Visual Half-field Research Articles

Effects of stimulus content and brain lateralization on the habituation of the electrodermal orienting reaction (OR)

Slides with either a six-letter word or a complex spatial pattern were repeatedly flashed either to the left or to the right of a center fixation point (i.e. visual half-field technique) in an electrodermal orienting paradigm. Skin conductance (SC) was recorded from both the left and right hand. Half the subjects had the slides projected 6.0° of visual angle lateral to fixation, the other half had the stimuli projected 2.5° lateral to fixation. There were 15 presentations of each stimulus with a mean inter-trial interval (ITI) of 30 sec. Results showed significantly larger mean SCR-amplitudes across trials to the verbal stimuli compared to the spatial patterns when presented in the right visual half-field, and larger amplitudes to the spatial stimuli when presented in the left half-field. However, this was only true for the 6.0° condition, but not for the 2.5° condition. No differences were found between left and right hand recording. The present data imply a functional relationship between electrodermal orienting habituation and hemispheric asymmetry.

Word matching and Lexical Decisions: A Visual Half-Field study

In unilateral Visual Half-Field tasks visuospatial and linguistic processing were compared. In a Word Matching task subjects judged the physical identity of simultaneously presented pairs of three-letter words or legal nonwords. No mainfield effects were found, but word pairs were recognized better and faster as “same” than nonword pairs. Latencies and errors in “different” pairs increased monotonically with position of letter change in the left but not in the right visual field (RVF), suggesting a serial, letter-by-letter way of processing for the right hemisphere and a whole word approach for the left. At this perceptual level the ability to store lexical information from the icon is stressed as a hemisphere-specific factor. In a Lexical Decision task the same subjects judged the same items on the word/nonword dimension. A RVF advantage associated with words as compared to nonwords occurred, as expected. Additional analysis suggests that order and difficulty of tasks may influence females' laterality, as compared to that of males.

Sex differences and asymmetry of lexical processing: effects of responding hand, stimulus familiarity and intraexperimental experience.

The possibility that language processing functions are more nearly equally represented in the two hemispheres of women than of men was investigated tachistocsopically by means of a lexical decision task in which words and nonwords were controlled for familiarity, and exposed vertically in the left and right visual half-fields. Analysis of both unimanual reaction times and response accuracy revealed differences in asymmetry as well as differences between male and female subjects which tended to decrease as a function of intraexperimental experience. Theoretical and methodological problems associated with reaction time and response accuracy as measures of language lateralization are discussed.

Cerebral Asymmetries in Processing Proper Names: Evidence of an Efficiency Difference

An investigation of the capacities of the cerebral hemispheres to process proper names was conducted using a memory-scanning paradigm. The results indicated that rate at which the test name was compared against the memory set items varied with the visual half-field stimulated. This is interpreted as indicating that both hemispheres employed the same comparison process but that the left hemisphere was more efficient, reflecting a quantitative hemisphere asymmetry.

Mirror-reading in right- and left-handers

In mirror-reading, words are read from right to left and letters are read in a reverse right-to-left orientation. In one experiment we compared the ability of normal right- and left-handed subjects to mirror-read and found that the left-handers made fewer errors and could read mirror print more rapidly. In a second experiment we attempted to learn whether there is a hemifield superiority for reading mirror words and whether there are any differences between left- and right-handers in a hemifield. We found that although both right- and left-handers more rapidly detected mirror words projected to the left visual half-field, there were no differences between groups. However, in the right visual half-field, the performance of left-handers was superior to that of the right-handers. The results of the hemifield study suggest that left-handers may be superior at reading mirror words because they can more easily reverse their scanning pattern.

Surface distribution of steady-state cortical potentials evoked by visual half-field stimulation.

The surface distribution of steady-state cortical potentials (VECP) evoked by visual half-field stimulation was analyzed by using the fast Fourier transform (FFT). For all ten normal subjects, checkerboard stimulation of the lower visual half-field evoked the largest response at electrode location Oz, with stimulation for the upper visual half-field at Pz. Recording at Pz, a phase difference of approximately 180 degrees was observed for cortical potentials evoked by lower and upper half-field stimulation, the response being bigger for upper field than for full-field stimulation. Comparing the VECP elicited by stimulation of the right and the left half-field, six of ten subjects displayed the highest amplitude at the contralateral cortex (anatomical type), three subjects at the midline (central type), and one subject at the ipsilateral cortex (paradoxical lateralization type). At Oz there was little phase difference in the VECP with stimulation of the right and left visual half-field, and the amplitude was about half that for full-field stimulation. However, with the electrode placed at the temporal region of the skull there was a big phase difference of VECP signals; consequently, the sum of the amplitudes did not amount to the amplitude for full-field stimulation. The dipole theory of scalp distribution of VECP signals was found to be also applicable to conditions of steady-state stimulation, including polarity reversal for upper and lower visual half-field stimulation.

Stimulus-response compatibility for left-right discriminations as a function of stimulus position.

In two experiments, choice response times to visual stimuli (word and arrow) were measured. The stimuli were presented briefly (180 msec) in left and right visual half-field (VHF). Each stimulus required a left-right discrimination; however, half the stimuli were positive (e.g., LEFT), and half were negative (e.g., NOT RIGHT). In Experiment 1, button-pressing responses in the midsagittal plane were used; in Experiment 2, vocal responses were used. There was a strong stimulus-response (S-R) compatibility effect, influenced by the interaction of negation (positive vs. negative) and stimulus position (VHF). Latencies were faster to positive stimuli whose direction and VHF matched than to positive stimuli whose direction and VHF did not correspond. Conversely, latencies were faster to negative stimuli when response direction and VHF did not match than when direction and VHF did correspond. These results replicate the S-R compatibility effect found by Whitaker (1980) using foveal stimuli. The results were analyzed with regard to a hemisphere activation model proposed by Cotton, Tzeng, and Hardyck (1980) but were found to fit Whitaker's (1980) model better.

Visual stimuli recognition asymmetry in probabilistic prognosing

The aim of this investigation was to determine the dependence of the recognition asymmetry of different curvature bows on the probability of stimuli appearance in one of visual half-fields. Under monocular condition the quality of correct recognitions as well as the character of asymmetry largely depends on the probability of stimuli presentation. Under dichoptic condition the asymmetry depends on the probability of the appearance of monocular stimuli scattered among dichoptic pairs in one of visual half-fields.

Hemispheric Lateralization and Aesthetic Judgement

Pairs of slides depicting works of art were presented tachistoscopically to the left or right visual half-fields. Subjects performed an aesthetic judgement task, selecting the better work of art in each pair. Subjects with highly lateralized cerebral organization, as inferred by handedness or sex, performed significantly better in response to slides presented in one visual half-field (VHF) than in response to slides presented in the opposite VHF. Some of these subjects showed a left VHF superiority, while others showed a right RHF superiority. Subjects who were less lateralized showed no significant tendency to perform better in response to slides presented in one VHF or the other. The results are interpreted as an indication that subjects will perform a given task in a lateralized or a non-lateralized manner as a function of the interaction between individual differences in cerebral organization and the cognitive processes used to perform the task.

Structural, spatial, and age effects on visual threshold

The aim of the current research was to determine whether observers who are simultaneously presented with structural and spatial cues would demonstrate differential sensitivity to the structural characteristics of the stimulus, the spatial relationships between the stimulus and the visual field, or some interaction between these variables. A concurrent aim of the experiment was to determine the effects of aging on visual form detection. The results indicate that in the case of structural characteristics alone, subjects of all ages were influenced by size rather than visual angle or sidedness. The examination of the independent effect of spatial characteristics upon visual thresholds of younger and older subjects demonstrated greater observer sensitivity to parafoveal positions on the horizontal plane above the central horizontal meridian independent of which half visual field was stimulated. When the simultaneous effects of structural and spatial characteristics on sensitivity of younger and older subjects were observed, it was determined that position rather than size influences visual form detection. Although significant age differences were obtained between the two groups, both age groups were similarly influenced by the independent and interactive effects of structural and spatial characteristics.

Attempt to improve the reliability of acoustically evoked slow vertex responses : T. Itabashi, G. Ichikawa and N. Uehara (Tokyo, Japan)

Kana, simple Kanji, complex Kanji characters differing in figural complexity (number of strokes) were tachistoscopically presented to the right and left visual half-fields of 115 German subjects. The subjects had to decide whether a stimulus (lasting 150 ms) was the same as or different from a sample stimulus (lasting 1000 ms) presented immediately before to the center of the visual field. An increased left field advantage in reaction time with higher figural complexity was hypothesized (Visual Field × Type of Script interaction). Analyses of variance, however, did not show this interaction. Because of a significant Type of Script × Response Type interaction simple main effects were calculated which were all significant. Pairwise comparisons for type of script were significant except for Kana vs. simple Kanji. No other significant effects were obtained. Reaction times were shortest for simple Kanji, intermediate for Kana and longest for complex Kanji. The results indicate that high figural complexity of Japanese characters does not favour the left visual field.

Visual properties of neurons in a polysensory area in superior temporal sulcus of the macaque.

1. We recorded from single neurons in the dorsal bank and fundus of the anterior portion of the superior temporal sulcus, an area we term the superior temporal polysensory area (STP). Five macaques were studied under anesthesia ( N20) and immobilization in repeated recording sessions. 2. Almost all of the neurons were visually responsive, and over half responded to more than one sensory modality; 21% responded to visual and auditory stimuli, 17% responded to visual and somesthetic stimuli, 17% were trimodal, and 41% were exclusively visual. 3. Almost all the visual receptive fields extended into both visual half-fields, and the majority approached the size of the visual field of the monkey, including both monocular crescents. Somesthetic receptive fields were also bilateral and usually included most of the body surface. 4. Virtually all neurons responded better to moving visual stimuli than to stationary visual stimuli, and almost half were sensitive to the direction of movement. Several classes of directional neurons were found, including a) neurons selective for a single direction of movement throughout their receptive field, b) neurons selective for directions of movement radially symmetric about the center of gaze, and c) neurons selective for movement in depth. 5. The majority of neurons (70%) had little or no preference for stimulus size, shape, orientation, or contrast. The minority (30%) responded best to particular stimuli. Some of these appeared to be selective for faces. 6. The properties of most STP neurons, such as large receptive fields, sensitivity to movement, insensitivity to form, and polymodal responsiveness, suggest that STP is more involved in orientation and spatial functions than in pattern recognition.

Visual checkerboard-evoked potentials from upper and lower retinal halves, and variation of check size

Human visually evoked potentials were studied with checkerboard reversal stimulation of the upper and lower halves of the visual field, using different check sizes and field diameters. Although attenuation of the overall amplitude was seen in the potentials with stimulation of the upper visual half-field, the steady-state response amplitude vs spatial frequency curves for upper and lower half-field stimulation were similar. Decrease of field size reduced the amplitude but did not change the shape of the amplitude vs spatial frequency curve with its peak of 14 min of arc check size. Dissimilar characteristics of half-field responses were seen with 2/sec reversal: stimulation of the lower visual half-field evoked wave forms with a positive component of 102 (112) msec peak latency, which was delayed by 21.5 (24) msec when the upper half-field was stimulated, using 56 (14) min checks.

Lateral asymmetry of the Hoffmann reflex: relation to cortical laterality.

Lateral asymmetry of the Hoffmann reflex (H-reflex) recovery curve was found in seven subjects with no personal or family history of neurological or psychiatric disorder. Differences between recovery curves from the right and left leg were larger than differences in the same leg on two successive test days. In a group of 27 psychiatric inpatients, lateral asymmetry of the later portion of the recovery curve was correlated with cortical laterality, as measured by selective identification of differing verbal stimuli presented simultaneously to both ears (DL) and to total laterality scores, a sum of visual half-field, DL, and motor laterality scores. Asymmetry of the recovery curve is related in part to cortical laterality, possibly through selective activation of cortical motor centres on the preferred side.

Beyond averaging. II. Single-trial classification of exogenous event-related potentials using stepwise discriminant analysis

Using stepwise discriminant analysis (SWDA), single-trial event-related potentials (ERPs) were classified as to whether they were elicited by a checkerboard presented to the upper or lower visual half-field. Discriminant functions were computed on the basis of ‘training sets’ constructed of upper and lower half-field ERPs, and applied to ‘test sets’ of other ERPs elicited by the same stimuli. Individual-subject discriminant functions for data recorded at Pz classified the single ERPs in the test sets with a mean accuracy of 83.7% correct. The mean accuracy attained by individual-subject functions from the most discriminable scalp site for each subject was 87.8% correct, and that attained by an across-subjects function was 78.1% correct. Averaged ERPs showed the previously reported polarity reversal of corresponding exogenous components in the upper and lower half-field wave forms. Moreover, the SWDA procedure chose ERP time points at the latencies of these exogenous components for discriminating the half-field ERPs. The results demonstrate that SWDA can accurately classify single ERPs in which the systematic variance is localized in exogenous components, having periods within the range of frequencies which typically compose the background EEG.

Hemispheric laterality differences among four levels of reading achievement.

80 male children between the ages of 8 and 10 yr. were divided into four groups on the basis of their reading ages. 20 words were tachistoscopically presented to the left and right visual half-fields to determine if incomplete hemispheric laterality is associated with all levels of reading deficiency or only with the more severe cases. The results support the hypothesis that incomplete hemispheric laterality is only associated with reading deficiency when the deficit exceeds 18 mo.

Spécialisation hémisphérique, perception et mémoire des mots

Summary In two experiments, performance of right-handed adult subjects was compared in tasks involving identification, free recall and recognition of tachistoscopically presented lists of nouns, as a function of their position in the visual field. The results show significantly higher performance in the identification, free recall and recognition of five-letter words when they are presented in the right visual half-field. However, three-letter nouns which have an equivalent probability of identification are better recalled but not better recognized when presented in the right visual half-field as compared with the left one. These findings are interpreted as the resuit of a functional superiority of the left cerebral hemisphere in the perception and semantic processing of verbal material.

Pseudoneglect: Effects of hemispace on a tactile line bisection task

The purpose of this study was to determine whether tactile laterality effects can be attributed to an anatomical pathway-transmission model or to some hemispheric mechanism involved in the perception and/or mediation of activities in the contralateral hemispatial field. Hemispace is not the same as the visual half field, but refers to the external space to the left or right of body midline. To differentiate between these two hypotheses, 24 normal dextrals performed a tactile line bisection task using the left or right hand in each of three spatial conditions: at midline, in left hemispace and right hemispace. The findings indicated that both hemisphere-hemispace mechanisms and hemisphere-hand connections contributed to laterality effects. Furthermore, a pseudoneglect phenomenon was observed.

Laterality and Reading Proficiency in Children

THIS PAPER DISCUSSES SOME CURRENT concepts of the lateralityreading relationship. An overview of Orton's hypotheses of cerebral dominance and strephosymbolia is taken as a starting point in the discussion. Both visual half-field and dichotic listening studies as direct, empirical tests of laterality are discussed. Some methodological and conceptual problems in dichotic listening are pointed out. The laterality-reading relationship is best interpreted as consisting of complementary contributions of the two hemispheres to different stages of reading, to lingual and perceptual types of reading errors, to differential task requirements and to processing strategies used by readers.

Visual areas in the temporal cortex of the macaque

Visual receptive fields and responsiveness of neurons to somesthetic and auditory stimuli were studied in the inferior temporal cortex and adjacent regions of immobilized macaques. Neurons throughout cytoarchitectonic area TE were responsive only to visual stimuli and had large receptive fields that almost always included the center of gaze and usually extended into both visual half-fields. There was no indication of any visuotopic organization within area TE. Neurons in an anterior and in a dorsal portion of TE tended to have larger receptive fields. By contrast, dorsal, ventral and anterior to area TE, units often responded to somesthetic and auditory as well as to visual stimuli. In these regions visual receptive fields were even larger than in TE and often included the entire visual field. Posterior to TE the neurons were exclusively visual and had much smaller receptive fields that were confined to the contralateral visual field and were topographically organized.