Remapping high-capacity, pre-attentive, fragile sensory memory

Abstract

Humans typically make several saccades per second. This provides a challenge for the visual system as locations are largely coded in retinotopic (eye-centered) coordinates. Spatial remapping, the updating of retinotopic location coordinates of items in visuospatial memory, is typically assumed to be limited to robust, capacity-limited and attention-demanding working memory (WM). Are pre-attentive, maskable, sensory memory representations (e.g. fragile memory, FM) also remapped? We directly compared trans-saccadic WM (tWM) and trans-saccadic FM (tFM) in a retro-cue change-detection paradigm. Participants memorized oriented rectangles, made a saccade and reported whether they saw a change in a subsequent display. On some trials a retro-cue indicated the to-be-tested item prior to probe onset. This allowed sensory memory items to be included in the memory capacity estimate. The observed retro-cue benefit demonstrates a tFM capacity considerably above tWM. This provides evidence that some, if not all sensory memory was remapped to spatiotopic (world-centered, task-relevant) coordinates. In a second experiment, we show backward masks to be effective in retinotopic as well as spatiotopic coordinates, demonstrating that FM was indeed remapped to world-centered coordinates. Together this provides conclusive evidence that trans-saccadic spatial remapping is not limited to higher-level WM processes but also occurs for sensory memory representations.

Figure 1

Hypotheses examined in Experiment 1. The retro-cue benefit demonstrates a higher memory capacity when using a retro-cue (i.e. FM). If this difference is also observed in the saccade condition, then this demonstrates trans-saccadic FM. Dashed circles indicate within-fixation capacity, circles with a solid outline indicate across-saccade capacity.

Figure 2

Schematic representation of trials in each experimental condition in Experiment 1 and 2. Red dots represent the currently active fixation. Sizes not to scale and colours modified for clarity. Every trial began with an array of oriented bars, the stimuli to be memorized. This was followed by a blank or a saccade cue. A retro-cue followed by a blank and a probe array was presented in the FM conditions, a probe display was presented in the WM conditions. In Experiment 2 a colour noise mask was presented after the memory array and different masks were presented after the saccade.

Figure 3

Results Experiment 1. (left) Individual proportions correct and means of proportion correct. Dashed circles indicate within-fixation capacity, circles with a solid outline indicate across-saccade capacity. Error bars represent SE. Shaded gray areas are violin plots to visualize the shape of the distributions. (right) Posterior probability densities in log odds space. As can be seen, tFM capacity (cyan) is larger than tWM capacity (red).

Figure 4

Results Experiment 2. (left) Proportions correct per participant and means of proportions correct per condition. Dashed circles indicate within-fixation capacity, circles with a solid outline indicate across-saccade capacity. Error bars represent SE. Shaded gray areas are violin plots to visualize the shape of the distributions. The mask type used is visualized below the violin plots of each condition. The transparent bar indicates the future target location. (right) Posterior probability densities in log odds space, which provide strong support that both spatiotopic and retinotopic masks interfered with memory representations (difference between cyan and gray distributions), as well as a replication of Experiment 1 (difference between cyan and red distributions).