Understanding the function of visual short-term memory: transsaccadic memory, object correspondence, and gaze correction

Abstract

Visual short-term memory (VSTM) has received intensive study over the past decade, with research focused on VSTM capacity and representational format. Yet, the function of VSTM in human cognition is not well understood. Here, the authors demonstrate that VSTM plays an important role in the control of saccadic eye movements. Intelligent human behavior depends on directing the eyes to goal-relevant objects in the world, yet saccades are very often inaccurate and require correction. The authors hypothesized that VSTM is used to remember the features of the current saccade target so that it can be rapidly reacquired after an errant saccade, a task faced by the visual system thousands of times each day. In 4 experiments, memory-based gaze correction was accurate, fast, automatic, and largely unconscious. In addition, a concurrent VSTM load interfered with memory-based gaze correction, but a verbal short-term memory load did not. These findings demonstrate that VSTM plays a direct role in a fundamentally important aspect of visually guided behavior, and they suggest the existence of previously unknown links between VSTM representations and the occulomotor system.

Figure 1

Sequence of events in a rotation trial of Experiment 1. The top row shows the full-array condition and the bottom row the single-object condition

Figure 2

Eye movement scan paths for the full-array rotation trials of a single participant in Experiment 1. Panel A shows all 12 trials on which the array started at the clock positions and rotated clockwise during the saccade. Panel B shows all 12 trials on which the array started at the clock positions and rotated counterclockwise during the saccade. The white disks indicate object positions after the rotation. White dotted circles indicate the scoring regions used for data analysis. Black lines represent saccades and small black dots fixations. The initial saccade directed from central fixation to the array typically landed between target and distractor, as expected given the rotation of the array during the saccade. Then, gaze was corrected. Numerical values indicate correction latency (duration of the fixation before the corrective saccade) in ms for each depicted trial. Note that corrective saccades were directed to the appropriate clockwise (Panel A) or counterclockwise (Panel B) target object.

Figure 3

Distributions of correction latencies for the full-array and single-object conditions in Experiment 1.

Figure 4

Sample full array of novel objects in Experiment 2.

Figure 5

Distributions of correction latencies for the full-array and single-object conditions in Experiment 2.

Figure 6

Gaze correction accuracy for full-array, rotation trials in Experiment 2 as a function of the difference in distance of the target and distractor from the landing position of the initial saccade. Small differences in distance (center of the figure) represent trials on which the eyes landed near the midpoint between target and distractor. Large differences in distance (far right and left of figure) represent trials on which the eyes landed much closer to one object than to the other. Trials on which the eyes landed closer to the distractor than to the target are plotted on the left. Trials on which the eyes landed closer to the target than to the distractor are plotted on the right. For each type of trial, the distance difference data were split into thirds. Mean distance difference in each third is plotted against mean gaze correction accuracy in that third.

Figure 7

Sequence of events in a rotation trial of the dual-task condition of Experiment 3.

Figure 8

Gaze correction accuracy for full-array, rotation trials in Experiment 3 as a function of the difference in distance of the target and distractor from the landing position of the initial saccade. For each type of trial, the distance difference data were split into halves. Mean distance difference in each half is plotted against mean gaze correction accuracy in that half Data are plotted separately for the gaze-correction-only and dual-task conditions.

Figure 9

Object array illustrating the outer ring in Experiment 4.