visual trace that represents the results of the early, precategorical processing stages. Beyond 100 msec, or earlier if the trace is degraded by a masking field (Experiment 4), a left-field advantage is observed. Experiment 5 showed that higher order comparisons between photographs and caricatures yield a left-field superiority even in a memory-free situation. Together, the results indicate only higher order processes, such as are needed to maintain a relatively permanent memory representation or to compare caricatures with photographs, require the specialized functions peculiar to the right hemisphere. Lower-order, precategorical processes seem to be common to both hemispheres.     

Asymmetrical vertical phorias indicating dissociated vertical deviation in subjects with normal binocular vision

We measured the symmetry of phoria angles in six normal subjects. Subjects were selected on the basis of good visual acuity and stereopsis, normal binocular eye alignment and, apart from mild refraction errors, absence of ocular abnormalities. They were instructed to look at a word on a reading chart at 2 m distance. Each measurement consisted of five subsequent intervals of 5 s duration. During these five intervals viewing was binocular, with the right eye only, binocular, with the left eye only, and binocular, respectively. Each experiment consisted of twelve measurements. Eye movements were measured with scleral coils suited for measuring in horizontal, vertical and torsional directions. Five out of six subjects displayed an asymmetrical vertical phoria; one subject showed an alternating hyperphoria; four displayed a left over right vertical phoria that was largest for left eye occlusion. Only one subject showed a symmetrical vertical phoria. Both the size of the vertical phorias and the size of the asymmetries in these vertical phorias were very small: on average 0.16 +/- 0.01 and 0.17 +/- 0.01 degree, respectively. The direction of the vertical phoria asymmetries (the largest left over right was found with left eye occlusion) and the fact that asymmetries were found more often in vertical than horizontal and torsional phorias suggest that these asymmetries are related to dissociated vertical deviation. These results suggest that dissociated vertical deviation, often observed in subjects with a disruption of binocular vision early in life, reflects the enhancement of a phenomenon that is present in normal subjects as well.     

Visual search asymmetries within color-coded and intensity-coded displays.

Color and intensity coding provide perceptual cues to segregate categories of objects within a visual display, allowing operators to search more efficiently for needed information. Even within a perceptually distinct subset of display elements, however, it may often be useful to prioritize items representing urgent or task-critical information. The design of symbology to produce search asymmetries (Treisman & Souther, 1985) offers a potential technique for doing this, but it is not obvious from existing models of search that an asymmetry observed in the absence of extraneous visual stimuli will persist within a complex color- or intensity-coded display. To address this issue, in the current study we measured the strength of a visual search asymmetry within displays containing color- or intensity-coded extraneous items. The asymmetry persisted strongly in the presence of extraneous items that were drawn in a different color (Experiment 1) or a lower contrast (Experiment 2) than the search-relevant items, with the targets favored by the search asymmetry producing highly efficient search. The asymmetry was attenuated but not eliminated when extraneous items were drawn in a higher contrast than search-relevant items (Experiment 3). Results imply that the coding of symbology to exploit visual search asymmetries can facilitate visual search for high-priority items even within color- or intensity-coded displays. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual lateralization in birds: from neurotrophins to cognition?

Birds which are tested monocularly in visual discrimination tasks generally show higher performance levels with the right eye seeing. Due to the virtual complete decussation of the optic nerves, a right eye superiority is probably related to a left hemisphere dominance. If visual processes between the hemispheres differ, each half-brain might be differently prone to be deceived by visual illusions. Indeed pigeons tested with the herringbone illusions are deceived to a stronger extent with the right eye. These functional asymmetries are accompanied by anatomical left-right differences in the ascending thalamo- and tectofugal visual pathways in chicks and pigeons, respectively. The neuroanatomical and behavioral assymmetries result from an asymmetrical posture before hatching in which the embryo keeps his head turned to the right, such that the right eye is stimulated by light shining through the shell. The lateralization of adult animals are induced by this prehatching asymmetric photic stimulation since dark incubation abolishes behavioral and anatomical asymmetries. It is conceivable that the asymmetrical embryonal light stimulation increases the release of neurotrophins in the developing avian visual system in an activity dependent matter. Neurotrophins play an important role in neuronal survival and morphology and thus might represent a molecular switch bridging the gap from embryonal light stimulation to asymmetries of visual cognition in adults.