Enumeration Processes under Attack: The Role of Working Memory in Subitizing and Serial Counting

Enumeration of visual stimuli is supported by two distinct psychological processes: serial counting and subitizing. Serial counting is an effortful, slow, and controlled process employed for the enumeration of large sets of objects. Subitizing is defined as a fast and accurate assessment of small quantities. Over the past two decades, there has been an on-going debate on whether subitizing and serial counting are based on shared or distinct cognitive mechanisms. Recent theories suggest that subitizing is supported by visual skills related to perception while serial counting requires working memory. The current study examines the respective roles of phonological and spatial working memory in enumeration processes. The main task used was an enumeration task, in which participants named the quantities of randomly arranged dots in the subitizing (1-3 dots) and counting (7-9 dots) ranges. The performance in the enumeration naming task was compared to a dual-task setting in which participants performed the enumeration naming task while they retained a phonological load or a spatial load. Load type had differential impact on enumeration processes. Importantly, it was found that phonological load, but not spatial load, decreased the effectiveness of serial counting. Subitizing ability was not affected by spatial or phonological load. In line with the majority of previous studies on enumeration, our results indicate that enumeration of small and large quantities are based on different cognitive processes. Moreover, the present finding demonstrate that, phonological working memory plays a significant role in serial counting but not in subitizing and that spatial load is not involved in enumeration.