Massive memory revisited: Limitations on storage capacity for object details in visual long-term memory

Abstract

Previous work suggests that visual long-term memory (VLTM) is highly detailed and has a massive capacity. However, memory performance is subject to the effects of the type of testing procedure used. The current study examines detail memory performance by probing the same memories within the same subjects, but using divergent probing methods. The results reveal that while VLTM representations are typically sufficient to support performance when the procedure probes gist-based information, they are not sufficient in circumstances when the procedure requires more detail. We show that VLTM capacity, albeit large, is heavily reliant on gist as well as detail. Thus, the nature of the mnemonic representations stored in VLTM is important in understanding its capacity limitations.

Figure 1.

Examples of the study phase and memory test phases.

Figure 2.

Memory performance on the ONR memory test (left) and 2AFC memory test (right) that were given after the study phase. The dashed box above the “Repetition” bar indicates the proportion of miss trials. The raw correct rejection score is equal to the total bar height for each of the lure conditions. The lure discrimination index (Yassa et al. 2011) accounts for response bias by subtracting the number of “new” responses attributed to misses from each of the lure conditions. This proportion is shown in the hashed portion on the top of each lure condition (novel, exemplar, and state).

Figure 3.

Detailed object memory for the 2AFC memory test compared with the ONR memory test. The y-axis is the ratio of performance in a lure condition divided by performance in the novel (baseline) condition. This ratio is a measure of the change in performance as a function of the degree of detailed memory that is probed. The x-axis represents the different lure conditions. Performance in the ONR memory test is significantly lower than performance in the 2AFC memory test across both exemplar and state conditions.