The native coordinate system of spatial attention is retinotopic - PubMed (original) (raw)

Comparative Study

The native coordinate system of spatial attention is retinotopic

Julie D Golomb et al. J Neurosci. 2008.

Abstract

Visual processing can be facilitated by covert attention at behaviorally relevant locations. If the eyes move while a location in the visual field is facilitated, what happens to the internal representation of the attended location? With each eye movement, the retinotopic (eye-centered) coordinates of the attended location change while the spatiotopic (world-centered) coordinates remain stable. To investigate whether the neural substrates of spatial attention reside in retinotopically and/or spatiotopically organized maps, we used a novel gaze-contingent behavioral paradigm that probed spatial attention at various times after eye movements. When task demands required maintaining a spatiotopic representation after the eye movement, we found facilitation at the retinotopic location of the spatial cue for 100-200 ms after the saccade, although this location had no behavioral significance. This task-irrelevant retinotopic representation dominated immediately after the saccade, whereas at later delays, the task-relevant spatiotopic representation prevailed. However, when task demands required maintaining the cue in retinotopic coordinates, a strong retinotopic benefit persisted long after the saccade, and there was no evidence of spatiotopic facilitation. These data suggest that the cortical and subcortical substrates of spatial attention primarily reside in retinotopically organized maps that must be dynamically updated to compensate for eye movements when behavioral demands require a spatiotopic representation of attention. Our conclusion is that the visual system's native or low-level representation of endogenously maintained spatial attention is retinotopic, and remapping of attention to spatiotopic coordinates occurs slowly and only when behaviorally necessary.

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Figures

Figure 1

Figure 1. Tasks and conditions, Experiment 1

A, Example trial for “Saccade” task. While subjects maintained fixation on the white fixation dot, 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 in either the cue’s spatiotopic (top), retinotopic (middle), or control (bottom) location. Subjects made a button press 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. B, In the “No Saccade” task, subjects remained fixated on the original location for an equivalent amount of time, so that probe delays relative to the cue were consistent across tasks. Probes appeared in the spatiotopic/retinotopic (top) or control (bottom) locations. C, In the “Return Saccade” task, subjects held fixation at the second location for 750ms before making a return saccade back to the first fixation location. Probes appeared at the spatiotopic/retinotopic (top), updated retinotopic (middle; reported in supplement) or control (bottom) locations; probe delays were the same as in the “Saccade” task relative to onset of the final fixation. Gray arrows indicating saccades did not actually appear on screen. Stimulus configurations illustrated here represent only one of 108 possible cue-saccade configurations for each task (see Supplemental Fig. 1 for additional examples, available at

www.jneurosci.org

as supplemental material).

Figure 2

Figure 2. Attentional facilitation: Task-relevant spatiotopic location

Experiment 1. Attentional facilitation is plotted as the difference in RT for probes appearing in the spatiotopic and retinotopic locations compared to the control location baseline (zero). Positive values indicate attentional facilitation (RTs faster than at control locations). Data are plotted as a function of probe delay. Right column illustrates sample probe locations for each experimental condition colored according to the plot legends on the left with white indicating the control location. White and gray dots indicate final and previous fixation locations, respectively; squares indicate cued locations, and arrows indicate saccade patterns. A, “No Saccade” task. B, “Return Saccade” task. C, “Saccade” task. Error bars indicate standard error of the mean (SEM) after normalization to remove between-subject variability (Loftus and Masson, 1994); n=16.

Figure 3

Figure 3. Attentional facilitation: Task-relevant spatiotopic location, early delays

Attentional facilitation is plotted as the difference in RT for probes appearing in the spatiotopic and retinotopic locations compared to the control location baseline (zero). Data are plotted as a function of probe delay. Right panel illustrates sample probe locations for the “Saccade” task, colored according to the plot legends on the left with white indicating the control location. Gray dot indicates initial fixation location, white dot is current fixation, and arrow indicates saccade pattern. Error bars indicate standard error of the mean (SEM) after normalization to remove between-subject variability (Loftus and Masson, 1994); n=16.

Figure 4

Figure 4. Attentional facilitation: Task-relevant spatiotopic location, accuracy task

A, Experiment 2. Attentional facilitation is plotted as the difference in accuracy for masked probes appearing in the spatiotopic and retinotopic locations compared to the control location baseline (zero). Positive values indicate facilitation (accuracy better than at control locations). B, Experiment 1. RT data from the 75ms and 400ms probe delays of the “Saccade” task re-plotted for comparison. Error bars indicate standard error of the mean (SEM) after normalization to remove between-subject variability (Loftus and Masson, 1994); n=16.

Figure 5

Figure 5. Attentional facilitation: Task-relevant retinotopic location

Experiment 3. Attentional facilitation is plotted as the difference in RT for probes appearing in the spatiotopic and retinotopic locations compared to the control location baseline (zero). Data are plotted as a function of probe delay. Right panel illustrates probe locations for a sample configuration, colored according to the plot legend with white indicating the control location. Gray dot indicates initial fixation locations, white dot is current fixation, and arrow indicates saccade pattern. The solid gray square represents the initial cued location; the dotted gray square represents the task-relevant retinotopic location to be held in memory. Error bars indicate SEM after normalization to remove between-subject variability (Loftus and Masson, 1994); n=12.

Figure 6

Figure 6. Memory test performance, Experiment 1

A, Arrangement of possible fixation locations (white dots) and cue/probe locations (black squares). Each of the nine cue/probe regions contained four possible positions; the memory test stimulus always appeared in the same region as the cue. Separation distance between test positions was adjusted after every run to keep performance around 75% correct. Separation distance was increased following blocks of poorer performance and decreased following blocks of better performance. Inset illustrates relationship of test positions within a region: “same” (S) position as the cue, “near different” (ND) position in the adjacent horizontal or vertical direction, and “far different” (FD) position along the diagonal. B, Task difficulty is plotted for each of the three tasks, given as the separation distance in degrees of visual angle required to correctly perform the memory task 75% of the time. Larger values indicate increased difficulty. C, Accuracy on the memory task when equated for difficulty. Percent correct is given when the test stimulus appeared in the “same”, “near different”, and “far different” locations for each of the three tasks. “Near different” positions should be more difficult to correctly reject due to their close proximity to the cued location. Error bars indicate SEM after normalization to remove between-subject variability (Loftus and Masson, 1994); n=16.

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