Although alcohol consumption is known to degrade performance in a variety of tasks, the exact character of alcohol induced impairments is currently not well understood. The present work examines to what extent acute alcohol intoxication impairs visual processing and oculomotor control on different processing levels. Understanding the impact of alcohol on the visual system is critical because the most important way humans navigate in and communicate with the environment is through the acquisition and processing of visual information. Virtually all complex cognitive tasks rely on visual input, obtained via the planning and execution of rapid eye movements. Within the theoretical framework of “active vision” (Findlay & Gilchrist, 2003) the traditional dissociation of perception from motor control is loosened and eye movements are regarded as ‘part and parcel’ of an integrated process of information acquisition. In order to better understand the stages at which alcohol affects oculomotor control, five paradigms were used to map alcohol effects on different hierarchically organized levels of visuomotor control and additionally two complex visual cognitive tasks were examined. On the lowest level (automatic), reflexive processes were tested using the pro saccade task. The next level (automated) incorporates implicit learning and memory processes that can influence reflexive behavior, but are still unconscious. This level was examined using the double step paradigm. The highest processing level represents voluntary modification of behavior and was studied using two versions of the anti saccade paradigm and the memory guided saccade paradigm. The two complex visual cognitive tasks were task switching and reading. Task switching requires participants to switch between two or more distinct tasks, which usually results in switch costs or benefits. Such effects are explained with the interplay of inhibition and activation and to date no study has examined effects of alcohol on performance in task switching. The sentence reading experiment offered the possibility to study visuomotor control in combination with a precisely controlled cognitive processing load in an ecologically valid everyday task. For all paradigms, participant’s performance were measured in an “alcohol” and a “no alcohol” session. A total of 62 students participated and the mean breath alcohol concentration in the “alcohol session” was 70mg%. Results indicate specific effects of alcohol on different levels of visual processing and oculomotor control. Functioning on the automatic level was intact, except for a slowing in saccade latencies. Even though alcohol is known to reduce simple reaction times, the present work could show for the first time that in comparison with higher processing levels, such a “general slowing” is less pronounced on this lower processing level. Regarding the automated level deficits with in the ability to adaptively reprogram saccades on the basis of new visual information were found under alcohol. More time is necessary to achieve the same amount of reprogramming when eye movements need to be directed to new target locations. This finding is especially important, because adaptive reprogramming is a core ingredient of effective visuomotor behavior in everyday tasks such as reading or visual search. Impairments on the voluntary processing level became apparent in hypermetric (i.e., prolonged) saccade amplitudes under alcohol, whenever a reprogramming of the initial saccade target was necessary. This effect was found under conditions that required endogenous representation as well as in situations when a visual marker was present at the target location. In addition, a small effect of alcohol on visuospatial short term memory was found. Interestingly, no alcohol related effects were found regarding inhibitory functioning. In addition, performance measures in the complex visual cognitive tasks did not differ between alcohol conditions as a result of compensatory mechanisms. Apparently, longer processing time that is available under alcohol can be used in the task switching condition to activate a task set more completely. In a similar way, the trade-off between increased fixation duration and decreased number of fixations during reading suggests that the extra processing time under alcohol can be used for linguistic processing, which in itself does not seem to be impaired. This finding is supported by the fact no interaction between alcohol and word frequency was found. In conclusion, this thesis explored the effects of acute alcohol intoxication on visual processing and oculomotor control. The carefully selected paradigms have yielded interesting findings that begin to map alcohol related impairments on different levels of oculomotor control. In addition, findings and discussions afford multiple approaches for further research that should help to achieve a deeper understanding of the effects of alcohol and its underlying mechanisms
