Visual Long-Term Memory Has the Same Limit on Fidelity as Visual Working Memory

Timothy F Brady,Talia Konkle,Jonathan Gill,Aude Oliva,George A Alvarez

doi:10.1177/0956797612465439

Abstract

Visual long-term memory can store thousands of objects with surprising visual detail, but just how detailed are these representations, and how can one quantify this fidelity? Using the property of color as a case study, we estimated the precision of visual information in long-term memory, and compared this with the precision of the same information in working memory. Observers were shown real-world objects in random colors and were asked to recall the colors after a delay. We quantified two parameters of performance: the variability of internal representations of color (fidelity) and the probability of forgetting an object’s color altogether. Surprisingly, the fidelity of color information in long-term memory was comparable to the asymptotic precision of working memory. These results suggest that long-term memory and working memory may be constrained by a common limit, such as a bound on the fidelity required to retrieve a memory representation.

Highlights

Previous attempts to quantify the fidelity of long-term memory representations used simple stimuli like oriented gratings (Magnussen & Dyrnes, 1994; Magnussen et al 2003)
As more items are added to working memory, the fidelity of these memory representations reaches an asymptotic limit, and surprisingly, this limit is almost identical to the fidelity of representations we find in long-term memory
These results suggest that a common limit may be at work in both visual working memory and long-term memory: the asymptotic fidelity observed in visual working memory may not be a consequence of a slot-like architecture (Zhang & Luck, 2008, 2009; Anderson, Vogel & Awh, 2011) or a limited pool of resources (Wilken & Ma, 2004; Bayes, Catalao, & Husain, 2009); rather, the fidelity of visual working memory may reflect a more general upper bound on how noisy a memory representation can be before it is unable to be retrieved

Summary

Introduction

Previous attempts to quantify the fidelity of long-term memory representations used simple stimuli like oriented gratings (Magnussen & Dyrnes, 1994; Magnussen et al 2003). Observers were shown an object with a randomly chosen hue and, after a delay, asked to choose from a color wheel what hue the object was Such continuous report methods have been used with simple geometric shapes in working memory (e.g.,Wilken & Ma, 2004; Zhang & Luck, 2008; Brady & Alvarez, 2011), but have never been adapted for long-term memory.

Methods

Results

Discussion

Conclusion