# Visual Demands of Walking Are Reflected in Eye-Blink-Evoked EEG-Activity
## 4 Discussion
This was found for both the waveshape morphology and the sensitivity of the different measures to the experimental conditions. Strong time-on-task effects were only observed for the duration of blinks that increased in later parts of the experiment. Block modulation of the Alpha base level was restricted to walking on the meadow. At this point, it must be noted that, in contrast to the rather monotonous experiments in which mental fatigue has been investigated thus far, complex behavior in a natural surrounding does not lead to decreased engagement and, consequently, decreased motivation. Thus, no signs of mental fatigue were found, despite the extended duration of the experiment. The lack of a modulation of parameters across blocks before most indicate the high reliability of the measures extracted. Blink duration was reduced in locomotive states, relative to standing still. This suggests increased visual information processing while walking [49; 50]. Additionally, the parietal P2 amplitude and Theta base level were increased, which would be expected for stronger attentional allocation [51; 52]. This indicates that more effort had to be invested to filter out relevant information during locomotion [30; 53]. Looking into effects of walk load, the decrease in amplitude of the fronto-central N2, the occipital P2, and the P3 may indicate the reduced availability of mental resources when walking conditions become more demanding [13]. However, the effects in the N2 and the P3 may also be interpreted in terms of attentional narrowing when processing complex input [42]. The same interpretations can be applied to the decrease in Theta perturbations. There are also results that do not follow the hypothesized directions of effects. Both head dynamics and the occipital N1 were maximal when walking on the meadow. The increase in these parameters when compared to the standing condition can be explained by locomotion. Increases in head motion and visual attention must be applied to succeed in the task. The inversion of the effects when traversing the obstacle course can be explained as outlined in the introduction. Aspects of head motion tend towards stabilization when walking conditions become more complex [24]. Such a behavior might help to increase eye fixation stability for the elevated step planning demands in obstacle course conditions [15; 16]. In this situation, attention is both focused and narrowed to the information of interest. Considering the modulation of the N1 topography, we see a central contribution of the visual system. In the beginning, the narrow spot indicates a contribution of early visual areas, whereas the spread after 120 ms indicates the propagation towards higher-order areas [54; 55]. Such attentional narrowing is consistent with the observations of differences in the fronto-central N2 and other components, and is strongly supported by the modulation of Alpha activity. From laboratory data, it is well-known that Alpha power decreases with task complexity [56; 57]. This effect has been attributed to attentional withdrawal or the internalization of attention for easy tasks [58]. The inversion of this effect indicates that parts of the attentional system have been idled to receive only relevant information. In summary, blink-related EEG activity provides meaningful information about mental load and visual processing during walking. Although we found characteristics of the blinks themselves (e.g., duration) and behavioral measures--such as head motion--to indicate specific cognitive states, electrophysiological-event-related components were found to be even more insightful. While the occipital N1 was sensitive to the selective adjustment of visual demands, changes in later and more cognitively driven components (N2, P3) indicated an overall narrowing of attention. This was also evident in Alpha and Theta power, with functionally plausible patterns of increases and decreases in line with the respective walk load.