Psychoanatomy of visual attention: a unified account of quadrant and hemifield effects

摘要

The two hemispheres of the brain anatomically divide the right and left visual field along the vertical meridian (hemi-field representation). Cortical areas V2, V3, and V4 further subdivide the representation of the visual field along the horizontal meridian (quadrant representation). These anatomical divisions have been used in a number of studies as psychoanatomical landmarks to attribute functional processes to cortical visual areas. Hemifield effects have been shown in crowding and multiple object tracking (MOT) studies; and, quadrant effects have been observed in MOT and object priming studies. The psychoanatomical conclusion drawn from these studies is that visual processes that exhibit hemifield effects are mediated by areas with a hemifield representation, and those that exhibit quadrant effects are mediated by areas with a quadrantic representation. In the present study, we tested a unified framework to account for these findings. Attention plays a critical role in performing all of the aforementioned tasks, and is potentially a mediating factor. We propose that these findings can be attributed a scaling spotlight of visual attention that selectively enhances cortical activity in visual areas according to the scale/size of the selected target. Stimuli were constructed based on the average receptive field size of neurons in V1 (fine scale, hemifield representation) and V2a??V4 (coarse scale, quadrant representation). The scaling hypothesis predicts that fine scale targets will exhibit hemifeld effects, while coarse targets will show quadrant effects. The study examined two forms of the lateral inhibition (masking and crowding), which have been previously shown to exhibit hemifeld effects using small stimuli targets. We replicated these findings and further showed that quadrant effects emerge with large coarse scale stimuli. The outcome of our experiments is concordant with the scaling hypothesis, and supports an attention account of hemifield and quadrant effects.