Attention reorienting is crucial to human survival in a constantly changing environment. In order to react and respond to novel and potentially threatening stimuli in the environment, we have to first reorient our attention to the stimuli themselves. While numerous studies in the past have attempted to uncover the principles of how our brain processes new stimuli and reorients our attention, they typically employed standardized paradigms such as an oddball or a cueing paradigm that do not represent how humans actually reorient attention in the real world. This dissertation seeks to directly address this issue by investigating the brain dynamics underlying attention reorienting in an immersive and naturalistic environment. We employ a virtual reality (VR)-based target detection paradigm that closely mimics how human would reorient their attention in real-world situations. During the experiments, subjects are instructed to reorient their attention between a primary visual task (driving simulation) and a secondary visual task (target detection) while their electroencephalography (EEG), eyetracking and behavioral inputs are being recorded. Each set of experiments and subsequent data analysis methods are tailored to answer different questions based on the three specific aims of this dissertation (1) how do eye movements affect attention reorienting signals? (2) how do we integrate the information obtained from the neural and ocular signals to decode reorienting? and (3) what is the relationship between attention reorienting and the arousal system? We found that while eye movements result in greater temporal variation of neural signals associated with attention reorienting, namely the P300 signal, time-locking the event-related potentials (ERPs) to image onset or saccade intersection still results in the best overall performance in classifying target vs. distractor stimuli. Similarly to eye movements, we also found that allowing for head movements results in greater temporal variations of both the neural (P300) and pupil-linked attention reorienting signals. However, by combining the EEG, pupil dilation and dwell time signals, a multi-modal hybrid classifier we developed using the hierarchical discriminant component analysis (HDCA) was able to capture and integrate the neural and ocular attention reorienting signals with similar performance both in the condition with and without head movements. In addition, the hybrid classifier outperformed single-modality classifiers (EEG-only, pupil dilation-only and dwell time-only) in all comparisons. Lastly, we reported a close-knit relationship between pupil-linked arousal and network-level EEG dynamics underlying attention reorienting. We observed improvements in overall performance as pupil-linked arousal increased. We also observed increased oscillatory activity across multiple frequency bands in regions associated with the dorsal and ventral attention networks as pupil-linked arousal increased. Additionally, we found a decrease in functional connectivity across nodes in the salience network and the ventral attention network as pupil-linked arousal increased. The findings of this dissertation have the potential to serve as the basis for the development of the next generation of non-invasive brain-computer interfaces (BCIs) that can function in real-world environments. Furthermore, these findings may also serve to help physicians and neuroscientists better understand the neurophysiology underlying attention-related disorders including attention-deficit disorder (ADD) or attention-deficit/hyperactivity disorder (ADHD).

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There are currently many statements about the effects of hemispheric specialization of the brain upon children's cognitive processing and therefore, upon content or modes of instruction. Before educators can accept or even test these statements, it is important to devise easy-to-use measures of hemispheric functioning and to study their relationship to established measures of achievement and linguistic and cognitive development. Current research in brain functioning has indicated that conjugate-lateral eye movement direction (the direction in which a person looks while thinking) can be a sensitive indicator of which cerebral hemisphere is initially activated. The central purpose of this investigation was to analyze the effects of the stimulus characteristics of reflective questions of verbal and spatial nature on the conjugate-lateral eye movement (CLEM) behavior of right-handed children from fourth, fifth, and sixth grades. A major objective was to determine whether data on children’s CLEM responses would better support a model of characteristic individual differences or a model of differentiation by question type. The testing instrument devised for this purpose was the Reflective Questions Test (RQT) which included both Verbal and Spatial subtests. In an experimenter-facing-subject paradigm with a sample of 60 (30 boys, 30 girls), conjugate-lateral eye movement was found to be easily observable and question type was found to influence the direction of eye movement, thus supporting a differentiation by question type model. Verbal questions elicited significantly more rightward CLEMs than spatial questions and spatial questions elicited significantly more leftward CLEMs than verbal questions fn the sample studied. No significant sex differences were found. These results seem to be consistent with the neuropsychological theory that once hemispheric specialization has occurred with normal right-handed children, the left hemisphere mediates language functions and the right hemisphere mediates spatial functions. Examining the number of directionally appropriate CLEM responses, a two-way analysis of variance (verbal and spatial question type by grade level) yielded no main or interaction effects. The results suggest that although children in grades four, five, and six tended to gaze in different directions while responding to verbal than while responding to spatial questions, the rate of responses appropriate to the question (gazing in the direction predicted) was no greater for verbal than for spatial questions. Further, the means for question types were almost identical across grade levels for CLEM responses to verbal and to spatial questions, supporting a no-change model of neuropsychological function, which contends that within the later childhood years, hemispheric specialization is well developed. The Reflective Questions Test was found to have high inter-rater reliability (.94) and temporal stability (.78). These results indicate that the RQT produced reliable and stable results for the sample studied and support the appropriateness of the RQT for future refinement and use in educational research of this type. Correlations of the RQT with other measures of linguistic and cognitive development, and educational ability were found to be nonsignificant. These results suggest that hemispheric activation as indexed by the RQT at this age range may be largely independent of measures traditionally associated with school performance. The results of this investigation have provided normative data on normal right-handed children, thereby providing a comparative basis for future research with children of the same age from other populations such as the learning disabled. / Ed. D.

An important problem for the human factors specialist involves specifying the extent to which the quality of a displayed image will affect observer performance. One approach to this problem has been to develop metrics of image quality and to correlate measured image quality with observer performance. Of the metrics that have been developed, the Modulation Transfer Factor Area (MTFA) has proven to be a useful predictor of observer performance. The MTFA metric takes into account the system's Modulation Transfer Function and observer threshold curves. Two experiments were performed to assess the effects of the quality of a televised image on eye movements and search-related dependent measures. The first experiment search task involved having subjects perform an air-to-ground search during simulated flight. The quality of the image presented was varied by either passing, low-pass filtering, or attenuating the video signal and by adding electrical white noise to the video signal. The results of this experiment indicate that (1) at the highest level of electrical noise added, the percent of correct target acquisitions was decreased moderately, (2) the larger the target, the higher the percent correct responses, (3) the low-pass filtering of the video signal led to shorter ground ranges at acquisition for the large-sized targets, and (4) that the larger the target, the longer the fixation duration. Low to moderate correlations between MTFA and performance measures generally indicated that as MTFA increases performance improves, and that as MTFA increases fixation duration decreases. The search task of the second experiment consisted of having the subjects search for a designated letter or numeral across a televised picture of randomly positioned letters and numerals. The quality of the picture was varied by either passing, low-pass filtering, high-pass filtering, or attenuating the video signal and by adding electrical white noise to the video signal. The results of this experiment indicated that (1) the high-pass filtered high noise level condition led to significantly longer search times; and (2) the fixation times associated with the high-pass filtered condition were longer than those associated with the low-pass filtered, at- tenuated, and unfiltered unattenuated conditions, and that this effect was most pronounced under high noise level conditions. Correlations between MTFA and performance measures indicated that increases in MTFA lead to decreases in search time and decreases in fixation duration. The results of tests among fixation and saccade duration distribution across both experiments consistently showed significant individual differences and non-normality. Examination of pooled fixation duration distributions showed large dispersion differences across the static and dynamic imagery experiments. This result, and the differences of pooled fixation and saccade duration distribution ranges do not support the search model assumption of constant glimpse durations and reveal serious.flaws in the structure of search models. / Ph. D.

No / In this paper, we investigate how controlled changes to image properties and orientation affect eye movements for repeated viewings of images of natural scenes. We make changes to images by manipulating low-level image content (such as luminance or chromaticity) and/or inverting the image. We measure the effects of these manipulations on human scanpaths (the spatial and chronological path of fixations), additionally comparing these effects to those predicted by a widely used saliency model (L. Itti & C. Koch, 2000). Firstly we find that repeated viewing of a natural image does not significantly modify the previously known repeatability (S. A. Brandt & L. W. Stark, 1997; D. Noton & L. Stark, 1971) of scanpaths. Secondly we find that manipulating image features does not necessarily change the repeatability of scanpaths, but the removal of luminance information has a measurable effect. We also find that image inversion appears to affect scene perception and recognition and may alter fixation selection (although we only find an effect on scanpaths with the additional removal of luminance information). Additionally we confirm that visual saliency as defined by L. Itti and C. Koch's (2000) model is a poor predictor of real observer scanpaths and does not predict the small effects of our image manipulations on scanpaths.