Visual Working Memory Capacity for Color Is Independent of Representation Resolution

Abstract

BackgroundThe relationship between visual working memory (VWM) capacity and resolution of representation have been extensively investigated. Several recent ERP studies using orientation (or arrow) stimuli suggest that there is an inverse relationship between VWM capacity and representation resolution. However, different results have been obtained in studies using color stimuli. This could be due to important differences in the experimental paradigms used in previous studies.Methodology/Principal FindingsWe examined whether the same relationship between capacity and resolution holds for color information. Participants performed a color change detection task while their electroencephalography was recorded. We manipulated representation resolution by asking participants to detect either a salient change (low-resolution) or a subtle change (high-resolution) in color. We used an ERP component known as contralateral delay activity (CDA) to index the amount of information maintained in VWM. The result demonstrated the same pattern for both low- and high-resolution conditions, with no difference between conditions.Conclusions/SignificanceThis result suggests that VWM always represents a fixed number of approximately 3–4 colors regardless of the resolution of representation.

A two-phase model of resource allocation in visual working memory.

“…However, when there was enough exposure duration to enter the late voluntary phase, VWM precision variation would be observed either with a smaller set-size (Experiment 2) or with a longer exposure duration (Experiment 3). As we will discuss, these results and the new two-phase allocation model can further reconcile previous conflicting results (Gao, Yin, et al, 2011; He et al, 2015; Machizawa et al, 2012; Murray et al, 2012; Ye et al, 2014). …”

“…Our experiments were conducted with the same procedure using identical stimuli, allowing us to make direct comparisons across experiments. In addition, most of these prior studies adopted the change detection task and thus can only indirectly infer how memory precision changed based on a single accuracy measure of performance (He et al, 2015; Machizawa et al, 2012; Murray et al, 2012; Ye et al, 2014). In our study, we used an orientation recall task and performed quantitative model fitting to separately assess the probability that a memory was stored and the precision of the memory.…”

“…Previous studies have found support for both the involuntary and voluntary hypotheses (Gao, Yin, Xu, Shui, & Shen, 2011; He, Zhang, Li, & Guo, 2015; Machizawa et al, 2012; Murray et al, 2012; Ye, Zhang, Liu, Li, & Liu, 2014). For example, Murray et al (2012) manipulated payoff schemes to emphasize either the quality or quantity of memory and found no voluntary resource allocation in VWM, supporting the involuntary allocation hypothesis.…”

The contralateral delay activity as a neural measure of visual working memory

“…Studies that directly manipulated color resolution also found that it had no effect on the CDA (Ikkai et al, 2010; Luria et al, 2010; Ye et al, 2014) and studies that manipulated orientation resolution reported mixed results (Gao et al, 2011a,b; Machizawa et al, 2012). Note that increasing the number of relevant features within an object did not affect the CDA (Luria and Vogel, 2011a; Woodman and Vogel, 2008).…”

“…Several studies reported that manipulating the stimulus contrast in the change detection paradigm, while resulting in an impaired behavioral performance, did not have any effect on the CDA (Gao et al, 2013; Ikkai et al, 2010; Luria et al, 2010; Ye et al, 2014). This result is significant because it reveals a dissociation between the low accuracy performance (usually taken as a marker of VWM capacity) and the intact CDA amplitude, and serves as additional evidence that the CDA does not simply reflect the task difficulty.…”