PubMed · 8509266
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R M Caplan. 1993. Be a critical reader.. https://pubmed.ncbi.nlm.nih.gov/8509266/
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By voluntarily directing attention to a specific region of a visual scene, we can improve our perception of stimuli at that location. This ability to focus attention upon specific zones of the visual field has been described metaphorically as a moveable spotlight or zoom lens that facilitates the processing of stimuli within its 'beam'. A long-standing controversy has centred on the question of whether the spotlight of spatial attention has a unitary beam or whether it can be divided flexibly to disparate locations. Evidence supporting the unitary spotlight view has come from numerous behavioural and electrophysiological studies. Recent experiments, however, indicate that the spotlight of spatial attention may be divided between non-contiguous zones of the visual field for very brief stimulus exposures (&<100 ms). Here we use an electrophysiological measure of attentional allocation (the steady-state visual evoked potential) to show that the spotlight may be divided between spatially separated locations (excluding interposed locations) over more extended time periods. This spotlight division appears to be accomplished at an early stage of visual-cortical processing.
The aims of this study were to assess cognitive function in obstructive sleep apnea (OSA) patients and to evaluate the effect of short- and long-term treatment with continuous positive airway pressure treatment (CPAP). A battery of neuropsychological tests, the Epworth Sleepiness Scale (ESS), and the Beck Inventory Scale were administered to 23 patients with severe OSA (age: 56.5+/-6.13; AHI: 54.9+/-13.37) and to 23 age- and education-matched controls. The OSA patients were evaluated in a baseline condition and in two follow-up treatment sessions (after 15 days and 4 months of CPAP, respectively). At baseline, OSA patients had a significant impairment, compared to controls, in tests of sustained attention, visuospatial learning, executive function, motor performance, and constructional abilities. The longitudinal evaluation showed that after a 15-days CPAP treatment attentive, visuospatial learning, and motor performances returned to normal levels. A 4-months CPAP treatment did not result in any further improvement in cognitive tests. Performance on tests evaluating executive functions and constructional abilities was not affected by short- and long-term treatment with CPAP. The findings of this study confirm the hypothesis of partial reversibility of cognitive dysfunction in OSA patients after CPAP.
Vision tells us not only what and where objects are but also when they appear and disappear. We have found that patients with right parietal damage have an unusual loss in the ability to differentiate object onset from offset. Specifically, when a single target flickers at the same frequency as five distractors, but out of phase (it is light when they are dark and vice versa), right parietal patients require much slower rates than normals or left parietal patients to detect the target. When we shifted the phase of the flicker in the target relative to the distractors so that the onsets and offsets were not simultaneous, the performance of the patients improved dramatically. Remarkably, the patients showed this loss equally in both visual fields. Since flicker detection was normal for the patients, we suggest that the deficit lies at a level where stimulus transients are interpreted as the appearance or disappearance of objects.