Electrophysiological evidence of a perceptual precedence of global vs. local visual information

Aim of the present study was to investigate the mechanisms of attentional selection of hierarchically organized visual patterns (compound letter stimuli), while subjects were engaged in target selection at either the global or local level. Event-related brain potentials (ERPs) were recorded using a high density electrode montage. Reaction times (RTs) to target stimuli were also recorded. RT data indicated the interference effect of global incongruent information with the local one. ERP data were consistent with behavioral data. In fact, the early sensory N115 component recorded at the primary visual areas exhibited smaller responses to locally attended elements when the global configuration was incongruent rather than congruent, suggesting an interference effect of the global with the local level. Conversely, no interference effect was found for globally attended configurations. These results strongly support the view of a perceptual advantage of globally conveyed information, very likely mediated by low spatial frequency channels. At later processing levels, N1 and P3 components were faster and larger when attention was paid to the global configuration. The difference between target and nontarget responses, indexing the attentional target selection, yielded a broad occipital-temporal negativity focused onto the left hemisphere in the attend-local, and over the right hemisphere in the attend-global condition. The present findings indicate a hemispheric asymmetry in cerebral activation during local/global processing. In addition, they provide robust evidence of a sensory precedence of global information.

Hemispheric asymmetries for spatial frequency discrimination in a selective attention task

Hemispheric specialization for spatial frequency processing was investigated by measuring reaction times to sinusoidal gratings in 12 healthy subjects. Stimuli of 1.5, 3, and 6 c/deg were randomly presented at two peripheral locations in the left (LVF) and right (RVF) upper visual hemifields during a selective attention task. Subjects were instructed to pay covert attention and to respond to a frequency in a given hemifield ignoring all other stimuli. Results showed that RTs were significantly faster at LVF than RVF for low frequency gratings, and at RVF than LVF for high frequency gratings. Furthermore, RTs were faster to 6 than 1.5 c/deg at the RVF, while there was not a significant difference at the LVF. In our view, these findings in a task requiring fast and accurate spatial frequency discriminations may be interpreted in terms of a hemispheric asymmetry for spatial frequency processing.

ERP signs of early selective attention effects to check size

In ERP literature on visual selective attention evidence has been provided that selectively directing attention to a spatial frequency affects the visual processing of the attended frequency, and of unattended frequencies within the same channel bandwidth, starting at a relatively late level of post-stimulus processing, i.e., after about 150 msec. Nevertheless, little knowledge is available about the topographic distribution of these attention effects. This study investigated attentional selection of stimulus relative size at occipital and latero-occipital sites, as well as at fronto-lateral sites. ERPs from posterior scalp electrode sites showed that attention to check sizes enhanced the early sensory components, thus indicating that feature-based attention may result in a modulation of sensory processing. Comparisons of the ERPs to relevant and irrelevant patterns showed an enhanced latero-occipital P90 positivity as well as an occipital N115 negativity to relevant patterns, thus also suggesting possible differential mechanisms of early attentional selectivity at these locations. Later effects of attention consisted of a selection negativity to relevant patterns at posterior electrodes, and a selection positivity at latero-frontal sites. A larger late positivity to irrelevant patterns at anterior sites also suggested an active suppression of attentional response to irrelevant information. Moreover, right-and left-sided asymmetries were found to be respectively consistent for the P90 and N115 with left hemispheric specialization for high, and right hemispheric specialization for low spatial frequencies. A stronger left-sided attentional selectivity has also been found.

ERP and RT signs of a rightward bias for spatial orienting in a split-brain patient

Neuropsychological data have shown that the two cerebral hemispheres differ in the control of spatial attention. The present study investigated hemispheric asymmetries and visuomotor integration in a split-brain patient and three control subjects. Simple reaction times (RTs) and event-related potentials (ERPs) were recorded to lateralized stimuli presented at different eccentricities in the left and right visual hemifields. Both electrophysiological and behavioural data showed that, unlike controls, the split-brain patient showed a strong rightward attentional bias resulting in shorter RTs and larger P300 potentials to stimuli falling in the rightmost space. Furthermore, ERPs also showed that while the RH has a bilateral control of visual space, the LH spatial orienting capability is most restricted to the contralateral hemifield.

Brain evoked responses reflect information processing changes with the menstrual cycle in young female athletes

In sport activity, information processing plays a role crucial for sport performance. Neuropsychological and psychophysiological evidence based on behavioral and psychophysical tasks has been accumulated showing that the latter changes over the course of the menstrual cycle, but the available data are rather inconsistent. On the other hand, in sport literature, not much attention has been devoted to these topics by researchers who have mainly been asked to investigate changes in mood and well-being. Therefore, a study has been undertaken to investigate the relationships between the menstrual cycle and information processing in young female athletes, some of whom took oral contraceptives. The study was based on Auditory Evoked Responses that, unlike behavioral and psychophysical techniques, were revealed to be an exceptionally reliable tool for the study of neural activity during sensory information processing. The results showed the existence of clear fluctuations over the course of the menstrual cycle in time taken to handle information and in the amount of information processing that, with differences and similarities, could be observed both in spontaneously menstruating and on-pill athletes. In addition, neuroanatomical differences were evident in the response of different neural structures of the auditory pathways. In fact, the effects of the hormonal changes accompanying the menstrual cycle appear to be more effective and influential at higher central levels of the auditory pathway.

Time-of-day preference, pattern evoked potentials, and hemispheric asymmetries: a preliminary statement

7 "morning-type" and 6 "evening-type" individuals were subjected to pattern reversal steady-state Event-related Potentials (ERPs) recording to obtain data with respect to time of day, diurnal typology, and hemispheric asymmetries. A significant interaction between these factors suggested a model of hemispheric functioning much more complex than suspected.

Differences in hemispheric functional asymmetry between athletes and nonathletes: evidence from a Unilateral Tactile Matching Task

To study the hemispheric specialization for spatial information processing in athletes and nonathletes a Unilateral Tactile Matching Task was administered. Athletes showed more marked hemispheric specialization than nonathletes. The right hemisphere of the former, in fact, indicated a more pronounced accuracy than those of the latter in perceiving rod orientations.