Visual short-term memory load weakens attentional selection by increasing the size of attentional zoom

Visual short-term memory (VSTM) load has been known to modulate attentional selection, but the direction of the modulation is inconsistent across studies (Konstantinou et al. 2014; Roper & Vecera, 2014; Zhang & Luck, 2015; Lee & Yi, 2018). A recent study showed that high VSTM load hampers attentional selection (Zhang & Luck, 2015). However, the size of attentional zoom has also been shown to influence selective attention (Eriksen & St. James, 1986), and VSTM load is typically correlated with the size of attentional zoom as a greater number of items occupies a larger area of the display in high VSTM load. In the current study, we aimed to dissociate VSTM load and the size of attentional zoom to better understand the effects of VSTM load on attentional selection. Participants conducted a flanker task whilst maintaining 1 or 4 colored squares. In the high load condition, four color patches appeared simultaneously on the periphery (high load/wide zoom). In the low load conditions, one color patch appeared in the center of the display (low load/narrow zoom) or on the periphery with three white placeholders to keep the size of attentional zoom widened (low load/wide zoom). Results showed that the flanker interference of high load/wide zoom condition was greater than that of the low load/narrow zoom condition, replicating Zhang & Luck (2015). Interestingly, the low load/wide zoom condition showed the same amount of interference effect as the high load/wide zoom condition, suggesting that attentional selection was modulated by the size of attentional zoom regardless of VSTM load. The current result implies the attentional zoom is an essential factor for modulating attentional selection.