When walking on an uneven surface or complex terrain, humans tend to gaze downward. This behaviour is usually interpreted as an attempt to acquire useful information to guide locomotion. Visual information, however, is not used exclusively for guiding locomotion; it is also useful for postural control. Both locomotive and postural control have been shown to be sensitive to the visual flow arising from the respective motion of the individual and the three-dimensional environment. This flow changes when a person gazes downward and may present information that is more appropriate for postural control. To investigate whether downward gazing can be used for postural control, rather than exclusively for guiding locomotion, we quantified the dynamics of standing and walking posture in healthy adults, under several visual conditions. Through these experiments we were able to demonstrate that gazing downward, just a few steps ahead, resulted in a steadier standing and walking posture. These experiments indicate that gazing downward may serve more than one purpose and provide sufficient evidence of the possible interplay between the visual information used for guiding locomotion and that used for postural control. These findings contribute to our understanding of the control mechanism/s underlying gait and posture and have possible clinical implications.

Since the earliest studies on human eye movements, it has been repeatedly demonstrated that observers fixate the center of visual stimuli more than their periphery, regardless of visual content. Subsequent research suggested only little effect of typical biases in experimental setups, such as observer’s position relative to the screen or the relative location of the cue marker. While comparative studies of the screen center vs. stimulus center revealed that both conspire in the process, much of the prior art is still confounded by experimental details that leave the origins of the center-bias debatable. We thus propose methodological novelties to rigorously test the effect of the stimulus center, isolated from other factors. In particular, eye movements were tracked in a free-viewing experiment in which stimuli were presented at a wide range of horizontal displacements from a counterbalanced cue marker in a wide visual field. Stimuli spanned diverse natural scene images to allow inherent biases to surface in the pooled data. Various analyses of the first few fixations show a robust bias toward the center of the stimulus, independent of its position on the display, but affected by its distance to the cue marker. Center bias is thus a tangible phenomenon related to the stimulus.

When walking on an uneven surface or complex terrain, humans tend to gaze downward. Previous investigations indicate that visual information can be used for online control of stepping. Behavioral investigations suggest that, during walking, the availability of visual information increases stepping accuracy, but probably through a feedforward control mechanism. Consequently, downward gazing (DWG) is usually interpreted as a strategy used to acquire useful information for online and/or feedforward control of stepping. Visual information is not exclusively used for guiding locomotion; a wealth of literature has been published on the usefulness of visual information for feedback postural control. Critically, postural control has been shown to be sensitive to the visual flow arising from the respective motion of the individual and the 3D environment. To investigate whether DWG can be used to enhance feedback control of posture, rather than feedforward/online control of gait, we conducted a series of experiments that explore this possible interplay. Through these experiments we were able to show that DWG, just a few steps ahead, results in a steadier standing and walking posture, without the need for accuracy. Moreover, we were able to demonstrate that humans resort to DWG when walking stability is compromised, even when destabilizing features were visually unpredictable. This series of experiments provides sufficient evidence of the possible interplay between visual information used for guiding locomotion and that used for postural control. Moreover, this evidence raises concerns regarding the way we interpret gaze behavior without the knowledge of the type and use of the information gathered.