Eye movements during mental imagery: A closer look at the spatial reference frame

People tend to look back at spatial locations of visually encoded information when they recall this information through visual imagery. Multiple studies confirmed this so-called looking-at-nothing (LAN) effect, but the nature of the spatial reference frame underlying this effect remains unclear. Specifically, the location of an object can be associated either with the absolute location of the object in the visual environment (i.e., its fixed coordinates) or with its relative location in relation to other spatial cues (e.g., other objects or some kind of spatial reference frame within the environment).
In this study, we aimed to gain new insights into the underlying mechanisms of the LAN effect by investigating which spatial indexes (absolute vs. relative) play a role for eye movements to absent objects during visual imagination of previously seen objects. Participants (N = 34) were asked to memorize different objects that were subsequently presented in one of four possible quadrants in a central 2x2 grid during the encoding phase. In the following recall phase, they were asked to visualize each object in their mind’s eye for 7 s, and then answer to a verbally presented question about the object. Crucially, the position of the 2x2 empty grid during recall either remained centered ("static trials") or was shifted sidewards ("dynamic trials"), so that one of the four quadrants corresponded to the object's absolute position on the screen and a second quadrant to the object's relative position within the grid during encoding.
The distribution of eye fixations in the four quadrants during recall was analyzed for static and dynamic trials. In static trials, the results confirmed that participants looked longer at the quadrant in which the object was previously presented. In dynamic trials, we mainly observed LAN behavior to the object's relative location for most of the recall time. However, for a short period during recall, we also observed LAN behavior to the object's absolute location.
We conclude that the LAN effect can be divided into two different effects due to the recruitment of both a relative and an absolute spatial reference frame, while the former seems to dominate the latter.