Attention doesn't slide: spatiotopic updating after eye movements instantiates a new, discrete attentional locus

Abstract

During natural vision, eye movements can drastically alter the retinotopic (eye-centered) coordinates of locations and objects, yet the spatiotopic (world-centered) percept remains stable. Maintaining visuospatial attention in spatiotopic coordinates requires updating of attentional representations following each eye movement. However, this updating is not instantaneous; attentional facilitation temporarily lingers at the previous retinotopic location after a saccade, a phenomenon known as the retinotopic attentional trace. At various times after a saccade, we probed attention at an intermediate location between the retinotopic and spatiotopic locations to determine whether a single locus of attentional facilitation slides progressively from the previous retinotopic location to the appropriate spatiotopic location, or whether retinotopic facilitation decays while a new, independent spatiotopic locus concurrently becomes active. Facilitation at the intermediate location was not significant at any time, suggesting that top-down attention can result in enhancement of discrete retinotopic and spatiotopic locations without passing through intermediate locations.

Fig. 1

Possible models of attentional updating. Black square indicates cued location; white dots and arrows indicate fixation and saccade positions. In the no-saccade case, an attentional locus (white circle) is deployed to the spatiotopic/retinotopic (SR) location of the cue. After the eye movement, attention is initially directed at the retinotopic (R) location and updates over time to occupy the correct spatiotopic (S) location. The three models depict different possible spatiotemporal dynamics of this transition. C, control location; I, intermediate location; C_i, intermediate-control location. a A single locus of attention slides progressively from retinotopic to spatiotopic locations. b A single locus of attention transiently expands to include both locations, then contracts back to the spatiotopic location. c The old locus of attention decays at the retinotopic location while a new, discrete locus of attention arises at the spatiotopic location

Fig. 2

Task: Example trial. Subjects maintained fixation on the white fixation dot, while a memory cue appeared briefly at another location. Subjects were instructed to hold this cued location in memory throughout the trial. The fixation dot then moved, and after completion of a saccade to the new fixation location, a probe stimulus (oriented bar) appeared after a variable delay (shown here in the control location; a schematic of all five locations is shown in the inset at bottom). Subjects made a buttonpress response to indicate probe orientation. A memory test stimulus then appeared, and subjects indicated whether it occupied the same spatiotopic location as the memory cue. Gray arrow indicating a saccade did not actually appear on screen. The stimulus configuration illustrated here represents one example cue–saccade configuration; configurations were randomly intermixed from the four possible fixation locations and nine possible stimulus locations

Fig. 3

Attentional facilitation results. Attentional facilitation is plotted as the difference in reaction time (RT) for probes appearing in the spatiotopic, retinotopic, and intermediate locations, as compared with the control and intermediate-control location baselines (zero). Positive values indicate attentional facilitation (RTs shorter than those at the control locations). a Attentional facilitation after saccade (n = 20); data are plotted as a function of probe delay. b Attentional facilitation in no-saccade task (n = 18). Insets illustrate sample probe locations colored according to the plot legends, with white indicating the control location. Intermediate and intermediate-control locations are shown as hashed lines. White and gray dots indicate final and previous fixation locations, respectively; a square indicates the cued location, and an arrow indicates the saccade. Error bars are standard errors of the means (SEMs); asterisks indicate facilitation significantly greater than zero (Bonferroni-corrected). The dashed gray line indicates baseline facilitation at the intermediate location in the no-saccade task; intermediate facilitation after the saccade never exceeded this baseline