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Can gaze position reveal concealed knowledge? During visual processing, gaze allocation is influenced not only by features of the visual input, but also by previous exposure to objects. However, the dynamics of gaze allocation toward personally familiar items remains unclear, especially in the context of revealing concealed familiarity. When memorizing four pictures of faces on a short term memory task, participants' gaze was initially directed toward a personally familiar face, followed by a strong avoidance from it. This avoidance was evident even when participants were instructed to conceal their familiarity and direct their gaze equally to all faces. On the other hand, participants were partially able to control the initial preference to fixate on the familiar face. By exploiting these patterns, a machine learning classification algorithm and signal detection analysis revealed impressive detection efficiency estimates, suggesting practical applications of recent theoretical insights from the domains of eye tracking and memory.

Background What can theories regarding memory-related gaze preference contribute to the field of deception detection? While abundant research has examined the ability to detect concealed information through physiological responses, only recently has the scientific community started to explore how eye tracking can be utilized for that purpose. However, previous attempts to detect deception through eye movements have led to relatively low detection ability in comparison to physiological measures. In the current study, we demonstrate that the modulation of gaze behavior by familiarity, changes considerably when participants perform a visual detection task in comparison to a short-term memory task (that was used in a previous study). Thus, we highlight the importance of theory-based selection of task demands for improving the ability to detect concealed information using eye-movement measures. Results During visual exploration of four faces (some familiar and some unfamiliar) gaze was allocated preferably on familiar faces, manifested by more fixations. However, this preference tendency vanished once participants were instructed to convey countermeasures and conceal their familiarity by deploying gaze equally to all faces. This gaze behavior during the visual detection task differed significantly from the one observed during a short-term memory task used in a previous study in which a preference towards unfamiliar faces was evident even when countermeasures were applied. Conclusions Different tasks elicit different patterns of gaze behavior towards familiar and unfamiliar faces. Moreover, the ability to voluntarily control gaze behavior is tightly related to task demands. Adequate ability to control gaze was observed in the current visual detection task when memorizing the faces was not required for a successful accomplishment of the task. Thus, applied settings would benefit from a short-term memory task which is much more robust to countermeasure efforts. Beyond shedding light on theories of gaze preference, these findings provide a backbone for future research in the field of deception detection via eye movements. Electronic supplementary material The online version of this article (10.1186/s41235-019-0162-7) contains supplementary material, which is available to authorized users.

Through a series of studies, we investigate how people direct gaze toward familiar and unfamiliar objects. When an observer tries to encode objects, gaze is first directed preferentially to the familiar object followed by a later prioritization of the unfamiliar ones. We demonstrate that the initial preference reflects prioritization of personally significant information and could be volitionally controlled. The latter prioritization of the unfamiliar objects is determined by the immediate goals due to the task and is less controllable. These findings imply that the mechanism that guides gaze is flexible, affected by both long-term significance and short-term goals and could be only partially controlled. This study has also imperative practical implications for detecting concealed information using eye tracking.

The underlying factors that determine gaze position are a central topic in visual cognitive research. Traditionally, studies emphasized the interaction between the lowlevel properties of an image and gaze position. Later studies examined the influence of the semantic properties of an image. These studies explored gaze behavior during a single presentation, thus ignoring the impact of familiarity. Sparse evidence suggested that across repetitive exposures, gaze exploration attenuates but the correlation between gaze position and the lowlevel features of the image remains stable. However, these studies neglected two fundamental issues: (a) repeated scenes are displayed later in the testing session, such that exploration attenuation could be a result of lethargy, and (b) even if these effects are related to familiarity, are they based on a verbatim familiarity with the image, or on high-level familiarity with the gist of the scene? We investigated these issues by exposing participants to a sequence of images, some of them repeated across blocks. We found fewer, longer fixations as familiarity increased, along with shorter saccades and decreased gaze allocation towards semantically meaningful regions. These effects could not be ascribed to tonic fatigue, since they did not manifest for images that changed across blocks. Moreover, there was no attenuation of gaze behavior when participants observed a flipped version of the familiar images, suggesting that gist familiarity is not sufficient for eliciting these effects. These findings contribute to the literature on memory-guided gaze behavior and provide novel insights into the mechanism underlying the visual exploration of familiar environments.