Distinguishing guesses from fuzzy memories: Further evidence for item limits in visual working memory

Abstract

There is consistent debate over whether capacity in working memory (WM) is subject to an item limit, or whether an unlimited number of items can be held in this online memory system. The item limit hypothesis clearly predicts guessing responses when capacity is exceeded, and proponents of this view have highlighted evidence for guessing in visual working memory tasks (e.g, Adam et al., 2017; Zhang & Luck, 2008). Nevertheless, various models that deny item limits can explain the same empirical patterns by asserting extremely low fidelity representations that cannot be distinguished from guesses. To address this ambiguity, we employed a task for which random guess responses elicited a qualitatively distinct pattern from low fidelity memories. Inspired by work from Rouder et al. (2014), we employed an orientation WM task that required subjects to recall the precise orientation of each of six memoranda presented one second earlier. The orientation stimuli were created by rotating the position of a “clock hand” inside a circular region that was demarcated by four colored quadrants. Critically, when observers guess with these stimuli, the distribution of responses is biased towards the center of demarcated quadrants, creating a “banded” pattern that cannot be explained by a low precision memory. We confirmed the presence of this guessing pattern using formal model comparisons, and we show that the prevalence of this pattern matches observers’ own reports of when they thought they were guessing. Thus, these findings provide further evidence for the guessing behaviors predicted by item limit models of WM capacity.

Data and Code

Preprint

PDF

Add to Zotero