The spread of attention across modalities and space in a multisensory object

Attending to a stimulus is known to enhance the neural responses to that stimulus. Recent experiments on visual attention have shown that this modulation can have object-based characteristics, such that, when certain parts of a visual object are attended, other parts automatically also receive enhanced processing. Here, we investigated whether visual attention can modulate neural responses to other components of a multisensory object defined by synchronous, but spatially disparate, auditory and visual stimuli. The audiovisual integration of such multisensory stimuli typically leads to mislocalization of the sound toward the visual stimulus (ventriloquism illusion). Using event-related potentials and functional MRI, we found that the brain's response to task-irrelevant sounds occurring synchronously with a visual stimulus from a different location was larger when that accompanying visual stimulus was attended versus unattended. The event-related potential effect consisted of sustained, frontally distributed, brain activity that emerged relatively late in processing, an effect resembling attention-related enhancements seen at earlier latencies during intramodal auditory attention. Moreover, the functional MRI data confirmed that the effect included specific enhancement of activity in auditory cortex. These findings indicate that attention to one sensory modality can spread to encompass simultaneous signals from another modality, even when they are task-irrelevant and from a different location. This cross-modal attentional spread appears to reflect an object-based, late selection process wherein spatially discrepant auditory stimulation is grouped with synchronous attended visual input into a multisensory object, resulting in the auditory information being pulled into the attentional spotlight and bestowed with enhanced processing

Concentrated Defects in PuO2

From Battelle colloquium on defects in oxides; Columbus, Ohio, USA (17 Sep 1973). The accumulation of concentrated defects in /sup 238/PuO/sub 2/ by selfradiation damage is shown to proceed by a simple exponential function for samples which are initially defect free. Anomalous behavior for both ingrowth and damage recovery is related to helium inventory, but not to uranium, which is the daughter product of the alpha decay. The annealing of samples having achieved a saturation of defects at 25 deg C proceeds through a two-stage mechanism, the first having an activation energy of 0.17 eV. Both defect production and annealing behavior are characterizBd by x-ray diffraction and electrical conductivity measurements for 25 deg C < T < 1000 deg C. (auth