Right Visual Hemifield Research Articles

Stronger interference from distractors in the right hemifield during visual search

ABSTRACTThe orientation-bias hypothesis states that there is a bias to attend to the right visual hemifield (RVF) when there is spatial competition between stimuli in the left and right hemifield [Pollmann, S. (1996). A pop-out induced extinction-like phenomenon in neurologically intact subjects. Neuropsychologia, 34(5), 413–425. doi:10.1016/0028-3932(95)00125-5]. In support of this hypothesis, stronger interference was reported for RVF distractors with contralateral targets. In contrast, previous studies using rapid serial visual presentation (RSVP) found stronger interference from distractors in the left visual hemifield (LVF). We used the additional singleton paradigm to test whether this discrepancy was due to the different distractor features that were employed (colour vs. orientation). Interference from the colour distractor with contralateral targets was larger in the RVF than in the LVF. However, the asymmetrical interference disappeared when observers had to search for an inconspicuous colour target instead of the inconspicuous shape target. We suggest that the LVF orienting-bias is limited to situations where search is driven by bottom-up saliency (singleton search) instead of top-down search goals (feature search). In contrast, analysis of the literature suggests the opposite for the LVF bias in RSVP tasks. Thus, the attentional asymmetry may depend on whether the task involves temporal or spatial competition, and whether search is based on bottom-up or top-down signals.

Magnetic Stimulation of the Left Visual Cortex Impairs Expert Word Recognition

One of the hallmarks of expert reading is the ability to identify arrays of several letters quickly and in parallel. Such length-independent reading has only been found for word stimuli appearing in the right visual hemifield (RVF). With left hemifield presentation (LVF), response times increase as a function of word length. Here we investigated the comparative efficiency with which the two hemispheres are able to recognize visually presented words, as measured by word length effects. Repetitive transcranial magnetic stimulation (rTMS) of the left occipital cortex disrupted expert processing of the RVF such that a length effect was created (Experiment 1). Right occipital rTMS, on the other hand, had no such effect on RVF words and nor did it modulate the length effect already present in the LVF. Experiment 2 explored the time course of these TMS-induced effects by applying single pulses of TMS at various stimulus-onset asynchronies for the same task. We replicated the TMS-induced length effect for RVF words, but only when a single pulse was applied to the left visual cortex 80 msec after target presentation. This is the first demonstration of TMS-induced impairment producing a word length effect, and as such confirms the specialization of the left hemisphere in word recognition. It is likely that anatomical differences in the pathway linking retinal input to higher level cortical processing drive this effect.

Assessing the Role of Hemispheric Specialisation, Serial-Position Processing, and Retinal Eccentricity in Lateralised Word RecognitioN

The advantage for words in the right visual hemifield (RVF) has been assigned parallel orthographic processing by the left hemisphere and sequential by the right. However, an examination of previous studies of serial position performance suggests that orthographic processing in each hemifield is modulated by retinal eccentricity. To investigate this issue, we presented words at eccentricities of 1, 2, 3, and 4 degrees. Serial position performance was measured using the Reicher-Wheeler task to suppress influences of guesswork and an eye-tracker controlled fixation location. Greater eccentricities produced lower overall levels of performance in each hemifield although RVF advantages for words obtained at each eccentricity (Experiments 1 and 2). However, performance in both hemifields revealed similar U-shaped serial position performance at all eccentricities. Moreover, this performance was not influenced by lexical constraint (high, low; Experiment 2) or status (word, nonword; Experiment 3), although only words (not nonwords) produced an RVF advantage. These findings suggest that although each RVF advantage was produced by left-hemisphere function, the same pattern of orthographic analysis was used by each hemisphere at each eccentricity.

Interhemispheric cooperation for familiar but not unfamiliar face processing

Evidence for interhemispheric cooperation during language processing has been demonstrated for words, but not for meaningless pseudowords. Specifically, responses were found to be faster and more accurate when identical copies of a word were presented bilaterally to both hemispheres, relative to unilateral single presentations. This bilateral advantage for words seems to be a robust effect in normals. The present study addressed the question of whether the bilateral advantage is restricted to lexical material or whether it is a more global phenomenon occurring for meaningful material in general. Thirty healthy participants performed a familiarity decision in which one copy of familiar and unfamiliar faces was presented tachistoscopically to the right visual hemifield (RVF), the left visual hemifield (LVF) or simultaneously to both visual hemifields (bilateral condition, BVF). We obtained a highly significant familiarity by visual field interaction ( P<0.006) showing that only for familiar faces, a bilateral advantage was obtained. Unfamiliar face processing did not yield a bilateral advantage. We conclude that interhemispheric cooperation only occurs for meaningful material for which cortical representations can be assumed.

Processing of global and local visual information and hemispheric specialization in humans (Homo sapiens) and baboons (Papio papio).

Global precedence was examined in 8 baboons and 14 humans using compound stimuli presented in the left visual hemifield (LVF) or the right visual hemifield (RVF). Humans showed a global advantage and global-to-local interference. Baboons showed a local advantage and no interference. For humans and baboons, a LVF advantage appeared for global matching and an unsignificant RVF advantage appeared for local matching. The local advantage in baboons still emerged when the memory load of the task was removed and when the local elements were connected by lines or were adjacent. Moreover, global precedence in humans persisted with unfamiliar forms. Species differences suggest that global precedence is not a universal trait and that this effect in humans does not have a purely perceptual or sensory basis.

Subjective Mood State and Perception of Emotion in Chimeric Faces

Levy, Heller, Banich, and Burton (1983) have shown that hemispheric activational, or arousal, style, as measured by direction and consistency of choice of the “happer face” on a free-viewing Chimeric Faces Test, is highly reliable and varies across individuals who otherwise presumably have similar cortical organization (e.g., right-handed college students). The current experiment asks whether such individual differences in hemispheric arousal style are moderated by long-term, in the sense of enduring, individual differences in mood, as measured by the Profile of Mood States (POMS) questionnaire.Like Levy et al.'s subjects, most of our subjects (126 right-handed college students) made most of their choices on the Chimeric Faces Test based on the emotional cue (the smile) positioned in the half of the face to the viewer's left, or left visual hemifield (LVH), whereas a small minority were equally consistent in making their choice based on the emotional cue positioned in the half of the face to the viewer's right, or right visual hemifield (RVH). Performance on the Chimeric Faces Test, however, proved to be unrelated to scores on the POMS questionnaire. This suggests that hemispheric arousal style, as indexed by the Chimeric Faces Test, is robust enough, for a population of normal right-handers, to transcend any differences in mood as measured by the POMS questionnaire.

Psychopathy and cerebral asymmetry in semantic processing

A divided visual field (DVF) procedure was used to investigate the cerebral organization of language processes in psychopaths. The subjects consisted of four groups of 13 right-handed males: noncriminals (NC), and criminals with high (H), medium (M), and low (L) scores on the Psychopathy Checklist (Hare, 1980). The subject had to decide if a concrete noun, tachistoscopically presented in either the left (LVF) or the right visual hemifield (RVF), matched a pretrial work (SR task), or was an exemplar of a specific category (SC task) or an abstract category (AC task). There were no group differences in reaction time. As predicted, group differences in errors were confined to the AC task; Groups L and NC made fewer RVF than LVF errors (thus showing the sort of RVF advantage expected with semantic categorization), whereas the opposite was true of Group H. The results, along with those obtained in a recent dichotic listening study, lead us to speculate that psychopathy may be associated with weak or unusual lateralization of language function, and that psychopaths may have fewer left hemisphere resources for processing language than do normal individuals.

Different methods of lexical access for words presented in the left and right visual hemifields

Right-handed adults were asked to identify by name bilaterally presented words and pronounceable nonwords. For words in the normal horizontal format, word length (number of letters) affected left visual hemifield (LVF) but not right visual hemifield (RVF) performance in Experiments 1, 2, 3, 5, and 6. This finding was made for words of high and low frequency (Experiment 6) and imageability (Experiment 5). It also held across markedly different levels of overall performance (Experiments 1 and 2), and across different relative positionings of short and long words in the LVF and RVF (Experiment 3). Experiment 4 demonstrated that the variable affecting LVF performance is the number of letters in a word, not its phonological length. For pronounceable nonwords (Experiment 7) and words in unusual formats (Experiment 8), however, length affected both LVF and RVF performance. The characteristics identified for RVF performance in these experiments also hold for the normal reading system. In this (normal) system the absence of length effects for horizontally formatted words is generally taken to reflect the processes involved in lexical access. Length effects in the normal reading system are thought to arise when lexical access for unusually formatted words and for the pronunciation of nonwords requires the short-term storage of information at a graphemic level of analysis. The characteristics of LVF performance indicate that horizontally formatted words presented to the right cerebral hemisphere can only achieve lexical access by a method that requires the short-term storage of graphemic information. This qualitative difference in methods of lexical access applies regardless of whether the right hemisphere is seen as accessing words in the left hemisphere's lexicon or words in a lexicon of its own.

Right cerebral hemisphere superiority for constructing facial representations

Right-handed people were asked to decide whether or not stimuli presented in the left visual hemifield (LVF) or in the right visual hemifield (RVF) were faces. Manual reaction times and error rates were recorded under three conditions. In Condition A, stimuli were line drawings of faces and moderately scrambled nonfaces made by rearranging the facial features. In Condition B, stimuli were line drawings of faces and highly scrambled nonfaces. In Condition C, stimuli were line drawings of faces and objects. The results show that faces are identified more quickly from the LVF than from the RVF in Condition A (faces vs moderately scrambled nonfaces), with no visual hemifield difference in reaction times to Condition B (faces vs highly scrambled nonfaces) and Condition C (faces vs objects). These findings are taken to indicate that both cerebral hemispheres are able to assign stimuli to the “face” category, but the right hemisphere is better than the left hemisphere at constructing facial representations. This cerebral hemisphere difference in ability to construct facial representations becomes evident when a detailed representation is required (as in Condition A).

Identification and Storage of Line Drawings Presented to the Left and Right Cerebral Hemispheres of Adults and Children

Line drawings of common objects were presented bilaterally, with one drawing in each visual hemifield,,Io right-handed children aged five, seven and eleven years, and to adults, who were required to name them. Left-right or right-left order for report was counterbalanced by means of a cue consisting of underlining the drawing to be reported first. No visual hemifield difference was found for subjects' first reports, and a small right visual hemifield (RVF) superiority was found for subjects' second reports. This visual hemifield × report interaction was unrelated to age.The result is taken to indicate that there is no change in the age range studied in the relative abilities of the left and right cerebral hemispheres to recognise the drawings used, but that at all ages the right hemisphere is less able than the left to effect the temporary storage needed when a drawing is to be reported second.

Studies toward a model of laterality effects for picture and word naming

Experiments requiring the naming of bilaterally presented nouns, picturable nouns, consonant-vowel-consonant (CVC) nonwords, and line drawings are reported. In order to eliminate order of report strategies and facilitate comparison across experiments, the stimulus to be reported first was cued by underlining at presentation of each trial. Large right visual hemifield (RVF) superiorities were found to arise from both first and second reports for naming nouns and CVC nonwords. Drawings and picturable nouns, however, produced only a small RVF superiority arising entirely from subjects' second reports. It is proposed that hemispheric laterality effects for naming visually presented stimuli can arise from three principal sources, and the application of this model to existing studies is outlined.