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

ABSTRACT: 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.

SUBMITTER: Busse L

PROVIDER: S-EPMC1317940 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Several stimulus factors are important in multisensory integration, including the spatial and temporal relationships of the paired stimuli as well as their effectiveness. Changes in these factors have been shown to dramatically change the nature and magnitude of multisensory interactions. Typically, these factors are considered in isolation, although there is a growing appreciation for the fact that they are likely to be strongly interrelated. Here, we examined interactions between two of these factors - spatial location and effectiveness - in dictating performance in the localization of an audiovisual target. A psychophysical experiment was conducted in which participants reported the perceived location of visual flashes and auditory noise bursts presented alone and in combination. Stimuli were presented at four spatial locations relative to fixation (0°, 30°, 60°, 90°) and at two intensity levels (high, low). Multisensory combinations were always spatially coincident and of the matching intensity (high-high or low-low). In responding to visual stimuli alone, localization accuracy decreased and response times (RTs) increased as stimuli were presented at more eccentric locations. In responding to auditory stimuli, performance was poorest at the 30° and 60° locations. For both visual and auditory stimuli, accuracy was greater and RTs were faster for more intense stimuli. For responses to visual-auditory stimulus combinations, performance enhancements were found at locations in which the unisensory performance was lowest, results concordant with the concept of inverse effectiveness. RTs for these multisensory presentations frequently violated race-model predictions, implying integration of these inputs, and a significant location-by-intensity interaction was observed. Performance gains under multisensory conditions were larger as stimuli were positioned at more peripheral locations, and this increase was most pronounced for the low-intensity conditions. These results provide strong support that the effects of stimulus location and effectiveness on multisensory integration are interdependent, with both contributing to the overall effectiveness of the stimuli in driving the resultant multisensory response.

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

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