By examining eye movements in an immersive 3D setting we can investigate in a more natural environment how individuals differentially engage the oculomotor system and spatial information in visual imagery of previously seen objects. This may be especially the case when the relative location of a target object is embedded in a 3D spatial layout when compared to a target presented on a blank screen in front of the participants (see 15). On the other hand, eye movements can induce processing costs they are time-consuming 27, require the activation of motor programs and can lead to interference with concurrent perceptual information from the external world 28.
On the one hand, eye movements may aid memory retrieval as they serve to reinstate the spatial index associated with previously inspected visual information 4, 8, 12. found comparable memory performance between participants who moved their eyes and those who remained with their eyes on the center of the screen, thus suggesting an individual trade-off between the benefits and costs of using eye movements during visual imagery and visual memory 26. For example, eye movement dispersion during imagery of simple visual patterns 10 and of complex images 1, 25 have been found to vary between individuals and some people tend to spatially constrain their fixations around the location of initial gaze position during memory retrieval of previously seen objects 15, 26. Interestingly, several studies showed remarkable differences in eye movements. Moreover, findings from studies on visual working memory support the idea that spatial location serves as mental index for object representations 21 and that spatial location supports the integration of visual features (i.e., color and shape) into coherent memory representations 22, 23, 24. There is ample empirical support for this proposition, indeed, several studies suggest that spatial location is encoded and maintained automatically (e.g., 19) and some findings suggest that eye movements to absent objects plays a beneficial role for memory 8, 12, 13, 20, although some researchers reported inconclusive results 11, 14, 16. During recall, the spatial location is reactivated and triggers eye movements towards empty but relevant locations and thereby serves to facilitate memory retrieval of other object-related features (i.e., visual, linguistic, and conceptual). It has been proposed that eye movements to absent objects are triggered by integrated memory representations 17, 18: During encoding, different features including spatial location are combined into a coherent representation. In a recent study we were able to demonstrate that participants looked back to relevant locations also in a seated immersive three-dimensional (3D) setting 15. This effect, known as looking at nothing, is well established in healthy subjects and has been found when objects were encoded on 2D computer screens, even then when spatial memory was not probed in the recall task 8, 12, 13, 14, 15, 16. For example, Spivey and Geng found that participants tend to re-fixate the spatial location of previously inspected stimuli, when they were questioned about visual details (i.e., color and orientation) in a subsequent recall task 11 Experiment 2. Such eye movements have been shown to reinstate the spatial layout of previously inspected images 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. When we recall detailed visual information from memory, we tend to move our eyes despite the fact that there is nothing to look at. This finding indicates that eye movements during imagery are subject to individual strategies, and the immersive setting in 3D space made individual differences more likely to unfold. We suggest that object visualizers rely less on spatial information because they tend to process and represent the visual information in terms of color and shape rather than in terms of spatial layout. Furthermore, we found that looking back to relevant locations depends on individual differences in visual object imagery abilities.
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We show that participants also look back to relevant locations when they are free to move in 3D space. In the present study we used immersive virtual reality to investigate how individual tendencies to process and represent visual information contribute to eye fixation patterns in visual imagery of previously inspected objects in three-dimensional (3D) space. The reason for these differences remains unclear. Previous studies indicated that such eye movements are related to the spatial location of previously seen items on 2D screens, but they also showed that eye movement behavior varies significantly across individuals. During recall of visual information people tend to move their eyes even though there is nothing to see.
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