Human eye-head co-ordination in natural exploration

Abstract

During natural behavior humans continuously adjust their gaze by moving head and eyes, yielding rich dynamics of the retinal input. Sensory coding models, however, typically assume visual input as smooth or a sequence of static images interleaved by volitional gaze shifts. Are these assumptions valid during free exploration behavior in natural environments? We used an innovative technique to simultaneously record gaze and head movements in humans, who freely explored various environments (forest, train station, apartment). Most movements occur along the cardinal axes, and the predominance of vertical or horizontal movements depends on the environment. Eye and head movements co-occur more frequently than their individual statistics predicts under an independence assumption. The majority of cooccurring movements point in opposite directions, consistent with a gaze-stabilizing role of eye movements. Nevertheless, a substantial fraction of eye movements point in the same direction as co-occurring head movements. Even under the very most conservative assumptions, saccadic eye movements alone cannot account for these synergistic movements. Hence nonsaccadic eye movements that interact synergistically with head movements to adjust gaze cannot be neglected in natural visual input. Natural retinal input is continuously dynamic, and cannot be faithfully modeled as a mere sequence of static frames with interleaved large saccades.

Walking along curved paths of different angles: the relationship between head and trunk turning

“…Although we did not measure eye position in our study, it has been shown that changes in gaze direction are generally implemented by a combination of eye and head movements in the same direction (Barnes 1979;Guitton and Volle 1987). This is especially true for large gaze shifts (Einhäuser et al 2007). For example, during a simple walking task consisting of a 90° turn it has been found that the eyes smoothly lead the head by looking further into the direction of turning (Imai et al 2001).…”

Visual orienting in dynamic broadband (1/f) noise sequences

“…In those studies, the image was presented statically, but in our present study, it was used as the source for a one-dimensional movie by iterating row-wise through the source image: Each row was stretched vertically in space and presented as a frame ( Figure 2); the movie thus appeared as a flickering bar code. The choice of spatial one-dimensionality was done for technical simplicity, but is justifiable by the fact that a large number of saccades are made along the cardinal axes (Einhäuser et al, 2007).…”

Dynamic feature detection using virtual correction and camera oscillations

“…It is known that during the human walk the head moves in a horizontal plane from side to side [7,13]. Head motion is observed not only in humans, but also for animals.…”