title: What limits working memory capacity? Evidence for modality-specific sources to the simultaneous storage of visual and auditory arrays.
abstract: There is considerable debate on whether working memory (WM) storage is mediated by distinct subsystems for auditory and visual stimuli (Baddeley, 1986) or whether it is constrained by a single, central capacity-limited system (Cowan, 2006). Recent studies have addressed this issue by measuring the dual-task cost during the concurrent storage of auditory and visual arrays (e.g., Cocchini, Logie, Della Sala, MacPherson, & Baddeley, 2002; Fougnie & Marois, 2006; Saults & Cowan, 2007). However, studies have yielded widely different dual-task costs, which have been taken to support both modality-specific and central capacity-limit accounts of WM storage. Here, we demonstrate that the controversies regarding such costs mostly stem from how these costs are measured. Measures that compare combined dual-task capacity with the higher single-task capacity support a single, central WM store when there is a large disparity between the single-task capacities (Experiment 1) but not when the single-task capacities are well equated (Experiment 2). In contrast, measures of the dual-task cost that normalize for differences in single-task capacity reveal evidence for modality-specific stores, regardless of single-task performance. Moreover, these normalized measures indicate that dual-task cost is much smaller if the tasks do not involve maintaining bound feature representations in WM (Experiment 3). Taken together, these experiments not only resolve a discrepancy in the field and clarify how to assess the dual-task cost but also indicate that WM capacity can be constrained both by modality-specific and modality-independent sources of information processing.
authors.affiliation: Department of Psychology, Harvard University, 33 Kirkland Street, Harvard University, Cambridge, MA 02138, USA. darylfougnie@gmail.com
authors.forename: Daryl
authors.initials: D
authors.lastname: Fougnie
authors.forename: René
authors.initials: R
authors.lastname: Marois
mesh_terms: D000161:Acoustic Stimulation; D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001288:Attention; D001307:Auditory Perception / Q000502:physiology*; D003118:Color Perception / Q000502:physiology*; D004192:Discrimination, Psychological; D005260:Female; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D009483:Neuropsychological Tests; D010775:Photic Stimulation; D011601:Psychophysics; D011930:Reaction Time; D055815:Young Adult