Multiple Time Intervals of Visual Events Are Represented as Discrete Items in Working Memory

Abstract

Previous studies on time perception and temporal memory have focused primarily on single time intervals; it is still unclear how multiple time intervals are perceived and maintained in working memory. In the present study, using Sternberg's item recognition task, we compared the working memory of multiple items with different time intervals and visual textures, for sub- and supra-second ranges, and investigated the characteristics of working memory representation in the framework of the signal detection theory. In Experiments 1-3, gratings with different spatial frequencies and time intervals were sequentially presented as study items, followed by another grating as a probe. Participants determined whether the probe matched one of the study gratings, in either the temporal dimension or in the visual dimension. The results exhibited typical working memory characteristics such as the effects of memory load, serial position, and similarity between probe and study gratings, similarly, to the time intervals and visual textures. However, there were some differences between the two conditions. Specifically, the recency effect for time intervals was smaller, or even absent, as compared to that for visual textures. Further, as compared with visual textures, sub-second intervals were more likely to be judged as remembered in working memory. In addition, we found interactions between visual texture memory and time interval memory, and such visual-interval binding differed between sub- and supra-second ranges. Our results indicate that multiple time intervals are stored as discrete items in working memory, similarly, to visual texture memory, but the former might be more susceptible to decay than the latter. The differences in the binding between sub- and supra-second ranges imply that working memory for sub- and supra-second ranges may differ in the relatively higher decision stage.

Keywords: memory load; serial position; signal detection theory; similarity; time intervals; working memory.

FIGURE 1

Time course of the recognition/working memory task in Experiments 1 and 3. The number of study items (N) was either one, two, or three in Experiment 1, and was always three in Experiment 3.

FIGURE 2

Memory load effects in Experiment 1. (A) Proportion of correct responses as a function of memory load. Filled and open circles represent target and lure trials, respectively. (B) d′, as a function of memory load. (C) C, as a function of memory load. Red and blue represent interval and texture trials, respectively. Error bars represent ± 1 standard error of the mean.

FIGURE 3

Proportion of correct responses as a function of serial position in Experiment 1. Red and blue represent interval and texture trials, respectively. Filled and open circles represent target and lure trials, respectively. Error bars represent ± 1 standard error of the mean.

FIGURE 4

Proportion of correct responses as a function of similarity in Experiment 1. Red and blue represent interval and texture trials, respectively. Error bars represent ± 1 standard error of the mean.

FIGURE 5

Effects of the context on the proportion of correct responses in Experiment 1. Red and blue represent interval and texture trials, respectively. Filled and open circles represent target and lure trials, respectively. Error bars represent ± 1 standard error of the mean.

FIGURE 6

Time course of the recognition/working memory task in Experiment 2.

FIGURE 7

Receiver operating characteristic curves (hit rate as a function of false-alarm rate) in Experiment 2. Red and blue represent interval and texture trials, respectively.

FIGURE 8

Proportion of correct responses as a function of serial position in Experiment 2. Red and blue represent interval and texture trials, respectively. Filled and open circles represent target and lure trials, respectively. Error bars represent ± 1 standard error of the mean.

FIGURE 9

Proportion of correct responses as a function of similarity in Experiment 2. Red and blue represent interval and texture trials, respectively. Error bars represent ± 1 standard error of the mean.

FIGURE 10

Proportion of correct responses as a function of context in Experiment 2. Red and blue represent interval and texture trials, respectively. Filled and open circles represent target and lure trials, respectively. Error bars represent ± 1 standard error of the mean.

FIGURE 11

Proportion of correct responses as a function of serial position in Experiment 3. Red and blue represent sub- and supra-second trials, respectively. Filled circles and triangles represent target trials, and open circles and triangles represent lure trials. Error bars represent ± 1 standard error of the mean.

FIGURE 12

Similarity effect in Experiment 3. (A) Proportion of correct responses as a function of similarity. Open circles and triangles show lure trials. (B) d′ as a function of similarity. (C) C as a function of similarity. Red and blue represent sub- and supra-second trials, respectively. Error bars represent ± 1 standard error of the mean.

FIGURE 13

Effects of context on proportion of correct responses in Experiment 3. Red and blue represent sub- and supra-second trials, respectively. Filled circles and triangles show target trials, and open circles and triangles show lure trials. Error bars represent ± 1 standard error of the mean.