Differential right hemispheric memory storage of emotional and non-emotional faces

Seventy-two female subjects memorized two photographed faces and subsequently discriminated these “target” faces from two “non-target” faces. The faces were presented unilaterally for 150 msec, and manual reaction times for the discriminations served as the dependent variable. The face stimuli were either “neutral” or “emotional” in facial expression, these attributes having been shown, by a preliminary study, to be highly reliable. Faster reaction times were obtained for left visual field than for right visual presentation. Subjects (N = 36) who memorized emotional faces showed significantly faster discrimination of faces presented in the left than in the right visual field (25·7 msec); subjects (N = 36) who memorized faces lacking emotional expression also showed significant left visual field superiority (11·6 msec), but this left field superiority was significantly smaller than that of subjects memorizing emotional faces. Results are consistent with previous tachistoscopic evidence of right hemisphere superiority in face recognition speed and with diverse non-tachistoscopic evidence of preferential memory storage of affective material. The pattern of latencies for the different visual field-response hand conditions supported a model of lateral specialization in which the specialized hemisphere normally processes both directly-received and interhemispherically- transferred stimuli.     

Normal-Mirrored Letter Recognition, Same-Different Judgment and Cerebral Dominance

Abstract: Either normal or mirror images of Kana, Kanji and capital letters were presented tachistoscopically in a left or right visual field, and then normal letters were flashed simultaneously at the fixation point. Subjects were trained to give same (BB, BB) or different (BC, BB) judgments to pairs of stimuli. Reaction time (RT) and percentage of errors (PE) were measured. Generally, normal letters with same judgments revealed a right field advantage, while with different judgments, there were not significant laterality differences. In the case of mirrored letters, each of two judgments showed no lateral asymmetries for each kind of letters excepting a left field advantage for mirrored Kana words with different judgments. PE methods tended to produce a right field advantage more consistently than did RT methods.     

Difference in P300 response between hemi-field visual stimulation

We investigated differences in the cognitive/attention process following visual stimulation of the left and right hemi-visual fields. Visual P300 was recorded in 31 healthy right-handed subjects following target and non-target stimuli presented randomly in both visual fields. Counting and reaction time (RT) tasks using the left and right hands were performed. The P300 amplitude was significantly smaller in the RT session using the left hand. The amplitude was larger following target stimulation in the left hemi-visual field in the RT sessions using both the left and right hands. The P300 latency did not change in each stimulus condition and session, but the RT was longer for the target in the right hemi-visual field in the RT session using the left hand. We showed asymmetry of P300 response following each hemi-visual field in healthy subjects, and visual stimuli in the left hemi-visual field were dominantly processed.     

A longitudinal study of the development of visual field advantage for letter matching

The visual field advantage for letter matching was investigated longitudinally from 5 to 7 yr. A right visual advantage was found with very little indication of any increase with age. Cross-sectional controls exhibited somewhat less of a right visual field advantage. In a group of 4-yr-olds who could not name letters a left visual field advantage was observed for boys. It is suggested that the right visual field advantage for visual-verbal material occurs from a mapping on to an already existing left hemisphere language system.     

What do lateralized displays tell us about visual word perception? A cautionary indication from the word-letter effect

A common assumption underlying laterality research is that visual field asymmetries in lateralized word perception indicate the hemispheric specialisation of processes generally available for the perception of words, including words viewed in a more typical setting (i.e. in the central visual field). We tested the validity of this assumption using a phenomenon (the word-letter effect) frequently reported for displays viewed in the central visual field, where letters in words are perceived more accurately than the same letters in isolation. Words and isolated letters were presented in the left visual field (LVF), right visual field (RVF) and central visual field (CVF), the Reicher-Wheeler task was used to suppress influences of guesswork, and an eye-tracker ensured central fixation. In line with previous findings, lateralized displays revealed a RVF-LVF advantage for words (but not isolated letters) and CVF displays revealed an advantage for words over isolated letters (the word-letter effect). However, RVF and LVF displays both produced an advantage for isolated letters over words (a letter-word effect), indicating that processing subserving the advantage for words when participants viewed stimuli in the central visual field was unavailable for lateralized displays. Implications of these findings for studies of lateralized word perception are discussed.     

Imagery in a commissurotomized patient

A commissurotomized patient, L.B., was tested on several imagery tasks, in which the stimuli were flashed tachistoscopically in the left or right visual half-field. On tests requiring the generation of images of lowercase letters from their uppercase versions, or the generation of the positions of the hands on a clockface from digitally presented times, there was a strong right half-field (left-hemispheric) advantage in accuracy, but a left half-field (right-hemispheric) advantage in reaction time (RT). On tests requiring the mental rotation of letters or stickfigures to the upright, however, there was a strong left half-field (right-hemispheric) advantage in accuracy, RT, and conformity of RTs to an ideal "mental-rotation" function when plotted against angular orientation. These data provide strong evidence that the right hemisphere was capable of mental rotation comparable to that of normal subjects; the left hemisphere, by contrast, seemed virtually incapable of mental rotation in the early testing sessions, and never achieved the proficiency of the right.     

Visual field differences in the magnitude of the tilt after-effect

Following monocular adaptation to a grating tilted 10° clockwise from the vertical, subjects judged the orientation of a single bar tilted 1–7° clockwise from the vertical presented monocularly for 30 msec in the left or in the right visual field. The effect of counter-rotation of the subjectively perceived orientation was observed. The value of tilt at which the apparent orientation of the bar changed from clockwise to anticlockwise was established for each individual. The effects of the right vs the left field of exposure and of the ipsiocular (the same eye adapted and tested) vs interocular transfer (different eyes adapted and tested) condition of testing on the value of the tilt after-effect (TAE) were analysed. The results showed higher values of TAE for the left field presentations. A significant loss of TAE was observed for the interocular transfer condition. The hypothesis is discussed that stronger tilt after-effect produced by the right hemisphere results from wider spreading inhibition in the net of orientation specific neurons of this hemisphere.     

Lateral asymmetry: Hard or simple-minded?

A letter or a three-dimensional shape was presented in the center of the visual field. Following the off-set of this stimulus either a comparison letter or a three-dimensional shape was flashed briefly in either the right or left visual field. The subject's task was to respond SAME, or DIFFERENT. The stimuli could be in the same plane, rotated in two dimensions (letters) or in three dimensions (three-dimensional shapes). The left visual field presentations (right hemisphere) of same-pair matches for letters only produced faster reaction times and fewer errors. In all other conditions reaction time measures showed no hemisphere effects. By contrast, error score data indicated that the left hemisphere was overwhelmingly more accurate.     

Right hemispheric dominance and interhemispheric cooperation in gaze-triggered reflexive shift of attention

Aims: The neural substrate for the processing of gaze remains unknown. The aim of the present study was to clarify which hemisphere dominantly processes and whether bilateral hemispheres cooperate with each other in gaze‐triggered reflexive shift of attention. Methods: Twenty‐eight normal subjects were tested. The non‐predictive gaze cues were presented either in unilateral or bilateral visual fields. The subjects localized the target as soon as possible. Results: Reaction times (RT) were shorter when gaze‐cues were congruent toward than away from targets, whichever visual field they were presented in. RT were shorter in left than right visual field presentations. RT in mono‐directional bilateral presentations were shorter than both of those in left and right presentations. When bi‐directional bilateral cues were presented, RT were faster when valid cues were presented in the left than right visual fields. Conclusion: The right hemisphere appears to be dominant, and there is interhemispheric cooperation in gaze‐triggered reflexive shift of attention.     

The role of perceptual reference frames in visual field asymmetries

The direct access model of hemispheric asymmetry was tested in a letter reflection (normal of reflected) judgement task. In the baseline condition letters were presented in their upright orientation, and reaction times were faster to letters presented in the right visual field than to those presented in the left visual field. In two other conditions the slides, and thus the letters, were rotated +90 degrees clockwise (Rotated +90) from upright or -90 degrees counterclockwise (Rotated -90). This resulted in the letters in both rotated conditions being shown in the upper or lower visual field through the sagittal plane but rotated 90 degrees. Despite this fact a "right field" advantage was again found when the right field was defined relative to the orientation of the tops of the rotated letters (lower visual field in the Rotated +90 condition and upper visual field in the Rotated -90 condition). These results demonstrate that the internal representation of locations in space is more important in predicting visual field asymmetries, at least in the present task, than the field of stimulus presentation relative to the fovea.     

Evaluating a split fovea model of visual word recognition: effects of case alternation in the two visual fields and in the left and right halves of words presented at the fovea

Two experiments are reported exploring the effect of cAsE aLtErNaTiOn on lexical decisions to words and nonwords presented laterally or centrally. In line with previous research, Experiment 1 found that case alternation slowed lexical decision responses to words more in the right visual field (RVF) than in the left visual field (LVF). In Experiment 2, the words and nonwords were all presented centrally. There were three conditions, a condition in which the word and nonwords were presented in lower case letters, a condition in which the letters to the left of the central fixation were case alternated (e.g., aMbItion, mOdLants) and a condition in which the letters to the right of fixation were case alternated (e.g., collApSe, pireNtOl). Alternating the case of letters to the right of fixation slowed lexical decision responses more than alternating letter case to the left of fixation. The results provide further support for a split fovea account of visual word recognition according to which those letters of a centrally-fixated word that fall to the left of fixation are processed initially by the right cerebral hemisphere while those letters that fall to the right of fixation are processed initially by the left cerebral hemisphere, with the characteristics of the left and right hemispheres being revealed in the processing of initial and final letters in centrally presented words.     

Tachistoscopic Recognition of Normal and Mirror Images of Kana and Kanji Characters

Abstract: Accuracy of recognition was investigated for normal and mirror images of Kana (syllabic symbols) and Kanji (ideographic symbols) characters tachistoscopically presented in the left and right visual fields in normal right-handed Japanese subjects. A significant right field superiority was obtained for the recognition of each type of normal letter. In the case of mirrored letters, Kanji characters were better recognized in the right field while no lateral asymmetry for the recognition of Kana characters was shown. The results indicated that Kanji processing is somewhat different from the processing of Kana characters.     

Laterality differences in recognition of Japanese and Hangul words by monolinguals and bilinguals

Two-character nonsense Kana words, individual Kanji words and individual Hangul words are presented tachistoscopically in the left or right visual field to 20 normal, right-handed Japanese students and 13 normal, right-handed Korean subjects. The former did not know Hangul letters. The latter were born and raised in Japan, in exclusively Japanese-speaking families, but they could read Hangul letters and write them a little because they have learned the Hangul language for 6 months. In each of three conditions (Kana, Kanji and Hangul work recognition), each subject was required to move the index finger of his right or left hand leftwards as fast as possible after the presentation of two of four stimuli and rightwards after the presentation of the other two. The reaction time was measured. A significant right field superiority for the recognition of Kana words and no lateral asymmetry for Kanji words were shown in both Japanese and Korean groups. However, for the Hangul recognition, a significant left field superiority for Japanese subjects and a significant right field superiority for Korean subjects were obtained. These findings are interpreted as follows. Kana and Kanji are processed somewhat differently in the cerebral hemispheres. Japanese subjects do not recognize Hangul stimuli as orthographic characters but as shapes or figures. Korean subjects can identify Hangul stimuli as letters. Both the first language (Kana) and second language (Hangul) are processed in the dominant left hemisphere by right-handed Korean subjects.     

Hemispheric differences for visual search: Serial vs parallel processing revisited

Subjects were tachistoscopically presented with arrays of two, three or four stimuli to the right or left hemisphere and judged whether all of the items were the same or whether one was physically different from the rest. Separate groups of right-handed subjects viewed letters of featurally similar symbols as stimulus items. Faster and more accurate responding was obtained for left hemisphere presentations for both same and different response judgments. Response time was independent of array size, with same judgments made faster than different judgments for both visual field conditions. Extensive practice shortened reaction time and decreased error rate, but did not change the pattern of hemispheric or judgment effects. Virtually identical results were observed for both stimulus conditions. These findings suggest that the left hemisphere can process information in parallel when the task situation requires featural analysis of stimulus materials.     

Central visual fields in pure alexia "without hemianopsia"--visual dysfunction in the right hemifield, and alexia for "kana" words in the left]

Following a left occipito-temporal subcortical hematoma, a 57-year-old, right-handed man developed pure alexia that was more prominent in kana words, especially in kana nonwords, than in kanji letters. Although a kinetic perimetry with a Goldmann perimeter showed his visual fields to be full, a static perimetry with a Humphrey visual field analyzer disclosed decreased visual sensitivity in the right visual field in its central 30 degrees. In addition, a tachnistoscopic examination with Landolt rings revealed his visual acuity (the ability of two points discrimination) to have decreased in the right half of his central visual filed in its 3 degrees. In the right central vision, he was unable to recognize the letters, pictures or colors presented by the tachistoscope. Concerning the reading, the more letters in kana words or the higher the number of strokes in kanji letters, the more difficulty he experienced in orally reading both kana and kanji. On the contrary, in the left central vision, kanji reading was not so affected by an increased number of strokes as the kana-word reading which became difficult when the number of the letters increased. CT scan showed subcortical hematoma in the left occipitotemporal region. Magnetic resonance imaging 3 months after onset revealed a localized injury in the region between the left postero-inferior temporal lobe and the infero-lateral occipital lobe, including the fusiform gyrus. None of the splenium, the lingual gyrus or the optic area were affected. The spared structures also included the angular gyrus, the Wernicke area and their subcortical white matter.(ABSTRACT TRUNCATED AT 250 WORDS)     

Single representation of the visual midline in humans

A choice reaction time experiment was performed to find evidence of dual representation of the visual midline in normal humans. Visual targets were presented either to the left or right of fixation and subjects responded by pressing one of two keys. Major variables were: retinal locus (4, 3.5, 3, 2.5, 2, 1.5, 1, 0.75, 0.5 and 0.25° from fixation); visual field (left or right), eye (left or right) and responding hand (left or right). RT was 25 msec faster when the target projected to the hemisphere controlling the responding hand (uncrossed) than when the two separate hemispheres were involved (crossed). The RT difference was maintained even for targets 15 min arc from fixation, provided no evidence for dual representation.     

Evaluating a split processing model of visual word recognition: effects of word length

A new theory of visual word recognition is based on the fact that the fovea is split in humans. When a reader fixates the center of a written word, the initial letters of the word that are to the left of fixation are projected first to the right cerebral hemisphere (RH) while the final letters are projected to the left cerebral hemisphere (LH). This paper explores the possibility that this has consequences for the early processing of the beginning and ends of centrally fixated words: specifically that lexical decision RTs are affected by the number of letters to the left of fixation but not by the number of letters to the right of fixation. For centrally presented five- and eight-letter words, we manipulated number of letters presented to the right or to the left of a fixation point (Experiment 1). We found that longer latencies to longer letter strings characterised the processing of the initial letters of words while LH word recognition features characterised the ends of words. Experiment 2 was a lateralized version of Experiment 1, and revealed the well established visual field and word length interaction. The results supported the split fovea theory.     

Interaction between local and global visual orientation signals in subjects with unilateral brain lesions

Two groups of right handed, male stroke patients with lesions confined to the left (LH, n=10) or right (RH, n=10) cerebral hemisphere were tested on visual vertical judgements with isolated line stimuli and lines presented in the context of a tilted frame. The psychometric functions indicate no reduction in the precision of orientation judgements among the brain injured subjects when compared with age-matched controls (n=6) with cardiovascular disease, but the systematic shift in perceived vertical induced by a tilted visual frame was significantly larger for RH-subjects than for LH-subjects or controls (mean illusion 6 and 3° respectively). The results are interpreted within the “two visual systems”-theory of the rod-and-frame effect and it is suggested that the right hemisphere is dominantly involved in the integration of visual and vestibular input.     

Opposite visual hemifield superiorities in face recognition as a function of cognitive style

Twenty-four women, classified as field dependent or field independent on the Rod-and Frame Test, memorized sets of upright and inverted faces and were then tested for recognition in a tachistoscopic visual hemifield paradigm using upright and inverted faces as probes. A significant triple interaction of probe orientation, visual hemifield and cognitive style was found. For upright probes, field independent subjects responded faster and more accurately when probes were in the left visual field; in contrast, field dependent subjects showed a right visual field advantage. For inverted probes, there was little evidence of lateralization. The findings are interpreted as reflecting a difference in the strategies used by these subjects for tachistoscopic face discrimination; however, this interpretation rests upona particular model of laterality effects.     

Interhemispheric differences in the planning and execution of sequences of skilled finger movements

An index-middle finger (double) tapping task was used to examine hemispheric differences in the planning and execution of skilled finger movements. In two experiments, subjects responded to a simple cue presented tachistoscopically in the left or right visual field, by performing a predetermined number of double taps, (between one and eight inclusive), with either the left or right hand. Reaction times (RT) increased linearly as a function of increasing number of taps, when response sequences were controlled by the left hemisphere. In contrast, an inverse quadratic trend was obtained with right hemisphere control. When both hemispheres were involved in the stimulus-response sequence, the latency function incorporated elements of both trends, suggesting interaction between the hemispheres. The RT trends reflect differences in motor planning between the hemispheres. The conditions engaging only the right or left hemispheres did not differ in motor execution, as measured by tapping duration, variability or errors. However, when both hemispheres were involved there was evidence of interaction, which was evident as interference when the right visual field or left hemisphere was cued but the motor response was under the control of the right hemisphere (left hand). Overall, the results indicate that hand differences in fine motor skill may be determined by hemispheric differences associated with motor preparation rather than response execution.