A Breadth-First Survey of Eye Tracking Applications <s> Natural Tasks <s> The very limited capacity of short-term or working memory is one of the most prominent features of human cognition. Most studies have stressed delimiting the upper bounds of this memory in memorization tasks rather than the performance of everyday tasks. We designed a series of experiments to test the use of short-term memory in the course of a natural hand-eye task where subjects have the freedom to choose their own task parameters. In this case subjects choose not to operate at the maximum capacity of short-term memory but instead seek to minimize its use. In particular, reducing the instantaneous memory required to perform the task can be done by serializing the task with eye movements. These eye movements allow subjects to postpone the gathering of task-relevant information until just before it is required. The reluctance to use short-term memory can be explained if such memory is expensive to use with respect to the cost of the serializing strategy. <s> BIB001 </s> A Breadth-First Survey of Eye Tracking Applications <s> Natural Tasks <s> A great deal of evidence suggests that early in processing, retinal images are filtered by parallel, spatial frequency selective channels. We attempt to incorporate this view of early vision with the principle of global precedence, which holds that Gestalt-like processes sensitive to global image configurations tend to dominate local feature processing in human pattern perception. Global precedence is inferred from the pattern of reaction times observed when visual patterns contain multiple cues at different levels of spatial scale. Specifically, it is frequently observed that global processing times are largely unaffected by conflicting local cues, but local processing times are substantially lengthened by conflicting global cues. The asymmetry of these effects suggests the dominant role of global configurations. Since global spatial information is effectively represented by low spatial frequencies, global precedence potentially implies a low frequency dominance. The thesis is that low spatial frequencies tend to be available before information carried by higher frequency bands, producing a coarse-to-fine temporal order in visual spatial perception. It is suggested that a variety of factors contribute to the “prior entry” of low frequency information, including the high contrast gain of the magnocellular pathway, the amplitude spectra typical of natural images, and inhibitory interactions between the parallel frequency-tuned channels. Evidence suggesting a close relationship between global precedence and spatial frequency channels is provided by observations that the essential features of the global precedence effect are obtained using patterns consisting of low and high frequency sinusoids. The hypothesis that these asymmetric interference effects are due to interactions between parallel spatial channels is supported by an analysis of reaction times (RTs), which shows that RTs to redundant low and high frequency cues produce less facilitation than predictions that assume the channels are independent. In view of previous work showing that global precedence depends upon the low frequency content of the stimuli, we suggest that low spatial frequencies represent the sine qua non for the dominance of configurational cues in human pattern perception, and that this configurational dominance reflects the microgenesis of visual pattern perception. This general view of the temporal dynamics of visual pattern recognition is discussed, is considered from an evolutionary perspective, and is related to certain statistical regularities in natural scenes. Potential adaptive advantages of an interactive parallel architecture that confers an initial processing advantage to low resolution information are explored. <s> BIB002 </s> A Breadth-First Survey of Eye Tracking Applications <s> Natural Tasks <s> Visual perception is an inherently complex task, yet the bulk of studies in the past were undertaken with subjects performing relatively simple tasks under reduced laboratory conditions. In the research reported here, we examined subjects' oculomotor performance as they performed two complex, extended tasks. In the first task, subjects built a model rocket from a kit. In the second task, a wearable eyetracker was used to monitor subjects as they walked to a restroom, washed their hands, and returned to the starting point. For the purposes of analysis, both tasks can be broken down into smaller sub-tasks that are performed in sequence. Differences in eye movement patterns and high-level strategies were observed in the model building and hand-washing tasks. Fixation durations recorded in the model building tasks were significantly shorter than those reported in simpler tasks. Performance in the hand-washing task revealed look-ahead eye movements made to objects well in advance of a subject's interaction with the object. Often occurring in the middle of another task, they provide overlapping temporal information about the environment, providing a mechanism to produce our conscious visual experience. <s> BIB003
Studies of visual search are expanding to consider more complex stimuli such as natural scenery BIB002 . However, viewing of pictures projected on a laboratory display still constitutes a somewhat artificial task. Recent advancements in wearable and virtual displays now allow collection of eye movements in more natural situations, usually involving the use of generally unconstrained eye, head, and hand movements. Important work in this area has been reported by Land, Mennie, and Rusted (1999) and Land and Hayhoe (2001) . The aim of the first study was to determine the pattern of fixations during the performance of a well-learned task in a natural setting (making tea), and to classify the types of monitoring action that the eyes perform. Results of this study indicate that even automated routine activities require a surprising level of continuous monitoring. Foveal direction was always close to the object being manipulated, and very few fixations were irrelevant to the task. Land et al. conclude that although the actions of tea-making are 'automated' and proceed with little conscious involvement, the eyes closely monitor every step of the process. Investigating a similar natural task, Land and Hayhoe (2001) examined the relations of eye and hand movements in extended food preparation tasks, tea-making and making peanut butter and jelly sandwiches. Gaze usually reached the next object in the sequence before any sign of manipulative action, indicating that eye movements are planned into the motor pattern and lead each action. The eyes usually fixated the same object throughout the action upon it, although they often moved on to the next object in the sequence before completion of the preceding action. General conclusions provided by Land and Hayhoe are that the eyes provide information on an 'as needed' basis, and the relevant eye movements usually precede the motor acts they mediate by a fraction of a second. Eye movements are thus in the vanguard of each action plan, and are not simply responses to circumstances. Land and Hayhoe conclude that their studies lend no support to the idea that the visual system builds up a detailed model of the surroundings and operates from that. Rather, most information is actively obtained from the scene as it is needed. BIB001 investigated the use of short-term memory in the course of a natural eye-hand task. The investigation focused on the minimization of subjects' use of short-term memory by employing deictic primitives through serialization of the task with eye movements (e.g., using the eyes to "point to" objects in a scene in lieu of memorizing all of the objects' positions and other properties). Ballard et al. argue that a deictic strategy in a pickand-place task employs a more efficient use of a frame of reference centered at the fixation point rather than a viewercentered reference frame which might require memorization of objects in the world relative to coordinates centered at the viewer. By recording eye movements during the block pickand-place task, Ballard et al. were able to show that subjects frequently directed gaze to the model pattern before arranging blocks in the workspace area, suggesting that information is acquired incrementally during the task and is not acquired in toto at the beginning of the task. That is, subjects appeared to use short-term memory frugally, acquiring information just prior to its use, and did not appear to memorize the entire model block configuration before making a copy of the block arrangement. In a similar block-moving experiment,  were able to show that horizontal movements of gaze, head, and hand followed a coordinated pattern. A shift of gaze was generally followed by a movement of the head, which preceded the movement of the hand. This relationship is to a large extent task-dependent. In goaldirected tasks in which future points of interest are highly predictable, Smeets et al. hypothesize that while gaze and head movements may decouple, the actual position of the hand is a likely candidate for the next gaze shift. A recent example of such intentional visual attention was demonstrated by BIB003 . Using a wearable eye tracker, Pelz et al. observed intentionallybased eye movements, which they termed "look-ahead" eye movements. During a simple hand-washing task, recorded eye movements showed that gaze moved to a location (soap dispenser) prior to the movement of the hands to the same location. To further examine issues raised by observations of natural behavior,  have recently begun using complex virtual environments which can be manipulated by the experimenter at critical points during task performance. In a virtual environment where subjects copy toy models, Hayhoe et al. show that regularities in the spatial structure are used by subjects to control eye movement targeting. Other experiments in a virtual environment with haptic feedback show that even simple visual properties like size are not continuously available or processed automatically by the visual system, but are dynamically acquired and discarded according to the momentary task demands.