Figure 1.
Leaky hourglass analogy for information processing and storage capacity.
The initial information processing stages, such as the retina and the early areas of visual cortex, have a parallel structure that allows them to process a large amount of information. The contents of this stage are transferred to sensory storage which has a large capacity but limited time-span of storage. In the leaky hourglass analogy, the limited time-span of storage is depicted by the leak of information from the hourglass. VSTM, which is the visual component of working memory, has limited capacity and represents the major bottleneck of the hourglass. LTM, represented by the bottom half of the hourglass, can accumulate a very large amount of information throughout our lifespan. Finally, the selection and filtering functions of attention can potentially impose their limits upon these three stages.
Figure 2.
Schematic depiction of the stimulus and sequence of events on each trial.
In the first experiment, cue delay was fixed at 0
Figure 3.
Stimulus encoding performance as a function of distractor and target set-sizes.
The magnitude of the error angle is shown on the right y-axis. The left y-axis shows the equivalent transformed measure defined as
. According to this transformed measure, 1 and 0.5 correspond to perfect and chance levels of performance, respectively. Although both target and distractor set sizes have a significant influence on performance, the effect of target set size is more pronounced. Data points correspond to the mean across observers (N = 4) and error bars represent ±1 SEM.
Table 1.
Results of linear fits to data from Experiment 1.
Figure 4.
An example of the fit of the Gaussian+Uniform model to empirical error distributions for observer OEK at target set-size T = 9.
Figure 5.
Precision (A) and intake (B) as a function of target set-size.
Also included in the plots are guess rate (1-w) and standard deviation (σ). Note that the left and right y-axes have different offsets and scales. Data points correspond to the mean across observers (N = 4) and error bars represent ±1 SEM.
Figure 6.
Transformed performance as a function of cue delay.
In the upper row, each panel corresponds to a different target set-size. To show the difference between target and distractor effects, the lower row plots the same data with each panel corresponding to a different distractor set-size. Data points represent the mean across observers (N = 4) and ±1 SEM. Left and right y-axes are the same as in Fig. 3.
Figure 7.
Transformed performance as a function of the cue delay for the condition in Experiment 2 with target set-size = 9 targets and distractor set-size = 7.
Separate exponential fits are shown for the data of the 4 observers.
Table 2.
The results of the exponential fits to data from Experiment 2 for T = 9 and D = 7.
Table 3.
Results of significance tests and estimated effect size (ηp2) for target and distractor set-sizes at each cue-delay in Experiment 2.
Figure 8.
Precision (A) and intake (B) as a function of target and distractor set-sizes.
Different panels represent different cue delays. Data points correspond to the mean across observers (N = 4) and ±1 SEM. Lines represent linear fits.
Figure 9.
Precision (A) and intake (B) as a function of cue delay.
The horizontal dashed line and the arrows in each panel highlight the relative share of drop in the quality (A) and quantity (B) of information between the stimulus encoding stage (cue delay = 0 s; leftmost data points) and VSTM (cue delay = 3 s, rightmost data points). Note that y-axes for the left and right panels start at 0.02 and 0.4, respectively. Data points correspond to the mean across observers (N = 4) and ±1 SEM.
Figure 10.
The single leaky hourglass of Fig. 1 is replaced by two leaky flasks, one for precision and one for intake to highlight the different characteristics of these two aspects of bottlenecks. The top portions are narrower than the hourglass model to illustrate the bottlenecks occurring at the stages prior to VSTM. Also shown in this figure are the constraints imposed by attentional processes. While the selection function of attention applies to all three stages, the filtering function of attention applies mainly to the intake of sensory memory stage.