Current Research...

Eye and Head Movements = Gaze Movement Behavior

The eyes - thought as windows into the world - are characterized by areas with different spatial resolution. The fovea is the region with the highest resolution caused by the densest distribution of photo-receptors has to be oriented by eye movements to extract information with highest precision.
Saccadic eye movements are typically made at a rate of about 3 per second and per day, we make on the order of 105 saccades. Eye fixations are at the boundary of perception and cognition, in that they are an overt indicator that information is being represented in cognitive processes. Attempts to understand the cognitive role of eye movements focus either on the eye movement patterns - scanpaths - ,or on the duration of fixation patterns themselves.
Head movements occur allways in natural circumstances. But the frequency of these movements is much lower than for eye saccades. When the head is moving, the eyeballs are moving too because they are associated with the skull. In order to calculate gaze movements, you have to measure head-in-body (or in-space) and eye-in-head movements seperately and add both variables together.
In our lab, we measure both variables with infrared-light based trackers. In an offline analysis all data were converted referring to degrees.

Representations within Working Memory

All kind of information (visual, spatial, haptic, acoustic etc.) extracted from the environment and obtained to guide forthcoming behavior must be stored and represented within working memory. In this area of research we are interested in the manner of how information is represented regarding the kind of information and the nature of the task. Furthermore, we investigate the quality of representation during alterations of the relevance of objects or object properties in regard to the task. Moreover, the time course of such representations will be considered.

Visual Exploration of complex and dynamic Scenes

The majority of research concerning eye movements and visual exploration was conducted by using simple and static sets of stimuli. Hence, a substantial amount on understanding in terms of the function of vision while scanning such primitives could be obtained. A new direction of research is focused on the role of vision in extracting task-relevant information from complex and dynamic scenes. Such stimuli are rather likely to confront subjects within natural environments. One experimental approach to this field is termed "multiple object tracking". In our lab we try to understand the function of gaze movements during obstacle avoidance under dynamic conditions. Therefor, subjects have to cross a street in an intersection paradigm without causing a crash with other cars. Participants can change their own speed by the use of a joystick.

Trade-off Modulation between Working Memory and Gaze or Body Movements

For almost each extended behavior involving working memory a certain amount of task-relevant information has to be taken in to account to match the demands of the task. This information can be acquired by the sensors at that time point needed during the task or gathered from memory where relevant representations are available through memorization processes applied earlier. Both operations (i.e., sensory-motor and memorization processes) involve certain costs to the user. These costs can be stable or vary over the course of a task. The executive function of the brain, thought as process operated by working memory, is that process which is engaged in managing the actual involvement of memory or sensory recourses. Such a process is known as trade-off function.
In this field we investigate the characteristics of such trade-offs while varying the costs of task-relevant recourses. On the sensory-motor side, costs can be increased by presenting relevant stimuli further apart from each other or by changing the motor system itself (i.e., saccadic vs. locomotion behavior). Memorization costs can be manipulated by changing the complexity of stimuli sets according to representation, maintenance, and rehearsal processes.

Language and Spatial Cognition (Navigation)

Recent theories of embodied cognition suggest that verbal representations are given meaning by “simulation” processes performed in non-verbal, sensory-motor representations. This theory seems to suggest that non-verbal representations alone would be sufficient to generate functional behavior. Another perspective claims that action and language are interwoven in the way of „grounding language in action“. Language has been recognized as playing an influential role in establishing concepts about objects or events.
In a series of recent experiments, we have tested this (alternative) hypothesis that language-based representations do support spatial behavior even in monologic situations. Subjects were trained to find goals in virtual environments comprising an iterated Y-maze with clearly nameable landmark information at each decision point. In three conditions, subjects were either allowed to explore and learn on their own (baseline condition), or were instructed at each place to select from a list either a suitable name (word condition) or an icon summarizing the gist of the landmarks presented at each place (icon condition). The experiment was performed for a route and for a map learning task.

Visual-field Compensation in visually impaired Patients

Homonymous visual ﬁeld defects (HVFDs) represent the most frequent type of visual deﬁcits after acquired brain injury affecting nearly 80% of patients with unilateral postchiasmal brain damage. Sufﬁcient spontaneous recovery of the visual ﬁeld is seldom and may occur within the ﬁrst 6 months. In the majority of patients, HVFDs are chronic manifestations that create a marked amount of subjective inconvenience in
everyday life. Patients typically complain about difﬁculties with reading (i.e. hemianopic dyslexia) and visual exploration. The visual exploration impairment is characterized by the disability to gain a quick overview of the visual scene especially in unfamiliar surroundings or complex situations. With this line of research we investigate strategies adequate for the functional compensation of the visual deficits. Such strategies include compensation by eye and head movements, involvement of working memory (i.e., for memory guided saccades), or both together. In a variety of experiments differing in their demands concerning visual perception, processing of information within working memory, and visuo-motor interactions, HVFD patiants as well as unimpaired subjects were investigated.

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PD Dr. Gregor Hardiess - Cognitive Neuroscience - Tübingen University