@phdthesis{Chandra2020,
  author    = {Chandra, Johan},
  title     = {The role of the oculomotor control in eye movements during reading},
  doi       = {10.25932/publishup-47593},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-475930},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiii, 115},
  year      = {2020},
  abstract  = {Most reading theories assume that readers aim at word centers for optimal information processing. During reading, saccade targeting turns out to be imprecise: Saccades' initial landing positions often miss the word centers and have high variance, with an additional systematic error that is modulated by the distance from the launch site to the center of the target word. The performance of the oculomotor system, as reflected in the statistics of within-word landing positions, turns out to be very robust and mostly affected by the spatial information during reading. Hence, it is assumed that the saccade generation is highly automated. The main goal of this thesis is to explore the performance of the oculomotor system under various reading conditions where orthographic information and the reading direction were manipulated. Additionally, the challenges in understanding the eye movement data to represent the oculomotor process during reading are addressed. Two experimental studies and one simulation study were conducted for this thesis, which resulted in the following main findings: (i) Reading texts with orthographic manipulations leads to specific changes in the eye movement patterns, both in temporal and spatial measures. The findings indicate that the oculomotor control of eye movements during reading is dependent on reading conditions (Chapter 2 \& 3). (ii) Saccades' accuracy and precision can be simultaneously modulated under reversed reading condition, supporting the assumption that the random and systematic oculomotor errors are not independent. By assuming that readers increase the precision of sensory observation while maintaining the learned prior knowledge when reading direction was reversed, a process-oriented Bayesian model for saccade targeting can account for the simultaneous reduction of oculomotor errors (Chapter 2). (iii) Plausible parameter values serving as proxies for the intended within-word landing positions can be estimated by using the maximum a posteriori estimator from Bayesian inference. Using the mean value of all observations as proxies is insufficient for studies focusing on the launch-site effect because the method exhibits the strongest bias when estimating the size of the effect. Mislocated fixations remain a challenge for the currently known estimation methods, especially when the systematic oculomotor error is large (Chapter 4). The results reported in this thesis highlight the role of the oculomotor system, together with underlying cognitive processes, in eye movements during reading. The modulation of oculomotor control can be captured through a precise analysis of landing positions.},
  language  = {en}
}
@phdthesis{Rolfs2007,
  author    = {Rolfs, Martin},
  title     = {In-between fixation and movement : on the generation of microsaccades and what they convey about saccade generation},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-14581},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {Microsaccades are an important component of the small eye movements that constitute fixation, the basis of visual perception. The specific function of microsaccades has been a long-standing research problem. Only recently, conclusive evidence emerged, showing that microsaccades aid both visual perception and oculomotor control. The main goal of this thesis was to improve our understanding of the implementation of microsaccade generation within the circuitry of saccade control, an unsolved issue in oculomotor research. We make a case for a model according to which microsaccades and saccades result from mutually dependent motor plans, competing for expression. The model consists of an activation field, coding for fixation at its center and for saccades at peripheral locations; saccade amplitude increases with eccentricity. Activity during fixation spreads to slightly peripheral locations in the field and, thus, may result in the generation of microsaccades. Inhibition of remote and excitation of neighbouring locations govern the dynamics of the field, resulting in a strong competition between fixation and saccade generation. We propose that this common-field model of microsaccade and saccade generation finds a neurophysiological counterpart in the motor map of the superior colliculus (SC), a key brainstem structure involved in the generation of saccades. In a series of five behavioral experiments, we tested implications of the model. Predictions were derived concerning (1) the behavior of microsaccades in a given task (microsaccade rate, amplitude, and direction), (2) the interactions of microsaccades and subsequent saccades, and (3) the relationship between microsaccadic behavior and neurophysiological processes at the level of the SC. The results yielded strong support for the model at all three levels of analysis, suggesting that microsaccade statistics are indicative of the state of the fixation-related part of the SC motor map.},
  language  = {en}
}