Saccadic eye movements are the result of neural decisions about where to move the eyes. These decisions are based on visual information accumulated before the saccade; however, during an Ϸ100-ms interval immediately before the initiation of an eye movement, new visual information cannot influence the decision. Does the brain simply ignore information presented during this brief interval or is the information used for the subsequent saccade? Our study examines how and when the brain integrates visual information through time to drive saccades during visual search. We introduce a new technique, saccade-contingent reverse correlation, that measures the time course of visual information accrual driving the first and second saccades. Observers searched for a contrast-defined target among distractors. Independent contrast noise was added to the target and distractors every 25 ms. Only noise presented in the time interval in which the brain accumulates information will influence the saccadic decisions. Therefore, we can retrieve the time course of saccadic information accrual by averaging the time course of the noise, aligned to saccade initiation, across all trials with saccades to distractors. Results show that before the first saccade, visual information is being accumulated simultaneously for the first and second saccades. Furthermore, information presented immediately before the first saccade is not used in making the first saccadic decision but instead is stored and used by the neural processes driving the second saccade. Saccadic eye movements are used to reorient the line of sight of the fovea to explore objects of interest. Each saccade is the result of a neural decision that is based on the processing of visual information. Neural activity related to motor preparation and visual selection has been measured in different brain areas before saccade execution (1-4); however, it is still unknown when and how the brain accumulates visual information used to choose the destination of each saccade. Immediately before each saccade's execution, as a consequence of sensory transduction and motor pathway delays (5), there is a ''dead time,'' an Ϸ100-ms time interval in which visual information does not influence the destination of the saccade. What is the impact of this on performance and strategy in a search task? Searching for an object in a scene typically requires a sequence of several saccades. If each saccade were based on a concatenation of separate independent neural decisions, each with its own dead time, then searching a complex scene would be very inefficient and difficult. Instead, for some conditions, it appears that a fast sequence of saccades is programmed in parallel (6-12). Subsequent saccadic latencies can be very short compared with the initial saccade's latency (7,8), and in some cases the second saccade even disregards visual information presented after the execution of the first saccade (10, 11). Recently, a study measuring neural activity in the superior colliculus of monkeys provided evidence that...

Humans use saccadic eye movements when they search for visual targets. We investigated the relationship between the visual processing used by saccades and perception during search by comparing saccadic and perceptual decisions under conditions in which each had access to equal visual information. We measured the accuracy of perceptual judgments and of the first search saccade over a wide range of target saliences [signal-to-noise ratios (SNRs)] in both a contrast-detection and a contrast-discrimination task. We found that saccadic and perceptual performances (1) were similar across SNRs, (2) showed similar task-dependent differences, and (3) were well described by a model based on signal detection theory that explicitly includes observer uncertainty [M. P. Eckstein et al., J. Opt. Soc. Am. A 14, 2406 (1997)1]. Our results demonstrate that the accuracy of the first saccade provides much information about the observer's perceptual state at the time of the saccadic decision and provide evidence that saccades and perception use similar visual processing mechanisms for contrast detection and discrimination.

Although numerous studies have examined the relationship between smooth-pursuit eye movements and motion perception, it remains unresolved whether a common motion-processing system subserves both perception and pursuit. To address this question, we simultaneously recorded perceptual direction judgments and the concomitant smooth eye-movement response to a plaid stimulus that we have previously shown generates systematic perceptual errors. We measured the perceptual direction biases psychophysically and the smooth eye-movement direction biases using two methods (standard averaging and oculometric analysis). We found that the perceptual and oculomotor biases were nearly identical, suggesting that pursuit and perception share a critical motion processing stage, perhaps in area MT or MST of extrastriate visual cortex.

Are the body's actions and the mind's perceptions the result of shared neural processing, or are they performed largely independently? The brain has two major processing streams, and some have proposed that this division segregates visual processing for action and perception. The ventral pathway is claimed to support conscious experience (perception), whereas the dorsal pathway is claimed to support the control of movement (action). Others have argued that perception and action share much of their visual processing within the primate cortex. During visual search, the brain performs a sophisticated deployment of eye movements (saccadic actions) to gather information to subserve perceptual judgments. The relationship between the neural mechanisms mediating perception and action in visual search remains unexplored. Here, we investigate the visual representation of target information in the human brain, both for perceptual decisions and for saccadic actions during visual search. We use classification image analysis, a form of reverse correlation, to estimate the behavioral receptive fields of the visual mechanisms responsible for saccadic and perceptual responses during the same visual search task. Results show that the behavioral receptive fields mediating the perceptual decisions are indistinguishable from those driving the oculomotor decisions, suggesting that similar neural mechanisms are responsible for both perception and oculomotor action during search. Diverging target representations would result in an inefficient coupling between eye movement planning and perceptual judgments. Thus, a common target representation would be more optimal and might be expected to have evolved through natural selection in the neural systems responsible for visual search.

In previous studies of saccadic targeting, the issue how visually guided saccades to unambiguous targets are programmed and executed has been examined. These studies have found different degrees of guidance for saccades depending on the task and task difficulty. In this study, we use ideal-observer analysis to estimate the visual information used for the first saccade during a search for a target disk in noise. We quantitatively compare the performance of the first saccadic decision to that of the ideal observer (ie absolute efficiency of the first saccade) and to that of the associated final perceptual decision at the end of the search (ie relative efficiency of the first saccade). Our results show, first, that at all levels of salience tested, the first saccade is based on visual information from the stimulus display, and its highest absolute efficiency is approximately 20%. Second, the efficiency of the first saccade is lower than that of the final perceptual decision after active search (with eye movements) and has a minimum relative efficiency of 19% at the lowest level of saliency investigated. Third, we found that requiring observers to maintain central fixation (no saccades allowed) decreased the absolute efficiency of their perceptual decision by up to a factor of two, but that the magnitude of this effect depended on target salience. Our results demonstrate that ideal-observer analysis can be extended to measure the visual information mediating saccadic target-selection decisions during visual search, which enables direct comparison of saccadic and perceptual efficiencies.