The strategic retention of task-relevant objects in visual working memory

Abstract

The serial and spatially extended nature of many real-world visual tasks suggests the need for control over the content of visual working memory (VWM). We examined the management of VWM in a task that required participants to prioritize individual objects for retention during scene viewing. There were 5 principal findings: (a) Strategic retention of task-relevant objects was effective and was dissociable from the current locus of visual attention; (b) strategic retention was implemented by protection from interference rather than by preferential encoding; (c) this prioritization was flexibly transferred to a new object as task demands changed; (d) no-longer-relevant items were efficiently eliminated from VWM; and (e) despite this level of control, attended and fixated objects were consolidated into VWM regardless of task relevance. These results are consistent with a model of VWM control in which each fixated object is automatically encoded into VWM, replacing a portion of the content in VWM. However, task-relevant objects can be selectively protected from replacement.

Figure 1

Background workshop scene.

Figure 2

Panels A and B show the two token versions of the ten manipulated objects (aerosol can, bucket, electric drill, fire extinguisher, hammer, lantern, scissors, screwdriver, watering can, wrench).

Figure 3

Sequence of key events in a trial of Experiment 1. Each trial began with central fixation on the background workshop scene, followed by between one and five randomly selected filler objects presented sequentially (not pictured). The last five objects in the sequence (pictured) could be tested at the end of the trial. Each object was presented for 1000 ms, and its removal coincided with the presentation of the next object in the sequence. In the figure, these objects are numbered 5 through 1, with Object 5 being the fifth object before the test and Object 1 the last object before the test. Each object was accompanied by a tone. A low-pitched tone (black symbol) indicated that the current object was unlikely to be tested. A high-pitched tone (red symbol), indicated that the current object was likely to be tested. After the last object in the sequence was displayed, participants fixated the center of the scene. Finally, the test object was displayed, and participants reposed to indicate “same” or “changed” (different token). In the present example trial, the last five objects before the test were, in order, aerosol can, fire extinguisher, electric drill, hammer, and lantern. A cue-position-2 trial is illustrated, in which the second object before the test was cued by the high-pitched tone. Cuing was valid in this example, as the cued object was tested at the end of the trial. The correct response for this trial was “changed”.

Figure 4

Illustration of the three cuing conditions in Experiment 1. In cue-position-2 and cue-position-3 conditions, either the second or third object before the test, respectively, was cued by the high-pitched tone (represented by red border) and had a 60% probability of being the tested item. In the neutral condition, none of the objects was cued, and all five were equally likely to be the tested item.

Figure 5

Percentage correct on the token change detection task for each cuing condition in Experiment 1. The cue-position-2 condition refers to the condition in which the second object before test was cued as most likely to be tested. The cue-position-3 condition refers to the condition in which the third object before test was cued as most likely to be tested. The neutral condition refers to the condition in which none of the objects was cued as most likely to be tested. Error bars are standard errors of the means.

Figure 6

The two cuing conditions in Experiment 2. In the simultaneous-cue condition, the cue was presented 100 ms after the onset of the object (as in Experiment 1). In the post-cue condition, the cue was presented 100 ms after the onset of the mask.

Figure 7

Illustration of the object masks used in Experiment 2 with the aerosol can (top row) and electric drill (bottom row) as examples.

Figure 8

Percentage correct in the token change detection task in each of the cue conditions of Experiment 2. Error bars are standard errors of the means.

Figure 9

Percentage correct in the token change detection task in each of the cue conditions of Experiment 3. Error bars are standard errors of the means.