Priority maps are theorized to be composed of large populations of neurons organized topographically into a map of gaze-centered space whose activity spatially tags salient and behaviorally relevant information. Here, we identified four priority map candidates along human posterior intraparietal sulcus (IPS0–3) and two along the precentral sulcus (PCS) that contained reliable retinotopically organized maps of contralateral visual space. Persistent activity increased from posterior to anterior IPS areas and from inferior to superior PCS areas during the maintenance of a working memory representation, the maintenance of covert attention, and the maintenance of a saccade plan. Moreover, decoders trained to predict the locations on one task (e.g., working memory) cross-predicted the locations on other tasks (e.g., attention) in superior PCS and IPS2, suggesting that these patterns of maintenance activity may be interchangeable across the tasks. Such properties make these two areas in frontal and parietal cortex viable priority map candidates.

The local spatiotemporal pattern of light on the retina is often consistent with a single translational velocity which may also be interpreted as a superposition of spatial patterns translating with different velocities. Human perception reflects such interpretations, as can be demonstrated using stimuli constructed from a superposition of two drifting gratings. Depending on a variety of parameters, these stimuli may be perceived as a coherently moving plaid pattern or as two transparent gratings moving in different directions. Here, we propose a quantitative model that explains how and why such interpretations are selected. An observer's percept corresponds to the most probable interpretation of noisy measurements of local image motion, based on separate prior beliefs about the speed and singularity of visual motion. This model accounts for human perceptual interpretations across a broad range of angles and speeds. With optimized parameters, its components are consistent with previous results in motion perception.

Summary Most neurons in area MT (V5) are strongly direction selective [1–4], and their activity is closely associated with the perception of visual motion [reviewed in 5]. These neurons have large receptive fields, built by combining inputs with smaller receptive fields that respond to local motion [6]. Humans integrate motion over large areas and can perceive what has been referred to as global motion. The large size and direction selectivity of MT receptive fields suggests that MT neurons may represent global motion. We have explored this possibility by measuring responses to a stimulus in which the directions of simultaneously presented local and global motion are independently controlled. Surprisingly, MT responses depended only on the local motion, and were unaffected by the global motion. Yet, under similar conditions, human observers perceive global motion, and are impaired in discriminating local motion. While local motion perception might depend on MT signals, global motion perception depends on mechanisms qualitatively different from those in MT. Motion perception therefore does not depend on a single cortical area, but reflects the action and interaction of multiple brain systems.

We investigated the effect of spatial uncertainty on motor planning by using the cueing method in a reaching task (experiment 1). Discrete spatial cues indicated the different locations in which the target could be presented. The number of cues as well as their direction changed from trial to trial. We tested the adequacy of two models of motor planning to account for the data. The switching model assumes that only one motor response can be planned at a time, whereas the capacity-sharing model assumes that multiple motor responses can be planned in parallel. Both models predict the same relation between average reaction time (RT) and number of cues, but they differ in their prediction of the shape of the distribution of the reaction time. The results showed that RT increased with the number of cues independently from their spatial dispersion. This relation was well described by the function predicted by both models, whereas it was poorly described by the Hick-Hyman law. In addition, the distribution of RT conformed to the prediction of the capacity-sharing model and not to that of the switching model. We investigated the role that the requirement of a spatially directed motor response might have had on this pattern of results by testing subjects in a simple RT task (experiment 2) with the same cueing presentation as in experiment 1. The results contrasted with those in experiment 1 and showed that RT was dependent on the spatial dispersion of the cues and not on their number. The results of the two experiments suggest that the mode of processing of potential targets is dependent on the spatial constraints of the task. The processing resources can be either divided relative to the spatial distribution of possible targets or across multiple independent discrete representations of these targets.