Parallel encoding of information into visual short-term memory

Abstract

Humans can temporarily retain information in their highly limited short-term memory. Traditionally, objects are thought to be attentionally selected and committed to short-term memory one-by-one. However, few studies directly test this serial encoding assumption. Here, we demonstrate that information from separate objects can be encoded into short-term memory in parallel. We developed models of serial and parallel encoding that describe probabilities of items being present in short-term memory throughout the encoding process, and tested them in a whole-report design. Empirical data from four experiments in healthy individuals were fitted best by the parallel encoding model, even when items were presented unilaterally (processed within one hemisphere). Our results demonstrate that information from several items can be attentionally selected and consequently encoded into short-term memory simultaneously. This suggests the popular feature integration theory needs to be reformulated to account for parallel encoding, and provides important boundaries for computational models of short-term memory.

Sequential versus simultaneous presentation of memoranda in verbal working memory: (How) does it matter?

“…Nevertheless, the influence of presentation mode (sequential versus simultaneous) on recall performance has barely been investigated and it is unclear whether WM performance and the nature of encoding mechanisms differ between sequentially versus simultaneously presented sequences. A few prior studies have observed differences in WM performance between these two presentation modes, but empirical evidence allowing to understand these differences remains scarce and is sometimes contradictory (Battacchi et al, 1990;Crowder, 1966;Dalmaijer et al, 2018;Frick, 1985;LeCompte, 1992;Marcer, 1967). In the present study, we therefore examined performance in both sequentially and simultaneously presented list material and proposed detailed analyses by comparing serial position curves for recall performance and the nature of recall errors between conditions.…”

“…However, again, findings are controversial, as LeCompte (1992) did not find an enhanced recency effect when stimuli are distributed over space, even though they meticulously followed the method used by Battacchi at al. Moreover, some studies have shown that visual information (e.g., letters or shapes), when presented simultaneously, leads to better recall performance compared to when it is presented sequentially, that is, one item at a time (Crowder, 1966;Dalmaijer et al, 2018;Marcer, 1967). Marcer observed that presenting all stimuli simultaneously encouraged participants to encode the entire sequence as a single chunk which in turn led to more similar recall performance between positions (i.e., flatter serial position curves) compared to situations in which stimuli are presented sequentially, rather encouraging the encoding of each stimulus as a single chunk leading to differences in terms of recall performance per position (e.g., primacy and/or recency effects).…”

“…These findings suggest that the presentation mode not only affects overall recall performance but more specifically the very nature of the encoding and maintenance of serial order information. In sum, the observed advantage for simultaneous presentation has been suggested to involve the spontaneous use of chunking mechanisms facilitated by the left-to-right spatial arrangement of the simultaneous list of items (Crowder, 1966;Dalmaijer et al, 2018;Marcer, 1967).…”

The pupillary light response reflects visual working memory content.

“…VWM consists of encoding and maintenance. During encoding, visual stimuli are visible and a VWM representation is created (Bundesen, 1990;Dalmaijer, Manohar, & Husain, 2018). During maintenance, stimuli are no longer visible, and their VWM representations therefore need to be rehearsed so that they can be used later (Zokaei, Heider, & Husain, 2014).…”

The Pupillary Light Response Reflects Visual Working Memory Content

“…VWM consists of encoding and 53 maintenance. During encoding, visual stimuli are visible and a VWM representation is 54 created (Bundesen, 1990;Dalmaijer, Manohar, & Husain, 2018). During maintenance, 55 stimuli are no longer visible, and their VWM representations therefore need to be 56 rehearsed so that they can be used later (Zokaei, Heider, & Husain, 2014).…”