Are there two visual short-term memory stores? A state-trace analysis

Mainstream theories of visual short-term memory (VSTM) posit that VSTM consists of a single, limited capacity store (e.g., Luck & Vogel, 2013). Recently, however, some researchers (Sligte, Scholte & Lamme, 2008; van Moorselaar et al., 2015; Vandenbroucke et al., 2015) have proposed that VSTM consists of two separate components, a limited capacity (3–4 item) durable store and a fragile, high-capacity (5–7 item) store. To assess the structure of VSTM, these authors used a change detection task that required participants to compare two arrays (a memory array and a test array) separated by a brief temporal interval. Critically, these researchers compared performance under conditions when a cue was shown prior to the test array (retro-cue), or after the test array was shown (post-cue). They reported that participants could recall at least twice as many items in the retro-cue condition as in the post-cue condition and interpreted this as evidence for the existence of an initial stage of VSTM with a much higher capacity than was previously thought. The view that VSTM may consist of two distinct stores challenges decades of evidence and theory on the structure of VSTM. In the current study, we directly examined the architecture of VSTM using state-trace analysis, a direct method for assessing the dimensionality of psychological constructs. We replicated the benefit of presenting retro- versus post-cues on memory. However, the results of the state-trace analysis were consistent with a single store model of VSTM. We conclude that the improvement in performance in the retro-cue condition reflects increased attentional processing of the probed item rather than a distinct memory store.