Hemispheric differences in global and local processing with orientation classification tasks

Hemispheric differences in global and local processing were examined in one experiment with hierarchical stimuli. The figures consisted of large squares with the right or left side missing made up of small squares with the right or left side missing. The subjects were asked to decide the opening (left/right) of the square either at the global level or at the local level. The findings showed that with the task and stimuli used here global judgements were as fast and accurate as local judgements, the interference was bidirectional and symmetrical and, finally, that the right hemisphere and the left hemisphere had the same ability to manage with global and local information. So, the experiment does not provide evidence for hemispheric specialisation in global and local processing.     

Schizotypy and patterns of lateral asymmetry on hemisphere-specific language tasks.

Following the notion that abnormalities of hemispheric asymmetry may underlie schizophrenia, patterns of cognitive hemispheric asymmetries, as assessed by left and right hemisphere language tasks, were examined in relation to schizotypal symptoms. Ninety right-handed undergraduates completed the Oxford-Liverpool Inventory of Feelings and Experiences questionnaire (O-LIFE; Mason, O., Claridge, G., Jackson, M., 1995. New scales for the assessment of schizotypy. Personality and Individual Differences, Vol. 53, pp. 727-730), which measures different aspects of schizotypy symptomatology. Low scores on right, but not left, hemisphere language tasks were significant predictors of high scores on positive schizotypal symptomatology scales (Unusual Experiences and the STA) over and above the contributions of the left hemisphere language tasks and demographic variables. Low scores on both left and right hemisphere language tasks were significant predictors of high scores on the Cognitive Disorganisation factor, over and above the contributions of tasks related to the contralateral hemisphere and demographic variables. Neither the right nor the left hemisphere language tasks resulted in a significantly good degree of prediction of introvertive anhedonia (an index of negative schizotypal symptomatology) or impulsive non-conformity. The findings provide partial support for some current theories of hemispheric differences in schizophrenia and schizotypy.     

Hemispheric differences in global versus local processing of hierarchical visual stimuli by normal subjects: new data and a meta-analysis of previous studies

Twenty-four normal right-handed male subjects classified hierarchical visual stimuli (small letters arranged to form larger letters), which were presented separately to each cerebral hemisphere. Previous studies using similar paradigms have yielded mixed evidence for the specialization of local, analytic processing in the left hemisphere and global, holistic processing in the right hemisphere. No statistically significant evidence for such a pattern of specialization was evident in the results of the present study. However, when meta-analytic techniques were used to combine the present results with those from previous studies, there was evidence that the hypothesized left-hemisphere/local, right-hemisphere/global specialization does in fact exist.     

Directed and divided attention during hierarchical processing in patients with visuo-spatial neglect and matched healthy volunteers

Hierarchically organized figures (for example, a large E made up of smaller N's) are frequently used to investigate directed and divided attention. Investigations of neurological and psychiatric patients, and also tachistoscopic and functional neuroimaging studies on healthy subjects, typically find the right hemisphere to be specialized for the processing of global stimuli and the left hemisphere to be specialized for the processing of local stimuli. In the current study, a group of 12 patients with visuo-spatial neglect (NP) after right hemisphere lesions and 12 age and sex-matched control subjects (CO) performed a directed and a divided attention task with hierarchically organized letters. As expected, faster reaction times were found for control subjects than for neglect patients, especially for the directed global attention task. Lower error rates were found for CO and NP for local than for global targets during the divided attention condition. Local on global interference was found for both groups in reaction times. These local processing advantages for older healthy adults have been reported previously. Additionally, an impairment in the divided attention task was found in both groups, but especially for global targets in NP. This impairment is consistent with other evidence of difficulty in disengaging attention shown by patients with visuo-spatial neglect.     

The interference of local over global information processing in children with attention deficit hyperactivity disorder of the inattentive type

A classic finding in perception of compound patterns is normal individuals cannot skip global analysis in local-oriented processing, but they can successfully resist local analysis in global-oriented processing-the so-called global interference [1]. Recently, studies examining the role of brain hemisphere activity in the Navon task have indicated that the processing of global and local information can be, respectively, attributed to the right and left hemispheres. Moreover, many neuroimaging researches have revealed that certain core symptoms of attention deficit hyperactivity disorder (ADHD) are related to dysfunction of right hemisphere. These findings imply that global interference will be substantially less evident, and possibly even replaced by local interference in ADHD. The present study compared the performance of children with and without attention deficit hyperactivity disorder of the inattentive type (ADHD-I) in the processing of global and local information to examine the local interference hypothesis in ADHD. An ADHD-I group (n=15) and a paired control group (n=19) completed tasks using two versions of the Navon task, one requiring divided attention, in which no information was given to participants regarding the level at which a target would appear, and the other requiring selective attention, in which participants were instructed to attend to either the local or the global level. The results showed that children with ADHD-I exhibited local interference, regardless of which attention procedure was used. These results support the weak right hemisphere hypothesis in ADHD, and provide evidence against the deficit hypotheses for ADHD in the DSM-IV criteria [29], which postulates that inattention symptoms may manifest as a failure to provide close attention to details.     

Bilateral hemispheric processing deficits in schizophrenia

Schizophrenics are known to have an early visual processing deficit, but the exact nature of that deficit is unclear. The present research was undertaken in order to establish the difference between schizophrenic and normal subjects in their processing of visual stimuli. Previous studies have shown that short duration stimuli activate a transient visual system which is associated with the right hemisphere, while longer duration stimuli activate the sustained system associated with the left hemisphere. The present study was designed to determine the effects of activation/inactivation of both the sustained and transient channels on hemispheric processing in normal compared to schizophrenic patients. The task was a forced choice continuity of form. The subject was required to detect two grating pulses, separated by a blank interval (interstimulus interval-ISI) vs. a single grating pulse, which was shown for the same total duration as the two pulse condition. Threshold ISI was obtained and used as the index of visible persistence/speed of visual processing, 19 schizophrenics, 12 depressives, 6 schizoaffectives, and 11 controls participated in the study. Stimuli were sinusoidal spatial frequency (SF) gratings of 0.9 and 15 c/degrees presented independently to the left and right hemisphere for durations of 50 and 250 ms. The results revealed statistical significance for Diagnosis, Diagnosis x SF, and Position x Diagnosis. Normal controls and depressed subjects did not statistically differ from each other, while schizophrenic and schizoaffectives differed from both control groups and on some conditions from each other. No hemispheric asymmetries were observed for any group. The results are discussed in terms of differential deficits in schizophrenics in the absence of early occurring asymmetries.     

Hemisphere priming through practice in a musical chords task

In a study of selective hemisphere activation, the performance of 30 subjects given either a "local" or "global" priming activity before and after a monoaurally presented chord analysis task was compared with an unprimed control group. The hypothesis was that ear advantage scores on the chords task would show increased left hemisphere involvement following local priming and increased right hemisphere involvement following global priming. The results failed to support this hypothesis. All subjects, however, regardless of priming condition, showed a very strong practice effect represented by a shift from a weak initial left ear (right hemisphere) advantage towards a significant right ear (left hemisphere) advantage (P less than 0.00006). The findings suggest that although the local/global priming activity did not lead to selective hemisphere activation, repeated exposure to the chords task resulted in increased use of analytic left hemisphere processing strategies as subjects became familiar with its processing requirements.     

Effects of lesions of temporal-parietal junction on perceptual and attentional processing in humans

When stimuli with larger forms (global) containing smaller forms (local) are presented to subjects with large lesions in the right hemisphere, they are more likely to miss the global form than the local form, whereas subjects with large lesions in the left are more likely to miss the local than the global form. The present study tested whether the global/local impairment in subjects with posterior lesions was due to deficits in controlled attentional processes, passive perceptual processes, or both. Attentional control was examined by measuring reaction time changes when the probability of a target appearing at either the global or local level was varied. Patients with unilateral right or left lesions centered in temporal-parietal regions and age-matched controls served as subjects. Because neurophysiological and neuropsychological evidence have implicated temporal regions in visual discrimination and inferior parietal regions in the allocation of attention to locations in the visual field, patients with left hemisphere lesions were further subdivided into those with lesions centered in the superior temporal gyrus (LSTG) or rostral inferior parietal lobule (LIPL). Patients with right hemisphere injury could not be analogously subdivided. The results revealed that the LSTG group was able to control the allocation of attention to global and local levels normally, while the LIPL group was not. In contrast, the LSTG group showed a strong baseline reaction time advantage toward global targets, while normals and the LIPL group showed no advantage toward one level or the other. Finally, the perceptual component was affected differentially by lesions in the right hemisphere and LSTG, with lesions in the left favoring global targets and lesions in the right favoring local targets. These findings indicate that the hemispheric global/local asymmetry is due to a perceptual mechanism with a critical anatomical locus centered in the STG.     

Dichotic Ear Preference for C-V-C Words in Wernicke's and Broca's Aphasias

A dichotic listening task was administered to subjects with a relatively distinct Broca's aphasia, subjects with a relatively distinct Wernicke's aphasia, and normal subjects. The dichotic stimuli consisted of C-V-C words differing in initial consonant only. Subjects were instructed to respond only to the stimulus of which they were most sure by pointing to a picture representing the dichotic stimuli or foils. While normal subjects demonstrated the usual right ear effect, both the Broca's and Wernicke's aphasia groups demonstrated left ear effects. One salient explanation for these results was that any severe defect in the language systems of the left hemisphere affects the way that the left hemisphere processes linguistic information. It was postulated that left ear stimuli, which arrive at the left hemisphere later, disrupt the processing of right ear stimuli in subjects with aphasia. However, a more definitive explanation requires further research.     

Elevated nailfold plexus visibility aggregates in families and is associated with a specific negative symptom pattern in schizophrenia

Twenty-four individuals with schizophrenia and 28 of their first-degree biological relatives were studied using clinical scales, functional ratings, and neuropsychological tests. An assessment of Nailfold Plexus Visibility (NPV) was also performed on these individuals. In keeping with the literature, we found an increased prevalence of high NPV in our schizophrenia subjects relative to controls and community norms, and also found that high NPV patients had significantly more negative symptoms and poorer social functioning. Measures of negative symptoms indicative of the deficit syndrome did a better job of distinguishing high from low NPV subjects than did more broadly defined negative symptom indices. As predicted, the prevalence of high NPV in first-degree relatives of high NPV schizophrenia subjects was increased compared with relatives of low NPV schizophrenia subjects. These two relative groups did not differ on overall level of schizotypy symptoms or on negative symptom schizotypy indices. However, relatives of low NPV patients scored significantly higher on scales of positive symptom schizotypy. Overall, these results support the hypothesis that high NPV is a marker of risk for a distinct subtype of schizophrenia.     

Left but not right hemisphere semantic processing abnormalities in language comprehension in subjects with schizotypy traits

Thought and language disorders in schizophrenia and schizotypy are thought to result from hemispheric dysfunction during semantic processing. Left hemisphere (LH) abnormalities are well established, but little is known about right hemisphere (RH) semantic processes. We explored hemispheric processing in 50 healthy volunteers assigned to high (h-SZT) or low schizotypy (l-SZT) group using the Schizotypal Personality Questionnaire (SPQ). Subjects were asked to make semantic judgments on sentence pair ending with a target that was either expected word (EW) or an unexpected word from the same (related violation, RV) or a different category (unrelated violation, URV). Targets were presented in a dichotic manner to the left or right ear. Analyses of reaction times in the l-SZT group showed semantic compatibility effect (URV-EW) in the LH and semantic memory activation effect (RV-URV) as well as semantic compatibility effect in the RH. The h-SZT group showed semantic memory activation but no semantic compatibility effect in the LH, the RH pattern resembling that of the l-SZT group. The magnitude of the LH semantic compatibility effect was inversely correlated with SPQ total scores and SPQ Cognitive-perceptual factor. Thus, RH semantic processes are effective and there is a deficit in LH focused activation in schizotypy.     

Why is magical ideation related to leftward deviation on an implicit line bisection task?

Right hemispatial inattention is a neurocognitive deficit observed in thought-disordered schizophrenia patients, persons with schizotypal personality disorder and healthy participants with high scores on schizotypy scales. We administered a schizotypy inventory, the Magical Ideation (MI) scale, to forty healthy, right-handed men who had copied and later recalled the Rey-Osterrieth complex figure. Implicit line bisection performances were defined as the bisecting lines of the complex figure's large rectangle and were recorded for the copy and delay conditions. MI scores were significantly correlated with a leftward shift in bisections in the delay but not copy condition, indicating a significant relationship between the degree of right hemispatial inattention and number of magical beliefs in healthy participants. We describe a model in which these beliefs are conceptualized as a consequence of a hemispheric imbalance, specifically, of a "right hemisphere processing bias". This model accounts for (1) the leftward shifts in spatial attention and (2) the language deficits associated with psychosis and related symptom clusters which have hitherto been addressed in separate literatures. Clinically, the Rey-Osterrieth test may provide a means to assess implicit hemispatial inattention in psychotic patients.     

Paw preferences in cats and dogs: Meta-analysis

Many cognitive neuroscience studies show that the ability to attend to and identify global or local information is lateralised between the two hemispheres in the human brain; the left hemisphere is biased towards the local level, whereas the right hemisphere is biased towards the global level. Results of two studies show attention-focused people with a right ear preference (biased towards the left hemisphere) are better at local tasks, whereas people with a left ear preference (biased towards the right hemisphere) are better at more global tasks. In a third study we determined if right hemisphere-biased followers who attend to global stimuli are likely to have a stronger relationship between attention and globally based supervisor ratings of performance. Results provide evidence in support of this hypothesis. Our research supports our model and suggests that the interaction between attention and lateral preference is an important and novel predictor of work-related outcomes.     

Hemispheric asymmetries in hierarchical stimulus processing are modulated by stimulus categories and their predictability

Hemispheric dominance has been behaviourally documented for the local (left hemisphere, LH) or global (right hemisphere, RH) processing of hierarchical letters. However, Fink et al. (1997) indicated that stimulus category modulates this hemispheric asymmetry. The purpose of this study was to investigate the influence of the category (letters versus objects) on hemispheric specialisation for global and local processing using a visual half-field presentation in a task where participants ignored whether the target appeared at the global or local level. In Experiment 1 we replicated the classic hemispheric asymmetry for global/local processing of hierarchical letters. In Experiment 2, which consisted of hierarchical object processing, a RH dominance for the local level was observed. In Experiment 3 a within-participant design was used where anticipation about the stimulus category was precluded, resulting in the classic RH and LH specialisations for global and local processing for both letter-based and object-based stimuli. Taken together, these results suggest that the highly demanding local processing stage engages one hemisphere more than the other, according to the lateralisation of cerebral networks specialised for stimulus category. In addition, the direction of lateralisation for the local level was also modulated by the predictability of the stimulus category.     

Hemispheric asymmetries in hierarchical stimulus processing are modulated by stimulus categories and their predictability

Hemispheric dominance has been behaviourally documented for the local (left hemisphere, LH) or global (right hemisphere, RH) processing of hierarchical letters. However, Fink et al. (1997) indicated that stimulus category modulates this hemispheric asymmetry. The purpose of this study was to investigate the influence of the category (letters versus objects) on hemispheric specialisation for global and local processing using a visual half-field presentation in a task where participants ignored whether the target appeared at the global or local level. In Experiment 1 we replicated the classic hemispheric asymmetry for global/local processing of hierarchical letters. In Experiment 2, which consisted of hierarchical object processing, a RH dominance for the local level was observed. In Experiment 3 a within-participant design was used where anticipation about the stimulus category was precluded, resulting in the classic RH and LH specialisations for global and local processing for both letter-based and object-based stimuli. Taken together, these results suggest that the highly demanding local processing stage engages one hemisphere more than the other, according to the lateralisation of cerebral networks specialised for stimulus category. In addition, the direction of lateralisation for the local level was also modulated by the predictability of the stimulus category.     

Hemispheric Differences in Matching Stroop-Type Letter Stimuli

Two experiments are reported in which normal right-handed males and females had to match two Stroop-type letter stimuli, according to either their global level (Experiment 1) or their local level (Experiment 2).Stimulus presentation was sequential with the first letter presented foveally and the second letter presented to either the right visual field (RVF) or the left visual field (LVF). A manual “Same-Different” response was required.In Experiment 1, the left hemisphere (RVF) showed interference from the irrelevant local level features, supporting an analytic processing mechanism, while the right hemisphere (LVF) showed no such effect, supporting a holistic matching mechanism. In Experiment 2, both hemispheres showed interference from the irrelevant global features, with the right showing a non-significant tendency towards a larger Stroop effect.     

Visual half-field tests of lateralized letter presentations: differences between preliterate and literate children

In the present study, hemispheric differences in global and analytic processing were investigated in preliterate and literate children, using the "dual-letter" matching task paradigm (Navon, 1977). The stimuli consisted of lateralized visual presentations of large uppercase letters made up of small uppercase letters. The task of the subject was to decide on each trial if the large or small letters were the same or not. Vocal reaction time (VRT) and error-frequency were used as dependent measures. In Experiment 1, 28 right-handed 8-years old children participated. The children were split into a preliterate and a literate group depending on teachers evaluations, and on scores on a reading test. The results showed longer VRTs for the preliterate children when the stimuli were initially presented to the right hemisphere and especially when the subjects were required to match the small letters. These results were followed up in Experiment 2, where the preliterate subjects were split into "fast" and "slow" readers. The results showed that the "slow" readers were more impaired in processing the letter stimuli when the stimuli were initially presented to the right hemisphere. It is concluded that hemispheric asymmetry for letter processing interacts with the development of normal reading ability in children.     

Differential processing of hierarchical visual stimuli in young and older healthy adults: implications for pathology

Hierarchical figures in which large (global) forms are constructed from smaller (local) forms (Navon, 1977) have proved valuable in studies of perceptual organisation and hemispheric specialisation in both healthy volunteers and a wide range of neurological and psychiatric patients. In studies using Navon figures, normal young adults typically identify global forms faster than local forms. When the global and local forms are incongruent (e.g., a large E made of smaller Rs), global forms often interfere with local form identification more than vice versa. In two conditions on the same subjects, we contrasted the performance of young (mean age 22 years) and older (mean age 58 years) healthy volunteers on global and local processing. In the directed attention task, subjects were instructed to detect a target letter that occurred at the prespecified local or global level. The young subjects showed, as expected, faster reaction times (RTs) to detect global targets. In contrast, the older subjects showed significantly faster RTs to the local targets. Likewise, in a divided attention task, in which subjects were instructed to detect a target letter that could occur at either the local or the global level, the young adults were slightly quicker to detect the global targets and the older subjects were significantly quicker to detect the local targets. Error rates were generally low and there was no significant speed/accuracy trade-off in either condition. The observed local precedence effects in healthy older subjects were unexpected and are discussed in reference to previous work on differential hemispheric aging. That work has suggested that the left hemisphere is preferentially biased toward local processing and ages relatively slowly while the right hemisphere is biased toward global processing and ages relatively quickly. The implications of such putative differential aging for the interpretation of pathological local/global processing in neurological and psychiatric diseases are also emphasised.     

Modulation of Global and Local Processing Biases in Adults with Autistic-like Traits

Previous work shows that doing a continuous performance task (CPT) shifts attentional biases in neurotypical individuals towards global aspects of hierarchical Navon figures by selectively activating right hemisphere regions associated with global processing. The present study examines whether CPT can induce similar modulations of attention in individuals with high levels of autistic traits who typically show global processing impairments. Participants categorized global or local aspects of Navon figures in pre- and post-CPT blocks. Post-CPT, high trait individuals showed increased global interference during local categorization. This result suggests that CPT may be useful for temporarily enhancing global processing in individuals with high levels of autistic traits and possibly those diagnosed with autism.     

Speech lateralization and attention/executive functions in a Finnish family with specific language impairment (SLI)

Hemisphere lateralization for speech perception was investigated in a Finnish family with specific language impairment. We used dichotic presentations of consonant-vowel (CV) syllables, consisting of the six stop-consonants paired with the vowel /a/, under three different attentional instructions. The dichotic listening technique means that two different speech stimuli are presented simultaneously, one in each ear. Left hemisphere dominance for speech perception is assessed from a preference for the right ear stimulus. Response accuracy was compared in five members, over three generations, of a family with SLI with 5 healthy control subjects. The dichotic listening task was performed under three different instructions, to attend only to the right ear stimulus, to attend only to the left ear stimulus, or with no instruction about attention. The subjects indicated orally which of the six CV-syllables they heard on each trial. There were 36 dichotic presentations of the CV-syllables for each instruction. The CV-syllables were played from a CD with digitized stimuli. The results showed no difference between the groups during the no instruction condition, indicating normal speech lateralization in the SLI group. However, the SLI group was deficient in modifying the ear advantage through focused attention to the left ear, thus indicating an attentional/executive deficit in addition to a deficit in left hemisphere lateralization. It is concluded that individuals with specific language impairment may have a cognitive deficit related to attention in addition to a language processing deficit related to left hemisphere function.