Biomedical subjects

Stephanie A McMains

Publications and source records attributed to Stephanie A McMains.

3 recordsLinked to original sources

PubMed2006

Combined activation and deactivation of visual cortex during tactile sensory processing.

The involvement of occipital cortex in sensory processing is not restricted solely to the visual modality. Tactile processing has been shown to modulate higher-order visual and multisensory integration areas in sighted as well as visually deprived subjects; however, the extent of involvement of early visual cortical areas remains unclear. To investigate this issue, we employed functional magnetic resonance imaging in normally sighted, briefly blindfolded subjects with well-defined visuotopic borders as they tactually explored and rated raised-dot patterns. Tactile task performance resulted in significant activation in primary visual cortex (V1) and deactivation of extrastriate cortical regions V2, V3, V3A, and hV4 with greater deactivation in dorsal subregions and higher visual areas. These results suggest that tactile processing affects occipital cortex via two distinct pathways: a suppressive top-down pathway descending through the visual cortical hierarchy and an excitatory pathway arising from outside the visual cortical hierarchy that drives area V1 directly.

Adult↗

PubMed2005

Processing efficiency of divided spatial attention mechanisms in human visual cortex.

Many visual tasks require deployment of attention to multiple objects or locations. We used functional magnetic resonance imaging and behavioral experiments to investigate the relative processing efficiency of two putative attentional mechanisms for performing such tasks: the "zoom lens" and "multiple spotlights." Two key questions were investigated: (1) does splitting the spotlight into multiple foci incur an overhead cost that diminishes the efficacy of attention compared with the zoom lens, and (2) does splitting the spotlight provide a benefit relative to the zoom lens by conserving attention resources that otherwise would be directed to task irrelevant stimuli? For both mechanisms, attending to multiple object locations decreased processing efficiency at a single location, resulting in both decreased behavioral performance and decreased blood oxygenation level-dependent (BOLD) signal attentional modulation. When the two mechanisms attended to multiple objects across the same spatial extent, the multiple spotlight mechanism, which ignores intervening stimuli, yielded better performance and higher BOLD signal. When the two mechanisms processed the same number of stimuli, splitting the spotlight neither impaired performance nor diminished BOLD signal in occipital cortex. The surprising efficiency of the multiple spotlight mechanism supports the emerging view that spatial attention is easily deployed in a diverse range of spatial configurations.

Attention↗

PubMed2004

Multiple spotlights of attentional selection in human visual cortex.

Spatially directed attention strongly enhances visual perceptual processing. The metaphor of the "spotlight" has long been used to describe spatial attention; however, there has been considerable debate as to whether spatial attention must be unitary or may be split between discrete regions of space. This question was addressed here through functional MR imaging of human subjects as they performed a task that required simultaneous attention to two briefly displayed and masked targets at locations separated by distractor stimuli. These data reveal retinotopically specific enhanced activation in striate and extrastriate visual cortical representations of the two attended stimuli and no enhancement at the intervening representation of distractor stimuli. This finding of two spotlights was obtained within a single cortical hemisphere and across the two hemispheres. This provides direct evidence that spatial attention can select, in parallel, multiple low-level perceptual representations.

Attention↗