Salient features in gaze-aligned recordings of human visual input during free exploration of natural environments

Abstract

During free exploration, humans adjust their gaze by combining body, head, and eye movements. Laboratory experiments on the stimulus features driving gaze, however, typically focus on eye-in-head movements, use potentially biased stimuli, and restrict the field of view. Our novel wearable eye-tracking system (EyeSeeCam) overcomes these limitations. We recorded gaze- and head-centered videos of the visual input of observers freely exploring real-world environments (4 indoor, 8 outdoor), yielding approximately 10 h of data. Global power spectra reveal little difference between head- and gaze-centered recordings. Local stimulus features exhibit spatial biases in head-centered coordinates, which are environment-dependent, but consistent across observers. Eye-in-head movements center these biases in gaze-centered coordinates, leading to elevated "salient" features at center of gaze. This shows that central biases in image feature distributions in "natural" photographs are not a property of environments, but of stimuli already gaze-centered by the photographer. Further central biases in laboratory subjects' fixation distributions do not result from re-centering of the eyes but are an artifact of display restrictions. Hence, our findings demonstrate that the concept of feature "saliency" transfers from the laboratory to free exploration, but also highlight the importance of experiments with freely moving eyes, head, and body.

Reactivity effects in video-based classroom research: an investigation using teacher and student questionnaires as well as teacher eye-tracking

“…This focus on instruction was demonstrated by the longer durations of teacher gaze towards non-research regions in contrast to research regions of the classroom. As expected, participating teachers' gaze demonstrated that the complexity (Chisholm, Caird & Lockhart, 2008), difficulty (Rötting, 2001) and importance (Mackworth & Morandi, 1967;Schumann et al, 2008) of the non-research areas dramatically outweigh those of research areas in the classroom. We were not surprised that video research imposed minimal attentional distraction on teachers, given the pressured, sophisticated and unpredictable nature of classroom teaching (e.g., Berliner, 2001).…”

Gaze allocation in natural stimuli: Comparing free exploration to head-fixed viewing conditions

“…Gaze-centred and head-centred videos were recorded using the ''EyeSeeCam'' setup, which is described in detail elsewhere (Brandt, Glasauer, & Schneider, 2006;Schneider et al, 2005Schneider et al, , 2006Vockeroth, Bardins, Bartl, Dera, & Schneider, 2007), as is the recording procedure and the stimulus material (Schumann et al, 2008). In brief, an eyetracking system attached to swimming goggles controls a gaze-centred camera, while an identical camera (head camera) is fixed to the observer's forehead.…”

“…EyeÁhead-coordination analysis suggested a profound influence of nonsaccadic eye movements to gaze-centred stimulus statistics (Einhäuser et al, 2007;Einhäuser, Moeller, et al, 2009), and the spatial statistics of features at the centre of gaze transferred the concept of feature saliency from the laboratory to the real world Schumann et al, 2008). A direct comparison between free exploration and laboratory data with the same visual input has, however, yet to be performed.…”

Mindful movement and skilled attention

“…Natural shifts of attention to a large degree occur through movement, in particular via overt whole-body movements of gaze including eye-, head and body (Land and Hayhoe, 2001;Schumann et al, 2008;'t Hart et al, 2009). On the one hand, attention can move automatically and transiently between places in the world via exogenous reflexive stimulusdriven processes, presumably to direct the sense organs to highly salient aspects and potential danger (Posner, 1980;Prinzmetal et al, 2005).…”