Oculomotor behavior and perceptual strategies in complex tasks.

While we know a great deal about the dynamics and characteristics of eye movements in relatively simple tasks performed under reduced laboratory conditions, we know less about oculomotor behavior in complex, multi-step tasks. Complex tasks are not necessarily difficult. Part of the transition from 'hard' to 'easy' in completing complex tasks is the gradual reduction in conscious effort required to complete the sub-tasks. We are interested in learning whether high-level perceptual strategies can aid that transition. In the past, subjects performed relatively simple tasks or the eye movements themselves were the instructed task. But outside the laboratory vision is a tool, not the task. To study the oculomotor system in its native mode, we developed a wearable eyetracker that allows natural eye, head and whole-body movements. Using the over-learned, common task of hand-washing, we measured the global characteristics of fixation duration, saccade amplitude, and the spatial distribution of fixation positions. An important observation was the emergence of higher-order perceptual strategies in the complex task: while most fixations were related to the immediate action, a small number of fixations were made to objects relevant only to future actions. Based on a control task that differed only in the high-level goal, we conclude that the look-ahead fixations represent a task-dependent strategy, not a general behavior elicited by the salience or conspicuity of objects in the environment. We propose that the strategy of looking ahead to objects of future relevance supports the conscious percept of an environment seamless in time as well as in space.

The role of exocentric reference frames in the perception of visual direction.

One classic piece of evidence for an efference copy signal of eye position is that a small, positive afterimage viewed in darkness is perceived to move with the eye. When a small stationary reference point is visible the afterimage appears to move relative to the reference point. However, this is true only when the afterimage is localized to a small area. We have observed that when an extended afterimage of a complex scene is generated by a brief, bright flash it does not appear to move, even with large changes in eye position. When subjects were instructed to maintain their direction of gaze, we observed small saccades (typically < 1 deg) and slow drift movements often totalling more than 10 deg over a 30 sec period. When the instructions were to simply inspect the extended afterimage, subjects made larger saccades (up to 5 deg) which were not accompanied by afterimage movement. The smaller movements observed under the first instructions are greater than those observed in the dark or with small afterimages. When a visible reference is present with these large afterimages, the afterimage appears stationary, while the reference point appears to move. Eye position was monitored following the generation of such afterimages. In general, the perceived motion of the stationary reference point was in a direction opposite to the motion of the eye. Similar drift movements of smaller magnitude were observed with localized afterimages, but the motion was attributed to the afterimage.(ABSTRACT TRUNCATED AT 250 WORDS)

Memory representations in natural tasks.

Abstract 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.