![]() One was suggested by Miller (1956): the mean maximal number of serially processed items a healthy adult can store in short-term memory is about 7 (☒). The limit to how much information can be held in the short-term container has been the focus of research, and some ideas have been proposed with regard to the average size of the store capacity (i.e., memory span). The short-term store itself has been assumed to be of limited capacity. Long-term memory can hold a large amount of information for years or even decades. Short-term memory is the system involved in storing small amounts of information for a brief period. In a traditional two-store model of memory, information is retained in short-term memory and long-term memory systems (e.g., Atkinson & Shiffrin, 1968 Broadbent, 1958). Some strengths and limitations of the current EEG headset system are also discussed. This pattern of results supports a hypothesis that additional mental effort is required for short-term retention of verbal items when the number of stimulus items exceeds the newly proposed limit of short-term memory capacity. Moreover, frontal theta power in response to a list of six to eight digits increased significantly. ![]() The outcomes of the DS task showed that the memory span of the participants was at least eight items. The headset system was validated in this study by replicating the EEG (an enhancement of frontal theta power) as well as event-related potential (N200 and P300) responses to the deviant tone stimuli in the PL task. Considering that the digit span paradigm has often been conducted in a non-laboratory location, the EEG data were collected with a wireless single-channel headset system. Fourteen healthy adults ( M age = 26.1 years) performed a passive listening (PL) task and an auditory digit span (DS) task, and electroencephalography (EEG) data were recorded simultaneously during the two tasks. The present study was conducted to show that the dynamic change of underlying mental effort can be further estimated by measuring the strength of theta oscillations at a forehead site on the scalp. Task performance of digit span has been widely used in the research on human short-term memory.
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