Hemispheric asymmetries for global and local processing as a function of stimulus exposure duration

Time-of-day effects on objective and subjective short-term memory task performance

The time-of-day along with the synchrony effect (better performance at optimal times of the day according to the chronotype) on the cognitive performance has been well established in previous research. This influence is mediated by both circadian and homeostatic processes consistent with the Borbély two-process model. This experiment focused on the objective and subjective performance of the visual short-term memory task requiring holistic processing. Sixty-five young, healthy participants including 40 females were divided into morning and evening types and performed a given task in two sessions - in the morning and in the evening. Type division was made according to the chronotype questionnaire and polymorphism of the PER3 clock gene. The task was a modified version of Deese-Roediger-McDermott paradigm adjusted to study short-term memory, in which visual, abstract stimuli were used. The analysis was based on an exploratory approach investigating the influence of circadian and individual (sex) factors on execution of memory task. Evening types were more accurate in the task compared to morning types, regardless of the part of the day. The time-of-day effect was revealed on objective measures (reaction times for hits and false alarms) and subjective effort put into the performance. The reaction times were slower in the morning unlike the effort that was greater in the evening. The time-of-day × sex interaction was observed in the case of subjective effort: men described the task as more demanding in the evening. The results could be explained by differences in hemispheric dominance depending on the time-of-day. The report provides new patterns of behavioral data analysis, investigating sex aspects and use of self-assessment scales of performance.

Forest Before Trees: Letter Stimulus and Sex Modulate Global Precedence in Visual Perception

The global precedence effect (GPE), originally referring to processing hierarchical visual stimuli composed of letters, is characterised by both global advantage and global interference. We present herein a study of how this effect is modulated by the variables letter and sex. The Navon task, using the letters “H” and “S,” was administered to 78 males and 168 females (69 follicular women, 52 luteal women, and 47 hormonal contraceptive users). No interaction occurred between the letter and sex variables, but significant main effects arose from each of these. Reaction times (RTs) revealed that the letter “H” was identified more rapidly in the congruent condition both in the global and the local task, and the letter “S” in the incongruent condition for the local task. Also, although RTs showed a GPE in both males and females, males displayed shorter reaction times in both global and local tasks. Furthermore, luteal women showed higher d’ index (discrimination sensitivity) in the congruent condition for the local task than both follicular women and hormonal contraceptive users, as well as longer exploration time of the irrelevant level during the global task than males. We conclude that, according to the linear periodicity law, the GPE is enhanced for compound letters with straight vs. curved strokes, whereas it is stronger in males than in females. Relevantly, luteal phase of the menstrual cycle seems to tilt women to rely on finer grained information, thus exhibiting an analytical processing style in global/local visual processing.

Contralateral Hemisphere Activation by Unilateral Hand Contraction: ReExamining Global and Local Attention

While previous studies have shown that left- (vs. right-) hand contractions can improve the performance of global (vs. local) attention, these results were inconsistent in certain behavioral studies in which the left cerebral hemisphere was found to be specialized for local attention, while the right hemisphere was not specialized for global attention. Thus, we reexamined whether different global (vs. local) attention performances follow left- (vs. right-) hand contractions due to right (vs. left) hemisphere activation. We recruited 100 right-handed healthy female, university student (aged 19-26 years) participants. We used the Navon task to present 80 letter-stimuli (40 in the global task; 40 in the local task) to either the participants' left or right visual fields. Half of the participants (randomly selected) were instructed to squeeze a dynamometer with the left hand, while the other half squeezed with the right hand, prior to completing the Navon task. In line with previous research, we observed a perceptual advantage of global (large letters) over local (small letters) stimuli. Participants who contracted the right hand showed an enhanced local attention performance (from left hemisphere activation), whereas those who contracted the left hand did not improve global attention performance (from right hemisphere activation). Thus, we supported prior behavioral research suggesting that hemispheric asymmetry for attention processing is evident for left but not right cortical hemisphere processing.

Hemispheric specialization for global and local processing: A direct comparison of linguistic and non-linguistic stimuli

It is often assumed that the human brain processes the global and local properties of visual stimuli in a lateralized fashion, with a left hemisphere (LH) specialization for local detail, and a right hemisphere (RH) specialization for global form. However, the evidence for such global-local lateralization stems predominantly from studies using linguistic stimuli, the processing of which has shown to be LH lateralized in itself. In addition, some studies have reported a reversal of global-local lateralization when using non-linguistic stimuli. Accordingly, it remains unclear whether global-local lateralization may in fact be stimulus-specific. To address this issue, we asked participants to respond to linguistic and non-linguistic stimuli that were presented in the right and left visual fields, allowing for first access by the LH and RH, respectively. The results showed global-RH and local-LH advantages for both stimulus types, but the global lateralization effect was larger for linguistic stimuli. Furthermore, this pattern of results was found to be robust, as it was observed regardless of two other task manipulations. We conclude that the instantiation and direction of global and local lateralization is not stimulus-specific. However, the magnitude of global,-but not local-, lateralization is dependent on stimulus type.

Strabismic amblyopia disrupts the hemispheric asymmetry for spatial stimuli in cortical visual processing

Hemispheric asymmetry in processing visual stimuli was assessed in anisometropic and strabismic amblyopia and control subjects. Measurements of contrast sensitivity for low and high spatial frequencies were performed psychophysically and tested under functional magnetic resonance imaging (fMRI) using a stimulus configuration that generates measurements for each temporal and nasal hemifield. The fMRI and the psychophysics results showed a marked hemispheric asymmetry in processing spatial frequencies for normal and anisometropic adults, in which low spatial frequencies were mainly processed in the left visual field – right hemisphere (LVF-RH: 0.3 cycles per degree [cpd]; F = 12.548; p = .002) and the high spatial frequencies were predominating processed in the right visual field – left hemisphere (RVF-LH: 2.0 cpd; F = 4.582; p = .021 and 8.3 cpd; F = 8.561; p = .001). No asymmetry was present in the amblyopic and the fellow eye of the strabismic amblyopia subjects. We conclude that the developmental organization of visual cortex in strabismic amblyopia is impaired differently from what happens in the anisometropic amblyopia and support the impairment of high-level visual-related functions observed in strabismic children.

Switching between global and local levels: the level repetition effect and its hemispheric asymmetry

The global level of hierarchical stimuli (Navon’s stimuli) is typically processed quicker and better than the local level; further differential hemispheric dominance is described for local (left hemisphere, LH) and global (right hemisphere, RH) processing. However, neuroimaging and behavioral data indicate that stimulus category (letter or object) could modulate the hemispheric asymmetry for the local level processing. Besides, when the targets are unpredictably displayed at the global or local level, the participant has to switch between levels, and the magnitude of the switch cost increases with the number of repeated-level trials preceding the switch. The hemispheric asymmetries associated with level switching is an unresolved issue. LH areas may be involved in carrying over the target level information in case of level repetition. These areas may also largely participate in the processing of level-changed trials. Here we hypothesized that RH areas underly the inhibitory mechanism performed on the irrelevant level, as one of the components of the level switching process. In an experiment using a within-subject design, hierarchical stimuli were briefly presented either to the right or to the left visual field. 32 adults were instructed to identify the target at the global or local level. We assessed a possible RH dominance for the non-target level inhibition by varying the attentional demands through the manipulation of level repetitions (two or gour repeated-level trials before the switch). The behavioral data confirmed a LH specialization only for the local level processing of letter-based stimuli, and detrimental effect of increased level repetitions before a switch. Further, data provides evidence for a RH advantage in inhibiting the non-target level. Taken together, the data supports the notion of the existence of multiple mechanisms underlying level-switch effects.

Hemispheric Differences for Global and Local Processing: Effect of Stimulus Size and Sparsity

The present experiment was designed to assess the hemispheric differences for global and local processing in healthy participants under different conditions of stimuli visibility, by means of varying the size and sparsity. Three different sizes and three different matrixes of hierarchical stimuli were introduced. Stimuli consisted of incomplete squares with one side missing. Participants were asked to carry out an orientation classification task (left/right), indicating the orientation of the square opening either at global or local levels. The results do not support the hemispheric differences for global and local processing, showing the same efficiency of right and left hemispheres for analyzing global and local information. Nevertheless, other results found are consistent with the hypothesis of right hemisphere superiority under degraded stimulus conditions.

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.

Reciprocal organization of the cerebral hemispheres

The cerebral hemispheres are anatomically and neurophysiologically asymmetrical. The evolutionary basis for these differences remains uncertain. There are, however, highly consistent differences between the hemispheres, evident in reptiles, birds, and mammals, as well as in humans, in the nature of the attention each applies to the environment. This permits the simultaneous application of precisely focused, but narrow, attention, needed for grasping food or prey, with broad, open, and uncommitted attention, needed to watch out for predators and to interpret the intentions of conspecifics. These different modes of attention can account for a very wide range of repeated observations relating to hemisphere specialization, and suggest that hemisphere differences lie not in discrete functional domains as such, but distinct modes of functioning within any one domain. These modes of attention are mutually incompatible, and their application depends on inhibitory transmission in the corpus callosum. There is also an asymmetry of interaction between the hemispheres at the phenomenological level.

Contribution of callosal connections to the interhemispheric integration of visuomotor and cognitive processes

In recent years, cognitive neuroscience has been concerned with the role of the corpus callosum and interhemispheric communication for lower-level processes and higher-order cognitive functions. There is empirical evidence that not only callosal disconnection but also subtle degradation of the corpus callosum can influence the transfer of information and integration between the hemispheres. The reviewed studies on patients with callosal degradation with and without disconnection indicate a dissociation of callosal functions: while anterior callosal regions were associated with interhemispheric inhibition in situations of semantic (Stroop) and visuospatial (hierarchical letters) competition, posterior callosal areas were associated with interhemispheric facilitation from redundant information at visuomotor and cognitive levels. Together, the reviewed research on selective cognitive functions provides evidence that the corpus callosum contributes to the integration of perception and action within a subcortico-cortical network promoting a unified experience of the way we perceive the visual world and prepare our actions.

Differential Lateralization for Words and Faces: Category or Psychophysics?

This set of three experiments assessed the influence of different psychophysical factors on the lateralization of the N170 event-related potential (ERP) component to words and faces. In all experiments, words elicited a left-lateralized N170, whereas faces elicited a right-lateralized or nonlateralized N170 depending on presentation conditions. Experiment 1 showed that lateralization for words (but not for faces) was influenced by spatial frequency. Experiment 2 showed that stimulus presentation time influenced N170 lateralization independently of spatial frequency composition. Finally, Experiment 3 showed that stimulus size and resolution did not influence N170 lateralization, but did influence N170 amplitude, albeit differentially for words and faces. These findings suggest that differential lateralization for words and faces, at least as measured by the N170, is influenced by spatial frequency (words), stimulus presentation time, and category.

Lateralized cognition: Asymmetrical and complementary strategies of pigeons during discrimination of the “human concept”

This study was aimed at revealing which cognitive processes are lateralized in visual categorizations of "humans" by pigeons. To this end, pigeons were trained to categorize pictures of humans and then tested binocularly or monocularly (left or right eye) on the learned categorization and for transfer to novel exemplars (Experiment 1). Subsequent tests examined whether they relied on memorized features or on a conceptual strategy, using stimuli composed of new combinations of familiar and novel humans and backgrounds (Experiment 2), whether the hemispheres processed global or local information, using pictures with different levels of scrambling (Experiment 3), and whether they attended to configuration, using distorted human figures (Experiment 4). The results suggest that the left hemisphere employs a category strategy and concentrates on local features, while the right hemisphere uses an exemplar strategy and relies on configuration. These cognitive dichotomies of the cerebral hemispheres are largely shared by humans, suggesting that lateralized cognitive systems already defined the neural architecture of the common ancestor of birds and mammals.

Local-global interference is modulated by age, sex and anterior corpus callosum size

To identify attentional and neural mechanisms affecting global and local feature extraction, we devised a global-local hierarchical letter paradigm to test the hypothesis that aging reduces functional cerebral lateralization through corpus callosum (CC) degradation. Participants (37 men and women, 26-79 years) performed a task requiring global, local, or global+local attention and underwent structural MRI for CC measurement. Although reaction time (RT) slowed with age, all participants had faster RTs to local than global targets. This local precedence effect together with greater interference from incongruent local information and greater response conflict from local targets each correlated with older age and smaller callosal genu (anterior) areas. These findings support the hypothesis that the CC mediates lateralized local-global processes by inhibition of task-irrelevant information under selective attention conditions. Further, with advancing age smaller genu size leads to less robust inhibition, thereby reducing cerebral lateralization and permitting interference to influence processing. Sex was an additional modifier of interference, in that callosum-interference relationships were evident in women but not in men. Regardless of age, smaller splenium (posterior) areas correlated with less response facilitation from repetition priming of global targets in men, but with greater response facilitation from repetition priming of local targets in women. Our data indicate the following dissociation: anterior callosal structure was associated with inhibitory processes (i.e., interference from incongruency and response conflict), which are vulnerable to the effects of age and sex, whereas posterior callosal structure was associated with facilitation processes from repetition priming dependent on sex and independent of age.

Effect of temporal constraints on hemispheric asymmetries during spatial frequency processing

Studies on functional hemispheric asymmetries have suggested that the right vs. left hemisphere should be predominantly involved in low vs. high spatial frequency (SF) analysis, respectively. By manipulating exposure duration of filtered natural scene images, we examined whether the temporal characteristics of SF analysis (i.e., the temporal precedence of low on high spatial frequencies) may interfere with hemispheric specialization. Results showed the classical hemispheric specialization pattern for brief exposure duration and a trend to a right hemisphere advantage irrespective of the SF content for longer exposure duration. The present study suggests that the hemispheric specialization pattern for visual information processing should be considered as a dynamic system, wherein the superiority of one hemisphere over the other could change according to the level of temporal constraints: the higher the temporal constraints of the task, the more the hemispheres are specialized in SF processing.

Effect of short and long exposure duration and dual-tasking on a global-local task

Past research has demonstrated a global advantage in responses to visually presented hierarchical stimuli such that, on incongruent trials, the global form interferes with responses to the local level [Kimchi, R. (1992). Primacy of wholistic processing and global/local paradigm: A critical review. Psychological Bulletin, 112, 24-38]. In Experiment 1, 32 adults performed alternating blocks of global or local identification of hierarchical letter stimuli in which the global and local letters were congruent, incongruent, or neutral, and were presented at either a short (17 ms) or long (100 ms) exposure duration. A global advantage was demonstrated at both durations. In the local-directed task, interference on incongruent, relative to neutral, trials was observed at both exposure durations, but facilitation on congruent trials, relative to neutral trials, was present only when stimuli were presented at the long exposure duration. In Experiment 2, global or local identification was performed by another group of 24 adults at either a long or short exposure duration, and also under conditions of full attention (FA) or dual-task (DT) conditions with a digit-monitoring task. Under FA, we again found significant interference at both exposure durations, but facilitation only at the long exposure duration. Under DT conditions, the pattern of facilitation and interference at the short duration remained unchanged. At the long duration, however, dual-tasking eliminated interference in the RT but not error data, while facilitation was present in both sets of data. Results are in line with a perceptual account of the global advantage, and suggest that facilitation requires consciously-mediated processes, whereas interference does not.

Behavioral and electrophysiological evidence of a right hemisphere bias for the influence of negative emotion on higher cognition

We examined how responses to aversive pictures affected performance and stimulus-locked event-related potentials (ERPs) recorded during a demanding cognitive task. Numeric Stroop stimuli were brief ly presented to either left or right visual hemifield (LVF and RVF, respectively) after a centrally presented aversive or neutral picture from the International Affective Picture System. Subjects indicated whether a quantity value from each Stroop stimulus matched the preceding Stroop stimulus while passively viewing the pictures. After aversive pictures, responses were more accurate for LVF Stroops and less accurate for RVF Stroops. Early-latency extrastriate attention-dependent visual ERPs were enhanced for LVF Stroops. The N2 ERP was enhanced for LVF Stroops over the right frontal and parietal scalp sites. Slow potentials (300-800 msec) recorded over the frontal and parietal regions showed enhanced picture related modulation and amplitude for LVF Stroops. These results suggest that emotional responses to aversive pictures selectively facilitated right hemisphere processing during higher cognitive task performance.

The Integration of Object Levels and Their Content: A Theory of Global/Local Processing and Related Hemispheric Differences

This article presents and tests the authors' integration hypothesis of global/local processing, which proposes that at early stages of processing, the identities of global and local units of a hierarchical stimulus are represented separately from information about their respective levels and that, therefore, identity and level information have to be integrated at later stages. It further states that the cerebral hemispheres differ in their capacities for these binding processes. Three experiments are reported in which the integration hypothesis was tested. Participants had to identify a letter at a prespecified level with the viewing duration restricted by a mask. False reporting of the letter at the nontarget level was predicted to occur more often when the integration of identity and level could fail. This was the case. Moreover, visual-field effects occurred, as expected. Finally, a multinomial model was constructed and fitted to the data.

On the role of response conflicts and stimulus position for hemispheric differences in global/local processing: an ERP study

It is widely assumed that the local and global levels of hierarchical stimuli are processed more efficiently in the left and right cerebral hemispheres, respectively. However, corresponding effects were not observed under all circumstances. In ERP studies, they occurred more often with centrally presented stimuli than with laterally presented ones, whereas reaction-time studies revealed that a response conflict between the levels is relevant. The present study examines which of these two factors is more important by presenting conflicting and non-conflicting stimuli to the left or right visual field and recording ERPs as well as collecting behavioral data. If a central stimulus position is crucial, then no effects should show up. Contrary to this prediction, the expected hemispheric differences were observed in the behavioral data as well as in the later occurring (N2 and P3) ERP amplitudes. However, in all variables, the effects were more pronounced for conflicting stimuli. The results suggest that response conflicts are more important for obtaining hemispheric differences in global/local processing than a central stimulus presentation. This is interpreted in the way that hemispheric differences vary with respect to the stimulus representation that is needed to select a proper response.

Hemispheric asymmetry for spatially filtered stimuli belonging to different semantic categories

The hemispheric specialization for processing visual stimuli as a function of spatial-frequency content and semantic category was investigated. Spatially filtered pictures of animals and tools were displayed to both hemifields at nine levels of spatial-frequency filtering following a coarse-to-fine design. Results showed a differential hemispheric specialization in relation to the semantic category of stimuli. Animals might be identified at low spatial frequencies (coarse information) in a similar extent in both hemifield conditions, while a hemispheric dissociation was found for tools (the increasing of levels of high-spatial frequency information was especially needed when such stimuli were presented to the left visual field /right hemisphere (RH) relative to that for right visual field/left hemisphere presentations).