Location-probe diminishes the effects of memory load on recall.

<p>(A) Trial structure. When the memory load was three, the target to be recalled was identified by highlighting the location of the two non-target items. When the memory load was one the appearance of the cursor indicated the beginning of the recall period. (B) The error standard deviation is shown as a function of target azimuth, when the memory load is one (in blue) and three (in red), and (C) as a function of target elevation. Along azimuth, the variable error increases monotonically with target eccentricity. Along elevation, however, the variable error shows a peak at eccentricities intermediate between the display center and its boundaries. (D) Recalled targets were systematically displaced outward and downward (in blue) relative to their location in the sample display (in black) when the memory load was one, (E) while they were displaced toward the center of the display when the memory load was three (in red). (see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0107969#pone.0107969.s001" target="_blank">Figures S1A-C</a>).</p

Fine-Grained, Local Maps and Coarse, Global Representations Support Human Spatial Working Memory

<div><p>While sensory processes are tuned to particular features, such as an object's specific location, color or orientation, visual working memory (vWM) is assumed to store information using representations, which generalize over a feature dimension. Additionally, current vWM models presume that different features or objects are stored independently. On the other hand, configurational effects, when observed, are supposed to mainly reflect encoding strategies. We show that the location of the target, relative to the display center and boundaries, and overall memory load influenced recall precision, indicating that, like sensory processes, capacity limited vWM resources are spatially tuned. When recalling one of three memory items the target distance from the display center was overestimated, similar to the error when only one item was memorized, but its distance from the memory items' average position was underestimated, showing that not only individual memory items' position, but also the global configuration of the memory array may be stored. Finally, presenting the non-target items at recall, consequently providing landmarks and configurational information, improved precision and accuracy of target recall. Similarly, when the non-target items were translated at recall, relative to their position in the initial display, a parallel displacement of the recalled target was observed. These findings suggest that fine-grained spatial information in vWM is represented in local maps whose resolution varies with distance from landmarks, such as the display center, while coarse representations are used to store the memory array configuration. Both these representations are updated at the time of recall.</p></div

Memory load affects systematic recall error.

<p>(A) Recalled targets were systematically displaced outward and downward (in blue) relative to their location in the sample display (in black) when the memory load was one. (B) Recalled targets were displaced toward the center of the display when the memory load was three (in red). (C) The six spatial components of the systematic error are shown, including constant offsets (translation) along azimuth and elevation, and four linear tensors. (D) Memory load only affected the divergence of the error field. For the sake of convenience, the error size is expressed in degrees for the tensors as well. These values correspond to the displacement associated with each component, averaged over all target locations. (E) Proportional recall bias in center of screen (CS) coordinates (in blue) when the memory load is one. (F) Proportional recall bias in CS (in blue) and center of the memory items' configuration (CM) coordinates (in red) when the memory load is three. Target azimuth, in CS coordinates, was overestimated both when the memory load was one and three. In addition, when the memory load was three, participants underestimated both target azimuth and elevation in CM coordinates. <i>trans</i> - translation, <i>diverge</i> - divergence, <i>rota_cw</i> - clockwise rotation. *p<0.05.</p

Location-probe displacement affects target recall.

<p>(A) The target was identified by displaying the position of the non-target memory items at recall. The position of the non-target items was either translated obliquely (straight arrows) or rotated around an axis through the display center (curved arrows). (B) Translation of the non-target items, whose direction and magnitude is portrayed by a black arrow of normalized length, caused the recalled target location, portrayed by the red arrow, to be displaced in the same direction, albeit by a smaller magnitude. (C) In contrast, following rotation, the recalled target location was displaced in a direction opposite the one required to preserve the distances between the memory items. For illustrative purposes, the displacement of the non-target memory items is represented by the black line and the average displacement of the target items by the red line.</p