The number of expected targets modulates access to working memory: A new unified account of lag-1 sparing and distractor intrusions.

Abstract

In rapid serial visual presentation (RSVP) tasks, failures of attentional selectivity are frequently observed when a single target is followed by a potentially reportable distractor (distractor intrusions). However, in tasks with two targets, accuracy for both targets is typically high when they are presented in immediate succession (lag-1 sparing). To account for this apparent contradiction, we tested whether expectations about the number of targets affects the number of items encoded in working memory (WM). Coloured target digits were embedded among grey letters and digits. The first target was followed either by a grey digit, or a second target (another coloured digit). To manipulate expectations, the ratio of one-target and two-targets trials (75%-25% or vice versa) was varied between blocks. Participants were much more likely to report seeing two targets when two targets were expected. Analogous results were obtained in an additional experiment where two successive coloured digits appeared on all trials, and participants were instructed to either report both or only the first digit. ERP markers of attentional allocation (N2pc) and WM storage processes (CDA) were larger when two targets were expected, regardless of the actual number of targets. These results show that the number of expected targets modulates the activation of sensory representations during attentional episodes, which affects the probability that they are subsequently encoded in WM. These findings suggest that a single mechanism can account both for lag-1 sparing and distractor intrusions in RSVP tasks. They also provide new evidence for strategic top-down control over WM encoding.

The diachronic account of attentional selectivity

“…Overall, these behavioural findings suggest that competitive interactions between items within the same attentional episode can affect the ability of any of these items to be encoded within WM and become accessible to perceptual reports. In a recent study (Zivony & Eimer, 2020; see also Zivony & Eimer, 2021b), we provided more direct behavioural and electrophysiological evidence for this claim. In a task with two lateral RSVP streams, participants were allowed two guesses about the target's identity.…”

“…Such N2pc amplitude modulations may reflect the amount of amplification of specific objects during the attentional episode. If N2pc onsets and N2pc amplitudes reflect the start and the degree of attentional amplification, respectively, it is important to track the effects of attentional manipulations on both of these variables independently (e.g., Bachman et al, 2020;Zivony & Eimer, 2021b).…”

Categorization templates modulate selective attention.

“…Starting from approximately 270 ms after target onset (i.e., 170 ms after PTD onset), matching PTDs resulted in a larger target-locked N2pc than irrelevant PTDs. As mentioned above, the presence of the matching PTD is also associated with lower accuracy of target reports (Zivony & Eimer, 2020, 2021c see Figure 1). The result of Experiment 1 therefore provides a clear link between attentional enhancement and interference by the matching PTD.…”

“…Accuracy in reporting T2 was high when it was also a letter but dropped precipitously when T2 was a digit (from 87.9% to 25.5%). Di Lollo et al (2005) suggested that these results reflect a failure of attentional selection, but later studies provided evidence against this account (see Zivony & Eimer, 2021c; Zivony & Lamy, 2022). The current study suggests that these switching costs may be linked to two different levels at which categorization templates operate.…”

“…We compared target-locked N2pcs on trials with irrelevant PTDs versus matching PTDs. The N2pc is very often measured in a single 100-ms time window, between 200 and 300 ms after the target (e.g., Berggren & Eimer, 2019; Callahan-Flintoft et al, 2018; Luck, 2014; Kiss et al, 2008; Zivony & Eimer, 2020, 2021b, 2021c). However, we assumed that if the PTD (which appears 100 ms after the target) would have any effect on the target-locked N2pc, it would be at a relatively late period and would not affect the N2pc’s onset.…”