Integration of Distinct Objects in Visual Working Memory Depends on Strong Objecthood Cues Even for Different-Dimension Conjunctions

Abstract

What makes an integrated object in visual working memory (WM)? Past evidence suggested that WM holds all features of multidimensional objects together, but struggles to integrate color-color conjunctions. This difficulty was previously attributed to a challenge in same-dimension integration, but here we argue that it arises from the integration of 2 distinct objects. To test this, we examined the integration of distinct different-dimension features (a colored square and a tilted bar). We monitored the contralateral delay activity, an event-related potential component sensitive to the number of objects in WM. The results indicated that color and orientation belonging to distinct objects in a shared location were not integrated in WM (Experiment 1), even following a common fate Gestalt cue (Experiment 2). These conjunctions were better integrated in a less demanding task (Experiment 3), and in the original WM task, but with a less individuating version of the original stimuli (Experiment 4). Our results identify the critical factor in WM integration at same- versus separate-objects, rather than at same- versus different-dimensions. Compared with the perfect integration of an object's features, the integration of several objects is demanding, and depends on an interaction between the grouping cues and task demands, among other factors.

Neural and Behavioral Evidence for an Online Resetting Process in Visual Working Memory

“…Because resetting involves abandoning existing representations and then individuating and encoding new objects, we expected the CDA amplitude in the separating shapes condition to drop sharply after the separation (during resetting) and then to gradually recover until it reflected the new number of items. In contrast, if VWM can simply update after the separation, then we should observe only a gradual change in CDA amplitude until it reflects the new object status, without a drop (Vogel et al, 2005;Drew et al, 2011;Luria and Vogel, 2014;Balaban and Luria, 2016b); more specifically, the amplitude should rise because more items are present after the separation.…”

“…Aside from changes in the items themselves, interactions between items can also lead to VWM updating. Specifically, representations of independent items can be integrated into one chunk according to different objecthood cues (Wilson et al, 2012;Luria and Vogel, 2014;Peterson et al, 2015;Balaban and Luria, 2016b). This demonstrates the dynamic nature of VWM representations, which is maintained through their ability to update in a wide range of situations from basic perceptual changes to complex changes regarding task demands (Vergauwe and Cowan, 2015;Balaban and Luria, 2016a).…”

“…One mechanism that helps us make sense of this "object chaos" is visual working memory (VWM), which stores a limited amount of information in an online state (GoldmanRakic, 1995;Cowan, 2001;Luck and Vogel, 2013). VWM updates its representations according to the dynamic status of the objects so that when the location, form, or even the interpretation of an object changes, VWM modifies the corresponding representation (Blaser et al, 2000;Drew et al, 2011;Schlegel et al, 2013;Luria and Vogel, 2014;Balaban and Luria, 2016a). We suggest that updating relies on a distinctive correspondence between a specific object in the environment and a unique VWM representation (Kahneman et al, 1992;Levillain and Flombaum, 2012).…”

“…Participants memorized the shape-parts for a change-detection task (Luck and Vogel, 1997; Zhang and Luck, 2008; Gao et al, 2009). The initial integrated movement phase conveyed a strong common-fate Gestalt cue intended to create one integrated object representation in VWM (Luria and Vogel, 2014;Balaban and Luria, 2016b), forming a link between the moving shape and a single VWM representation. Once the shape separated into its comprising parts, the correspondence between the object and the unique VWM representation broke: now, there were two moving items that had to be followed and represented independently to perform the change-detection task (Xu, 2002).…”

“…The CDA amplitude reaches a stable asymptote that is strongly correlated with individual VWM capacity (Vogel and Machizawa, 2004;Drew and Vogel, 2008;Tsubomi et al, 2013;Kang and Woodman, 2014; for review, see Luria et al, 2016). Notably, the CDA does not reflect the number of attended locations (Ikkai et al, 2010;Luria and Vogel, 2014;Balaban and Luria, 2016a;Balaban and Luria, 2016b), eye movements (Kang and Woodman, 2014), or other low-level perceptual factors (Ikkai et al, 2010).…”