Behavioural and neural correlates of visual working memory reveal metacognitive aspects of mental imagery

Abstract

Mental imagery (MI) is the ability to generate visual phenomena in the absence of sensory input. MI is often likened to visual working memory (VWM): the ability to maintain and manipulate visual representations. How MI is recruited during VWM is yet to be established. In a modified orientation change-discrimination task, we examined how behavioural (proportion correct) and neural (contralateral delay activity; CDA) correlates of precision and capacity map onto subjective ratings of vividness and number of items in MI within a VWM task. During the maintenance period, seventeen participants estimated the vividness of their MI or the number of items held in MI while they were instructed to focus on either precision or capacity of their representation and to retain stimuli at varying set sizes (1, 2 and 4). Vividness and number ratings varied over set sizes; however, subjective ratings and behavioral performance were not correlated, except for vividness rating at set size 1. There were no statistical differences in CDA between reported high and low vividness and non-divergent (reported the probed number of items in mind) or divergent (reported number of items diverged from probed) rating trials. We observed greater CDA in higher compared to lower set sizes. Participants were more accurate in low set sizes compared to higher set sizes and in fine (15º) orientation changes compared to coarse (35º) orientation changes. This evidence indicates that the subjective sensory experience of precision and capacity in MI may be distinct from the visual precision and capacity of VWM.