Hemispheric differences in processing handwritten cursive

Hemispheric asymmetry was examined for native English speakers identifying consonant-vowel-consonant (CVC) non-words presented in standard printed form, in standard handwritten cursive form or in handwritten cursive with the letters separated by small gaps. For all three conditions, fewer errors occurred when stimuli were presented to the right visual field/left hemisphere (RVF/LH) than to the left visual field/right hemisphere (LVF/RH) and qualitative error patterns indicated that the last letter was missed more often than the first letter on LVF/RH trials but not on RVF/LH trials. Despite this overall similarity, the RVF/LH advantage was smaller for both types of cursive stimuli than for printed stimuli. In addition, the difference between first-letter and last-letter errors was smaller for handwritten cursive than for printed text, especially on LVF/RH trials. These results suggest a greater contribution of the right hemisphere to the identification of handwritten cursive, which is likely related visual complexity and to qualitative differences in the processing of cursive versus print.     

Hemispheric differences in processing visual patterns

The dichotomies verbal/visuospatial, serial/parallel and analytic/holistic are reviewed with respect to differences in hemispheric processing. A number of experimental parameters may be varied in such tasks, and together with certain frequently-occurring weaknesses of experimental design may account for the often discrepant results hitherto reported. The above factors are systematically reviewed, and three further experiments are reported which attempt to fill in the missing designs. Further evidence is given in support of the hypothesis that right-hemisphere superiority is most apparent in processes leading to identity matching. It is quantitative rather than qualitative, and may depend upon operations on the entire gestalt, such as holistic matching, mental rotation, reflection, distortion, etc., rather than, e.g., simultaneous (parallel) processing of discretely analysed or isolated features or elements. On the other hand left-hemisphere involvement in visuospatial processing is thought to reflect analysis of the configuration into its separable components; such processing may be either serial or parallel, and may frequently lead to a judgement different.     

Hemispheric differences in processing emotions and faces.

Visual field differences for the recognition of emotional expression were investigated using a tachistoscopic procedure. Cartoon line drawings of five adult male characters, each with five emotional expressions ranging from extremely positive to extremely negative, were used as stimuli. Single stimuli were presented unilaterally for 85 msec. Subjects (N = 20) were asked to compare this target face to a subsequent centrally presented face and to decide whether the emotional expressions of the two faces, or the character represented by the two faces, were the same or different. Significant left visual field (LVF) superiorities for both character and emotional expression recognition were found. Subsequent analyses demonstrated the independence of these effects. The LVF superiority for emotional judgments was related to the degree of affective expression, but that for character recognition was not. The results of this experiment are consistent with experimental and clinical literature which has indicated a right hemispheric superiority for face recognition and for processing emotional stimuli. The asymmetry for emotion recognition is interpreted as being an expression of the right hemisphere's synthetic and integrative characteristics, its holistic nature, and its use of imagic associations.     

Hemispheric differences for orthographic and phonological processing

The role of hemispheric differences for the encoding of words was assessed by requiring subjects to match tachistoscopically presented word pairs on the basis of their rhyming or visual similarity. The interference between a word pair's orthography and phonology produced matching errors which were differentially affected by the visual field/hemisphere of projection and sex of subject. In general, right visual field/left hemisphere presentations yielded fewer errors when word pairs shared similar phonology under rhyme matching and similar orthography under visual matching. Left visual field/right hemisphere presentations yielded fewer errors when word pairs were phonologically dissimilar under rhyme matching and orthographically dissimilar under visual matching. Males made more errors and demonstrated substantially stronger hemispheric effects than females. These patterns suggested visual field/hemispheric differences for orthographic and phonological encoding occurred during the initial stages of word processing and were more pronounced for male compared to female subjects.     

Categorization versus distance: Hemispheric differences for processing spatial information

It has been hypothesized that the brain computes two different kinds of spatial-relation representations: one used to assign a spatial relation to a category and the other used to specify metric distance with precision. The present visual half-field experiment offers support for this distinction by showing that the left and right cerebral hemispheres make more effective use of the categorization and metric distance representations, respectively. Furthermore, the inclusion of a bilateral stimulus presentation condition permits the computation of a reversed association that offers additional support for the distinction between two types of spatial-relation representation.     

Hemispheric differences in picture-word interference

In a picture-word version of the Stroop task, 30 right-handed subjects were tested under each of six conditions in which a picture alone or a picture plus a word were presented to the left, the right, or both hemispheres. In two additional conditions the picture was presented to the right hemisphere and the word was simultaneously presented to the left hemisphere, or vice versa. For all conditions, subjects were instructed to name the picture only, as rapidly as possible. Picture naming times were significantly slower for the conditions in which the pictures were accompanied by words than in the respective picture alone conditions. Moreover, simultaneous presentation of a picture and a word to both hemispheres resulted in greater interference (slower picture naming times) than did the simultaneous presentation of the picture and the word to either the left hemisphere alone or the right hemisphere alone. The latter two conditions, in turn, resulted in significantly more interference than did the simultaneous presentation of the picture to one hemisphere and the word to the other hemisphere. This pattern of results suggests that the Stroop effect obtained under normal circumstances is in large part a function of the interference caused by the simultaneous processing of items in the same hemisphere. In contrast to hemispheric differences reported for the color-word Stroop task, the effect of presenting a picture and word simultaneously to the right hemisphere did not differ reliably from that of presenting a picture and word to the left hemisphere. The failure to replicate this aspect of the color-word Stroop is attributed to differences in the abilities of the two hemispheres to process the respective target items (the color or the picture) of the two tasks.     

Hemispheric differences in temporal resolution

A review of the relevant clinical and experimental literature gives the conclusion that the cerebral hemispheres differ in temporal resolution of input, with the language-dominant hemisphere showing finer acuity. This conclusion is supported by evidence from performance of patients with unilateral brain damage on tests of temporal resolution, performance of developmental dyslexics on similar tasks, and left-right sensory field differences in temporal acuity in normal human subjects. While it is unlikely that a hemispheric difference in temporal resolution is sufficient to give a complete account of lateralized functions, such attempts to show more primitive physiological differences between the hemispheres are more likely to be fruitful than attempts which differentiate the hemispheres in terms of higher-order psychological functions.     

Hemispheric differences in stimulus identification

Subjects were presented with either verbal (letters) or nonverbal (outline forms) stimuli to their left or right cerebral hemispheres. Verbal items presented with a lateral masking stimulus were identified more quickly and accurately when presented to the right hemisphere rather than to the left. When the letters were presented without a masking stimulus, weak hemispheric effects were obtained. Nonverbal forms demonstrated faster reaction time and fewer errors for right-hemisphere presentations under both masked and unmasked conditions. Retinal locus of the display item was also varied and produced faster responding with fewer errors when the stimulus was presented foveally rather than peripherally under all display conditions. These effects were attributed to the use of a manual response procedure that effectively reduced the ability of subjects to employ names for the stimulus objects.     

Hemispheric differences in object identification

Although the right hemisphere is thought to be preferentially involved in visuospatial processing, the specialization of the two hemispheres with respect to object identification is unclear. The present study investigated the effects of hemifield presentation on object and word identification by presenting objects (Experiment 1) and words (Experiment 2) in a rapid visual stream of distracters. In Experiment 1, object images presented in the left visual field (i.e., to the right hemisphere) were identified with shorter display times. In addition, the left visual field advantage was greater for inverted objects. In Experiment 2, words presented in the right visual field (i.e., to the left hemisphere) under similar conditions were identified with shorter display times. These results support the idea that the right hemisphere is specialized with regard to object identification.     

Hemispheric differences in semantic-relatedness judgments

Subjects judged the semantic relatedness of word pairs presented to the left or right visual field. The word pairs were presented one below the other. On critical trials, the words' referents had a typical spatial relation, with one referent oriented above the other (e.g. ATTIC/BASEMENT). The spatial relation of the words either matched or mismatched the spatial relation of their referents. When presented to the left hemisphere, the match or mismatch did not have an effect. However, there was a reliable mismatch effect for pairs presented to the right hemisphere. The results are interpreted in the context of perceptual theories of mental representation.     

Hemispheric processing differences revealed by differential conditioning and reaction time performance.

Two different experimental procedures were used to examine (a) information-processing differences between two groups of subjects (Cs versus Vs) identified by the form of their conditioned eyeblinks; (b) information-processing differences between the right and left cerebral hemispheres; and (c) parallels between hypothesized C-V differences and right-left hemisphere differences. In the first experiment, the evocative command words BLINK and DON'T BLINK served as positive and negative conditioned stimuli. It was found that Vs gave more conditioned eyeblinks than Cs and that differential eyelid conditioning of Vs more than Cs was influenced by the semantic content of the stimuli. More importantly, the conditioning performance of Cs was more influenced by the semantic attributes of the stimuli when they were presented directly to the right visual field (left hemisphere) than when they were presented directly to the left visual field (right hemisphere). In contrast, the conditioning performance of Vs was equally influenced by the semantic attributes regardless of which hemisphere received direct stimulation. A second experiment was designed to determine whether such hemisphere-of-presentation differences for Cs versus Vs could also be obtained in a very different task. Subjects classified as Cs or Vs during a differential eyelid conditioning task then performed two same-different reaction time (RT) tasks that required discrimination of complex polygons in one case and the names of letters in another. On each RT trial both stimuli of a pair appeared briefly either in the center, left, or right visual field. For both Cs and Vs RTs to complex polygon pairs averaged 20 msec faster on left visual field trials than on right visual field trials, consistent with current hypotheses about right-hemisphere specialization for visuospatial processing. In contrast, the results for letter pairs generally confirmed the C-V differences found in Experiment 1. That is, the right visual field (left-hemisphere) advantage for these verbal stimuli was once again larger for Cs than for Vs. The present results suggest that the two groups of subjects (Cs versus Vs) differ qualitatively in the modes of information processing that they typically employ. The results also suggest that these different modes of processing are related to aspects of cerebral hemisphere organization and that even right-handed individuals may differ from each other in the extent to which each cerebral hemisphere is mobilized for a given experimental task. Such individual differences must be incorporated into both models of classical eyelid conditioning and models of cerebral hemisphere specialization.     

Hemispheric differences in stop task performance

This study examined hemispheric specialization for stop task performance. It was found that inhibitory performance was better for stop signals presented in the right visual field. This result provided support for the hypothesis that, during stop task performance, subjects call upon the left-lateralized neural system that is involved in active attention. It was suggested that a stop task requires such a mode of attention because subjects maintain a tonic readiness for inhibitory action while being engaged in the stop task's go routine. Subjects are continuously alert for possible stop signals while discriminating between go stimuli. The stop task may be considered a typical activation task.     

Hemispheric differences in grammatical class.

Although a number of studies have examined lexical asymmetries in hemispheric processing, few have systematically investigated differences between nouns and verbs. Lateralization effects of grammatical class were examined by presenting nouns and verbs of both high and low frequency to either the right or left visual field. Results from both a noun/verb categorization and a lexical decision task revealed a significant visual field by grammatical class interaction. Further analyses revealed that verbs were processed faster in the left compared to the right hemisphere, while there was no hemispheric advantage for the processing of nouns. The present study provides new evidence for the role of grammatical class in lexical processing.     

Hemispheric laterality and dissociative tendencies: differences in emotional processing in a dichotic listening task

The present work investigates whether the hemispheric processing of both verbal and emotional stimuli, studied by means of a dichotic listening task, differs between normal high and low dissociators as assessed by the Dissociative Experiences Scale (DES; Bernstein & Putnam (1986). Development, reliability and validity of a dissociation scale. Journal of Nervous and Mental Disease, 174(2), 727-735). Two groups of subjects (50 high and 50 low dissociators), participated in the experiment. The task consisted in identifying both verbal and emotional stimulus-targets, respectively, on successive sessions. Reaction time and response accuracy were registered and analysed using ANOVA (Analysis of Variance). The interaction between stimuli (verbal, emotional), channel (right ear, left ear), and dissociation level (high, low) reached statistical significance in terms of accuracy measures (d': F(1,98)=4.75; p<.05). Both high and low dissociators exhibited the expected right ear advantage (REA effect) on verbal targets. On the other hand, whereas low dissociators exhibited the expected left ear advantage (LEA effect) on emotional targets, high dissociators failed to follow this typical pattern of hemispheric asymmetry: both hemispheres exhibited similar performances. These results confirm the hypothesis that dissociation is related to changes in hemispheric processing, specifically of emotional information.     

Hemispheric differences for feature perception

Summary Hemisphere differences for featural processing were investigated in three experiments. Stimulus arrays composed of the same background letter were presented tachistoscopically and the subject instructed to detect an embedded target letter. Background and target letter features were manipulated across studies, while stimulus arrays were presented at different retinal loci within experiments. Signal detection analysis revealed that left hemisphere stimulus presentations demonstrated slightly better detection when target and background features were relatively dissimilar, while right hemisphere stimulus presentations demonstrated better detection when target and background features were highly similar. Retinal locus generally decreased detection performance when the stimulus letters were dissimilar and interacted with hemispheric advantages. Both of these factors also were affected by changes in response criterion across experiments which were linked to target/background perceptual confusions. The findings suggest that the left and right hemispheres differ in their feature extraction capabilities during the early stages of visual stimulus processing.     

Hemispheric visual processing in face recognition

Two experiments tested how facial details are used in recognizing face drawings presented to either the left or right visual field (VF). Subjects used inner and outer features about equally in both the left and right VFs. The major finding was a very strong tendency to recognize the upper facial features more accurately than the lower facial features. The top-to-bottom recognition difference occurred in both VFs, in contrast to an earlier study by J. Sergent (1982, Journal of Experimental Psychology: Human Perception and Performance, 8, 1-14). Methodological differences between the present experiments and Sergent's studies were discussed. It was concluded that both the left and right hemispheres recognize novel faces using top-to-bottom serial processing.     

Hemispheric differences in semantic processing: Category matching is not the same as category membership

Two closely related semantic processing tasks were studied under identical procedural conditions in order to examine lateral visual field effects on reaction times. In Experiment 1, reaction times did not differ as a function of visual field when subjects decided whether a lateral word was a member of a foveally presented category word (category membership task). On the other hand, reaction times were faster for right than for left visual field stimulus presentations when subjects decided whether two words, one lateral and one foveal, belonged to the same category (category matching task), although this advantage did not occur immediately. In Experiment 2, the laterality effect in the category matching task was studied as a function of word familiarity. Two groups of subjects performed the matching task for two blocks of trials, one group receiving the same word list in each block and the other receiving different lists. No visual field differences in reaction times were observed for either group during the first block of trials, but a distinct right field advantage appeared for both during the second block. The data from these experiments suggest that category matching strategies rely upon structures or processes localized in the left hemisphere, although their influence is not immediate. Category membership strategies, on the other hand, do not depend upon such localized structures.     

Hemispheric processing of multi-element displays

A visual detection paradigm was employed in two experiments to explore the relationship between stimulus configuration and hemispheric processing. Stimulus arrays composed of small vertical lines were presented tachistoscopically to the left and right hemispheres. Subjects judged whether all the lines within an array were vertically oriented (same) or whether a horizontal line was present (different). In general, right hemisphere presentations demonstrated a faster detection than the left for arrays consisting of all identical elements, whereas left hemisphere presentations demonstrated a faster detection than the right for arrays containing a different element. Similar results were obtained for both experiments, although the response patterns and error rates varied somewhat with the inter-item spacing and organization of stimulus elements. These effects suggest that differential hemispheric processing for target detection tasks is determined by the nature of the stimulus materials which governs the relative efficacy of the hemispheric and decision outcomes.     

Hemispheric differences in a letter classification task

The experiment examined hemispheric differences in same-different judgments for unilaterally presented letter pairs which could be classified as “same” on the basis of name identity (NI, e.g., Aa) or physical identity (PI, e.g., AA). Two groups of Ss were tested, a right-handed group and a predominantly left-handed group. The experiment employed a reaction time measure, and fixed the duration of brief exposures to yield an overall performance level of 90% correct. Analysis of the results focused on the difference between RTs for the NI matches and for the PI matches in each hemisphere. The method allowed differences in cognitive processing to be assessed while sensory and response factors were minimized. The right-handed group all showed a smaller mean NI-PI difference in the left hemisphere (84 msec) than in the right hemisphere (181 msec). The left-handed group showed smaller and less consistent differences, but the group as a whole had a reversed asymmetry, with a mean NI-PI difference of 128 msee in the left hemisphere and 90 msec in the right hemisphere.