PhD project (finished)


My Phd (2003 - 2007)...

Title: Gaze control and cognitive load in active vision - Task specific strategies in normal and visually impaired subjects

Part I - Projection Device

During the first part of the PhD-project a new projection device, appropriate for presenting visual stimuli to a large field of view (to a sitting subject), was established as methodological basis for all further investigations. Psychophysical experiments comprising virtual scenarios could be performed with this novel setup whereby subjects were free to move their eyes and the head in a natural manner. Furthermore, the tracking of the subjects’ eye and head movements could be successfully integrated.

follow the link to get more information about the projection device

Part II - Acquisition vs. Memorization Trade-offs in healthy Subjects

In a comparative visual search paradigm, performed in order to investigate gaze adaptations in healthy subjects under different cost requirements, the influence of working memory limitation due to the process of generating task dependent eye and head movements for visual search became obvious: As long as the costs for gaze movements remained in a lower range, the memory involvement was restricted. However, in adaptation to increased movement costs for acquiring information, subjects performed fewer gaze movements and their search strategy was shifted towards memory use.

follow the link to get the publication about this study

Part III - Compensation of the visual Field Loss in Hemianopic Patients

In this part of the PhD-project patients with homonymous hemianopia (H.H.), a kind of visual field loss (scotoma) were investigated in order to analyze their ability to compensate functionally for the visual limitations.
In Germany each year more than 135,000 patients falling ill of one kind of hemianopia. As main reasons strokes, brain tumors, and inflammations are known. Because H.H. is common and patients can become diseased with it in young years, this impairment takes place a special position within all other visual field losses. The patiens with H.H. are insufficient or not at all able to read, write, or to avoid obstacles or persons. With this, patients have a lot of problems to cope tasks of the everday life.
In different studies hemianopic patients have been investigated to get more information about their oculomotoric strategies due to compensation. It could be shown that patients with H.H. need more time to solve a dot counting task, have an increased scanpath length, and show a higher number of fixations compared with normal subjects as a control group. Also the repetition rate of the scanpath as well as the number of refixations were increased.
In order to assess the compensational strategies of H.H. patients in a variety of tasks with different demands concerning perception, processing, and memorization (i.e., cognitive demands), a experimental 'toolbox' including three tasks was introduced. Here, the cognitively least demanding task was dot-counting. More challenging and including feature extraction and a certain amount of memorization, comparative visual search was included as second task. In the third experiment, the intersection task, subjects were confronted with a dynamic, multi-object environment and had to interact with it. The task of collision avoidance in the intersection experiment was the most challenging one, concerning cognitive processing.
In all tasks eye and head movements were measured in order to investigate and evaluate the compensational mechanisms used by the patients.

follow the link to the Comparative Visual Search

follow the link to the Intersection Task

The published work about the PhD project can be found here.

This work was done in cooperation with the Dept. of Pathophysiology of Vision and Neuro-Ophthalmology in Tübingen (Prof. U. Schiefer).  Thanks!


   PD Dr. Gregor Hardiess - Cognitive Neuroscience - Tübingen University