Visual working memory (VWM) allows us to hold visual information briefly in our minds after its disappearance. It is important for bridging the present to the immediate past. Previous neuroscience studies on VWM have shown that several parietal, frontal, and occipitotemporal brain regions subserve this function. Those studies, however, have often focused on VWM for a single property, such as color. Yet, in behavior, the capacity of VWM is sensitive to the complexity of to-be-remembered visual features. How do different brain areas represent VWM for visual features of different complexity and for combination of features? To address this question, we used functional MRI to study the response profile of several brain regions in three VWM tasks. In all tasks, subjects saw 1 to 7 colored polygons and had to remember their color (a simple feature), shape (a complex feature), or both color and shape. Behavioral performance showed that VWM reached capacity limit at about 3 colors, 2 shapes, and 2 compound objects. In the fMRI data, we found different functional profiles for frontal, parietal, and occipitotemporal regions. Specifically, the posterior parietal cortex was sensitive to both featural and VWM load manipulations. The prefrontal regions were sensitive to VWM load manipulation but relatively insensitive to featural differences. The occipitotemporal regions were sensitive to featural differences, but not to VWM load manipulation. We propose that the response properties of these regions can jointly account for several findings in human VWM behavior.
Bibliographical noteFunding Information:
This study was supported in part by NSF 0345525 to YJ and NCRR P41RR14075 and MIND Institute grants to the MGH Martinos Center. JHS was supported by Korea Foundation for Advanced Studies. We thank George Alvarez, Hing Yee Eng, Livia King, Steven Luck, Wi-Ki Ma, Yankun Shen, Won Mok Shim, Rachel Sussman, Tim Vickery, Amanda Willis, and an anonymous reviewer for comments.
- Change detection
- Posterior parietal cortex
- Prefrontal cortex
- Visual working memory