The right parietal lobe is critical for visual working memory

Abstract

Visual working memory (VWM) permits the maintenance of object identities and their locations across brief delays such as those accompanying eye movements. Recent neuroimaging studies have emphasized the role of the posterior parietal lobe in this process although the specific nature of this involvement in VWM remains controversial. Neuroimaging findings suggest that the parietal lobe may have a general role in remembering various types of visual information whereas neuropsychological findings suggest that parietal involvement is primarily related to motor spatial attention and spatial memory. In the present study, patients with unilateral right parietal lobe damage, lacking symptoms of neglect, were tested in several VWM old/new recognition tasks. Parietal damage lead to impaired performance on all VWM tasks, including spatial, object, and object/spatial conjunction tasks. Deficits were found across several stimulus categories. These results provide neuropsychological support for neuroimaging results, and more generally indicate that the parietal lobe serves a general role in diverse forms of VWM.

Figure 1

Patient Lesion Traces. Lesions are shown on T2 fluid-attenuated inversion recovery (FLAIR) images in which the lesions appear as white higher intensity patches in parietal regions. Anatomical landmarks are marked in red and blue. Red lines mark the central sulcus, blue lines mark the intraparietal sulcus. Radiological convention is followed (left is on the right). Abbreviations: AG = angular gyrus, MOG = middle occipital gyrus, SPG = superior parietal gyrus.

Figure 2

Trial design of Experiment 1a. On each trial, four colors, abstract shapes, or tools were presented sequentially (1000 ms each) and after a brief delay of 1000 ms, a probe image was presented and remained on the computer screen until subjects responded as to which temporal position the probe item had previously occupied. In this example, the correct response would be 3.

Figure 3

Order recall and recognition performance (Experiments 1a and 1b) as a function of stimulus category. The order recall performance is measured by accuracy (left axis), and the order recognition is measured by corrected recognition (right axis). Error bars indicate the standard error of the mean (SEM).

Figure 4

Object recall and recognition performance (Experiments 2a and 2b). The pattern of behavior observed for tools was also observed with color and shape stimulus categories in the object recognition experiment (data not shown). Error bars indicate SEM.

Figure 5

Recall and recognition performance. Patients’ scores are in standardized units (z-scores) with regards to control subject performance. By convention, impaired performance is when z > 1.96.

Figure 6

Results of Experiment 3, non-repeating stimuli recognition. Corrected recognition performance as a function of group membership. Error bars indicate SEM.